ORTHOPEDIC MCQS with Answers ONLINE BASIC 06

1. A 20-year-old woman with a history of subtotal meniscectomy has a painful knee. What associated condition is a contraindication to proceeding with a meniscal allograft?

1- Grade I posterior cruciate ligament tear

2- Grade II medial collateral ligament tear

3- Lateral meniscal tear

4- 5 degrees of genu varum

5- 5- x 5-mm patellar chondral lesion

PREFERRED RESPONSE: 4

DISCUSSION: Patients with significant joint malalignment place increased stresses on the allograft, and this malalignment must be corrected to decrease the likelihood of meniscal allograft failure. None of the other options would lead to failure of the allograft.

REFERENCE: Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, p 499.

2. Long bone fracture repair following intramedullary stabilization occurs primarily through which of the following healing mechanisms?

1- Haversian remodeling

2- endosteal ossification only

3- Intramembranous ossification only

4- Endochondral ossification only

5- Intramembranous and endochondral ossification

PREFERRED RESPONSE: 5

DISCUSSION: The mechanical environment represents a major factor in the type of healing that occurs after a fracture. Intramedullary nail fixation allows for motion at the fracture site, which promotes bone formation both directly (intramembranous ossification) and through a cartilage intermediate (endochondral ossification). Absolute stability, as would be obtained with a compression plate, favors healing through the direct formation of bone without a cartilage intermediate (intramembranous ossification), or primary fracture repair. This type of healing would include the remodeling of the bone ends through the direct contact of bone, often referred to as contact healing or haversian remodeling.

REFERENCES: Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 385-386.

Buckwalter JA, Einhorn TA, Bolander ME: Healing of the musculoskeletal tissues, in Rockwood CA Jr, Green DP, Bucholz RW, et al (eds): Rockwood and Green’s Fractures in Adults, ed 4. Philadelphia, PA, Lippincott-Raven, 1996, pp 261-276.

3. The acceleration of an object under the influence of a force depends directly on the mass of the object. The angular acceleration of an object under the influence of a moment depends directly on the

1- area moment of inertia.

2- weight squared.

3- length of the lever arm.

4- mass moment of inertia.

5- initial velocity.

PREFERRED RESPONSE: 4

DISCUSSION: Similar to the action of a force, a moment tends to angularly accelerate an object in a manner proportional to a quantity related to the mass of the object. The concept of a more massive object requiring a larger force to cause the same straight line acceleration is straightforward. The concept for changing angular velocity is similar but not identical. The proportional constant between the moment and the resulting angular acceleration is the mass moment of inertia, which depends not only on the mass of the object, but also its distribution. The unit of mass moment of inertia is obtained by multiplying the mass of the object by the square of the distance between an equivalent location of the center of rotation of the object and an equivalent location of the center of mass. Orthopaedic surgeons can change both the amount of mass carried by a limb and the way that the mass is distributed. For example, in applying a cast to the leg, the physician can affect the mass of the cast by the choice of casting material and by the size of the cast. As the mass moment of inertia of the limb increases (eg, by applying the cast farther down on the leg or using a heavier casting material), the patient will need to exert larger moments to angularly accelerate the leg during gait.

REFERENCES: Andriacchi T, Natarajan RN, Hurwitz DE: Musculoskeletal dynamics, locomotion, and clinical applications, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 43-47.

Burstein AH, Wright TM: Fundamentals of Orthopaedic Biomechanics. Baltimore, MD, Williams and Wilkins, 1994, pp 3-7.

4. Figures 1a through 1c show the radiograph and MRI scans of a 16-year-old patient who has a painful hip. Examination reveals a significant limp, limited abduction and internal rotation, and severe pain with internal rotation and adduction. A biopsy specimen is shown in Figure 1d. What is the deposited pigment observed in this condition?

1- Hemoglobin

2- Myoglobin

3- Melanin

4- Copper

5- Hemosiderin

PREFERRED RESPONSE: 5

DISCUSSION: Pigmented villonodular synovitis (PVNS) is a synovial proliferative disorder that remains a diagnostic difficulty. The most common clinical features are mechanical pain and limited joint motion. On radiographs, the classic finding is often a large lesion, associated with multiple lucencies. Other findings may include a normal radiographic appearance, loss of joint space, osteonecrosis of the femoral head, or acetabular protrusion. MRI is the imaging modality of choice and will show the characteristic findings of a joint effusion, synovial proliferation, and bulging of the hip. The synovial lining has a low signal on T₁- and T₂-weighted images, secondary to hemosiderin deposition. Copper deposition occurs in patients with Wilson’s disease, which mainly affects the liver.

REFERENCES: Bhimani MA, Wenz JF, Frassica FJ: Pigmented villonodular synovitis: Keys to early diagnosis. Clin Orthop 2001;386:197-202.

Cotten A, Flipo RM, Chastanet P, et al: Pigmented villonodular synovitis of the hip: Review of radiographic features in 58 patients. Skeletal Radiol 1995;24:1-6.

5. Titanium and its alloys are unsuitable candidates for which of the following implant applications?

1- Fracture plates

2- Femoral heads in a hip prosthesis

3- Bone screws

4- Intramedullary nails

5- Porous coatings for bone ingrowth

PREFERRED RESPONSE: 2

DISCUSSION: Titanium alloy is highly biocompatible, has higher strength than stainless steel, and is highly resistant to corrosion. It is particularly suited for use in fracture plates, bone screws, and intramedullary nails because of its low modulus of elasticity (low stiffness), which can reduce stress shielding. It is also widely used for porous-ingrowth coatings. However, clinical experience has shown that titanium alloy bearing surfaces such as a femoral ball are highly susceptible to severe metallic wear, particularly in the presence of third-body abrasive particles (PMMA fragments, bone chips, metal debris, etc).

REFERENCES: McKellop HA, Sarmiento A, Schwinn CP, et al: In vivo wear of titanium-alloy hip prostheses. J Bone Joint Surg Am 1990;72:512-517.

Salvati EA, Betts F, Doty SB: Particulate metallic debris in cemented total hip arthroplasty. Clin Orthop 1993;293:160-173.

Evans BG, Salvati EA, Huo MH, et al: The rationale for cemented total hip arthroplasty. Orthop Clin North Am 1993;24:599-610.

6. What percent of patients initially diagnosed with classic, high-grade osteosarcoma of the extremity have visible evidence of pulmonary metastasis on CT of the chest?

1- 5% to 10%

2- 10% to 20%

3- 40% to 50%

4- 60% to 80%

5- 80% to 90%

PREFERRED RESPONSE: 2

DISCUSSION: CT studies show that approximately 10% to 20% of patients with high-grade osteosarcoma have pulmonary metastases at diagnosis. Although not visible on current staging studies, it is believed that up to 80% of patients have micrometastatic disease that requires systemic chemotherapy. Because it is not possible to identify those patients who do not have disseminated micrometastatic disease, most patients are treated presumptively with chemotherapy.

REFERENCES: Kaste SC, Pratt CB, Cain AM, et al: Metastases detected at the time of diagnosis of primary pediatric extremity osteosarcoma at diagnosis: Imaging features. Cancer 1999;86:1602-1608.

Link MP, Goorin AM, Miser AW, et al: The effect of adjuvant chemotherapy on relapse-free survival in patients with osteosarcoma of the extremity. N Engl J Med 1986;314:1600-1606.

7. Staphylococcus aureus develops methicillin resistance through production of which of the following agents?

1- Beta-lactam

2- Catalase

3- Oxidase

4- Penicillin-binding protein 2a

5- Glycocalix

PREFERRED RESPONSE: 4

DISCUSSION: Organisms may develop resistance to antibiotics by production of specific enzymes. S aureus develops methicillin resistance by production of penicillin-binding protein 2a (PBP2a). The strains of S aureus that have acquired the mecA gene for PBP2a are designated as methicillin-resistant S aureus (MRSA). The enzyme manifests resistance to covalent modification by beta-lactam antibiotics at the active-site serine residue in two ways. First, the microscopic rate constant for acylation (k2) is attenuated by three to four orders of magnitude over the corresponding determinations for penicillin-sensitive PBPs. Second, the enzyme shows elevated dissociation constants (Kd) for the noncovalent preacylation complexes with the antibiotics, the formation of which ultimately would lead to enzyme acylation. The two factors working in concert effectively prevent enzyme acylation by the antibiotics in vivo, giving rise to drug resistance. Catalase and oxidase are enzymes produced by some bacteria that confer virulence to the organism but do not make the organisms methicillin resistant. Glycocalix is the pericellular layer produced by bacteria that serves many functions including attachment to surfaces. Beta-lactam describes a class of antibiotics.

REFERENCES: Fuda C, Suvorov M, Vakulenko SB, et al: The basis for resistance to beta-lactam antibiotics by penicillin-binding protein 2a (PBP2a) of methicillin-resistant staphylococcus aureus. J Biol Chem 2004;279:40802-40806.

Lim D, Strynadka NC: Structural basis for the beta lactam resistance of PBP2a from methicillin-resistant Staphylococcus aureus. Nat Struct Biol 2002;9:870-876.

Schwarz EM: Infections in orthopaedics, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

8. A 30-year-old man reports pain and weakness in his right arm. Examination reveals grade 4 strength in wrist flexion and elbow extension, decreased sensation over the middle finger, and decreased triceps reflex. These symptoms are most compatible with impingement on what spinal nerve root?

1- C5

2- C6

3- C7

4- C8

5- T1

PREFERRED RESPONSE: 3

DISCUSSION: Motor impulses to the triceps, wrist flexion and elbow extension, and sensation to the middle finger are associated most commonly with the C7 root.

REFERENCES: Hoppenfeld S: Physical Examination of the Spine and Extremities. Upper Saddle River, NJ, Prentice Hall, 1976, p 125.

Lauerman WC, Goldsmith ME: Spine, in Miller MD (ed): Review of Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2000, pp 353-378.

9. Why is tendon considered an anisotropic material?

1- Young’s modulus is greater than that of bone.

2- Young’s modulus is greater than that of ligament.

3- Mechanical properties change with preconditioning.

4- Intrinsic mechanical properties vary depending on the direction of loading.

5- Intrinsic mechanical properties vary depending on the rate of loading.

PREFERRED RESPONSE: 4

DISCUSSION: Anisotropic materials have mechanical properties that vary based on the direction of loading. The relative values of Young’s modulus for tendon, ligament, and bone are not relevant to isotropy. The mechanical properties of tendon do change with preconditioning, but this change is related to viscoelasticity. The intrinsic mechanical properties of tendon do vary with the rate of loading, but this variance is related to viscoelasticity.

Lu L, Kaufman KR, Yaszemski MJ: Biomechanics, in Einhorn TA, O’Keefe RJ,
Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

10. What does Dual Energy X-ray Absorptiometry (DEXA) testing, as a technique, measure?

1- Qualitative value of core bone mineral content

2- Differentiation of trabecular and cortical bone content

3- Core bone mineral density unchanged by osteoarthritis at or around the site

4- Bone mineral content and soft-tissue composition

5- Bone mineral content and density without need for cross-sectional dimension

PREFERRED RESPONSE: 4

DISCUSSION: DEXA can provide data on bone mineral content and soft-tissue composition, and requires cross-sectional dimension for accuracy. DEXA provides a quantitative, not qualitative, measurement of bone mineral content and is incapable of differentiating between trabecular and cortical bone. Osteoarthritis falsely elevates the values, especially in the AP spinal analysis.

REFERENCES: Genant HK, Faulkner KG, Gluer CC: Measurement of bone mineral density: Current status. Am J Med 1991;91:49S-53S.

Genant HK, Engelke K, Fuerst T, et al: Review: Noninvasive assessment of bone mineral density and stature: State of the art. J Bone Miner Res 1996;11:707-730.

Engelke K, Gluer CC, Genant HK: Factors influencing short-term precision of dual X-ray bone absorptiometry (DXA) of spine and femur. Calcif Tissue Int 1995;56:19-25.

11. A 20-year-old athlete sustains a 2- x 3-cm grade IV chondral injury to the right knee. After failure of nonsurgical management, which of the following procedures would ensure the highest percentage of hyaline-like cartilage?

1- Arthroscopic chondroplasty

2- Autologous chondrocyte implantation

3- Microfracture

4- Arthroscopic drilling

5- Abrasion arthroplasty

PREFERRED RESPONSE: 2

DISCUSSION: Autologous chondrocyte implantation was first reported by Brittberg in 1994 and has resulted in predominantly type II collagen (hyaline-like articular cartilage) in the repair tissue. The extracellular matrix in articular cartilage is made up primarily of type II collagen, proteoglycans, and water. Arthroscopic chondroplasty, microfracture, drilling, and abrasion arthroplasty all result eventually in fibrocartilage fill of the defect (predominantly type I collagen).

REFERENCES: Brittberg M, Lindahl A, Nilsson A, et al: Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation. N Engl J Med 1994;331:889-895.

Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000, pp 787-804.

12. Which of the following changes to heart rate, blood pressure, and bulbocavernosus reflex are typical of spinal shock?

1- Tachycardia, hypertension, intact bulbocavernosus reflex

2- Tachycardia, hypotension, intact bulbocavernosus reflex

3- Tachycardia, hypotension, absent bulbocavernosus reflex

4- Bradycardia, hypotension, absent bulbocavernosus reflex

5- Bradycardia, hyperthermia, intact bulbocavernosus reflex

PREFERRED RESPONSE: 4

DISCUSSION: The term ‘spinal shock’ applies to all phenomena surrounding physiologic or anatomic transection of the spinal cord that results in temporary loss or depression of all or most spinal reflex activity below the level of the injury. Hypotension and bradycardia caused by loss of sympathetic tone is a possible complication, depending on the level of the lesion. The mechanism of injury that causes spinal shock is usually traumatic in origin and occurs immediately, but spinal shock has been described with mechanisms of injury that progress over several hours. Spinal cord reflex arcs immediately above the level of injury also may be depressed severely on the basis of the Schiff-Sherrington phenomenon. The end of the spinal shock phase of spinal cord injury is signaled by the return of elicitable abnormal cutaneospinal or muscle spindle reflex arcs. Autonomic reflex arcs involving relay to secondary ganglionic neurons outside the spinal cord may be affected variably during spinal shock, and their return after spinal shock abates is variable. The returning spinal cord reflex arcs below the level of injury are irrevocably altered and are the substrate on which rehabilitation efforts are based.

REFERENCE: Ditunno JF, Little JW, Tessler A, et al: Spinal shock revisited: A four-phase model. Spinal Cord 2004;42:383-395.

13. What is the primary intracellular signaling mediator for bone morphogenetic protein (BMP) activity?

1- Interleukin-1 (IL-1)

2- Runx2

3- NFK-B

4- SMADS

5- P53

PREFERRED RESPONSE: 4

DISCUSSION: BMPs signal through the activation of a transmembrane serine/threonine kinase receptor that leads to the activation of intracellular signaling molecules called SMADs. There are currently eight known SMADs, and the activation of different SMADs within a cell leads to different cellular responses. The other mediators are not believed to be directly involved with BMP signaling.

REFERENCES: Lieberman J, Daluiski A, Einhorn TA: The role of growth factors in the repair of bone: Biology and clinical applications. J Bone Joint Surg Am 2002;84:1032-1044.

Li J, Sandell LJ: Transcriptional regulation of cartilage-specific genes, in Rosier RN, Evans C (eds): Molecular Biology in Orthoapedics, Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 21-24.

Zuscik MJ, Drissi MH, Reynolds PR, et al: Molecular and cell biology in orthopaedics, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006,
in press.

14. Which of the following properties primarily provides the excellent corrosion resistance of metallic alloys such as stainless steel and cobalt-chromium-molybdenum?

1- High surface hardness

2- High levels of nickel

3- Adherent oxide layer

4- Low galvanic potential

5- Metallic carbides

PREFERRED RESPONSE: 3

DISCUSSION: All of the metals and metallic alloys used in orthopaedic surgery obtain their corrosion resistance from an adherent oxide layer. For stainless steel and cobalt alloy, the addition of chromium as an alloying element ensures the formation of a chromium oxide passive layer that forms on the surface and separates the bulk material from the corrosive body environment. Titanium alloy achieves the same result without chromium by forming an adherent passive layer of titanium oxide. Although these layers can indeed be hard, hardness does not in and of itself provide corrosion resistance. Adding nickel to both metallic alloys adds to strength but does not influence corrosion resistance appreciably. Galvanic potential can influence corrosion but does so by differences in potential between two contacting materials; for example, stainless steel and cobalt alloy have substantially different potentials, and if they were in contact within an aqueous environment, corrosion would commence with the stainless steel becoming the sacrificial anode. Metallic carbides are important in strengthening the alloys but have no role in providing corrosion resistance.

REFERENCES: Williams DF, Williams RL: Degradative effects of the biological environment on metal and ceramics, in Ratner BD, Hoffman AS, Shoen FJ, et al (eds): Biomaterials Science. San Diego, CA, Academic Press, 1996, pp 260-265.

Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 190-193.

Wright TM, Maher SA: Biomaterials, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

15. Which of the following infectious organisms may be associated with underlying malignancy?

1- Acinetobacter species

2- Clostridium septicum

3- Peptostreptococcus

4- Proteus mirabilis

5- Pseudomonas mendocina

PREFERRED RESPONSE: 2

DISCUSSION: Evidence implicates an association, albeit unexplained, between Clostridium septicum infection and malignancy, particularly hematologic or intestinal malignancy. The malignancy is often at an advanced stage, compromising survival of the patients. A bowel portal of entry is postulated for most patients. In the absence of an external source in the patient with clostridial myonecrosis or sepsis, the cecum or distal ileum should be considered a likely site of infection. Increased awareness of this association between Clostridium septicum and malignancy, and aggressive surgical treatment, may result in improvement in the present 50% to 70% mortality rate. Other organisms associated with malignancy include group Clostridium streptococci that are occasionally associated with upper gastrointestinal malignancies.

REFERENCES: Schaaf RE, Jacobs N, Kelvin FM, et al: Clostridium septicum infection associated with colonic carcinoma and hematologic abnormality. Radiology 1980;137:625-627.

Katlic MR, Derkac WM, Coleman WS: Clostridium septicum infection and malignancy. Ann Surg 1981;193:361-364.

16. Immobilization of human tendons leads to what changes in structure and/or function?

1- Decrease in tensile strength

2- Decrease in the likelihood of rupture

3- Increase in cellularity

4- Increase in aggrecan

5- Increase in collagen fibril diameter

PREFERRED RESPONSE: 1

DISCUSSION: Recent in vivo and in vitro experiments demonstrate that immobilization of tendon decreases its tensile strength, stiffness, and total weight. Microscopically, there is a decrease in cellularity, overall collagen organization, and collagen fibril diameter.

REFERENCE: Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000, p 687.

17. Human menisci are made up predominantly of what collagen type?

1- I

2- II

3- III

4- V

5- VI

PREFERRED RESPONSE: 1

DISCUSSION: Type I collagen accounts for more than 90% of the total collagen content. Other minor collagens present include types II, III, V, and VI.

REFERENCES: Mow VC, Arnoczky SP, Jackson DW (eds): Knee Meniscus: Basic and Clinical Foundations. New York, NY, Raven Press, 1992, p 41.

Kawamura S, Rodeo SA: Form and function of the meniscus, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

18. Type II collagen in nondiseased adult human articular cartilage has a half-life that
is generally

1- several months.

2- 6 months.

3- 1 year.

4- 10 years.

5- more than 25 years.

PREFERRED RESPONSE: 5

DISCUSSION: Type II collagen in articular cartilage is amazingly stable. This is important to know because matrix homeostasis generally is associated with minimal synthesis and degradation of type II collagen. Passive glycation has a consistent rate and occurs over decades. The relative amount of glycation in cartilage with age has been used as a measure of stability. Also, the rate of racemization of aspartic acid from the L to D form occurs spontaneously at a very slow rate. The relative stability of collagen can be estimated by calculating the percentage of D aspartic acid per dry weight of type II collagen.

REFERENCES: Maroudas A, Palla G, Gilav E: Racemization of aspartic acid in human articular cartilage. Connect Tissue Res 1992;28:161-169.

Verzijl N, DeGroot J, Thorpe SR, et al: Effect of collagen turnover on the accumulation of advanced glycation end products. J Biol Chem 2000;275:39027-39031.

19. What changes in muscle physiology would be expected in an athlete who begins a rigorous aerobic program for an upcoming marathon?

1- Hypertrophy of type I muscle fibers

2- Reduced fatigue resistance

3- Decreased capillary density

4- Decreased VO₂max

5- Decreased mitochondrial density per muscle cell

PREFERRED RESPONSE: 1

DISCUSSION: Muscle fibers can be categorized grossly into two types. Type I muscle, also known as slow-twitch muscle, is responsible for aerobic, oxidative muscle metabolism. It has a much lower strength and speed of contraction than fast-twitch type II muscle but is significantly more fatigue resistant. With training for endurance sports, the type I muscle undergoes adaptive changes to the increased stress. Increases in capillary density, oxidative capacity, mitochondrial density, and subsequent fatigue resistance are all observed changes. Hypertrophy of type IIb muscle is seen in strength training.

REFERENCES: Simon SR (ed): Orthopaedic Basic Science. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 89-125.

Thayer R, Collins J, Noble EG, et al: A decade of aerobic endurance training: Histological evidence for fibre type transformation. J Sports Med Phys Fitness 2000;40:284-289.

20. When a structure like a long bone is under a bending load, its maximum stress is most dependent on what factor?

1- Length of the bone

2- Type of structural support

3- Size of cross-sectional area

4- Plastic modulus of material used

5- Area moment of inertia of the cross section

PREFERRED RESPONSE: 5

DISCUSSION: The maximum stress in a bone occurs at the periosteal surface (the greatest distance from the center of the bone). The magnitude of the stress is equal to the magnitude of the applied moment (M) multiplied by the distance to the surface (roughly the radius of the bone, r) divided by the area moment of inertia (I), so that stress = Mr/I. Of the possible answers, only area moment of inertia of the cross section contains any of these three items. The stress can also depend on the length of the bone, but it cannot be determined without knowing the location at which the bending load is applied, information that was not given in the problem. The type of structural support may influence local stresses where the support contacts the bone, but it has little effect on the maximum stress in the bone. The cross-sectional area is not as important as the area moment of inertia because the stress is not evenly distributed over the cross-section. Plastic modulus is a material property, not a geometric or structural property, and it does not affect stress.

REFERENCES: Hayes WC, Bouxsein ML: Biomechanics of cortical and trabecular bone: Implications for assessment of fracture risk, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 76-82.

21. A 24-year-old man who works at a local oyster and clam farm sustained a laceration on his hand at work. Examination reveals a cellulitic index finger without evidence of tenosynovitis. After appropriate irrigation and debridement, what antibiotic is most appropriate?

1- Amoxicillin

2- Vancomycin

3- Clindamycin

4- Ceftazadime

5- Cefazolin

PREFERRED RESPONSE: 4

DISCUSSION: Injuries involving brackish water and shellfish can have devastating consequences caused by Vibrio vulnificus infections. Patients may have a severe invasive infection, with three main clinical features: primary septicemia, wound infection, and gastroenteritis. Antibiotic administration is crucial because mortality rates of up to 50% have been observed with Vibrio septicemia. The current recommendation is to give a third-generation cephalosporin such as ceftazadime.

REFERENCES: Chiang SR, Chuang YC: Vibrio vulnificus infection: Clinical manifestations, pathogenesis, and antimicrobial therapy. J Microbiol Immunol Infect 2003;36:81-88.

22. A 16-year-old girl has had anterior leg pain and a mass for the past 8 months. Figures 2a and 2b show a radiograph and an H & E histologic specimen. Which of the following disorders is believed to be a precursor of this lesion?

1- Nonossifying fibroma

2- Fibrous dysplasia

3- Unicameral bone cyst

4- Osteogenesis imperfecta

5- Osteofibrous dysplasia

PREFERRED RESPONSE: 5

DISCUSSION: The radiograph and pathology are consistent with adamantinoma. While the mechanism underlying adamantinoma has not been identified, it is believed to be closely related to osteofibrous dysplasia, which may represent a precursor. The other diagnoses are not known to give rise to adamantinoma.

REFERENCE: Springfield DS, Rosenberg AE, Mankin HJ, et al: Relationship between osteofibrous dysplasia and adamantinoma. Clin Orthop 1994;309:234-244.

23. Acetaminophen is an antipyretic medication. It exerts its pharmacologic effects by inhibiting which of the following enzymes?

1- Cyclooxygenase-2 (COX-2)

2- Interleukin-1 beta (IL-1 β)

3- Tumor necrosis factor alpha (TNF-α)

4- 5-Hydroxytryptamine (5-HT)

5- Metalloproteinases (MMPs)

PREFERRED RESPONSE: 2

DISCUSSION: Acetaminophen inhibits prostaglandin E2 production via IL-1 β, without affecting cyclooxygenase-2 enzymatic activity. The therapeutic concentrations of acetaminophen induce an inhibition of IL-1 β-dependent NF-kappa β nuclear translocation. The selectivity of this effect suggests the existence of an acetaminophen-specific activity at the transcriptional level that may be one of the mechanisms through which the drug exerts its pharmacologic effects. Acetaminophen does not affect any of the other enzymes named above.

REFERENCE: Mancini F, Landolfi C, Muzio M, et al: Acetaminophen down-regulates interleukin-1beta-induced nuclear factor-kappaB nuclear translocation in a human astrocytic cell line. Neurosci Lett 2003;353:79-82.

24. Nutritional rickets is associated with which of the following changes in chemical
blood level?

1- Low Vitamin D levels

2- High to normal calcium levels

3- High phosphate levels

4- Decreased PTH

5- Decreased alkaline phosphatase levels

PREFERRED RESPONSE: 1

DISCUSSION: Nutritional rickets is associated with decreased dietary intake of Vitamin D, resulting in low levels of Vitamin D that result in decreased intestinal absorption of calcium
and low to normal serologic levels of calcium. To boost serum calcium levels, there is a compensatory increase in PTH and bone resorption, leading to increased alkaline
phosphatase levels.

REFERENCES: Brinker MR: Cellular and molecular biology, immunology, and genetics in orthopaedics, in Miller MD (ed): Review of Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2001, pp 81-94.

Pettifor J: Nutritional and drug-induced rickets and osteomalacia, in Farrus MJ (ed): Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, ed 5. Philadelphia, PA, Lippincott Williams and Wilkins, 2003, pp 399-466.

Einhorn TA: Metabolic bone disease, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

25. What assay most directly assesses gene expression at the posttranslational level?

1- Real-time polymerase chain reaction (PCR)

2- Standard PCR

3- Northern blot

4- Western blot

5- Microarray expression profile analysis

PREFERRED RESPONSE: 4

DISCUSSION: Gene expression at the posttranslational level refers to proteins, as opposed to DNA or RNA. The only assay above that targets protein expression directly is the Western blot. Standard PCR is amplification of targeted DNA segments, regardless of whether or not they are actively expressed. Real-time PCR, Northern blot, and microarray expression profile analysis all quantify RNA as a means to determine posttranscriptional gene expression.

REFERENCES: Brinker MR: Cellular and molecular biology, immunology, and genetics in orthopaedics, in Miller MD (ed): Review of Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2001, pp 81-94.

26. Fully dense alumina and zirconia materials have been used as bearing materials in hip arthroplasty to provide greater wear resistance than polished metallic surfaces. Although both have shown reduced wear clinically, what concerns continue to exist about the use of zirconia?

1- Less tough than alumina, increasing the chance of brittle failure

2- May undergo a phase change that markedly reduces wear resistance

3- Not as biocompatible as other bearing materials

4- Susceptible to crevice corrosion

5- Susceptible to fatigue fracture

PREFERRED RESPONSE: 2

DISCUSSION: Zirconia as a bearing surface is “metastable,” meaning that, in the microstructure of the material the zirconia molecules are ordered in a tetragonal fashion, but they can easily transform to a monoclinic microstructure that is less wear resistant. Transformation can occur with input of enough energy (eg, thermal energy imparted by steam sterilization or mechanical energy at the bearing surface). Zirconia was introduced as an alternative to alumina because it has a higher toughness, making it less susceptible to gross fracture (ceramics do not undergo fatigue fracture, but rather fail from a process of slow crack growth). Zirconia is highly biocompatible (as are many ceramics) and is essentially immune to corrosive processes that can plague metallic alloys such as stainless steel.

REFERENCES: Clarke IC, Manaka M, Green DD, et al: Current status of zirconia used in total hip implants. J Bone Joint Surg Am 2003;85:73-84.

Haraguchi K, Sugano N, Nishii T, et al: Phase transformation of a zirconia ceramic head after total hip arthroplasty. J Bone Joint Surg Br 2001;83:996-1000.

27. A 36-year-old skier sustains a grade III posterior cruciate ligament (PCL) tear. Where will increased contact pressures develop over time?

1- Ligament of Humphrey

2- Patellar ligament

3- Quadriceps tendon

4- Lateral compartment

5- Medial compartment

PREFERRED RESPONSE: 5

DISCUSSION: Complete rupture of the PCL leads to increased contact pressures in the patellofemoral and medial compartments of the knee. However, whether degenerative arthritis will develop and in which compartments still remains controversial.

REFERENCE: Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000, p 767.

28. A 46-year-old patient with cervical myelopathy undergoes a multilevel posterior cervical laminectomy from C3 to C7. The risk of postlaminectomy kyphosis is greatest with removal of which of the following structures?

1- Greater than 80% of the lamina

2- Greater than 50% of each facet joint

3- Interspinous ligament

4- Facet joint capsules

5- Ligamentum flavum

PREFERRED RESPONSE: 2

DISCUSSION: Removal of more than 50% of a facet joint can lead to segmental instability and compromises the overall strength of the joint. Removal of the lamina, interspinous ligament, and ligamentum flavum are standard features of a cervical laminectomy. Most surgeons favor fusion with instrumentation of a laminectomized cervical spine. If the anterior part of the spine is already ankylosed from previous surgery or from degenerative conditions, or a posterior fusion with instrumentation is included, then the risk of kyphosis or instability is reduced.

REFERENCE: Zdeblick TA, Abitol JJ, Kunz DN, et al: Cervical stabilization after sequential capsule resection. Spine 1993;18:2005-2008.

29. A patient with a below-the-knee amputation is being evaluated for a new prosthesis.
He wants to improve his ability to walk on uneven surfaces. What modification to the prosthesis can be made to accommodate this request?

1- Shorten the keel

2- Lengthen the keel

3- Change the keel to a split keel

4- Change to a solid ankle, cushioned heel (SACH)

5- Change to carbon fiber

PREFERRED RESPONSE: 3

DISCUSSION: Changing from a solid keel to a keel with a sagittal split allows an amputee to navigate uneven terrain more easily. Changing the length of the keel affects the responsiveness of the prosthesis but does not address the surface conditions for ambulation. The SACH is not used as frequently anymore, because overload problems to the nonamputated foot have been observed.

REFERENCES: Koval K (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 31-45.

Goldberg B (ed): Atlas of Orthoses and Assistive Devices, ed 3. St Louis, MO, Mosby-Year Book, 1997.

30. What is the relative amount of type II collagen synthesis in disease-free adult articular cartilage compared to developing teenagers?

1- Less than 5%

2- 25%

3- 50%

4- 75%

5- 90%

PREFERRED RESPONSE: 1

DISCUSSION: Adult articular cartilage has less than 5% of the synthesis rate of type II collagen than that seen in developing teenagers. Both synthesis and degradation of type II collagen in normal adult articular cartilage is very low compared to children. In osteoarthrosis, both synthesis and degradation are increased, but the collagen does not properly incorporate into
the matrix.

REFERENCES: Lippiello L, Hall D, Mankin HJ: Collagen synthesis in normal and osteoarthritic human cartilage. J Clin Invest 1977;59:593-600.

Nelson F, Dahlberg L, Laverty S, et al: Evidence for altered synthesis of type II collagen in patients with osteoarthritis. J Clin Invest 1998;102:2115-2125.

31. What gene is expressed the earliest during the differentiation of a chondrocyte during endochondral ossification?

1- Aggrecan

2- Sox-9

3- Collagen type II

4- Collagen type IV

5- Collagen type XI

PREFERRED RESPONSE: 2

DISCUSSION: Transcription factors regulate the activation or repression of cartilage-specific genes. Sox-9, considered a major regulator of chondrogenesis, regulates several cartilage-specific genes during endochondral ossification, including collagen types II, IV, and XI and aggrecan.

REFERENCES: Li J, Sandell LJ: Transcriptional regulation of cartilage-specific genes, in Rosier RN, Evans C (eds): Molecular Biology in Orthoapedics, Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 21-24.

Sandell LJ: Genes and gene expression. Clin Orthop 2000;379:S9-S16.

32. The vascular supply to the medial meniscus comes primarily from what artery?

1- Lateral genicular

2- Lateral branch of the superior genicular

3- Medial branch of the superior genicular

4- Medial branch of the inferior genicular

5- Medial genicular

PREFERRED RESPONSE: 4

DISCUSSION: The vascular supply to the medial and lateral menisci originates predominantly from the medial and lateral genicular arteries. The popliteal artery splits into the superior genicular, which splits into medial and lateral branches supplying the patellar cartilage and the posterior cruciate ligament. The middle genicular artery also supplies the anterior curciate ligament, posterior cruciate ligament, and collateral ligaments. The inferior genicular splits into medial and lateral branches and supplies the menisci and other knee ligaments. Despite propagation of incorrect terminology, there is no superior or lateral genicular artery.

REFERENCE: Mow VC, Arnoczky SP, Jackson DW (eds): Knee Meniscus: Basic and Clinical Foundations. New York, NY, Raven Press, 1992, p 4.

33. A patient with a cobalt-chromium alloy (Co-Cr) femoral stem has a periprosthetic fracture that is to be fixed with a cable-plate device. The surgeon should make sure that the plate, screws, and cable, respectively, are made of

1- Co-Cr, stainless steel, stainless steel.

2- stainless steel, stainless steel, Co-Cr.

3- stainless steel, Co-Cr, Co-Cr.

4- titanium alloy, titanium alloy, titanium alloy.

5- titanium alloy, stainless steel, Co-Cr.

PREFERRED RESPONSE: 4

DISCUSSION: Contact between metals in a biologic environment leads to galvanic corrosion. Reduction potentials of Co-Cr and stainless steel produce the worst combination of metals in commonly used implants. Because the fixation implants are not intended to contact the existing implant, it is not as great a consideration as the plate and the screws and cables that will directly contact each other.

REFERENCES: Miller MD (ed): Review of Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2000, pp 119-144.

34. A college football player performs bicep curls as part of his weight lifting routine. During the flexion phase of the curl, what term defines the type of muscle contraction?

1- Isometric

2- Isokinetic

3- Isotonic

4- Eccentric

5- Plyometric

PREFERRED RESPONSE: 5

DISCUSSION: Muscle contractions can be classified by tension, length, and velocity. Isometric contractions involve changing tension in the muscle while the muscle stays at a constant length. An example would be pushing against a wall. Isokinetic contractions occur when the muscle maximally contracts at a constant velocity. Isotonic contractions involve constant tension throughout the range of motion. Eccentric contraction is when the muscle lengthens during contraction. Eccentric contractions have the highest risk of injury. Plyometrics are eccentric contractions at a rapid rate.

REFERENCES: Simon SR (ed): Orthopaedic Basic Science. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 89-125.

Evans WJ: Effects of exercise on senescent muscle. Clin Orthop 2002;403:S211-S220.

35. Which of the following statements most accurately describes the layers of articular cartilage?

1- The superficial zone has condensed proteoglycan and sparse collagen.

2- The intermediate zone transition is the thinnest layer and the chondrocytes are oriented tangentially.

3- The basal zone (middle, radial, deep) contains flattened chondrocytes.

4- Tidemark is found only in joints and not in the growing cartilage cap of an enchondroma.

5- Tidemark is more prominent in newborn joints.

PREFERRED RESPONSE: 4

DISCUSSION: Normal articular cartilage is composed of three zones that are based on the shape of the chondrocytes and the distribution of the type II collagen. The tangential zone has flattened chondrocytes, condensed collagen fibers, and sparse proteoglycan. The intermediate zone is the thickest layer with round chondrocytes oriented in perpendicular or vertical columns paralleling the collagen fibers. The basal layer is deepest with round chondrocytes. The tidemark is deep to the basal layer and separates the true articular cartilage from the deeper cartilage that is a remnant of the cartilage anlage, which participated in endochondral ossification during longitudinal growth in childhood. The tidemark divides the superficial uncalcified cartilage from the deeper calcified cartilage and also is the division between nutritional sources for the chondrocytes. The tidemark is the zone in which chondrocyte renewal took place in childhood. The tidemark is found only in joints and not in the cap of an enchondroma. It is seen most prominently in the adult, nongrowing joint.

REFERENCE: Schiller AL: Pathology of osteoarthritis, in Kuettner KE, Goldberg VM (eds): Osteoarthritic Disorders. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995,
pp 95-101.

36. What term best describes the process involved when a growth factor produced by an osteoblast stimulates the differentiation of an adjacent undifferentiated mesenchymal cell during fracture repair?

1- Mechanical

2- Autocrine

3- Paracrine

4- Endocrine

5- Systemic

PREFERRED RESPONSE: 3

DISCUSSION: Growth factors are proteins secreted by cells that can act on target cells to produce certain biologic actions. These actions can be described as autocrine, paracrine, and endocrine. Autocrine actions are those in which the growth factor influences an adjacent cell of its origin or identical phenotype. Paracrine actions are those in which the protein influences an adjacent cell that is different in its origin or phenotype. Endocrine actions are those in which the factor influences a cell located at a distant anatomic site.

REFERENCES: Lieberman J, Daluiski A, Einhorn TA: The role of growth factors in the repair of bone: Biology and clinical applications. J Bone Joint Surg Am 2002;84:1032-1044.

37. Vertebral fractures are common in the thoracolumbar spine. What is the most important factor that determines the strength of the cancellous bone in the vertebral body?

1- Mineral content

2- Rate of loading

3- Anatomic level of the vertebra

4- Apparent density

5- Trabecular number

PREFERRED RESPONSE: 4

DISCUSSION: Cancellous bone strength and stiffness are determined primarily by the apparent density (the amount of bone per unit volume). Strength varies approximately as the square of the density, and stiffness as the cube of the density; therefore, these are very strong relationships. Cancellous bone strength also depends on the mineral content, the rate of loading (it is viscoelastic), the anatomic level, and the trabecular number (an histomorphometry term), but all to a markedly lesser extent than density.

REFERENCES: Carter DR, Hayes WC: The compressive behavior of bone as a two-phase porous structure. J Bone Joint Surg Am 1977;59:954-962.

Keaveny TM: Strength of trabecular bone, in Cowin SC (ed): Bone Mechanics Handbook. Boca Raton, FL, CRC Press, 2001, pp 16-1-16-8.

38. What additional percentage of energy expenditure above baseline is required for ambulation after an above-the-knee amputation?

1- 0%

2- 5%

3- 20%

4- 65%

5- 90%

PREFERRED RESPONSE: 4

DISCUSSION: Patients with an above-the-knee amputation have a 65% increase in energy expenditure. A patient with a transtibial amputation requires 25% more energy above baseline values; however, bilateral transtibial amputations are associated with a 40% increase in energy expenditure.

REFERENCES: Otis JC, Lane JM, Kroll MA: Energy cost during gait in osteosarcoma patients after resection and knee replacement and after above-the-knee amputation. J Bone Joint Surg Am 1985;67:606-611.

Pinzur MS, Gold J, Schwartz D, et al: Energy demands for walking in dysvascular amputees as related to the level of amputation. Orthopedics 1992;15:1033-1036.

39. Bacitracin is a topical antibiotic agent that may be added to solutions and used for intraoperative lavage. What is this agent effective against?

1- Gram-positive bacteria

2- Gram-negative bacteria

3- Mixed flora

4- Bacterial spores

5- Fungi

PREFERRED RESPONSE: 1

DISCUSSION: Bacitracin is a polypeptide obtained from a strain (Tracy strain) of Bacillus subtilis. It is stable and poorly absorbed from the intestinal tract; its only use is for topical application to skin, wounds, or mucous membranes. Concentrations of 500 to 2,000 units per milliliter of solution or gram of ointment are used for topical application. Bacitracin is mainly bactericidal for gram-positive bacteria, including penicillin-resistant staphylococci. In combination with polymixin B or neomycin, bacitracin is useful for suppression of mixed bacterial flora in surface lesions. Bacitracin is toxic for the kidney, causing proteinuria, hematuria, and nitrogen retention; therefore, it has no place in systemic therapy. Bacitracin is said not to induce hypersensivity readily, but reactions to this agent have been described.

REFERENCES: Rosenstein BD, Wilson FC, Funderburk CH: The use of bacitracin irrigation to prevent infection in postoperative skeletal wounds: An experimental study. J Bone Joint Surg Am 1989;71:427-430.

Brooks GF, Butel JS, Morse SA (eds): Jawetz, Melnick, and Adelberg’ s Medical Microbiology: Antimicrobial Chemotherapy. New York, NY, McGraw-Hill, 1995, pp 187-188.

40. Ceramic bone substitutes have which of the following properties?

1- There is vascular ingrowth and subsequent graft resorption with host bone ingrowth.

2- Their interconnectivity is similar to that of cancellous bone.

3- They are brittle with significant tensile strength.

4- They are resorbed at a fairly constant rate.

5- Due to their strength, rigid stabilization of the surrounding bone is not necessary.

PREFERRED RESPONSE: 1

DISCUSSION: Ceramics have the following properties: They are resorbed at varying rates, and the chemical composition of the ceramic significantly affects the rate of resorption. For example, tricalcium phosphate (TCP) undergoes biologic resorption 10 to 20 times faster than hydroxyapatite. The partial conversion of TCP to hydroxyapatite once it is in the body significantly reduces the rate of resorption. Some segments of hydroxyapatite can remain in place in the body for 7 to 10 years. In clinical trials, TCP more readily remodels because of its porosity, but it is weaker. The success of converted corals as a bone graft substitute relies on a complex sequence of events of vascular ingrowth, differentiation of osteoprogenitor cells, bone remodeling, and graft resorption occurring together with host bone ingrowth into and on the porous coralline microstructure or voids left behind during resorption.

REFERENCES: Lane JM, Bostrom MP: Bone grafting and new composite biosynthetic graft materials. Instr Course Lect 1998;47:525-534.

Walsh WR, Chapman-Sheath PJ, Cain S, et al: A resorbable porous ceramic composite bone graft substitute in a rabbit metaphyseal defect model. J Orthop Res 2003;21:655-661.

41. Linazolid exerts its antimicrobial action by inhibiting bacterial

1- protein synthesis.

2- peptidoglycan wall synthesis.

3- DNA-gyrase activity.

4- mitochondrial enzymes.

5- oxidative phosphorylation.

PREFERRED RESPONSE: 1

DISCUSSION: Linazolid is the first agent of the oxazolidinone group of antibiotics and is very active against methicillin-sensitive Staphylococus aureus, S epidermidis, and vancomycin-resistant enterococci. The drug has no gram-negative activity. Linazolid inhibits protein synthesis by blocking formation of the 70S ribosomal translation complex. This mechanism of action is unique to the oxazolidinones.

REFERENCES: Rybak MJ, Cappelletty DM, Moldovan T, et al: Comparative in vitro activities and postantibiotic effects of the oxazolidinone compounds eperezolid (PNU-100592) and linezolid (PNU-100766) versus vancomycin against Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecalis, and Enterococcus faecium. Antimicrob Agents Chemother 1998;42:721-724.

Sweeney MT, Zurenko GE: In vitro activities of linezolid combined with other antimicrobial agents against Staphylococci, Enterococci, Pneumococci, and selected gram-negative organisms. Antimicrob Agents Chemother 2003;47:1902-1906.

42. Which of the following changes of calcium metabolism accompany the loss of bone during menopause?

1- Negative changes in external calcium balance with a decrease in intestinal calcium absorption and an increase in urinary calcium loss

2- A net negative change in calcium balance because of a decrease in intestinal absorption and a lesser decrease in urinary calcium loss

3- An increase of intestinal resorption with an increase of free 1,25-dihydroxyvitamin D

4- Loss of estrogen stimulating loss of calcium via increased PTH levels and subsequent decreased renal tubular absorption of calcium

5- No true change in calcium metabolism, but rather a net increased turnover of bone because of a decrease in circulating estrogen

PREFERRED RESPONSE: 1

DISCUSSION: There is a negative change of calcium balance with a decrease
in intestinal absorption and an increase in urinary calcium loss. The reduction of
intestinal absorption is accompanied by reduced circulating concentrations of total, but
not free 1,25-dihydroxyvitamin D. However, estrogen may also directly regulate intestinal calcium resorption independent of vitamin D. Tubular resorption of calcium is higher in the presence of estrogen. Studies of the levels of PTH in the presence of estrogen are controversial.

REFERENCES: Oh KW, Rhee EJ, Lee WY, et al: The relationship between circulating osteoprotegerin levels and bone mineral metabolism in healthy women. Clin Endocrinol (Oxf) 2004;61:244-249.

Reid IR: Menopause, in Favus MJ (ed): Primer on Metabolic Bone Diseases and Disorders of Mineral Metabolism, ed 4. Philadelphia, PA, Lippincott Williams & Wilkins, 1999, pp 55-57.

43. When compared with fresh-frozen bone allograft, freeze-dried bone allograft (FDBA) is characterized by

1- higher maximal stiffness in laboratory evaluation.

2- slower compaction rate requiring more impactions.

3- more stable fixation of the stem when tested in a hip simulator.

4- decreased compactness and stiffness.

5- decreased brittleness.

PREFERRED RESPONSE: 3

DISCUSSION: The compaction of FDBA is faster than that of fresh-frozen bone. The maximal stiffness reached by both materials when tested was the same (55 MPa), but the FDBA required fewer impactions to achieve that stiffness. Because it is easier to impact, the FDBA may be mechanically more efficient than the fresh-frozen bone in surgical conditions. The brittleness of irradiated FDBA, caused by loss of the capacity to absorb energy in a plastic way, increases the compactness and stiffness of morcellized grafts. The failure rate of fusion in adolescent idiopathic scoliosis has been shown to be much higher in FDBA than in either iliac crest bone graft or composite autograft with demineralized bone matrix. There is a greater erosive surface response to allograft when compared to autograft or frozen allograft, with a larger number of osteoclast and osteoblast nuclei seen microscopically.

REFERENCES: Cornu O, Libouton X, Naets B, et al: Freeze-dried irradiated bone brittleness improves compactness in an impaction bone grafting model. Acta Orthop Scand
2004;75:309-314.

Price CT, Connolly JF, Carantzas AC, et al: Comparison of bone grafts for posterior spinal fusion in adolescent idiopathic scoliosis. Spine 2003;28:793-798.

Leniz P, Ripalda P, Forriol F: The incorporation of different sorts of cancellous bone graft and the reaction of the host bone: A histomorphometric study in sheep. Int Orthop 2004;28:2-6.

44. A study is designed that examines fractures in children with osteogenesis imperfecta after being treated with bisphosphonates compared with a placebo. A difference is found for which the P value is greater than what is considered to be statistically significant. What is the next appropriate statistical analysis?

1- Repeated measures analysis of variance

2- F test

3- Power analysis

4- Analysis of variance

5- Kruskal-Wallis test

PREFERRED RESPONSE: 3

DISCUSSION: When a study yields a negative result between treatment groups, the next step is to perform a power analysis. The power, by definition, is the probability of rejecting the null hypothesis: in this example the null hypothesis would be that children treated with bisphosphonates would have fewer fractures than the untreated control population. The power analysis helps answer the question as to whether the null hypothesis should be rejected and the finding is real, or whether the sample size was too small or the effect of treatment too subtle to demonstrate a difference between the treatment and control groups.

Kocher MS, Zurakowski D: Clinical epidemiology and biostatistics: A primer for orthopaedic surgeons. J Bone Joint Surg Am 2004;86:607-620.

45. Which of the following best describes the relative content of the components of articular cartilage in decreasing order?

1- Water, collagen, proteoglycan, noncollagenous protein, chondrocytes

2- Water, proteoglycan, collagen, chondrocytes, noncollagenous protein

3- Water, noncollagenous protein, collagen, proteoglycan, chondrocytes

4- Collagen, noncollagenous protein, proteoglycan, chondrocytes, water

5- Collagen, proteoglycan, water, noncollagenous protein, chondrocytes

PREFERRED RESPONSE: 1

DISCUSSION: Water is the most abundant component of articular cartilage with a wet weight of 65% to 80%. Of the water, 80% is at the surface and 65% at the deep zone. Collagen accounts for 10% to 20% of the wet weight, with type II collagen accounting for 90% to 95% of the total collagen content. Small amounts of types V, VI, IX, X, and XI collagen are also present. Proteoglycans comprise 10% to 15% of the wet weight of collagen. The remainder of the wet weight is made up of other collagens, noncollagenous proteins, and chondrocytes.

REFERENCE: Schiller AL: Pathology of osteoarthritis, in Kuettner KE, Goldberg VM: Osteoarthritic Disorders. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995,
pp 95-101.

46. Human tendons are made up primarily of what collagen type (~95%)?

1- I

2- II

3- III

4- IV

5- V

PREFERRED RESPONSE: 1

DISCUSSION: Tendons are dense, primarily collagenous tissues that attach muscle to bone. Collagen content of the dry weight is slightly greater than that found in ligaments and is predominantly type I. Type III collagen makes up the remaining ~5% of total collagen content.

REFERENCES: Kasser JR (ed): Orthopaedic Knowledge Update 5. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1996, pp 10-12.

Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000, pp 21-37.

Frank CB, Shrive NG, Lo IK, et al: Form and function of tendon and ligament, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

47. The therapeutic effect of etanercept in the treatment of rheumatoid arthritis is primarily mediated through

1- antagonism of tumor necrosis factor-alpha (TNF-α).

2- antagonism of matrix metalloproteinases (MMPs).

3- inhibition of COX2.

4- stimulation of interleukin-1 (IL-1).

5- stimulation of tissue inhibitors of metalloproteinases (TIMPs).

PREFERRED RESPONSE: 1

DISCUSSION: Etanercept is a fusion protein that combines the ligand-binding domain of the TNF-α receptor to the Fc portion of human immunoglobulin G (IgG). Protein serves as a competitive inhibitor of TNF-α signaling. COX2 is the target of NSAIDs, including newer formulations that are more COX2-specific. The remaining responses are not direct targets of etanercept.

REFERENCES: Weinblatt ME, Kremer JM, Bankhurst AD, et al: A trial of etanercept, a recombinant tumor necrosis factor receptor: Fc fusion protein, in patients with rheumatoid arthritis receiving methotrexate. N Engl J Med 1999;340:253-259.

48. A 21-year-old woman has a nontraumatic rupture of the Achilles tendon. Which of the following commonly prescribed medications has been associated with this condition?

1- Ibuprofen

2- Fluoroquinolones

3- Bisphosphonates

4- Metoprolol

5- Simvistatin

PREFERRED RESPONSE: 2

DISCUSSION: Fluoroquinolones have been associated with increased rates of tendinitis, with special predilection for the Achilles tendon. Tenocytes in the Achilles tendon have exhibited degenerative changes when viewed microscopically after fluoroquinolone administration. Recent clinical studies have shown an increased relative risk of Achilles tendon rupture of 3.7. The other listed drugs have no known increase in tendon rupture rates nor tendinitis.

REFERENCES: van der Linden PD, van de Lei J, Nab HW, et al: Achilles tendinitis associated with fluoroquinolones. Br J Clin Pharmacol 1999;48:433-437.

Bernard-Beaubois K, Hecquet C, Hayem G, et al: In vitro study of cytotoxicity of quinolones on rabbit tenocytes. Cell Biol Toxicol 1998;14:283-292.

Maffulli N: Rupture of the Achilles tendon. J Bone Joint Surg Am 1999;81:1019-1036.

49. Bioabsorbable polymers are used in a wide range of orthopaedic devices, including anchors, staples, pins, plates, and screws. What is the primary drawback for bioabsorbable implants?

1- High cost

2- Increased rates of infection

3- High elastic modulus

4- Brittleness

5- Foreign body reaction

PREFERRED RESPONSE: 5

DISCUSSION: A number of bioabsorbable polymers are used in orthopaedic applications, and all have in common reports of foreign body reactions, which occur in more than 50% of patients in some series. In general, the high cost of these polymers is offset by the elimination of a second surgery to remove the implant. Bioabsorbable polymers are low strength in comparison to metallic alloys but of sufficient strength for many orthopaedic applications. The elastic modulus is not as high as many other orthopaedic biomaterials, making them suitable for applications where lower stiffness is an asset.

REFERENCES: Ambrose CG, Clanton TO: Bioabsorbable implants: Review of clinical experience in orthopedic surgery. Ann Biomed Eng 2004;32:171-177.

Bergsma JE, de Bruijn WC, Rozema FR, et al: Late degradation tissue response to poly
(L-lactide) bone plates and screws. Biomaterials 1995;16:25-31.

50. What ligament is the primary restraint to applied valgus loading of the knee?

1- Posteromedial capsule

2- Posterior cruciate ligament (PCL)

3- Superficial medial collateral ligament (MCL)

4- Deep MCL

5- Medial meniscus

PREFERRED RESPONSE: 3

DISCUSSION: The superficial portion of the MCL contributes 57% and 78% of medial stability at 5 degrees and 25 degrees of knee flexion, respectively. The deep MCL and posteromedial capsule act as secondary restraints at full knee extension. The anterior cruciate ligament and PCL also provide secondary resistance to valgus loads.

REFERENCE: Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000, p 767.

51. What region of the thoracic curve is most dangerous for pedicle screw insertion while performing a posterior fusion for adolescent idiopathic scoliosis?

1- Concave side at the stable vertebra

2- Concave side at the apex of the curve

3- Convex side at the stable vertebra

4- Convex side at the apex of the curve

5- Thoracolumbar junction

PREFERRED RESPONSE: 2

DISCUSSION: Morphologic and anatomic studies confirm the pedicle is smaller on the concave side of thoracic curves. The dura is also closer to the pedicle on the concave side of the curves.

REFERENCES: Liljenqvist U, Allkemper T, Hackenberg L, et al: Analysis of vertebral morphology in idiopathic scoliosis with use of magnetic resonance imaging and multiplanar reconstruction. J Bone Joint Surg Am 2002;84:359-368.

Parent S, Labelle H, Skalli W, et al: Thoracic pedicle morphometry in vertebrae from scoliotic spines. Spine 2004;29:239-248.

52. Plots of stress versus strain for four orthopaedic biomaterials are shown in Figure 3. Referring to the figure, what is the correct identification of the curves?

1- A = cortical bone; B = bone cement; C = cobalt alloy; D = titanium alloy

2- A = cortical bone; B = bone cement; C = cobalt alloy; D = stainless steel

3- A = bone cement; B = cortical bone; C = titanium alloy; D = stainless steel

4- A = bone cement; B = cortical bone; C = cobalt alloy; D = titanium alloy

5- A = polyethylene; B = cortical bone; C = stainless steel; D = titanium alloy

PREFERRED RESPONSE: 3

DISCUSSION: Stress-strain plots allow easy comparison of a number of important mechanical properties, including elastic modulus (the slope of the initial straight line portion of the curve) and yield stress (the stress at the break in the curves for bone, steel, and titanium alloy). Important considerations here are much lower modulus and ultimate stress of bone and cement compared to the two metallic alloys, the fact that titanium is lower modulus but higher strength than stainless steel, and the identification of cement as the only brittle material among the four.

REFERENCES: Burstein AH, Wright TM: Fundamentals of Orthopaedic Biomechanics. Baltimore, MD, Williams and Wilkins, 1994, pp 97-129.

53. A 54-year-old woman underwent prophylactic intramedullary fixation for an impending fracture of her right femur secondary to metastatic breast cancer. A bone scan revealed a second lesion in her inferior pubic ramus. Her oncologist has recommended that she receive the intravenous bisphosphonate, zoledronic acid, because the medication would

1- result in increased bone density.

2- accelerate healing of the femoral fracture.

3- lower the serum phosphate level.

4- reduce processing of future bone metastases.

5- heal other impending fractures.

PREFERRED RESPONSE: 4

DISCUSSION: Bisphosphonates have been reported to reduce the incidence of new osseous lesions and prevent an increase in size of existing lesions. Zoledronic acid has been reported in clinical trials to decrease the skeletal complications of patients with multiple myeloma and with bone metastases from solid tumors. Results also have demonstrated that zoledronic acid delays the initial onset of bone complications by more than 2 months in patients with non-small-cell lung cancer and other solid tumors. In two placebo-controlled clinical studies of zoledronic acid conducted in patients with bone metastases from prostate cancer or other solid tumors, there was a decrease in the number of patients with skeletal-related events compared to placebo, and the time to the first skeletal-related event was delayed.

REFERENCES: Mundy GR, Yoneda T: Bisphosphonates as anticancer drugs. N Engl J Med 1998;339:398-400.

Rosen LS, Gordon D, Kaminski M, et al: Zoledronic acid versus pamidronate in the treatment of skeletal metastases in patients with breast cancer or osteolytic lesions of multiple myeloma: A phase III, double-blind, comparative trial. Cancer J 2001;7:377-387.

54. What is the known manner in which the growth hormone-insulin-like growth factor-I (GH-IGF-I) system functions to stimulate bone growth?

1- The products of the system induce proliferation without maturation of the growth plate and thus induce linear skeletal growth.

2- The active metabolite enters target cells and signals via a nuclear receptor to stimulate both proliferation and maturation of the growth plate.

3- During puberty, increased amounts of the active hormone metabolite promote proliferation and maturation of the growth plate.

4- GH acts directly on the growth plate via cell surface receptors and circulation; IGF-I stimulates secondarily.

5- The GH-IGF-I system inhibits osteoclastic bone resorption and stimulates osteoblasts to bond to the collagen matrix of the growth plate.

PREFERRED RESPONSE: 1

DISCUSSION: IGF-I, formerly known as somatomedin-C, possibly acts by both paracrine and endocrine hormone pathways. The products of the GH-IGF-I system induce proliferation without maturation of the growth plate and thus induce linear skeletal growth. The action of the thyroid hormone axis is via an active metabolite that enters target cells and signals a nuclear receptor to stimulate both proliferation and maturation of the growth plate. Increased amounts of the active steroid hormone metabolite promote proliferation and maturation of the growth plate. Calcitonin inhibits bone resorption.

REFERENCES: Binder G, Grauer ML, Wehner AV, et al: Outcome in tall stature: Final height and psychological aspects in 220 patients with and without treatment. Eur J Pediatr 1997;156:905-910.

Wang J, Zhou J, Cheng CM, et al: Evidence supporting dual, IGF-I-independent and IGF-I-dependent, roles for GH in promoting longitudinal bone growth. Endocrinol 2004;180:247-255.

Gertner JM: Childhood and adolescence, in Favus MJ (ed): Primer on Metabolic Bone Diseases and Disorders of Mineral Metabolism, ed 4. Philadelphia, PA, Lippincott Williams & Wilkins, 1999, pp 45-47.

55. During particle-induced osteolysis around implants, what cell secretes most of the interleukin-6 (IL-6)?

1- Osteoblasts from surrounding bone

2- B-lymphocytes in the bone marrow

3- Fibroblastic cells in the periprosthetic lining

4- T-lymphocytes in the circulating blood

5- Macrophages in the granuloma

PREFERRED RESPONSE: 3

DISCUSSION: During osteolysis, IL-6 is secreted by fibroblasts in the membrane surrounding the prosthesis. IL-6 also can be secreted by osteoblasts in other settings, but they are not the predominant source of IL-6 in particle-induced osteolysis. The remaining cells are not major sources of IL-6.

REFERENCE: Bukata SV, Gelinas J, Wei X, et al: PGE2 and IL-6 production by fibroblasts in response to titanium wear debris particles is mediated through a Cox-2 dependent pathway. J Orthop Res 2004;22:6-12.

56. What mechanism is associated with the spontaneous resorption of herniated
nucleus pulposus?

1- Macrophage infiltration and phagocytosis

2- Granuloma formation

3- Antibody mediated destruction

4- Complement cascade activation

5- Major histocompatibility complex mediated pathways

PREFERRED RESPONSE: 1

DISCUSSION: Nonsurgical modalities remain the mainstay for treatment of herniated disks. Spontaneous resorption of herniated disks frequently is detected by MRI. Marked infiltration by macrophages and neovascularization are observed on histologic examination of herniated disks, and the resorption is believed to be related to this process. Many cytokines such as vascular endothelial growth factor, tumor necrosis factor-alpha, and metalloproteinases have been implicated in this process, but none has been found to be singularly responsible.

REFERENCES: Haro H, Kato T, Kamori H, et al: Vascular endothelial growth factor (VEGF)-induced angiogenesis in herniated disc resorption. J Orthop Res 2002;20:409-415.

Doita M, Kanatani T, Ozaki T, et al: Influence of macrophage infiltration of herniated disc tissue on the production of matrix metalloproteinases leading to disc resorption. Spine
2001;26:1522-1527.

57. A 68-year-old woman with metastatic breast carcinoma is seen in the emergency department. She appears lethargic, and she reports abdominal pain, nausea, and constipation. An EKG reveals a shortened QT interval. The only physical finding on examination is diffuse hyporeflexia. What is the most appropriate step in management?

1- Intravenous fluid administration

2- Intravenous bisphosphonates

3- Intranasal calcitonin

4- Methotrexate

5- Mithramycin by oral administration

PREFERRED RESPONSE: 1

DISCUSSION: Intravenous fluid administration is the best first step to treat the hypercalcemia of malignancy. Many of these patients are dehydrated, and the increased serum calcium impairs the ability of the kidney to concentrate the urine. The decreased glomerular filtration rate secondary to the hypovolemia also leads to increased tubular resorption of calcium. The establishment of normovolemia will help promote increased urinary excretion of calcium. Lasix can also be used to help promote calciuria. Mithramycin is an antibiotic derived from Streptomyces plicatus. It is part of a group of drugs referred to as chromomycin antibiotics and is the only one of this group used clinically in the United States. It is rarely used in cancer chemotherapy because of its toxicity. A number of drug-related deaths have occurred from the use of mithramycin. Its use is now limited to the treatment of hypercalcemia associated with malignancy where it is used in lower dosage than that used for the treatment of tumors. Methotrexate has no role in the treatment of hypercalcemia of malignancy. While intravenous bisphosphonates are helpful in slowing progression of metastases and may help lower cerum calcium, they are not appropriate in the emergent treatment of hypercalcemia in the metastatic cancer patient.

REFERENCE: Stewart AF: Clinical practice: Hypercalcemia associated with cancer. N Engl J of Med 2005;352:373-379.

58. What is the primary role of superficial zone protein (SZP) in articular cartilage?

1- Expression of interleukin-1

2- Downregulation of collagenase

3- Upregulation of tissue inhibitor of metalloproteinase (TIMP)

4- Orientation of superficial collagen fibrils

5- Boundary lubrication

PREFERRED RESPONSE: 5

DISCUSSION: Lubricin and SZP share a similar primary structure but may differ in posttranslational modifications with O-linked oligosaccharides. The primary physiologic function of SZP appears to be boundary lubrication. SZP does not influence interleukin-1, collagenase, or TIMP directly because these proteins are associated with articular cartilage turnover.

REFERENCES: Hlavacek M: The influence of the acetabular labrum seal, intact articular superficial zone and synovial fluid thixotropy on squeeze-film lubrication of a spherical synovial joint. J Biomech 2002;35:1325-1335.

Jay GD, Tantravahi U, Britt DE, et al: Homology of lubricin and superficial zone protein (SZP): Products of megakaryocyte stimulating factor (MSF) gene expression by human synovial fibroblasts and articular chondrocytes localized to chromosome 1q25. J Orthop Res 2001;19:677-687.

59. Clinical evidence suggests that grafts for replacing a torn anterior cruciate ligament often stretch after surgery. What is the most probable mechanism for this behavior?

1- Gross failure at the attachment sites

2- Fatigue failure of the ligament tissue

3- Creep of the graft material

4- Water absorption by the graft material

5- Elastic stretch of collagen fibers

PREFERRED RESPONSE: 3

DISCUSSION: The stretching of the graft occurs over time as the graft is loaded. Time-dependent deformation under load is called creep and is common in viscoelastic materials such as ligament tissue. Creep can occur under both static and cyclic load conditions; time-dependent deformation will occur as long as load is applied to the tissue. Similarly, when a graft is initially tensioned to a given deformation at surgery, the load generated in the graft will decrease over time; this behavior is called stress relaxation and also is indicative of a viscoelastic material. Water content may affect the viscoelastic properties by changing the friction between collagen fibers, but studies have shown little difference in water content between grafts and normal ligaments. Fatigue failures may manifest themselves through damage to the ligament tissue, but this would require higher loads than are routinely experienced by grafts. Elastic stretch is recoverable and, therefore, does not contribute to a permanent stretch. Similarly, gross failure at the attachment would not cause a stretch, but rather a catastrophic instantaneous instability.

REFERENCES: Boorman RS, Thornton GM, Shrive NG, et al: Ligament grafts become more susceptible to creep within days after surgery. Acta Orthop Scand 2002;73:568-574.

60. A 60-year-old man with diabetes mellitus is referred for evaluation of nonhealing ulcers of his left foot. Nonsurgical management has failed to provide relief, and a below-the-knee amputation is being considered. Which of the following studies best predicts successful amputation wound healing?

1- Hemoglobin A1c of 8.2

2- Serum albumin of 2.5 g/dL

3- Hemoglobin of 10 g/dL

4- Ankle-brachial index of 1.0

5- Transcutaneous partial pressure of O₂ (TcPO₂) of 50 mm Hg

PREFERRED RESPONSE: 5

DISCUSSION: The TcPO₂ measures the O₂ delivering capacity of the local vasculature. Values above 40 mm Hg have been shown to correlate with positive healing potential. The hemoglobin A1c is a good indicator of long-term glucose levels; however, it has no direct correlation with wound healing potential. Serum albumin is an indirect measure of nutritional status, and deficiencies in nutrition must be addressed before any surgery. Adequate hemoglobin levels are also necessary to promote adequate oxygenation to the amputation site. The ankle-brachial index may be falsely elevated as a result of calcified vessels in patients with diabetes mellitus.

REFERENCES: Wyss CR, Harrington RM, Burgess EM, et al: Transcutaneous oxygen tension as a predictor of success after amputation. J Bone Joint Surg Am 1988;70:203-207.

Dwars BJ,van den Broek TA, Rauwerda JA, et al: Criteria for reliable selection of the lowest level of amputation in peripheral vascular disease. J Vasc Surg 1992;15:536-542.

61. The wear resistance of ultra-high molecular weight polyethylene can be improved by exposing the polymer to high-energy radiation (eg, gamma or electron beam), followed by a thermal treatment. What is one detrimental side effect of this process?

1- Decreased resistance to oxidative degradation

2- Decreased toughness

3- Increased density of nonconsolidated particles

4- Increased elastic modulus

5- High levels of residual free radicals

PREFERRED RESPONSE: 2

DISCUSSION: Highly cross-linked polyethylene has gained widespread acceptance for joint arthroplasty components because of reported experimental and early clinical accounts of significant reductions in wear. Cross-linking is increased by imparting additional energy into the polymer (above that conventionally used for sterilization). The thermal treatments after cross-linking stabilize the material against oxidative degradation by quenching free radicals and also reduce the elastic modulus. One disadvantage of the increased cross-linking is a reduction in toughness that makes the polyethylene more susceptible to crack initiation and propagation. The reduced toughness raises concerns for gross component fracture and fracture at stress concentrations that can arise with the locking mechanisms used to secure polyethylene inserts into metallic backings. Nonconsolidated polyethylene particles have been associated with increased subsurface density secondary to oxidative degradation in conventional polyethylene implants. The quenching of free radicals by thermal treatment in highly cross-linked polyethylene should prevent this problem.

REFERENCES: Collier JP, Currier BH, Kennedy FE, et al: Comparison of cross-linked polyethylene materials for orthopaedic applications. Clin Orthop 2003;414:289-304.

62. Which of the following best characterizes the antigenicity of allograft bone?

1- Cell surface glycoproteins are primarily responsible for the antigenicity of the graft.

2- Fresh grafts have less antigenicity than cryopreserved grafts.

3- Immunosupression provides little difference in response to allogenic bone.

4- Hematopoietic elements are the primary cells causing antigenic response.

5- Lyophilization (freeze-drying) or chemical sterilization does not change the antigenicity of the graft.

PREFERRED RESPONSE: 1

DISCUSSION: Cell surface glycoproteins present in the heterogeneous population of the cells within the graft are primarily responsible for the antigenicity. Macromolocules of the matrix have also been implicated. Cryopreserved grafts have less antigenicity than fresh. Freezing, freeze-drying, or chemical sterilization and antigen extraction of the bone allograft have all been shown to reduce the antigenicity of the graft. Freeze-drying of retroviral-infected cortical bone and tendon does not inactivate retrovirus. Immunosuppression has been shown to decrease response. Hematopoietic elements along with osteogenic, chondrogenic, fibrous, and vascular cells have been shown to be antigenic.

REFERENCES: Crawford MJ, Swenson CL, Arnoczky SP, et al: Lyophilization does not inactivate infectious retrovirus in systemically infected bone and tendon allografts. Am J Sports Med 2004;32:580-586.

Stevenson S, Li XQ, Davy DT, et al: Critical biological determinants of incorporation of non-vascularized cortical bone grafts: Quantification of a complex process and structure. J Bone Joint Surg Am 1997;79:1-16.

Simon SR (eds): Orthopaedic Basic Science. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 277-320.

63. Which of the following clinical disorders is the result of a mutation in fibroblast growth factor recepter 3 (FGFR3)?

1- Cleidocranial dysplasia

2- Schmid metaphyseal chondrodysplasia

3- Achondroplasia

4- Fibrous dysplasia

5- Camptomelic dysplasia

PREFERRED RESPONSE: 3

DISCUSSION: Camptomelic dysplasia is caused by a heterozygous loss of function of the Sox9 gene. The alternatives have genetic causes, but are not linked to Sox9. Cleidocranial dysplasia is related to a defect in Cbfa-1 (Osf-2, Runx2). Schmid metaphyseal chondrodysplasia is related to Type X collagen. Fibrous dysplasia is related to a defect in the alpha subunit of stimulatory guanine-nucleotide-binding protein (Gs). Achondroplasia is related to a defect in fibroblast growth factor receptor 3.

REFERENCES: Wagner T, Wirth J, Meyer J, et al: Autosomal sex reversal and camptomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 1994;79:1111-1120.

Dietz FR, Murray JC: Update on the genetic bases of disorders with orthopaedic manifestations, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006,
in press.

64. Which of the following best characterizes bone mineralization?

1- Initial sites of mineralization occurring at hole zones between the collagen fibrils

2- High levels of adenosine triphosphate and proteoglycans at the site of nucleation

3- Highly pure and perfect crystals of hydroxyapatite increasing in dimension by adding ions in a linear fashion

4- An energy-limiting step of individual hydroxyapatite crystals combining in aggregate in one or more directions

5- Macromolecules binding to the crystal surface to promote further growth in that particular direction

PREFERRED RESPONSE: 1

DISCUSSION: Mineralization occurs at the site of hole zones between the collagen fibrils. Crystals begin from the necessary ions of the lattice that come together with the correct orientation to form the first stable crystal. Formation of this critical nucleus is the most energy-demanding step of crystallization. Enzymes within the extracellular matrix vesicles degrade inhibitors such as adenosine triphosphate, pyrophosphate, and proteoglycans found in the surrounding extracellular matrix. Bone mineral consists of numerous impurities (carbonate, magnesium) that are more soluble, allowing the bone to act as a reservoir for calcium, phosphate, and magnesium ions. Crystals may form by addition of ions or ion clusters to the critical nucleus in many directions, with ‘kink’ sites forming to branch and exponentially proliferate the crystals. Macromolecules facilitate formation of the critical nucleus and increasing local concentrations of necessary ions. Once the crystals are formed and proliferating, macromolecules bind to the surface and block the growth of the crystal, regulating size, shape, and number of crystals.

REFERENCES: Lian JB, Stein GS, Canalis E, et al: Bone formation: Osteoblast lineage cells, growth factors, matrix proteins, and the mineralization process, in Favus MJ (ed): Primer on Metabolic Bone Diseases and Disorders of Mineral Metabolism, ed 4. Philadelphia, PA, Lippincott Williams & Wilkins, 1999, pp 14-29.

Gehron RP, Boskey AL: The biochemistry of bone, in Marcus R, Feldman D, Kelsey J (eds): Osteoporosis. San Diego, CA, Academic Press, 1996, pp 95-184.

65. What is the main mechanism for nutrition of the adult disk?

1- Capillary network from the adjacent segmental arteries

2- Capillary network from the arterioles in the vertebral body

3- Diffusion through the anulus fibrosus

4- Diffusion through pores in the end plates

5- Diffusion through nerves in the dorsal root ganglion

PREFERRED RESPONSE: 4

DISCUSSION: Disk nutrition occurs via diffusion through pores in the end plates. The disk has no direct blood supply, and the anulus is not porous to allow diffusion. The dorsal root ganglion does not provide blood supply to the disc.

REFERENCES: Biyani A, Andersson GB: Low back pain: Pathophysiology and management. J Am Acad Orthop Surg 2004;12:106-115.

Urban JG, Holm S, Maroudas A, et al: Nutrition of the intervertebral disc: Effect of fluid flow on solute transport. Clin Orthop 1982;170:296-302.

Park AE, Boden SD: Intervertebral disk: Form and function, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

66. A study is conducted to measure the difference in bone mineral density between postmenopausal women taking a drug treatment versus those taking a placebo. What is the most important result to be reported from this study?

1- The P-value from a t-test comparing the mean densities

2- The P-value from a Wilcoxon rank test comparing the densities

3- The difference between the mean bone mineral densities of the two groups

4- The ratio of the mean mineral density of the experimental group to that of the control group, along with the P-value

5- The means and standard deviations of the bone mineral densities for the
two groups

PREFERRED RESPONSE: 5

DISCUSSION: A complete answer necessarily includes the means and standard deviations of bone mineral density in both groups. Given these, which are the basic results of the study, the P-value can be calculated if desired. All of the other options preclude assessment of the actual data, that is, the information collected by the study. P-values and confidence intervals should be perceived as additional information, which help to assess the certainty of relating the study’s findings to the general population, but they should not be reported instead of the results
(ie, the means and standard deviations).

REFERENCE: Ebramzadeh E, McKellop H, Dorey F, et al: Challenging the validity of conclusions based on P-values alone: A critique of contemporary clinical research design and methods. Instr Course Lect 1994;43:587-600.

67. Figures 4a through 4c show the radiographs, CT scans, and T1-weighted MRI scan of a 19-year old man who has had increasing right hip pain and decreasing range of motion for the past several years. He also reports intermittent “locking” of the hip. What is the most likely diagnosis?

1- Chondrosarcoma

2- Stress fracture

3- Osteochondroma

4- Osteosarcoma

5- Synovial osteochondromatosis

PREFERRED RESPONSE: 5

DISCUSSION: The radiographs reveal small ossified masses around the femoral neck. The CT scans also show these masses and suggest that they are separate from the underlying cortex of the femoral neck, although they abut it. The MRI scan does not reveal significant marrow changes in the proximal femur apart from some mild reactive changes immediately adjacent to the nodules. These findings suggest a synovial or joint-based disorder as opposed to a primary bone tumor. The most likely diagnosis is synovial osteochondromatosis, which is consistent with the patient’s mechanical symptoms.

REFERENCES: Crotty JM, Monu JU, Pope TL Jr: Synovial osteochondromatosis. Radiol Clin North Am 1996;34:327-342.

Frassica F: Orthopaedic pathology, in Miller M (ed): Review of Orthopaedics, ed 2. Philadelphia, PA, WB Saunders, 1996, pp 292-335.

68. The presence of S100B tumor marker typically corresponds with which of the following as being the most likely source of the metastasis?

1- Thyroid adenocarcinoma

2- Breast carcinoma

3- Gastrointestinal carcinoma

4- Melanoma

5- Astrocytoma

PREFERRED RESPONSE: 4

DISCUSSION: Advances in development of new tumor markers and techniques of antigen retrieval have enhanced the sensitivity and reliability of identifying the primary source of metastasis. New markers such as CK7, CK20, CA125, and thyroid transcription factor-1
(TTF-1) can help to determine the origin of an adenocarcinoma or aid in the recognition of other tumors. In patients who do not have an obvious primary site of disease or screening radiographs, these new markers can help focus the search for and guide the treatment of the underlying lesion. CA125 is positive in patients with ovarian cancer, CK7 is positive in patients with breast and lung carcinoma, and CK20 is indicative of colon carcinoma if the CK7 marker is negative. Gastrointestinal stromal tumor (GIST) is positive for CD117 (c-kit) and CD34, whereas 75% of bronchogenic carcinomas are positive for TTF-1. Histochemical staining of the S100 protein family has been used for many years in the diagnosis of malignant melanoma. Recent markers HMB-45, MART-1, and Melan-A have proved to be useful in diagnosis of melanoma. S100B protein has been implicated in downregulation of p53 (oncosuppressor gene).

REFERENCES: Harpio R, Einarsson R: S100 proteins as cancer biomarkers with focus on S100B in malignant melanoma. Clin Biochem 2004;37:512-518.

Roodman GD: Mechanisms of bone metastasis. N Engl J Med 2004;350:1655-1664.

69. Which of the following accurately describes the biosynthetic materials tricalcium phosphate (TCP) and hydroxyapatite?

1- The osteoblast is the cell responsible for resorption of hydroxyapatite.

2- Once in the body, TCP is partially converted to hydroxyapatite.

3- TCP undergoes biologic resorption at a rate 10 times slower than hydroxyapatite.

4- TCP is much stronger biomechanically in compression than hydroxyapatite.

5- Optimal pore size for both materials appears to be less than 150 µm.

PREFERRED RESPONSE: 2

DISCUSSION: TCP is resorbed more rapidly, at a rate of 10 to 20 times faster than hydroxyapatite, partially because its larger pore size makes it a weaker substance. It provides significantly less compressive strength than hydroxyapatite. It does partially convert to hydroxyapatite, thus slowing its resorption rate. The absorbing cell of hydroxyapatite is the foreign body giant cell, not the osteoclast. Optimum pore size appears to be between 150 and
500 µm.

REFERENCES: Lane JM, Bostrom MP: Bone grafting and new composite biosynthetic graft materials. Instr Course Lect 1998;47:525-534.

Walsh WR, Chapman-Sheath PJ, Cain S, et al: A resorbable porous ceramic composite bone graft substitute in a rabbit metaphyseal defect model. J Orthop Res 2003;21:655-661.

70. A patient undergoes cartilage implantation requiring amplification of donor cells. Which of the following statements best describes the transplants?

1- There is a linear relationship between biosynthetic activity and the number of chondrocytes seeded.

2- Osteochondral lesions of 12 mm in size may be treated with chondrocyte transplantation alone.

3- Mesenchymal stem cells are harvested and allowed to differentiate to chondrocytes ex vivo.

4- The cellular carrier has no effect on biosynthetic activity.

5- In animal studies using fluorescent-labeled articular chondrocytes, donor cells are found to persist for up to 5 years.

PREFERRED RESPONSE: 1

DISCUSSION: Chondrocytes are obtained from cartilage harvested from non-weight-bearing areas of the knee. The extracellular matrix is digested, and the chondrocytes are expanded for later transplantation. Cells implanted into a defect are secured with a flap of periosteum. Cells are expanded to obtain 20 to 50 times the original number of cells to transplant at a cell density of 3x10^-7 cells/mL. There is a direct relationship between cell number and biosynthetic activity. Osteochondral lesions of up to 8 mm may be treated with autologous transplant alone; larger depth lesions should be bone grafted at the time of harvest. Mesenchymal stem cells differentiate easily into fibrous tissue, bone, and fat; conversion of mesenchymal stem cells into cartilage in vitro currently is difficult to accomplish. Goldberg and Caplan, however, were able to obtain cartilage repair using mesenchymal stem cells transplanted into defects in rabbits in vivo. In animal studies, fluorescent-labeled cells persist for at least 14 weeks, integrate with the surrounding normal margins, and become part of the repaired tissue replete with sulfated proteoglycans and type II collagen.

REFERENCES: Brittberg M, Peterson L, Sjogren-Jansson E, et al: Articular cartilage engineering with autologous chondrocyte transplantation. J Bone Joint Surg Am
2003;85:109-115.

Caplan AI, Elyaderani M, Mochizuki Y, et al: Principles of cartilage repair and regeneration. Clin Orthop 1997;342:254-269.

71. The load versus deformation curve of the functional spinal unit (FSU) is made up of the neutral zone, the elastic zone, and the plastic zone. What is the plastic zone of the curve believed to represent?

1- Lining up of collagen fibers within the ligaments

2- Stretching of elastin within the disk and ligaments

3- Transition between flexion and extension

4- Reversible elongation of the soft tissues

5- Traumatic range of motion, resulting in damage to the soft tissues

PREFERRED RESPONSE: 5

DISCUSSION: Plastic deformation of viscoelastic tissues represents deformation of the soft tissues to the point of failure. The lining up of collagen fibers would be in the “toe region” of the curve, which, in the case of the FSU, would be mainly in the neutral zone. Elastin is a minor contributor to the composition of the ligaments and would be protected by the stiffer collagen fibers. The transition between flexion and extension occurs in the neutral zone, and reversible elongation occurs in the elastic zone.

REFERENCES: Fardon DF, Garfin SR, Abitbol J, et al (eds): Orthopaedic Knowledge Update: Spine 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 15-23.

Panjabi MM, White AA: Physical properties and functional biomechanics of the spine, in White AA, Panjabi MM: Clinical Biomechanics of the Spine, ed 2. Philadelphia, PA, JB Lippincott, 1990, pp 1-83.

72. A knock-out mouse for the Vitamin D receptor has which of the following phenotypes?

1- Osteopetrosis

2- Renal failure

3- Rickets

4- Jansen-type metaphyseal dysplasia

5- Compensatory hyperparathyroidism and no skeletal phenotype

PREFERRED RESPONSE: 3

DISCUSSION: A knock-out mouse to the Vitamin D receptor would cause loss of vitamin D function, resulting in rickets. Renal failure would not occur; although Vitamin D is converted from 25 (OH) D to 1,25 (OH) D in the kidney, the active hormone acts on the gut and bone. Osteopetrosis can be seen as the phenotype for the c fos knock-out mouse; the Jansen-type metaphyseal dysplasia phenotype results from overactivation of the PTH/PTHrp receptor. Although compensatory hyperparathyroidism would occur, excessive PTH would not be able to rescue the skeletal loss and instead phosphoturia and phosphotasia would result.

REFERENCES: Glowacki J, Hurwitz S, Thornhill TS, et al: Osteoporosis and vitamin-D deficiency among postmenopausal women with osteoarthritis undergoing total hip arthroplasty. J Bone Joint Surg Am 2003;85:2371-2377.

Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, p 51.

73. A 30-year-old woman injures her knee while skiing. Based on the MRI scan shown in Figure 5, treatment should consist of

1- anterior cruciate ligament reconstruction.

2- medial collateral ligament (MCL) reconstruction.

3- MCL repair.

4- functional rehabilitation and early motion.

5- medial meniscal repair.

PREFERRED RESPONSE: 4

DISCUSSION: The MRI scan demonstrates a grade III MCL tear. Basic science and clinical studies have shown that nonsurgical management is preferred for MCL tears. Functional rehabilitation and early motion have led to consistently better results than has surgical repair.

REFERENCE: Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000, p 43.

74. Intramembranous ossification during fracture repair is characterized by absence of which of the following elements?

1- Alkaline phosphatase

2- Osteonectin

3- Osteopontin

4- Collagen type I expression

5- Collagen type II expression

PREFERRED RESPONSE: 5

DISCUSSION: Intramembranous ossification occurs through the direct formation of bone without the formation of a cartilaginous intermediate. Clinically, both intramembranous and endochondral ossification occur simultaneously during fracture healing; however, the latter is characterized by the differentiation and maturation of chondrocytes, vascular invasion of a hypertrophic cartilage matrix, and bone formation. Collagens type II and X are cartilage specific and would be characteristic of endochondral ossification, not intramembranous ossification.

75. Patients with rheumatoid arthritis may exhibit an increase in viral load for which of the following viruses?

1- Human immunodeficiency virus (HIV)

2- Papilloma virus

3- Epstein-Barr virus (EBV)

4- Hepatitis C virus (HCV)

5- Hepatitis B virus( HBV)

PREFERRED RESPONSE: 3

DISCUSSION: Rheumatoid arthritis (RA) is a complex multisystem disorder. It has been suggested that patients with RA have an impaired capacity to control infection with Epstein-Barr virus. Epstein-Barr virus has oncogenic potential and is implicated in the development of some lymphomas. Recent publications provide evidence for an altered Epstein-Barr virus-host balance in patients with RA who have a relatively high Epstein-Barr virus load. Large epidemiologic studies confirm that lymphoma is more likely to develop in patients with RA than in the general population. The overall risk of development of lymphoma has not risen with the increased use of methotrexate or biologic agents. Histologic analysis reveals that most lymphomas in patients with RA are diffuse large B cell lymphomas, a form of non-Hodgkin lymphoma. Epstein-Barr virus is detected in a proportion of these. Patients with RA do not have prevalence for infection with any of the other mentioned viruses.

REFERENCES: Callan MF: Epstein-Barr virus, arthritis, and the development of lymphoma in arthritis patients. Curr Opin Rheumatol 2004;16:399-405.

Baecklund E, Sundstrom C, Ekbom A, et al: Lymphoma subtypes in patients with rheumatoid arthritis: Increased proportion of diffuse large B cell lymphoma. Arthritis Rheum
2003;48:1543-1550.

76. Osteopenia is defined by the World Health Organization (WHO) as a bone mineral density (BMD) that is

1- within 1 standard deviation of aged-matched normals.

3- within 1 and 2.5 standard deviations below aged-matched normals.

2- within 1 standard deviation of young normals.

4- within 1 and 2.5 standard deviations below young normals.

5- more than 2.5 standard deviations below aged-matched normals.

PREFERRED RESPONSE: 4

DISCUSSION: Osteopenia, decreased bone mass without fracture risk as defined by the WHO criteria for diagnosis of osteoporosis, is when a woman’s T-score is within -1 to -2.5 SD.
The T-score represents a comparison to young normals or optimum peak density. The Z-score represents a comparison of BMD to age-matched normals. Measurements of bone mineral density (BMD) at various skeletal sites help in predicting fracture risk. Hip BMD best predicts fracture of the hip, as well as fractures at other sites.

REFERENCE: Kanis JA, Johnell O, Oden A, et al: Risk of hip fracture according to the World Health Organization criteria for osteopenia and osteoporosis. Bone 2000;27:585-590.

77. Which of the following best describes the mechanism of action of gentamycin?

1- Inhibits cell wall synthesis by inhibiting peptidyl traspeptidase

2- Increases cell membrane permeability

3- Binds to the 30s ribosome subunit interfering with protein synthesis

4- Inhibits DNA gyrase

5- Forms oxygen radicals leading to loss of helical structure and breakage of DNA strands

PREFERRED RESPONSE: 3

DISCUSSION: Gentamycin and the aminoglycosides (ie, streptomycin, tobramycin, amikacin, and neomycin) work by binding to the 30s ribosome subunit, leading to the misreading of mRNA. This misreading results in the synthesis of abnormal peptides that accumulate intracellularly and eventually lead to cell death. These antibiotics are bactericidal. Cephalosporins, vancomycin, and penicillins interfere with cell wall synthesis by inhibiting the transpeptidase enzyme. Polymyxin, nystatin, and amphotericin increase cell membrane permeability by disrupting the functional integrity of the cell membrane. The quinolones inhibit the enzyme, DNA gyrase. Lastly, metronidazole forms oxygen radicals that are toxic to anaerobic organisms because they lack the protective enzymes, superoxide dismutase and catalase.

REFERENCE: Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 217-236.

78. What type of muscle contraction occurs while the muscle is lengthening?

1- Isometric

2- Isotonic

3- Concentric

4- Isokinetic

5- Eccentric

PREFERRED RESPONSE: 5

DISCUSSION: A muscle that lengthens as it is activated is an eccentric contraction. Isometric contraction involves no change in length. Concentric contraction occurs while the muscle is shortening. In isotonic contraction, the force remains constant through the contraction range. Isokinetic muscle contraction occurs at a constant rate of angular change of the involved joint.

REFERENCES: Garrett WE, Speer KP, Kirkendall DT (eds): Principles & Practice of Orthopaedic Sports Medicine. Philadelphia, PA, Lippincott Williams & Wilkins, 2000,
pp 12-13.

Lieber RL: Form and function of skeletal muscle, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

79. Osteoclasts originate from which of the following cell types?

1- Fibroblasts

2- Monocytes

3- Megakaryocytes

4- Plasma cells

5- Osteoprogenitor cells

PREFERRED RESPONSE: 2

DISCUSSION: Osteoclasts originate from the monocyte/macrophage lineage. Fibroblasts and osteoprogenitor cells originate from mesenchymal stem cells and do not form osteoclasts. Plasma cells reside in the bone marrow and are derivatives of the hematopoietic system. Megakaryocytes are also in the bone marrow and synthesize platelets.

REFERENCES: Zaidi M, Blair HC, Moonga BS, et al: Osteoclastogenesis, bone resorption, and osteoclast-based therapeutics. J Bone Miner Res 2003;18:599-609.

Brinker MR: Bone (Section 1), in Miller M (ed): Review of Orthopaedics, ed 2. Philadelphia, PA, WB Saunders, 1996, pp 1-35.

80. A study is being designed to compare the effectiveness of an antibiotic. The choice of the number of patients (ie, the sample size) depends on several factors. What type of calculation assesses the potential of the study to successfully address the effectiveness of the antibiotic?

1- Regression analysis

2- Power analysis

3- Correlation analysis

4- Nonparametric analysis

5- Analysis of variance

PREFERRED RESPONSE: 2

DISCUSSION: Power analysis is used to determine the minimum number of specimens (sample size) such that, if a difference is found that is large enough to be clinically important, the associated level of statistical reliability will be high enough (ie, the P-value will be small enough) for the investigators to conclude that the difference observed in the study also holds in general. For the statistician to do a power analysis, the investigators must first decide on the minimum difference that they consider to be clinically important, for example, a reduction of 3% in the rate of infection. It is important to recognize that the choice of what constitutes the minimum difference in the rate of infection that is clinically (ie, medically) important cannot and should not be done by the statistician. Rather, this is a clinical-medical issue and must be done by the physician researcher based on a comprehensive assessment of the medical risks and benefits. The power analysis also requires an estimate of the variance in the data, which may be based on previous similar studies, if available. A statistician can then calculate the minimum sample size (number of patients) required such that, if a clinically important difference does, in fact, exist between the full populations, there is a reasonable probability or power (typically 80% to 90%) that a difference this large also will occur between the sample populations at the desired level of statistical significance (usually, but not necessarily, P < 0.05). The other answers refer to types of analyses that are usually conducted after the data are collected.

81. What is the most common cause of mechanical failure of an orthopaedic biomaterial during clinical use?

1- Fatigue

2- Tension

3- Compression

4- Shear

5- Torsion

PREFERRED RESPONSE: 1

DISCUSSION: In most orthopaedic applications, the materials are strong enough to withstand a single cycle of loading in vivo. However, these loads may be large enough to initiate a small crack in the implant that can grow slowly over thousands or millions of cycles, eventually leading to gross failure. Such fatigue failure has occurred with virtually every type of implant, including stainless steel fracture plates and screws, bone cement in joint arthroplasty, and polyethylene inserts in total knee arthroplasty.

REFERENCES: Lewis G: Fatigue testing and performance of acrylic bone-cement materials: State-of-the-art review. J Biomed Mater Res Br 2003;66:457-486.

Stolk J, Verdonschot N, Huiskes R: Stair climbing is more detrimental to the cement in hip replacement than walking. Clin Orthop 2002;405:294-305.

82. Which of the following body positions is associated with the highest intradiskal pressure?

1- Standing, bending forward

2- Standing, bending back

3- Sitting, bending forward

4- Sitting, bending back

5- Supine, lateral decubitus

PREFERRED RESPONSE: 3

DISCUSSION: Intradiskal pressure is lowest when the patient is in the supine position. Sitting is associated with higher intradiskal pressures than standing. Flexion also increases intradiskal pressure. The combination of flexion and sitting produces the highest intradiskal pressure. Nachemson and Morris found that intradiskal pressure increases as position changes from lying supine, lying prone, standing, leaning forward, sitting, and sitting leaning forward. Twisting or straining in positions of relatively high intradiskal pressure may predispose patients to herniation of the intervertebral disk. Patients with a herniated disk may also notice their pain worsens with activities that increase the disk pressure, including the positions mentioned, or activities that increase intra-abdominal pressure (coughing, sneezing, straining).

REFERENCES: Nachemson A, Morris JM: In vivo measurements of intradiscal pressure.
J Bone Joint Surg Am 1964;46:1077-1092.

83. Figure 6 shows an object being held in an outstretched hand. To offset the moment created by the object (ignoring the weight of the forearm), the biceps must generate a force of

1- 7.5 N.

2- 15 N.

3- 30 N.

4- 75 N.

5- 150 N.

PREFERRED RESPONSE: 4

DISCUSSION: Answering this question requires understanding of two important biomechanics concepts. First, because neither the object being held in the hand nor the body is moving and, hence, their accelerations are zero, the problem is one of static equilibrium in which the sum of the moments acting on the body is zero. Second, a moment is the action of a force that causes an object to rotate about any point away from its line of action. The magnitude of the moment is the magnitude of the force multiplied by the perpendicular distance between the line of action and the point (often called the moment arm or lever arm). In this problem, two forces are causing moments about the elbow. The magnitude of the moment caused by the object in the hand is 5 N times 30 cm or 150 N-cm. To maintain equilibrium, the moment caused by the biceps force must also have a magnitude of 150 N-cm. Its moment arm is 2 cm, so the magnitude of the biceps force is 150 N-cm divided by 2 cm, which equals 75 N. In general, functional loads such as the object are always at a mechanical advantage (ie, have a longer moment arm) over the muscle. Therefore, muscles must generate large forces to overcome the moments caused by even small functional loads.

REFERENCES: An KN, Chao ES, Kaufman KR: Analysis of muscle and joint loads, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 1-14.

84. Which of the following best describes the function of the notochord?

1- The notochord becomes the medulla oblongata in adults.

2- The notochord induces tissues that eventually become the vertebral column.

3- The notochord disappears with ossification of vertebral bodies.

4- The notochord develops into the ring apophysis.

5- Remnants of the notochord are often found in the coccyx.

PREFERRED RESPONSE: 2

DISCUSSION: The notochord is the anatomic structure that defines the phylum Chordata. The notochord plays a fundamental role in the development of the skeleton, and it exists only for a short period of time. During its temporary existence, the notochord serves as a transient axis of support, provides for the initial axis of orientation of the developing embryo, and most importantly, plays a vital role in the induction of the tissues that eventually form the vertebral column.

REFERENCE: Rosenberg A: Embryology of the skull base and vertebral column, in Harsh G (ed): Chordomas and Chondrosarcomas of the Skull Base and Spine. New York, NY, Thieme, 2003, pp 3-8.

85. A patient undergoes a proximal tibial resection that is reconstructed with a fresh frozen osteoarticular allograft. Eleven months later, the graft is retrieved. Histologically, the articular cartilage and subchondral bone retrieved would be expected to show evidence of

1- host chondrocytes in the articular cartilage.

2- subchondral revascularization and fragmentation, without evidence of cartilage degeneration.

3- an articular surface covered with a pannus of synovial tissue.

4- radiographically normal thickness of the articular surface, with evidence of cellular debris in the lacuna.

5- severe degenerative changes in the articular cartilage surface with complete loss of the tidemark.

PREFERRED RESPONSE: 4

DISCUSSION: Osteoarticular allografts are devoid of host chondrocytes but do contain “mummified” cellular debris left over from donor processing. The cartilage architecture is preserved in the first 2 to 3 years after transplantation. The articular surface is covered with a pannus of fibrocartilage maintaining the joint space radiographically; this pannus later contains islands of fibrocartilage containing host mesenchymal stem cells. Degenerative changes to the joint surface occur earlier and are more severe in joints that are unstable. Only with degenerative changes at the surface is there histologic evidence of subchondral revascularization. Often degenerative changes involving the articular cartilage reach the tidemark, but the tidemark itself remains structurally intact.

REFERENCES: Enneking WF, Campanacci DA: Retrieved human allografts:
A clinicopathological study. J Bone Joint Surg Am 2001;83:971-986.

Enneking WF, Mindell ER: Observations on massive retrieved human allografts.
J Bone Joint Surg Am 1991;73:1123-1142.

86. Stiffness relates the amount of load applied to a structure like a long bone or an intramedullary nail to the amount of resulting deformation that occurs in the structure. What is the most important material property affecting the axial and bending stiffness of a structure?

1- Elastic modulus

2- Ductility

3- Ultimate stress

4- Yield stress

5- Toughness

PREFERRED RESPONSE: 1

DISCUSSION: The amount of deformation resulting in response to an applied load depends on the stress distribution that the load creates in the structure and the stress versus strain behavior of the material that makes up the structure. Axial and bending loads create stress distributions that involve normal stresses and normal strains. Although all five responses are indeed material properties, only one, elastic modulus, relates normal stresses to normal strains. In fact, axial and bending stiffness are directly proportional to modulus, so that a nail made from stainless steel will have nearly twice the stiffness of a nail made from titanium alloy (because their respective elastic moduli differ by about a factor of two).

REFERENCES: Hayes WC, Bouxsein ML: Analysis of muscle and joint loads, in Mow VC, Hayes WC (eds): Basic Orthopaedic Biomechanics, ed 2. New York, NY, Lippincott-Raven, 1997, pp 74-82.

87. Which of the following accurately defines changes in Vitamin D requirements as the result of aging?

1- Increase because of decreased levels of serum 25(OH)D

2- Increase, but calcium requirements remain the same

3- Remain the same, with a decrease in levels of serum 1,25(OH)D

4- Remain the same, but calcium requirements increase.

5- Decrease, with decreasing circulating PTH levels

PREFERRED RESPONSE: 1

DISCUSSION: Older individuals ingest less Vitamin D and are unable to generate as much as younger people via the skin in response to ultraviolet exposure; thus, there is a decrease in the levels of serum 25(OH) D. This reduction in 25(OH)D leads to a reduction in calcium absorption. There is also decreased conversion in the kidney of 25(OH)D to 1,25(OH)D. This all leads to an increase in the daily requirements of both calcium and Vitamin D. It also results in a responsive increase in PTH secretion in the elderly, as well as renal function impairment and possible renal resistance to PTH.

REFERENCES: Dawson-Hughes B, Harris SS, Krall EA, et al: Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age and older. N Engl J Med 1997;337:670-676.

Recker RR, Hinders S, Davies M, et al: Correcting calcium nutritional deficiency prevents spine fractures in elderly women. J Bone Miner Res 1996;11:1961-1966.

Rosen CJ, Kiel DP: The aging skeleton, in Favus, MJ (ed): Primer on Metabolic Bone Diseases and Disorders of Mineral Metabolism, ed 4. Philadelphia, PA, Lippincott Williams & Wilkins, 1999, pp 57-59.

88. Osteoclasts are primarily responsible for bone resorption of malignancy. Which of the following stimulates osteoclast formation?

1- RANKL gene (NF-kβ ligand)

2- Osteoprotegerin (OPG)

3- Interleukin-5 (IL-5)

4- Matrix metalloproteinase-2 (MMP-2)

5- Collagen type I

PREFERRED RESPONSE: 1

DISCUSSION: Bone destruction is primarily mediated by osteoclastic bone resorption, and cancer cells stimulate the formation and activation of osteoclasts next to metastatic foci. Increasing evidence suggests that receptor activator of NF-kβ ligand (RANKL) is the ultimate extracellular mediator that stimulates osteoclast differentiation into mature osteoclasts. In contrast, OPG inhibits osteoclast development. IL-8 but not IL-5 is known to play a role in osteoclastogenesis. MMP-2 and collagen type I do not have a direct role in osteoclastogenesis.

REFERENCES: Kitazawa S, Kitazawa R: RANK ligand is a prerequisite for cancer-associated osteolytic lesions. J Pathol 2002;198:228-236.

Einhorn TA: Metabolic bone diseases, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

89. Which of the following statements best describes synovial fluid?

1- Erythrocytes are present at one tenth the normal concentration of blood.

2- White blood cells are present at one tenth the normal concentration of blood.

3- Synovial fluid is produced by type A synoviocytes.

4- Synovial fluid exhibits non-Newtonian fluid characteristics.

5- Synovial fluid contains similar concentrations of clotting factors as serum.

PREFERRED RESPONSE: 4

DISCUSSION: Synovial tissue is composed of vascularized connective tissue that lacks a basement membrane. Two cell types (type A and type B) are present: type B cells produce synovial fluid. Synovial fluid is made of hyaluronic acid and lubricin, proteinases,and collagenases. It is an ultrafiltrate of blood plasma added to fluid produced by the synovial membrane. It does not contain erythrocytes, clotting factors, or hemoglobin. It lubricates articular cartilage and provides nourishment via diffusion. Synovial fluid exhibits non-Newtonian flow characteristics. The viscosity coefficient is not a constant, the fluid is not linearly viscous, and its viscosity increases as the shear rate decreases.

90. Collagen orientation is parallel to the joint surface in what articular cartilage zone?

1- Diagonal

2- Middle

3- Deep

4- Superficial

5- Calcified

PREFERRED RESPONSE: 4

DISCUSSION: The collagen orientation changes from parallel in the superficial zone to a more random pattern in the middle zone and finally to perpendicular in the calcified zone.

REFERENCES: Koval KJ (ed): Orthopaedic Knowledge Update 7. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, pp 498-499.

Mankin HJ, Mow VC, Buckwalter JA: Articular cartilage structure, composition, and function, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006,
in press.

91. Which of the following agents increases the risk for a nonunion following a posterior spinal fusion?

1- Ibuprofen

2- Intranasal calcitonin

3- Simvastatin

4- Gentamycin

5- Tamoxifen

PREFERRED RESPONSE: 1

DISCUSSION: Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to increase the risk of pseudarthrosis. In a controlled rabbit study, nonunions were reported with the use of toradol and indomethacin. NSAIDs are commonly used medications with the potential to diminish osteogenesis. Studies clearly have demonstrated inhibition of spinal fusion following the postoperative administration of several NSAIDs, including ibuprofen. Cigarette smoking is another potent inhibitor of spinal fusion.

REFERENCES: Glassman SD, Rose SM, Dimar JR, et al: The effect of postoperative nonsteroidal anti-inflammatory drug administration on spinal fusion. Spine 1998;23:834-838.

Martin GJ Jr, Boden SD, Titus L: Recombinant human bone morphogenetic protein-2 overcomes the inhibitory effect of ketorolac, a nonsteroidal anti-inflammatory drug (NSAID), on posterolateral lumbar intertransverse process spine fusion. Spine 1999;24:2188-2193.

92. What is the primary benefit of using rhBMP-2 instead of autogenous bone graft inside an anterior spinal fusion cage?

1- Substantially improved radiographic fusion success rate

2- Substantially decreased time to fusion healing

3- Substantially decreased hospital stay

4- Elimination of autograft harvest

5- Elimination of need for postoperative bracing

PREFERRED RESPONSE: 4

DISCUSSION: Radiographic fusion success rates are best described as slightly rather than substantially improved. Hospital stay and time to fusion also are not substantially decreased. Use of BMP does eliminate the need for autograft harvest for anterior lumbar interbody fusion/cage. The need for postoperative bracing is not altered based on graft choice. Early studies of posterolateral fusion applications appear to show a greater potential benefit of rhBMP-2 over autograft. Not all BMP formulations perform the same with regard to safety and effectiveness. Other osteoinductive proteins in clinical trials (BMP-7, GDF-5) will require individual analysis of these properties.

REFERENCE: Burkus JK, Gornet MF, Dickman CA, et al: Anterior lumbar interbody fusion using rhBMP-2 with tapered interbody cages. J Spinal Disord Tech 2002;15:337-349.

93. Cell signaling through the activation of a transmembrane receptor complex formed by serine/threonine kinase receptors occurs with which of the following growth factors?

1- Bone morphogenetic protein

2- Fibroblast growth factors

3- Insulin-like growth factors

4- Platelet-derived growth factors

5- Growth hormone

PREFERRED RESPONSE: 1

DISCUSSION: Cell activation and transcription varies with the target cell, the growth factor-receptor combination, and the biologic state of the cell. The growth factors in the transforming growth factor-beta (TGF-β) superfamily signal through serine/threonine kinase receptors. Fibroblast growth factors, insulin-like growth factors, and platelet-derived growth factors signal through tyrosine kinase receptors. Growth hormone is released by the pituitary and circulates to the liver where target cells are stimulated to release insulin-like growth factor.

REFERENCES: Lieberman J, Daluiski A, Einhorn TA: The role of growth factors in the repair of bone: Biology and clinical applications. J Bone Joint Surg Am 2002;84:1032-1044.

Schmitt JM, Hwang K, Winn SR, et al: Bone morphogenetic proteins: An update on basic biology and clinical relevance. J Orthop Res 1999;17:269-278.

94. A 67-year-old woman has persistent anterior thigh and knee pain after undergoing total knee arthroplasty 1 year ago. Examination and radiographs reveal no problems in the knee, mild hip flexor weakness (grade 4+), and decreased sensation over the anterior thigh including and proximal to the incision. MRI of the lumbar spine will most likely reveal which of the following findings?

1- Posterolateral herniated nucleus pulposus at L3-4

2- Posterolateral herniated nucleus pulposus at L4-5

3- Degenerative disk disease at L3-4 and L4-5 with no significant facet hypertrophy

4- Degenerative spondylolisthesis at L3-4 with central and foramenal stenosis

5- Degenerative spondylolisthesis at L4-5 with central stenosis

PREFERRED RESPONSE: 4

DISCUSSION: Degenerative spondylolisthesis at L3-4 is the most likely diagnosis. This spondylolisthesis would result in foraminal stenosis affecting the third lumbar root and leading to anterior thigh and knee pain and hip flexor weakness. L4-5 spondylolisthesis would impinge on the L4 root in the foramen. Degenerative disk disease without hypertrophy is unlikely to have root impingement. Posterolateral herniations typically affect the inferior root and are less common in this age group.

REFERENCES: Hoppenfeld S: Physical Examination of the Spine and Extremities. Upper Saddle River, NJ, Prentice Hall, 1976, p 250.

Lauerman WC, Goldsmith ME: Spine, in Miller MD (ed): Review of Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2000, pp 353-378.

95. Decreased activity of which of the following proteins may be predictive of an aggressive soft-tissue sarcoma?

1- Matrix metalloproteinases (MMP)

2- Interleukin-1

3- Vascular endothelial growth factor

4- Tissue inhibitor of metalloproteinases (TIMP)

5- Stromelysin

PREFERRED RESPONSE: 4

DISCUSSION: It has been proposed that an imbalance in the proteolytic cascade involving matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) may play a role in the development or progression of malignancy. TIMP activity has been shown to be weak or nonexistent and MMP activity to be high in patients with soft-tissue sarcoma. The level of vascular endothelial growth factor is shown to be a negative prognostic indicator because the expression of this factor is associated with angiogenesis and aggressive growth of many tumors including Ewing’ s sarcoma and chondrosarcoma. Stromelysin is a type of MMP. The biology of cytokines in malignancy is complex. A low level of interleukin-1 is not known to be associated with high-grade tumors.

REFERENCE: Benassi MS, Magagnoli G, Ponticelli F, et al: Tissue and serum loss of metalloproteinase inhibitors in high grade soft tissue sarcomas. Histol Histopathol 2003;18:1035-1040.

96. Passive glycation of articular cartilage results in

1- protection of collagen from degradation.

2- increased collagen stiffness and degradation.

3- increased chondrocyte proliferation.

4- increased proteoglycan association with type II collagen.

5- decreased synthesis of new collagen.

PREFERRED RESPONSE: 2

DISCUSSION: Passive glycation of articular cartilage occurs over decades. One of the consequences of this glycation appears to be the stiffening of collagen. This phenomenon appears to be associated with an increased collagen degradation and development of osteoarthrosis. Passive glycation also results in a relatively yellow appearance. Passive glycation does not directly influence chondrocyte proliferation.

REFERENCES: DeGroot J, Verzijl N, Wenting-van Wijk MJ, et al: Accumulation of advanced glycation end products as a molecular mechanism for aging as a risk factor in osteoarthritis. Arthritis Rheum 2004;50:1207-1215.

Chen AC, Temple MM, Ng DM, et al: Induction of advanced glycation end products and alterations of the tensile properties of articular cartilage. Arthritis Rheum 2002;46:3212-3217.

97. A study was conducted in 500 patients to measure the effectiveness of a new growth factor in reducing healing time of distal radial fractures. The authors reported that average healing time was reduced from 9.2 to 8.9 weeks (P < 0.0001). Because the difference was highly statistically significant, they recommended routine clinical use of this drug despite its high cost. A more appropriate interpretation of these results is that they are

1- clinically significant.

2- statistically significant but perhaps not clinically significant.

3- statistically and clinically significant.

4- not statistically or clinically significant.

5- nonconclusive.

PREFERRED RESPONSE: 2

DISCUSSION: The results are statistically significant (at the arbitrary level of P < 0.05). That is, they indicate a probability of only 1/10,000 that the observation that the drug is effective in reducing healing time by 0.3 weeks occurred by chance selection of the study subjects. However, because the statistical power of a study increases with the number of subjects included (sample size), a difference that is trivial clinically can occur with a very high level of statistical significance (a very small P-value) if enough patients are included in the study. Because of this, the P-value alone, no matter how small, does not establish clinical significance or importance. Rather, the clinical significance of the observed difference must be assessed taking into consideration the medical importance of the difference if it is, in fact, true in the general population. In this example, the reduction in healing time of only a few days is probably clinically unimportant, particularly if the use of the new growth factor is expensive, complex, and/or has substantial side effects.

98. In patients with suspected hepatitis C, which of the following tests is commonly used to confirm the diagnosis after a positive ELISA screening test?

1- Polymerase chain reaction (PCR)

2- Northern blot

3- Immunoblot assay

4- Microarray

5- Proteomics

PREFERRED RESPONSE: 3

DISCUSSION: The basic diagnostic test for hepatitis C (HCV) is detection of an antibody to epitopes on an enzyme-linked immunosorbent anti-HCV assay (ELISA). The currently used ELISA has high sensitivity (92%) and specificity (95%). False positives, however, still occur. The currently used supplemental test for HCV is strip immunoblot assay, which is based on detection of several HCV epitopes on nitrocellulose paper by antibody-capture techniques. Molecular amplification by PCR technology is very sensitive, but difficult to standardize and susceptible to contamination. Microarray and proteomics are relatively recent molecular techniques used for analysis of genes or proteins, respectively. A Northern blot is used to detect mRNA levels of specific genes but is not used in this situation.

REFERENCES: de Medina M, Schiff ER: Hepatitis C: Diagnostic assays. Semin Liver Dis 1995;15:33-40.

McGrory BJ, Kilby AE: Hepatitis C virus infection: Review and implications for the orthopedic surgeon. Am J Orthop 2000;29:261-266.

99. What type of multiple lesions is associated with Maffucci’s syndrome?

1- Nonossifying fibromas

2- Enchondromas

3- Langerhan’s cell histiocytosis

4- Osteochondromas

5- Giant cell tumors

PREFERRED RESPONSE: 2

DISCUSSION: Maffucci’s syndrome is a form of enchondromatosis associated with subcutaneous and deep hemangiomas. Similar to Ollier’s disease, the risk of malignant transformation of the enchondromas is much higher than that of a solitary enchondroma. Multifocal nonossifying fibromas associated with other clinical findings such as mental retardation and café-au-lait spots is known as Jaffe-Campanacci syndrome. There are two types of multifocal forms of histiocytosis: Letterer-Siwe and Hand-Schüller-Christian disease.

REFERENCES: Schwartz HS, Zimmerman NB, Simon MA, et al: The malignant potential of enchondromatosis. J Bone Joint Surg Am 1987;69:269-274.

Frassica F: Orthopaedic pathology, in Miller M (ed): Review of Orthopaedics, ed 2. Philadelphia, PA, WB Saunders, 1996, pp 292-335.

Yuan J, Fuchs B, Scully SP: Molecular basis of cancer, in Einhorn TA, O’Keefe RJ, Buckwalter JA (eds): Orthopaedic Basic Science: Foundations of Clinical Practice, ed 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, in press.

100. Joint contact pressure in normal or artificial joints can best be minimized by
what mechanism?

1- Increasing joint force and contact area

2- Increasing joint force and decreasing contact area

3- Decreasing joint force and contact area

4- Decreasing joint force and increasing contact area

5- Decreasing joint force only

PREFERRED RESPONSE: 4

DISCUSSION: Joint contact pressure is a stress and as such is defined as the load transferred across the joint divided by the contact area between the joint surfaces (the area over which the joint load is distributed). Therefore, any mechanism that decreases the load across the joint
(eg, a walking aid) will decrease the stress. Similarly, any mechanism that increases the area over which the load is distributed (eg, using a more conforming set of articular surfaces in a knee joint arthroplasty) will also decrease the stress. Other mechanisms that influence joint contact pressure include the elastic modulus of the materials (cartilage in the case of natural joints and polyethylene in joint arthroplasty) and the thickness of the structures through which the joint loads pass.

REFERENCES: Bartel DL, Bicknell VL, Wright TM: The effect of conformity, thickness, and material on stresses in UHMWPE components for total joint replacement. J Bone Joint Surg Am 1986;68:1041-1051.

Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000,
pp 265-274.