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1. General Principles & Basic Science MCQs

Practice Set 225 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 4481

Topic: 1. General Principles & Basic Science

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?

. High cost
. Increased rates of infection
. High elastic modulus
. Brittleness
. Foreign body reaction

Correct Answer & Explanation

. Foreign body reaction

Explanation

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

Question 4482

Topic: 1. General Principles & Basic Science

The mother of a 2-year-old boy reports that he had pain in the right hip all night and refuses to walk on the leg this morning. He is afebrile. Examination reveals pain on hip extension and adduction, but he is able to internally and externally rotate the hip approximately 20 degrees in each direction without pain. Laboratory studies reveal a WBC count of 7,400/mm3, with 62% polymorphonuclear neutrophil leukocytes. The AP radiograph shown in Figure 15 reveals a left teardrop distance of 8 mm, while the right side measures 10 mm. Which of the following diagnostic studies will best help confirm the diagnosis?

Pediatrics Board Review 2004: High-Yield MCQs (Set 2) - Figure 11

. Technetium Tc 99m bone scan
. Ultrasound of the hips
. CT of the pelvis
. MRI of the pelvis
. Aspiration of the hip joint

Correct Answer & Explanation

. Aspiration of the hip joint

Explanation

The differential diagnosis includes septic hip and transient synovitis. Both disorders may present with a joint effusion. The increased teardrop distance and loss of range of motion implies that there is excess fluid in the joint. While the other tests can confirm this, only aspiration can characterize the fluid further, thereby indicating the etiology of the effusion. Provided there is enough fluid obtained at aspiration, the joint fluid should be sent for Gram stain, culture, cell count, glucose, and protein studies.

Question 4483

Topic: Biomechanics & Biomaterials

Figure 19 shows the current radiograph of a 48-year-old man who reports hip pain and marked difficulty walking after undergoing revision of a failed total hip replacement 2 years ago. What is the mechanism of failure?

Hip Board Review 2001: High-Yield MCQs (Set 2) - Figure 19

. Fatigue
. Crevice corrosion
. Galvanic corrosion
. Loosening
. Wear

Correct Answer & Explanation

. Fatigue

Explanation

Fatigue from repetitive loading of the stem with the distal aspect well-fixed resulted in stem failure. If the stem had loosened, it would not have broken. Crevice corrosion occurs at a taper interface; galvanic corrosion occurs at the junction of two metals of differing electrochemical potentials, not along a uniform portion of the implant. Simon SR (ed): Orthopaedic Basic Science. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1994, pp 449-486.

Question 4484

Topic: Infection, Pharmacology & VTE

A 7-year-old boy sustained an acute puncture wound of the foot after stepping barefoot on a piece of glass 1 day ago. His mother states that she is not sure if she got the piece of glass out; however, she reports that his immunizations are up-to-date. Examination reveals that the wound is slightly erythematous, less than 1 mm in length on the heel, and is not currently draining. What is the next most appropriate step im management?

Foot & Ankle 2006 Practice Questions: Set 1 (Solved) - Figure 4

. Antibiotic coverage for pseudomonas
. Tetanus booster
. Radiographs of the foot
. MRI to evaluate for possible abscess or osteomyelitis
. Surgical debridement of the wound

Correct Answer & Explanation

. Radiographs of the foot

Explanation

The child has an up-to-date tetanus; therefore, a booster is not recommended. Pseudomonas coverage is most likely not needed because the child was barefoot. It is too early to evaluate for abscess or osteomyelitis with MRI, and a formal debridement is rarely indicated without signs of an abscess or a retained foreign body. Radiographs with soft-tissue penetration should be obtained to check for a retained foreign body. Richardson EG (ed): Orthopaedic Knowledge Update: Foot and Ankle 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2004, pp 199-205.

Question 4485

Topic: 1. General Principles & Basic Science

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

. The notochord becomes the medulla oblongata in adults.
. The notochord induces tissues that eventually become the vertebral column.
. Remnants of the notochord are often found in the coccyx.
. The notochord disappears with ossification of vertebral bodies.
. The notochord develops into the ring apophysis.

Correct Answer & Explanation

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

Explanation

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.

Question 4486

Topic: 1. General Principles & Basic Science

What is the most appropriate orthotic management for the lesion shown in Figure 6?

Foot & Ankle 2000 Practice Questions: Set 1 (Solved) - Figure 12

. Metatarsal pad
. Morton's extension orthosis
. Medial longitudinal arch support
. Budin splint
. Viscoelastic heel lift

Correct Answer & Explanation

. Metatarsal pad

Explanation

The figure shows an intractable plantar keratosis (IPK). The keratoma usually forms beneath a bony prominence. This can occur under the sesamoids, most commonly the tibial sesamoid, or under the fibular condyle of a prominent metatarsal head. The initial treatment of an IPK consists of paring down the callused lesion and placing a metatarsal pad proximal to the lesion to provide posting to unload the bony prominence.

Question 4487

Topic: Infection, Pharmacology & VTE
A 30-year-old patient has had severe left hip pain and difficulty ambulating, necessitating the use of a cane, for the past 6 months. A photomicrograph of the femoral head sectioned at the time of surgery is shown in Figure 31. What is the most likely diagnosis?
. Renal osteodystrophy
. Pyogenic osteomyelitis
. Osteoarthritis
. Osteonecrosis
. Tuberculosis osteomyelitis

Correct Answer & Explanation

. Osteonecrosis

Explanation

The photomicrograph demonstrates a wedge-shaped infarct with femoral head collapse; therefore, the diagnosis is osteonecrosis of the femoral head. Perthes disease and osteoarthritis do not involve a wedge-shaped defect. Tuberculosis of the hip joint results in greater destruction of the articular cartilage.

Question 4488

Topic: Infection, Pharmacology & VTE

A 6-year-old boy with acute hematogenous osteomyelitis of the distal femur is being treated with intravenous antibiotics. The most expeditious method to determine the early success or failure of treatment is by serial evaluations of which of the following studies?

Pediatrics Board Review 2007: High-Yield MCQs (Set 2) - Figure 12

. CBC count with differential
. MRI
. CT
. Radiographs
. C-reactive protein (CRP)

Correct Answer & Explanation

. C-reactive protein (CRP)

Explanation

Successful antibiotic treatment of osteomyelitis should lead to a rapid decline in the CRP. The CRP should decline after 48 to 72 hours of appropriate treatment. Imaging studies will take much longer to show resolution of bone infection. Unkila-Kallio L, Kallio MJ, Eskola J, et al: Serum C-reactive protein, erythrocyte sedimentation rate, and white blood cell count in acute hematogenous osteomyelitis of children. Pediatrics 1994;93:59-62.

Question 4489

Topic: 1. General Principles & Basic Science

A 27-year-old woman sustained a bilateral C5-6 facet subluxation in a motor vehicle accident. Neurologic evaluation reveals normal motor, sensory, and reflex functions. She is awake, alert, and cooperative. Initial management should consist of

Trauma Board Review 2000: High-Yield MCQs (Set 2) - Figure 14

. halo application.
. skeletal traction and attempted closed reduction.
. a soft cervical collar.
. immediate transfer to the operating room for closed reduction.
. immediate transfer to the operating room for open reduction and stabilization posteriorly.

Correct Answer & Explanation

. skeletal traction and attempted closed reduction.

Explanation

As long as the patient is alert and cooperative, an attempt can be made to reduce the dislocation. This should not be attempted in a patient who is obtunded, comatose, or uncooperative. If any neurologic changes are noted during the reduction maneuver, the attempt should be stopped, appropriate radiographic studies obtained, and open reduction and stabilization planned in the operating room.

Question 4490

Topic: 1. General Principles & Basic Science
The anticoagulant effect of the low-molecular-weight heparins (LMWH) is mediated by the binding affinity of antithrombin III to which of the following coagulation factors?
. III
. V
. IX
. Xa
. XII

Correct Answer & Explanation

. Xa

Explanation

Standard heparin mediates its anticoagulant effect largely through its interaction with antithrombin III. A conformational change in antithrombin III occurs that markedly accelerates its ability to inactivate the coagulation enzymes thrombin factor (II), factor Xa, and factor IXa. In contrast, LMWHs do not contain the necessary saccharide units to bind thrombin and antithrombin III simultaneously. The anticoagulant effect of LMWHs involves binding of antithrombin III to factor Xa.

Question 4491

Topic: 1. General Principles & Basic Science

Figure 24 shows the radiograph of a 4-year-old girl with spina bifida. Examination reveals an L3 motor level, excellent sitting and standing balance, and satisfactory range of motion at the hips. Management should consist of

Pediatrics Board Review 2001: High-Yield MCQs (Set 2) - Figure 12

. observation.
. closed reduction and cast immobilization.
. bilateral medial open reduction of the hips.
. anterior open reduction with femoral shortening.
. valgus osteotomy.

Correct Answer & Explanation

. observation.

Explanation

Children with spina bifida and bilateral symmetrical dislocation of the hips usually do not require treatment. A level pelvis and good range of motion of the hips are more important for ambulation than reduction of bilateral hip dislocations. Because the patient has good sitting and standing balance and good range of motion, maintenance of that range of motion and symmetry is more important than reduction. Surgery is not recommended.

Question 4492

Topic: 1. General Principles & Basic Science

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

. Decrease in tensile strength
. Decrease in the likelihood of rupture
. Increase in cellularity
. Increase in aggrecan
. Increase in collagen fibril diameter

Correct Answer & Explanation

. Decrease in tensile strength

Explanation

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.

Question 4493

Topic: Biomechanics & Biomaterials

When polyethylene is exposed to radiation and subsequently heated, certain chemical changes occur in the material. Which of the following statements best describes these changes?

. The process converts an otherwise interpenetrating networking structure of polymer chains into a linear, high molecular weight polyethylene macromolecule.
. The process increases the ductility of the material.
. The process leads to fewer particles that are larger in size than the untreated material.
. The process improves (lowers) the wear rate but may increase the risk of fracture.
. The process decreases the wear rate of the material, compared to untreated polyethylene, when tested against a rough counterface.

Correct Answer & Explanation

. The process improves (lowers) the wear rate but may increase the risk of fracture.

Explanation

Exposure of polyethylene to radiation and then heating it to quench the free radicals leads to a cross-linked material. It converts a high molecular weight polyethylene macromolecule to an interpenetrating network structure of polymer chains. The ductility of the material is decreased, hence the greater risk of fracture. While the wear rate (measured as fewer and smaller particles) against a smooth counterface is markedly reduced, cross-linked polyethylene has shown a larger increase in wear rate when a rougher counterface is used compared to noncross-linked material. Due to reduced mechanical strength, highly cross-linked polyethylene is less resistant to abrasive wear.

Question 4494

Topic: Surgical Anatomy & Approaches

Bleeding is encountered while developing the internervous plane between the tensor fascia lata and the sartorius during the anterior approach to the hip. The most likely cause is injury to what artery?

. Ascending branch of the lateral femoral circumflex
. Superior gluteal
. Femoral
. Profunda femoris
. Medial femoral circumflex

Correct Answer & Explanation

. Ascending branch of the lateral femoral circumflex

Explanation

The ascending branch of the lateral femoral circumflex artery crosses the gap between the tensor fascia lata and the sartorious and must be identified and ligated or coagulated. The other vessels are out of the field of dissection. Barrack RL, Booth RE Jr, Lonner JH, et al (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2006, p 312.

Question 4495

Topic: Infection, Pharmacology & VTE

A 45-year-old man who has had recurrent pain and swelling of the left Achilles tendon insertion for the past 10 years reports that physical therapy and activity modification have provided relief in the past. He now has continued pain despite these efforts. He also reports occasional bouts of dysuria that he attributes to a history of prostatitis. He also notes recent eye irritation that he attributes to allergies. A lateral heel radiograph is shown in Figure 33. Which of the following laboratory studies would best aid in diagnosis?

Foot & Ankle 2006 Practice Questions: Set 3 (Solved) - Figure 18

. Glucose tolerance test
. CBC count with differential
. Urethral swab and culture
. HLA-B27
. Antiphospholipid antibody

Correct Answer & Explanation

. HLA-B27

Explanation

Reiter's syndrome is a seronegative spondyloarthropathy characterized most commonly by a triad of asymmetric arthritis, urethritis, and uveitis. Tendon ensethopathies can also be present. It is most often seen in men and is associated with a positive HLA-B27 marker. Rheumatoid arthritis does not usually present with these features; more commonly it causes forefoot pain and synovitis of the metatarsophalangeal joints. A CBC count with differential would be helpful in a situation of possible infection. The urethral swab would help to diagnose a gonococcal infection which can cause a monoarticular septic arthritis. Antiphospholipid antibody is associated with a hypercoaguable state and increased risk of deep venous thrombosis.

Question 4496

Topic: 1. General Principles & Basic Science

Figure 15 shows possible locations of anterior pin sites for halo fixation. What location is considered most ideal?

Spine Surgery Board Review 2000: High-Yield MCQs (Set 2) - Figure 22

. A
. B
. C
. D
. E

Correct Answer & Explanation

. A

Explanation

The anterior pin should be placed just above and lateral to the eyebrow at the site labeled A. At site B, the supraorbital nerve can be damaged. At site C, the supratrochlear nerve or the frontal sinus can be damaged. The site labeled D is over the temporalis muscle; in this location the temple bone is thin and there is the risk of perforation. Site E is above the equator of the forehead; at this location there is a risk that the halo ring will slip off the head altogether. Garfin SR, Botte MJ, Waters RL, Nickel VL: Complications in the use of halo fixation device. J Bone Joint Surg Am 1986;68:320-325.

Question 4497

Topic: Surgical Anatomy & Approaches

Figure 44 shows the AP radiograph of the hip of a patient who underwent screw fixation of the acetabulum. Which of the following structures is at least risk for injury during screw placement in the acetabular component?

Anatomy Board Review 2002: High-Yield MCQs (Set 4) - Figure 6

. Common iliac artery
. Superior gluteal artery
. Obturator artery
. Sciatic nerve
. External iliac vein

Correct Answer & Explanation

. Common iliac artery

Explanation

Acetabular screws are inserted to supplement fixation. The acetabular component can be divided into four quadrants. Anatomic studies have shown that screws placed in the anterior superior and anterior inferior quadrants of the cup may injure the external iliac vein and obturator artery, respectively. Posterior superior and posterior inferior placement (in screws greater than 25 mm) may injure the sciatic nerve or the superior gluteal artery. The common iliac artery is proximal to the acetabulum and is at least risk for injury from acetabular screw placement.

Question 4498

Topic: Biology, Genetics & Bone Healing

A 42-year-old man reports the recent onset of right hip pain. A radiograph and MRI scan are shown in Figures 38a and 38b. A WBC count, erythrocyte sedimentation rate, and hip aspiration are within normal limits. Management should now consist of

. core decompression.
. biopsy of the femoral head.
. protected weight bearing and observation.
. total hip arthroplasty.
. percutaneous cannulated pin fixation of the femoral neck.

Correct Answer & Explanation

. protected weight bearing and observation.

Explanation

Transient osteoporosis of the hip is an uncommon problem, usually affecting women in the last trimester of pregnancy and middle-aged men. Symptoms include pain in the involved hip with temporary osteopenia; however, there is no joint space involvement. In this patient, the imaging findings are consistent with transient osteoporosis. Short TR/TE (repetition time/echo time) images reveal diffusely decreased signal intensity in the femoral head and intracapsular region of the femoral neck. Increased signal intensity is seen with increased T2-weighting. Within a few months, the pain, as well as the imaging findings, will completely resolve without intervention. Distinguishing the diffuse features of transient osteoporosis of the hip from the segmental findings of osteonecrosis is essential. Unlike transient osteoporosis of the hip, osteonecrosis will have a double-density signal on MRI and may progress radiographically. Surgical intervention and oral corticosteriods are not indicated for treatment. Protected weight bearing until the pain resolves may decrease symptoms while the transient osteoporosis resolves. Potter H, Moran M, Scheider R, et al: Magnetic resonance imaging in diagnosis of transient osteoporosis of the hip. Clin Orthop 1992;280:223-229. Bijl M, van Leeuwen MA, van Rijswijk MH: Transient osteoporosis of the hip: Presentation of typical cases for review of the literature. Clin Exp Rheumatol 1999;17:601-604.

Question 4499

Topic: Infection, Pharmacology & VTE

What is the typical MRI signal intensity of bone marrow affected by acute osteomyelitis?

Anatomy 2005 Practice Questions: Set 1 (Solved) - Figure 26

. Decreased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, increased on T2-weighted imaging
. Decreased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging
. Increased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, increased on T2-weighted imaging
. Increased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging
. Increased on T1-weighted imaging, decreased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging

Correct Answer & Explanation

. Decreased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging

Explanation

The classic MRI findings of osteomyelitis are a decrease in the normally high signal intensity of marrow on T1-weighted images and normal or increased signal intensity on T2-weighted images. This is the result of replacement of marrow fat by inflammatory cells and edema, which causes lower signal intensity than fat on T1-weighted images and higher signal intensity than fat on T2-weighted images. The addition of gadolinium to a T1-weighted sequence reveals increased signal intensity in the hyperemic marrow. Unger E, Moldofsky P, Gatenby R, et al: Diagnosis of osteomyelitis by MR imaging. Am J Roentgenol 1988;150:605-610. Dormans JP, Drummond DS: Pediatric hematogenous osteomyelitis: New trends in presentation, diagnosis and treatment. J Am Acad Orthop Surg 1994;2:333-341.

Question 4500

Topic: Biology, Genetics & Bone Healing

Figure 17 shows the radiograph of a 2-year-old girl who sustained a fracture of the femur in a fall while walking with her parents. History reveals that this is her third long bone fracture, having sustained a humerus fracture 1 year ago and a fracture of the opposite femur 9 months ago. There is no family history of any similar problem. Examination reveals distinctly blue sclerae, normal appearing teeth, and no skin lesions. What is the most likely cause of this patient's disorder?

Pediatrics Board Review 2001: High-Yield MCQs (Set 2) - Figure 1

. A quantitative defect of type I collagen synthesis
. A deficiency of vitamin D
. Parental abuse
. Abnormal osteoclast function
. Excess excretion of keratin sulfate in the urine

Correct Answer & Explanation

. A quantitative defect of type I collagen synthesis

Explanation

Osteogenesis imperfecta (OI) is a genetically determined disorder of type I collagen synthesis that is characterized by bone fragility. This patient has had three fractures of the long bones by age 2 years, with the last one occurring after relatively minor trauma. The patient's history and clinical features are consistent with a diagnosis of Sillence type IA OI. Type I OI is the mildest and most common form. Inheritance is autosomal-dominant; however, as in this patient, new mutations are frequent. Type I is subclassified into the A type (absence of dentinogenesis imperfecta) and B type (presence of dentinogenesis imperfecta). The sclerae are blue, and the first fractures usually occur in the preschool years after walking has begun. Cells from individuals with type I OI largely demonstrate a quantitative defect of type I collagen; they synthesize and secrete about half the normal amount of type I procollagen. Qualitative mutations that lead to an abnormal type I procollagen molecule result in more severe types of the disorder. There are no indications that this child has been abused. Radiographs of the femur show no evidence of rickets, pyknodysostosis, or osteopetrosis. Morquio syndrome, characterized by excess excretion of keratin sulfate in the urine, is not associated with bone fragility. Kocher MS, Shapiro F: Osteogenesis imperfecta. J Am Acad Orthop Surg 1998;6:225-236. Sillence DO, Senn A, Danks DM: Osteogenesis imperfecta: An expanding panorama of variants. Clin Orthop 1981;159:11-25.

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