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1. General Principles & Basic Science MCQs

Practice Set 227 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 4521

Topic: 1. General Principles & Basic Science

In performing an opening wedge high tibial osteotomy at the tibial tubercle, the osteotome extends 5 mm posteriorly and centrally out of the bone as shown in Figures 17a and 17b. What is the first structure it enters?

. Popliteal artery
. Popliteal vein
. Tibial nerve
. Popliteus muscle
. Soleus muscle

Correct Answer & Explanation

. Popliteus muscle

Explanation

The major risk of performing a high tibial osteotomy is neurovascular injury. The new version of the high tibial osteotomy makes a transverse osteotomy at the level of the tibial tubercle. The osteotome is protected by the oblique belly of the popliteus muscle. The popliteal artery and vein and tibial nerve all lie posterior to the muscle. The soleus muscle originates below this level. Clement CD: Anatomy: A Regional Atlas of Human Anatomy, ed 3. Baltimore, MD, Munich, Germany, Urban and Schwarzberg, 1987, Figure 422.

Question 4522

Topic: Biology, Genetics & Bone Healing

A 74-year-old woman has had acute medial right knee pain for the past 3 months. She denies any history of trauma or previous problems. Coronal and sagittal MRI scans are shown in Figures 11a and 11b. What is the most likely diagnosis?

. Osteoarthritis
. Rheumatoid arthritis
. Medial meniscal tear
. Osteonecrosis
. Transient osteoporosis

Correct Answer & Explanation

. Osteonecrosis

Explanation

Spontaneous osteonecrosis of the medial femoral condyle is seen in the MRI scans, and is most common in women older than age 60 years. Although usually present in the weight-bearing portion of the medial femoral condyle, spontaneous osteonecrosis has also been described involving the lateral femoral condyle and patella. Most patients are seen postcollapse, and the treatment of choice is arthroplasty. Optimal treatment in precollapse stages is controversial. Kidwai AS, Hemphill SD, Griffiths HJ: Spontaneous osteonecrosis of the knee reclassified as insufficiency fracture. Orthopedics 2005;28:236,333-336. Soucacos PN, Xenakis TH, Beris AE, et al: Idiopathic osteonecrosis of the medial femoral condyle: Classification and treatment. Clin Orthop 1997;341:82-89.

Question 4523

Topic: Infection, Pharmacology & VTE

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?

. Amoxicillin
. Vancomycin
. Clindamycin
. Ceftazadime
. Cefazolin

Correct Answer & Explanation

. Ceftazadime

Explanation

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

Question 4524

Topic: Biology, Genetics & Bone Healing

A 3-year-old child has bilateral genu varum and short stature. Radiographs show physeal widening and generalized osteopenia. The femora and tibiae show anterolateral bowing. Laboratory studies show low normal serum calcium values, significantly decreased serum phosphate levels, and normal parathyroid hormone (PTH), alkaline phosphatase, and vitamin-D levels. These findings are consistent with

. nutritional rickets.
. renal osteodystrophy.
. primary hyperparathyroidism.
. hypophosphatasia.
. vitamin D-resistant rickets.

Correct Answer & Explanation

. vitamin D-resistant rickets.

Explanation

Children with vitamin D-resistant rickets are short in stature and have genu varum, physeal widening, and generalized osteopenia. The abnormality in inherited vitamin D-resistant rickets is the renal tubule's inability to resorb phosphate leading to hypophosphatemia. Laboratory findings in the condition are normal or near normal serum calcium values, significantly decreased serum phosphate levels, elevated alkaline phosphatase levels, and normal PTH and vitamin-D levels. The most common form is inherited as an X-linked dominant trait. Nutritional rickets has a normal or low serum phosphate levels, normal or low serum calcium values, and decreased levels of 25(OH) vitamin D and 1,25-dihydroxyvitamin D. Hypophosphatasia is a rare condition characterized by a deficiency of alkaline phosphatase in the serum and tissues, leading to generalized abnormal mineralization of bone. Primary hyperparathyroidism usually is caused by a parathyroid adenoma, and the child generally has abdominal problems and hypercalcemic crisis. Laboratory findings include elevated serum calcium values, alkaline phosphatase levels, and PTH levels, and decreased serum phosphate levels. Children with renal osteodystrophy tend to have genu valgum, and laboratory findings include elevated serum phosphate, alkaline phosphatase, and PTH levels, and low serum calcium values. Findings of renal disease include elevated BUN and creatinine. Herring JA: Metabolic and endocrine bone diseases, in Herring JA (ed): Tachdjian's Pediatric Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2002, pp 1686-1710.

Question 4525

Topic: 1. General Principles & Basic Science

In a postganglionic brachial plexus lesion at Erb's point (point of formation of the upper trunk by the C5 and C6 nerve roots), which of the following nerves will still function normally?

Anatomy Board Review 2005: High-Yield MCQs (Set 2) - Figure 28

. Suprascapular
. Musculocutaneous
. Axillary
. Lateral pectoral
. Dorsal scapular

Correct Answer & Explanation

. Dorsal scapular

Explanation

In a postganglionic injury to the brachial plexus, the rhomboid muscle, innervated by the dorsal scapular nerve, would still be expected to function. This is a useful clinical sign that the brachial plexus lesion is postganglionic as opposed to preganlionic. The musculocutaneous, axillary, and suprascapular nerves are all located distal to Erb's point (the most common location of an upper nerve root brachial plexus injury), and all contain fibers from the C5 and C6 nerve roots. Therefore, these nerves are not expected to function normally following a postganglionic C5 and C6 nerve root injury. Netter F: The Ciba Collection of Medical Illustrations: The Musculoskeletal System: Part 1, Anatomy, Physiology and Metabolic Disorders. West Caldwell, NJ, Ciba-Geigy, 1991, vol 8, pp 28-29.

Question 4526

Topic: Biomechanics & Biomaterials

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?

. Gross failure at the attachment sites
. Fatigue failure of the ligament tissue
. Creep of the graft material
. Water absorption by the graft material
. Elastic stretch of collagen fibers

Correct Answer & Explanation

. Creep of the graft material

Explanation

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. 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. 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 596-609.

Question 4527

Topic: Surgical Anatomy & Approaches

A 25-year-old woman undergoes surgical treatment of a displaced proximal humeral fracture via a deltopectoral approach. At the first postoperative visit, she reports a tingling numbness along the anterolateral aspect of the forearm. What structure is most likely injured?

. Medial cord of the brachial plexus
. Radial nerve
. Median nerve
. Axillary nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

Sensation along the anterolateral aspect of the forearm is supplied by the lateral antebrachial cutaneous nerve, the terminal branch of the musculocutaneous nerve. The musculocutaneous nerve can be injured by proximal humeral fractures or dislocations, and is also at risk during surgical exposure if excessive retraction is placed on the conjoint tendon. The musculocutaneous nerve enters the conjoint tendon 1 cm to 5 cm distal to the coracoid process. McIlveen SJ, Duralde XA, D'Alessandro DF, et al: Isolated nerve injuries about the shoulder. Clin Orthop 1994;306:54-63.

Question 4528

Topic: 1. General Principles & Basic Science

Figures 25a and 25b show the radiograph and MRI scan of a 7 1/2-year-old boy who has been limping for 1 year. His pain has worsened over the past 2 weeks, and his parents note swelling over the dorsum of the foot for the past 4 days. Examination reveals no fever, and laboratory studies show a WBC of 6,700/mm3, an erythrocyte sedimentation rate of 26 mm/h, and a normal C-reactive protein level. What is the most likely diagnosis?

. Acute hematogenous osteomyelitis
. Kohler's disease
. Tarsal coalition
. Tuberculosis
. Lisfranc fracture-dislocation

Correct Answer & Explanation

. Tuberculosis

Explanation

The diagnosis of tuberculous osteomyelitis in children is often delayed. In one series of 23 children, the average interval between the onset of symptoms and definite diagnosis was 4.3 months. In these patients, the presenting signs and symptoms were found to be mild, with the most common signs being localized swelling (69.6%) and a painful disability of the involved limbs (65.2%). A mild elevation of the erythrocyte sedimentation rate may be present, but the C-reactive protein level is usually normal. In patients who have osteoarticular tuberculosis, an MRI scan generally shows large intra-articular effusions, periarticular osteoporosis, and gross thickening of the synovial membrane. Differential diagnosis between tuberculosis and pyogenic arthritis is difficult, and an accurate diagnosis usually requires biopsy of synovial tissue. Aspiration of synovial fluid often results in insufficient information to make a diagnosis. Treatment generally consists of surgical debridement and combined antituberculous chemotherapy with isoniazid, ethambutol, and rifampin. Wang MN, Chen WM, Lee KS, Chin LS, Lo WH: Tuberculous osteomyelitis in young children. J Pediatr Orthop 1999;19:151-155.

Question 4529

Topic: Infection, Pharmacology & VTE

A 3-year-old girl has had wrist pain, a fever, and has refused to move her right wrist for the past 10 days. She has an oral temperature of 102 degrees F (38.7 degree C). Laboratory studies show an erythrocyte sedimentation rate of 50 mm/h, a WBC count of 11,000/mm3, and a left shift. AP and lateral radiographs are shown in Figures 57a and 57b. What is the most likely diagnosis?

. Leukemia
. Eosinophilic granuloma
. Acute osteomyelitis
. Ewing's sarcoma
. Nonossifying fibroma

Correct Answer & Explanation

. Acute osteomyelitis

Explanation

The most likely diagnosis is acute osteomyelitis. She may also have a septic wrist; however, the lytic lesion in the distal radius has the typical presentation and radiographic appearance of metaphyseal osteomyelitis. In this area of sluggish vascular flow, low oxygen tension, and low pH, bacterial seeding is common and is the usual origin of metaphyseal osteomyelitis. Leukemia and Ewing's sarcoma can present as a lytic lesion with an elevated erythrocyte sedimentation rate, but they are much less common than osteomyelitis and are less focal and more destructive in appearance. Nonossifying fibroma is typically metaphyseal and eccentric; however, it is well circumscribed and uncommon in the upper extremity. Eosinophilic granuloma does not typically present with inflammatory indicies. Dormans JP, Drummond DS: Pediatric hematogenous osteomyelitis: New trends in presentation, diagnosis and treatment. J Am Acad Orthop Surg 1994;2:333-341.

Question 4530

Topic: 1. General Principles & Basic Science

A 32-year-old man has a Glasgow Coma Scale score of 8 and an open pelvic fracture. The patient's family reports that he is a Jehovah's Witness. Initial hemodynamic instability has resolved. In the operating room during a washout, the patient's blood pressure becomes unstable. What is the most appropriate action?

. Consult the ethics committee before giving blood.
. Use cell saver blood.
. Ask the patient's family for consent to give blood.
. Use plasma expanders.
. Give the patient blood.

Correct Answer & Explanation

. Give the patient blood.

Explanation

Certain medical procedures involving blood are specifically prohibited in the belief system of a Jehovah's Witness whereas others are not doctrinally prohibited. For procedures where there is no specific doctrinal prohibition, a Jehovah's Witness should obtain the details from medical personnel and make his or her own decision. Transfusions of allogeneic whole blood or its constituents or preoperative donated autologous blood are prohibited. Other procedures, while not doctrinally prohibited, are not promoted such as hemodilution, intraoperative cell salvage, use of a heart-lung machine, dialysis, epidural blood patch, plasmapheresis, white blood cell scans (labeling or tagging of removed blood returned to the patient), platelet gel, erythropoietin, or blood substitutes. The patient should not be given blood. Plasma expanders should be used first to restore hemodynamic stability. Cell saver blood from an open would is not recommended nor would there likely be enough from an open tibial fracture to salvage. The patient's family may be expressing their own beliefs rather than the patient's beliefs and it would be better to ask the patient when he or she is more alert to determine what procedures they would allow. A consult with the ethics committee will unnecessarily delay an intervention that should restore hemodynamic stability. Jimenez R, Lewis VO (eds): Culturally Competent Care Guidebook. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2007.

Question 4531

Topic: Biomechanics & Biomaterials

Which of the following statements best characterizes polymethylmethacrylate (PMMA) when it is used to secure joint components in bone and to distribute the forces evenly across the bone-implant interface?

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

. PMMA is stronger in tension than compression.
. Porosity reduction increases the fatigue strength of PMMA.
. Hypotension that occasionally results after PMMA is placed in the femoral canal is independent of a patient's intraoperative blood volume.
. Inclusion of antibiotics does not alter the strength of PMMA.
. PMMA bonds chemically to bone and the implant surface.

Correct Answer & Explanation

. Porosity reduction increases the fatigue strength of PMMA.

Explanation

PMMA has no adhesive properties and can be more accurately described as grout than glue. It does not chemically bond to bone or implants; however, mechanical bonding is accomplished with porous or coated components and with cancellous bone. PMMA is approximately three times stronger in compression than in tension. Peak blood levels of monomer are usually seen approximately 3 minutes after the cement is placed. The monomer is cleared by the lungs. Associated hypotension is more closely related to diminished blood volume than to circulating monomer levels. High porosity decreases the tensile and fatigue properties of cement. Manually mixed cement may have porosity as high as 27%. Porosity may be reduced to less than 1% through vacuum mixing or centrifugation of the cement. When adding antibiotics to cement, the compressive and tensile forces are not appreciably decreased, but the overall fatigue strength may be reduced. Canale ST (ed): Campbell's Operative Orthopaedics, ed 9. St Louis, MO, Mosby, 1998, pp 221-224.

Question 4532

Topic: 1. General Principles & Basic Science

Figure 6 shows a sagittal oblique MRI scan. The arrow is pointing to what structure?

Anatomy 2008 Practice Questions: Set 1 (Solved) - Figure 12

. Bucket-handle tear of the medial meniscus
. Ligament of Humphrey
. Ligament of Wrisberg
. Posterior intermeniscal ligament
. Partial tear of the posterior cruciate ligament

Correct Answer & Explanation

. Ligament of Wrisberg

Explanation

The meniscofemoral ligaments connect the posterior horn of the lateral meniscus to the intercondylar wall of the medial femoral condyle. The ligament of Humphrey (arrow) passes anterior to the posterior cruciate ligament, whereas the ligament of Wrisberg passes posterior to the posterior cruciate ligament. One or the other has been identified in 71% to 100% of cadaver knees, with the ligament of Wrisberg being more common. Clarke HD, Scott WN, Insall JN, et al: Anatomy, in Insall JN, Scott WN (eds): Surgery of the Knee, ed 4. Philadelphia, PA, Churchill Livingstone, 2006, vol 1, pp 3-66.

Question 4533

Topic: Surgical Anatomy & Approaches

A 39-year-old competitive cyclist sustains an injury to her left hip in a fall. Gadolinium arthrography, with an accompanying MRI scan, is shown in Figure 31. A cleft, or defect, identified by the arrow, indicates a detachment of the

Sports Medicine 2001 Practice Questions: Set 3 (Solved) - Figure 10

. acetabular labrum.
. zona orbicularis.
. iliofemoral ligament.
. acetabular pulvinar.
. retinacular vessels.

Correct Answer & Explanation

. acetabular labrum.

Explanation

The area indicated by the arrow represents gadolinium contrast extending into a separation between the lateral labrum and its acetabular attachment. This can be a traumatic detachment, but occasionally a cleft may be present as a normal variant of the labral morphology. The capsular attachment of the iliofemoral ligament is peripheral to the labrum. The pulvinar is the common name applied to the fat and overlying synovium contained within the acetabular fossa above the ligamentum teres. The zona orbicularis is a circumferential thickening of the capsule around the femoral neck, and the retinacular vessels travel within the capsular synovium up the femoral neck to supply the femoral head. Petersilge CA, Haque MA, Petersilge WJ, Lewin JS, Lieberman JM, Buly R: Acetabular labral tears: Evaluation with MR arthrography. Radiology 1996;200:231-235. Czerny C, Hofmann S, Neuhold A, et al: Lesions of the acetabular labrum: Accuracy of MR imaging and MR arthrography in detection and staging. Radiology 1996;200:225-230.

Question 4534

Topic: Biology, Genetics & Bone Healing

Gaucher's disease is manifested by reticuloendothelial system macrophage accumulation of

Basic Science 2002 Practice Questions: Set 1 (Solved) - Figure 34

. cholesterol.
. hydroxyproline.
. calcium pyrophosphate.
. homogentisic acid.
. glucocerebroside.

Correct Answer & Explanation

. glucocerebroside.

Explanation

Gaucher's disease is characterized by macrophage accumulation of glucocerebroside that is caused by a deficiency of lysosomal enzyme glucocerebrosidase. It is an autosomal-recessive trait and is most commonly found in Ashkenazi Jews. Orthopaedic surgeons see patients with Gaucher's disease usually because of osteonecrosis of the hip. Calcium pyrophosphate is associated with pseudogout. Hydroxyproline is a breakdown product of collagen and is found in high levels in patients with Paget's disease. Homogentisic acid is associated with ochronosis (alkaptonuria). Beatty JH: Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 247-252. Goldblatt J, Sacks S, Beighton P: The orthopedic aspects of Gaucher disease. Clin Orthop 1978;137:208-214.

Question 4535

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion. Biopsy shows multinucleated giant cells and mononuclear stromal cells. Denosumab therapy is considered. What is the precise mechanism of action of Denosumab?

. Binds to RANKL, preventing interaction with RANK
. Binds directly to RANK on osteoclasts
. Inhibits osteoprotegerin production
. Inhibits bisphosphonate absorption in the gut
. Directly inhibits vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Binds to RANKL, preventing interaction with RANK

Explanation

Denosumab is a monoclonal antibody that specifically binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding to RANKL, it prevents it from interacting with the RANK receptor on the surface of osteoclasts and giant cells, thereby profoundly inhibiting osteoclastogenesis and tumor-associated bone lysis in giant cell tumors.

Question 4536

Topic: Surgical Anatomy & Approaches

A 6-year-old boy falls on an outstretched hand. Radiographs of the elbow are shown below:

On physical examination, the child is unable to flex the interphalangeal joint of the thumb. Which nerve is most likely injured?

. Ulnar nerve
. Radial nerve
. Anterior interosseous nerve
. Posterior interosseous nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Anterior interosseous nerve

Explanation

The inability to flex the interphalangeal joint of the thumb indicates an injury to the flexor pollicis longus (FPL), which is innervated by the Anterior Interosseous Nerve (AIN). AIN neuropraxia is the most common nerve injury associated with extension-type supracondylar humerus fractures.

Question 4537

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a severe open distal femur fracture. Following debridement, a massive bone defect is treated with the induced membrane (Masquelet) technique. What is the peak time to harvest or graft the induced membrane for optimal vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) expression?

. 2 weeks
. 4 weeks
. 8 weeks
. 12 weeks
. 16 weeks

Correct Answer & Explanation

. 4 weeks

Explanation

The induced membrane created in the Masquelet technique possesses peak osteogenic and angiogenic properties, including maximum expression of VEGF, BMP-2, and TGF-beta, at approximately 4 weeks. Most surgeons perform the second-stage bone grafting between 4 and 6 weeks to capitalize on this biological peak.

Question 4538

Topic: Biomechanics & Biomaterials

When analyzing the mechanical properties of an orthopedic plate, the area under the stress-strain curve up to the point of failure represents which of the following material properties?

. Elastic modulus
. Yield strength
. Ultimate tensile strength
. Toughness
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures, which is graphically represented by the total area under the stress-strain curve. Elastic modulus is the slope of the linear elastic region. Yield strength is the stress at which plastic deformation begins.

Question 4539

Topic: Infection, Pharmacology & VTE
Rivaroxaban is a medication commonly prescribed for deep vein thrombosis prophylaxis following total joint arthroplasty. What is its specific mechanism of action in the coagulation cascade?
. Inhibits antithrombin III
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase inhibitor
. Enhances tissue plasminogen activator

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and Apixaban are Direct Oral Anticoagulants (DOACs) that specifically and reversibly inhibit Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin acts by inhibiting vitamin K epoxide reductase.

Question 4540

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, endochondral ossification is paramount. During the soft callus phase, chondrocytes proliferate and eventually undergo hypertrophy. Which type of collagen is uniquely and predominantly synthesized by hypertrophic chondrocytes to facilitate matrix calcification?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type X collagen

Explanation

Hypertrophic chondrocytes are the hallmark of the transition zone in endochondral ossification. They cease producing Type II collagen (which is characteristic of proliferating chondrocytes) and exclusively synthesize Type X collagen. Type X collagen alters the extracellular matrix to allow for calcification and subsequent vascular invasion, paving the way for osteoblasts to lay down woven bone.

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