Orthopedic Basic MCQs 2026 | Board Review & Answers

Question 1

A 16-year-old boy has had thigh pain for the past several months. He denies any history of trauma. Examination reveals a large, deeply fixed, soft-tissue mass in the thigh. Laboratory results show an elevated erythrocyte sedimentation rate (ESR) and leukocytosis. A plain radiograph and MRI scan are shown in Figures 1a and 1b. Biopsy specimens are shown in Figures 1c and 1d. What is the most likely diagnosis?

Explanation

1b 1c 1d Ewing's sarcoma typically can occur in the diaphysis of the long bones (50% to 55%). It is often accompanied by a large soft-tissue mass. Abnormal findings are common, including a low-grade fever, an elevated ESR, and leukocytosis. The histology is consistent with a small round blue cell tumor. The unique pathology and other findings exclude osteosarcoma. Giant cell tumor and chondrosarcoma have a different histologic appearance and typically are more metaphyseal in location. Chondrosarcoma typically is found in older age groups, has a different histologic pattern, and rarely occurs in the midshaft of the femur.

Question 2

A 14-year-old boy who is right handed reports right shoulder pain. Radiographs show a lucent lesion of the proximal humeral epiphysis with a narrow zone of transition. Results of an open biopsy confirm the presence of a chondroblastoma. Based on these findings, the next most appropriate step in management should consist of

Explanation

The patient has a chondroblastoma of the proximal humerus; therefore, the treatment of choice is curettage and bone grafting. Surgical resection of the proximal humerus is not indicated in the initial treatment of an intraosseous chondroblastoma. Mirra JM: Bone Tumors: Clinical, Radiologic, and Pathologic Correlations. Philadelphia, PA, Lea and Febiger, 1989, pp 589-623.

Question 3

A 25-year-old man has had an insidious onset of left hip pain over the past 11 months. A radiograph, coronal MRI scan, and histopathologic specimens are seen in Figures 2a through 2d. What is the most likely diagnosis?

Explanation

2b 2c 2d Ewing's sarcoma is the second most common primary sarcoma of bone in children and young adults. It is a malignant round cell tumor with uncertain histogenesis. Sheets of uniform small round blue cells with a high nuclear-to-cytoplasm ratio and the absence of osteoid formation differentiate this histologic diagnosis from the other conditions. Immunohistochemical staining and molecular diagnostic studies are useful to verify the diagnosis.

Question 4

What is the most common anatomic location for chondrosarcoma?

Explanation

The most common anatomic location of chondrosarcoma is the pelvis (30%), followed by the proximal femur (20%). Chondrosarcomas appear in the shoulder girdle in 15% of patients but rarely affect the spine or hands. Marcove RC, Mike V, Hutter RV, et al: Chondrosarcoma of the pelvis and upper end of the femur: An analysis of factors influencing survival time in one hundred and thirteen cases. J Bone Joint Surg Am 1972;54:561-572.

Question 5

In the spine, osteoblastomas usually originate in the

Explanation

Osteoblastomas are benign lesions that represent less than 5% of benign bone tumors. Most lesions are located in the spine, followed by the femur, tibia, and skull. Patients with spinal lesions usually have pain that may be associated with scoliosis. The most common location in the spine is within the posterior elements.

Question 6

A 64-year-old man with a history of metastatic lung cancer reports increasing right hip pain over the period of several months. Radiographs are shown in Figures 3a and 3b. Initial management should consist of

Explanation

3b The patient has lung cancer metastatic to the right proximal femur. The lesion is large, has destroyed a portion of the cortex, and involves the peritrochanteric region. All of these findings put the patient at high risk for pathologic fracture. The lesion is amenable to intramedullary fixation in the form of some type of reconstruction nail. Chemotherapy alone will not restore the bone stock. Given the extent of the lesion, radiation therapy, chemotherapy, or embolization will not prevent fracture. A proximal femoral replacement would be indicated in patients with bone destruction extending into the femoral head and neck. Bisphosphonates may diminish the risk of subsequent lesions but are not sufficient to treat this high-risk lesion. Radiation therapy should be given postoperatively to prevent further bone destruction.

Question 7

A 58-year-old woman has had a painless periscapular mass for the past year. An MRI scan and biopsy specimen are shown in Figures 4a and 4b. What is the most likely diagnosis?

Explanation

4b Elastofibroma is a rare tumor that most commonly occurs in adults who are older than age 55 years. The lesions usually grow between the chest wall and the scapula, and 10% are bilateral. Histologic analysis shows that they are composed of equal amounts of elastin and collagen with occasional fibroblasts. Briccoli A, Casadei R, Di Renzo M, Favale L, Bacchini P, Bertoni F: Elastofibroma dorsi. Surg Today 2000;30:147-152.

Question 8

A characteristic genetic translocation has been noted in which of the following tumors?

Explanation

There have been no characteristic gene translocations or rearrangements noted in osteosarcoma, chondrosarcoma, neurofibrosarcoma, or epithelioid sarcoma. In contrast, Ewing's sarcoma has been noted to have a consistent genetic translocation t(11:22). Brockstein BE, Peabody TD, Simon MA: Soft tissue sarcomas, in Vokes EE Golomb HM (eds): Oncologic Therapies. New York, NY, Springer-Verlag, 1999, pp 925-952.

Question 9

A 44-year-old man has right hip pain. Radiographs reveal a radiolucent lesion of the femoral head and neck. An MRI scan shows no extraosseous tumor extension. A histopathologic photomicrograph of the biopsy specimen is shown in Figure 5. The chance of metastatic disease developing from this lesion is approximately what percent?

Explanation

The risk of pulmonary metastasis from a benign giant cell tumor is estimated to be 5%.

Question 10

Figures 6a through 6d show the radiographs and biopsy specimens of an 8-year-old girl with leg pain. Management of the lesion should consist of

Explanation

6b 6c 6d The biopsy specimens show a chondromyxoid fibroma with varying amounts of cartilage, benign fibrous tissue, giant cells, and loose myxoid areas. Chondromyxoid fibroma is a benign active bone lesion that is best treated with aggressive curettage and bone grafting. Although recurrences are common, more aggressive treatment is not warranted initially. Wilson AJ, Kyriakos M, Ackerman LV: Chondromyxoid fibroma: Radiographic appearance in 38 cases and in a review of the literature. Radiology 1991;179:513-518.

Question 11

Which of the following is considered the treatment of choice for a chondroblastoma of the proximal tibial epiphysis without intra-articular extension?

Explanation

Curettage and bone grafting typically is the preferred method of treatment for chondroblastoma, with local recurrence rates of approximately 10%. Some clinicians advocate the addition of adjuvants such as phenol. Left alone, these lesions can destroy bone and invade the joint. Large intra-articular lesions may require major joint reconstruction. Wide local excision rarely is required to eradicate the tumor. Radiation therapy rarely is indicated and only for unresectable or multiply recurrent lesions. Springfield DS, Capanna R, Gherlinzoni F, Picci P, Campanacci M: Chondroblastoma: A review of seventy cases. J Bone Joint Surg Am 1985;67:748-755.

Question 12

An otherwise healthy 78-year-old woman has low back and buttock pain. Rectal examination reveals a large sacral mass. Figures 7a and 7b show a CT scan and a sagittal MRI scan of the lumbosacral spine. A biopsy specimen is shown in Figure 7c. What is the most likely diagnosis?

Explanation

7b 7c A chordoma is a malignant neoplasm originating from remnants of the notochord. It is usually localized to the midline with 50% at the sacrococcygeal area, 35% at the skull base, and 15% at the mobile portion of the spine. Large vacuolated cells (physaliferous cells) are a characteristic of the tumor. Mindell ER: Chordoma. J Bone Joint Surg Am 1981;63:501-505.

Question 13

Figures 8a through 8c show the lateral radiograph and T1- and T2-weighted MRI scans of a 14-year-old soccer player who reports aching thigh pain. The next most appropriate step in management should consist of

Explanation

8b 8c Although the MRI findings could be misinterpreted as an aggressive soft-tissue process, the periosteal-based ossification on the radiograph in an athlete most likely suggests myositis ossificans. The radiograph should be repeated to see further maturation of the ossification with a typical "zoning" pattern. The zoning pattern is one of peripheral ossification. This is often best seen on a CT scan. King JB: Post-traumatic ectopic calcification in the muscles of athletes: A review. Br J Sports Med 1998;32:287-290.

Question 14

A 51-year-old male truck driver has had progressive left hip pain for more than 2 years, and he reports that the pain has become severe in the past 9 months. He is now unable to work because of the pain. Examination reveals that range of motion of the hip is limited to 95 degrees of flexion, 0 degrees of internal rotation, and 20 degrees of external rotation. The plain radiograph, MRI scan, and intraoperative gross photographs are shown in Figures 9a through 9d. Management should consist of

Explanation

9b 9c 9d The diagnosis is synovial chondromatosis. While the plain radiograph fails to show any calcifications, the MRI scan shows an intra-articular mass that involves the capsule. Grossly multiple granular cartilage nodules are seen. Management should consist of removing all loose bodies along with the synovial membrane.

Question 15

Using methylmethacrylate to fill a biopsy hole in the diaphysis of a femur theoretically achieves what purpose?

Explanation

Placing cement over a bone biopsy site prevents tumor contamination by controlling hematoma. Even though the use of cement may impart some strength, the femur is still at significant risk for fracture. The use of bone cement in this manner has not been cleared by the FDA, but many physicians feel that it is appropriate when the patient's health status has been given careful consideration, and the physician has the necessary knowledge and training. The other options are not important reasons to use methylmethacrylate in biopsies. Simon MA, Springfield DS, et al: Biopsy: Surgery for Bone and Soft Tissue Tumors. Philadelphia, PA, Lippincott Raven, 1998, pp 55-65.

Question 16

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

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 17

A 14-year-old boy reports pain in the distal thigh. He denies any history of trauma. Examination reveals tenderness and swelling of the distal thigh without effusion. A radiograph and CT scan are shown in Figures 10a and 10b. A biopsy specimen is shown in Figure 10c. Management should consist of

Explanation

10b 10c Based on these findings, the patient has an aneurysmal bone cyst. Frequently, fluid-fluid levels can be detected on MRI or CT images. The histologic results show a lesion that consists of cavernous spaces filled with blood. The lining of the cavity contains spindle cells, multinucleated giant cells, and reactive bone. Curettage and bone grafting is the preferred treatment method. Without treatment, these lesions can become quite large and destructive. Radiation therapy is not recommended for resectable lesions. Chemotherapy is not required for these benign lesions. Simon MA, Springfield DS, et al: Common Benign Bone Tumors: Surgery for Bone and Soft Tissue Tumors. Philadelphia, PA, Lippincott Raven, 1998, pp 194-200.

Question 18

The dose of the chemotherapeutic agent doxorubicin (Adriamycin) is limited by which of the following factors?

Explanation

Doxorubicin is a chemotherapeutic agent that is best known for dose-limiting cardiotoxicity. This is related not only to the cumulative dose, but also the rate of infusion.

Question 19

A previously asymptomatic 12-year-old girl sustained a direct blow to the right lateral knee from a baseball bat. Examination reveals an area of ecchymosis and tenderness over the lateral thigh. The patient can walk without pain, but range of motion of the knee causes discomfort. Plain radiographs of the knee are shown in Figures 11a and 11b. To address the bone lesion, management should consist of

Explanation

11b The plain radiographs reveal a pedunculated osteochondroma with a fracture. There is a bony growth in the metaphysis of a long bone, on a stalk that is directed away from the nearby epiphysis. On the AP view, the host cortical and medullary bone are shown as "blending" with lesional bone. There is also a fracture through the lesion. Based on these radiographic findings, the diagnosis is an osteochondroma; therefore, initial management of an acute fracture of an osteochondroma is symptomatic treatment alone. Additional imaging studies are not indicated in this patient. At times it may be difficult to distinguish a sessile osteochondroma from a parosteal osteosarcoma. In the latter case, the host medullary bone and lesion bone are not confluent. A CT scan may be helpful to distinguish if the host medullary and cortical bone are confluent with the lesion.

Question 20

What is the most common pediatric soft-tissue sarcoma?

Explanation

Soft-tissue sarcomas are the sixth most common cancer in children. Rhabdomyosarcoma is the most common type of pediatric soft-tissue sarcoma. Nearly 50% of rhabdomyosarcomas are diagnosed in children who are age 5 years or younger. Unfortunately, there has not been a significant increase in survival in children with metastatic rhabdomyosarcoma despite aggressive therapy including multiple-drug chemotherapy regimens.

Question 21

A 53-year-old man has a 4- x 5-cm high-grade soft-tissue sarcoma in the midthigh. As part of the staging evaluation, regional nodes should be assessed by

Explanation

In general, soft-tissue metastases to regional nodes are a relatively rare occurrence (less than 5% overall). The incidence of lymphatic metastasis is highest for synovial sarcoma, rhabdomyosarcoma, clear cell sarcoma, and epithelioid sarcoma. Regional nodes should be assessed clinically. CT is not used to routinely assess regional nodes. Evaluation of a sentinal node is not indicated because of the low incidence of regional nodal involvement. Fine needle aspiration may be indicated to assess clinically suspicious nodes. Prophylactic inguinal node dissection is contraindicated because it may lead to unnecessary complications such as lymphedema.

Question 22

The risk of local recurrence after surgical resection of a soft-tissue sarcoma is most closely related to

Explanation

A positive margin is most closely related to subsequent local recurrence. The other factors cited, including the size and site of the tumor, may be related to local recurrence; however, they are more commonly prognostic because of the difficulty in obtaining wide surgical margins about large or proximal tumors. Radiation therapy has been noted to decrease the incidence of recurrence but is not felt to be as important as the surgical margin. The grade of the tumor has more influence on the prevalence of metastatic disease than the incidence of local recurrence. Lewis JJ, Leung D, Heslin M, Woodruff JM, Brennan MF: Association of local recurrence with subsequent survival in extremity soft tissue sarcoma. J Clin Oncol 1997;15:646-652.

Question 23

In a patient with a soft-tissue sarcoma treated by wide excision and radiation therapy, the risk of subsequent fracture is probably most influenced by

Explanation

While most pathologic fractures are in the lower extremity in patients treated for soft-tissue sarcomas by wide excision and adjuvant radiation therapy, risk factors for such fractures are bone resection associated with excision of the tumor and soft-tissue sarcomas of the thigh that require periosteal stripping at the time of resection. Such fractures can occur late, often more than 6 months after surgery, are difficult to treat, and often result in nonunion. Bell RS, O'Sullivan B, Nguyen C, et al: Fractures following limb-salvage surgery and adjuvant irradation for soft-tissue sarcoma. Clin Orthop 1991;271:265-271.

Question 24

Figures 12a and 12b show the radiographs of a 50-year-old patient who reports acute knee pain after sustaining a twisting injury while playing tennis. Examination is unremarkable. The next most appropriate step in management should consist of

Explanation

12b The radiographs show localized diffuse cortical thickening that is characteristic of melorheostosis. The condition may be monostotic or it may involve many bones in one extremity (monomelic) in the distribution of a sclerotome. Bone scans will show increased uptake at the site or sites of skeletal involvement. Long tubular bones are most commonly involved. Melorheostosis is usually asymptomatic and requires no treatment. On rare occasions, there may be associated soft-tissue contractures. Dorfman H, Czerniak B: Bone Tumors. St Louis, MO, Mosby Inc, 1998, pp 1105-1107. Campbell CJ, Papademetriou T, Bonfiglio M: Melorheostosis: A report of the clinical, roentgenographic, and pathological findings in fourteen cases. J Bone Joint Surg Am 1968;50:1281-1304.

Question 25

An adult patient has an 8- x 4- x 10-cm soft-tissue mass located within the adductor compartment of the thigh. Staging studies should consist of

Explanation

The appropriate staging studies should consist of MRI and a radiograph of the primary lesion and CT of the chest. MRI is superior to CT for soft-tissue imaging. CT may be useful for evaluating the cortex of bone for invasion by tumor. Bone scans are not commonly used because soft-tissue sarcomas rarely metastasize to bone. CT of the abdomen and pelvis is not typically ordered except for possible liposarcoma. With liposarcoma, there may be a synchronous or metastatic retroperitoneal liposarcoma. Demetri GD, Pollock R, Baker L, et al: NCCN sarcoma practice guidelines: National Comprehensive Cancer Network. Oncology (Huntingt) 1998;12:183-218.

Question 26

A 12-year-old boy presents with a painful mass in his distal femur. Biopsy confirms conventional high-grade osteosarcoma. Which of the following genetic syndromes is associated with a germline mutation in the RECQL4 helicase gene and a significantly increased risk of developing this malignancy?

Explanation

Rothmund-Thomson syndrome is an autosomal recessive disorder caused by a RECQL4 mutation, predisposing patients to osteosarcoma. Li-Fraumeni is associated with p53 mutations, while Hereditary Retinoblastoma involves the Rb1 gene.

Question 27

During fracture fixation, the mechanical properties of the implants must be considered. The torsional strength (resistance to breaking upon insertion) of a cortical bone screw is most closely proportional to the cube of which of the following screw parameters?

Explanation

A screw's torsional strength, or its resistance to fracture during torque, is proportional to the cube of its root (inner) diameter. In contrast, its pullout strength is related to the outer diameter and thread depth.

Question 28

In normal mature articular cartilage, which zone is characterized by the highest concentration of proteoglycans and the presence of the largest diameter collagen fibrils oriented perpendicular to the joint surface?

Explanation

The deep (radial) zone of articular cartilage features large-diameter collagen fibrils aligned perpendicular to the surface to resist compressive forces. It also contains the highest proteoglycan content and the lowest water content.

Question 29

If a stainless steel screw is placed through a titanium alloy plate in a saline physiological environment, galvanic corrosion may occur. Which of the following best describes the resulting electrochemical process?

Explanation

In a mixed-metal galvanic couple between stainless steel and titanium, the less noble stainless steel acts as the anode and undergoes accelerated corrosion. Titanium is more noble and acts as the cathode.

Question 30

Osteolysis following total hip arthroplasty is primarily driven by macrophage activation due to wear debris. What is the most biologically active size range of polyethylene particles that stimulates this aggressive inflammatory osteolytic response?

Explanation

Macrophages most readily phagocytize polyethylene particles in the 0.1 to 1.0 micrometer range. This specific size triggers the highest release of osteolytic cytokines such as TNF-alpha, IL-1, and IL-6.

Question 31

According to Perren's strain theory, absolute stability constructs (such as a properly applied lag screw and neutralization plate) promote primary bone healing. What is the maximum interfragmentary strain threshold compatible with primary bone healing?

Explanation

Primary bone healing (Haversian remodeling without visible callus) requires an absolute stability environment with less than 2% interfragmentary strain. Strains between 2% and 10% result in secondary healing with callus formation.

Question 32

Low molecular weight heparin (LMWH) is frequently utilized for deep vein thrombosis prophylaxis following major orthopedic surgery. Its primary mechanism of action involves binding to antithrombin III, which then predominantly inactivates which of the following coagulation factors?

Explanation

LMWH binds to antithrombin III and preferentially accelerates its inhibition of Factor Xa with minimal effect on thrombin (Factor IIa). This contrasts with unfractionated heparin, which equally inhibits both Factor Xa and Factor IIa.

Question 33

Biofilm formation is a critical and devastating step in the pathogenesis of periprosthetic joint infection. Which extracellular component makes up the vast majority of the biofilm's volume and protects the sessile bacteria from host defenses?

Explanation

The biofilm matrix is predominantly composed of a highly hydrated polysaccharide glycocalyx. This thick slime layer shields the embedded sessile bacteria from antibiotics, antibodies, and immune cell phagocytosis.

Question 34

A patient suffers a severe stretch injury to the brachial plexus, and a specific nerve lesion is categorized histologically as a Sunderland Grade III injury. Which of the following best describes the anatomical extent of this injury?

Explanation

A Sunderland Grade III nerve injury involves loss of continuity of both the axon and the endoneurium, while the perineurium remains intact. Spontaneous recovery is highly variable and often compromised by intrafascicular scarring.

Question 35

A 13-year-old boy with a BMI in the 99th percentile presents with hip pain and a diagnosis of a slipped capital femoral epiphysis (SCFE). The pathological mechanical failure in this condition occurs primarily through which specific histologic zone of the proximal femoral physis?

Explanation

SCFE represents a type I Salter-Harris equivalent injury that typically fails through the hypertrophic zone of the physis. This zone is mechanically the weakest because it lacks substantial collagen and has a high matrix-to-cell volume ratio.

Question 36

A 65-year-old woman presents with severe back pain and is found to have multiple osteolytic bone lesions. Biopsy reveals sheets of monoclonal plasma cells. Which of the following cell-signaling molecules is most directly responsible for the massive osteoclast activation seen in this disease process?

Explanation

Multiple myeloma cells stimulate local osteoblasts and marrow stromal cells to overexpress RANKL while downregulating OPG. RANKL binds directly to RANK on osteoclast precursors, driving extensive osteoclastogenesis and subsequent lytic bone destruction.

Question 37

A 60-year-old man with increasing hat size and bowing of his tibiae is diagnosed with Paget's disease of bone. During the active mixed phase of this metabolic disease, which of the following is the pathognomonic histological finding?

Explanation

The hallmark histologic feature of Paget's disease is a chaotic "mosaic" pattern of woven and lamellar bone, separated by irregular, heavily stained cement lines. This reflects the excessively rapid, uncoordinated turnover driven by hyperactive osteoclasts and osteoblasts.

Question 38

Denosumab is utilized effectively for treating severe osteoporosis and preventing skeletal-related events in metastatic bone disease. What is the specific molecular mechanism of action of this pharmacological agent?

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to and inhibits RANKL. By neutralizing RANKL, it prevents the activation and survival of osteoclasts, profoundly decreasing bone resorption.

Question 39

A thorough understanding of normal gait biomechanics is essential. During the normal human gait cycle, which muscle undergoes an eccentric contraction during the initial contact (heel strike) to loading response phase to safely lower the foot to the ground?

Explanation

The tibialis anterior muscle fires eccentrically immediately following heel strike to control plantarflexion and smoothly lower the forefoot to the floor. Weakness or paralysis of this muscle results in an uncontrolled "slap foot" gait.

Question 40

When preparing a diaphyseal femur fracture for intramedullary nailing, the surgeon reams the canal, allowing insertion of a larger diameter nail. If the radius of the chosen solid cylindrical nail is doubled, its bending rigidity (area moment of inertia) increases by what factor?

Explanation

The bending rigidity of a solid cylindrical intramedullary nail is proportional to its area moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, doubling the radius increases the bending rigidity by a factor of 16 (2^4).

Question 41

Fibrous dysplasia is a benign fibro-osseous bone lesion that can present as a solitary lesion or as part of a more complex syndrome. This condition is fundamentally caused by a somatic activating mutation in which of the following genes?

Explanation

Fibrous dysplasia results from a somatic activating missense mutation in the GNAS gene, which leads to constitutive activation of Gs-alpha and overproduction of intracellular cAMP. When associated with cafe-au-lait macules and precocious puberty, it is termed McCune-Albright syndrome.

Question 42

Which of the following bone graft substitutes possesses osteoconductive, osteoinductive, and osteogenic properties?

Explanation

Cancellous autograft provides scaffolding (osteoconductive), growth factors (osteoinductive), and live cells (osteogenic). DBM is primarily osteoconductive and osteoinductive but lacks live cells.

Question 43

During the toe region of a tendon's stress-strain curve, which of the following events is primarily occurring?

Explanation

The 'toe region' of the stress-strain curve corresponds to the uncrimping of collagen fibers. As the tendon is stretched further, it enters the linear elastic region where actual fiber stretching occurs.

Question 44

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants due to its biocompatibility. Compared to cobalt-chromium alloys, titanium has which of the following biomechanical properties?

Explanation

Titanium has a lower modulus of elasticity (closer to bone) compared to cobalt-chrome, which reduces stress shielding. However, it is highly notch-sensitive and has poor wear characteristics when articulating with polyethylene.

Question 45

In which zone of articular cartilage are the collagen fibers oriented parallel to the joint surface and contain the highest concentration of water?

Explanation

The superficial (tangential) zone features collagen fibers oriented parallel to the joint surface to resist shear forces. It also has the highest water concentration but the lowest proteoglycan content.

Question 46

A 4-year-old boy presents with disproportionate short stature, rhizomelic shortening of the limbs, and frontal bossing. A mutation in which of the following genes is most likely responsible for his condition?

Explanation

Achondroplasia is caused by an activating mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This leads to the inhibition of chondrocyte proliferation in the proliferative zone of the physis.

Question 47

A patient with osteopetrosis is scheduled for an elective orthopedic procedure. The pathogenesis of this disease is primarily linked to a defect in which of the following cellular mechanisms?

Explanation

Osteopetrosis is caused by impaired osteoclast function, frequently due to a defect in the formation of the ruffled border (e.g., carbonic anhydrase II deficiency). This prevents normal bone resorption and remodeling.

Question 48

In aseptic loosening of a total hip arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) wear debris primarily activates which of the following cell types to initiate the cascade of osteolysis?

Explanation

UHMWPE wear particles are phagocytosed by macrophages. These activated macrophages then release pro-inflammatory cytokines (e.g., TNF-alpha, IL-1, IL-6), leading to osteoclast activation and subsequent periprosthetic osteolysis.

Question 49

During a maximum voluntary muscle contraction, the theoretical maximum force generated by skeletal muscle is directly proportional to which of the following?

Explanation

The maximum force generated by a muscle is directly proportional to its physiologic cross-sectional area (PCSA). The excursion of a muscle relates to its overall fiber length.

Question 50

Secondary fracture healing occurs with the formation of a callus. Which of the following mechanical conditions is required for secondary fracture healing to occur rather than primary healing?

Explanation

Secondary healing relies on relative stability and appropriate micro-motion to stimulate robust callus formation. Primary healing requires absolute stability, compression, and virtually no interfragmentary strain.

Question 51

A 2-year-old child presents with bowing of the lower extremities and widening of the wrists. Laboratory testing shows normal serum calcium, significantly decreased serum phosphate, and elevated alkaline phosphatase. Which zone of the physis is most significantly expanded in this condition?

Explanation

In hypophosphatemic Rickets, there is a failure of mineralization in the zone of provisional calcification. This leads to a massive expansion and architectural disorganization of the zone of hypertrophy.

Question 52

A 15-year-old boy presents with a permeative lytic lesion in the diaphysis of the femur with a periosteal "onion-skin" reaction. Biopsy reveals uniform small round blue cells. Which chromosomal translocation is most characteristic of this tumor?

Explanation

Ewing sarcoma is classically associated with the t(11;22) translocation, resulting in the EWS-FLI1 fusion protein. The t(X;18) mutation is seen in synovial sarcoma, and t(9;22) in extraskeletal myxoid chondrosarcoma.

Question 53

Following a crush injury to the forearm, a patient suffers a nerve injury where the axon and myelin sheath are disrupted, but the endoneurium, perineurium, and epineurium remain completely intact. According to the Sunderland classification, what grade of injury is this?

Explanation

A second-degree nerve injury (axonotmesis) involves disruption of the axon and myelin sheath but preserves the endoneurium, perineurium, and epineurium. This allows for excellent potential for spontaneous regeneration.

Question 54

A patient presents with acute monoarticular knee swelling. A joint aspirate reveals 65,000 white blood cells/hpf, predominantly polymorphonuclear leukocytes, and negatively birefringent needle-shaped crystals. Which of the following crystals is present?

Explanation

Negatively birefringent, needle-shaped crystals under polarized light microscopy are characteristic of monosodium urate crystals seen in acute gout. Calcium pyrophosphate crystals are rhomboid-shaped and weakly positively birefringent.

Question 55

The pullout strength of a solid cortical bone screw is most significantly increased by maximizing which of the following geometric parameters?

Explanation

Screw pullout strength is directly proportional to the outer thread diameter and the length of thread engagement. It is inversely proportional to the thread pitch length.

Question 56

Bisphosphonates are frequently used in the management of osteoporosis and metastatic bone disease. What is the primary cellular mechanism of action for nitrogen-containing bisphosphonates such as alendronate?

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts osteoclast cytoskeletal function, preventing ruffled border formation and promoting osteoclast apoptosis.

Question 57

Rivaroxaban is commonly prescribed for deep vein thrombosis prophylaxis following total joint arthroplasty. Which step in the coagulation cascade is directly inhibited by this medication?

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that specifically inhibit Factor Xa. Dabigatran directly inhibits thrombin (Factor IIa), while warfarin inhibits Vitamin K epoxide reductase.

Question 58

A 14-year-old girl is diagnosed with conventional osteosarcoma of the distal femur. A mutation in which of the following tumor suppressor genes is most commonly implicated in the pathogenesis of this disease?

Explanation

Mutations in the TP53 (p53) tumor suppressor gene (as seen in Li-Fraumeni syndrome) and the RB1 (retinoblastoma) gene are the most frequently implicated genetic abnormalities in the development of osteosarcoma.

Question 59

In the pathogenesis of periprosthetic joint infection, bacteria commonly form a biofilm on the implant surface. Which phase of biofilm development involves the irreversible attachment of bacteria and synthesis of an extracellular polymeric substance (EPS) matrix?

Explanation

The maturation phase of biofilm formation is characterized by irreversible bacterial adhesion and robust production of the extracellular polymeric substance (EPS) matrix. This creates a highly antibiotic-resistant environment.

Question 60

In adult articular cartilage, what is the primary physiological mechanism by which deep chondrocytes receive oxygen and essential nutrients?

Explanation

Adult articular cartilage is entirely avascular, aneural, and alymphatic. Chondrocytes rely almost exclusively on diffusion from the synovial fluid, a process driven by the "pumping" mechanism of cyclic loading and unloading.

Question 61

In a growing child, a slipped capital femoral epiphysis (SCFE) occurs predominantly through a mechanical failure in which distinct cellular zone of the growth plate?

Explanation

The zone of hypertrophy is mechanically the weakest layer of the physis due to its high volume of large cells and lack of dense matrix calcification. Physeal fractures and conditions like SCFE typically shear through this zone.

Question 62

Viscoelastic materials such as ligaments and tendons exhibit which of the following properties when subjected to a constant physiological load over an extended period of time?

Explanation

Creep is the progressive deformation of a viscoelastic material when subjected to a constant load over time. Stress relaxation refers to a decrease in stress when the material is held at a constant deformation.

Question 63

A 30-year-old man presents with a slowly enlarging, deep soft-tissue mass near his knee. A core needle biopsy reveals a biphasic tumor consisting of epithelial and spindle cell components. Which of the following chromosomal translocations is highly specific for this diagnosis?

Explanation

The clinical presentation and biphasic histology indicate a synovial sarcoma. This tumor is characterized by the t(X;18) translocation, which results in the SYT-SSX fusion gene.

Question 64

In normal mature articular cartilage, which structural zone has the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers oriented parallel to the joint surface?

Explanation

The superficial zone of articular cartilage is designed to resist shear forces. It contains densely packed Type II collagen oriented parallel to the joint surface, with the highest water content and lowest proteoglycan content.

Question 65

Which of the following bone morphogenetic proteins (BMPs) is an FDA-approved osteoinductive agent for use as an adjunct in acute, open tibial shaft fractures treated with intramedullary nailing?

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for acute open tibial shaft fractures treated with an intramedullary nail. BMP-7 (OP-1) was previously approved under a humanitarian device exemption for recalcitrant long bone nonunions.

Question 66

A 24-year-old man complains of a dull ache in his lower back that is minimally relieved by NSAIDs. Radiographs show a 2.5-cm radiolucent lesion with surrounding sclerosis in the posterior elements of L4. Histology reveals disorganized osteoid surrounded by osteoblasts without malignant features. What is the most likely diagnosis?

Explanation

Osteoblastomas are histologically identical to osteoid osteomas but are distinguished by being larger than 2 cm. They also tend to be less responsive to NSAIDs and have a predilection for the posterior elements of the spine.

Question 67

Which of the following fracture fixation methods most heavily relies on primary bone healing (intramembranous ossification) without an intermediate cartilaginous phase?

Explanation

Primary bone healing occurs only under conditions of absolute stability, such as lag screw fixation with a neutralization plate. This process bypasses callus formation and relies on cutting cones to directly cross the fracture gap.

Question 68

A 45-year-old patient with chronic kidney disease presents with diffuse bone pain and proximal muscle weakness. Laboratory studies show low serum calcium, high parathyroid hormone (PTH), and elevated alkaline phosphatase. Histologic evaluation of this patient's bone would most likely show:

Explanation

The clinical scenario describes osteomalacia secondary to renal osteodystrophy. Osteomalacia is characterized histologically by defective mineralization, leading to thickened and increased unmineralized osteoid seams.

Question 69

A 35-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femur extending to the subchondral bone. Biopsy shows multinucleated giant cells and mononuclear stromal cells. The neoplastic cells in this tumor strongly express:

Explanation

In a Giant Cell Tumor of bone, the spindle-shaped mononuclear stromal cells are the true neoplastic cells and they express RANKL. The giant cells are reactive, non-neoplastic osteoclasts that express the RANK receptor.

Question 70

In a randomized controlled trial comparing two surgical techniques, the authors find no statistically significant difference in clinical outcomes. However, they conclude that a difference truly exists but their study failed to detect it. This scenario represents:

Explanation

A Type II error (beta error) occurs when a study fails to reject a false null hypothesis, meaning it misses a true difference. This is usually due to inadequate sample size and low statistical power.

Question 71

Parathyroid hormone (PTH) plays a crucial role in calcium homeostasis. Which of the following describes its direct physiologic action on the kidneys?

Explanation

In the kidney, PTH stimulates 1-alpha-hydroxylase, which converts 25-hydroxyvitamin D into the active 1,25-dihydroxyvitamin D (calcitriol). It also increases calcium reabsorption in the distal tubule and decreases phosphate reabsorption.

Question 72

A 9-year-old boy presents with a painful diaphyseal femur lesion showing an "onion skin" periosteal reaction. Biopsy reveals sheets of uniform small round blue cells. Immunohistochemical staining is typically positive for which of the following markers?

Explanation

The presentation is classic for Ewing sarcoma, which is driven by the t(11;22) translocation. These tumors are characteristically highly positive for the CD99 cell surface glycoprotein.

Question 73

Which of the following biomaterial combinations poses the highest risk for galvanic corrosion when used together in orthopedic internal fixation?

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic environment (like the human body). Mixing stainless steel and titanium implants is contraindicated due to the high risk of severe galvanic corrosion.

Question 74

During the pathogenesis of periprosthetic joint infection, Staphylococcus aureus produces a robust biofilm. What is the primary structural component of the extracellular polymeric substance in this biofilm?

Explanation

The biofilm matrix of S. aureus is primarily composed of polysaccharide intercellular adhesin (PIA), which is synthesized by products of the icaADBC operon. This matrix protects the bacteria from antibiotics and host immune cells.

Question 75

During skeletal muscle contraction, calcium ions released from the sarcoplasmic reticulum initiate cross-bridge cycling by binding directly to which of the following proteins?

Explanation

Calcium binds to Troponin C, which causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin. This allows myosin heads to attach and initiate contraction.

Question 76

A 65-year-old man presents with progressive hearing loss and an increasing hat size. Radiographs show mixed lytic and sclerotic changes in his skull and pelvis. Which of the following is the primary cellular abnormality initiating this condition?

Explanation

Paget disease of bone begins with an intensely destructive osteolytic phase driven by highly abnormal, multinucleated osteoclasts. This is followed by a disorganized blastic phase leading to structurally weak woven bone.

Question 77

Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is widely used in total joint arthroplasty to reduce wear rates. However, the cross-linking process results in which of the following mechanical trade-offs?

Explanation

While high cross-linking significantly decreases adhesive and abrasive wear, it concurrently reduces the material's fatigue strength, tensile strength, and fracture toughness. This can increase the risk of implant fracture, especially in thin components.

Question 78

According to the Sunderland classification of nerve injury, a fourth-degree injury involves disruption of all neural and supporting elements EXCEPT the:

Explanation

In a fourth-degree Sunderland nerve injury, the axon, endoneurium, and perineurium are disrupted, but the epineurium remains intact. Spontaneous recovery is extremely poor, and surgical intervention is usually required.

Question 79

A 55-year-old man presents with worsening shoulder pain. Radiographs reveal a large destructive lesion in the proximal humerus with intralesional "popcorn" calcifications and endosteal scalloping greater than two-thirds of the cortical thickness. The most appropriate initial definitive treatment is:

Explanation

The clinical and radiographic findings are highly characteristic of an intermediate- to high-grade chondrosarcoma. Because these tumors are generally resistant to chemotherapy and radiation, the mainstay of treatment is wide surgical resection.

Question 80

Which of the following enzymes is primarily responsible for the degradation of type II collagen in the pathogenesis of osteoarthritis?

Explanation

MMP-13 (collagenase-3) is the primary enzyme responsible for the cleavage and degradation of Type II collagen in articular cartilage during osteoarthritis. ADAMTS enzymes are primarily aggrecanases.

Question 81

A 65-year-old woman presents with diffuse skeletal pain and a pathological fracture of the proximal femur. Laboratories reveal anemia, hypercalcemia, and an elevated M-spike on serum protein electrophoresis. Which of the following radiographic findings is most characteristic of her condition?

Explanation

Multiple myeloma is a plasma cell dyscrasia characterized radiographically by sharply demarcated, "punched-out" lytic lesions with no surrounding reactive bone sclerosis. This is due to profound osteoclast activation and osteoblast inhibition.

Question 82

A 62-year-old man presents with chronic lower back pain and bowel incontinence. Radiographs demonstrate a destructive lesion involving the sacrum. Biopsy reveals physaliferous cells in a myxoid background. Which of the following immunohistochemical markers is most specific for confirming this diagnosis?

Explanation

Chordomas are locally aggressive malignant tumors arising from notochordal remnants. They uniquely stain positive for Brachyury, a transcription factor, which distinguishes them from chondrosarcomas.

Question 83

A 32-year-old woman undergoes biopsy of a lytic epiphyseal lesion in the proximal tibia. Pathology demonstrates multinucleated giant cells interspersed among mononuclear stromal cells. If systemic therapy is considered, which of the following is the primary cellular target of the most commonly used pharmacologic agent?

Explanation

Denosumab, a monoclonal antibody used for giant cell tumors, binds to RANKL. RANKL is produced by the neoplastic mononuclear stromal cells and recruits/activates the non-neoplastic osteoclast-like giant cells.

Question 84

A 12-year-old girl presents with a pathologic fracture of her proximal femur. Radiographs reveal a "ground-glass" appearance of the lesion with coxa vara deformity. A biopsy confirms fibrous dysplasia. Which of the following best describes the underlying pathophysiology of this condition?

Explanation

Fibrous dysplasia results from an activating somatic mutation in the GNAS gene, which encodes the alpha subunit of the Gs stimulatory protein. This leads to increased intracellular cAMP and abnormal osteoblast differentiation.

Question 85

A 15-year-old boy develops a highly malignant bone forming tumor in the distal femur. His medical history is significant for bilateral retinoblastoma treated during infancy. Loss of heterozygosity or mutation in which of the following genes most directly predisposes him to this skeletal malignancy?

Explanation

Patients with hereditary retinoblastoma have a germline mutation in the RB1 tumor suppressor gene. This significantly increases their lifetime risk of developing secondary primary malignancies, most notably osteosarcoma.

Question 86

A 28-year-old man presents with a slow-growing, painful mass near his knee joint. MRI shows a soft-tissue mass adjacent to but not within the joint space. Core needle biopsy reveals a biphasic tumor with both epithelial and spindle cell components. Which of the following chromosomal translocations is characteristic of this lesion?

Explanation

Synovial sarcoma is characterized by the t(X;18)(p11;q11) translocation, which fuses the SYT gene on chromosome 18 with SSX1, SSX2, or SSX4 on the X chromosome. This genetic fusion is diagnostic.

Question 87

A 68-year-old woman presents with severe back pain and fatigue. Laboratory investigations reveal hypercalcemia, normocytic anemia, and an elevated serum creatinine. Radiographs of the skull demonstrate multiple "punched-out" radiolucent lesions without sclerotic borders. Which of the following tests is most appropriate to confirm the underlying diagnosis?

Explanation

The clinical presentation of hypercalcemia, renal failure, anemia, and punched-out lytic bone lesions is classic for Multiple Myeloma (CRAB criteria). Serum and urine protein electrophoresis (SPEP/UPEP) with immunofixation are essential to detect the characteristic monoclonal protein spike.

Question 88

A 10-year-old girl presents with a rapidly expanding, painful lesion of the proximal humerus. Radiographs show an eccentrically located, expansile, lytic lesion. Biopsy reveals blood-filled spaces lacking an endothelial lining and interspersed with multinucleated giant cells. Which of the following genetic abnormalities is considered the primary driver of this lesion?

Explanation

Primary Aneurysmal Bone Cysts (ABCs) are now recognized as true neoplasms driven by translocations involving the USP6 gene on chromosome 17p13. This distinguishes primary ABCs from secondary ABCs which occur within other tumors.

Question 89

A 15-year-old boy presents with right knee pain. Imaging reveals a destructive, mixed lytic and sclerotic lesion in the distal femoral metaphysis with a periosteal sunburst reaction. Biopsy confirms high-grade intramedullary osteosarcoma. Which of the following genetic syndromes is most strongly associated with an increased risk of developing this specific malignancy?

Explanation

Li-Fraumeni syndrome is an autosomal dominant disorder caused by a germline mutation in the TP53 tumor suppressor gene and is strongly associated with osteosarcoma. Other known associations for osteosarcoma include familial retinoblastoma (RB1 mutation) and Rothmund-Thomson syndrome.

Question 90

During the endochondral ossification process of fracture healing, mesenchymal stem cells must differentiate into chondrocytes to form the soft callus. Which of the following transcription factors is the essential master regulator for this specific chondrocytic differentiation?

Explanation

SOX9 is the primary transcription factor required for the differentiation of mesenchymal stem cells into chondrocytes. In contrast, Runx2 and Osterix are the key transcription factors necessary for osteoblastic differentiation.

Question 91

A 65-year-old man undergoes a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following represents the primary biomechanical advantage of highly cross-linked polyethylene compared to conventional ultra-high molecular weight polyethylene (UHMWPE)?

Explanation

Highly cross-linked polyethylene significantly reduces adhesive and abrasive wear rates compared to conventional UHMWPE, decreasing the risk of osteolysis. However, the cross-linking process sacrifices mechanical properties, leading to decreased fatigue strength, ductility, and ultimate tensile strength.

Question 92

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the proximal tibial epiphysis extending to the subchondral bone.

Histology shows multinucleated giant cells in a stroma of mononuclear cells. The neoplastic cells in this lesion primarily express which of the following?

Explanation

In a Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear stromal cells, which heavily express RANKL. This overexpression stimulates the recruitment and fusion of normal host osteoclast precursors into the characteristic reactive multinucleated giant cells.

Question 93

A 28-year-old athlete undergoes surgical repair of an Achilles tendon rupture. During the remodeling phase of tendon healing, the biomechanical strength of the tendon significantly increases. This is primarily driven by the replacement of which collagen type with another?

Explanation

During the initial proliferative phase of tendon healing, fibroblasts lay down a disorganized, provisional matrix rich in Type III collagen. In the subsequent remodeling phase, this is gradually replaced by stronger, highly organized Type I collagen, thereby increasing the tendon's tensile strength.

Question 94

Articular cartilage relies on a unique extracellular matrix to withstand physiological joint loads. Which of the following molecular components is primarily responsible for providing the compressive stiffness of articular cartilage?

Explanation

Aggrecan is a large proteoglycan that provides compressive stiffness to articular cartilage via its negatively charged glycosaminoglycan side chains, which attract water and create significant swelling pressure. Type II collagen, in contrast, primarily provides tensile strength and restrains the swelling pressure.

Question 95

A 45-year-old man develops a chronic prosthetic joint infection one year after a total knee arthroplasty. Intraoperative cultures yield Staphylococcus epidermidis. The organism's ability to persistently colonize the implant surface and evade the host immune system is primarily mediated by the production of which of the following?

Explanation

Staphylococcus epidermidis forms a robust polysaccharide glycocalyx, or biofilm, that facilitates adherence to inert implant surfaces. This biofilm acts as a physical barrier, protecting the bacteria from both host cellular immunity and systemic antimicrobial therapy.

Question 96

A 70-year-old man presents with progressive hearing loss and an increasing hat size. Radiographs show profound cortical thickening and coarsened trabeculae of the skull.

The primary cellular defect initiating this condition involves which of the following?

Explanation

Paget's disease is initiated by an overactive, abnormal osteoclastic phase featuring large, hypermultinucleated osteoclasts. This intense resorption is followed by a disorganized compensatory osteoblastic response, resulting in weak, architecturally abnormal woven bone.

Question 97

A 65-year-old woman is prescribed alendronate for the management of severe osteoporosis. At the cellular and molecular level, nitrogen-containing bisphosphonates inhibit osteoclast function primarily by disrupting which of the following metabolic pathways?

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate) inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of essential small GTP-binding proteins (like Ras and Rho), leading to osteoclast apoptosis and decreased bone resorption.

Question 98

A 19-year-old man complains of localized right tibial pain that is worse at night and dramatically relieved by NSAIDs.

Imaging reveals a small radiolucent nidus surrounded by dense reactive sclerosis. The dramatic pain relief provided by NSAIDs in this condition is due to the local inhibition of which of the following?

Explanation

Osteoid osteomas uniquely secrete high levels of Prostaglandin E2 (PGE2) due to increased cyclooxygenase (COX) expression within the nidus. NSAIDs inhibit COX, effectively reducing PGE2 levels and providing the characteristic dramatic pain relief.

Question 99

A biomechanical engineer is attempting to redesign a cortical bone screw to maximize its pull-out strength in osteoporotic bone. Which of the following specific design modifications will most effectively increase the screw's pull-out strength?

Explanation

Pull-out strength is directly proportional to the volume of bone caught between the screw threads. It is maximized by increasing the outer thread diameter, decreasing the inner root diameter, and decreasing the thread pitch (resulting in more threads per unit length).

Question 100

A 2-year-old boy presents with progressive lower extremity bowing and widened wrists. Laboratory tests show normal serum calcium, significantly low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. This specific genetic defect leads to excessive production of which of the following?

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation, which leads to pathologically elevated levels of FGF23. Excess FGF23 causes severe renal phosphate wasting and decreases 1,25-dihydroxyvitamin D production, ultimately resulting in defective bone mineralization.

Orthopedic Board Review Mock Exam #603: 100 High-Yield MCQs

Orthopedic Basic 2026 MCQs: Board Review Questions & Answers (Part 1)

Key Takeaway

Orthopedic Basic 2026 MCQs: Board Review Questions & Answers (Part 1)

Chapter Index