Orthopedic Basic MCQs 2026 | Board Review & Answers

Question 1

An otherwise healthy 75-year-old man has a painful mass in the popliteal fossa of his right knee. A lateral radiograph of the knee, a CT scan of the distal femur, and a histopathologic specimen are shown in Figures 13a through 13c. Management should consist of

Explanation

13b 13c The patient has a parosteal osteosarcoma of the distal femur. The findings of mild knee pain, radiographic evidence of a radiodense mass involving the parosseous space or surface of the distal femur, and histologic findings of a spindle cell lesion forming immature osteoid with little to no necrosis most likely suggest a parosteal osteosarcoma. The treatment of choice is surgical resection. Okada K, Frassica FJ, Sim FH, Beabout JW, Bond JR, Unni KK: Parosteal osteosarcoma: A clinicopathological study. J Bone Joint Surg Am 1994;76:366-378.

Question 2

What type of metastatic tumor most often has a lytic radiographic appearance?

Explanation

Lung carcinoma most often has a lytic radiographic appearance. Bladder and prostate carcinoma are usually blastic. Breast carcinoma can be both blastic and lytic. Thyroid carcinoma may be difficult to visualize radiographically and may be seen only on MRI scans. Metastatic osteosarcomas typically produce bone. Frassica FJ, Frassica DA, McCarthy EF, Riley LH III: Metastatic bone disease: Evaluation, clinicopathologic features, biopsy, fracture risk, nonsurgical treatment, and supportive management. Instr Course Lect 2000;49:453-459.

Question 3

A 6-year-old boy has leg pain. A radiograph, MRI, CT, and bone scans, and a biopsy specimen are shown in Figures 14a through 14e. What is the most likely diagnosis?

Explanation

14b 14c 14d 14e From an imaging point of view, all of the diagnoses are possible. Biopsy results and cultures are necessary to make the diagnosis. The biopsy specimen shows inflammatory cells and necrotic bone, consistent with osteomyelitis. Fletcher BD, Hanna SL: Pediatric musculoskeletal lesions simulating neoplasms. Magn Reson Imaging Clin N Am 1996;4:721-747.

Question 4

A 13-year-old girl has had right groin pain for the past 3 weeks. She denies any history of trauma. Examination of the hip reveals no palpable soft-tissue mass or lymphadenopathy, and there is full range of motion. A plain radiograph and MRI scan are shown in Figures 15a and 15b. Biopsy specimens are shown in Figures 15c and 15d. What is the most likely diagnosis?

Explanation

15b 15c 15d Fibrous dysplasia frequently occurs in the proximal femur. Microfractures and remodeling can lead to the classic "Shepherd's crook deformity." The lesion has a ground-glass appearance on plain radiographs. The histologic appearance shows proliferating fibroblasts in a loose spindle cell background. Dysplastic metaplastic trabeculae are arranged in an irregular or "Chinese letter" appearance. Enneking WF, Gearen PF: Fibrous dysplasia of the femoral neck: Treatment by cortical bone grafting. J Bone Joint Surg Am 1986;68:1415-1422.

Question 5

What process is often found associated with other neoplasms?

Explanation

Aneurysmal bone cyst may be either a "pattern" or a "diagnosis." Therefore, aneurysmal bone cyst should be viewed as a diagnosis of exclusion. Hemorrhage into a variety of primary bone lesions (eg, giant cell tumor of bone, chondroblastoma, osteoblastoma, fibrous dysplasia, osteosarcoma, or vascular neoplasms) may result in intralesional, membrane-bone blood-filled cysts. Such secondary changes may be confused with aneurysmal bone cyst, resulting in inappropriate therapy because assessment should be focused on identifying the underlying primary process. The entire specimen should be examined histologically in an effort to locate an underlying primary bone tumor. Bonakdarpour A, Levy WM, Aegerter E: Primary and secondary aneurysmal bone cyst: A radiological study of 75 cases. Radiology 1978;126:75-83. Levy WM, Miller AS, Bonakdarpour A, Aegerter E: Aneurysmal bone cyst secondary to other osseous lesions: Report of 57 cases. Am J Clin Pathol 1975;63:1-8.

Question 6

A 14-year-old girl reports hip pain that is exacerbated by weight bearing. A radiograph and biopsy specimen are shown in Figures 16a and 16b. The best course of management should be

Explanation

16b The patient has a unicameral bone cyst. Because the subtrochanteric part of the femur is a high-stress region, the treatment of choice is bone curettage and grafting. Azouz EM, Karamitsos C, Reed MH, Baker L, Kozlowski K, Hoeffel JC: Types and complications of femoral neck fractures in children. Pediatr Radiol 1993;23:415-420.

Question 7

A 37-year-old man has left shoulder pain and weakness. Coronal T1- and axial T2-weighted MRI scans are shown in Figures 17a and 17b. The biopsy specimen is shown in Figure 17c. What is the most likely diagnosis?

Explanation

17b 17c A ganglion cyst arising from the posterior labrum of the shoulder is a known cause of suprascapular nerve impingement. The MRI characteristics of low-signal intensity on T1 and high-signal intensity on T2 are seen in lesions with a high fluid content. The histology shows a cavity with a thin fibrous lining. Ferrick MR, Marzo JM: Suprascapular entrapment neuropathy and ganglion cysts about the shoulder. Orthopedics 1999;22:430-434.

Question 8

Of the following factors, which is considered the most important prognostic indicator in soft-tissue sarcomas?

Explanation

Histologic grade, the presence or absence of metastatic disease, and tumor size are important prognostic factors. Of the available choices, however, the size of the sarcoma is the most important prognostic indicator. A tumor size of greater than 5 cm is a more important prognostic factor than tumor location. Patients with sarcomas that measure 5 cm or less have nearly identical 3-year survival rates regardless of whether the tumor is subcutaneous or deep. Histologic grade (high versus low) is an important factor. However, histologic subtype frequently is not as important a factor as tumor size.

Question 9

Radiographs of a 15-year-old girl with knee pain reveal a radiopaque lesion of the distal femoral metaphysis and epiphysis with a small associated soft-tissue mass. A biopsy specimen shows osteoid and pleomorphic cells with multiple mitotic figures. Staging studies show no other sites of disease. Treatment should consist of

Explanation

Based on the location and extent of the tumor, most patients are candidates for limb salvage surgery. The patient has an osteosarcoma; therefore, the treatment of choice is preoperative chemotherapy, wide resection, and reconstruction. There is no difference in survival rates between patients who undergo limb salvage surgery and those who undergo amputation. Curettage and placement of methylmethacrylate is used to treat benign lesions of bone and would not be appropriate in this patient.

Question 10

What form of fixation is associated with the highest incidence of osseous union when using segmental allograft reconstruction following tumor resection?

Explanation

Plate and screw fixation of allograft is associated with the highest incidence of union but also the highest prevalence of allograft fracture. Conversely, intramedullary fixation is associated with a higher incidence of nonunion but fewer fractures. Step-cut osteotomies are not associated with a higher incidence of union.

Question 11

A 51-year-old woman has had progressively increasing right knee pain for the past 6 months. She has a history of metastatic renal cell carcinoma to the lung and the skeletal system. Radiographs are seen in Figures 18a and 18b. The next step in management of the right distal femur lesion should consist of

Explanation

18b In a patient with known metastatic disease, the surgeon must rule out additional lesions throughout the femur prior to surgical management. Lesions located in the diaphysis or in the peritrochanteric region may influence the surgical procedure. Frassica FJ, Gitelis S, Sim FH: Metastatic bone disease: General principles, pathophysiology, evaluation, and biopsy. Instr Course Lect 1992;41:293-300.

Question 12

Following resection of malignant tumors, complications related to endoprosthetic reconstruction are most common in what anatomic location?

Explanation

It is generally accepted that reconstructions of the proximal tibia are associated with the highest incidence of failure, probably because of poor soft-tissue coverage, the need for extensor mechanism reconstruction, and other anatomic issues. It also may be related to the fact that patients with tumors of the proximal tibia, in general, have a better prognosis and better survival rates than patients with tumors located elsewhere in the body. Reconstructions of the proximal humerus may be more durable because they are not involved in weight-bearing activities.

Question 13

Figures 19a and 19b show the AP and lateral radiographs of an 18-year-old man who has had knee pain for 3 months. Figure 19c shows a histopathologic photomicrograph of the biopsy specimen. Which of the following factors is most likely to affect his survival?

Explanation

19b 19c The presence of metastatic disease at diagnosis is the most significant prognostic factor in a patient with osteosarcoma. Limb-sparing surgery, when compared with amputation, is not noted to be associated with any difference in the rate of survival. The presence of a mutated p53 gene has been noted in a minority of patients with osteosarcoma; however, the prognostic importance on an individual basis is unclear. Tumor location and a relative poor response to chemotherapy would be secondary to the presence of metastatic disease in estimating a patient's prognosis. Weis L: Common malignant bone tumors: Osteosarcoma, in Simon MA, Springfield DS (eds): Surgery for Bone and Soft Tissue Tumors. Philadelphia, PA, Lippincott-Raven, 1998, pp 265-274.

Question 14

What anatomic site is considered at highest risk for pathologic fracture?

Explanation

The subtrochanteric femur has been identified as an anatomic site that is particularly prone to pathologic fracture. An avulsion fracture of the lesser trochanter is a sign of impending femoral fracture. While the other anatomic locations are also frequently involved in metastatic bone disease, pathologic fractures occur less commonly. Simon MA, Springfield DS, et al: Surgery for Bone and Soft Tissue Tumors. Philadelphia, PA, Lippincott Raven, 1998, p 683.

Question 15

What clinical finding is associated with the least favorable prognosis in an adolescent patient who has been diagnosed with a high-grade osteosarcoma of the distal femur?

Explanation

The presence of synchronous bone disease in young patients carries a dismal prognosis, one that is even worse than the presence of resectable pulmonary metastasis. Many osteosarcomas cross the physis; therefore, this has not been shown to be of prognostic importance. Similarly, the presence of the soft-tissue mass has less prognostic significance.

Question 16

A 65-year-old man has a painful mass of the middle finger. A clinical photograph, lateral radiograph, coronal MRI scan, and biopsy specimen are seen in Figures 20a through 20d. What is the most likely diagnosis?

Explanation

20b 20c 20d Although the degeneration of an isolated benign cartilaginous lesion into a chondrosarcoma is rare, it occurs in roughly 10% of patients with Ollier's disease. Pain is the most common symptom of chondrosarcoma. The treatment of low-grade chondrosarcoma ranges from intralesional excision to wide amputation. The intent of the surgery is to remove all the disease to decrease the chance of local recurrence. Lee FY, Mankin HJ, Fondren G, et al: Chondrosarcoma of bone: An assessment of outcome. J Bone Joint Surg Am 1999;81:326-338.

Question 17

Figures 21a and 21b show the radiograph and CT scan of a 14-year-old patient with thigh pain. The next most appropriate step in management should consist of

Explanation

21b The radiographs show increased density and reactive bone formation. A faint nidus can be seen on the radiograph but is obvious on the CT scan. The initial therapy for an osteoid osteoma should be oral anti-inflammatory drugs. A biopsy or SPECT bone scan is not indicated because the osteoid osteoma is clearly seen on the CT scan. If the patient fails to respond to nonsurgical therapy, CT-guided radiofrequency ablation or surgical excision is indicated depending on the anatomic location. Frassica FJ, Waltrip RL, Sponseller PD, Ma LD, McCarthy EF Jr: Clinicopathologic features and treatment of osteoid osteoma and osteoblastoma in children and adolescents. Orthop Clin North Am 1996;27:559-574. Kneisl JS, Simon MA: Medical management compared with operative treatment for osteoid osteoma. J Bone Joint Surg Am 1992;74:179-185.

Question 18

A 14-year-old boy has a midshaft fibular lesion. Biopsy results are consistent with Ewing's sarcoma. Following induction chemotherapy, local control typically consists of

Explanation

Current treatment regimens for Ewing's sarcoma typically involve induction chemotherapy followed by local control and further chemotherapy. Local control consists of surgery alone, radiation therapy alone, or a combination of the two. In bones that are easily resectable (or expendable) with wide margins, surgery alone is usually recommended. For areas that are unresectable (ie, large, bulky pelvic tumors), radiation therapy alone is sometimes the preferred method of local control. If surgery is chosen and margins are close, radiation therapy can be used as an adjuvant. Amputation rarely is required for an isolated fibular lesion. Observation without adequate local therapy results in local recurrence. Nesbit ME Jr, Gehan EA, Burgert EO Jr, et al: Multimodal therapy for the management of primary, nonmetastatic Ewing's sarcoma of bone: A long-term follow-up of the First Intergroup study. J Clin Oncol 1990;8:1664-1674.

Question 19

An otherwise healthy 65-year-old man reports thigh pain of insidious onset. He states that the pain is increased with weight bearing and also occurs at night. He denies any history of cancer. Radiographs are shown in Figures 22a and 22b. A bone scan shows an isolated lesion. CT scans of the chest and abdominal are negative for any other lesions. Initial management should consist of

Explanation

22b The patient has a solitary lesion that is at high risk for fracture. While metastatic lesions are most common in this age group, a stabilization procedure is contraindicated until results of a biopsy confirm the presence of a metastasis. Because of the lytic lesion and the associated calcification shown on the radiograph, the most likely diagnosis is a chondrosarcoma. Therefore, any type of stabilization procedure with a rod or plate would compromise a wide surgical excision to remove the entire proximal femur. Radiation therapy and chemotherapy are also contraindicated until biopsy results are obtained. Because of these factors, obtaining a frozen section biopsy specimen is considered the next most appropriate step in management. If a metastatic lesion is confirmed on the frozen section, a stabilization procedure could then be performed under the same anesthetic. Therefore, it is important to have a pathologist available at the time of a biopsy. Frassica FJ, Frassica DA, McCarthy EF, Riley LH III: Metastatic bone disease: Evaluation, clinicopathologic features, biopsy, fracture risk, nonsurgical treatment, and supportive management. Instr Course Lect 2000;49:453-459.

Question 20

What is the most appropriate next step in the work-up of a patient with the asymptomatic lesion shown in Figure 23?

Explanation

The eccentric metaphyseal location, skeletal maturity, narrow zone of transition, and lack of symptoms suggest a benign process and are consistent with a healed nonossifying fibroma. These lesions typically fill in (ossify) with skeletal maturity, eventually remodeling and disappearing. Radiographic monitoring is indicated. Biopsy is not recommended unless the lesion changes radiographically. Marks KE, Bauer TW: Fibrous tumors of bone. Orthop Clin North Am 1989;20:377-393. Bullough PG, Walley J: Fibrous cortical defect and non-ossifying fibroma. Postgrad Med J 1965;41:672-676.

Question 21

A 63-year-woman has an elbow flexion contracture. History reveals that she underwent three previous surgeries to remove a malignant fibrous histiocytoma of the forearm. An MRI scan reveals a locally recurrent tumor at the site of the previous surgery. Which of the following is considered the most predictive factor for local recurrence?

Explanation

The greatest risk factor for local recurrence is an inadequate surgical margin. The tumor grade, histologic subtype, and size are predictive of systemic relapse. Sarcomas that arise in some anatomic sites, such as the forearm or retroperitoneum, may be more difficult to completely resect compared with other sites. The optimum margin is generally considered to be a cuff of normal tissue beyond the tumor. Bell RS, O'Sullivan B, Liu FF, et al: The surgical margin in soft-tissue sarcoma. J Bone Joint Surg Am 1989;71:370-375. Sadoski C, Suit HD, Rosenberg A, Mankin H, Efird J: Preoperative radiation, surgical margins, and local control of extremity sarcomas of soft tissues. J Surg Oncol 1993;52:223-230.

Question 22

A 19-year-old woman has a painful right knee. A radiograph, MRI scan, CT scan, and histopathologic specimen are shown in Figures 24a through 24d. What is the most likely oncologic stage of the lesion?

Explanation

24b 24c 24d The patient has a high-grade osteosarcoma of the distal femur with a skip lesion, and pulmonary metastasis is seen on the CT scan. This corresponds to a stage III lesion according to the Musculoskeletal Tumor Society System as adopted from Enneking.

Question 23

Calcitonin acts as an antiresorptive agent by

Explanation

Calcitonin is a hormone that binds to osteoclasts and acts to decrease both osteoclast activity and number. Calcitonin is most effective in reducing vertebral compression fractures in high-turnover osteoporosis. It is also effective in treating regional osteoporosis. Because of its analgesic effect, it is helpful in treating painful acute compression fractures associated with osteoporosis.

Question 24

An 8-year-old girl has had a painless enlarging mass of insidious onset in the left thigh for the past 3 weeks. Her mother denies any history of trauma, fever, or disease. Examination reveals a nontender, mobile mass in the left medial thigh. Her gait is normal. Figures 25a through 25d show the frog-lateral radiograph, the axial and coronal T1-weighted MRI scans, and the axial T2-weighted MRI scan. Biopsy results reveal a nonrhabdomyosarcoma soft-tissue sarcoma. The most appropriate treatment should consist of

Explanation

25b 25c 25d In childhood, the more common soft-tissue sarcomas are rhabdomyosarcoma, synovial sarcoma, and fibrosarcoma. Rhabdomyosarcoma, treated with radiation therapy and chemotherapy, is a round cell tumor and is inconsistent with this patient's histologic findings. Synovial sarcoma can be monophasic or biphasic with both spindle and epithelial-like cells and is associated with the characteristic reciprocal chromosomal translocation of t(x:18)(p11;q11) which is not found in fibrosarcoma. Synovial sarcoma also can be associated with cystic loculated areas best seen in a T2-weighted MRI scan. Nonrhabdomyosarcoma childhood soft-tissue sarcomas are treated with surgical excision in conjunction with chemotherapy and/or radiation therapy. The histology reveals no inflammatory cells to suggest an abscess; therefore, antibiotics and drainage are unnecessary. The MRI scans clearly show a mass of soft tissue and no bone involvement; therefore, proximal femoral resection is not appropriate. Serial observation is not appropriate because of the history of enlargement and insidious onset. Enzinger FM, Weiss SW: Soft Tissue Tumors, ed 3. St Louis, MO, Mosby Year Book, 1995, p 757.

Question 25

Histologically, synovial chondromatosis is characterized by

Explanation

Histologically, there is metaplastic cartilage arising from the synovium. These lobules of zonates hyaline cartilage are of variable size, are embedded within edematous synovium, and protrude into the joint. The lobules calcify and ossify, leading to the characteristic radiographic appearance. Inflammatory synovitis is not characteristic of synovial chondromatosis. The fluid is clear and serosanguin, not blood tinged. Milgram JM: Synovial osteochondromatosis: A histopathological study of thirty cases. J Bone Joint Surg Am 1977;l59:792-801.

Question 26

A 32-year-old woman presents with a lytic lesion in the distal femur. Biopsy confirms a giant cell tumor of bone. She is treated with denosumab to downstage the tumor prior to surgery. What is the mechanism of action of this medication?

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL. This prevents RANKL from interacting with the RANK receptor on osteoclasts, thereby inhibiting osteoclast formation, function, and survival.

Question 27

A 14-year-old boy is diagnosed with high-grade conventional osteosarcoma of the proximal tibia. Following neoadjuvant chemotherapy, what percentage of tumor necrosis on the resection specimen is considered the threshold for a good histologic response?

Explanation

According to the Huvos grading system, a good histologic response to neoadjuvant chemotherapy in osteosarcoma is defined as 90% or greater tumor necrosis (Grade III or IV response). This correlates with significantly improved disease-free survival.

Question 28

Which of the following best describes the viscoelastic property of "creep" in orthopedic tissues?

Explanation

Creep is the gradual, time-dependent deformation of a viscoelastic material when subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when held at a constant deformation.

Question 29

Which of the following biochemical changes occurs in articular cartilage during the early stages of osteoarthritis but NOT in normal aging?

Explanation

In the early stages of osteoarthritis, the collagen network is disrupted, allowing proteoglycans to swell and leading to an increase in water content. In normal aging, the water content of articular cartilage decreases.

Question 30

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

Explanation

Titanium alloys have a lower modulus of elasticity than cobalt-chromium alloys or stainless steel, making them closer to the elasticity of cortical bone. This helps reduce stress shielding around implants.

Question 31

A 12-year-old girl presents with thigh pain and a permeative diaphyseal lesion with a periosteal "onion-skin" reaction on radiographs. Biopsy reveals small round blue cells. Which of the following chromosomal translocations is most characteristic of this diagnosis?

Explanation

The clinical scenario is classic for Ewing sarcoma. Over 85% of Ewing sarcomas are characterized by the t(11;22) chromosomal translocation, resulting in the EWS-FLI1 fusion protein.

Question 32

Following a diaphyseal fracture, rigid fixation with compression plating is performed, resulting in absolute stability. By which of the following primary mechanisms will the fracture heal?

Explanation

Rigid fixation providing absolute stability prevents fracture callus formation. The fracture heals via primary bone healing, which involves direct Haversian remodeling (cutting cones) across the fracture site.

Question 33

A 6-year-old child presents with joint pain, perifollicular hemorrhages, and radiographic evidence of a radiolucent band adjacent to the physis (Trümmerfeld zone). The underlying biochemical defect involves the impaired function of which of the following enzymes?

Explanation

The presentation is consistent with scurvy (Vitamin C deficiency). Ascorbic acid is a required cofactor for prolyl hydroxylase and lysyl hydroxylase, which are essential for proper collagen cross-linking and stability.

Question 34

According to the Enneking surgical staging system for malignant musculoskeletal tumors, a high-grade intra-compartmental lesion without regional or distant metastasis is classified as:

Explanation

In the Enneking staging system, Stage II designates a high-grade tumor. The suffix 'A' denotes an intra-compartmental location, while 'B' indicates an extra-compartmental location.

Question 35

Polymethylmethacrylate (PMMA) bone cement is commonly used in total joint arthroplasty. Which of the following occurs during the polymerization process of PMMA?

Explanation

The polymerization of PMMA is a highly exothermic reaction. Temperatures can exceed 80-100°C, which poses a risk of thermal necrosis to the surrounding bone.

Question 36

During the remodeling phase of tendon healing, the newly synthesized extracellular matrix undergoes maturation. This phase is characterized primarily by an increase in which of the following?

Explanation

The remodeling phase of tendon healing is marked by decreasing cellularity and an increasing synthesis of Type I collagen. The newly formed collagen fibers align longitudinally along lines of mechanical stress.

Question 37

A 65-year-old woman receives intravenous zoledronic acid for the treatment of severe osteoporosis. At the cellular level, this medication inhibits osteoclast-mediated bone resorption primarily by inhibiting which of the following enzymes?

Explanation

Nitrogen-containing bisphosphonates, such as zoledronic acid and alendronate, inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis.

Question 38

A patient presents with acute knee swelling. Aspiration yields cloudy synovial fluid with a white blood cell count of 65,000 cells/mm³, predominantly polymorphonuclear leukocytes. Polarized light microscopy shows negatively birefringent, needle-shaped crystals. What is the composition of these crystals?

Explanation

The clinical picture and fluid analysis are diagnostic of acute gout. Monosodium urate crystals are classically needle-shaped and exhibit strong negative birefringence under polarized light.

Question 39

In normal articular cartilage, the highest concentration of water and lowest concentration of proteoglycans are found in which structural zone?

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (approx. 80%) and the lowest proteoglycan content. The collagen fibers are aligned parallel to the joint surface to resist shear forces.

Question 40

A focal peripheral nerve conduction block without Wallerian degeneration, from which complete clinical recovery is expected within days to weeks, is classified as:

Explanation

Neuropraxia (Sunderland Grade I) represents a temporary conduction block due to focal demyelination. There is no disruption of the axon or surrounding connective tissue, and full recovery typically occurs without Wallerian degeneration.

Question 41

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

Explanation

Fresh autogenous cancellous bone is considered the gold standard for bone grafting because it provides a structural scaffold (osteoconduction), growth factors (osteoinduction), and viable osteoprogenitor cells (osteogenesis).

Question 42

Intermittent administration of low-dose parathyroid hormone (PTH), such as teriparatide, is used to treat severe osteoporosis. The primary mechanism underlying its anabolic effect on bone is:

Explanation

While continuous high levels of PTH cause bone resorption, intermittent low-dose PTH promotes bone formation. It does so by stimulating osteoblast proliferation, promoting their differentiation, and preventing osteoblast apoptosis.

Question 43

An infant presents with multiple fractures and generalized increased bone density on radiographs, lacking clear medullary canals. The severe infantile form of this disease is most commonly caused by a mutation affecting which of the following?

Explanation

The patient has osteopetrosis, a condition caused by defective osteoclast function. Mutations in the gene encoding carbonic anhydrase II, or more commonly TCIRG1, impair the osteoclast's ability to acidify the resorption pit.

Question 44

A 25-year-old man presents with a slow-growing, painful soft tissue mass in the plantar aspect of his foot. Biopsy identifies a biphasic tumor with both epithelial and spindle cell components. Which genetic abnormality is diagnostic for this tumor?

Explanation

Synovial sarcoma classically presents in young adults and can occur in the foot or ankle. It is genetically defined by the t(X;18) chromosomal translocation, resulting in the SYT-SSX fusion gene.

Question 45

A 16-year-old boy presents with knee pain. Radiographs reveal an expansile, eccentric lytic lesion in the proximal tibial metaphysis. MRI demonstrates multiple fluid-fluid levels. Genetic analysis of this lesion would most likely reveal an abnormality involving which of the following genes?

Explanation

The imaging findings are classic for an aneurysmal bone cyst (ABC). Primary ABCs are true neoplasms driven by recurrent translocations involving the USP6 gene on chromosome 17p13.

Question 46

A 28-year-old man presents with a slowly enlarging, painless mass around his knee joint. An incisional biopsy is performed, and cytogenetic analysis reveals a t(X;18)(p11;q11) chromosomal translocation. Which of the following is the most likely diagnosis?

Explanation

Synovial sarcoma is uniquely characterized by the t(X;18)(p11;q11) translocation, resulting in the SYT-SSX fusion gene. It often presents in young adults as a slow-growing mass near large joints.

Question 47

A 16-year-old boy presents with severe right thigh pain that is significantly worse at night and dramatically relieved by ibuprofen. Radiographs show a distinct radiolucent nidus surrounded by intense reactive sclerosis in the femoral diaphysis. The profound pain response to nonsteroidal anti-inflammatory drugs in this condition is primarily due to high levels of which of the following locally produced substances?

Explanation

Osteoid osteoma lesions produce high levels of Prostaglandin E2 (PGE2), which causes the characteristic night pain. This is why nonsteroidal anti-inflammatory drugs (NSAIDs) typically provide dramatic relief.

Question 48

A 65-year-old man with a history of renal cell carcinoma presents with thigh pain. Radiographs reveal a large, purely lytic lesion in the proximal femur with a high risk of impending fracture. If surgical stabilization is planned, which of the following is the most appropriate preoperative intervention?

Explanation

Metastatic renal cell carcinoma is highly vascular and carries a severe risk of massive intraoperative hemorrhage. Preoperative selective embolization of the feeding vessels is strongly recommended before orthopedic stabilization.

Question 49

A 35-year-old woman is diagnosed with an aggressive giant cell tumor of the distal femur. She is prescribed denosumab to shrink the tumor prior to surgical curettage. Denosumab exerts its effect in this disease process by binding directly to which of the following targets?

Explanation

Denosumab is a monoclonal antibody that binds directly to RANK ligand (RANKL), preventing it from activating the RANK receptor. In giant cell tumors, the neoplastic stromal cells overexpress RANKL, driving the recruitment of reactive multinucleated giant osteoclasts.

Question 50

A 12-year-old boy presents with localized pain and swelling in the diaphyseal region of the fibula. Imaging shows a permeative, destructive lesion with an "onion-skin" periosteal reaction. Biopsy reveals small blue cells. Which of the following gene fusions is most commonly associated with this tumor?

Explanation

This presentation is classic for Ewing sarcoma, which frequently exhibits a permeative diaphyseal lesion with onion-skin periostitis. The most common genetic abnormality is a t(11;22) translocation yielding the EWS-FLI1 fusion protein.

Question 51

Which of the following metastatic bone lesions most consistently exhibits an osteoblastic (sclerotic) appearance on plain radiographs?

Explanation

Metastatic prostate cancer classically produces osteoblastic (sclerotic) lesions in bone. In contrast, renal, thyroid, lung, and multiple myeloma typically produce purely lytic lesions.

Question 52

A 45-year-old man undergoes distraction osteogenesis of the tibia using an Ilizarov frame following a complex nonunion. The formation of new bone in the distraction gap primarily occurs via which of the following biologic processes?

Explanation

Distraction osteogenesis relies on intramembranous ossification, where bone forms directly from mesenchymal cells without a cartilaginous intermediate. This process occurs under stable, controlled tension.

Question 53

An 8-year-old boy has a history of easy bruising, swollen gums, and poor wound healing. Radiographs of his lower extremities show a dense zone of provisional calcification at the metaphyses (Frankel line). The underlying pathophysiology involves a defect in the synthesis of which of the following proteins?

Explanation

The clinical picture describes scurvy caused by Vitamin C deficiency, leading to impaired hydroxylation of proline and lysine. This primarily affects the structural integrity and cross-linking of Type I collagen.

Question 54

A 55-year-old woman is evaluated for a localized mass in the proximal humerus. Radiographs show a poorly marginated lesion with "ring and arc" calcifications. Biopsy confirms an intermediate-grade chondrosarcoma. What is the standard of care for managing this lesion?

Explanation

Conventional chondrosarcomas are generally resistant to both chemotherapy and radiation. The definitive treatment for intermediate or high-grade conventional chondrosarcoma is wide surgical excision.

Question 55

The resistance of articular cartilage to compressive loads is primarily provided by which of the following extracellular matrix components?

Explanation

Aggrecan (a large proteoglycan) binds vast amounts of water due to its highly charged glycosaminoglycan side chains. This hydrated gel structure gives articular cartilage its ability to withstand significant compressive forces.

Question 56

During the incorporation of a structural cortical bone allograft, the process by which osteoclasts resorb the graft and osteoblasts lay down new viable bone is termed:

Explanation

Creeping substitution is the physiologic process where dead structural bone graft is slowly resorbed by osteoclasts and concurrently replaced with host viable bone by osteoblasts.

Question 57

Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its mechanism of action?

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively binds to the lysine-binding sites on plasminogen, preventing its activation into plasmin and thereby inhibiting fibrinolysis.

Question 58

Aseptic loosening is the most common cause of long-term total hip arthroplasty failure. The classic osteolysis seen in this condition is predominantly initiated by the activation of which of the following cell types in response to wear debris?

Explanation

Particulate wear debris (commonly polyethylene) is phagocytosed by macrophages. This activates the macrophages to release pro-inflammatory cytokines, driving RANKL-mediated osteoclastogenesis and periprosthetic osteolysis.

Question 59

A 68-year-old woman with severe osteoporosis is started on teriparatide. Which of the following describes the mechanism by which this medication increases bone mineral density?

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH) analog. When administered intermittently (daily injections), it preferentially stimulates osteoblast activity over osteoclast activity, leading to net bone formation.

Question 60

When comparing the mechanical properties of orthopedic implant materials, which of the following correctly orders the Young's modulus of elasticity from highest (stiffest) to lowest (most flexible)?

Explanation

Cobalt-chrome is the stiffest (highest modulus), followed by stainless steel (not listed), then titanium alloys. Cortical bone has a much lower modulus of elasticity than these metals, which can lead to stress shielding.

Question 61

A 60-year-old man presents with diffuse bone pain, fatigue, and recurrent infections. A skeletal survey reveals multiple "punched-out" lytic bone lesions, but his technetium-99m bone scan is largely unremarkable. What is the most likely diagnosis?

Explanation

Multiple myeloma characteristically produces lytic "punched-out" bone lesions without stimulating an osteoblastic response. Because technetium-99m bone scans detect osteoblastic activity, they are typically cold (unremarkable) in myeloma.

Question 62

Which of the following histologic findings is the hallmark of Paget disease of bone in its mixed phase?

Explanation

The classic histologic finding in Paget disease is a disorganized, "mosaic" pattern of woven and lamellar bone characterized by prominent, irregular cement lines. This results from uncoupled and chaotic osteoclast and osteoblast activity.

Question 63

In the peripheral nervous system, the myelin sheath that surrounds axons to facilitate rapid nerve conduction is produced by which of the following cell types?

Explanation

Schwann cells are responsible for myelination in the peripheral nervous system, allowing for rapid saltatory conduction. Oligodendrocytes perform this function in the central nervous system.

Question 64

The Mirels' classification is utilized to estimate the risk of pathologic fracture in metastatic bone disease. Which of the following is NOT a parameter included in the Mirels' scoring system?

Explanation

Mirels' criteria evaluate the risk of pathologic fracture based on four factors: site (upper vs lower extremity, peritrochanteric), pain level, nature of the lesion (blastic, mixed, lytic), and size relative to cortex thickness. Histologic grade is not included.

Question 65

During orthopedic implant infections, bacteria such as Staphylococcus epidermidis evade host immunity and antibiotics by forming a biofilm. The crucial structural component of this biofilm is the extracellular polymeric substance (EPS), which is primarily composed of:

Explanation

The extracellular polymeric substance (EPS), or glycocalyx, forms the bulk of a mature biofilm. It is a hydrated matrix primarily composed of polysaccharides, along with proteins and extracellular DNA, shielding bacteria from systemic antibiotics and immune cells.

Question 66

A 28-year-old man presents with a deep-seated, slowly growing mass in his plantar foot. Biopsy reveals a biphasic tumor with both epithelial and spindle cell components. Immunohistochemistry is positive for epithelial membrane antigen (EMA) and cytokeratin. What is the characteristic chromosomal translocation associated with this diagnosis?

Explanation

Synovial sarcoma classically exhibits a t(X;18) chromosomal translocation, resulting in the SYT-SSX fusion gene. It often presents in young adults as a slow-growing mass in the extremities, classically around the foot or knee.

Question 67

A 35-year-old man presents with a painful mass around his knee. Biopsy reveals a biphasic tumor with spindle cells and epithelial cells. Which of the following chromosomal translocations is most characteristic of this lesion?

Explanation

Synovial sarcoma typically presents in young adults as a painful mass near a joint. It is characterized by the t(X;18)(p11;q11) translocation, which fuses the SYT gene with SSX1 or SSX2.

Question 68

During endochondral ossification, which zone of the physis is primarily affected in achondroplasia?

Explanation

Achondroplasia is caused by an activating mutation in FGFR3, which inhibits chondrocyte proliferation. Thus, the proliferative zone of the physis is primarily affected, leading to shortened long bones.

Question 69

A 65-year-old woman is starting treatment for severe osteoporosis. Her physician prescribes a medication that acts as a recombinant form of parathyroid hormone (PTH). What is the primary mechanism of action of this drug when administered intermittently?

Explanation

Teriparatide (recombinant PTH) administered intermittently stimulates osteoblastic activity, leading to net bone formation. Continuous endogenous PTH elevation, conversely, leads to bone resorption.

Question 70

Which of the following bone graft substitutes is considered osteoinductive, osteoconductive, and osteogenic?

Explanation

Cancellous autograft contains surviving cells (osteogenic), a scaffolding structure (osteoconductive), and growth factors (osteoinductive). Other options lack at least one of these three essential properties.

Question 71

A 12-year-old boy presents with severe, unrelenting mid-shaft thigh pain that is worse at night and relieved by NSAIDs. Radiographs show a small radiolucent nidus with surrounding dense reactive sclerosis. What is the primary mediator responsible for the nocturnal pain?

Explanation

The clinical and radiographic presentation is classic for an osteoid osteoma. The nidus secretes high levels of PGE2, which mediates the characteristic night pain that responds well to NSAIDs.

Question 72

A researcher is evaluating the mechanical properties of different materials used in total hip arthroplasty. Increasing the radiation dose during the cross-linking process of ultra-high-molecular-weight polyethylene (UHMWPE) has which of the following effects?

Explanation

Highly cross-linking UHMWPE significantly improves its wear resistance, reducing the risk of osteolysis. However, the cross-linking process reduces the material's fatigue strength and toughness.

Question 73

A 20-year-old man develops a large, eccentric, lytic lesion in the distal femur epiphysis. Biopsy shows numerous multinucleated giant cells in a background of mononuclear stromal cells. The neoplastic cells in this tumor express high levels of which of the following?

Explanation

In Giant Cell Tumor of bone, the neoplastic mononuclear stromal cells express high levels of RANKL. This stimulates the recruitment and activation of non-neoplastic osteoclast-like giant cells that express RANK, leading to bone resorption.

Question 74

Which type of collagen is the predominant structural protein in the annulus fibrosus of the intervertebral disc?

Explanation

The annulus fibrosus is composed predominantly of Type I collagen, which provides high tensile strength. In contrast, the inner nucleus pulposus is rich in Type II collagen and proteoglycans.

Question 75

In the context of peripheral nerve injury, a Seddon axonotmesis corresponds most closely to which Sunderland classification?

Explanation

Axonotmesis (Seddon) involves disruption of the axon and myelin sheath but preservation of the epineurium, perineurium, and endoneurium. This correlates with a Sunderland Type II injury, which typically has a favorable prognosis for regeneration.

Question 76

A 40-year-old woman is diagnosed with osteomalacia. Laboratory evaluation is likely to show which of the following profiles?

Explanation

Osteomalacia is often caused by Vitamin D deficiency, leading to decreased intestinal calcium and phosphorus absorption. Secondary hyperparathyroidism occurs, which further lowers phosphorus, while alkaline phosphatase rises due to increased osteoblast activity trying to mineralize osteoid.

Question 77

A 7-year-old child sustains a fracture. During the repair process, which cells are primarily responsible for clearing the necrotic tissue and hematoma in the initial inflammatory phase?

Explanation

During the initial inflammatory phase of fracture healing, macrophages and neutrophils infiltrate the fracture hematoma. They clear necrotic tissue and secrete cytokines that initiate the repair cascade.

Question 78

What is the primary function of sclerostin in bone metabolism?

Explanation

Sclerostin is a glycoprotein secreted by osteocytes that binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/beta-catenin signaling pathway. This inhibition results in decreased bone formation, making it a target for osteoporosis therapies.

Question 79

A 50-year-old man presents with progressive weakness in his upper extremities. Imaging reveals a chordoma at the cervical spine. Histological examination of this tumor classically demonstrates which of the following cells?

Explanation

Chordomas arise from notochord remnants and typically occur in the sacrococcygeal region or base of the skull, though they can present in the mobile spine. Histologically, they are characterized by physaliferous cells, which are large cells with vacuolated cytoplasm.

Question 80

In normal articular cartilage, the fluid component relies on interaction with which specific molecule to maintain tissue hydration and resistance to compressive loads?

Explanation

Aggrecan is the predominant proteoglycan in articular cartilage. Its negatively charged glycosaminoglycan (GAG) side chains attract water, creating osmotic swelling pressure that strongly resists compressive loads.

Question 81

A newborn is noted to have multiple fractures, blue sclerae, and hearing loss. This condition is primarily due to a genetic defect affecting which process?

Explanation

Osteogenesis imperfecta is characterized by brittle bones, blue sclerae, and hearing loss. It is most commonly caused by mutations in the COL1A1 or COL1A2 genes, which impair the synthesis and structure of Type I collagen.

Question 82

High molecular weight polyethylene (UHMWPE) wear debris causes osteolysis primarily through the activation of which of the following cell types?

Explanation

Wear debris is phagocytosed by macrophages, which then release inflammatory cytokines like TNF-alpha, IL-1, and IL-6. This cascade stimulates osteoclastogenesis via the RANK/RANKL pathway, leading to periprosthetic osteolysis.

Question 83

According to Perren's strain theory, which type of tissue will primarily form in a fracture gap subjected to 5% to 10% strain?

Explanation

Under Perren's strain theory, low strain (<2%) promotes primary bone healing, while 2-10% strain promotes endochondral ossification (cartilage formation). Strains between 10-100% result in granulation tissue, and >100% leads to fibrous tissue or nonunion.

Question 84

The pullout strength of a cortical bone screw is most directly proportional to which of the following design parameters?

Explanation

The pullout strength of a screw is most significantly determined by its outer (thread) diameter. Increased thread depth and volume of bone between threads also contribute, but outer diameter is the dominant geometric factor.

Question 85

A 45-year-old man presents with an inability to actively extend his digits at the metacarpophalangeal joints, but he retains normal wrist extension with radial deviation. Entrapment of the involved nerve is most likely to occur at which of the following anatomic structures?

Explanation

The patient has posterior interosseous nerve (PIN) syndrome, characterized by loss of digit extension but preserved wrist extension. The most common site of PIN entrapment is the proximal edge of the supinator muscle, known as the Arcade of Frohse.

Question 86

A 15-year-old boy is diagnosed with a conventional high-grade osteosarcoma of the distal femur. Molecular analysis of the tumor is most likely to reveal mutations in which of the following genes?

Explanation

Alterations in tumor suppressor genes such as TP53 and RB1 are frequently implicated in the pathogenesis of conventional osteosarcoma. Patients with Li-Fraumeni syndrome (germline TP53 mutation) have a markedly increased risk of developing this malignancy.

Question 87

A 30-year-old woman has a slow-growing soft tissue mass in her foot. Biopsy reveals a biphasic tumor with both epithelial and spindle cell components. Which of the following chromosomal translocations is highly specific for this diagnosis?

Explanation

The patient has a synovial sarcoma, which is characterized by the t(X;18) translocation resulting in the SYT-SSX fusion gene. It commonly presents as a deep-seated soft tissue mass in the extremities of young adults.

Question 88

During the development of a periprosthetic joint infection, bacteria adhere to the implant surface and begin to communicate via signaling molecules to coordinate gene expression and biofilm maturation. This communication process is known as:

Explanation

Quorum sensing is the mechanism by which bacteria in a biofilm communicate via secreted autoinducers. This allows the bacterial population to coordinate collective behaviors, such as exopolysaccharide matrix production and virulence factor expression.

Question 89

In normal articular cartilage, the highest concentration of proteoglycans and the lowest water content are found in which of the following zones?

Explanation

The deep zone of articular cartilage is characterized by vertically aligned collagen fibers, the lowest water content, and the highest concentration of proteoglycans. Conversely, the superficial zone has the highest water content and lowest proteoglycan concentration.

Question 90

Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Its primary mechanism of action involves:

Explanation

TXA is a synthetic antifibrinolytic agent that competitively and reversibly inhibits the activation of plasminogen to plasmin. It does so by binding to the lysine receptor sites on plasminogen, thereby preventing the degradation of fibrin clots.

Question 91

Adverse local tissue reaction (ALTR) or aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) following metal-on-metal hip arthroplasty is primarily mediated by which type of hypersensitivity reaction?

Explanation

ALVAL is an adverse host immune response to metal wear debris that behaves as a Type IV delayed, cell-mediated hypersensitivity reaction. Histologically, it is characterized by a dense perivascular infiltration of T-lymphocytes and macrophages.

Question 92

A patient with a congenital disorder presents with multiple fractures, anemia, and cranial nerve palsies. Radiographs show a "bone-within-a-bone" appearance and diffuse sclerosis. The primary cellular defect involves an inability to produce an acidic extracellular environment due to a mutation affecting:

Explanation

Osteopetrosis is caused by defective osteoclast function, preventing normal bone resorption. A common mutation involves carbonic anhydrase II, which is essential for generating the hydrogen ions needed to acidify the ruffled border and dissolve bone mineral.

Question 93

A nerve injury resulting in complete disruption of the axon and its myelin sheath, but preservation of the endoneurium, perineurium, and epineurium, is classified as:

Explanation

According to Seddon's classification, axonotmesis involves loss of axonal continuity with intact supporting connective tissue sheaths. This anatomy allows for potential spontaneous recovery via Wallerian degeneration and subsequent distal axonal sprouting.

Question 94

When plating a comminuted diaphyseal fracture using a bridge plating technique, increasing the "working length" of the plate will have which of the following biomechanical effects?

Explanation

The working length of a plate is the distance between the two closest screws on either side of the fracture. Increasing the working length decreases construct stiffness, allowing the deformation to be spread over a larger area and thereby decreasing the strain at the fracture gap.

Question 95

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia. Biopsy shows multinucleated giant cells in a background of mononuclear stromal cells. The neoplastic cells in this lesion primarily express which of the following?

Explanation

In a giant cell tumor of bone, the actual neoplastic cells are the mononuclear spindle stromal cells, which heavily express RANKL. This overexpression stimulates the recruitment and activation of non-neoplastic multinucleated giant cells that drive bone destruction.

Question 96

Placing a stainless steel screw through a titanium plate in an orthopaedic construct can lead to accelerated degradation of the less noble metal. This phenomenon is known as:

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within an electrolytic environment, such as bodily fluids. The less noble metal acts as an anode and undergoes accelerated oxidation compared to a monometallic construct.

Question 97

The majority of the blood supply to the body of the talus is provided by the artery of the tarsal canal. This vessel is primarily a branch of which of the following arteries?

Explanation

The artery of the tarsal canal is typically a branch of the posterior tibial artery and provides the dominant blood supply to the talar body. Injury to this vessel, particularly in displaced talar neck fractures, significantly increases the risk of avascular necrosis.

Question 98

A 68-year-old man has bowing of his tibiae and an increasing hat size. Radiographs show cortical thickening and coarse trabeculae. Histologic evaluation of his affected bone is most likely to show:

Explanation

The patient has Paget disease of bone, characterized by disorganized bone remodeling. The classic histologic finding is a "mosaic" or "jigsaw puzzle" pattern of prominent cement lines due to haphazard bone resorption and formation.

Question 99

The skeletal manifestations of achondroplasia are primarily due to a gain-of-function mutation that leads to which of the following cellular events?

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. Overactivity of the FGFR3 receptor strongly inhibits chondrocyte proliferation and differentiation in the growth plate, severely impairing endochondral ossification.

Question 100

A viscoelastic material, such as a tendon or ligament, is subjected to a constant, prolonged load. Over time, the material continues to deform despite the load remaining unchanged. This biomechanical property is known as:

Explanation

Creep is the progressive deformation of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation refers to the gradual decrease in internal stress when the material is held at a constant length.

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

Orthopedic Basic 2026 MCQs: Board Review Questions & Answers (Part 2)

Key Takeaway

Orthopedic Basic 2026 MCQs: Board Review Questions & Answers (Part 2)

Chapter Index