ABOS Basic Science MCQs (Set 2): Bone Healing Questions

Question 1

What is the current 5-year survival rate for patients with classic nonmetastatic, high-grade osteosarcoma of the extremity?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 1

Explanation

Multidisciplinary treatment combining systemic chemotherapy and adequate surgical resection has resulted in a 5-year survival rate of 70% in patients with nonmetastatic osteosarcoma of the extremity . The advent of effective chemotherapy has increased the overall survival rate from 20% to 70% in current studies. Arndt CA, Crist WM: Common musculoskeletal tumors of childhood and adolescence. N Engl J Med 1999;341:342-352.

Question 2

A 43-year-old woman has had pain in the left hip for the past 2 months. A radiograph, CT scan, MRI scan, and biopsy specimens are shown in Figures 16a through 16e. What is the most likely diagnosis?

Explanation

The imaging studies are consistent with a chondrosarcoma. The radiograph shows a radiolucent lesion in the pelvis, and there are stippled calcifications on the CT scan. The histology shows a low-grade cellular hyaline cartilage neoplasm with stellate, occasionally binucleated chondrocytes. Enchondroma has a more benign histologic appearance.

Question 3

A 40-year-old man with amyloidosis injured his left knee while walking. Figure 17a shows an AP radiograph that was obtained 2 weeks after the injury. The radiograph shown in Figure 17b was obtained after the patient wore a hinged knee brace for 3 months. A clinical photograph is shown in Figure 17c. What is the most likely diagnosis?

Explanation

The patient has a Charcot arthropathy of the knee, which is associated with amyloidosis. The rapid joint destruction shown in the radiographs is most consistent with that diagnosis. Drennan D, Fahey J, Maylahn D: Important factors in achieving arthrodesis of the Charcot knee. J Bone Joint Surg Am 1971;53:1180-1193. Soudry M, Binazzi R, Johanson N, et al: Total knee arthroplasty in Charcot and Charcot like joints. Clin Orthop 1986;208:199-204.

Question 4

Following preoperative chemotherapy, the percent of tumor necrosis has been shown to be of prognostic value for which of the following tumors?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 10

Explanation

The grading of response to chemotherapy for osteosarcoma was introduced by Huvos and associates. Patients with tumors that show more than 90% necrosis after neoadjuvant chemotherapy are considered to have had a good response and have better survival rates than those with less than 90% necrosis. However, it should be noted that survival rates for patients with a poor response are still better than in patients who do not receive neoadjuvant chemotherapy. More recently, similar results have been reported in patients with Ewing's sarcoma. Chemotherapy is not typically used for giant cell tumor of bone. Meyers PA, Heller G, Healey J, Huvos A, Lane J, Marcove R, et al: Chemotherapy for nonmetastatic osteogenic sarcoma: The Memorial Sloan- Kettering experience. J Clin Oncol 1992;10:5-15.

Question 5

Which of the following procedures is not part of the routine evaluation of a patient with suspected metastatic disease to bone?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 11

Explanation

The work-up for a patient with an unknown primary lesion that is metastatic to bone includes a search for the primary tumor and other sites of metastasis. This involves conducting a thorough history and physical examination, appropriate laboratory studies, bone scan, chest radiograph, and CT of the chest, abdomen, and pelvis. In women, a mammogram may be indicated. CT of the brain is not necessary in the early stages of a metastatic work-up. Simon MA, Bartucci EJ: The search for the primary tumor in patients with skeletal metastases of unknown origin. Cancer 1986;58:1088-1095.

Question 6

A 43-year-old man has had right groin pain for the past 3 months. A radiograph, CT scan, and biopsy specimen are shown in Figures 18a through 18c. What is the most likely diagnosis?

Explanation

The radiographic appearance of the lesion is lytic with calcifications in the supra-acetabular region. The CT scan shows bone destruction and periosteal reaction, which rules out an enchondroma. The histologic appearance is that of cellular cartilage, with a high cytoplasmic:nuclear ratio and basophilic appearance to the cytoplasm; these findings rule out chordoma and metastatic renal cell carcinoma. In addition, chordomas are most frequently found in the sacrum and base of the skull. Because there is no high-grade spindle cell component to suggest dedifferentiation, the most likely diagnosis is chondrosarcoma. Pring M, Weber KL, Unni K, Sim FH: Chondrosarcoma of the pelvis: A review of sixty-four cases. J Bone Joint Surg Am 2001;83:1630-1642.

Question 7

What malignant disease most commonly develops in conjunction with chronic osteomyelitis?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 15

Explanation

The most common malignant disease to arise in conjunction with chronic osteomyelitis is squamous cell carcinoma particularly in patients with a long-standing draining sinus tract. Dell PC: Hand, in Simon MA, Springfield D (eds): Surgery for Bone and Soft Tissue Tumors. Philadelphia, PA, Lippincott-Raven, 1998, pp 405-420.

Question 8

A 77-year-old man has had increasing right knee pain for the past 3 months. A radiograph and coronal T1-weighted MRI scan are shown in Figures 19a and 19b. A biopsy specimen is shown in Figure 19c. What is the most likely diagnosis?

Explanation

The radiograph shows a calcified lesion in the medullary canal of the distal femoral diaphysis. The MRI scan shows extensive marrow change distal to the lesion, which is not consistent with an enchondroma. The histology shows a biphasic pattern with low-grade cartilage just apposed to high-grade spindle cell sarcoma. The overall appearance is consistent with dedifferentiated chondrosarcoma. The radiographic appearance is not consistent with enchondroma, and the histologic appearance is not consistent with the other choices. Mitchell AD, Ayoub K, Mangham DC, et al: Experience in the treatment of dedifferentiated chondrosarcoma. J Bone Joint Surg Br 2000;82:55-61.

Question 9

A 10-year-old girl reports activity-related bilateral arm pain. Examination reveals no soft-tissue masses in either arm, and she has full painless range of motion in both shoulders and elbows. The radiograph and bone scan are shown in Figures 20a and 20b, and biopsy specimens are shown in Figures 20c and 20d. What is the most likely diagnosis?

Explanation

Based on these findings, the most likely diagnosis is fibrous dysplasia. Twenty percent of patients with fibrous dysplasia have multifocal disease. The lesions show a typical ground glass appearance. Fibrous dysplasia frequently involves the diaphysis of the long bones. There is no associated soft-tissue mass and no periosteal reactions to these lesions, suggesting a benign lesion. The histology shows proliferating fibroblasts in a dense collagen matrix. Trabeculae are arranged in an irregular or "Chinese letter" appearance. Osteogenic sarcoma and Ewing's sarcoma have a much different radiographic appearance of malignant osteoid and small round blue cells. Periosteal chondroma does occur in the proximal humerus but is not typically multifocal. It appears as a surface lesion with saucerization of the underlying bone and a bony buttress adjacent to the lesion. Some patients with multifocal lesions have associated endocrine abnormalities (McCune-Albright syndrome). Wold LA, et al: Atlas of Orthopaedic Pathology. Philadelphia, PA, WB Saunders, 1990, pp 118-119.

Question 10

After excising a mass from the thigh that was thought to be a lipoma, the pathology reveals that the mass is a high-grade sarcoma. Subsequent treatment should include

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 23

Explanation

Following excision of a suspected benign soft-tissue tumor that proves to be malignant, repeat excision of the tumor bed is recommended. The initial surgical margins are inadequate after an intralesional or marginal excision, necessitating additional surgery for more definitive local control. While radiation therapy and/or chemotherapy may help to reduce the risk of local recurrence in patients with microscopic residual disease, local control is improved following repeat excision. Radiation therapy alone is inadequate to address poor surgical margins, and would likely be given postoperatively. Bisphosphonates have no current role in the treatment of soft-tissue sarcoma. Noria S, Davis A, Kandel R, et al: Residual disease following unplanned excision of soft-tissue sarcoma of an extremity. J Bone Joint Surg Am 1996;78:650-655.

Question 11

Chemotherapy is routinely included in the treatment of which of the following soft-tissue sarcomas?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 24

Explanation

Most soft-tissue sarcomas are treated with a combination of radiation therapy and wide resection. Rhabdomyosarcomas are an exception, where chemotherapy is included in all treatment plans. Chemotherapy for other soft-tissue sarcomas is controversial. Enzinger FM, Weiss SW: Rhabdomyosarcoma, in Soft Tissue Tumors, ed 3. St Louis, MO, CV Mosby, 1995, p 539.

Question 12

A 10-year-old child reports acute leg pain after wrestling with his brother. AP and lateral radiographs are shown in Figures 21a and 21b. What is the best course of action?

Explanation

The radiographs show an eccentric metaphyseal lesion with a well-defined reactive rim of bone that is consistent with a nonossifying fibroma. Pathologic fractures through benign lesions should be treated as appropriate for the fracture, allowing the fracture to heal. Biopsy is not needed when the radiographic diagnosis is benign. MRI, in the presence of a fracture, is not particularly helpful because of the hematoma. If radiographic findings reveal that the lesion appears aggressive, a biopsy should be performed, obtaining tissue away from the fracture site. Marks KE, Bauer TW: Fibrous tumors of bone. Orthop Clin North Am 1989;20:377.

Question 13

An 83-year-old man has a painful mass of the great toe. Radiographs and a biopsy specimen are seen in Figures 22a and 22b. What is the most likely diagnosis?

Explanation

Gouty arthritis, pseudogout, and infection can all present with inflammatory arthritis and periarticular erosions. Strongly negative birefringent crystals are seen in gout. The histologic image shows elongated "needle-like" crystals of gout. Epidermal inclusion cysts are rarely painful and usually have a history of localized penetrating trauma. Hamilton W, Breedman KB, Haupt HM, Lackman R: Knee pain in a 40-year-old man. Clin Orthop 2001;383:282-285,290-292.

Question 14

Eosinophilic granuloma frequently occurs as a solitary lesion in the tubular long bones. After biopsy, what is the best course of action?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 29

Explanation

Most lesions of eosinophilic granuloma are simply observed, but larger aggressive lesions may require curettage and bone grafting. Frequently, biopsy is required to rule out a malignant diagnosis. The differential diagnosis of eosinophilic granuloma is osteomyelitis, Ewing's sarcoma of bone, or osteogenic sarcoma. The biopsy alone can be followed by spontaneous resolution. In some patients, low-dose radiation therapy is used. Chemotherapy or amputation is not indicated for these benign lesions.

Question 15

A 52-year-old man has had back pain radiating to the left leg for the past 5 weeks. A radiograph, MRI scans, and biopsy specimens are shown in Figures 23a through 23f. What is the most likely diagnosis?

Explanation

The histology shows cells with bubbly, abundant clear cytoplasm typical of physaliphorous cells; therefore, the most likely diagnosis is chordoma. These tumors arise from notocord rests in the upper and lower spine.

Question 16

A 15-year-old boy has had pain in the right knee for the past 3 months. He denies any history of trauma. Examination reveals a firm mass in the distal thigh; the remainder of the examination is unremarkable. A radiograph is shown in Figure 24. What further work-up should be completed prior to biopsy?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 36

Explanation

The radiograph shows an aggressive destructive lesion. In this age group, and based on the anatomic location, a primary malignant tumor (osteosarcoma) is likely. Additional staging studies to identify metastatic disease are imperative prior to any biopsy. MRI of the femur helps to reveal skip metastasis and provides information regarding the anatomic location of the lesion. CT of the chest and a bone scan evaluate for distant metastatic spread. A bone scan is also useful in evaluating the extent of local bone activity about the lesion. Simon MA, Finn HA: Diagnostic strategy for bone and soft tissue tumors. J Bone Joint Surg Am 1993;75:622-631.

Question 17

What is the most common primary malignant tumor of bone in childhood?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 37

Explanation

Osteosarcoma is the most common primary malignant tumor of bone in childhood, followed by Ewing's sarcoma. Rhabdomyosarcoma is a soft-tissue sarcoma of childhood. Chondrosarcoma rarely occurs in childhood. Osteochondromas are benign tumors of the bone. Simon M, Springfield D, et al: Osteogenic Sarcoma: Surgery for Bone and Soft Tissue Tumors. Philadelphia, PA, Lippincott Raven, 1998, p 226.

Question 18

A patient with a 5-cm synovial sarcoma located in the distal portion of the rectus femoris muscle undergoes excision of the mass. The procedure is performed through a 10-cm longitudinal incision. Only a portion of the rectus femoris is removed; the vast majority of the muscle is preserved. The plane of dissection is beyond the reactive zone, and the pathology reveals that the margins are negative. This procedure is classified as

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 1

Explanation

The patient underwent a wide resection, which involves excision of the tumor along with a cuff of normal tissue that completely surrounds the tumor. The plane of resection is beyond the reactive zone. A radical resection involves removal of the entire affected muscle from origin to insertion. In a marginal excision, the plane of dissection is through the reactive zone of the tumor. A marginal excision is generally considered inadequate surgery for high-grade sarcomas. In an intralesional resection, the plane of dissection is through the tumor. Excision within the reactive zone but beyond the tumor is the same as a marginal excision. Enneking WF: Staging of musculoskeletal neoplasms, in Current Concepts of Diagnosis and Treatment of Bone and Soft Tissue Tumors. Heidelberg, Germany, Springer-Verlag, 1984.

Question 19

Which of the following tumors is most likely to present with a pathologic fracture in a child?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 38

Explanation

In nearly 50% of patients with a unicameral bone cyst, the lesion remains asymptomatic until a fracture occurs, usually as the result of relatively minor trauma. If the lesion expands, the bone is weakened and may cause pain. Fibrous cortical defects are usually an incidental finding and typically asymptomatic. Malignant bone tumors such as osteosarcoma and Ewing's sarcoma most commonly cause pain, and pathologic fracture occurs in less than 10% of patients. Giant cell tumors are uncommon in children and usually are painful. Wilkins RM: Unicameral bone cysts. J Am Acad Orthop Surg 2000;8:217-224. Dormans JP, Pill SG: Fractures through bone cysts: Unicameral bone cysts, aneurysmal bone cysts, fibrous cortical defects, and nonossifying fibromas. Instr Course Lect 2002;51:457-467.

Question 20

A 60-year-old woman has a mass in the right scapula. Figures 25a and 25b show a CT scan and a biopsy specimen. The cells are lymphocyte common antigen positive, Ewing's specific antigen (CD99) negative, and keratin negative. What is the next step in management?

Explanation

The clinical history, CT scan, and histology are most consistent with a lymphoma of bone. An important part of the staging is bone marrow aspiration and biopsy. The other studies listed are not indicated. Lymphoma of bone, when localized, is usually treated with chemotherapy and radiation therapy and has excellent survival rates. Widespread lymphoma has a worse prognosis. Finiewicz K, van Biesen K: Non-Hodgkins lymphoma, in Golomb H, Vokes E (eds): Oncologic Therapies, ed 2. Berlin, Germany, Springer, 2003, pp 295-318.

Question 21

The use of multiagent adjuvant chemotherapy is associated with a clear survival benefit in which of the following diseases?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 41

Explanation

The use of multiagent chemotherapy has been shown to be associated with a survival benefit in patients with osteosarcoma. The use of chemotherapy in adults with soft-tissue sarcoma remains somewhat controversial. It has not been associated with improved survival rates in patients with renal carcinoma, dedifferentiated chondrosarcoma, or melanoma. Menendez LR (ed): Orthopaedic Knowledge Update: Musculoskeletal Tumors. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002, p 53.

Question 22

Which of the following definitions best describes Batson's vertebral vein system?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 42

Explanation

The venous plexus was described by Batson and helps to explain the common distribution of metastatic cells to the vertebrae, skull, ribs, and proximal long bones. Batson studied the vertebral vein system extensively by using contrast agents in human cadavers and live monkeys. Batson's plexus is a valveless system that allows retrograde embolism from the major organs such as the breast, prostate, lung, kidney, and thyroid. It is located within the thoracoabdominal cavity and has connections to the proximal long bones and an intercommunicating network of thin-walled veins with a low intraluminal pressure. Batson OV: Function of vertebral veins and their role in spread of metastases. Ann Surg 1940;112:138-149.

Question 23

Figure 26 shows the radiograph of a 48-year-old woman who has right arm pain and hematuria. A bone scan reveals increased uptake in the left ribs and thoracic spine. A needle biopsy specimen shows that the lesion is highly keratin positive and composed primarily of clear cells. What is the best course of action?

Basic Science Board Review 2005: High-Yield MCQs (Set 2) - Figure 43

Explanation

The lesion has the typical "blown out" lytic radiographic appearance that is most commonly found in thyroid or renal cell metastases. Given the history of hematuria and histology findings, the most likely diagnosis is metastatic renal cell carcinoma. This tumor is relatively resistant to chemotherapy. Radiation therapy is used as a postoperative adjuvant treatment with varying response rates. Surgery should be performed after preoperative embolization to decrease the risk of intraoperative bleeding, as no tourniquet can be used in this location. Patients with metastatic renal cell carcinomas may survive for years, resulting in a higher likelihood of local tumor progression with ineffective adjuvant therapy. Intramedullary fixation combined with curettage and cementation will provide the best chance of local control while maintaining the patient's native shoulder and elbow joints. A total humeral resection is an extensive surgery with considerable morbidity and is not indicated for this patient because less extensive surgery is likely to be effective. Harrington KD, Sim FH, Enis JE, Johnston JO, Diok HM, Gristina AG: Methylmethacrylate as an adjunct in internal fixation of pathological fractures: Experience with three hundred and seventy-five cases. J Bone Joint Surg Am 1976;58:1047-1054. Sun S, Lang EV: Bone metastases from renal cell carcinoma: Preoperative embolization. J Vasc Interv Radiol 1998;9:263-269.

Question 24

A 15-year-old boy has had pain in the right shoulder for the past 3 months. He denies any history of trauma and has no constitutional symptoms. Examination reveals a large firm mass in the proximal arm. A radiograph and MRI scan are shown in Figures 27a and 27b. Biopsy specimens are shown in Figures 27c and 27d. Management should consist of

Explanation

The patient has an aneurysmal bone cyst. The fluid-fluid levels seen on the MRI scan are typical for aneurysmal bone cyst, and the histology is consistent with a cystic lining. Vascular lakes, multinucleated giant cells, reactive bone, fibrovascular tissue, and an absence of atypical cells or numerous mitoses are seen histologically. Aneurysmal bone cysts will typically continue to grow and cause further bone destruction; therefore, observation is not recommended. Steroid injections are not effective. A thorough curettage of the cyst lining and bone grafting are required. Wide resection and chemotherapy are reserved for more aggressive tumors. There is no evidence of infection radiographically or histologically. Telangiectatic osteosarcoma should also be considered in the differential diagnosis; therefore, biopsy is an important part of the work-up. Wold LA, et al: Atlas of Orthopaedic Pathology. Philadelphia, PA, WB Saunders, 1990, pp 232-233.

Question 25

A 38-year-old woman with metastatic thyroid carcinoma has had increasing pain in the left hip for the past 3 months. An AP radiograph and coronal T1-weighted MRI scan are shown in Figures 28a and 28b. Management should consist of

Explanation

The radiograph and MRI scan reveal a lytic lesion in the left femoral neck region that extends to the lesser trochanter. Although external beam radiation and radioactive iodine infusion may be helpful in controlling the local disease, the patient is at high risk for femoral neck fracture given the location of the lesion. Prophylactic surgery is indicated; therefore, the treatment of choice is a cemented bipolar hemiarthroplasty. The use of a compression hip screw and side plate or an intramedullary nail has a high likelihood of failure with disease progression. Postoperative treatment with radiation therapy and bisphosphonates is also indicated. Mirels H: Metastatic disease in long bones: A proposed scoring system for diagnosing impending pathologic fractures. Clin Orthop 1989;249:256-264. Swanson KC, Pritchard DJ, Sim FH: Surgical treatment of metastatic disease of the femur. J Am Acad Orthop Surg 2000;8:56-65.

Question 26

A 45-year-old man undergoes fixation of a comminuted femoral shaft fracture with a bridging locked plate. To decrease the construct stiffness and promote secondary bone healing via callus formation, which of the following technical modifications is most appropriate?

Explanation

Leaving empty holes over the fracture increases the working length of the plate. This decreases construct stiffness and promotes interfragmentary motion, which is necessary for secondary bone healing.

Question 27

Which of the following bone graft substitutes possesses osteoinductive properties but lacks both osteoconductive structural support and osteogenic cells?

Explanation

Demineralized bone matrix (DBM) is produced by acid extraction of bone, leaving behind collagen and BMPs that provide osteoinductive potential. However, it lacks structural integrity (osteoconduction) and viable cells (osteogenesis).

Question 28

In comparing orthopedic implant materials, which of the following accurately describes the relationship between the Young's modulus of elasticity of titanium, stainless steel, and cortical bone?

Explanation

Stainless steel has a higher modulus of elasticity (~200 GPa) than titanium alloys (~100 GPa). Both are significantly stiffer than cortical bone (~15-20 GPa), which can lead to stress shielding.

Question 29

Bone morphogenetic proteins (BMPs) initiate intracellular signaling primarily through which of the following pathways to promote osteoblastic differentiation?

Explanation

BMPs act via cell surface serine/threonine kinase receptors. These receptors phosphorylate downstream Smad proteins, which then translocate to the nucleus to regulate gene transcription for osteoblast differentiation.

Question 30

Cortical bone exhibits viscoelastic properties, meaning its biomechanical behavior depends on the rate of loading. Which of the following best describes the response of cortical bone to high-rate loading compared to low-rate loading?

Explanation

As a viscoelastic material, cortical bone becomes stiffer and can withstand higher loads before failing when it is loaded at higher strain rates. This increases both its modulus and ultimate strength.

Question 31

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

Explanation

Screw pullout strength is directly proportional to the outer diameter of the thread, the length of thread engagement, and the shear strength of the bone. Decreasing thread pitch also helps, but maximizing outer diameter is a primary factor.

Question 32

During revision of an uncemented total hip arthroplasty, severe polyethylene wear is noted secondary to retained bone and cement particles from a previous surgery acting between the articular surfaces. What type of wear mechanism is this?

Explanation

Third-body wear occurs when hard particles (e.g., bone fragments, cement, or metal debris) become trapped between two articulating surfaces. This leads to accelerated gouging and damage of the bearing surface.

Question 33

A surgeon considers using a titanium locking plate with stainless steel screws for fracture fixation. Why is this combination traditionally contraindicated in orthopedic surgery?

Explanation

Mixing dissimilar metals with different electropotentials in a conductive fluid environment (like the human body) creates a battery effect. This can lead to accelerated galvanic corrosion of the less noble metal.

Question 34

Which of the following biomechanical conditions is strictly required to achieve primary (direct) bone healing without intermediate callus formation?

Explanation

Primary bone healing (contact healing via cutting cones) requires absolute stability and anatomic reduction with strain less than 2%. All other options describe relative stability, which leads to secondary healing with callus.

Question 35

A patient presents with a pseudotumor around a modular total hip arthroplasty secondary to adverse local tissue reaction. The primary mechanism generating metal ions at the modular head-neck taper interface is:

Explanation

Fretting corrosion is mechanically assisted crevice corrosion caused by micromotion at the interface of two contacting surfaces. This micromotion continually disrupts the protective passive oxide layer on modular tapers.

Question 36

During secondary fracture healing, the transition from soft callus to hard callus is characterized primarily by the replacement of which type of collagen with another?

Explanation

During secondary bone healing, the soft cartilaginous callus is rich in Type II collagen. As endochondral ossification occurs, this cartilage is replaced by woven bone, which is primarily composed of Type I collagen.

Question 37

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is currently FDA-approved for use in which of the following orthopedic scenarios?

Explanation

rhBMP-2 is FDA-approved for acute open tibial shaft fractures treated with an intramedullary nail and for anterior lumbar interbody fusion (ALIF). It is not approved for posterolateral lumbar fusion or routine upper extremity fractures.

Question 38

A clubfoot is treated with serial Ponseti casting. The gradual stretching and elongation of the tightened medial ligaments and tendons under a constant applied load over time demonstrates which viscoelastic property?

Explanation

Creep is the progressive deformation of a viscoelastic material over time when subjected to a constant force. Stress relaxation, by contrast, is a decrease in internal stress over time when held at a constant deformation.

Question 39

A surgeon chooses to ream the femoral canal to upsize a solid intramedullary nail from 10 mm to 12 mm in diameter. By what approximate factor does the bending stiffness of the solid nail increase?

Explanation

The bending stiffness of a solid cylinder is proportional to the area moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, increasing diameter by a factor of 1.2 yields a stiffness increase of (1.2)^4, or roughly 2.07.

Question 40

According to Perren's strain theory of fracture healing, which of the following tissues can tolerate the highest interfragmentary strain before rupturing?

Explanation

Perren's strain theory posits that tissues will only form in a fracture gap if the local strain is below their yield point. Granulation tissue tolerates up to 100% strain, fibrocartilage up to 15%, and lamellar bone only about 2%.

Question 41

Which of the following represents the primary mechanical disadvantage of ceramic-on-ceramic bearings in total hip arthroplasty?

Explanation

Ceramics are highly resistant to wear and possess excellent compressive strength. However, they are brittle materials with very low tensile strength, making them susceptible to sudden catastrophic fracture under tension or impact.

Question 42

A surgeon is applying a unilateral uniplanar external fixator for a tibial shaft fracture. Which of the following modifications will most effectively INCREASE the bending stiffness of the construct?

Explanation

Increasing the distance (spread) between pins within the same fragment dramatically increases the working length of the pins within the bone, thereby increasing overall construct stiffness. Placing the rod closer to bone also increases stiffness.

Question 43

A patient develops significant proximal femoral bone loss two years after an uncemented total hip arthroplasty utilizing a diaphyseal-fitting, extensively porous-coated cobalt-chromium stem. The primary mechanism for this bone loss is:

Explanation

Extensively porous-coated cobalt-chromium stems provide rigid distal fixation and possess a very high modulus of elasticity. This offloads the proximal femur (stress shielding), leading to adaptive bone resorption according to Wolff's Law.

Question 44

An empty 3 mm unicortical drill hole is accidentally made in the anterior cortex of a tibia during surgery. Under torsional loading, how much does this defect approximately reduce the bone's torsional strength?

Explanation

An empty cortical hole acts as a significant stress riser. A defect as small as 20% of the bone's diameter can decrease the bone's torsional strength by up to 50% due to stress concentration at the margins.

Question 45

Which of the following material properties represents the total energy absorbed by a material before it fails, corresponding to the total area under the stress-strain curve?

Explanation

Toughness is the energy absorbed by a material prior to failure, represented by the total area under the stress-strain curve. Stiffness refers to the elastic region's slope (Young's modulus), while ductility is the amount of plastic deformation before failure.

Question 46

Mesenchymal stem cells differentiate into osteoblasts through the activation of specific transcription factors. Which of the following is considered the master transcription factor essential for osteoblast lineage commitment?

Explanation

RUNX2 (Cbfa1) is the master transcription factor required for the differentiation of mesenchymal stem cells into osteoblasts. SOX9 is essential for chondrogenesis, and PPAR-gamma drives adipogenesis.

Question 47

In cortical bone screw fixation, which geometric modification to the screw design will most significantly increase its pull-out strength?

Explanation

The outer diameter is the most significant geometric determinant of screw pull-out strength. While increasing the core diameter improves fatigue strength, it minimally impacts pull-out strength compared to changes in the outer diameter.

Question 48

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated for primary (contact) bone healing to occur via cutting cones?

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% promote secondary bone healing via callus formation, while strains >10% lead to fibrous nonunion.

Question 49

Which zone of normal articular cartilage contains 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, characterized by a high water content, low proteoglycan content, and densely packed collagen fibers parallel to the articular surface.

Question 50

When utilizing a bridging plate for a comminuted diaphyseal fracture, what is a direct biomechanical consequence of increasing the working length (the distance between the closest inner screws) of the construct?

Explanation

Increasing the working length of a bridging plate decreases the overall axial and bending stiffness of the construct. This increased flexibility permits more interfragmentary motion, which stimulates secondary bone healing via callus formation.

Question 51

Which Bone Morphogenetic Protein (BMP) is currently FDA-approved as an adjunct for the treatment of acute open tibial shaft fractures treated with an intramedullary nail?

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use in acute open tibial shaft fractures treated with an IM nail, as well as for anterior lumbar interbody fusion (ALIF). rhBMP-7 was historically used for recalcitrant tibial nonunions.

Question 52

Which structural property is the primary determinant of torsional rigidity in a solid intramedullary nail?

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, small increases in the diameter of an IM nail result in massive increases in torsional rigidity.

Question 53

During the soft callus phase of secondary fracture healing, the initial cartilaginous matrix is predominantly composed of which type of collagen?

Explanation

The soft callus primarily consists of hyaline cartilage and fibrocartilage, which are rich in Type II collagen. As the healing progresses to the hard callus phase, Type II is replaced by Type I collagen during endochondral ossification.

Question 54

A dynamic splint is applied to a patient's contracted elbow, delivering a constant force. Over several days, the joint progressively gains extension. Which biomechanical property of viscoelastic materials does this best describe?

Explanation

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

Question 55

To minimize stress shielding in total joint arthroplasty, engineers seek materials that match the mechanical properties of bone. Which of the following implant materials has a modulus of elasticity closest to that of human cortical bone?

Explanation

Titanium alloy has a modulus of elasticity (approx. 110 GPa) that is closer to cortical bone (15-20 GPa) than stainless steel (200 GPa) or CoCr (210 GPa). This closer match reduces the extent of stress shielding.

Question 56

Which of the following medications is known to impair early fracture healing by specifically inhibiting a pathway critical for the differentiation of osteoblasts during early endochondral ossification?

Explanation

Celecoxib, a selective COX-2 inhibitor, blocks the synthesis of prostaglandins (like PGE2) that are essential for osteoblast differentiation and the early stages of endochondral ossification, thereby impairing fracture healing.

Question 57

What is the primary biomechanical advantage of using a locked plate construct over a conventional non-locked compression plate in osteoporotic bone?

Explanation

Locked plates function as fixed-angle constructs and do not rely on friction between the plate and the bone. This distributes forces evenly across all locked screws, preventing the sequential screw failure common in osteoporotic bone.

Question 58

Denosumab is an effective pharmacological agent for treating osteoporosis. What is its specific molecular mechanism of action?

Explanation

Denosumab is a fully human monoclonal antibody that binds specifically to RANKL. By neutralizing RANKL, it prevents it from binding to the RANK receptor on osteoclasts, severely inhibiting osteoclastogenesis and bone resorption.

Question 59

When a tendon is tested in tension, the initial region of its stress-strain curve demonstrates low stiffness before becoming linear. What is responsible for this initial 'toe region'?

Explanation

The toe region corresponds to the initial uncrimping or straightening of the naturally wavy collagen fibers at low strains. Once the fibers are straight, the curve enters the linear (elastic) region.

Question 60

A 50-year-old smoker presents with a 9-month-old humeral shaft nonunion. Radiographs reveal a widened fracture gap with rounded, sclerotic bone ends and absent callus formation. What is the most appropriate management principle?

Explanation

The radiographic appearance (sclerotic ends, no callus) is characteristic of an atrophic nonunion, which lacks biological healing potential. Successful treatment requires both mechanical stabilization (rigid fixation) and biological augmentation (bone grafting).

Question 61

Which of the following non-collagenous bone matrix proteins contains an RGD (Arg-Gly-Asp) sequence that is essential for osteoclast attachment via alpha-v beta-3 integrins?

Explanation

Osteopontin and bone sialoprotein both contain the RGD sequence, which binds specifically to the alpha-v beta-3 integrin on the osteoclast membrane, facilitating the formation of the sealing zone for bone resorption.

Question 62

When designing an external fixator, a surgeon opts to increase the diameter of the Schanz pins from 4 mm to 5 mm. How does this specific change mathematically alter the bending stiffness of the pins?

Explanation

The bending stiffness of a pin is proportional to its area moment of inertia, which correlates with the radius to the fourth power (r^4). Thus, a minor increase in pin diameter yields a profound increase in construct stiffness.

Question 63

Following a microfracture procedure for a focal full-thickness articular cartilage defect in the knee, what type of tissue predominantly fills the defect?

Explanation

Microfracture penetrates the subchondral bone, releasing marrow elements and mesenchymal stem cells. These cells differentiate to form a repair tissue predominantly composed of fibrocartilage (rich in Type I collagen) rather than native hyaline cartilage.

Question 64

Romosozumab has recently been utilized for the treatment of severe osteoporosis. What is the precise mechanism of action of this agent?

Explanation

Romosozumab is a monoclonal antibody that binds and inhibits sclerostin. Since sclerostin is an endogenous inhibitor of the Wnt/beta-catenin pathway, neutralizing it increases osteoblast activity and dramatically enhances bone formation.

Question 65

Which of the following parameters most significantly increases the pullout strength of a cortical screw?

Explanation

Pullout strength is most significantly determined by the outer thread diameter, as it is proportional to the square of the thread diameter. Other secondary factors include the length of engagement and shear strength of the surrounding bone.

Question 66

A 35-year-old man sustains a diaphyseal tibia fracture treated with an unreamed intramedullary nail. Which of the following biomechanical adjustments will most effectively decrease the torsional stiffness of this construct?

Explanation

The working length of an intramedullary nail is the unsupported distance between the points of fixation on either side of the fracture. Increasing the working length significantly decreases both the torsional and bending stiffness of the construct.

Question 67

In the context of bone healing, primary (strain-free) bone healing relies fundamentally on which of the following processes?

Explanation

Primary bone healing occurs strictly under conditions of absolute stability and relies on direct Haversian remodeling via cutting cones. Unlike secondary healing, it progresses without intermediate cartilaginous callus formation.

Question 68

Which of the following cellular mechanisms correctly describes the action of denosumab in the treatment of osteoporosis?

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL in the extracellular space. This prevents RANKL from engaging the RANK receptor on osteoclast precursors, thereby halting osteoclast differentiation and activity.

Question 69

A surgeon applies a unilateral external fixator for a severe open tibial shaft fracture. To maximize the bending stiffness of the construct, which of the following single modifications is most effective?

Explanation

Pin diameter is the most critical factor for external fixator stiffness, as bending stiffness is proportional to the pin's radius to the fourth power (r^4). Decreasing the bone-to-bar distance and increasing pin spread also increase stiffness but to a lesser mathematical extent.

Question 70

During cyclic loading of a tendon, a steady increase in deformation over time while the applied load remains strictly constant is best described by which viscoelastic property?

Explanation

Creep is defined as the time-dependent deformation of a viscoelastic material under a constant load. In contrast, stress relaxation is the progressive decrease in stress over time when the material is held at a constant deformation.

Question 71

Which of the following best describes the inherent mechanical behavior of cortical bone?

Explanation

Cortical bone is highly anisotropic, meaning its mechanical properties vary depending on the direction of the applied load. It is strongest in compression, significantly weaker in tension, and weakest in shear.

Question 72

Polyethylene wear particles in total hip arthroplasty predominantly induce periprosthetic osteolysis through the initial activation of which cell type?

Explanation

Ultra-high-molecular-weight polyethylene (UHMWPE) wear debris (typically 0.1-1.0 µm) is phagocytosed by macrophages. This triggers the release of pro-inflammatory cytokines like TNF-alpha and IL-1, which heavily upregulate osteoclastic bone resorption.

Question 73

In mature articular cartilage, which zone is characterized by the highest concentration of water and collagen fibers oriented parallel to the joint surface?

Explanation

The superficial zone of articular cartilage contains the highest water content and the lowest proteoglycan concentration. Its collagen fibrils are aligned parallel to the articular surface to optimize resistance to shear forces.

Question 74

Which of the following bone graft or graft substitute options distinctly possesses osteoinductive, osteoconductive, and osteogenic properties simultaneously?

Explanation

Cancellous autograft provides all three properties essential for bone healing: osteogenic (viable donor cells), osteoinductive (native growth factors), and osteoconductive (a structural scaffold). Synthetics and allografts generally lack the osteogenic cellular component.

Question 75

A locking compression plate (LCP) functions primarily by which biomechanical principle when utilized to bridge a highly comminuted diaphyseal fracture?

Explanation

A locking plate functions effectively as an internal external-fixator, relying on the threaded interface between the screw head and the plate to create a rigid fixed-angle construct. Because it does not require friction against the bone to maintain stability, it preserves periosteal blood supply.

Question 76

Which intracellular signaling pathway is directly activated by Bone Morphogenetic Proteins (BMPs) to stimulate osteoblast differentiation?

Explanation

BMPs bind to cell surface serine/threonine kinase receptors, which subsequently phosphorylate intracellular SMAD proteins (SMAD 1, 5, and 8). The resulting SMAD complex translocates to the nucleus to directly regulate osteogenic gene transcription.

Question 77

Which of the following physical properties accurately describes polymethylmethacrylate (PMMA) bone cement when utilized in arthroplasty?

Explanation

PMMA functions strictly as a grout, relying purely on macro- and micro-mechanical interlock with the surrounding cancellous bone and the implant, not as a chemical adhesive. It is strongest in compression, weakest in tension, and undergoes a highly exothermic curing process.

Question 78

On a classic stress-strain curve for a typical metallic implant, the exact point at which the material ceases to deform elastically and begins to deform permanently is known as the:

Explanation

The yield point marks the critical transition from elastic (fully reversible) deformation to plastic (irreversible) deformation on a stress-strain curve. The linear portion leading up to this point represents the material's modulus of elasticity.

Question 79

What is the primary cellular mechanism of action of parathyroid hormone (PTH) when administered intermittently at low doses (e.g., Teriparatide) for fracture healing or osteoporosis?

Explanation

While continuous endogenous PTH exposure typically leads to net bone resorption, intermittent administration of low-dose PTH (Teriparatide) exerts a powerful anabolic effect. It directly stimulates osteoblasts, leading to net bone formation.

Question 80

Regarding the modulus of elasticity (Young's modulus), which of the following sequences correctly orders common orthopedic materials from most stiff to least stiff?

Explanation

The modulus of elasticity is a measure of material stiffness. Cobalt-chromium is the stiffest (approx. 220 GPa), followed by stainless steel (200 GPa), titanium alloy (110 GPa), and finally cortical bone (15-20 GPa).

Question 81

When a surgeon applies a rigid plate to the lateral aspect of the femur to stabilize a subtrochanteric fracture, the plate functions primarily via which biomechanical principle?

Explanation

The lateral cortex of the femur naturally experiences tension during physiologic weight-bearing. A plate applied to the tension side of an eccentrically loaded bone acts as a tension band, converting disruptive tensile forces into stabilizing compressive forces at the opposite (medial) cortex.

Question 82

Galvanic corrosion in orthopedic implants is most highly accelerated and likely to occur under which of the following specific conditions?

Explanation

Galvanic corrosion requires two dissimilar metals with different anodic indices (such as stainless steel and cobalt-chromium) placed in electrical contact within an electrolytic solution (like physiologic saline). This electrochemical cell leads to accelerated corrosion of the less noble metal.

Question 83

Which specific collagen type is predominantly expressed by cells during the soft callus (chondrogenic) phase of secondary fracture healing?

Explanation

During the soft callus phase of secondary fracture healing, local chondrocytes proliferate and synthesize a cartilage matrix that is highly rich in Type II collagen. This matrix is later calcified and replaced by Type I collagen as the soft callus converts to hard woven bone.

Question 84

Stress shielding, frequently observed radiographically as proximal femoral osteopenia around a stiff primary arthroplasty stem, is a direct clinical manifestation of which biomechanical principle?

Explanation

Wolff's Law dictates that bone adapts and remodels in direct response to the mechanical stresses placed upon it. When a stiff implant (such as a cobalt-chromium stem) bears the majority of the physiological load, the relatively unloaded surrounding bone resorbs due to stress shielding.

Question 85

Increasing the working length of a locked plate construct has which of the following biomechanical effects?

Explanation

Increasing the working length of a locked plate construct decreases its axial and torsional stiffness. This allows for greater interfragmentary motion, which promotes secondary bone healing through robust callus formation.

Question 86

Which of the following signaling pathways is most directly inhibited by the administration of nonsteroidal anti-inflammatory drugs (NSAIDs) during fracture healing?

Explanation

NSAIDs inhibit both COX-1 and COX-2 enzymes. COX-2 is highly upregulated during fracture healing, and its inhibition impairs endochondral ossification and callus formation by reducing prostaglandin E2 synthesis.

Question 87

On a standard stress-strain curve for an orthopedic biomaterial, the slope of the curve strictly within its linear elastic region represents which of the following material properties?

Explanation

Young's modulus, a direct measure of a material's intrinsic stiffness, is defined as the slope of the stress-strain curve within its linear elastic region. Toughness, in contrast, represents the total energy absorbed before failure (total area under the curve).

Question 88

Increasing the radiation dose during the cross-linking process of ultra-high molecular weight polyethylene (UHMWPE) for total joint arthroplasty has what primary effect on its material properties?

Explanation

Increasing the radiation dose increases the density of cross-links, which significantly reduces the volumetric wear of the polyethylene. However, this process sacrifices mechanical properties, notably decreasing the material's ductility, fatigue strength, and fracture toughness.

Question 89

Which of the following modifications to an intramedullary nail design will most significantly increase its torsional rigidity?

Explanation

The torsional rigidity of a solid or hollow cylinder is proportional to the radius raised to the fourth power. Therefore, increasing the outer diameter is the most effective way to exponentially increase both torsional and bending rigidity.

Question 90

Bone morphogenetic proteins (BMPs) promote osteoinduction primarily through the activation of which of the following intracellular signaling pathways?

Explanation

BMPs bind to cell-surface serine-threonine kinase receptors on mesenchymal stem cells, leading to the phosphorylation of intracellular SMAD 1/5/8 proteins. This complex then translocates to the nucleus to upregulate osteogenic transcription factors like Runx2.

Question 91

In the biphasic model of articular cartilage, which structural component is primarily responsible for generating the internal swelling pressure that resists compressive loads?

Explanation

Chondroitin sulfate and keratin sulfate are glycosaminoglycans on aggrecan molecules that possess fixed negative charges. These charges repel each other and draw in water via Donnan osmosis, creating the inherent swelling pressure that provides compressive stiffness.

Question 92

A patient undergoes an ACL reconstruction. When the graft is tensioned and secured at a constant fixed length, the tension within the graft is observed to gradually decrease over time. What is this specific viscoelastic property called?

Explanation

Stress relaxation is the viscoelastic property where a tissue or material experiences a decrease in stress (tension) over time when held at a constant strain (length). In contrast, creep refers to continued deformation over time under a constant load.

Question 93

The pullout strength of a standard cortical screw is directly proportional to which of the following geometric parameters?

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, length of thread engagement, and the shear strength of the host bone. It is inversely proportional to the thread pitch.

Question 94

Primary bone healing is characterized by direct Haversian remodeling without the formation of a visible fracture callus. What is the maximum interfragmentary strain threshold compatible with primary bone healing?

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2 percent. At this low strain, osteoclastic cutting cones can cross the fracture site without being disrupted by mechanical motion.

Question 95

Trunnionosis in total hip arthroplasty, characterized by wear and localized failure at the modular head-neck junction, is primarily initiated by which specific type of corrosion?

Explanation

Trunnionosis is primarily driven by fretting corrosion, which occurs due to mechanical micromotion at the modular head-neck interface. This mechanical wear constantly strips the protective passive oxide layer, leading to severe electrochemical degradation.

Question 96

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is frequently used off-label in anterior cervical discectomy and fusion (ACDF). This specific application is strongly associated with which of the following complications?

Explanation

The off-label use of rhBMP-2 in the anterior cervical spine has been strongly linked to life-threatening prevertebral soft tissue swelling and severe dysphagia. Consequently, the FDA issued a direct warning regarding its use in this anatomical location.

Question 97

According to beam theory, the bending stiffness of a solid rectangular fracture plate is a function of its width (b) and thickness (h). Assuming the material remains constant, how does doubling the plate's thickness affect its area moment of inertia?

Explanation

The area moment of inertia for a rectangular structure subjected to bending is calculated as (b * h^3) / 12. Therefore, doubling the thickness (h) increases the bending stiffness exponentially by a factor of eight (2^3 = 8).

Question 98

Long-term bisphosphonate therapy is associated with an increased risk of atypical subtrochanteric femur fractures. At the cellular level, how do nitrogen-containing bisphosphonates primarily alter bone metabolism?

Explanation

Nitrogen-containing bisphosphonates disrupt the mevalonate pathway by inhibiting the enzyme farnesyl pyrophosphate synthase in osteoclasts. This leads to osteoclast apoptosis, severely impairing normal bone remodeling and allowing microdamage to accumulate.

Question 99

Cortical bone exhibits significantly higher ultimate tensile strength when loaded parallel to the osteons (longitudinally) compared to when it is loaded perpendicularly (transversely). Which of the following mechanical terms best describes this direction-dependent property?

Explanation

Anisotropy refers to a material exhibiting different mechanical properties depending on the direction of the applied load. Cortical bone is highly anisotropic, largely due to the longitudinal orientation of its Haversian systems.

AAOS & ABOS Basic Science MCQs (Set 3): Bone Biology, Biomechanics & Anatomy Review

AAOS Basic Science MCQs (Set 2): Bone Healing & Orthopedic Biomechanics | ABOS, OITE Prep

Key Takeaway

AAOS Basic Science MCQs (Set 2): Bone Healing & Orthopedic Biomechanics | ABOS, OITE Prep

Chapter Index