Question 1

A 12-year-old girl presents with a chronic limp and mild thigh pain. Radiographs reveal a ground-glass expansile lesion in the proximal femur with a characteristic shepherd's crook deformity. What is the underlying molecular pathogenesis of this condition?

Explanation

Fibrous dysplasia is caused by a somatic activating mutation in the GNAS1 gene. This leads to increased intracellular cAMP, which impairs normal osteoblast differentiation and results in the production of structurally weak woven bone.

Question 2

A 60-year-old man with metastatic lung cancer complains of severe, unrelenting pain in his right thigh. Radiographs reveal a 4 cm lytic lesion in the femoral diaphysis that involves approximately 50% of the cortical diameter. According to Mirels' criteria, what is his score and the corresponding recommendation?

Explanation

Mirels' score is calculated based on site (lower limb = 2), pain (severe = 3), type (lytic = 3), and size (1/3 to 2/3 of cortex = 2), totaling 10. A score of 9 or greater indicates a high risk of pathologic fracture, mandating prophylactic fixation.

Question 3

A 45-year-old man undergoes an arthroscopic procedure for chronic knee locking. The surgeon removes dozens of uniformly sized, loose cartilaginous bodies. Which of the following histologic findings is classically associated with the primary form of this disease and must not be misdiagnosed as malignancy?

Explanation

Primary synovial chondromatosis characteristically exhibits cellular atypia, hypercellularity, and binucleate cells. Despite these aggressive-appearing features, it is a benign metaplastic condition and should not be mistaken for low-grade chondrosarcoma.

Question 4

A 50-year-old man presents with rapid, painless swelling and severe radiographic destruction of the right shoulder joint over the past 3 months. Neurological exam reveals a loss of pain and temperature sensation in a cape-like distribution over the upper extremities. What is the most appropriate next step in diagnosis?

Explanation

Neuropathic arthropathy (Charcot joint) of the upper extremity, combined with a loss of pain/temperature sensation in a cape-like distribution, is highly suspicious for syringomyelia. An MRI of the cervical spine is the diagnostic modality of choice.

Question 5

A 15-year-old boy with polyostotic fibrous dysplasia presents with a progressing proximal femur deformity.

Surgical management is planned to restore mechanical alignment. Which of the following is the most appropriate biomechanical approach for reconstruction?

Explanation

In fibrous dysplasia, load-sharing intramedullary devices are essential because plates often fail due to the poor quality of the surrounding bone. Additionally, cortical bone grafts are preferred because cancellous grafts are rapidly resorbed and replaced by dysplastic tissue.

Question 6

A 65-year-old man is scheduled for prophylactic intramedullary nailing of a solitary, painful lytic lesion in the right humerus.

Biopsy confirmed metastatic renal cell carcinoma. To prevent a catastrophic intraoperative complication, what critical intervention should be performed 24 to 48 hours prior to surgery?

Explanation

Renal cell carcinoma and thyroid carcinoma bone metastases are notoriously hypervascular. Preoperative selective arterial embolization is critical to prevent massive, potentially fatal intraoperative hemorrhage.

Question 7

A 60-year-old woman with a 15-year history of primary synovial chondromatosis of the hip presents with acute worsening of pain and a rapidly enlarging soft tissue mass. Imaging reveals new cortical destruction and marrow invasion. What is the most likely diagnosis?

Explanation

While rare, primary synovial chondromatosis carries a small risk of malignant transformation into secondary chondrosarcoma. Rapid clinical deterioration, bone destruction, or marrow invasion on MRI should raise suspicion for this transformation.

Question 8

The pathogenesis of Charcot arthropathy is debated between the neurotraumatic and neurovascular theories. Which of the following best describes the fundamental mechanism proposed by the neurovascular theory?

Explanation

The neurovascular theory postulates that autonomic neuropathy abolishes sympathetic vasoconstriction, causing profound local hyperemia. This increased blood flow triggers active bone resorption, weakening the bone and predisposing the joint to collapse.

Question 9

A 35-year-old woman with polyostotic fibrous dysplasia

complains of a painless, deep-seated soft tissue mass in her right thigh. If this mass is associated with her skeletal condition, a biopsy would most likely reveal which of the following?

Explanation

Mazabraud syndrome is the rare but classic association of polyostotic fibrous dysplasia with single or multiple intramuscular myxomas. These benign soft-tissue tumors usually appear in the same anatomical region as the most severely affected bones.

Question 10

A patient is evaluated for surgical stabilization of an impending pathologic femur fracture due to metastatic disease. Among the following options, which primary tumor generally carries the most favorable long-term survival prognosis after bony metastasis?

Explanation

Among the common bone-metastasizing carcinomas, thyroid and breast cancer carry relatively favorable long-term prognoses even after skeletal dissemination. Conversely, lung and gastrointestinal primaries with bone metastases carry very poor survival rates.

Question 11

A diabetic patient presents with a warm, erythematous, and swollen midfoot. Radiographs demonstrate periarticular fragmentation, bony debris, and subluxation at the tarsometatarsal joints, but no signs of coalescence. According to the Eichenholtz classification, what is the stage and best initial management?

Explanation

The patient is in Eichenholtz Stage 1 (Developmental/Fragmentation), defined by profound swelling, erythema, bony debris, and subluxation. The standard of care is rigid immobilization with a total contact cast to arrest progression and prevent further deformity.

Question 12

When surgically managing an impending pathologic fracture of the femoral shaft due to metastatic breast cancer

, which biomechanical principle must guide the choice of implant?

Explanation

In the management of long bone metastases, intramedullary nails are preferred as they are load-sharing devices that protect the entire bone. This prevents subsequent failure if new metastatic lesions develop in the same bone.

Question 13

Which of the following is the primary pathophysiologic mechanism underlying primary synovial chondromatosis?

Explanation

Primary synovial chondromatosis is characterized by benign metaplasia of the synovial membrane, which forms cartilaginous nodules. These nodules can eventually detach, calcify, and become free-floating loose bodies within the joint space.

Question 14

A 45-year-old male with a long-standing history of recurrent synovial chondromatosis of the knee presents with sudden, rapidly increasing pain and swelling. MRI reveals a large soft tissue mass eroding into the distal femur. What is the most likely diagnosis?

Explanation

Malignant transformation of primary synovial chondromatosis to secondary chondrosarcoma is rare, occurring in about 5% of cases. It should be strongly suspected when there is rapid clinical deterioration, severe pain, or aggressive bone erosion.

Question 15

According to the Eichenholtz classification of Charcot arthropathy, which of the following radiographic findings is hallmark for the Coalescence stage (Stage 2)?

Explanation

Eichenholtz Stage 2 (Coalescence) is marked by the absorption of fine intra-articular debris, early fusion of larger bone fragments, and increased sclerosis. Stage 1 is characterized by fragmentation, while Stage 3 involves reconstruction and remodeling.

Question 16

The neurovascular theory of Charcot arthropathy suggests that autonomic neuropathy leads to which of the following physiological changes?

Explanation

The neurovascular theory postulates that autonomic neuropathy causes a loss of sympathetic tone, leading to uncontrolled vasodilation and hyperemia. This increased blood flow stimulates osteoclastic bone resorption, weakening the bone and making it susceptible to microtrauma.

Question 17

Fibrous dysplasia is caused by a somatic activating mutation in which of the following genes?

Explanation

Fibrous dysplasia results from a post-zygotic, somatic activating mutation in the GNAS1 gene. This leads to abnormally high intracellular cAMP levels, promoting the proliferation of pre-osteoblasts and replacing normal bone with fibrous tissue.

Question 18

When evaluating a patient with metastatic bone disease of the femur, which of the following factors would contribute the highest point value in Mirels' scoring system for prophylactic fixation?

Explanation

In Mirels' criteria, a lytic lesion scores the maximum 3 points for the 'radiographic appearance' category, whereas a mixed lesion scores 2, and a blastic lesion scores 1. A total score of 9 or greater strongly indicates the need for prophylactic internal fixation.

Question 19

Which histological feature helps differentiate primary synovial chondromatosis from secondary synovial chondromatosis?

Explanation

Primary synovial chondromatosis often exhibits hypercellularity, cellular atypia, pleomorphism, and binucleated chondrocytes, which can easily mimic a low-grade chondrosarcoma. Secondary chondromatosis typically shows mature cartilage with rings of ossification and lacks significant atypia.

Question 20

A diabetic patient presents with a hot, swollen, erythematous foot without an open ulceration. X-rays show acute periarticular fragmentation at the midfoot. What is the most appropriate initial management?

Explanation

The patient is in the acute fragmentation stage (Eichenholtz Stage 1) of Charcot arthropathy. The gold standard initial treatment is immediate immobilization with a total contact cast (TCC) and non-weight bearing to prevent further structural collapse.

Question 21

A 9-year-old girl presents with a limp and a shepherd's crook deformity of the proximal femur. She also has large, irregularly bordered hyperpigmented skin macules. What endocrine abnormality is most commonly associated with this syndrome?

Explanation

The presentation describes McCune-Albright syndrome, which consists of polyostotic fibrous dysplasia, café-au-lait spots (Coast of Maine borders), and hyperfunctioning endocrinopathies. Precocious puberty is the most common endocrine manifestation.

Question 22

A 65-year-old male presents with a purely blastic metastatic lesion in his lumbar spine. Which primary malignancy is the most likely source?

Explanation

Prostate cancer metastases to the bone are characteristically osteoblastic. In contrast, renal cell carcinoma, thyroid carcinoma, and multiple myeloma typically present with purely lytic bone lesions.

Question 23

Which joint is most frequently affected by primary synovial chondromatosis, and what is the typical patient demographic?

Explanation

Primary synovial chondromatosis most commonly affects the knee joint (accounting for over 50% of cases). It typically presents in males during their 3rd to 5th decades of life.

Question 24

Which imaging modality or technique is most specific for differentiating an acute Charcot neuroarthropathy from pedal osteomyelitis in a diabetic foot with an overlying ulcer?

Explanation

Differentiating acute Charcot arthropathy from osteomyelitis is notoriously difficult on MRI due to overlapping edema patterns. A combined WBC (Indium-111) and bone marrow (Tc-99m sulfur colloid) scan provides the highest specificity for diagnosing superimposed osteomyelitis.

Question 25

A routine radiograph of a 25-year-old patient reveals an expansile, intramedullary lesion in the proximal femur with a hazy, 'ground-glass' appearance and endosteal scalloping. What is the recommended surgical management if the lesion is completely asymptomatic and structurally stable?

Explanation

Asymptomatic, structurally stable fibrous dysplasia lesions are typically managed with observation. Curettage and grafting generally fail because the graft is resorbed and rapidly replaced by dysplastic host tissue.

Question 26

A patient with a known history of renal cell carcinoma requires intramedullary nailing for an impending pathologic fracture of the femur. Which preoperative intervention is strongly recommended?

Explanation

Metastatic bone lesions from renal cell and thyroid carcinomas are extremely vascular. Preoperative selective arterial embolization 24-48 hours before surgery is highly recommended to minimize massive, potentially life-threatening intraoperative blood loss.

Question 27

What is the surgical treatment of choice for symptomatic primary synovial chondromatosis of the knee to minimize the risk of recurrence?

Explanation

Removal of loose bodies alone is associated with a high recurrence rate. Combining loose body removal with an extensive synovectomy removes the metaplastic source tissue, significantly reducing the likelihood of recurrence.

Question 28

In a patient with established Charcot arthropathy of the foot and ankle, which of the following is the most widely accepted indication for surgical reconstruction or arthrodesis?

Explanation

Surgery for Charcot arthropathy is primarily indicated for patients with severe, unstable, or unbraceable deformities that lead to recurrent ulceration. It is typically deferred until the chronic or coalescent stages (Stage 2 or 3) to minimize failure rates.

Question 29

Which pharmacological agent has shown efficacy in reducing bone pain and potentially decreasing the rate of abnormal bone turnover in patients with polyostotic fibrous dysplasia?

Explanation

Intravenous bisphosphonates (such as pamidronate or zoledronic acid) are widely utilized in symptomatic polyostotic fibrous dysplasia. They effectively reduce bone pain and inhibit osteoclastic resorption at the dysplastic sites.

Question 30

Which of the following factors is considered in the Spinal Instability Neoplastic Score (SINS) to determine the need for surgical stabilization in spinal metastases?

Explanation

The SINS criteria evaluate six parameters: spinal location, pain (mechanical vs non-mechanical), bone lesion type (lytic/blastic), radiographic spinal alignment, vertebral body collapse, and posterolateral involvement. Mechanical pain is heavily weighted as a marker of instability.

Question 31

A 12-year-old girl presents with a persistent limp. Radiographs demonstrate an expansile proximal femur lesion with a "ground-glass" appearance.

What is the underlying molecular pathogenesis of this condition?

Explanation

Fibrous dysplasia is caused by a somatic, activating missense mutation in the GNAS gene. This leads to increased intracellular cAMP, causing abnormal proliferation and differentiation of osteoblasts. The characteristic radiographic finding is a "ground-glass" matrix.

Question 32

A 40-year-old male presents with mechanical knee pain, clicking, and intermittent locking. MRI shows multiple intra-articular loose bodies of uniform size with a "ring and arc" enhancement pattern. What is the primary histological process driving this condition?

Explanation

Primary synovial chondromatosis involves the benign metaplasia of synovial lining cells into hyaline cartilage nodules. These nodules can detach to form loose bodies that may subsequently calcify or ossify. Unlike secondary chondromatosis, the loose bodies in the primary form are typically uniform in size.

Question 33

A 62-year-old female with known breast cancer presents with moderate thigh pain. Radiographs reveal a lytic lesion in the femoral diaphysis involving 75% of the cortical diameter.

According to Mirels' criteria, what is her score and the most appropriate recommendation?

Explanation

The Mirels score dictates fracture risk based on site, pain, lesion type, and size. Lower extremity (2), moderate pain (2), lytic nature (3), and size >2/3 cortex (3) yields a score of 10. A score of 9 or greater is a strong indication for prophylactic fixation.

Question 34

A 55-year-old diabetic male presents with a swollen, erythematous, and warm foot without skin ulceration. Radiographs show extensive bone fragmentation, periarticular debris, and joint subluxation. Which stage of the Eichenholtz classification does this represent, and what is the primary initial treatment?

Explanation

Eichenholtz Stage I (Developmental/Fragmentation) is characterized by acute inflammation, osteopenia, bone fragmentation, and subluxation. The mainstay of initial treatment is immobilization and offloading, typically utilizing a total contact cast (TCC).

Question 35

A 35-year-old female with known polyostotic fibrous dysplasia presents with a painless, deep-seated soft tissue mass in her right thigh.

Excisional biopsy of the mass reveals an intramuscular myxoma. Which syndrome is this patient exhibiting?

Explanation

Mazabraud syndrome is a rare condition characterized by the association of fibrous dysplasia (usually polyostotic) with single or multiple intramuscular myxomas. The myxomas typically occur in the same anatomic region as the bony lesions.

Question 36

A 68-year-old male with a history of renal cell carcinoma presents with a solitary lytic metastasis in the proximal humerus and an impending fracture.

What is an essential step prior to surgical stabilization of this lesion?

Explanation

Metastases from renal cell carcinoma and thyroid carcinoma are notoriously hypervascular. Preoperative selective arterial embolization within 24 to 48 hours of surgery is critical to minimize massive intraoperative blood loss.

Question 37

The pathogenesis of Charcot arthropathy involves multiple factors. The 'French theory' of Charcot pathogenesis specifically emphasizes which of the following mechanisms?

Explanation

The French (neurovascular) theory proposes that autonomic neuropathy leads to loss of sympathetic tone, causing hyperemia and active bone resorption (osteopenia), making the bone susceptible to injury. The German (neurotraumatic) theory focuses on unperceived repetitive microtrauma.

Question 38

A 50-year-old male with a long-standing history of primary synovial chondromatosis of the hip presents with acute worsening of pain and rapid joint swelling. MRI demonstrates a new, aggressive soft tissue mass with marrow invasion. What is the most likely diagnosis?

Explanation

Malignant transformation of primary synovial chondromatosis into secondary chondrosarcoma occurs in approximately 5% of cases. Rapid clinical deterioration, new aggressive mass, and marrow invasion on MRI are highly suspicious for this transformation.

Question 39

A 72-year-old male presents with severe back pain. Radiographs show multiple dense, blastic lesions in the lumbar spine and pelvis.

Which of the following combinations of tumor marker and primary cellular mechanism is characteristic of this malignancy?

Explanation

Prostate cancer classically produces osteoblastic bone metastases. Prostate cancer cells secrete factors such as endothelin-1 (ET-1), which directly stimulate osteoblast proliferation and bone formation, leading to blastic lesions. PSA is the classic tumor marker.

Question 40

A 22-year-old male with polyostotic fibrous dysplasia presents with a severe Shepherd's crook deformity of the proximal femur.

When planning corrective osteotomy and fixation, which biomechanical principle is most critical to prevent mechanical failure?

Explanation

In the surgical treatment of fibrous dysplasia deformities (like Shepherd's crook), intramedullary nailing spanning the entire length of the bone is required. Plates and screws have an unacceptably high failure rate because the abnormal host bone cannot adequately hold screws or share loads.

Question 41

Which of the following best describes the underlying molecular pathophysiology of fibrous dysplasia?

Explanation

Fibrous dysplasia is caused by a post-zygotic somatic activating mutation in the GNAS gene, which encodes the alpha subunit of the Gs stimulatory protein. This leads to increased intracellular cAMP, causing abnormal proliferation and differentiation of osteoblasts.

Question 42

A 45-year-old male with a long-standing history of primary synovial chondromatosis of the hip presents with acutely worsening pain and rapid swelling. Radiographs show new cortical erosion and marrow involvement. Which of the following is the most likely diagnosis?

Explanation

Primary synovial chondromatosis carries a rare but recognized risk (1-5%) of malignant transformation to secondary chondrosarcoma. Clinical clues include rapid worsening of symptoms, marrow invasion, and new cortical erosion on imaging.

Question 43

A diabetic patient presents with a red, hot, swollen foot. Radiographs show joint debris, fragmentation of subchondral bone, and subluxation, but no signs of consolidation. According to the Eichenholtz classification, what is the most appropriate initial management?

Explanation

The patient is in Eichenholtz Stage 1 (Development/Fragmentation) of Charcot arthropathy, characterized by a red, hot, swollen joint with bony fragmentation. The gold standard treatment in the acute active phase is immobilization with a total contact cast to prevent further deformity, as surgery carries an unacceptable risk of hardware failure.

Question 44

When evaluating a patient with a metastatic lesion to the long bone, the Mirels' scoring system is used to predict the risk of pathologic fracture. Which of the following combinations yields the highest score (3 points) for each respective category?

Explanation

Mirels' criteria assign 3 points for: peritrochanteric location, functional (mechanical) pain, purely lytic nature, and size >2/3 of the cortical diameter. A total score of 9 or greater is a strong indication for prophylactic surgical fixation.

Question 45

A 9-year-old girl presents with a limp and a history of early-onset puberty. Radiographs reveal multiple expansile ground-glass lesions in the femur and tibia. Physical exam notes large, irregular hyperpigmented skin macules. What is the classic term for these skin lesions?

Explanation

The patient has McCune-Albright syndrome, characterized by the triad of polyostotic fibrous dysplasia, precocious puberty, and cafe-au-lait spots. The cafe-au-lait spots in this syndrome have irregular borders, classically described as the 'Coast of Maine', unlike the smooth 'Coast of California' spots seen in neurofibromatosis.

Question 46

Primary synovial chondromatosis is fundamentally a disease driven by which of the following pathophysiological processes?

Explanation

Primary synovial chondromatosis is a benign neoplastic process characterized by cartilaginous metaplasia of the synovial membrane. The metaplastic tissue forms nodular hyaline cartilage masses that can detach and become loose bodies within the joint space.

Question 47

A 62-year-old male presents with a purely lytic impending pathologic fracture of the proximal femur secondary to metastatic renal cell carcinoma. Before proceeding with prophylactic intramedullary nailing, what critical step should be taken to minimize perioperative complications?

Explanation

Renal cell carcinoma and thyroid carcinoma bone metastases are notoriously hypervascular. Preoperative selective arterial embolization is highly recommended 24 to 48 hours prior to surgery to minimize life-threatening intraoperative hemorrhage.

Question 48

The "neurovascular theory" of Charcot neuropathic arthropathy pathogenesis primarily implicates which of the following mechanisms?

Explanation

The neurovascular theory suggests that autonomic neuropathy causes a loss of sympathetic vascular tone, leading to continuous arteriovenous shunting and local hyperemia. This increased localized blood flow stimulates osteoclastic resorption, making the bone osteopenic and susceptible to fragmentation.

Question 49

A 25-year-old patient with polyostotic fibrous dysplasia presents with increasing hip pain and a progressive varus deformity of the proximal femur. What is the most appropriate surgical management for this characteristic "shepherd's crook" deformity?

Explanation

The shepherd's crook deformity in fibrous dysplasia requires correction of the mechanical axis via a valgus osteotomy, followed by load-sharing intramedullary fixation to bypass the entire abnormal bone segment. Cancellous bone grafts should be avoided as they resorb and are rapidly replaced by dysplastic host bone.

Question 50

A 55-year-old female with a history of breast cancer presents with severe thoracic back pain. Imaging demonstrates a blastic and lytic lesion at T8 with posterior element involvement but no spinal cord compression. In addition to localized radiation, what pharmacological agent is indicated to reduce skeletal-related events?

Explanation

In patients with bone metastases from breast cancer, antiresorptive agents such as bisphosphonates (e.g., zoledronic acid) or RANKL inhibitors (e.g., denosumab) are indicated to reduce the risk of skeletal-related events. Teriparatide is strictly contraindicated in patients with skeletal malignancies.

Question 51

Differentiating primary from secondary synovial chondromatosis on imaging can sometimes be challenging. Which of the following features is most characteristic of PRIMARY synovial chondromatosis?

Explanation

Primary synovial chondromatosis typically presents with innumerable loose bodies that are relatively uniform in size and shape within an otherwise normal joint. Secondary synovial chondromatosis features fewer, variably sized loose bodies and is associated with significant pre-existing degenerative joint disease.

Question 52

A 42-year-old male presents with chronic knee pain and mechanical catching. Radiographs demonstrate multiple radiopaque bodies within the joint space. MRI reveals a large effusion with numerous uniform-sized, intra-articular nodules. Which of the following best describes the pathophysiology of this condition?

Explanation

Primary synovial chondromatosis is a benign neoplastic process characterized by hyaline cartilage metaplasia within the synovial membrane. Unlike secondary chondromatosis (caused by trauma or osteoarthritis), the loose bodies in the primary form are typically uniform in size.

Question 53

A 45-year-old man with a known history of primary synovial chondromatosis of the hip presents with sudden, rapidly progressive pain and a new palpable mass. Plain radiographs demonstrate cortical destruction and extension into the surrounding soft tissues. Which of the following is the most reliable histologic indicator of malignant transformation in this condition?

Explanation

Malignant transformation of primary synovial chondromatosis to chondrosarcoma is rare. Because primary synovial chondromatosis naturally exhibits cellular atypia, binucleation, and hypercellularity, marrow invasion remains the most reliable hallmark of malignant transformation.

Question 54

Primary synovial chondromatosis is a benign neoplastic process rather than a purely reactive metaplasia. Which of the following cytogenetic abnormalities is most frequently associated with the primary form of this disease?

Explanation

Primary synovial chondromatosis is a benign clonal neoplasm often associated with chromosome 6p21 abnormalities or FN1-ACVR2A gene fusions. The other options refer to Ewing sarcoma, synovial sarcoma, myxoid liposarcoma, and fibrous dysplasia, respectively.

Question 55

A 35-year-old woman presents with a 2-year history of episodic knee pain and mechanical catching. MRI reveals a large joint effusion with multiple intra-articular nodules that are isointense to muscle on T1-weighted images and hyperintense on T2-weighted images, but show no mineralization on plain radiographs. What is the most appropriate management for the primary underlying pathology?

Explanation

The patient has synovial chondromatosis prior to the calcification phase. Treatment of choice is complete removal of loose bodies along with anterior and posterior synovectomy to minimize the recurrence rate, which is about 10-20 percent.

Question 56

A 55-year-old man with poorly controlled type 2 diabetes presents with a red, hot, swollen right foot. He denies fevers or chills. Plain radiographs show early fragmentation of the tarsometatarsal joints without frank dislocation. Elevating the leg for 10 minutes leads to a significant decrease in erythema. What is the most appropriate next step in management?

Explanation

This patient is in Stage 1 (development/fragmentation) of a Charcot arthropathy. The loss of erythema upon elevation differentiates it from infection; the standard of care is immediate immobilization with a total contact cast and strict offloading.

Question 57

Differentiating between acute Charcot arthropathy and osteomyelitis in a diabetic foot can be challenging. Which of the following imaging modalities or combinations provides the highest specificity for diagnosing superimposed osteomyelitis in a patient with an active midfoot Charcot joint?

Explanation

A combined tagged white blood cell scan and sulfur colloid marrow scan is the most specific non-invasive test to differentiate osteomyelitis from Charcot neuroarthropathy. Concordant uptake indicates normal reactive marrow, whereas discordant uptake (WBCs present without marrow) indicates infection.

Question 58

The pathogenesis of Charcot neuroarthropathy is multifactorial, involving both neurotraumatic and neurovascular pathways. Which of the following best describes the neurovascular theory (French theory) of this disease?

Explanation

The neurovascular (French) theory postulates that autonomic neuropathy abolishes sympathetic tone, causing arteriovenous shunting and local hyperemia. This increased blood flow stimulates osteoclastic bone resorption, predisposing the structurally weakened bone to fracture.

Question 59

A 14-year-old boy presents with progressive bowing and pain in his right femur. Radiographs display an expansile ground-glass lesion in the diaphysis. Biopsy confirms fibrous dysplasia. What is the precise genetic etiology of this condition?

Explanation

Fibrous dysplasia is caused by a post-zygotic somatic activating mutation in the GNAS gene. This leads to constitutive activation of the Gs-alpha protein and increased intracellular cAMP, disrupting normal osteoblast differentiation.

Question 60

A 65-year-old man with a history of radical nephrectomy presents with severe right thigh pain. Radiographs reveal a large, impending pathologic fracture of the proximal femur due to a lytic lesion. What is the most critical intervention to perform prior to intramedullary nailing?

Explanation

Metastatic renal cell carcinoma lesions are notoriously hypervascular. Preoperative angiography and embolization are highly recommended to minimize life-threatening intraoperative hemorrhage during internal fixation.

Question 61

A 55-year-old diabetic male presents with an acutely swollen, erythematous, and warm right foot. He is afebrile and his pedal pulses are bounding. Radiographs show soft tissue swelling and early bony fragmentation of the midfoot without ulceration. What is the best initial management?

Explanation

This patient presents with Stage I (Fragmentation) Charcot arthropathy. The primary treatment in the acute phase is strict immobilization and off-loading, best achieved with a total contact cast, to prevent further deformity.

Question 62

Which radiographic feature is most characteristic for differentiating primary synovial chondromatosis from secondary synovial chondromatosis?

Explanation

Primary synovial chondromatosis is a metaplastic process producing numerous cartilaginous loose bodies of uniform size. Secondary synovial chondromatosis results from fragmented osteophytes in severe osteoarthritis, producing loose bodies of variable sizes.

Question 63

A 25-year-old woman with known fibrous dysplasia presents with increasing thigh pain and a progressive shepherd's crook deformity. What is the most appropriate surgical management to address her symptoms and deformity?

Explanation

Surgical management of a shepherd's crook deformity involves valgus producing osteotomies stabilized with intramedullary nailing. Plate fixation is prone to failure due to the poor quality of dysplastic bone, and cancellous bone grafts are rapidly resorbed.

Question 64

A 50-year-old woman with metastatic breast cancer presents with a newly discovered lytic lesion in the peritrochanteric region of her femur. The lesion involves 50% of the cortical diameter. She reports severe pain with weight-bearing. What is her Mirels' score?

Explanation

Mirels' criteria scores: Site (Peritrochanteric = 3), Pain (Severe = 3), Lesion type (Lytic = 3), and Size (1/3 to 2/3 = 2). The total score is 3+3+3+2 = 11, indicating a high risk of fracture requiring prophylactic fixation.

Question 65

A 42-year-old man presents with painless, massive swelling and crepitus of his right shoulder. Radiographs demonstrate severe destruction of the humeral head and glenoid with multiple bony fragments. Which underlying condition is most likely responsible?

Explanation

Charcot arthropathy of the upper extremity, particularly the shoulder, is classically associated with syringomyelia. Diabetes usually affects the foot and ankle, while Tabes dorsalis typically involves the lower extremity joints like the knee.

Question 66

A 50-year-old man with long-standing primary synovial chondromatosis of the hip presents with rapid worsening of pain and swelling. MRI reveals a new, large soft tissue mass invading the adjacent marrow cavity with cortical destruction. What is the most likely diagnosis?

Explanation

Primary synovial chondromatosis carries a rare but documented risk (approx 5%) of malignant transformation into secondary chondrosarcoma. Rapid progression and marrow invasion are classic radiologic signs of this transformation.

Question 67

A 35-year-old female is diagnosed with polyostotic fibrous dysplasia. During her workup, an MRI of her thigh unexpectedly reveals multiple well-circumscribed, T2-hyperintense soft tissue masses within her skeletal muscle. What is the correct diagnosis for this presentation?

Explanation

Mazabraud syndrome is the rare combination of polyostotic fibrous dysplasia and multiple intramuscular myxomas. The myxomas are typically benign and appear hyperintense on T2-weighted MRI.

Question 68

A 72-year-old man with metastatic prostate cancer has multiple dense, osteoblastic lesions in his lumbar spine and pelvis. Which of the following factors, secreted by the tumor cells, is primarily responsible for the osteoblastic nature of these metastases?

Explanation

Prostate cancer metastases are classically osteoblastic. This is primarily mediated by the secretion of Endothelin-1, which stimulates osteoblast proliferation and bone formation.

Question 69

According to the neurovascular theory of Charcot arthropathy, which mechanism directly contributes to bone resorption and subsequent joint destruction?

Explanation

The neurovascular theory postulates that autonomic neuropathy leads to sympathetic denervation, causing loss of vasomotor control and hyperemia. The increased blood flow washes out bone minerals and activates osteoclasts.

Question 70

Which classic histologic feature clearly distinguishes fibrous dysplasia from normal bone and other reactive fibro-osseous lesions?

Explanation

Fibrous dysplasia is histologically characterized by irregular, "Chinese character" shaped trabeculae of woven bone that arise directly from a fibrous stroma without normal osteoblastic rimming.

Question 71

A 60-year-old woman presents with a destructive humeral diaphyseal lesion. Biopsy confirms metastatic follicular thyroid carcinoma. What defines the most appropriate operative strategy for this patient?

Explanation

Metastatic thyroid carcinoma is highly vascular. Preoperative embolization is heavily recommended to limit intraoperative blood loss prior to stabilization, which is best achieved with intramedullary nailing in diaphyseal lesions.

Question 72

Primary synovial chondromatosis is considered a benign neoplastic process. Which of the following genetic fusions or chromosomal abnormalities is frequently implicated in its pathogenesis?

Explanation

Primary synovial chondromatosis has been shown to harbor recurrent FN1-ACVR2A fusions and abnormalities in chromosome 6p21, confirming it as a benign neoplastic process rather than simply a reactive metaplasia.

Question 73

A 24-year-old with polyostotic fibrous dysplasia presents with a progressively painful Shepherd's crook deformity of the proximal femur.

If surgical intervention is elected to correct the deformity and prevent fracture, which of the following is the most appropriate biomechanical and biological strategy?

Explanation

Fibrous dysplasia replaces normal bone with weak woven bone. Cancellous bone grafts are consistently resorbed by the host dysplastic tissue, so cortical allografts or intramedullary devices spanning the entire bone are required for durable fixation.

Question 74

A 45-year-old male with a long-standing history of primary synovial chondromatosis of the hip presents with acute worsening of pain and a rapidly enlarging mass. Which of the following is the most reliable histologic or clinical indicator of malignant transformation to secondary chondrosarcoma in this specific setting?

Explanation

Primary synovial chondromatosis inherently demonstrates significant cellular atypia and binucleate cells, mimicking malignancy. Therefore, true tissue invasion into the marrow or surrounding structures is the most reliable criterion for diagnosing malignant transformation to chondrosarcoma.

Question 75

A 55-year-old diabetic patient presents with a warm, swollen, erythematous foot. Radiographs show periarticular debris, fragmentation, and joint subluxation. According to the Eichenholtz classification, what is the current stage of this neuropathic arthropathy and the corresponding initial management?

Explanation

Eichenholtz Stage 1 (Development) is characterized by acute inflammation, osteopenia, fragmentation, and debris. The cornerstone of treatment is immobilization, typically with a total contact cast, to prevent further deformity until the acute inflammatory phase resolves.

Question 76

A 62-year-old man presents with a pathologic fracture of the proximal humerus secondary to a metastatic renal cell carcinoma lesion.

Prior to surgical stabilization, which of the following interventions is most strongly recommended to minimize intraoperative morbidity?

Explanation

Bone metastases from renal cell carcinoma and thyroid cancer are highly vascular. Preoperative selective arterial embolization (typically 24-48 hours before surgery) is strongly recommended to significantly reduce the risk of massive, life-threatening intraoperative hemorrhage.

Question 77

A 9-year-old girl is evaluated for precocious puberty and café-au-lait spots with irregular "coast of Maine" borders. Radiographs of her lower extremities demonstrate multiple lucent, ground-glass bone lesions.

Which of the following best describes the underlying genetic anomaly in this patient?

Explanation

This patient presents with McCune-Albright syndrome (polyostotic fibrous dysplasia, endocrinopathy, café-au-lait spots). It is caused by a post-zygotic somatic missense mutation in the GNAS gene; a germline mutation of this gene is lethal.

Question 78

Differentiating between acute Charcot neuroarthropathy and osteomyelitis in a diabetic foot can be challenging. Which of the following MRI findings is most specific for diagnosing osteomyelitis over acute Charcot arthropathy?

Explanation

Both acute Charcot and osteomyelitis present with prominent bone marrow edema and soft tissue swelling on MRI. However, the presence of a sinus tract, replacement of subchondral fat (ghost sign), and adjacent ulceration are highly specific for osteomyelitis.

Question 79

A 72-year-old man presents with severe back pain. Radiographs reveal multiple osteoblastic lesions in the lumbar spine and pelvis. Laboratory studies show elevated alkaline phosphatase. Which of the following pathophysiologic mechanisms best explains the osteoblastic nature of these specific metastatic bone lesions?

Explanation

Prostate cancer metastases are classically osteoblastic. This occurs because prostate carcinoma cells secrete factors such as endothelin-1 (ET-1) and bone morphogenetic proteins (BMPs), which directly stimulate osteoblast proliferation and bone formation.

Question 80

A 38-year-old woman undergoes arthroscopic removal of dozens of uniformly sized cartilaginous loose bodies from her knee for primary synovial chondromatosis. To minimize the risk of disease recurrence, which of the following additional intraoperative steps is strictly indicated?

Explanation

Primary synovial chondromatosis involves metaplasia of the synovium. Removal of the loose bodies alone is insufficient and carries a high recurrence rate; therefore, a thorough synovectomy is required to remove the diseased tissue and minimize recurrence.

Question 81

A 35-year-old woman with known polyostotic fibrous dysplasia presents with a painless, deep-seated soft tissue mass in her right thigh. Biopsy of the mass reveals an intramuscular myxoma. This patient is at an increased risk of developing which of the following?

Explanation

Mazabraud syndrome is the rare association of polyostotic fibrous dysplasia with intramuscular myxomas. These patients have a significantly higher risk of malignant transformation of their bone lesions, most commonly to osteosarcoma.

Question 82

A 65-year-old man presents with a pathologic fracture of the proximal humerus. Workup reveals a solitary large, destructive lytic lesion. Biopsy confirms metastatic clear cell renal cell carcinoma. What is the most critical step prior to operative stabilization?

Explanation

Renal cell carcinoma and thyroid carcinoma bone metastases are highly vascular. Preoperative angiographic embolization 24-48 hours before surgery is critical to minimize life-threatening intraoperative blood loss.

Question 83

A 55-year-old man with long-standing, poorly controlled diabetes presents with a swollen, erythematous, and warm left foot. He denies pain or recent trauma. Radiographs show osseous fragmentation, joint subluxation, and debris around the midfoot. What is the most appropriate initial management?

Explanation

The patient is in Eichenholtz Stage I (developmental/fragmentation) of Charcot arthropathy. The gold standard treatment is immobilization in a total contact cast and strict non-weight-bearing to prevent further deformity while the acute inflammation subsides.

Question 84

A 40-year-old man with a 10-year history of recurrent primary synovial chondromatosis of the hip presents with a sudden, rapid increase in pain and joint swelling. Imaging shows a large new soft tissue mass with 'ring and arc' calcifications invading the surrounding acetabulum. What is the most likely diagnosis?

Explanation

Primary synovial chondromatosis carries a small but documented risk (1-5%) of malignant transformation into secondary chondrosarcoma. A sudden increase in symptoms, rapidly expanding soft tissue mass, and marrow invasion on MRI are highly suspicious for this complication.

Question 85

A 55-year-old woman with metastatic breast cancer presents with mild hip pain. Radiographs reveal a lytic lesion involving 75% of the cortex in the peritrochanteric region of the right femur. According to Mirels' criteria, what is her score and recommended treatment?

Explanation

Mirels score calculation: Site (Peritrochanteric = 3), Nature (Lytic = 3), Size (>2/3 cortex = 3), Pain (Mild = 1). Total score = 10. A score of 9 or greater is an absolute indication for prophylactic internal fixation.

Question 86

A biopsy of a ground-glass rib lesion in a 14-year-old boy reveals fibrous stroma with irregular, woven bone trabeculae lacking osteoblastic rimming. The pathogenesis of this disease is linked to a somatic mutation leading to the substitution of arginine by histidine or cysteine. Which signaling pathway is directly upregulated by this mutation?

Explanation

Fibrous dysplasia is caused by a somatic activating mutation in the GNAS gene, which encodes the alpha subunit of the Gs stimulatory protein. This mutation leads to constitutive activation of adenylyl cyclase, drastically increasing intracellular cAMP levels and downstream Protein Kinase A activity.

Question 87

Which of the following best describes the 'neurovascular theory' in the pathogenesis of Charcot neuropathic arthropathy?

Explanation

The neurovascular theory posits that autonomic neuropathy leads to a loss of sympathetic tone and subsequent vasodilation. The resulting hyperemia increases osteoclastic activity, leading to bone resorption, osteopenia, and structural collapse.

Question 88

A 62-year-old woman undergoes intramedullary nailing for a pathologic fracture of the femur secondary to metastatic follicular thyroid carcinoma. Following surgical stabilization and appropriate wound healing, what is the preferred adjuvant treatment to specifically address the remaining microscopic disease at the bone metastasis site?

Explanation

Differentiated thyroid cancers (follicular and papillary) are unique in that their bone metastases often retain the ability to concentrate iodine. Radioactive iodine (I-131) ablation is the preferred adjuvant treatment to target the metastatic deposits, improving both local control and survival.

Orthopaedic Surgery Board Exam Review: ABOS Part I & AAOS OITE Prep Questions | Part 22210

Orthopaedic Board Review: Synovial Chondromatosis, Charcot Joint, Fibrous Dysplasia, Bone Metastases | Part 21

Key Takeaway

Orthopaedic Board Review: Synovial Chondromatosis, Charcot Joint, Fibrous Dysplasia, Bone Metastases | Part 21

Chapter Index