Question 1

A 55-year-old male with long-standing ankylosing spondylitis presents with new-onset neck pain after a minor low-energy fall. His neurological exam is currently intact, and initial cervical radiographs are unrevealing.

What is the most appropriate next step in management?

Explanation

Patients with ankylosing spondylitis have a highly rigid spine, making them susceptible to unstable fractures even from minor trauma. A CT scan is the standard of care for initial evaluation as plain radiographs frequently miss these fractures due to altered anatomy and osteopenia.

Question 2

A 45-year-old man with a history of ankylosing spondylitis presents to the emergency department after a low-energy fall. He reports new-onset neck pain but no neurologic deficits. Radiographs demonstrate an undisplaced fracture through the C5-C6 disc space. What is the most appropriate management?

Explanation

Fractures in ankylosing spondylitis are often highly unstable 'chalk-stick' fractures that can displace catastrophically. They require rigid stabilization, typically with long-segment posterior instrumentation, even if initially undisplaced.

Question 3

Synovial chondromatosis is a benign nodular condition characterized by which of the following pathophysiologic mechanisms?

Explanation

Primary synovial chondromatosis results from benign cartilaginous metaplasia of the subintimal mesenchymal cells in the synovium. These foci can subsequently calcify, ossify, and break off to form loose bodies.

Question 4

A 55-year-old woman presents with a deep thigh mass. MRI reveals a large, predominantly lipomatous tumor with thickened, nodular septa. Biopsy shows mature adipocytes with focal hyperchromatic, atypical stromal cells. Which genetic alteration is most specific for this diagnosis?

Explanation

Atypical lipomatous tumors (ALT) and well-differentiated liposarcomas (WDLPS) share the hallmark MDM2 gene amplification on chromosome 12q13-15. This distinguishes them from benign lipomas, which often have 12q13-15 rearrangements but lack MDM2 amplification.

Question 5

An 18-year-old male with multiple hereditary exostoses (MHE) is evaluated. He has multiple bony prominences around his knees and ankles. The genetic mutation associated with this condition primarily affects the synthesis of which of the following?

Explanation

MHE is an autosomal dominant disorder caused by mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for the biosynthesis of heparan sulfate, which regulates chondrocyte proliferation and differentiation.

Question 6

A 35-year-old male with advanced ankylosing spondylitis presents with progressive chin-on-chest deformity impairing his horizontal gaze. Preoperative evaluation determines that an extension osteotomy of the cervical spine is necessary. At which anatomical level is this osteotomy most safely and commonly performed?

Explanation

Cervicothoracic extension osteotomies for correcting chin-on-chest deformity in AS are most safely performed at the C7-T1 level. This location has a wider spinal canal, which lowers the risk of spinal cord injury, and avoids the vertebral artery, which typically enters the transverse foramen at C6.

Question 7

A 42-year-old man presents with chronic knee pain and mechanical symptoms. Radiographs show multiple intra-articular calcific bodies of uniform size. What is the most appropriate management for symptomatic primary synovial chondromatosis of the knee?

Explanation

The standard of care for symptomatic primary synovial chondromatosis without severe secondary osteoarthritis is complete removal of the loose bodies combined with synovectomy to reduce the risk of recurrence.

Question 8

A 62-year-old male with a 30-year history of ankylosing spondylitis presents to the emergency department with severe neck pain following a ground-level fall.

Given the rigid nature of his spine, what is the most common and characteristic cervical fracture pattern seen in this patient population?

Explanation

Due to extensive ossification and altered biomechanics, the spine in ankylosing spondylitis acts as a long, rigid lever arm. Ground-level falls typically cause highly unstable hyperextension injuries that shear across the disc space or vertebral body.

Question 9

A 34-year-old male with confirmed ankylosing spondylitis has persistent axial pain and morning stiffness despite maximum continuous therapy with two different nonsteroidal anti-inflammatory drugs (NSAIDs) for three months. What is the most appropriate next step in medical management?

Explanation

TNF-alpha inhibitors (e.g., etanercept, infliximab) are the established first-line biologic therapy for axial ankylosing spondylitis in patients who have failed or are intolerant to NSAIDs. Traditional disease-modifying antirheumatic drugs (DMARDs) like methotrexate lack efficacy for isolated axial disease.

Question 10

Which of the following best describes the fundamental pathogenesis underlying primary synovial chondromatosis?

Explanation

Primary synovial chondromatosis is a benign neoplastic process characterized by cartilaginous metaplasia of the synovial membrane. This contrasts with secondary synovial chondromatosis, which results from mechanical fragmentation in degenerative joint disease.

Question 11

Multiple Hereditary Exostoses (MHE) is characterized by multiple osteochondromas throughout the skeleton. Mutations in the EXT1 and EXT2 genes are causative. What is the primary molecular function impaired by these mutations?

Explanation

EXT1 and EXT2 encode glycosyltransferases essential for the synthesis of heparan sulfate. Defective heparan sulfate synthesis disrupts normal physeal signaling, leading to abnormal cartilage proliferation and osteochondroma formation.

Question 12

A 55-year-old male presents with a large, slow-growing, deep soft tissue mass in his posterior thigh. Histopathology demonstrates mature adipocytes with focal variation in cell size and hyperchromatic stromal cells.

Which molecular finding specifically differentiates an Atypical Lipomatous Tumor (ALT) from a benign lipoma?

Explanation

Atypical lipomatous tumors (ALTs) are characterized by supernumerary ring or giant rod chromosomes leading to the amplification of the 12q13-15 region, which contains the MDM2 and CDK4 genes. Benign lipomas do not exhibit this amplification.

Question 13

Patients with advanced ankylosing spondylitis undergoing total hip arthroplasty (THA) are at a significantly higher risk for which of the following postoperative complications compared to patients with primary osteoarthritis?

Explanation

Patients with ankylosing spondylitis have a strong systemic tendency for new bone formation, placing them at a significantly elevated risk for severe heterotopic ossification following THA. Prophylaxis with NSAIDs or radiation is strongly recommended.

Question 14

An 18-year-old male with a known solitary osteochondroma of the proximal tibia presents with increasing localized pain and recent growth of the lesion over the past 6 months. MRI reveals a cartilage cap measuring 2.8 cm in thickness.

What is the most likely diagnosis?

Explanation

In a skeletally mature individual, growth of an osteochondroma and a cartilage cap thicker than 1.5-2.0 cm are highly suspicious for malignant transformation to a secondary peripheral chondrosarcoma. Excision and histologic evaluation are warranted.

Question 15

A 45-year-old male with long-standing ankylosing spondylitis presents with localized, progressive mechanical back pain. Radiographs demonstrate a destructive discovertebral lesion with surrounding reactive sclerosis. Inflammatory markers are mildly elevated.

What is the most likely diagnosis?

Explanation

An Andersson lesion represents a localized discovertebral pseudarthrosis in the rigid ankylosed spine, usually secondary to an unrecognized fracture. It presents with mechanical pain and destructive radiographic changes that can mimic infection.

Question 16

Histologically, an Atypical Lipomatous Tumor (ALT) and a Well-Differentiated Liposarcoma (WDLPS) are identical. What is the primary criterion used to differentiate these two entities in nomenclature?

Explanation

The term ALT is used for extremity lesions because they do not metastasize and wide surgical margins are often obtainable. WDLPS is reserved for lesions in the retroperitoneum or mediastinum, where complete excision is difficult and uncontrolled local growth can be fatal.

Question 17

A 55-year-old patient with long-standing ankylosing spondylitis is scheduled for orthopedic surgery under general anesthesia. Which of the following represents the most critical anesthetic challenge in this patient?

Explanation

Ankylosing spondylitis results in a rigid, often kyphotic cervical spine and restricted temporomandibular joint mobility. This makes direct laryngoscopy and endotracheal intubation exceptionally difficult, often requiring awake fiberoptic intubation.

Question 18

A 40-year-old male with a history of recurrent primary synovial chondromatosis of the hip presents with rapid clinical deterioration, severe pain, and extensive bony destruction on imaging.

What is the most feared complication in this setting?

Explanation

Although primary synovial chondromatosis is benign, it carries a rare (approx. 5%) but well-documented risk of malignant transformation into secondary chondrosarcoma, particularly in cases with multiple recurrences and rapid clinical changes.

Question 19

Which of the following describes the characteristic forearm deformity frequently observed in patients with Multiple Hereditary Exostoses (MHE)?

Explanation

Osteochondromas frequently affect the distal ulna in MHE, causing relative growth arrest (ulnar shortening). The continuously growing radius becomes tethered, leading to radial bowing, radial head dislocation, and ulnar deviation of the hand.

Question 20

A 50-year-old male with ankylosing spondylitis presents with a severe chin-on-chest deformity, rendering him unable to look straight ahead. The primary kyphosis is located at the cervicothoracic junction. What is the surgical procedure of choice to correct this deformity?

Explanation

Fixed cervicothoracic kyphosis (chin-on-chest deformity) in ankylosing spondylitis is best addressed with a posterior opening wedge extension osteotomy, most commonly performed at the C7-T1 level due to the wider spinal canal and avoidance of the vertebral artery.

Question 21

An osteochondroma is defined as a cartilage-capped exostosis.

Which of the following imaging features is pathognomonic and strictly required for the diagnosis of an osteochondroma?

Explanation

The hallmark imaging finding that defines an osteochondroma, distinguishing it from other surface osseous lesions, is the direct continuity of its medullary cavity and cortical bone with those of the host bone.

Question 22

On a standard radiograph, the presence of multiple, uniform-sized, spherical calcified loose bodies within the joint capsule of the knee strongly suggests which of the following diagnoses?

Explanation

Primary synovial chondromatosis is characterized by the metaplasia of synovium leading to multiple intra-articular cartilaginous nodules that calcify. A key distinguishing feature from secondary synovial chondromatosis (due to osteoarthritis) is that the loose bodies in the primary form are numerous and uniform in size.

Question 23

A 45-year-old male with long-standing ankylosing spondylitis presents after a minor fall with severe neck pain. Radiographs reveal a fracture through the C6-C7 disc space extending through the posterior elements. What is the most appropriate management?

Explanation

Patients with ankylosing spondylitis are at high risk for unstable "chalk-stick" fractures even from minor trauma. These injuries are highly unstable and typically require long-segment posterior instrumentation and fusion, sometimes combined with anterior fixation.

Question 24

A 35-year-old male presents with chronic knee pain, swelling, and mechanical catching. Radiographs show multiple intra-articular calcified bodies of uniform size.

Which of the following is the underlying pathophysiology of this condition?

Explanation

Primary synovial chondromatosis involves the benign metaplastic transformation of synovial cells into chondrocytes. These form cartilaginous nodules that can detach and calcify or ossify within the joint space.

Question 25

A 16-year-old boy with multiple hereditary exostoses (MHE) is being evaluated. Which of the following characteristics is most suggestive of malignant transformation of an osteochondroma in an adult patient?

Explanation

Growth of an osteochondroma after skeletal maturity or a cartilage cap thickness greater than 2 cm in an adult is highly suspicious for malignant transformation to secondary chondrosarcoma. Pain and new neurovascular symptoms are also red flags.

Question 26

A 28-year-old male presents with alternating buttock pain and morning stiffness improving with activity. Radiographs reveal bilateral sacroiliitis.

Which of the following extra-articular manifestations is most commonly associated with this condition?

Explanation

Acute anterior uveitis is the most common extra-articular manifestation of ankylosing spondylitis, occurring in up to 25-30% of patients. Cardiac and pulmonary complications are less common.

Question 27

A 55-year-old male presents with a deep, slow-growing painless mass in his thigh. Biopsy reveals mature adipocytes with focal nuclear atypia and hyperchromatic stromal cells.

Which genetic abnormality is the hallmark of this lesion?

Explanation

Atypical lipomatous tumors (well-differentiated liposarcomas) are characterized by amplification of the MDM2 and CDK4 genes, usually on ring or giant rod chromosomes derived from chromosome 12. This distinguishes them from benign lipomas.

Question 28

A 12-year-old girl is diagnosed with multiple hereditary exostoses (MHE). Radiographs show multiple bony projections with cortico-medullary continuity.

The genetic mutation responsible for this condition primarily affects the synthesis of which of the following?

Explanation

Multiple hereditary exostoses are caused by mutations in the EXT1 or EXT2 genes, which are tumor suppressors involved in the biosynthesis of heparan sulfate. This disruption affects Indian Hedgehog signaling and normal growth plate regulation.

Question 29

A 42-year-old male with long-standing ankylosing spondylitis

has severe bilateral hip pain and stiffness and is scheduled for a total hip arthroplasty (THA). Which of the following is the most significant perioperative concern specific to his disease?

Explanation

Patients with ankylosing spondylitis frequently have cervical spine rigidity and deformity, making intubation extremely difficult and posing a risk for iatrogenic cervical fractures. Anesthesia must be carefully planned, often requiring awake fiberoptic intubation.

Question 30

A 40-year-old woman is diagnosed with primary synovial chondromatosis of the hip. She complains of progressive pain, catching, and limited range of motion. What is the recommended definitive surgical treatment to minimize recurrence?

Explanation

The standard treatment for primary synovial chondromatosis involves the removal of all loose bodies combined with an extensive synovectomy to remove the metaplastic synovium and reduce the recurrence rate.

Question 31

A 19-year-old male presents with a painless, hard mass about the medial proximal tibia. Radiographs confirm a pedunculated osteochondroma pointing away from the joint.

He complains of occasional snapping over the mass. What is the most common non-malignant complication of an osteochondroma in this location?

Explanation

The most common complication of an osteochondroma is the formation of a symptomatic reactive bursa (exostosis bursitis) over the cartilaginous cap. Vascular and neurologic complications can occur but are less common.

Question 32

Which of the following anatomic locations is most strongly associated with a higher risk of local recurrence and potential for dedifferentiation in atypical lipomatous tumors (ALT/WDLPS)?

Explanation

ALTs located in deep anatomical spaces such as the retroperitoneum or mediastinum have a much higher risk of repeated local recurrences. These repeated recurrences significantly increase the risk of dedifferentiation into higher-grade sarcomas.

Question 33

A patient with advanced ankylosing spondylitis sustains a minimal trauma fracture of the thoracic spine.

The fracture is noted to be a completely unstable, transdiscal shear injury. Which pathological process makes the spine biomechanically susceptible to this fracture pattern?

Explanation

In ankylosing spondylitis, the spine becomes a continuous, rigid bone due to syndesmophyte formation and facet ankylosis, acting as a long lever arm. This, combined with secondary osteoporosis, makes it highly susceptible to unstable "chalk-stick" shear fractures from minimal trauma.

Question 34

A 25-year-old male with a known distal femoral osteochondroma notes recent enlargement.

An MRI is ordered. Which finding would most strongly indicate a biopsy for suspected malignant transformation?

Explanation

A cartilage cap thickness greater than 2 cm in a skeletally mature adult is highly suspicious for malignant transformation into secondary chondrosarcoma. Irregular contrast enhancement of the cap or a new soft-tissue mass further supports this diagnosis.

Question 35

How can primary synovial chondromatosis be distinguished radiographically and histologically from secondary synovial chondromatosis (such as that caused by severe osteoarthritis)?

Explanation

Primary synovial chondromatosis is characterized by numerous, uniform-sized nodules that may exhibit mild, benign cellular atypia. Secondary chondromatosis usually features a few, large, irregularly sized bodies resulting from fragmented osteophytes in the setting of degenerative joint disease.

Question 36

A 55-year-old man with a long-standing history of ankylosing spondylitis presents to the emergency department after a low-energy fall. He complains of severe neck pain but has normal neurology. CT scan reveals a transverse fracture through the C6-C7 disc space extending through the posterior elements. What is the most appropriate management for this injury?

Explanation

Spine fractures in ankylosing spondylitis act like long bone fractures and are highly unstable, often involving all three columns. They require long-segment posterior fixation (often 3 levels above and below) to achieve stability and prevent catastrophic neurologic decline.

Question 37

A 28-year-old man presents with chronic lower back pain and morning stiffness lasting over an hour. Radiographs of the sacroiliac joints are unremarkable.

What is the earliest MRI finding of sacroiliitis in patients with this condition?

Explanation

The earliest sign of sacroiliitis in ankylosing spondylitis is active inflammation manifesting as subchondral bone marrow edema on STIR or T2-weighted fat-suppressed MRI. This finding precedes any structural changes seen on plain radiographs.

Question 38

A 45-year-old male with severe hip pain secondary to ankylosing spondylitis is scheduled for a total hip arthroplasty (THA). Compared to a patient with primary osteoarthritis, this patient is at a significantly higher risk for which of the following postoperative complications?

Explanation

Patients with ankylosing spondylitis are at a high risk for developing heterotopic ossification following THA. Prophylaxis with NSAIDs (e.g., Indomethacin) or low-dose localized radiation is generally recommended.

Question 39

A 16-year-old boy presents with a painless, hard mass around his distal femur. Imaging shows a sessile lesion with cortico-medullary continuity with the host bone.

The pathogenesis of this condition is most commonly associated with a mutation in a gene responsible for the synthesis of which of the following?

Explanation

Osteochondromas are associated with mutations in the EXT1 or EXT2 genes, which are tumor suppressor genes. These genes encode glycosyltransferases essential for the biosynthesis of heparan sulfate, leading to disordered physeal growth.

Question 40

A 60-year-old woman presents with a slowly enlarging, painless mass deep in her right thigh. Biopsy reveals mature adipocytes with focal cellular atypia and hyperchromatic stromal cells.

Which of the following genetic abnormalities is most characteristic of this tumor?

Explanation

Atypical lipomatous tumors (ALTs) and well-differentiated liposarcomas are characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q13-15. This molecular finding is diagnostic and differentiates them from benign lipomas.

Question 41

A 40-year-old man presents with chronic knee pain, swelling, and mechanical locking. Radiographs show multiple, uniform, calcified loose bodies within the joint capsule.

What is the underlying pathophysiology of this primary condition?

Explanation

Primary synovial chondromatosis involves the benign nodular cartilaginous metaplasia of synovial connective tissue. It is idiopathic and not caused by joint trauma or degenerative changes.

Question 42

When evaluating a patient with multiple intra-articular loose bodies, which of the following radiographic features best differentiates primary synovial chondromatosis from secondary synovial chondromatosis?

Explanation

Primary synovial chondromatosis typically presents with multiple loose bodies that are uniform in size and shape due to simultaneous metaplasia. Secondary synovial chondromatosis (e.g., from osteoarthritis) features fewer bodies of varying sizes.

Question 43

A 35-year-old man with a known history of an asymptomatic distal femur osteochondroma presents with new-onset pain and enlargement of the mass. An MRI is obtained. Which of the following findings is most predictive of malignant transformation to a secondary chondrosarcoma?

Explanation

In a skeletally mature adult, a cartilage cap thicker than 2 cm on MRI is highly suspicious for malignant transformation to a secondary chondrosarcoma. Benign lesions typically have a cap less than 1 cm thick.

Question 44

A 60-year-old male with long-standing ankylosing spondylitis presents with localized, severe back pain. Radiographs demonstrate a destructive intervertebral disc lesion with endplate sclerosis and adjacent pseudarthrosis. What is the eponymous term for this lesion?

Explanation

An Andersson lesion is an inflammatory or traumatic pseudarthrosis of the disc space or fractured vertebra in the ankylosed spine. It is often caused by an unrecognized stress fracture leading to instability and sterile inflammation.

Question 45

Which of the following best explains why an "atypical lipomatous tumor" and a "well-differentiated liposarcoma" are classified differently despite having identical histological features?

Explanation

Atypical lipomatous tumor (ALT) and well-differentiated liposarcoma share identical histology. The terminology differs based on anatomical location; lesions in deep resectable areas (extremities) are ALTs, while those in unresectable areas (retroperitoneum) are called well-differentiated liposarcomas due to higher morbidity and mortality.

Question 46

A 12-year-old girl is found to have a pedunculated bony mass on her proximal tibia that points away from the joint line.

Which of the following best describes the embryologic/developmental origin of this lesion?

Explanation

Osteochondromas are developmental anomalies resulting from the herniation of a fragment of the epiphyseal growth plate through the periosteal cuff (node of Ranvier). They grow via endochondral ossification.

Question 47

A 45-year-old patient with known, long-standing primary synovial chondromatosis of the hip returns with rapidly progressive pain. Advanced imaging is ordered. Which of the following MRI findings is the most reliable indicator of malignant transformation to a synovial chondrosarcoma?

Explanation

Malignant transformation of synovial chondromatosis to chondrosarcoma is rare (~5%). The most reliable imaging indicator of this transformation is invasion into the adjacent bone marrow, whereas simple erosions or increased loose bodies are typical of benign disease.

Question 48

A 50-year-old man with ankylosing spondylitis presents with a severe chin-on-chest deformity, preventing forward gaze. He is scheduled for a corrective spinal osteotomy. Which of the following anatomical levels is the safest and most optimal site for a pedicle subtraction osteotomy (PSO) to correct this cervicothoracic kyphosis?

Explanation

C7 is the preferred site for a cervicothoracic osteotomy (like a PSO) in ankylosing spondylitis. The spinal canal is widest at this level, reducing the risk of spinal cord compression, and the vertebral artery typically enters the transverse foramen at C6, avoiding injury at C7.

Question 49

A 10-year-old boy with Multiple Hereditary Exostoses (MHE) is being evaluated for progressive forearm deformity. Which of the following represents the most classic pattern of forearm deformity seen in this syndrome?

Explanation

The classic forearm deformity in MHE includes an osteochondroma in the distal ulna causing relative ulnar shortening, secondary bowing of the radius, an increased ulnar tilt of the distal radius, and eventual radial head dislocation.

Question 50

When evaluating an intramuscular lipomatous tumor of the thigh on MRI, which of the following features is most suggestive of an Atypical Lipomatous Tumor (ALT) rather than a simple benign lipoma?

Explanation

MRI features suspicious for an atypical lipomatous tumor (ALT) include a deep/intramuscular location, size >5 cm, thickened/nodular septa (>2 mm), and the presence of non-adipose tissue areas that enhance with contrast.

Question 51

A 65-year-old patient with end-stage ankylosing spondylitis presents with a restrictive pattern on pulmonary function tests. The patient denies any history of smoking or primary pulmonary disease. This restrictive lung physiology is primarily due to ankylosis of which of the following structures?

Explanation

Restrictive lung disease in ankylosing spondylitis is primarily caused by the fusion (ankylosis) of the costovertebral joints and thoracic spine. This severely limits chest wall excursion and lung expansion during respiration.

Question 52

Which of the following is considered the standard surgical management for a symptomatic patient with primary synovial chondromatosis of the knee to minimize the risk of recurrence?

Explanation

The standard treatment for primary synovial chondromatosis is the removal of all loose bodies combined with an extensive synovectomy. Removing the loose bodies alone without addressing the metaplastic synovium leads to high recurrence rates.

Question 53

An 18-year-old runner with a known sessile osteochondroma on the proximal medial tibia complains of recent focal pain and swelling directly over the lesion. Imaging reveals a fluid-filled sac overlying the cartilage cap with no increase in cap thickness. What is the most likely diagnosis?

Explanation

Mechanical irritation of adjacent soft tissues over an osteochondroma can lead to the formation of a bursa (exostosis bursa). Inflammation of this bursa is a common, benign cause of new-onset pain and swelling, mimicking malignant transformation.

Question 54

A 70-year-old man with ankylosing spondylitis suffers a hyperextension injury to his cervical spine resulting in a fracture.

Due to the altered biomechanics of the ankylosed spine, this patient is at uniquely high risk for which of the following acute complications?

Explanation

Patients with ankylosing spondylitis who sustain spinal fractures are at a highly elevated risk of forming a post-traumatic epidural hematoma. The rigid spine fractures like a long bone, leading to significant bleeding and tearing of epidural vessels.

Question 55

A 52-year-old man is diagnosed with an atypical lipomatous tumor (ALT) in the anterior compartment of his thigh. There is no evidence of metastasis. What is the most appropriate surgical treatment approach?

Explanation

ALTs in the extremity do not possess metastatic potential, although they have a risk of local recurrence. Marginal excision is the standard of care to minimize morbidity, reserving wide resection for cases where it does not cause significant functional deficit.

Question 56

A 28-year-old male with multiple hereditary exostoses presents with a newly enlarging mass around his right knee.

MRI shows an osteochondroma with a cartilaginous cap. What cartilage cap thickness on MRI is most highly suggestive of secondary malignant transformation to chondrosarcoma in an adult?

Explanation

In adults, a cartilage cap thickness greater than 1.5 to 2.0 cm on MRI is highly suspicious for malignant transformation to secondary chondrosarcoma. Excisional biopsy or wide resection is typically warranted for these enlarging lesions.

Question 57

A 45-year-old male with severe ankylosing spondylitis is planning to undergo a corrective spinal osteotomy for rigid cervicothoracic kyphosis.

Which of the following clinical parameters is most useful for calculating the exact amount of sagittal correction required preoperatively?

Explanation

The chin-brow vertical angle (CBVA) is essential for preoperative planning in AS patients with severe kyphosis to ensure horizontal gaze postoperatively. The surgical goal is typically to correct the CBVA to between 10 and 20 degrees.

Question 58

Primary synovial chondromatosis of the knee in a 40-year-old male is best described by which of the following histological processes?

Explanation

Primary synovial chondromatosis is a rare, benign condition that occurs via chondroid metaplasia of the synovial membrane. This leads to the formation of multiple cartilaginous nodules that frequently detach to become loose bodies.

Question 59

A 55-year-old female presents with a deep-seated intramuscular thigh mass. Biopsy reveals an atypical lipomatous tumor.

Which of the following genetic alterations is diagnostic for this specific lesion?

Explanation

Atypical lipomatous tumors (ALTs) and well-differentiated liposarcomas are characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q. This molecular signature reliably differentiates them from benign lipomas.

Question 60

A 35-year-old male with ankylosing spondylitis is scheduled for a total hip arthroplasty (THA) due to severe bilateral hip involvement. He is at significantly increased risk for which of the following postoperative complications compared to patients with primary osteoarthritis?

Explanation

Patients with ankylosing spondylitis undergoing THA have a notoriously high risk of developing postoperative heterotopic ossification (HO). Prophylaxis with postoperative NSAIDs or low-dose radiation should be strongly considered in these cases.

Question 61

Multiple hereditary exostoses (MHE) is an autosomal dominant condition linked to mutations in EXT1 and EXT2. These genes encode for glycosyltransferases primarily involved in the synthesis of which of the following?

Explanation

EXT1 and EXT2 encode for glycosyltransferases responsible for the synthesis of heparan sulfate proteoglycans. A deficiency in heparan sulfate disrupts Indian hedgehog (Ihh) signaling at the growth plate, triggering the formation of osteochondromas.

Question 62

A 62-year-old man with ankylosing spondylitis sustains a seemingly minor cervical spine fracture after a ground-level fall.

He presents with delayed, rapidly progressive quadriparesis 24 hours after admission despite a stable and immobilized fracture pattern. What is the most likely cause?

Explanation

Epidural hematoma is a well-documented and devastating complication in AS patients following spinal fractures due to altered epidural space dynamics and highly vascularized inflammatory tissue. Delayed neurological decline should prompt immediate MRI evaluation.

Question 63

A 45-year-old patient with a long-standing history of multiple loose bodies in the hip joint diagnosed as primary synovial chondromatosis presents with sudden onset of severe rest pain and rapid swelling.

What is the most feared complication that must be ruled out?

Explanation

Primary synovial chondromatosis carries a documented risk of malignant transformation to secondary chondrosarcoma in approximately 5% of long-standing cases. Sudden exacerbation of symptoms, particularly rest pain, warrants advanced imaging and biopsy.

Question 64

What is the most definitive pathognomonic radiographic and histologic feature of an osteochondroma?

Explanation

The pathognomonic hallmark of an osteochondroma is the direct continuity of both the cortex and the medullary cavity of the lesion with that of the underlying host bone. This feature distinguishes it from other surface-based osseous lesions.

Question 65

First-line medical therapy for a patient with severe ankylosing spondylitis who experiences persistent axial symptoms despite continuous, maximized use of NSAIDs involves targeted inhibition of which of the following cytokines?

Explanation

For patients with AS who fail to respond adequately to continuous NSAID therapy, TNF-alpha inhibitors (e.g., etanercept, infliximab, adalimumab) are the recommended first-line biologic therapy. They significantly reduce systemic inflammation and improve spinal mobility.

Question 66

A 60-year-old male is diagnosed with an atypical lipomatous tumor (ALT) in the deep posterior compartment of the thigh. There is no clinical or radiographic evidence of dedifferentiation. What is the most appropriate surgical treatment?

Explanation

Atypical lipomatous tumors do not metastasize unless they undergo dedifferentiation. For ALTs in the extremities, marginal excision is generally sufficient and preferred to preserve function, accepting a small risk of local recurrence.

Question 67

Which of the following clinical or pathologic features best distinguishes primary synovial chondromatosis from secondary synovial chondromatosis?

Explanation

Primary synovial chondromatosis typically presents with numerous cartilaginous loose bodies of relatively uniform size due to synchronous synovial metaplasia. Secondary synovial chondromatosis (due to OA or trauma) features fewer loose bodies of varying, unequal sizes.

Question 68

A 22-year-old male with a known, untreated osteochondroma of the distal posterior femur complains of a new, expanding pulsatile mass in the popliteal fossa and severe calf claudication. What is the most likely diagnosis?

Explanation

A well-known vascular complication of distal femoral osteochondromas, particularly those pointing posteriorly, is mechanical abrasion of the popliteal artery leading to a pseudoaneurysm. This presents with a pulsatile mass, thrill, and ischemic claudication.

Question 69

A 24-year-old male complains of severe morning stiffness and inflammatory back pain. Plain radiographs of the pelvis are completely negative for sacroiliitis.

Which MRI sequence is most sensitive for detecting the early, active inflammatory phase of sacroiliitis in suspected ankylosing spondylitis?

Explanation

STIR (Short Tau Inversion Recovery) or T2-weighted fat-suppressed MRI sequences are highly sensitive for detecting periarticular bone marrow edema. This edema represents the earliest diagnostic sign of active sacroiliitis in AS before structural radiographic changes appear.

Question 70

Which of the following best describes the typical fracture pattern seen in the cervical spine of a patient with advanced ankylosing spondylitis following a low-energy fall?

Explanation

In advanced ankylosing spondylitis, the stiff, osteopenic spine acts as a long lever arm. Minor trauma commonly results in highly unstable extension-distraction fractures (chalk stick fractures) typically occurring through the ossified disc space.

Question 71

A 16-year-old male presents with a painless, palpable mass about the distal femur.

Which radiographic finding is considered pathognomonic for this lesion?

Explanation

The diagnosis is an osteochondroma. The hallmark radiographic and histological feature is the direct continuity of the lesion's cortex and medullary cavity with that of the native host bone.

Question 72

A 50-year-old male with long-standing ankylosing spondylitis presents with progressive weakness in both lower extremities following a minor ground-level fall. CT of the cervical spine reveals a completely displaced, extension-distraction fracture at C6-C7. Which of the following is the most likely additional complication seen in this demographic?

Explanation

Patients with ankylosing spondylitis who sustain spinal fractures are at a significantly increased risk for spinal epidural hematomas due to bleeding from the fractured epidural venous plexus or bone. This complication must be considered if neurological deterioration occurs.

Question 73

A 55-year-old male presents with a large, slow-growing, deep-seated mass in the posterior thigh.

Biopsy demonstrates mature adipocytes with focal nuclear atypia. Which genetic alteration is most characteristic of this lesion?

Explanation

Atypical lipomatous tumors (ALT) and well-differentiated liposarcomas are characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q13-15. This genetic finding distinguishes them from benign lipomas.

Question 74

Which clinical feature most reliably distinguishes Primary Synovial Chondromatosis from Secondary Synovial Chondromatosis?

Explanation

Primary synovial chondromatosis results from a benign metaplasia of the synovium, causing the synchronous formation of multiple loose bodies of uniform size. Secondary synovial chondromatosis occurs due to underlying joint degeneration, resulting in fewer loose bodies of varied sizes.

Question 75

A 12-year-old boy with multiple hereditary exostoses (MHE) is evaluated for bilateral knee bumps. The underlying genetic defect in this condition primarily impairs which of the following cellular processes?

Explanation

MHE is caused by autosomal dominant mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for heparan sulfate biosynthesis, which regulates chondrocyte proliferation and differentiation.

Question 76

A 35-year-old male with severe ankylosing spondylitis requires bilateral total hip arthroplasties (THA) for end-stage auto-fusion of his hips. Postoperatively, this patient is at the highest risk for which of the following complications?

Explanation

Patients with ankylosing spondylitis undergoing THA have a significantly higher risk of developing heterotopic ossification compared to the general population. Routine prophylaxis with NSAIDs or radiation is highly recommended.

Question 77

A 25-year-old male with a known sessile osteochondroma of the proximal tibia reports a recent onset of pain and rapid growth of the mass. An MRI is obtained. Which finding most strongly suggests malignant transformation?

Explanation

Malignant transformation to secondary chondrosarcoma should be suspected in adults if an osteochondroma rapidly grows, becomes painful, or if the cartilaginous cap is thicker than 2 cm on MRI.

Question 78

A 45-year-old male with ankylosing spondylitis presents with a severe fixed, forward-flexed posture. He reports difficulty looking straight ahead. He wishes to undergo surgical deformity correction. What is the most appropriate surgical intervention to correct his sagittal imbalance?

Explanation

For severe fixed sagittal imbalance in ankylosing spondylitis, a closing-wedge lumbar osteotomy, such as a Pedicle Subtraction Osteotomy (PSO) at L3, provides significant lordotic correction (around 30-40 degrees) without lengthening the anterior column.

Question 79

Which joint is most frequently affected by primary synovial chondromatosis?

Explanation

Primary synovial chondromatosis most commonly affects large monoarticular joints. The knee is by far the most frequently involved joint, followed by the hip and elbow.

Question 80

A patient with undiagnosed ankylosing spondylitis is most likely to present with which of the following extra-articular manifestations prior to definitive spinal fusion?

Explanation

Acute anterior uveitis (iritis) is the most common extra-articular manifestation of ankylosing spondylitis, occurring in 25-30% of patients. It typically presents as acute unilateral eye pain, photophobia, and blurred vision.

Question 81

An incidental cartilaginous lesion is identified in the proximal humerus of a 50-year-old female. Which of the following MRI findings differentiates a low-grade chondrosarcoma from a benign enchondroma?

Explanation

Endosteal scalloping that exceeds 2/3 of the cortical thickness, cortical breakthrough, soft tissue extension, and significant perilesional edema on MRI are strong indicators of a low-grade chondrosarcoma rather than an enchondroma.

Question 82

A 30-year-old female is diagnosed with symptomatic primary synovial chondromatosis of the knee. What is the most appropriate initial surgical management?

Explanation

The treatment of choice for symptomatic primary synovial chondromatosis is surgical removal of the intra-articular loose bodies combined with a thorough synovectomy to reduce the rate of recurrence.

Question 83

A 22-year-old male presents with a painless mass about his distal femur. Radiographs demonstrate a pedunculated exostosis pointing away from the joint.

Which of the following gene mutations and corresponding molecular mechanisms is most likely responsible for this condition?

Explanation

Osteochondromas are commonly associated with mutations in the EXT1 or EXT2 tumor suppressor genes. This mutation leads to a defect in heparan sulfate synthesis, which disrupts normal chondrocyte proliferation and differentiation at the growth plate.

Question 84

A 45-year-old male presents with worsening knee pain and swelling after years of stable, mild discomfort. Radiographs reveal multiple uniformly sized periarticular calcified bodies.

MRI demonstrates a new, large, non-calcified soft tissue mass invading the adjacent femur. What is the most likely diagnosis of this new lesion?

Explanation

Primary synovial chondromatosis carries a small risk (1-5%) of malignant transformation into secondary chondrosarcoma. Rapid worsening of symptoms, bone marrow invasion, and the appearance of large non-calcified masses on MRI are highly suspicious for this transformation.

Question 85

A 55-year-old female undergoes a core needle biopsy of a deep, 10-cm intramuscular thigh mass.

Histology shows mature adipocytes with focal nuclear atypia. Which of the following molecular markers is most specific for distinguishing this lesion from a benign lipoma?

Explanation

Atypical lipomatous tumors (ALT) or well-differentiated liposarcomas are characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q. This molecular finding reliably differentiates ALTs from benign lipomas, which lack this amplification.

Question 86

A 60-year-old man with a 30-year history of ankylosing spondylitis presents with localized, progressive thoracolumbar back pain. Radiographs demonstrate an established bamboo spine with a localized, destructive radiolucent cleft at the T11-T12 disc space with sclerotic margins. What is the most appropriate initial management for this specific radiographic finding?

Explanation

The scenario describes an Andersson lesion, a pseudarthrosis occurring in the fused spine of patients with ankylosing spondylitis due to unhealed stress fractures. Treatment focuses on rigid immobilization with an orthosis or surgical stabilization if non-operative measures fail.

Question 87

A 48-year-old man with ankylosing spondylitis presents with a severe chin-on-chest deformity, significantly impairing his horizontal gaze and ability to eat.

A surgical correction is planned. At which anatomic level is an extension osteotomy most safely and effectively performed to correct this specific deformity?

Explanation

The cervicothoracic junction (C7-T1) is the preferred site for an extension osteotomy to correct a chin-on-chest deformity. This level has a relatively wide spinal canal, minimizing spinal cord injury risk, and avoids the vertebral arteries which typically enter the transverse foramen at C6.

Question 88

A 40-year-old male with ankylosing spondylitis presents with localized, worsening back pain and progressive kyphosis. Radiographs reveal a focal destructive discovertebral lesion with surrounding sclerotic margins. What is the most likely diagnosis?

Explanation

Andersson lesions are aseptic discovertebral pseudarthroses commonly seen in ankylosing spondylitis. They often result from non-union of unrecognized shear fractures and present with focal destruction and sclerosis, sometimes requiring surgical stabilization.

Question 89

A 35-year-old male with severe ankylosing spondylitis is scheduled for bilateral total hip arthroplasty due to disabling hip ankylosis. What is the most appropriate perioperative intervention to mitigate a highly prevalent postoperative complication in this population?

Explanation

Patients with ankylosing spondylitis undergoing total hip arthroplasty are at a significantly increased risk of developing heterotopic ossification (HO). Prophylaxis with NSAIDs (like indomethacin) or low-dose localized radiation is indicated to preserve postoperative range of motion.

Question 90

A 50-year-old female with a 10-year history of primary synovial chondromatosis of the knee presents with rapid worsening of pain, significant new swelling, and restricted motion. MRI demonstrates aggressive soft tissue expansion and new marrow invasion. What is the most likely cause of her acute deterioration?

Explanation

While primary synovial chondromatosis is a benign condition, it has a roughly 5% risk of malignant transformation into secondary chondrosarcoma. Rapid clinical deterioration, soft tissue expansion, and marrow invasion on MRI are hallmark signs of this transformation.

Question 91

A 15-year-old male presents with multiple painless, bony bumps around his knees and wrists. Radiographs reveal multiple pedunculated lesions growing away from the adjacent joints. Genetic testing is ordered. What is the underlying biochemical consequence of the most likely genetic mutation?

Explanation

This patient has Multiple Hereditary Exostoses (MHE), an autosomal dominant condition caused by mutations in the EXT1 or EXT2 genes. These genes are responsible for the synthesis of heparan sulfate proteoglycans, which are essential for normal physeal signaling.

Question 92

A 60-year-old male presents with a deep, painless, slow-growing 10 cm mass in the posterior thigh. Core needle biopsy shows mature adipose tissue with scattered focal atypia and hyperchromatic stromal cells. Which molecular finding confirms the diagnosis of an atypical lipomatous tumor rather than a benign lipoma?

Explanation

Atypical lipomatous tumors (well-differentiated liposarcomas) are characterized by supernumerary ring or giant marker chromosomes leading to the amplification of MDM2 and CDK4 genes on chromosome 12q. This differentiates them from benign lipomas.

Question 93

A 30-year-old male with a known solitary sessile osteochondroma of the distal femur presents with new-onset, progressive pain at the site. Which of the following MRI findings is most indicative of malignant transformation in a skeletally mature patient?

Explanation

In skeletally mature adults, an osteochondroma cartilage cap thicker than 2 cm is highly suspicious for malignant transformation to a secondary chondrosarcoma. Pain and interval growth after growth plate closure are key clinical warning signs.

Question 94

A 45-year-old male with severe ankylosing spondylitis presents with a fixed chin-on-chest deformity, severely limiting his forward horizontal gaze and ability to eat. An extension osteotomy is planned for correction. Which anatomical level is generally considered the safest and most effective for this procedure?

Explanation

The cervicothoracic junction (C7-T1) is the preferred and safest site for an extension osteotomy in ankylosing spondylitis. The wider spinal canal at this level accommodates the spinal cord better during the corrective hinge maneuver, minimizing neurologic risk.

Question 95

A 40-year-old female presents with chronic catching and locking in her right hip. Radiographs demonstrate numerous uniform, intra-articular calcified loose bodies. What is the definitive surgical management required to minimize the risk of recurrence?

Explanation

Primary synovial chondromatosis is a metaplastic process of the synovial lining. Definitive treatment requires a complete synovectomy in addition to the removal of all loose bodies to eliminate the source of the metaplasia and lower the recurrence rate.

Question 96

A 55-year-old male with long-standing ankylosing spondylitis suffers a minor mechanical fall and sustains a transdiscal fracture at the T10-T11 level. Why do spinal fractures in this patient population carry an exceptionally high risk of neurologic compromise?

Explanation

In ankylosing spondylitis, the multi-level ossification of spinal ligaments and fusion of facet joints create a rigid biomechanical lever. Consequently, fractures behave like long bone fractures traversing all three columns, making them highly unstable and prone to translation.

Question 97

A general surgeon performs an unplanned excisional biopsy of an atypical lipomatous tumor located deep in the anterior thigh using a transverse incision. How does this initial approach primarily complicate the definitive orthopedic oncology management?

Explanation

Biopsy tracts for musculoskeletal tumors must be longitudinal and placed within the planned definitive resection boundaries. Transverse incisions contaminate previously uninvolved tissue planes and compartments, requiring extensive, morbid resections to achieve clear oncologic margins.

Question 98

Pathological evaluation of a solitary sessile mass resected from the proximal humerus of a 14-year-old boy reveals host trabecular bone merging with a superficial cartilage cap. Which histologic feature of the cartilage cap characterizes it as a classic benign osteochondroma?

Explanation

The cartilage cap of a benign osteochondroma histologically mirrors a normal, functioning physis. The chondrocytes are neatly organized into columns (proliferative and hypertrophic zones) undergoing ordered endochondral ossification.

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

Orthopedic Board Review: Musculoskeletal Tumors, Ankylosing Spondylitis, Synovial Chondromatosis | Part 15

Key Takeaway

Orthopedic Board Review: Musculoskeletal Tumors, Ankylosing Spondylitis, Synovial Chondromatosis | Part 15

Chapter Index