Question 1

A 62-year-old male with long-standing ankylosing spondylitis presents to the emergency department with new-onset mechanical neck pain after a low-energy fall from a standing height. Neurological examination is unremarkable. Standard AP and lateral radiographs of the cervical spine demonstrate extensive syndesmophytes but no obvious fracture. What is the most appropriate next step in management?

Explanation

Patients with ankylosing spondylitis are at extremely high risk for highly unstable, occult cervical spine fractures even after minor trauma. An MRI (or CT) is mandatory to rule out a fracture or epidural hematoma when radiographs are negative.

Question 2

A 14-year-old boy presents with progressively worsening thigh pain and low-grade fevers. Imaging reveals a permeative diaphyseal lesion with an "onion-skin" periosteal reaction. Biopsy demonstrates sheets of small round blue cells. Which chromosomal translocation is most characteristically associated with this pathology?

Explanation

The clinical and radiographic presentation, along with small round blue cells, is diagnostic of Ewing Sarcoma. Over 90% of Ewing sarcomas are characterized by the t(11;22)(q24;q12) translocation, resulting in the EWS-FLI1 fusion protein.

Question 3

In the evaluation of congenital scoliosis, predicting the natural history of curve progression is critical. Which of the following congenital spinal anomalies has the highest rate of spontaneous curve progression?

Explanation

A unilateral unsegmented bar with a contralateral hemivertebra at the same level creates a severe growth mismatch (growth on one side, none on the other). This configuration carries the highest risk of rapid curve progression.

Question 4

The fundamental pathophysiology of achondroplasia involves a gain-of-function mutation in the FGFR3 gene. What is the specific effect of this mutation on the physeal growth plate?

Explanation

The mutated FGFR3 receptor in achondroplasia is constitutively active, which paradoxically inhibits chondrocyte proliferation. This primarily affects the proliferative zone of the physis, leading to defective endochondral ossification and short-limbed dwarfism.

Question 5

A 55-year-old man presents with a painful, enlarging mass in his right hemipelvis. Biopsy confirms dedifferentiated chondrosarcoma. Staging scans are negative for metastasis. What is the mainstay of definitive treatment for this lesion?

Explanation

Chondrosarcomas are generally resistant to both chemotherapy and radiation therapy. The primary and most effective treatment for localized, high-grade or dedifferentiated chondrosarcoma is wide surgical resection with negative margins.

Question 6

A 14-year-old girl with adolescent idiopathic scoliosis has a progressive right thoracic curve that now measures 52 degrees. Her Risser stage is 4, and she has had menarche 2 years ago. What is the most appropriate management?

Explanation

For adolescents with idiopathic scoliosis, a curve exceeding 50 degrees is highly likely to progress even after skeletal maturity. Posterior spinal fusion is the gold standard treatment for a 52-degree curve in a near-skeletally mature patient.

Question 7

A 12-year-old girl is diagnosed with the bone tumor seen in the provided radiograph, characterized histologically by Homer-Wright rosettes and a strong PAS-positive reaction. Which immunohistochemical surface marker is characteristically highly expressed in this tumor?

Explanation

Ewing sarcoma characteristically demonstrates strong, diffuse membranous staining for CD99 (MIC2). S-100 is for neural/melanocytic tumors, and Desmin/MyoD1 are for muscle-derived tumors like rhabdomyosarcoma.

Question 8

A 45-year-old man with advanced ankylosing spondylitis undergoes bilateral total hip arthroplasty due to severe secondary osteoarthritis and autofusion. Which postoperative complication is he at significantly higher risk for compared to the general THA population?

Explanation

Patients with ankylosing spondylitis have a high propensity for forming new bone and are at a significantly increased risk for developing severe heterotopic ossification after total hip arthroplasty. Prophylaxis with NSAIDs (e.g., indomethacin) or localized radiation is standard.

Question 9

A 4-year-old child presents with frequent long bone fractures after minimal trauma, blue sclerae, and dentinogenesis imperfecta. Genetic testing confirms Osteogenesis Imperfecta. Which of the following describes the underlying molecular defect?

Explanation

Osteogenesis Imperfecta is primarily caused by mutations in the COL1A1 or COL1A2 genes, leading to qualitative or quantitative defects in Type I collagen. Type I collagen is the major structural protein in bone, sclera, and dentin.

Question 10

A 12-year-old non-ambulatory boy with Duchenne muscular dystrophy presents with a 45-degree thoracolumbar scoliosis and progressive difficulty maintaining a seated posture. Pulmonary function is declining but acceptable for surgery. What is the most appropriate surgical strategy?

Explanation

In Duchenne muscular dystrophy, scoliosis is rapidly progressive and associated with severe pelvic obliquity. Standard surgical management involves posterior spinal fusion extending from the upper thoracic spine down to the pelvis to ensure sitting balance.

Question 11

Which of the following primary malignant bone tumors is classically associated with mutations in the retinoblastoma (RB1) gene and the TP53 gene?

Explanation

Osteosarcoma has a strong genetic association with mutations in the RB1 gene (hereditary retinoblastoma) and the TP53 gene (Li-Fraumeni syndrome). Both conditions drastically increase the risk of developing osteosarcoma.

Question 12

A 60-year-old male with long-standing ankylosing spondylitis presents with a severe chin-on-chest deformity and a global sagittal imbalance preventing him from looking straight ahead. A lumbar pedicle subtraction osteotomy (PSO) is planned. Which vertebral level is most commonly chosen for a PSO to correct global sagittal imbalance?

Explanation

The L3 vertebra is the most common site for a pedicle subtraction osteotomy (PSO) in ankylosing spondylitis. It sits at the apex of normal lumbar lordosis, allowing for maximal correction of global sagittal imbalance and shifting the center of gravity posteriorly without injuring the spinal cord.

Question 13

A newborn is evaluated for skeletal dysplasia. Physical examination reveals short-limbed dwarfism, bilateral rigid clubfeet, "hitchhiker" thumbs, and cystic swelling of the external ears (cauliflower ears). Which gene is most likely mutated in this patient?

Explanation

The clinical picture describes diastrophic dysplasia, which is inherited in an autosomal recessive manner. It is caused by a mutation in the SLC26A2 gene (also known as DTDST), which impairs sulfate transport leading to undersulfated proteoglycans in cartilage.

Question 14

In the Lenke classification system for adolescent idiopathic scoliosis, a lumbar modifier of "C" indicates the relationship between the center sacral vertical line (CSVL) and the apical lumbar vertebra. Which of the following defines a "C" modifier?

Explanation

In the Lenke classification, a lumbar C modifier means the center sacral vertical line (CSVL) falls completely outside the apical lumbar vertebra (i.e., it does not touch any part of the vertebral body). This implies a significant structural lumbar curve.

Question 15

A 15-year-old male is diagnosed with Ewing sarcoma of the proximal fibula, as suggested by the aggressive periosteal reaction in the provided radiograph. Which of the following best outlines the standard modern treatment protocol for localized Ewing sarcoma?

Explanation

Ewing sarcoma is a systemic disease at presentation even if metastases are not clinically evident. Standard treatment mandates multidrug neoadjuvant chemotherapy, followed by local control (wide surgical resection and/or radiation), and then adjuvant chemotherapy.

Question 16

A 12-year-old boy presents with severe thigh pain, swelling, and low-grade fever. Radiograph shows a permeative diaphyseal lesion with an 'onion-skin' periosteal reaction. Which chromosomal translocation is most characteristically associated with this pathology?

Explanation

The clinical and radiographic presentation is classic for Ewing's sarcoma. It is characterized by the t(11;22) chromosomal translocation, which results in the EWSR1-FLI1 fusion protein in over 85% of cases.

Question 17

A 55-year-old man with advanced ankylosing spondylitis sustains a minor ground-level fall. He complains of severe new-onset neck pain but is neurologically intact. CT scan shows a minimally displaced extension-distraction fracture through the C6-C7 disc space. What is the most appropriate management?

Explanation

Spine fractures in ankylosing spondylitis are highly unstable due to the rigid lever arms created by the fused spine. Long-segment posterior instrumented fusion (typically at least three levels above and below) is the gold standard to provide necessary biomechanical stability.

Question 18

In the Lenke classification for adolescent idiopathic scoliosis, a curve characterized by a structural proximal thoracic curve, a structural main thoracic curve, and a non-structural thoracolumbar/lumbar curve is classified as which type?

Explanation

Lenke Type 2 is a 'Double Thoracic' curve. This means both the proximal thoracic and main thoracic curves are structural, while the thoracolumbar/lumbar curve remains non-structural.

Question 19

What is the underlying genetic mutation and its functional effect in a patient presenting with achondroplasia?

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the FGFR3 gene. This leads to constitutive inhibition of chondrocyte proliferation in the proliferative zone of the physis, resulting in rhizomelic dwarfism.

Question 20

Which of the following is the most significant adverse prognostic factor for overall survival in a patient with conventional high-grade osteosarcoma?

Explanation

The percentage of tumor necrosis (histologic response) following neoadjuvant chemotherapy is the most critical prognostic factor for overall survival in osteosarcoma. Less than 90% necrosis indicates a poor response and a worse prognosis.

Question 21

A 45-year-old man with ankylosing spondylitis and fused sacroiliac joints is scheduled for a total hip arthroplasty (THA). Which of the following is a key consideration regarding acetabular cup positioning to minimize the risk of postoperative dislocation?

Explanation

In ankylosing spondylitis, the stiff spine and fused SI joints cause a fixed posterior pelvic tilt that does not adapt dynamically during sitting. Surgeons must often increase acetabular cup anteversion to compensate for this lack of spino-pelvic mobility and prevent posterior dislocation.

Question 22

A 2-year-old child presents with congenital scoliosis due to a fully segmented hemivertebra at T8. The curve has progressed 15 degrees over the last 6 months. What is the most appropriate surgical treatment?

Explanation

A fully segmented hemivertebra has high growth potential on one side and typically causes rapid, unrelenting curve progression. Early hemivertebra excision with short-segment fusion is the treatment of choice to halt progression and minimize the number of fused vertebral segments.

Question 23

A 60-year-old man presents with a painful shoulder. Radiographs reveal a large destructive lesion in the proximal humerus with 'ring and arc' calcifications. Biopsy confirms a grade II chondrosarcoma. What is the optimal treatment?

Explanation

Intermediate and high-grade (Grade II and III) chondrosarcomas are notoriously resistant to both chemotherapy and radiation. The standard of care is wide surgical resection with negative margins to prevent local recurrence and metastasis.

Question 24

Which type of Osteogenesis Imperfecta is characterized by profound bone fragility, multiple in utero fractures, and is typically lethal in the perinatal period?

Explanation

Osteogenesis Imperfecta Type II is the most severe and lethal form of the disease. Infants typically die in the perinatal period due to severe pulmonary hypoplasia and massive trauma from multiple fractures.

Question 25

A 14-year-old presents with a destructive diaphyseal femur lesion. Biopsy reveals sheets of small round blue cells. Which immunohistochemical marker is highly sensitive and typically strongly positive in this tumor?

Explanation

Ewing's sarcoma is a classic small round blue cell tumor that strongly and diffusely expresses CD99 (MIC2) on immunohistochemistry. This marker, along with molecular testing for EWSR1 translocations, confirms the diagnosis.

Question 26

A patient with ankylosing spondylitis presents with a severe chin-on-chest deformity causing difficulty with forward gaze and swallowing. A cervical extension osteotomy is planned. Which anatomical level is most commonly chosen for correcting this specific deformity?

Explanation

The cervicothoracic junction (C7-T1) is the preferred site for a cervical extension osteotomy. The vertebral canal is relatively wide here, and the vertebral arteries typically enter the transverse foramen at C6, minimizing the risk of vascular injury during the osteotomy at C7.

Question 27

In a non-ambulatory patient with Duchenne muscular dystrophy, at what scoliotic curve magnitude is spinal fusion typically recommended to prevent severe pulmonary decline and loss of sitting balance?

Explanation

In Duchenne muscular dystrophy, scoliosis progresses rapidly once the patient becomes wheelchair-bound. Early spinal fusion is advocated (typically at 20-30 degrees) before the inevitable pulmonary compromise makes the patient an unacceptable surgical risk.

Question 28

A 7-year-old child presents with a waddling gait, knee pain, and short stature. Radiographs show delayed, irregular ossification of multiple epiphyses, but the spine is radiographically normal. Which gene mutation is most commonly associated with the autosomal dominant form of this condition?

Explanation

Multiple Epiphyseal Dysplasia (MED) affects the epiphyses with a normal spine, distinguishing it from spondyloepiphyseal dysplasia. Mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene are the most common cause of autosomal dominant MED.

Question 29

Denosumab is increasingly used for unresectable or recurrent Giant Cell Tumor of bone (GCTB). What is its specific mechanism of action in this disease?

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, which is heavily overexpressed by the neoplastic stromal cells in GCTB. By neutralizing RANKL, it prevents the activation of RANK on the multinucleated osteoclast-like giant cells, halting bone destruction.

Question 30

A 13-year-old girl with adolescent idiopathic scoliosis has a 35-degree right thoracic curve. Pelvic radiographs show ossification over the lateral 50% of the iliac apophysis, with no fusion to the ilium. What is her Risser stage?

Explanation

Risser 2 indicates ossification of the lateral 25% to 50% of the iliac apophysis without fusion. This implies significant spinal growth still remains, placing her at high risk for curve progression and making her an ideal candidate for bracing.

Question 31

A 16-year-old boy presents with nocturnal thigh pain that is dramatically relieved by NSAIDs. Imaging reveals a 7mm radiolucent nidus surrounded by dense sclerosis in the femoral diaphysis. What is the biochemical basis for the profound pain relief with NSAIDs?

Explanation

The classic night pain of an osteoid osteoma is mediated by extremely high levels of prostaglandins (specifically PGE2) produced by the nidus. NSAIDs inhibit cyclooxygenase (COX), drastically reducing PGE2 production and providing profound pain relief.

Question 32

What percentage of white patients with Ankylosing Spondylitis are positive for the HLA-B27 antigen, and what is the underlying inheritance pattern of the disease?

Explanation

Approximately 90-95% of white patients with Ankylosing Spondylitis are HLA-B27 positive. The disease does not follow a simple Mendelian inheritance pattern; rather, it is polygenic and multifactorial, with HLA-B27 acting as a major genetic susceptibility factor.

Question 33

A patient presents with absent clavicles, delayed closure of cranial sutures, and supernumerary teeth. Which transcription factor gene is mutated in this autosomal dominant condition?

Explanation

The clinical presentation is classic for Cleidocranial Dysplasia. This condition is caused by a mutation in the RUNX2 (formerly CBFA1) gene, a master transcription factor essential for osteoblast differentiation and intramembranous bone formation.

Question 34

Differentiating an active enchondroma from a low-grade (Grade I) chondrosarcoma can be challenging. Which of the following radiographic features is most suggestive of a low-grade chondrosarcoma rather than a benign enchondroma?

Explanation

Deep endosteal scalloping (greater than 2/3 of the cortical depth), cortical thickening, increasing pain, and lesion size >5 cm are hallmark signs suggestive of malignant transformation or a low-grade chondrosarcoma over a benign enchondroma.

Question 35

A 14-year-old boy presents with a 2-month history of thigh pain. Radiographs show a permeative diaphyseal lesion with an 'onion-skin' periosteal reaction. Biopsy is performed.

Which of the following chromosomal translocations is most characteristic of this diagnosis?

Explanation

Ewing sarcoma typically presents as a permeative diaphyseal lesion with an 'onion-skin' periosteal reaction. It is characterized genetically by the t(11;22) translocation resulting in the EWS-FLI1 fusion protein in over 85% of cases.

Question 36

A 55-year-old man with a 20-year history of ankylosing spondylitis sustains a low-energy fall. He complains of severe neck pain, but initial plain radiographs in the emergency department are read as negative. He subsequently develops bilateral upper extremity weakness. What is the most appropriate next step in management?

Explanation

Patients with ankylosing spondylitis are highly susceptible to unstable shear fractures even with minor trauma, which can be radiographically occult. An urgent MRI is critical to evaluate for a fracture, spinal cord injury, or an epidural hematoma, which is a common complication.

Question 37

When evaluating a 14-year-old female with adolescent idiopathic scoliosis, the Center Sacral Vertical Line (CSVL) falls between the medial aspect of the pedicle and the lateral margin of the apical lumbar vertebra. According to the Lenke Classification system, what is the correct lumbar modifier?

Explanation

In the Lenke classification, a lumbar modifier B is assigned when the CSVL falls between the medial border of the pedicle and the lateral margin of the apical lumbar vertebra. Modifier A is when it passes between the pedicles, and C is when it falls completely medial to the lateral margin.

Question 38

A newborn is evaluated for frontal bossing, midface hypoplasia, and rhizomelic shortening of the limbs. Genetic testing confirms a gain-of-function mutation in the FGFR3 gene. Which physeal zone is primarily affected by this mutation?

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This mutation inhibits normal chondrocyte proliferation, directly affecting the proliferative zone of the physis.

Question 39

A 12-year-old male is diagnosed with Ewing sarcoma of the pelvis.

Which of the following represents the most significant adverse prognostic factor for this patient?

Explanation

The most significant adverse prognostic factor in Ewing sarcoma is the presence of distant metastases at the time of diagnosis. A pelvic location and large tumor size are also considered poor prognostic indicators compared to distal extremity lesions.

Question 40

A 48-year-old man with ankylosing spondylitis presents with a severe chin-on-chest deformity and loss of forward gaze. After thorough clinical and radiographic evaluation, a pedicle subtraction osteotomy (PSO) is planned. Which anatomical level is generally considered the safest and most effective for this procedure?

Explanation

A Pedicle Subtraction Osteotomy (PSO) for severe fixed sagittal imbalance in ankylosing spondylitis is typically performed at L2 or L3. This lumbar location safely maximizes lordosis correction because the spinal canal is capacious and the conus medullaris ends above this level.

Question 41

A newborn infant is noted to have a congenital scoliosis secondary to a fully segmented hemivertebra at T8. Which of the following screening examinations is mandatory as part of the initial workup?

Explanation

Congenital scoliosis is frequently associated with VACTERL anomalies, particularly genitourinary (up to 30%) and cardiovascular defects. Therefore, a renal ultrasound and an echocardiogram are mandatory components of the initial evaluation.

Question 42

A 2-year-old child presents with short-limbed dwarfism, hitchhiker thumbs, bilateral rigid clubfeet, and cystic swelling of the pinnae. What is the underlying genetic defect responsible for this condition?

Explanation

Diastrophic dysplasia is characterized by hitchhiker thumbs, cauliflower ears, and severe clubfeet. It is caused by a mutation in the SLC26A2 gene, which encodes a sulfate transport protein, leading to undersulfated proteoglycans in the cartilage.

Question 43

A 16-year-old male presents with deep nocturnal aching in his proximal tibia that is dramatically relieved by ibuprofen. Radiographs show localized cortical thickening with a small 5mm radiolucent nidus. What is the primary mechanism by which the pharmacologic agent provides pain relief in this condition?

Explanation

Osteoid osteomas produce high levels of prostaglandins (specifically PGE2) within the nidus, which cause the characteristic nocturnal pain. NSAIDs provide dramatic relief by inhibiting cyclooxygenase and decreasing local prostaglandin synthesis.

Question 44

A 12-year-old non-ambulatory boy with Duchenne muscular dystrophy presents with a progressive scoliosis measuring 35 degrees. His forced vital capacity (FVC) is 45% of predicted. What is the most appropriate management regarding his spinal deformity?

Explanation

In non-ambulatory patients with Duchenne muscular dystrophy, scoliosis surgery (posterior spinal fusion to the pelvis) is indicated for curves greater than 20-30 degrees. Early surgery is recommended before respiratory decline (FVC < 30-35%) makes the procedure prohibitively high-risk.

Question 45

A 45-year-old man with long-standing ankylosing spondylitis presents with localized, severe back pain after a bout of coughing. Radiographs reveal a destructive discovertebral lesion at T11-T12 with surrounding sclerosis and localized kyphosis. What is the most likely diagnosis?

Explanation

An Andersson lesion is a localized non-infectious inflammatory or pseudarthrotic discovertebral lesion seen in Ankylosing Spondylitis. It usually occurs secondary to stress fractures in the rigidly ankylosed spine and often requires surgical stabilization if symptomatic and progressive.

Question 46

A 10-year-old girl with Neurofibromatosis Type 1 (NF1) presents with a 40-degree sharp, short-segment thoracic scoliosis. Radiographs demonstrate severe vertebral scalloping and penciling of three adjacent ribs on the convex side. Which of the following is the most appropriate surgical strategy?

Explanation

Dystrophic scoliosis in NF1 is characterized by short, sharp curves, rib penciling, and vertebral scalloping. It has a significantly high rate of pseudarthrosis and curve progression, thus typically requiring a combined anterior and posterior spinal fusion to ensure adequate stabilization.

Question 47

A 15-year-old boy completes neoadjuvant chemotherapy for a conventional osteosarcoma of the distal femur and subsequently undergoes wide local excision. Histopathologic analysis of the resected specimen shows 95% tumor necrosis. What is the clinical significance of this finding?

Explanation

The degree of tumor necrosis following neoadjuvant chemotherapy is the single most important prognostic factor for overall survival in osteosarcoma. Greater than 90% necrosis is classified as a 'good response' and is correlated with significantly higher long-term survival rates.

Question 48

A 4-year-old child with a history of recurrent fractures, blue sclerae, and dentinogenesis imperfecta is started on intravenous pamidronate. What is the primary mechanism of action of this medication in treating this patient's underlying condition?

Explanation

Osteogenesis imperfecta is typically caused by mutations affecting Type 1 collagen. Bisphosphonates like pamidronate increase bone mineral density and reduce fracture rates by inhibiting osteoclast-mediated bone resorption, which preserves the existing abnormal bone matrix.

Question 49

A 13-year-old premenarchal female with a Risser 0 score presents with a 24-degree right thoracic idiopathic scoliosis. What is the primary indication for initiating brace treatment in this patient?

Explanation

Bracing in adolescent idiopathic scoliosis is indicated for curves between 25 and 40 degrees in skeletally immature patients (Risser 0-2) to prevent curve progression. Curves greater than 45-50 degrees often require surgical intervention.

Question 50

A 45-year-old man with long-standing Ankylosing Spondylitis sustains a minor fall. He complains of severe lower cervical neck pain but is neurologically intact. Initial plain radiographs of the cervical spine are reported as negative. What is the most appropriate next step in management?

Explanation

Patients with Ankylosing Spondylitis are at high risk for highly unstable, three-column extension-type spinal fractures even after minor trauma. CT scanning is the modality of choice because plain radiographs frequently miss cervicothoracic fractures due to altered anatomy and osteopenia.

Question 51

A 15-year-old boy presents with progressive knee pain and a palpable mass. Biopsy reveals small round blue cells. The provided radiograph is shown.

Which chromosomal translocation is most characteristically associated with this pathology?

Explanation

The clinical picture and image describe Ewing sarcoma, an aggressive primary bone tumor. Over 85% of Ewing sarcomas are characterized by the t(11;22)(q24;q12) translocation, which forms the EWS-FLI1 fusion gene.

Question 52

A 6-month-old infant with achondroplasia presents with central sleep apnea, progressive hyperreflexia, and poor head control. What is the most likely anatomic cause of this presentation?

Explanation

Infants with achondroplasia have defective endochondral bone formation, placing them at high risk for foramen magnum stenosis. This can cause cervicomedullary compression leading to central sleep apnea, quadriparesis, and sudden death, requiring prompt neurosurgical decompression.

Question 53

A 12-year-old girl is diagnosed with the bone lesion shown in the provided imaging.

Immunohistochemistry of the biopsy specimen is most likely to be strongly positive for which of the following cell surface markers?

Explanation

The image shows a diaphyseal permeative lesion with periosteal reaction typical of Ewing sarcoma. Immunohistochemistry for Ewing sarcoma classically exhibits strong, diffuse membranous staining for CD99 (MIC2).

Question 54

A 14-year-old non-ambulatory male with spastic quadriplegic cerebral palsy presents with a 75-degree thoracolumbar scoliosis and significant pelvic obliquity. What is the most critical biomechanical objective when planning posterior surgical stabilization?

Explanation

In non-ambulatory patients with severe neuromuscular scoliosis and pelvic obliquity, spinal fusion must typically extend to the pelvis (e.g., using iliac or S2AI screws) to provide a level and stable foundation for sitting. Stopping short of the pelvis often leads to recurrent obliquity and poor seating balance.

Question 55

A 55-year-old man with ankylosing spondylitis presents with a severe chin-on-chest deformity. Preoperative planning for a single-level lumbar pedicle subtraction osteotomy (PSO) is performed. Which of the following best describes the expected sagittal correction from a single-level lumbar PSO?

Explanation

A pedicle subtraction osteotomy (PSO) is a closing-wedge, three-column osteotomy hinged at the anterior longitudinal ligament. It reliably provides approximately 30 to 40 degrees of sagittal plane correction at a single surgical level.

Question 56

A 12-year-old premenarchal female presents with a right thoracic adolescent idiopathic scoliosis (AIS) measuring 25 degrees. Her Risser stage is 0. Based on standard progression risk charts, what is her approximate risk of curve progression?

Explanation

Risk of progression in AIS depends heavily on remaining growth and current curve magnitude. A 20-29 degree curve in a Risser 0 or 1 patient has an approximately 68% risk of progression.

Question 57

A 65-year-old male with long-standing ankylosing spondylitis presents after a low-energy fall with severe neck pain. CT reveals a highly displaced, unstable extension-type fracture through the C6-C7 disc space. Neurological exam is intact. What is the most appropriate definitive management?

Explanation

Fractures in ankylosing spondylitis are highly unstable due to the rigid lever arms of the fused spine. Combined anterior and posterior instrumentation is generally recommended to provide rigid fixation and prevent pseudoarthrosis.

Question 58

An 11-year-old boy presents with progressive leg pain and fever. Radiographs show a permeative diaphyseal lesion with an "onion skin" periosteal reaction. Biopsy confirms the diagnosis.

Which genetic translocation is most commonly associated with this pathology?

Explanation

The clinical presentation and imaging are classic for Ewing sarcoma. The t(11;22) translocation resulting in the EWS-FLI1 fusion protein is found in approximately 85% of Ewing sarcoma cases.

Question 59

A 4-year-old boy with achondroplasia presents with delayed walking. Physical examination reveals a flexible thoracolumbar kyphosis. What is the most appropriate initial management for his spinal deformity?

Explanation

Thoracolumbar kyphosis is present in up to 90% of infants with achondroplasia but typically resolves spontaneously as the child begins to walk. Observation is the most appropriate initial management unless the curve becomes fixed.

Question 60

Which type of congenital vertebral anomaly carries the highest risk for rapid, relentless scoliosis progression during skeletal growth?

Explanation

A unilateral unsegmented bar with a contralateral hemivertebra results in severe, relentless progression due to highly asymmetric growth. This configuration typically requires early surgical intervention.

Question 61

A 14-year-old female is diagnosed with Ewing sarcoma of the distal femur.

Which of the following is the most important prognostic factor for her overall survival?

Explanation

The presence of distant metastasis (most commonly to lungs or bone) at the time of diagnosis is the single most important adverse prognostic factor in Ewing sarcoma. Patients with metastatic disease have a significantly lower 5-year survival rate.

Question 62

A 45-year-old male with severe ankylosing spondylitis presents with a fixed thoracolumbar kyphosis. A pedicle subtraction osteotomy (PSO) is planned. Which anatomical level is typically the safest and most appropriate for a PSO to correct global sagittal imbalance?

Explanation

An L3 pedicle subtraction osteotomy is typically preferred for correcting severe sagittal imbalance in ankylosing spondylitis. L3 is safely below the conus medullaris and is close to the normal apex of lumbar lordosis.

Question 63

A 10-year-old boy presents with multiple bony prominences around his knees and wrists.

He is diagnosed with Multiple Hereditary Exostoses (MHE). What is the underlying pathophysiology of this disorder?

Explanation

Multiple Hereditary Exostoses is primarily caused by autosomal dominant mutations in EXT1 or EXT2 genes, which are involved in heparan sulfate synthesis. This leads to disorganized chondrocyte proliferation and osteochondroma formation.

Question 64

A 15-year-old male presents with persistent distal femoral pain. Biopsy reveals high-grade osteosarcoma. Following neoadjuvant chemotherapy, surgical resection is performed. What percentage of tumor necrosis in the resection specimen is required to be considered a favorable response?

Explanation

In high-grade osteosarcoma, a histologic response to neoadjuvant chemotherapy of greater than 90% tumor necrosis (Huvos grade III or IV) is considered favorable. This metric is a critical predictor of long-term survival.

Question 65

A 14-year-old non-ambulatory male with Duchenne Muscular Dystrophy (DMD) has a progressive 45-degree scoliosis. His FVC is currently 40% of predicted. What is the most appropriate management?

Explanation

In DMD, progressive scoliosis is almost inevitable and bracing is ineffective. Posterior spinal fusion to the pelvis is indicated when curves exceed 20-30 degrees and should be done before FVC severely declines (typically <30%).

Question 66

A 32-year-old female presents with an eccentric, lytic, epiphyseal lesion in the proximal tibia. Biopsy confirms Giant Cell Tumor (GCT). Which targeted medical therapy has proven effective as a neoadjuvant treatment for advanced or unresectable GCTs?

Explanation

Denosumab, a monoclonal antibody against RANKL, is highly effective in treating Giant Cell Tumors of bone. It inhibits osteoclast-like giant cells, leading to tumor consolidation.

Question 67

A newborn presents with multiple fractures, blue sclerae, and severe osteopenia. Which type of Osteogenesis Imperfecta is universally lethal in the perinatal period?

Explanation

Osteogenesis Imperfecta Type II is the most severe form of the disease. It is universally lethal in the perinatal period due to severe pulmonary hypoplasia and profound skeletal fragility.

Question 68

A 24-year-old male presents with chronic insidious-onset lower back pain that improves with exercise but not with rest. Which initial radiographic finding is most characteristic of early Ankylosing Spondylitis?

Explanation

The earliest radiographic changes in Ankylosing Spondylitis occur in the sacroiliac joints, characterized by symmetric widening, blurring, and subchondral sclerosis (sacroiliitis). Vertebral squaring and "bamboo spine" are late findings.

Question 69

A 19-year-old male reports persistent nocturnal thigh pain that is completely relieved by ibuprofen. Imaging reveals a 7mm radiolucent nidus surrounded by reactive sclerosis in the femoral diaphysis. What is the standard, minimally invasive definitive treatment?

Explanation

Radiofrequency ablation (RFA) is the current gold standard and least invasive definitive treatment for an osteoid osteoma. It provides excellent success rates with minimal morbidity compared to open surgical resection.

Question 70

A 3-year-old child presents with a progressive 60-degree idiopathic scoliosis. What is the primary rationale for utilizing a growth-friendly construct rather than an immediate definitive spinal fusion?

Explanation

Early spinal fusion in young children arrests thoracic growth, leading to restricted lung volumes and thoracic insufficiency syndrome. Growth-friendly constructs allow continued spine and thoracic growth, facilitating crucial alveolar development.

Question 71

In the multidisciplinary management of Ewing sarcoma of the extremity, what is the standard sequence of treatment?

Explanation

The standard of care for Ewing sarcoma includes neoadjuvant chemotherapy to shrink the tumor and treat micrometastases. This is followed by local control via surgery or radiation, and then adjuvant chemotherapy.

Question 72

A 12-year-old premenarchal female presents for evaluation of adolescent idiopathic scoliosis. Radiographs demonstrate a 28-degree right thoracic curve. Her Risser stage is 0. What is the most appropriate next step in management?

Explanation

Bracing is indicated for immature patients (Risser 0-2, premenarchal) with curves between 25 and 45 degrees. A TLSO worn for at least 18 hours a day has been shown to significantly decrease the risk of curve progression to surgical magnitude.

Question 73

An 18-year-old male presents with a 6-month history of painful scoliosis. Imaging reveals a 3.5 cm expansile, radiolucent lesion in the posterior elements of L4. He reports the pain is dull, continuous, and not significantly relieved by NSAIDs. What is the most likely diagnosis?

Explanation

Osteoblastomas are benign bone forming tumors that frequently occur in the posterior elements of the spine causing painful scoliosis. Unlike osteoid osteomas, they are typically larger than 2 cm, locally aggressive, and the pain is less predictably relieved by NSAIDs.

Question 74

A 55-year-old male with long-standing ankylosing spondylitis sustains a low-energy fall. CT imaging reveals an acute extension-distraction fracture through the T10-T11 ossified disc space. Due to the altered biomechanics of the ankylosed spine, this patient is at the highest risk for which of the following acute complications?

Explanation

The ankylosed spine fractures like a long tubular bone ("chalk-stick" fracture), often resulting in highly unstable shear or extension-distraction injuries. There is a high risk of epidural hematoma and neurologic deterioration due to tearing of the epidural venous plexus and continuous bleeding from the cancellous bone.

Question 75

Achondroplasia is the most common form of short-limb dwarfism and frequently presents with spinal manifestations. Which of the following radiographic findings is a hallmark of the lumbar spine in patients with this condition?

Explanation

In normal individuals, the interpedicular distance increases from L1 to L5. In achondroplasia, short and thickened pedicles result in a pathognomonic progressive decrease in interpedicular distance from L1 to L5, strongly predisposing the patient to symptomatic spinal stenosis.

Question 76

A 10-year-old boy presents with progressive thigh pain and low-grade fever. Radiographs and subsequent MRI demonstrate a large permeative lesion in the femoral diaphysis.

Biopsy confirms Ewing sarcoma. Aside from the presence of metastasis, which of the following is an independent poor prognostic factor for survival?

Explanation

In Ewing sarcoma, the presence of metastasis at presentation is the most significant poor prognostic factor. Other independent predictors of poor outcome include a pelvic primary tumor location, tumor volume greater than 100 mL, and poor histologic response to chemotherapy.

Question 77

In the evaluation of a 6-month-old infant with infantile idiopathic scoliosis, which of the following radiographic parameters is most highly predictive of curve progression?

Explanation

Mehta's rib-vertebra angle difference (RVAD) is critical in evaluating infantile idiopathic scoliosis. An RVAD greater than 20 degrees (Phase II) strongly correlates with a high likelihood of progressive deformity, whereas curves with an RVAD less than 20 degrees often resolve spontaneously.

Question 78

A 60-year-old male presents with deep pelvic pain. Imaging reveals a 10 cm destructive iliac wing lesion with intralesional stippled and "popcorn" calcifications. Core biopsy confirms a Grade II conventional chondrosarcoma. What is the most appropriate definitive management?

Explanation

Conventional chondrosarcomas are typically resistant to both chemotherapy and radiation therapy. The mainstay of treatment for intermediate and high-grade (Grade II and III) chondrosarcomas is wide surgical excision with negative margins.

Question 79

Osteogenesis imperfecta (OI) leads to frequent fractures and progressive spinal deformity. According to the Sillence classification, which type of OI is characterized as perinatal lethal?

Explanation

In the Sillence classification of osteogenesis imperfecta, Type II is the perinatal lethal form, often resulting in death in utero or shortly after birth due to severe pulmonary hypoplasia and profound skeletal fragility. Type I is mild, and Type III is the most severe non-lethal form.

Question 80

A 45-year-old male with severe ankylosing spondylitis presents with a fixed "chin-on-chest" deformity, rendering him unable to gaze horizontally. Surgical correction is planned. Which anatomic level is generally preferred for an extension osteotomy to correct this specific deformity?

Explanation

The cervicothoracic junction (C7-T1) is the preferred site for a corrective extension osteotomy in ankylosing spondylitis. The spinal canal is relatively wide at this level, and the osteotomy is performed below the cervical enlargement, reducing the risk of devastating spinal cord injury.

Question 81

A 14-year-old male undergoes 10 weeks of neoadjuvant chemotherapy for an osteosarcoma of the distal femur, followed by wide surgical resection. Histologic mapping of the resected specimen demonstrates 95% tumor necrosis. What is the significance of this finding according to the Huvos grading system?

Explanation

In the Huvos grading system for osteosarcoma, a "good response" to neoadjuvant chemotherapy is defined as greater than 90% tumor necrosis (Grade III is 90-99%, Grade IV is 100%). This is a strong independent predictor of improved long-term disease-free survival.

Question 82

A 13-year-old boy with Duchenne Muscular Dystrophy (DMD) has recently become wheelchair-bound. His forced vital capacity (FVC) is 50% of predicted, and standing radiographs reveal a progressive 35-degree thoracolumbar scoliosis with significant pelvic obliquity. What is the most appropriate management?

Explanation

In DMD, once a patient is wheelchair-bound and develops a curve over 20-30 degrees, prompt posterior spinal fusion to the pelvis is indicated. Delaying surgery leads to further decline in pulmonary function, dramatically increasing perioperative morbidity, and bracing is ineffective for these paralytic curves.

Question 83

Denosumab is highly effective in the management of unresectable Giant Cell Tumors of bone. What is the exact mechanism of action of this pharmacological agent?

Explanation

Denosumab is a human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which is expressed by the neoplastic stromal cells in Giant Cell Tumor. By neutralizing RANKL, it prevents the recruitment and activation of osteoclast-like giant cells.

Question 84

A neonate is evaluated for severe micromelic dwarfism. Clinical examination reveals a "hitchhiker" thumb, cauliflower ears, and rigid clubfeet. Radiographs of the spine are notable for severe kyphoscoliosis. A mutation in which of the following genes is responsible for this condition?

Explanation

The clinical presentation is classic for Diastrophic Dysplasia. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) gene, which encodes a sulfate transporter critical for normal cartilage matrix sulfation.

Question 85

In predicting the natural history of congenital scoliosis, the morphological type of the vertebral anomaly is the most critical factor. Which of the following anomalies carries the highest risk for rapid and severe curve progression?

Explanation

A unilateral unsegmented bar with a contralateral fully segmented hemivertebra has the highest rate of progression (often exceeding 5-10 degrees per year). This occurs because growth is tethered on the concave side while unchecked growth continues on the convex side.

Question 86

A 40-year-old male with long-standing, severe ankylosing spondylitis is scheduled to undergo bilateral total hip arthroplasty for debilitating hip ankylosis. Postoperatively, this specific patient population is at a drastically increased risk for which of the following complications?

Explanation

Patients with ankylosing spondylitis have a markedly elevated risk of developing massive heterotopic ossification (HO) following total hip arthroplasty. Prophylaxis with indomethacin or localized single-dose radiation is strongly recommended in these patients.

Question 87

A 9-year-old girl presents with an aggressive lytic lesion of the fibula.

Biopsy demonstrates uniform sheets of small round blue cells. Cytogenetics reveals a t(11;22) translocation. Which immunohistochemical marker is characteristically strongly positive in this tumor?

Explanation

Ewing sarcoma is a small round blue cell tumor characterized by the t(11;22) translocation, resulting in the EWS-FLI1 fusion protein. Immunohistochemistry classically shows strong, diffuse membranous staining for CD99 (MIC2).

Question 88

Scoliosis is the most common musculoskeletal manifestation of Neurofibromatosis Type 1 (NF1). When evaluating an NF1 patient with a progressive spinal deformity, which combination of radiographic features is pathognomonic for "dystrophic" scoliosis?

Explanation

Dystrophic scoliosis in NF1 is characterized by short, sharp, angular curves. Classic radiographic features include "penciling" (thinning) of the ribs, posterior vertebral body scalloping, severe apical rotation, and dural ectasia. These curves are highly progressive and usually require combined anterior and posterior fusion.

Question 89

A 12-year-old premenarchal female (Risser 0) presents with a right thoracic adolescent idiopathic scoliosis curve measuring 35 degrees. According to the Bracing in Adolescent Idiopathic Scoliosis Trial (BRAIST), which of the following is the most appropriate recommendation to prevent curve progression to surgical magnitude?

Explanation

The BRAIST trial demonstrated that rigid bracing (TLSO) significantly decreases the progression of high-risk adolescent idiopathic scoliosis curves to the surgical threshold (≥50 degrees). A dose-response relationship was found, with maximum benefit observed in patients wearing the brace for at least 18 hours per day.

Question 90

A 55-year-old male with long-standing ankylosing spondylitis sustains an extension-distraction fracture through the C6-C7 disc space. Following posterior instrumentation and fusion, he experiences an unexpected postoperative neurological decline in the recovery room. What is the most likely cause of this complication?

Explanation

Patients with ankylosing spondylitis are at a significantly higher risk for epidural hematomas following spinal trauma and subsequent surgery compared to the general population. This is due to altered epidural venous plexus dynamics, bleeding from fractured ossified ligaments, and the highly vascular nature of the inflammatory bone.

Question 91

A 15-year-old boy presents with progressive diaphyseal thigh pain. Radiographs demonstrate the lesion shown below.

A biopsy confirms a CD99 positive small round blue cell tumor. What is the most critical prognostic factor for overall survival in this patient?

Explanation

The presence of distant metastases at the time of diagnosis is the most important independent prognostic factor for overall survival in patients with Ewing sarcoma. While tumor volume and response to chemotherapy also influence prognosis, metastatic disease lowers the survival rate significantly.

Question 92

A 4-year-old boy with frontal bossing, rhizomelic shortening, and a trident hand presents for an orthopedic evaluation. He has a known mutation in the FGFR3 gene. Which of the following best describes the pathophysiologic mechanism of his bone dysplasia?

Explanation

Achondroplasia is the most common form of short-limbed dwarfism and is caused by an autosomal dominant gain-of-function mutation in FGFR3. This overactive receptor abnormally inhibits chondrocyte proliferation and differentiation within the proliferative zone of the physis.

Question 93

A 14-year-old male with non-ambulatory spastic cerebral palsy presents with a progressive 85-degree thoracolumbar scoliosis and severe pelvic obliquity. Posterior spinal fusion to the pelvis is planned. What is the primary biomechanical advantage of utilizing S2-alar-iliac (S2AI) or iliac screws over traditional Galveston rod techniques?

Explanation

S2AI and iliac screws offer superior biomechanical pullout strength and rotational stability compared to the Galveston technique. They also eliminate the need for complex, three-dimensional rod bending and reduce the incidence of hardware prominence.

Question 94

A 16-year-old girl is undergoing treatment for a conventional high-grade osteosarcoma of the distal femur. Following neoadjuvant chemotherapy, she undergoes wide surgical resection. The pathology report indicates 95% tumor necrosis. What does this histologic finding predict?

Explanation

The degree of tumor necrosis following neoadjuvant chemotherapy is one of the most reliable prognostic indicators in osteosarcoma. Tumor necrosis of 90% or greater (a "good response") is strongly associated with improved overall survival and event-free survival.

Question 95

A 28-year-old male with HLA-B27 positive ankylosing spondylitis presents with progressive sacroiliitis and morning stiffness. He has failed a 3-month trial of continuous treatment with two different nonsteroidal anti-inflammatory drugs (NSAIDs). According to current clinical guidelines, what is the most appropriate next pharmacological intervention?

Explanation

For patients with active axial spondyloarthritis who have an inadequate response to NSAIDs, the next recommended step is biologic therapy, typically a TNF-alpha inhibitor (e.g., etanercept, adalimumab). Conventional disease-modifying antirheumatic drugs (DMARDs) like methotrexate lack efficacy for purely axial disease.

Question 96

A 6-year-old girl with multiple recurrent long bone fractures, blue sclerae, and dentinogenesis imperfecta is diagnosed with Osteogenesis Imperfecta (Type III). Her orthopedic surgeon recommends the initiation of intravenous pamidronate. What is the primary mechanism by which this medication improves bone density in this patient?

Explanation

Pamidronate is a bisphosphonate, which works by inhibiting osteoclast-mediated bone resorption and inducing osteoclast apoptosis. This increases bone mineral density, reduces the incidence of fractures, and improves mobility in children with moderate-to-severe osteogenesis imperfecta.

Question 97

A 32-year-old female presents with an eccentric, lytic lesion in the proximal tibia extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor of Bone (GCTB). Due to the tumor's proximity to the joint, neoadjuvant denosumab is planned to consolidate the lesion before curettage. What is the specific mechanism of action of denosumab?

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor on osteoclasts and their precursors, thereby halting the osteoclast-mediated bone destruction characteristic of Giant Cell Tumors.

Skeletal Dysplasias of the Spine - Arab Board MCQ Prep

ABOS Orthopedic Board Review: Scoliosis, Ankylosing Spondylitis, Bone Tumors & Dysplasias | Part 31

Key Takeaway

ABOS Orthopedic Board Review: Scoliosis, Ankylosing Spondylitis, Bone Tumors & Dysplasias | Part 31

Chapter Index