ABOS Review: JIA, Bone Tumors, Syringomyelia - Part 8

Question 1

A 35-year-old male presents with a painless burn on his right hand. Neurological examination reveals a loss of pain and temperature sensation in a cape-like distribution over his shoulders and upper extremities, while light touch and proprioception remain intact.

Which of the following neuroanatomical structures is primarily affected in the early stages of this condition?

Explanation

This patient has syringomyelia, characterized by a central cavitary lesion in the spinal cord. It typically first compresses the anterior white commissure, disrupting crossing spinothalamic fibers and causing a dissociated sensory loss (loss of pain/temperature with preserved light touch/proprioception).

Question 2

A 48-year-old woman presents with severe, progressive right shoulder swelling and instability over the last 6 months. She reports minimal pain despite significant deformity. Radiographs show extensive bone resorption of the humeral head and glenoid with intra-articular loose bodies.

What is the most appropriate initial management for this specific shoulder pathology?

Explanation

The clinical picture describes a neuropathic (Charcot) arthropathy of the shoulder, highly associated with syringomyelia. Surgical interventions like arthroplasty or arthrodesis have exceptionally high failure rates due to lack of protective sensation, making non-operative management the standard of care.

Question 3

A 13-year-old male presents with a left-sided thoracic scoliotic curve that has rapidly progressed by 15 degrees in the last 6 months. On physical examination, he has absent superficial abdominal reflexes on the left side.

What is the most appropriate next step in evaluation?

Explanation

Atypical scoliosis features, such as a left thoracic curve, rapid progression, or abnormal neurologic findings (absent abdominal reflexes), strongly suggest an underlying intraspinal anomaly like syringomyelia. An MRI of the entire neuroaxis is mandatory to evaluate for a syrinx or Chiari malformation.

Question 4

Which of the following associated conditions is most commonly identified on imaging in a patient diagnosed with syringomyelia?

Explanation

Syringomyelia is most commonly associated with a Chiari I malformation, which involves the downward herniation of the cerebellar tonsils through the foramen magnum. This alters CSF flow dynamics, leading to the formation of the syrinx in the spinal cord.

Question 5

A 24-year-old female with long-standing polyarticular Juvenile Idiopathic Arthritis (JIA) is scheduled for a bilateral total hip arthroplasty due to severe secondary osteoarthritis. Which of the following preoperative assessments is most critical for preventing a catastrophic intraoperative complication?

Explanation

Patients with JIA frequently develop cervical spine involvement, most notably atlantoaxial subluxation and basilar invagination. Preoperative flexion-extension radiographs are essential to assess stability and guide safe endotracheal intubation, preventing fatal spinal cord compression.

Question 6

A 5-year-old girl is diagnosed with oligoarticular Juvenile Idiopathic Arthritis primarily affecting her right knee. She has an antinuclear antibody (ANA) positive titer. In addition to monitoring for leg length discrepancies, what mandatory screening must be instituted?

Explanation

Children with ANA-positive oligoarticular JIA are at a high risk for developing asymptomatic chronic anterior uveitis. Frequent screening with a slit-lamp examination by an ophthalmologist is critical to prevent permanent vision loss.

Question 7

During a total hip arthroplasty in a young adult with advanced Juvenile Idiopathic Arthritis (JIA), the surgeon must be prepared for which of the following common anatomic challenges?

Explanation

The classic hip morphology in patients with severe JIA includes protrusio acetabuli, a narrow (stovepipe) medullary canal, excessive femoral anteversion, and a small overall skeleton. Surgeons often require specialized or pediatric-sized implants to address these features.

Question 8

A 16-year-old male with a history of systemic JIA is currently treated with Etanercept. He sustained an anterior cruciate ligament tear and is scheduled for reconstruction. What is the recommended perioperative management of his biologic medication?

Explanation

Etanercept is a TNF-alpha inhibitor. To minimize the risk of postoperative infection, current guidelines recommend withholding biologic agents for one to two dosing intervals before an elective orthopedic surgery, resuming once wound healing is satisfactory.

Question 9

A 14-year-old male is diagnosed with high-grade osteosarcoma of the distal femur. He undergoes 10 weeks of neoadjuvant chemotherapy followed by wide surgical resection. Pathologic analysis of the resected specimen reveals 95% tumor necrosis. What does this finding indicate?

Explanation

The percentage of tumor necrosis following neoadjuvant chemotherapy is the most important prognostic factor for non-metastatic high-grade osteosarcoma. A necrosis rate of >90% indicates a good response and correlates with significantly improved survival.

Question 10

A 12-year-old boy presents with knee pain and a large soft tissue mass around the proximal fibula. Biopsy reveals small round blue cells. Molecular analysis confirms a t(11;22) chromosomal translocation. Which fusion protein is typically generated by this translocation?

Explanation

The t(11;22)(q24;q12) translocation is the hallmark of Ewing sarcoma, present in about 85% of cases. This translocation results in the EWS-FLI1 fusion gene, which acts as an aberrant transcription factor promoting tumorigenesis.

Question 11

When performing an incisional biopsy of a suspected malignant primary bone tumor in the lower extremity, which of the following principles must be strictly adhered to?

Explanation

Biopsy tracts are considered contaminated with tumor cells and must be entirely excised during the definitive wide resection. Therefore, the biopsy incision must be strictly longitudinal and placed within the planned surgical excision ellipse.

Question 12

A 55-year-old male presents with deep pelvic pain. Radiographs reveal a large, destructive lesion in the ilium with 'rings and arcs' calcification. Biopsy confirms conventional high-grade chondrosarcoma. What is the mainstay of treatment?

Explanation

Conventional chondrosarcoma is notoriously resistant to both chemotherapy and radiation therapy due to its low mitotic fraction and poor vascularity. Wide surgical resection with negative margins is the only potentially curative treatment.

Question 13

A 22-year-old female presents with a destructive, eccentric, lytic lesion in the distal radius subchondral bone. Histology shows sheets of mononuclear cells with numerous multinucleated giant cells. Which targeted pharmacological therapy is indicated if the tumor is deemed unresectable or for massive recurrence?

Explanation

The patient has a Giant Cell Tumor (GCT) of bone. Denosumab, a monoclonal antibody against RANKL, inhibits osteoclast-like giant cell formation and is effectively used to downstage unresectable or recurrent GCTs.

Question 14

A 6-year-old boy with oligoarticular JIA presents with an asymmetric gait. His right knee is swollen and warm but painless. On examination, his right leg is 2 cm longer than his left. What is the most likely mechanism for this leg length discrepancy?

Explanation

Chronic inflammation and synovitis in JIA cause localized hyperemia around the affected joint. In young children, this increased blood flow stimulates the adjacent physes, leading to accelerated bone growth and limb overgrowth on the affected side.

Question 15

A 68-year-old man complains of severe lower back pain and fatigue. Radiographs show multiple 'punched-out' lytic lesions in his skull and pelvis. Which of the following tests is the most appropriate next step to confirm the suspected diagnosis?

Explanation

Multiple myeloma is the most common primary malignancy of bone in adults, characterized by punched-out lytic lesions without reactive sclerosis. The best initial diagnostic tests are SPEP and UPEP to detect a monoclonal paraprotein spike.

Question 16

A 19-year-old male reports right thigh pain that is worse at night and dramatically relieved by ibuprofen. Imaging shows a 0.8 cm radiolucent nidus surrounded by dense sclerotic bone in the femoral diaphysis. What is the treatment of choice if he fails medical management?

Explanation

The clinical presentation and imaging are classic for an osteoid osteoma. If symptoms persist despite NSAIDs, minimally invasive percutaneous radiofrequency ablation (RFA) is the treatment of choice, offering high success rates with minimal morbidity.

Question 17

A 40-year-old patient presents with pain in the proximal humerus. MRI shows a cartilaginous lesion. Which of the following MRI findings most strongly supports a diagnosis of low-grade chondrosarcoma rather than a benign enchondroma?

Explanation

Differentiating enchondroma from low-grade chondrosarcoma can be difficult. MRI findings favoring chondrosarcoma include deep endosteal scalloping (greater than two-thirds of the cortical thickness), extensive marrow edema, soft tissue extension, and large size (>5 cm).

Question 18

In a patient with known syringomyelia who presents with rapidly progressive neuropathic arthropathy (Charcot joint) of the elbow, what is the primary pathophysiological mechanism leading to joint destruction?

Explanation

Charcot neuroarthropathy results from a loss of deep pain and proprioceptive sensation. This lack of protective feedback leads to unrecognized repetitive microtrauma, ligamentous laxity, and eventual catastrophic joint destruction.

Question 19

A patient with systemic Juvenile Idiopathic Arthritis is scheduled for cervical spine fusion due to basilar invagination. Which of the following airway complications is most frequently anticipated in this specific patient population by the anesthesia team?

Explanation

Patients with severe JIA often develop growth disturbances of the mandible leading to severe micrognathia (bird-face deformity) and restricted mouth opening due to TMJ ankylosis. This makes intubation exceptionally difficult, often requiring fiberoptic awake intubation.

Question 20

A 30-year-old female presents with dull aching in her distal femur. Imaging shows an ill-defined, sclerotic, intramedullary lesion. Biopsy reveals woven bone stroma lacking osteoblastic rimming, forming a permeative pattern. Which of the following is an absolute contraindication for limb-salvage surgery in this disease?

Explanation

This patient has an osteosarcoma. The absolute contraindication to limb-salvage surgery is the inability to achieve negative margins while preserving a functional limb, typically due to major neurovascular bundle encasement. Pathologic fractures and lung metastases are relative, not absolute, contraindications.

Question 21

A 45-year-old male presents with massive, painless swelling of his right shoulder and noticeable crepitus on range of motion. Neurological examination reveals a loss of pain and temperature sensation in a 'cape-like' distribution over his shoulders and back, but intact light touch and proprioception.

Based on the clinical presentation, what is the most likely diagnosis of the shoulder pathology?

Explanation

The clinical presentation of a massively swollen, painless shoulder with 'cape-like' loss of pain and temperature sensation is classic for neuropathic (Charcot) arthropathy secondary to syringomyelia. The syrinx damages the decussating spinothalamic tracts, leading to the sensory deficit.

Question 22

In the pathogenesis of the neurological deficits seen in the patient from the previous question, which spinal cord structure is initially affected by the expanding central cystic cavity?

Explanation

Syringomyelia typically begins in the central canal of the spinal cord. It first compresses the anterior white commissure, disrupting the decussating fibers of the spinothalamic tract and causing a bilateral loss of pain and temperature sensation.

Question 23

A 4-year-old girl is diagnosed with pauciarticular juvenile idiopathic arthritis (JIA). Her laboratory tests reveal she is ANA positive and Rheumatoid Factor (RF) negative. According to current guidelines, what is the most appropriate screening protocol for extra-articular manifestations in this patient?

Explanation

Patients with pauciarticular JIA who are ANA positive and under 7 years old are at the highest risk for asymptomatic anterior uveitis. They require frequent slit-lamp screening by an ophthalmologist every 3 to 4 months.

Question 24

A 12-year-old girl with long-standing systemic juvenile idiopathic arthritis presents with neck stiffness. Radiographs of the cervical spine are obtained. Which of the following is the most characteristic cervical spine radiographic finding in this condition?

Explanation

The hallmark of cervical spine involvement in juvenile idiopathic arthritis is ankylosis of the apophyseal (facet) joints. This most frequently occurs at the C2-C3 level.

Question 25

A 12-year-old boy presents with a permeative, diaphyseal lesion in his femur with a periosteal 'onion-skin' reaction. A biopsy is performed. Which specific chromosomal translocation is most strongly associated with this tumor?

Explanation

The presentation is classic for Ewing sarcoma. Over 85% of Ewing sarcomas are characterized by the t(11;22)(q24;q12) translocation, resulting in the EWSR1-FLI1 fusion gene.

Question 26

A 15-year-old male is diagnosed with conventional high-grade osteosarcoma of the distal femur. He undergoes 10 weeks of neoadjuvant chemotherapy followed by wide surgical resection. Pathologic analysis of the resected tumor is performed. Which of the following is the most significant prognostic factor for long-term survival?

Explanation

The histologic response to neoadjuvant chemotherapy, defined by the percentage of tumor necrosis, is the most important prognostic factor in osteosarcoma. Greater than 90% necrosis is considered a good response and correlates with improved survival.

Question 27

A 32-year-old female presents with a purely lytic, eccentric lesion in the epiphysis extending into the metaphysis of the distal femur. A biopsy reveals numerous multinucleated giant cells in a stroma of mononuclear cells. If medical therapy is considered, which drug specifically targets the primary molecular pathway driving this tumor?

Explanation

The diagnosis is Giant Cell Tumor of bone. The neoplastic mononuclear stromal cells express RANKL, which recruits and activates the multinucleated osteoclast-like giant cells; Denosumab is a monoclonal antibody that binds and inhibits RANKL.

Question 28

A 55-year-old male presents with a proximal humerus lesion displaying characteristic 'rings and arcs' of calcification on radiographs. Biopsy confirms a grade 2 chondrosarcoma. What is the most appropriate definitive management?

Explanation

Grade 2 (intermediate) and Grade 3 (high-grade) chondrosarcomas are locally aggressive with metastatic potential and do not respond well to chemotherapy or radiation. Wide surgical resection is the standard of care to minimize local recurrence.

Question 29

A 14-year-old female presents for evaluation of a newly noted left thoracic scoliosis. Neurological examination reveals absent abdominal reflexes. What is the most appropriate next step in management?

Explanation

A left-sided thoracic scoliosis and absent abdominal reflexes are significant 'red flags' for an intraspinal anomaly, such as syringomyelia or a tethered cord. An MRI of the entire spine and brainstem is indicated before any orthopaedic intervention.

Question 30

A 5-year-old boy has unilateral pauciarticular juvenile idiopathic arthritis predominantly affecting his right knee. If left untreated, what is the most likely long-term effect on his lower extremities?

Explanation

In young children with active inflammatory arthritis of a single lower extremity joint (like the knee), chronic hyperemia of the physis stimulates bone growth. This classically results in limb overgrowth (leg-length discrepancy where the affected leg is longer).

Question 31

An 18-year-old male complains of deep, aching pain in his proximal femur that is worse at night and dramatically relieved by ibuprofen. Imaging shows a 1 cm radiolucent nidus surrounded by dense reactive sclerosis. The pain is primarily mediated by high local concentrations of which of the following?

Explanation

Osteoid osteomas produce extremely high levels of Prostaglandin E2 (PGE2) and cyclooxygenase (COX-2) within the nidus. This accounts for the intense, night-time pain that is characteristically relieved by NSAIDs.

Question 32

A 7-year-old girl is admitted with daily spiking fevers up to 39.5°C, a salmon-pink macular rash on her trunk, polyarthritis, and hepatosplenomegaly. Which of the following laboratory markers is most characteristically elevated out of proportion to other inflammatory markers in this specific condition?

Explanation

The clinical picture is classic for Systemic Juvenile Idiopathic Arthritis (Still's disease). Extremely high levels of serum ferritin are characteristic and correlate with disease activity, helping distinguish it from other inflammatory arthritides.

Question 33

A 13-year-old patient with a rapidly progressing 45-degree scoliosis curve is found to have a Chiari I malformation and a large cervicothoracic syrinx on MRI. What is the recommended sequence of surgical management?

Explanation

In patients with scoliosis secondary to syringomyelia/Chiari malformation, the neurosurgical decompression should be performed first. In a significant percentage of patients, the curve may stabilize or even improve after syrinx decompression, delaying or preventing the need for spinal fusion.

Question 34

A 40-year-old presents with a Charcot shoulder joint.

An MRI of the cervical spine and craniocervical junction is performed, showing a syrinx. Which cranial malformation is most frequently associated with this pathology?

Explanation

Syringomyelia in adults is most commonly associated with a Chiari I malformation, which is defined by cerebellar tonsillar herniation of more than 5 mm below the foramen magnum. This alters CSF flow, leading to syrinx formation.

Question 35

When evaluating a cartilaginous lesion in the distal femur of a 45-year-old patient, which radiographic feature most strongly suggests a low-grade chondrosarcoma rather than a benign enchondroma?

Explanation

Deep endosteal scalloping (greater than 2/3 of the cortical thickness), cortical breakthrough, and pain in the absence of a fracture are key features differentiating a low-grade chondrosarcoma from a benign enchondroma.

Question 36

An 8-year-old boy presents to the emergency department after a minor fall. Radiographs show a fracture through a central, radiolucent, cystic lesion in the proximal humerus metaphysis. A cortical fragment is seen resting at the dependent portion of the cyst ('fallen leaf' sign). What is the most appropriate initial management?

Explanation

The 'fallen leaf' sign is pathognomonic for a Unicameral Bone Cyst (UBC). When a fracture occurs through a UBC, the initial management is immobilization to allow the fracture to heal; the cyst may occasionally heal and obliterate itself as the fracture remodeling occurs.

Question 37

A 65-year-old male presents with widespread lytic bone lesions, renal insufficiency, and hypercalcemia. A diagnosis of Multiple Myeloma is established. Which of the following best describes the molecular mechanism responsible for the osteolytic bone lesions in this disease?

Explanation

In Multiple Myeloma, malignant plasma cells secrete cytokines such as MIP-1 alpha and upregulate RANKL. This creates a highly osteoclastogenic microenvironment, leading to unchecked bone resorption and lytic lesions.

Question 38

A 58-year-old male presents with a painful, destructive osteolytic lesion in the distal phalanx of his right thumb. Biopsy confirms metastatic adenocarcinoma. What is the most common primary malignancy to metastasize to locations distal to the knee or elbow (acrometastasis)?

Explanation

Metastases to the hands or feet (acrometastases) are rare and account for about 0.1% of all bone metastases. Lung carcinoma is by far the most common primary source for acrometastases, accounting for approximately 50% of cases.

Question 39

A 50-year-old female with known syringomyelia presents with advanced Charcot arthropathy of the glenohumeral joint, experiencing severe instability and progressive loss of function that has failed extensive conservative management.

If surgical intervention is absolutely necessary, which procedure is generally considered the most appropriate salvage option despite high complication rates?

Explanation

In true neuropathic (Charcot) joints, standard joint replacement (arthroplasty) is strongly contraindicated due to extreme rates of early loosening and failure. Shoulder arthrodesis is the preferred surgical salvage procedure for severe instability, though pseudoarthrosis and hardware failure rates remain high.

Question 40

A 10-year-old girl with polyarticular juvenile idiopathic arthritis develops severe involvement of her temporomandibular joints (TMJs). Which of the following facial abnormalities is the expected consequence of chronic TMJ destruction during her growth phase?

Explanation

Chronic inflammation and destruction of the temporomandibular joint in growing children with JIA leads to early closure of the mandibular condylar growth centers. This characteristically results in micrognathia (a small, recessed lower jaw) and a typical 'bird-face' appearance.

Question 41

A 4-year-old girl is diagnosed with oligoarticular Juvenile Idiopathic Arthritis (JIA) after presenting with a swollen, painless right knee. Laboratory testing reveals a positive antinuclear antibody (ANA). Which of the following is the most critical routine screening study required for this patient?

Explanation

Oligoarticular JIA with a positive ANA carries a very high risk of asymptomatic anterior uveitis (iridocyclitis). Routine slit-lamp screening is mandatory, as untreated uveitis can rapidly lead to synechiae, cataracts, and permanent blindness.

Question 42

A 35-year-old male presents with painless burn scars on his hands. Neurological examination reveals loss of pain and temperature sensation in a 'cape-like' distribution over his shoulders and arms, but intact proprioception and vibratory sense.

What is the most likely diagnosis?

Explanation

Syringomyelia typically presents with dissociated sensory loss (loss of pain and temperature with preserved dorsal column function) in a cape-like distribution. This is due to the expansion of the central syrinx disrupting the decussating spinothalamic fibers.

Question 43

A 16-year-old boy presents with progressive right thigh pain that is noticeably worse at night and dramatically relieved by taking ibuprofen. Radiographs demonstrate a diaphyseal cortical thickening with a central radiolucent nidus measuring 8 mm. Which of the following is the most likely diagnosis?

Explanation

Osteoid osteoma classically presents with nocturnal pain that is exquisitely sensitive to NSAIDs due to high local prostaglandin production. Imaging typically shows a small (<1.5 cm) radiolucent nidus surrounded by dense reactive sclerosis.

Question 44

A 14-year-old boy is diagnosed with a permeative diaphyseal lesion of the femur with an 'onion-skin' periosteal reaction. Biopsy confirms small round blue cells. Which of the following chromosomal translocations is most characteristic of this tumor?

Explanation

Ewing sarcoma is characterized by small round blue cells and is classically driven by the t(11;22) chromosomal translocation. This creates the EWS-FLI1 fusion protein, which acts as an aberrant transcription factor.

Question 45

A 10-year-old boy with polyarticular JIA is scheduled for elective bilateral total hip arthroplasty due to severe joint destruction. During the preoperative assessment, which of the following cervical spine abnormalities must be carefully ruled out before administering general anesthesia?

Explanation

Patients with polyarticular JIA frequently develop cervical spine involvement, most notably atlantoaxial instability and apophyseal joint ankylosis. Flexion-extension cervical spine radiographs are mandatory prior to intubation to prevent catastrophic spinal cord injury.

Question 46

A 55-year-old male presents with a painful, enlarging mass in his proximal femur. Radiographs show a destructive lytic lesion with 'popcorn' intralesional calcifications. Biopsy confirms a grade II conventional chondrosarcoma. What is the most appropriate primary management?

Explanation

Conventional chondrosarcomas are largely resistant to both chemotherapy and radiation therapy. Wide surgical resection with negative margins is the definitive and most effective treatment modality.

Question 47

A 45-year-old patient with known syringomyelia presents with massive, painless swelling and instability of the right shoulder. Radiographs demonstrate severe articular destruction, loose bodies, and debris consistent with a neuropathic joint.

Which of the following mechanisms best explains this joint pathology?

Explanation

Neuropathic (Charcot) arthropathy in syringomyelia results from a loss of deep pain and proprioceptive sensation. This allows for repeated, unperceived joint microtrauma, leading to progressive and severe joint destruction.

Question 48

A 28-year-old female presents with an expansile, purely lytic epiphyseal lesion of the distal femur extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor. If the tumor is deemed surgically unresectable due to its size and location, which of the following pharmacological agents is most appropriate to downstage the tumor?

Explanation

Giant cell tumors of bone are characterized by neoplastic stromal cells that express high levels of RANKL, driving the proliferation of multinucleated giant cells. Denosumab, a monoclonal antibody against RANKL, is highly effective for downstaging unresectable lesions.

Question 49

A 6-year-old boy presents with daily high spiking fevers, an evanescent salmon-pink macular rash on his trunk, generalized lymphadenopathy, and symmetric polyarthritis. Laboratory tests show elevated ferritin, CRP, and leukocytosis. What is the most likely diagnosis?

Explanation

Systemic JIA (Still's disease) presents with classic extra-articular manifestations including high daily spiking fevers, a characteristic salmon-pink rash that appears with the fever, and prominent systemic inflammation.

Question 50

A 15-year-old male is suspected of having an osteosarcoma of the distal femur. A core needle biopsy is planned. Which of the following is a critical orthopedic oncology principle regarding the placement of the biopsy tract?

Explanation

Biopsy tracts must be placed longitudinally and strictly in line with the planned definitive surgical incision. This ensures that the entire biopsy tract, which is considered contaminated with tumor cells, can be excised en bloc during the definitive tumor resection.

Question 51

In a patient developing syringomyelia, the expanding syrinx initially causes bilateral loss of pain and temperature sensation while preserving touch and proprioception. Which specific spinal cord structure is compressed first to cause this presentation?

Explanation

The syrinx typically originates in or near the central canal and expands outward. The earliest structure it compromises is the anterior white commissure, where the lateral spinothalamic tracts decussate, leading to bilateral loss of pain and temperature sensation.

Question 52

A 9-year-old boy sustains a minor fall and presents with arm pain. Radiographs reveal a central, purely radiolucent metaphyseal lesion in the proximal humerus with a cortical fragment resting at the bottom of the cyst. What is the most likely diagnosis?

Explanation

A Unicameral Bone Cyst (UBC) is a benign, fluid-filled, central metaphyseal lesion typically found in the proximal humerus or femur of children. The 'fallen leaf' or 'fallen fragment' sign is pathognomonic and indicates a pathologic fracture through the cyst.

Question 53

A 5-year-old girl with active, untreated oligoarticular JIA affecting solely her left knee is evaluated in the orthopedic clinic. Which of the following growth disturbances is most likely to be observed in the affected limb during the active inflammatory phase?

Explanation

In the early, active phase of JIA involving a large joint like the knee, chronic inflammation and hyperemia stimulate the adjacent physes. This frequently leads to accelerated longitudinal bone growth and an ipsilateral leg length discrepancy (affected leg is longer).

Question 54

A 65-year-old male presents with generalized bone pain, fatigue, and renal insufficiency. Radiographs of the skull and pelvis demonstrate numerous 'punched-out' purely lytic lesions without reactive sclerosis. What is the most common primary malignant bone tumor in this age group?

Explanation

Multiple myeloma is the most common primary malignancy of bone in adults. It classically presents with the CRAB criteria (Hypercalcemia, Renal failure, Anemia, Bone lesions) and sharply demarcated, purely lytic 'punched-out' lesions on imaging.

Question 55

A 30-year-old female undergoes an MRI of the cervical spine due to progressive bilateral upper extremity weakness and sensory loss. The MRI reveals a large cervical syrinx. What is the most common congenital malformation associated with this finding?

Explanation

Syringomyelia is highly associated with Chiari type I malformations, characterized by downward displacement (herniation) of the cerebellar tonsils through the foramen magnum. This disrupts normal CSF flow dynamics, promoting syrinx formation.

Question 56

A 12-year-old girl presents with knee pain. MRI of the distal femur demonstrates an eccentric, expansile metaphyseal lesion containing multiple cystic spaces with distinct fluid-fluid levels. Histology shows blood-filled spaces separated by cellular septa. What is the most likely diagnosis?

Explanation

Aneurysmal bone cysts (ABCs) are benign, expansile, eccentric metaphyseal lesions. MRI classically demonstrates fluid-fluid levels due to the settling of blood components within the cystic spaces.

Question 57

A 7-year-old child with systemic JIA suddenly deteriorates in the hospital, developing an unremitting fever, hepatosplenomegaly, and encephalopathy. Laboratory studies reveal a paradoxical sharp drop in the erythrocyte sedimentation rate (ESR), profound thrombocytopenia, and a serum ferritin level of 15,000 ng/mL. What life-threatening complication has developed?

Explanation

Macrophage Activation Syndrome (MAS) is a severe, life-threatening complication of systemic JIA. It is characterized by unremitting fever, hepatosplenomegaly, massive hyperferritinemia, cytopenias, and a paradoxical drop in ESR due to hypofibrinogenemia.

Question 58

A 22-year-old patient presents with multiple palpable, hard masses on his hands and severe deformities. Imaging reveals multiple enchondromas. Physical examination also reveals numerous bluish soft tissue nodules which are identified as hemangiomas. What is the diagnosis?

Explanation

Maffucci syndrome is a rare nonhereditary disorder characterized by multiple enchondromas associated with soft tissue hemangiomas. Patients with Maffucci syndrome have a significantly higher risk of malignant transformation to chondrosarcoma compared to those with Ollier disease.

Question 59

As a cervical syrinx progressively enlarges ventrally, it begins to compress and destroy adjacent structures beyond the central commissure. Which of the following neurological findings in the upper extremities is a classic consequence of this ventral extension?

Explanation

As a syrinx expands ventrally into the anterior horns of the spinal cord, it destroys the lower motor neurons located there. This results in classic lower motor neuron signs in the upper extremities, including profound flaccid weakness, muscle atrophy, and areflexia.

Question 60

A 35-year-old male with a known long-standing asymptomatic distal femoral osteochondroma presents with new-onset, progressive pain and enlargement of the mass. An MRI is performed. Which of the following findings is most highly suspicious for secondary malignant transformation to a chondrosarcoma?

Explanation

Osteochondromas (exostoses) typically stop growing when the skeleton matures. In an adult, new pain, growth, and an MRI demonstrating a cartilage cap thicker than 2.0 cm are highly suspicious for malignant transformation to a secondary chondrosarcoma.

Question 61

A 12-year-old girl with long-standing polyarticular Juvenile Idiopathic Arthritis (JIA) presents with new-onset clumsiness in her hands and hyperreflexia in her lower extremities. Which of the following is the most likely cervical spine radiographic finding?

Explanation

Anterior atlantoaxial subluxation is the most common cervical spine manifestation in JIA. Neurologic symptoms like clumsiness and hyperreflexia indicate cervical myelopathy, necessitating urgent MRI and possible fusion.

Question 62

A 28-year-old male presents with painless swelling and instability of his right shoulder over the past 6 months. Neurological examination reveals a loss of pain and temperature sensation over his shoulders and upper back, with preserved light touch and proprioception.

What is the underlying pathophysiology of his shoulder pathology?

Explanation

The patient presents with a Charcot shoulder and a cape-like dissociated sensory loss, classic for syringomyelia. A syrinx typically expands and destroys the crossing spinothalamic tracts in the anterior white commissure first, leading to loss of pain and temperature sensation.

Question 63

In the management of high-grade intramedullary osteosarcoma, which of the following factors is considered the most significant predictor of overall patient survival?

Explanation

The degree of tumor necrosis following neoadjuvant chemotherapy (Huvos grading) is the single most important prognostic factor for overall survival in high-grade osteosarcoma. Greater than 90% necrosis indicates a favorable response and improved prognosis.

Question 64

Which of the following pediatric patients with Juvenile Idiopathic Arthritis (JIA) requires the most frequent slit-lamp examinations to screen for asymptomatic uveitis?

Explanation

Young girls (onset <7 years) with oligoarticular JIA and a positive ANA are at the highest risk for developing chronic, asymptomatic anterior uveitis. They require screening slit-lamp exams every 3 to 4 months.

Question 65

A 13-year-old boy presents with a rapidly progressive left-sided thoracic scoliosis and absent abdominal reflexes. MRI of the spine reveals a large syrinx extending from C5 to T8.

What is the most appropriate sequencing of treatment?

Explanation

In a patient with scoliosis secondary to syringomyelia, neurosurgical decompression of the syrinx (or addressing the underlying Chiari malformation) must be performed first. Scoliosis may stabilize or improve post-decompression, and proceeding directly to deformity correction risks severe neurologic injury.

Question 66

A 35-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms Giant Cell Tumor (GCT). If medical management is considered prior to intralesional curettage to downstage the tumor, which agent is most appropriate?

Explanation

Denosumab is a monoclonal antibody against RANKL, which is heavily expressed by the stromal cells in Giant Cell Tumor of bone. It inhibits osteoclast-like giant cells, leading to tumor ossification and facilitating subsequent intralesional curettage.

Question 67

A 6-year-old girl with persistent oligoarticular JIA affecting her right knee presents with a noticeable leg length discrepancy. Which of the following best describes the expected discrepancy and its mechanism?

Explanation

In the early, active stages of JIA involving a single large joint like the knee, chronic inflammation causes localized hyperemia. This increased blood flow stimulates the adjacent physes, resulting in overgrowth and a longer affected limb.

Question 68

A 14-year-old boy has an eccentric, expansile, lytic metaphyseal lesion in his proximal humerus. MRI demonstrates multiple fluid-fluid levels. Genetic analysis of the tissue would most likely reveal a translocation involving which of the following genes?

Explanation

Primary aneurysmal bone cysts (ABCs) are genuine neoplasms characterized by rearrangements of the USP6 gene on chromosome 17p13. MRI classically shows fluid-fluid levels due to blood settling within the cystic spaces.

Question 69

Which of the following is the most common etiology of syringomyelia in the pediatric population?

Explanation

Chiari I malformation, characterized by caudal displacement of the cerebellar tonsils through the foramen magnum, is the most common cause of syringomyelia. Altered CSF flow dynamics at the craniocervical junction lead to syrinx formation.

Question 70

A 5-year-old boy with systemic Juvenile Idiopathic Arthritis (sJIA) suddenly develops unremitting fever, hepatosplenomegaly, purpura, and profound lethargy. Laboratory tests show marked hyperferritinemia, hypofibrinogenemia, and pancytopenia. What is the most critical immediate complication?

Explanation

Macrophage Activation Syndrome (MAS) is a severe, potentially life-threatening complication of systemic JIA, characterized by a sudden drop in cell counts, low fibrinogen, and extremely high ferritin. It requires immediate aggressive immunosuppressive therapy.

Question 71

A 60-year-old man presents with deep thigh pain. Radiographs reveal a large diaphyseal lesion in the femur with endosteal scalloping greater than two-thirds of the cortical thickness and /"popcorn/" calcifications. What is the mainstay of treatment for this lesion?

Explanation

The patient has a conventional chondrosarcoma, indicated by age, endosteal scalloping, and chondroid matrix calcifications. Conventional chondrosarcomas are highly resistant to both chemotherapy and radiation, making wide surgical resection the primary treatment.

Question 72

When performing an incisional biopsy of a suspected malignant primary bone tumor in the distal femur, which of the following principles must be strictly adhered to?

Explanation

Biopsy tracts are considered contaminated with tumor cells and must be entirely excised during definitive tumor resection. Therefore, the biopsy incision must be longitudinal and placed directly in line with the planned surgical approach, avoiding neurovascular structures.

Question 73

Which of the following subsets of Juvenile Idiopathic Arthritis (JIA) carries the highest risk for developing chronic, asymptomatic anterior uveitis?

Explanation

Children with oligoarticular JIA who are ANA-positive are at the highest risk for asymptomatic anterior uveitis. Routine slit-lamp screening is essential as this condition can lead to blindness if untreated.

Question 74

A 14-year-old female with long-standing polyarticular Juvenile Idiopathic Arthritis (JIA) is scheduled for a total hip arthroplasty. Before proceeding with endotracheal intubation, which of the following is the most critical preoperative radiographic evaluation?

Explanation

Patients with severe JIA are at high risk for cervical spine instability, particularly atlantoaxial subluxation. Flexion-extension cervical radiographs are mandatory before any procedure requiring intubation to prevent catastrophic neurologic injury.

Question 75

A 45-year-old male presents with a painless, grossly swollen right shoulder. Examination reveals palpable crepitus, severe instability, and diminished pain and temperature sensation in the upper extremity.

What is the most likely underlying diagnosis?

Explanation

The clinical presentation of a painless, destructive arthropathy in the upper extremity combined with dissociated sensory loss (loss of pain/temperature) is classic for Charcot arthropathy secondary to syringomyelia. The cervical syrinx interrupts the decussating spinothalamic tracts.

Question 76

In a patient who has undergone neoadjuvant chemotherapy and wide resection for a conventional osteosarcoma of the distal femur, which of the following histologic findings is the most significant prognostic indicator for long-term survival?

Explanation

The histologic response to neoadjuvant chemotherapy, defined by the percentage of tumor necrosis, is the single most important prognostic factor in osteosarcoma. Greater than 90% necrosis (Huvos grade III/IV) correlates with a significantly higher survival rate.

Question 77

A 12-year-old boy presents with left-sided mid-back pain and is found to have a left thoracic scoliotic curve of 35 degrees. Abdominal reflexes are absent asymmetrically. What is the most appropriate next step in management?

Explanation

A left thoracic curve, severe pain, and asymmetric or absent abdominal reflexes are "red flag" signs for an underlying neural axis abnormality, such as syringomyelia or a Chiari malformation. An MRI of the entire spine is mandatory.

Question 78

A biopsy is planned for a suspected high-grade sarcoma of the distal femur. Which of the following is a critical principle when performing the incisional biopsy?

Explanation

A biopsy tract is considered contaminated and must be excised en bloc during definitive tumor resection. Therefore, the biopsy incision must be longitudinal and placed directly in line with the planned surgical approach.

Question 79

A 16-year-old girl is diagnosed with Ewing sarcoma of the femoral diaphysis. Cytogenetic analysis of the tumor cells is most likely to reveal which of the following translocations?

Explanation

Ewing sarcoma is characterized by the t(11;22)(q24;q12) translocation in approximately 85% of cases, resulting in the EWS-FLI1 fusion protein. This molecular marker is highly specific and used for diagnostic confirmation.

Question 80

A 55-year-old male undergoes wide surgical resection for a conventional Grade II chondrosarcoma of the proximal femur. Which of the following best describes the role of adjuvant therapy for this condition?

Explanation

Conventional chondrosarcomas are notably resistant to both chemotherapy and radiotherapy. The mainstay of curative treatment relies solely on achieving wide surgical resection margins.

Question 81

A 6-year-old child with a known history of systemic-onset JIA (Still's disease) suddenly develops a high unremitting fever, hepatosplenomegaly, bleeding gums, and profound lethargy. Laboratory tests show a rapidly dropping platelet count and an exceptionally high serum ferritin level. What is the most likely diagnosis?

Explanation

Macrophage Activation Syndrome (MAS) is a life-threatening complication of systemic JIA, characterized by a sudden drop in blood counts, hepatosplenomegaly, coagulopathy, and extremely high ferritin. It requires immediate, aggressive immunosuppressive treatment.

Question 82

Giant Cell Tumor (GCT) of bone frequently causes significant local bone destruction. The osteolysis in GCT is driven by the interaction between RANKL and RANK. In this tumor, which cells express RANKL?

Explanation

In Giant Cell Tumor of bone, the mononuclear stromal cells are the true neoplastic components and they heavily express RANKL. This cytokine recruits and activates normal, reactive multinucleated osteoclast-like giant cells that cause the bone destruction.

Question 83

A 10-year-old girl is found to have a 45-degree right thoracic scoliosis and an enlarging cervicothoracic syrinx associated with a Chiari I malformation. What is the most appropriate management strategy?

Explanation

When a significant syrinx or Chiari malformation is the underlying cause of scoliosis, neurosurgical decompression must be performed prior to any spinal fusion. In many young patients, the scoliotic curve will stabilize or even improve following decompression.

Question 84

A 16-year-old male complains of severe back pain, especially at night. Imaging reveals a 2.5 cm lytic lesion with central calcification in the posterior elements of L4. What is the most likely diagnosis?

Explanation

While both osteoid osteoma and osteoblastoma have similar histology, an osteoblastoma is distinguished by a nidus size greater than 2 cm and a predilection for the posterior elements of the spine. Osteoblastomas are also less predictably relieved by NSAIDs compared to osteoid osteomas.

Question 85

A 7-year-old child with oligoarticular JIA affecting the right knee is noted to have a leg length discrepancy, with the right leg being 1.5 cm longer than the left. What is the primary mechanism causing this overgrowth?

Explanation

In children with active JIA, chronic inflammation in a large joint (like the knee) leads to local hyperemia. This increased blood flow stimulates the adjacent physes, leading to accelerated bone growth and a resultant ipsilateral leg length discrepancy.

Question 86

A 50-year-old patient with known syringomyelia presents with massive, painless swelling and instability of the elbow joint.

The exact neuroanatomic lesion in syringomyelia that leads to this neuropathic joint typically originates in which structure of the spinal cord?

Explanation

Syringomyelia typically begins as a cystic enlargement of the central canal, which first compresses the decussating spinothalamic fibers in the anterior white commissure. This causes the classic bilateral loss of pain and temperature sensation leading to neuropathic arthropathy.

Question 87

A 65-year-old male presents with bone pain and a pathologic fracture of the proximal humerus. Radiographs show multiple "punched-out" lytic lesions. A technetium-99m bone scan is performed and shows no significant uptake in the lesions. What is the most likely diagnosis?

Explanation

Multiple myeloma lesions characteristically appear as "cold" or show no increased uptake on a technetium-99m bone scan. This is because myeloma cells secrete factors that suppress osteoblastic activity, and bone scans primarily detect osteoblast-mediated bone turnover.

Question 88

A 30-year-old male presents with an eccentric, purely lytic lesion in the epiphysis of the distal femur extending to the subchondral bone. Biopsy confirms Giant Cell Tumor (GCT). If systemic therapy is considered, which of the following agents is most appropriate?

Explanation

Denosumab is a monoclonal antibody against RANKL, which is the primary cytokine driving bone destruction in Giant Cell Tumor of bone. It is used as targeted therapy to consolidate the tumor, especially in unresectable or recurrent cases.

Question 89

In patients with severe, long-standing Juvenile Idiopathic Arthritis (JIA) undergoing Total Hip Arthroplasty (THA), the surgeon must anticipate distinct anatomic challenges. Which of the following is most commonly encountered in this patient population?

Explanation

Patients with severe JIA often suffer from early physeal closure and systemic growth retardation, leading to "miniature" bone anatomy that requires custom or very small implants. They also frequently develop osteopenia and protrusio acetabuli due to chronic inflammation.

Question 90

A 22-year-old patient with Multiple Hereditary Exostoses (MHE) reports new, increasing pain and sudden growth of a previously stable lesion on the proximal tibia. What specific imaging finding is most indicative of malignant transformation?

Explanation

In adults, a cartilage cap thicker than 2 cm (or 1.5 cm in some literature) on MRI is highly suspicious for malignant transformation of an osteochondroma into a secondary chondrosarcoma. Growth of a lesion or new pain after skeletal maturity also strongly suggests malignancy.

Question 91

Aneurysmal bone cysts (ABCs) are expansile, blood-filled cystic lesions. While they can be secondary to other tumors, primary ABCs are now known to be true neoplasms driven by a specific genetic rearrangement. Which gene translocation is diagnostic for a primary ABC?

Explanation

Primary Aneurysmal Bone Cysts are characterized by translocations involving the USP6 gene on chromosome 17p13. This finding helps differentiate primary ABCs from secondary ABC-like changes that occur in other tumors like giant cell tumor or osteoblastoma.

Question 92

Which of the following joint deformities is classically associated with the natural progression of untreated polyarticular Juvenile Idiopathic Arthritis in the hand and wrist?

Explanation

Unlike adult Rheumatoid Arthritis (which typically causes ulnar deviation at the MCP joints), polyarticular JIA classically presents with radial deviation of the fingers at the MCP joints and ulnar deviation at the wrist. This "zigzag" deformity is characteristic of the juvenile form.

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

Orthopedic & Rheumatology Board Review: JIA, Bone Tumors, Syringomyelia Cases | Part 8

Key Takeaway

Orthopedic & Rheumatology Board Review: JIA, Bone Tumors, Syringomyelia Cases | Part 8

Chapter Index