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Self-Assessment Questions

Orthopaedic Surgery

Answer 1
  1. Osteosarcoma. Classic osteosarcoma is a malignant spindle cell sarcoma that produces osteoids. After myeloma, osteosarcoma is the most common primary bone tumor. It typically occurs in patients aged 10 to 25 years and is more common in males than females (1.5:1). Osteosarcoma is often found in the distal femoral metaphysis (35%), the proximal tibial metaphysis (20%), and the proximal humerus (10%).1 Pain, the most common symptom, is often exacerbated with physical activity. Plain radiographs typically show lesions with mixed lytic and blastic areas in the metaphysis of a long bone.1 There is a wide zone of transition between tumor and normal bone, and often an extraosseous soft tissue mass with fluffy irregular densities of bone formation is seen (Figure 1). MRI defines the extent of the soft tissue lesion and the involvement of neurovascular structures. Pathologic findings depict malignant cells producing osteoid.1 There is also a strong correlation between retinoblastoma and osteosarcoma; the retinoblastoma gene is mutated in 25% to 80% of cases of osteosarcoma.1 Chondrosarcoma is unlikely in this patient, as most cases occur in adults over age 40 years. Ewing’s sarcoma involves small round cells and is not associated with the retinoblastoma gene. Osteochondroma is a benign tumor with a characteristic large cartilaginous cap. Chondromyxoid fibroma, a rare tumor of the long bones and short tubular bones of the foot, typically occurs in the third or fourth decades of life and does not match the radiologic or histologic findings in this case.

     Gibbs CP Jr, Weber K, Scarborough MT. Malignant bone tumors. Instr Course Lect 2002;51:413-28.

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