Orthopedic Oncology and Metabolic Bone Disease
What you must understand
Know the approach to a bone or soft-tissue mass: history, imaging (radiograph first, then MRI), staging, and biopsy principles (refer to a sarcoma center; avoid contaminating compartments). Understand benign versus malignant lesions by age and location - osteosarcoma (metaphysis, distal femur), Ewing sarcoma (diaphysis, children), chondrosarcoma (adults, axial), giant cell tumor (epiphysis), and metastases (adults, axial). Be fluent in metabolic bone disease: osteoporosis, Paget disease, osteomalacia, and hyperparathyroidism.
Traps in questions
- Osteosarcoma: aggressive periosteal reaction (Codman triangle, sunburst), metaphyseal, adolescents.
- Ewing sarcoma: diaphyseal, children, "onion-skin" periosteal reaction, t(11;22).
- Giant cell tumor: epiphyseal, after physeal closure, soap-bubble appearance.
- Metastases: most common bone tumor in adults; prostate, breast, lung, kidney, thyroid.
- Paget disease: mosaic pattern, elevated alkaline phosphatase, risk of pathologic fracture and sarcoma transformation.
Worked rule of thumb
For any bone lesion, ask: age, location (epiphysis/metaphysis/diaphysis), margin (well-defined vs permeative), and periosteal reaction. These four features narrow the differential dramatically.
Exam strategy
Never biopsy a suspected sarcoma without staging and referral - a poorly placed biopsy can compromise limb salvage.