Musculoskeletal Radiology
Describing a fracture
State the bone, the site (epiphysis, physis, metaphysis, diaphysis), the pattern (transverse, oblique, spiral, comminuted), displacement, angulation, articular extension and whether the injury is open. A single fracture should prompt a search for a second injury, particularly in the spine, ribs and pelvis.
Bone lesions
Age and site narrow the differential before histology. The margin is the best single predictor of behaviour: a narrow zone of transition with a sclerotic rim and no periosteal reaction indicates a benign process, whereas a wide zone with cortical destruction and aggressive periosteal reaction (spiculated, Codman triangle, onion-skin) suggests malignancy or infection. Matrix helps: chondroid rings and arcs, osteoid cloud-like density.
Arthritis
Osteoarthritis produces asymmetric joint space loss, osteophytes, subchondral sclerosis and cysts, and no erosions. Rheumatoid arthritis shows symmetric loss, marginal erosions, periarticular osteopenia, and favours MCP and PIP joints. Psoriatic arthritis involves DIP joints with pencil-in-cup change, periostitis and new bone formation.
MRI
Meniscal signal not reaching an articular surface is degeneration, not a tear. Rotator cuff tendinopathy shows intermediate signal without a defect; a full-thickness tear shows a fluid-filled gap.
Traps
Normal physis versus slipped upper femoral epiphysis; osteomyelitis mimicking Ewing sarcoma; insufficiency fractures producing marrow oedema with a subtle sclerotic line that is invisible on radiographs.
Rule of thumb
Narrow zone of transition, sclerotic margin and no periosteal reaction indicate a benign lesion; a wide zone with cortical breach is treated as aggressive until proven otherwise.