Musculoskeletal Imaging
Musculoskeletal Imaging tests fracture description, bone tumour analysis, arthritis patterns and MRI of joints and soft tissues.
Describing a bone lesion
Use a systematic approach: age, location (epiphysis, metaphysis, diaphysis), margin (narrow zone of transition suggests benign), matrix (osteoid, chondroid, fibrous), periosteal reaction and soft tissue mass. Aggressive features include wide zone of transition, cortical destruction and an interrupted periosteal reaction.
Fractures and arthritis
Describe fractures by bone, location, displacement, angulation and intra-articular extension. Osteoarthritis: asymmetric joint space loss, osteophytes, subchondral sclerosis, no erosions. Rheumatoid arthritis: symmetric erosions at bare areas, osteopenia, joint space loss. Gout: punched-out erosions with overhanging edges.
MRI
Use fluid-sensitive sequences (STIR, T2 fat-saturated) for oedema and marrow signal; T1 for anatomy. Anterior cruciate ligament tears show discontinuity and oedema on T2. Osteomyelitis: marrow oedema with low T1 and high T2 signal, with enhancement.
Worked example
A 15-year-old has 3 months of knee pain and a metaphyseal femoral lesion with a wide zone of transition, sunburst periosteal reaction and a soft tissue mass. This is an aggressive lesion, most likely osteosarcoma; the next step is MRI of the whole bone for staging plus chest CT, and biopsy at the treating centre - not simple curettage.
Traps
Calling a Brodie abscess a benign cyst; missing a stress fracture on radiographs (use MRI); describing fracture displacement without stating the direction; confusing gout and rheumatoid erosions; forgetting that marrow oedema is non-specific.