Musculoskeletal Imaging
Core concepts
Understand fracture description: location, pattern, displacement, angulation, and joint involvement. Know bone tumour approach: age, location (epiphysis/metaphysis/diaphysis), margin, matrix, and periosteal reaction (benign vs aggressive). Learn arthritis patterns: osteoarthritis (joint space narrowing, osteophytes, subchondral sclerosis), rheumatoid (erosions, periarticular osteopenia), seronegative (enthesopathy, new bone), and gout (punched-out erosions with overhanging edges). Know soft tissue signs: lipohaemarthrosis, joint effusion, and the fat pad signs. Understand MRI of ligaments, menisci, and bone marrow oedema.
Traps
- Aggressive periosteal reaction (sunburst, Codman triangle) suggests malignancy or infection-not benign.
- Osteophyte vs erosion: OA has osteophytes; RA has erosions.
- A normal radiograph does not exclude fracture-use MRI/CT for occult fractures.
- Bone marrow oedema is non-specific (trauma, infection, tumour, CRPS).
- Do not mislabel chondrocalcinosis as gout.
Worked example / rule of thumb
A young patient with knee pain and a lytic metaphyseal lesion with a wide zone of transition: think aggressive lesion (osteosarcoma, infection) and refer urgently. Rule of thumb: narrow zone of transition and sclerotic margin = slow-growing benign; wide zone and aggressive periosteal reaction = aggressive. For arthritis, erosions favour inflammatory; osteophytes favour degenerative.
Key points
- Describe fractures systematically.
- Bone tumour: age, location, margin, matrix, periosteal reaction.
- OA vs RA vs seronegative vs gout patterns.
- Occult fractures need MRI/CT.
- Marrow oedema is non-specific.