SYNOVIOCHONDROMETAPLASIA (Synovial osteochondromatosis):
It is a benign arthropathy characterised by tissue undergoing metaplastic transfrmation to produce foci of cartilage. This results in multiple loose bodies within the joint (at least 2 cms of synovium is involved).
Epidemiology:
3rd - 5th decades, Males : females = 3 : 1
Knee is the commonest site of affection (70%), followed by hip (20%), elbow, ankle, shoulder, wrist.
Pathology:
Primary - arises spontaneously. May be due to recurrent microtrauma.
Secondary - as a sequela to degenerative and neuropathic joint disease, osteochondritis dissecans, osteochondral fractures, joint dislocations
Malignant transformation to synovial chondrosarcoma is very rare.
Radiographic features:
Multiple calcified / ossified loose bodies of uniform size without joint space narrowing / osteoporosis.
Extrinsic intraarticular pressure erosions - hip (apple core deformity) of femoral neck, wrist
CT - useful in detecting small bodies, erosions
MRI - when uncalcified, signal intensity resembles fluid on all pulse sequences. When calcified, hypointense signal is seen on both T1 and T2 weighted images.
Differential diagnosis:
Sesamoid bones, osteochondritis dissecans, pseudo- gout, synovioma, pigmented villonodular synovitis, chondrosarcoma.