Imaging the joint and enthesis: insights into pathogenesis of psoriatic arthritis.

The distinct radiographic features of psoriatic arthritis (PsA) help confirm it as a distinct entity from rheumatoid arthritis and highlight some unique non-synovial based disease imaging features. The advent of magnetic resonance imaging and a better understanding of joint microanatomy including the complexity of joint entheses provide a unifying anatomical and biomechanical concept that links disease at the apparently disparate sites of involvement in PsA, including the synovium, the enthesis, the bone and the periosteum. These findings suggest a reason for the localisation of disease to skeletal sites that are subject to repeated mechanical stressing.