The main pathological feature of rheumatoid arthritis (RA) is synovitis, which may become erosive and extend to cartilage and bone and cause bone resorption with subsequent joint instability. In contrast, the spondyloarthropathies are characterised by enthesitis, which may bring about new bone formation with osteophytes and ankylosis.

Only recently these important differences in pathogenesis have become elucidated.1 Earlier, ankylosis had been accepted as a part of RA.2 Interestingly, in palaeopathological publications the existence of ankylosis in RA has for a long time been a matter of dispute and even denied.3^–5

To examine this subject further, the occurrence of spontaneous ankylosis was studied in patients attending the rheumatology unit at Kristianstad County Hospital in southern Sweden …