Microfocal radiographic examination of erosions in the wrist and hand of patients with rheumatoid arthritis.

The microfocal x-ray unit, a new type of x-ray machine characterised by an extremely small x-ray source, enables great detail to be recorded in the projection radiographs owing to the high object magnification and resolution obtained with this system. Microfocal radiographic examinations were carried out on the wrists and hands of 26 patients with early or moderately advanced rheumatoid arthritis. The macroradiographs confirmed the presence or absence of erosions in patients with early disease activity who otherwise had no detectable lesions visible in standard radiographs. The site of onset, development, and distribution of erosions are described. Their approximate order of appearance is listed. The first to appear occurred in the medial carpal bones, second and third metacarpophalangeal joints and third and fourth proximal interphalangeal joints. In origin they were subperiosteal either immediately adjacent to the insertion of an interosseous ligament or at the transitional zone of the articular cartilage. Erosions in the subchondral bone appeared subsequently and were either indirect (subperiosteal) or direct (subchondral) in origin. Cyst formation was frequently associated with the enlargement of an erosion which it often replaced.