Coracoclavicular involvement--an atypical manifestation in rheumatoid arthritis.

An inception cohort of 74 patients with seropositive and erosive RA were followed up for 15 years. All 148 shoulders were radiographed with a standard method at the 15-year follow-up. The coracoclavicular region was evaluated from each radiograph. In addition, the distance between the processus coracoideus and the superior margin of the clavicle was measured. Only one clavicle had elongated, shallow erosion on the undersurface at the insertion area of the coracoclavicular ligaments. In this case the distance between the coracoid process and clavicle was 25 mm, whereas the mean distance of all shoulders (n = 148) was 17.4 mm (range 9 25 mm). We conclude that resorption on the undersurface of the distal clavicle is an atypical manifestation in rheumatoid arthritis. The origin of this atypical lesion is a not diminished distance between the processus coracoideus and the clavicle. Inflammation of the coracoclavicular ligaments is most likely the reason for this lesion.