Incidence of acromioclavicular joint involvement in rheumatoid arthritis: a 15 year endpoint study.

OBJECTIVE: To evaluate the incidence of involvement and nature of destruction of acromioclavicular joints (AC) in a prospectively followed cohort of 74 patients with rheumatoid factor positive and erosive rheumatoid arthritis (RA). METHODS: At the 15 year followup, radiographs of 148 AC joints were evaluated, and the grade of destruction was assessed by the Larsen method. RESULTS: No surgical procedures had been performed on the AC joints. Rheumatoid involvement (Larsen Grade > or = 2) was observed in 87/148 (59%) of the AC joints in 50/74 (68%) patients: 37 bilaterally and 13 unilaterally. Incidence of mild erosions (Larsen Grade 2) was 39%, and of severe (Larsen 3-5) 20%. Erosions were most often observed on the inferior edge of the clavicular joint margin. Degenerative features without rheumatoid changes were present in 11 joints. Larsen score (0-100) of peripheral joints correlated well with the AC joint Larsen Grade in both sides: right, r = 0.56 (95% CI 0.38 to 0.70), left, r = 0.49 (95% CI 0.30 to 0.65). CONCLUSION: After 15 years two-thirds of the patients with RA showed involvement of the AC joints. Erosions were located most often on the inferior margin of the joint.