Influence of joint stability on the results of arthroscopic subacromial decompression.

We performed arthroscopic subacromial decompression on 70 patients. Each of them had either type I or type II impingement according to Neer. Sixty-five patients were then observed for a postoperative period of three years. The follow-up checks were performed by ultrasound in order to assess the extent of passive inferior shift of the humeral head, compared with the preoperative stage. A shoulder score of 100 was used as a reference. Whereas the average preoperative score was 58.5 (standard deviation +/- 12.2), postoperative results showed an increased average value of 79.7 (standard deviation +/- 11.4). In twenty cases (31% of all treated patients), the postoperative score was less than 85 points, i.e. treatment had shown no results. Comparing these patients with the other 45 who had a score above 85 points, we noted that the age of patients, the preoperative duration of complaints, the preoperative score and duration of the postoperative stay in hospital were of no relevance to the results. However, among all patients, ultrasound measurements showed significant deviations in the extent of passive inferior shift of the humeral head. Patients in the group with unsuccessful treatment had an average shift value of 5.1 mm. (+/- 2.0 mm), compared with an average value of only 2.4 mm (+/- 0.9 mm) among patients in the successful group. The statistical negative Pearson correlation coefficient of -5.36 between postoperative score and inferior shift of the humeral head is very significant. We conclude that hypermobile glenohumeral joints or unstable joints should not be treated by subacromial decompression in the presence of any subacromial pathology.