Glenohumeral movement patterns after puncture of the joint capsule: An experimental study.

In on experimental series comprising 22 shoulder specimens obtained at autopsy, we investigated the influence of an intact capsule on glenohumeral stability. Puncture of the capsule resulted in significant glenohumeral translation in unloaded and loaded specimens during shoulder abduction. A maximum of 16.6 mm of distal translation was observed at 20° of abduction. Concomitant with this translation the humerus spontaneously rotated externally, with a maximum rotation of 15.8° at 50° of abduction. After venting the capsule, anterior and posterior translation and external rotation were increased significantly. Maximum total increase in anteroposterior translation was 14 mm at 30° of abduction. The external rotation was increased up to 7.1° at 40° of abduction. These findings indicate that studies evaluating glenohumeral instability are compromised unless the translations resulting from capsular venting ore corrected. Evaluation of shoulder stability should be performed before violation of the intraarticular pressure mechanisms.