Humeral head retroversion in patients with unstable humeroscapular joints. Humeral head retroversion and shoulder rotation in both the frontal and scapular plane were studied in 34 patients with anterior glenohumeral instability. Twenty-two patients had traumatic anterior shoulder dislocations and another 12 patients had nontraumatic dislocations with generalized joint laxity. Patients with traumatic recurrent dislocations had a smaller than normal retroversion angle in the unstable shoulder. The angles were 26 degrees on the dominant side and 23 degrees on the nondominant side compared with 33 degrees and 29 degrees, respectively, in normal shoulders. The stable contralateral shoulder joint was clinically and roentgenographically similar to the normal shoulder. The patients with nontraumatic dislocations had increased rotation and smaller retroversion angles, irrespective of stability in the shoulder joint. The retroversion angles were 18 degrees for unstable shoulders on the dominant side and 15 degrees on the nondominant side. The retroversion angle of the stable contralateral joint in these patients was less in five of eight shoulders. 