A study of glenohumeral orientation in patients with anterior recurrent shoulder dislocations using computerized axial tomography.

Thirty-six patients with recurrent anterior shoulder dislocations and 11 normal patients who had no history of shoulder problems were evaluated by a G.E. 8800 fourth generation computerized axial tomographer to quantitate humeral head retrotorsion and glenoid tilt. The study objective was to determine if osseous orientation was a major etiologic factor in patients with recurrent anterior shoulder dislocations. The normal position of the humeral head as determined by CT scan is 30 degrees retroversion with respect to its distal articular axis. In dislocations this value changes to a more anteverted position of 24 degrees retroversion. Glenoid tilt could not be given a single value since it changes from retroversion superiorly toward more anteversion inferiorly. This change in glenoid tilt was greater in the dislocators with inferior sections measuring 2 degrees anteversion in the dislocators and 1 degree retroversion in the uninvolved shoulder and in the normal population. The change in humeral retroversion and glenoid tilt in the recurrent dislocators was statistically significant when compared with the uninvolved shoulder and to the normal population. Thus, the glenoid humeral orientation appears to be a significant predisposing factor to recurrent anterior shoulder dislocations.