The rotary influence of articular contours during passive glenohumeral abduction

Automatic external rotation at the glenohumeral joint is an essential component of active as well as passive elevation of the arm through abduction. Recent studies have demonstrated this automatic rotation to be present during passive abduction using cadaveric glenohumeral joints even in the absence of extra-articular influences like the coraco-acromial arch and glenohumeral muscles. In the present study, simulated abduction in disarticulated cadaveric joints was shown to be associated with automatic external rotation suggesting a role in this mechanism for the articular contours.