Glenohumeral abduction and the long head of the biceps.

The role of the long head of the biceps in glenohumeral abduction and the accompanying external rotation is an unsettled issue. Automatic external rotation however has been previously demonstrated during passive abduction, with intact long head and the absence of factors traditionally considered to influence the rotation such as the coracoacromial arch and muscles surrounding the joint. The present study on the anatomy of the tendon of the long head in relation to passive abduction shows that not only is the tendon likely to be harmed by forced abduction without external rotation but the course of the tendon itself is such that activity in the long head during abduction is likely to influence external rotation that in turn prevents tendon impingement between greater tuberosity and glenoid labrum and allows glenohumeral abduction to be carried further towards completion.