OBJECTIVETo investigate the in vivo and three-dimensional (3D) length changes of the glenohumeral ligaments during shoulder abduction using open magnetic resonance imaging (MRI).

METHODSFrom 2007 to 2008 3D attachment points of the glenohumeral ligaments were obtained by anatomical study and computed tomographic scanning of 10 embalmed cadaveric shoulders, including the superior glenohumeral ligament (SGHL), middle glenohumeral ligament (MGHL), the anterior band of the inferior glenohumeral ligament (AIGHL), axillary pouch and the posterior band of the inferior glenohumeral ligament (PIGHL). Then an in vivo study was conducted, in which 14 right shoulder joints of 14 healthy volunteers were evaluated in 7 isometric abduction positions (0 degrees , 30 degrees , 60 degrees , 90 degrees , 120 degrees , 150 degrees and 180 degrees ) using a noninvasive 3D motion-analysis system. 3D models of the shoulders and located the attachment points of the ligaments were created. Ligament lengths were based on the shortest calculated paths between each origin and insertion in 3D space along the 3D bone surface for each abduction position.

RESULTSDuring shoulder abduction, the 3D distance of SGHL was found to elongated and attained maximal length at 30 degrees abduction (P = 0.2). MGHL and AIGHL attained maximal length at 60 degrees (P < 0.05) and 120 degrees (P < 0.05) abduction, respectively. Pouch and PIGHL reached the maximal length at 180 degrees abduction (P < 0.05).

CONCLUSIONSThe SGHL limits inferior translation of the humeral head at 30 degrees of abduction. MGHL maintains maximum anterior stability at 60 degrees of abduction. AIGHL prevents anterior dislocation of the humeral head at 120 degrees of abduction. In 180 degrees abduction, pouch provided anterior stability and PIGHL has the contribution to the inferior stability.