Glenohumeral translation during active and passive elevation of the shoulder — a 3D open-MRI study

Despite its importance for the understanding of joint mechanics in healthy subjects and patients, there has been no three-dimensional (3D) in vivo data on the translation of the humeral head relative to the glenoid during abduction under controlled mechanical loading. The objective was therefore to analyze humeral head translation during passive and active elevation by applying an open MR technique and 3D digital postprocessing methods. Fifteen healthy volunteers were examined with an open MR system at different abduction positions under muscular relaxation (30–150° of abduction) and during activity of shoulder muscles (60–120°). After segmentation and 3D reconstruction, the center of mass of the glenoid and the midpoint of the humeral head were determined and their relative position calculated. During passive elevation, the humeral head translated inferiorly from +1.58 mm at 30° to +0.36 mm at 150° of abduction, and posteriorly from +1.55 mm at 30° to −0.07 mm at 150° of abduction. Muscular activity brought about significant changes in glenohumeral translation, the humeral head being in a more inferior position and more centered, particularly at 90 and 120° of abduction (p<0.01). In anterior/posterior direction the humeral head was more centered at 60 and 90° of abduction during muscle activity. The data demonstrate the importance of neuromuscular control in providing joint stability. The technique developed can also be used for investigating the effect of muscle dysfunction and their relevance on the mechanics of the shoulder joint.