Magnetic resonance based motion analysis of the shoulder during elevation

Changes in shoulder motion patterns are relevant in various shoulder diseas es, but no in vivo information exists about the relative positions in vivo of the shoulder girdle bones and the supraspinatus muscle in three-dimensio nal space. Thus, the objective of this study was to perform a motion analys is of these structures during passive arm elevation using open magnetic res onance imaging and three-dimensional image processing, Fourteen volunteers were examined in five positions of abduction (30 degrees-150 degrees) with an open magnetic resonance system. After segmentation and three-dimensional reconstruction, the axis of the supraspinatus, humerus, clavicle., and the plane of the glenoid were determined, and the relative movements were calc ulated, The ratio for glenohumeral to scapulothoracic motion was 1.5:1 at 6 0 degrees and 2:4:1 at 120 degrees abduction. At 30 degrees, the axis of th e supraspinatus was nearly horizontal, and during abduction a continuous el evation (+123 degrees at 150 degrees abduction) was measured. in the transv erse plane, the angle between the supraspinatus and the clavicle sues becam e larger during abduction because of an increasing retroversion of the clav icle, The study shows specific three-dimensional motion patterns for each b one of the shoulder girdle and the supraspinatus muscle during passive elev ation, The technique and results can be used for future studies in patients with pathologic changes of shoulder girdle motion.