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 dat a on the translation of the humeral head relative to the glenoid during abd uction under controlled mechanical loading. The objective was therefore to analyze humeral head translation during passive and active elevation by app lying an open MR technique and 3D digital postprocessing methods. Fifteen h ealthy volunteers were examined with an open MR system at different abducti on positions under muscular relaxation (30-150 degrees of abduction) and du ring activity of shoulder muscles (60-120 degrees). After segmentation and 3D rt construction, the center of mass of the glenoid and the midpoint of t he humeral head were determined and their relative position calculated. Dur ing passive elevation, the humeral head translated inferiorly from + 1.58 m m at 30 degrees to + 0.36 mm at 150 degrees of abduction, and posteriorly f rom + 1.55 mm at 30 degrees to - 0.07 mm at 150 degrees of abduction, vascu lar activity brought about significant changes in glenohumeral translation, the humeral head being in a more inferior position and more centered, part icularly at 90 and 120 degrees of abduction (p < 0.01). In anterior/posteri or direction the humeral head was more centered at 60 and 90 degrees of abd uction during muscle activity. The data demonstrate the importance of neuro muscular control in providing joint stability. The technique developed can also be used for investigating the effect of muscle dysfunction and their r elevance on the mechanics of the shoulder joint. (C) 2000 Elsevier Science Ltd. All rights reserved.