The stabilizing function of the glenohumeral joint capsule. Current aspects of the biomechanics of instability

Abstract

The purpose of the study was to determine the influence of rotation torques on superior-inferior and anterior-posterior translation in various degrees of abduction in the glenohumeral joint. 16 cadaveric shoulders were tested using a specifically designed four-degrees-of-freedom mounting apparatus and a 6-degrees-of-freedom tracking system which allowed of dynamic and static measurements by means of ultrasound (Zebris) Internal/external rotation torques and translation forces in the inferior-superior and anterior-posterior plane were applied in 0 degrees, 45 degrees, 75 degrees and 85 degrees of abduction. Shoulders were tested intact, vented, after severing of the acromion and coracoid (7 shoulders) and after subsequent division of the anterior capsule at the glenoid margin including a T-shaped incision (8 shoulders). Venting of the capsule resulted in a significant increase in ap-translation only in abduction of less than 45 degrees. Rotation torques and an abduction of more than 45 degrees effected a centering of the humeral head against translation-forces in the anterior-posterior and superior-inferior direction. The weakening of the anterior capsule by a T-shaped incision, in which circular fibers were also severed, significantly increased the anterior translation in comparison to that obtained after an incision along the glenoid margin.(ABSTRACT TRUNCATED AT 250 WORDS)