[Measurement of glenohumeral joint translation with a dynamic shoulder model]

Translation of the glenohumeral joint was measured with a dynamic shoulder model, during elevation of the arm in eight cadaveric specimens. Controlled hydrodynamic actuator forces were applied to the deltoid muscle and the rotator cuff through wire cables. Using a constant force ratio, the glenohumeral joint was elevated to 90 degrees. The position of the arm in all spatial orientations was measured with an ultrasonic device. Reproducibility of glenohumeral joint motion was demonstrated on the basis of five cycles of glenohumeral joint elevation. The rotational center of the humeral head was used as the reference point for translation. Translation during elevation of the glenohumeral joint between 20 degrees and 90 degrees averaged 9.0 mm +/- 5.2 mm superiorly and 4.4 mm +/- 1.3 mm anteriorly. In vivo, this may be diminished by coordinated activity of the rotator cuff. The presence of significant glenohumeral joint translation underlines the importance of active, muscular guidance at the shoulder. Physiologic translation of total shoulder arthroplasty, in shoulder instability and in the impingement syndrome.