Introduction: Rotator cuff tears (RCT) are linked with decreased joint centring in the shoulder. Comprehensive understanding of glenohumeral biomechanics is, however, lacking. We conducted a preliminary ex-vivo study to assess the glenohumeral joint centring in one human shoulder. Methods: The shoulder was clamped in a muscular controlled glenohumeral simulator. The tendons of the supraspinatus, infraspinatus, teres minor, inferior and superior part of the subscapularis, deltoid anterior portion, deltoid middle portion, deltoid posterior portion, latissimus dorsi and pectoralis major were connected to a motorized pulley system and muscle forces were applied according to a static muscle optimization scheme. An abduction-adduction cycle of 30° was performed in the scapular plane under different rotator cuff tear types. Each tear type was repeated with additional weight simulating handheld weight ranging from 0 to 3 kg. The instantaneous contact pressure has been assessed with a 6-component force sensor. Results: Fig. 1 illustrates the path of the contact pressure during 30 ° abduction. The contact path in the healthy shoulder moves central in the glenoid. The contact path is translated superiorly with increasing RCT severity and additional handheld weight. Discussion: Patients with RCT are at higher risk for glenohumeral impingement or even subluxation of the joint. Our preliminary results of one shoulder clearly show the feasibility of using our shoulder simulator and experimental setup to further elucidate the contribution of rotator cuff components to glenohumeral stability and the biomechanical implications of rotator cuff tears.
Genter et al. (Wed,) studied this question.