The long head of the biceps has a stabilizing effect on the glenohumeral joint in simulated infraspinatus or subscapularis but not supraspinatus rotator cuff deficiency - a biomechanical study

Katthagen, J. Christoph; Wermers, Jens; Paus, Christoph; Michel, Philipp A.; Köhler, Alina; Schliemann, Benedikt; Raschke, Michael J.

Zusammenfassung

PURPOSE - METHODS - RESULTS - CONCLUSIONS; To investigate the stabilizing role of the long head of the biceps (LHB) for different simulated rotator cuff (RC) tears.; Human cadaveric specimen (n = 8) were fixed in a robotic-based experimental setup with a static loading of the RC, deltoid and the LHB. RC tears were simulated by unloading of the corresponding muscles. A throwing motion and an anterior load-and-shift test were simulated under different RC conditions by unloading the supraspinatus (SS), subscapularis (SSc), infraspinatus (IS) and combinations (SS+SSc, SS+IS, SS+SSc+IS). The LHB was tested in three conditions: unloaded, loaded, tenotomy. Translation of the humeral head and anterior forces depending on loading of the RC and the LHB were captured.; Loading of LHB produced no significant changes in anterior force or glenohumeral translation for the intact RC or a simulated SS tear. However, if SSc or IS were unloaded, LHB loading resulted in a significant increase of anterior force ranging from 3.9 N (p = 0.013, SSc unloaded) to up to 5.2 N (p = 0.001, simulated massive tear) and glenohumeral translation ranging from 2.4 mm (p = 0.0078, SSc unloaded) to up to 7.4 mm (p = 0.0078, simulated massive tear) compared to the unloaded LHB. Tenotomy of the LHB led to a significant increase in glenohumeral translation compared to the unloaded LHB in case of combined SS+SSc (2.6 mm, p = 0.0391) and simulated massive tears of all SS+SSc+IS (4.6 mm, p = 0.0078). Highest translation was observed in simulated massive tears between loaded LHB and tenotomy (8.1 mm, p = 0.0078).; Once SSc or IS are simulated to be torn, the LHB has a stabilizing effect for the glenohumeral joint and counteracts humeral translation. With a fully loaded RC, LHB loading has no influence.