Role of the long head of the biceps brachii in glenohumeral stability: a biomechanical study in cadavera.

Ten cadaveric shoulders were tested to evaluate the effect of simulated contraction of the long head of the biceps brachii on glenohumeral translation. The shoulders were mounted on a special apparatus attached to a servo-controlled hydraulic testing device. Sequential 50 N anterior, posterior, superior, and inferior forces and a 22 N joint compressive load were applied to the shoulders. An air cylinder applied a constant force to the tendon of the long head of the biceps brachii. The shoulders were tested in seven positions of glenohumeral elevation and rotation. Application of a force to the long head of the biceps brachii resulted in statistically significant decreases in humeral head translation. The influence of the long head of the biceps was more pronounced at middle and lower elevation angles. When the shoulder was placed in 45 degrees of elevation and neutral rotation, application of a 55 N force to the biceps tendon reduced anterior translation by 10.4 mm (p = 0.001), inferior translation by 5.3 mm (p = 0.01), and superior translation by 1.2 mm (p = 0.004).