Variation of tension in the long head of the biceps tendon as a function of limb position with simulated biceps contraction

PURPOSE: This study was designed to quantify tensile forces within the intra-articular long head of the bicep tendon (LHBT) under conditions of passive limb positioning and physiologic load, which simulate contraction of the LHBT. MATERIALS AND METHODS: A force probe was inserted into the intra-articular LHBT, just distal to its supra-glenoid origin, in six fresh-frozen cadaveric specimens. Initially, specimens were manually manipulated through 30 glenohumeral joint positions, combining humeral rotation and elbow/forearm position. In the second phase, a 55 N tensile load was applied through the LHBT in 18 limb positions. Intra-tendinous tension was recorded in all positions under both conditions. RESULTS: External humeral rotation significantly increased tension with glenohumeral forward flexion (P<0.0001). Conversely, internal humeral rotation significantly increased tension with glenohumeral abduction and extension (P<0.0001). A position of glenohumeral extension and internal rotation, with the elbow extended and forearm pronated, produced the highest tension in the intra-articular LHBT (P<0.0001). Under applied load conditions, observed LHTB tension was not statistically different in any glenohumeral position (P=0.1468, power = 88%). The greater tuberosity was noted to impinge on the force probe in forward flexion and internal rotation in two specimens. CONCLUSIONS: Variable tensile forces are seen in the intra-articular LHBT as a function of both limb position and simulated biceps contraction. Our findings provide a thorough data set that may be used to help substantiate or refute current or future hypotheses regarding LHBT function, pathology, and clinical tests. CLINICAL RELEVANCE: Identifying positions of glenohumeral motion, which affect LHBT tension will provide an anatomic basis for clinical tests proposed to be for diagnosing LHBT lesions, including superior labral anterior and posterior tears.