Stress distribution in the superior labrum during throwing motion

Background: Superior labrum anterior posterior lesions are common among athletes participating in overhead throwing sports. One described mechanism of injury is application of high local stress via repetitive loading of the long head of the biceps tendon attached to the superior labrum; however, the stress environment within the labrum has not been investigated to date. Hypothesis: Biceps origin locations and throwing phases determine the stress distributions causing lesions of the superior labrum within the labrum itself. Study Design: Descriptive laboratory study. Methods: Three-dimensional finite element models of the labrum glenoid complex with anterior, central, and posterior biceps origins were developed at 4 orientations to simulate the phases of pitching: early cocking, late cocking, acceleration, and deceleration. Results: The stress magnitudes at the labrum glenoid interface for the deceleration phase were highest for all biceps origins. Anatomical variations of the biceps insertion affected the stress only during the deceleration phase. Both the biceps origin and throwing phase influenced the location of high stress. Conclusion: Deceleration could be the throwing phase that causes tearing at the superior labrum. This finding provides further understanding for localizing the possible initiation of superior labrum anterior posterior lesions.