The role of altered loading in pathological changes in the long head of the biceps tendon following rotator cuff tears in a rat model

Damage to the biceps tendon is common clinically and is frequently seen in the presence of rotator cuff tears. However, there is some debate over the role of the biceps tendon at the shoulder following a rotator cuff tear with some believing the biceps to play a significant role as a humeral head depressor while others believe the biceps plays no role at all. Therefore, controversy exists regarding its optimal treatment, with physicians relying mostly on anecdotal experience. Unfortunately, most clinical studies are not able to address the underlying causes in a controlled manner and cadaveric studies cannot monitor the injury process with time. Tendon degeneration and inflammation are both thought to play a role; however, the mechanisms responsible remain unknown, making clinical management of this problem difficult. Therefore, the objective of this study was to examine the effect of alterations in loading on the initiation of pathological changes in the long head of the biceps tendon following rotator cuff tears in order to determine its role as a mechanism for these changes. We hypothesized that rotator cuff tears result in altered loading that lead to degeneration of the biceps tendon, beginning at the insertion site and continuing along the length with time. Additionally, we hypothesized that increased loading following rotator cuff tears would result in further degeneration while decreased loading would result in improved tendon properties. We created an animal model of biceps tendon pathology in the presence of rotator cuff tears and utilized this model to examine the early, intermediate and late changes in histological, organizational, compositional and mechanical properties of the biceps tendon. We found that changes began in the intra-articular portion of the tendon before progressing to the extra-articular portion with time. We also investigated the effect of altered loading on these properties and found that increased loading resulted in further detrimental changes while decreased loading resulted in improved properties. These results indicate that the biceps tendon plays an increased role as a load bearing structure in the presence of rotator cuff tears and that these changes may be recoverable with decreased loading