Tendon mechanical properties and measures of shoulder function are altered after multiple tendon detachment in a rat rotator cuff model

While most tears of the rotator cuff occur in the supraspinatus tendon, only half of those tears are isolated to that one tendon. It is presumed that damage in the remaining (untorn) tendons occurs in the presence of an isolated supraspinatus tendon or multiple tendon tear, which may facilitate tear progression. Additionally, loss of shoulder function due to tears, such as reduced range of motion and stiffness can lead to decreases in the ability to work and perform activities of daily living. Clinically, rating systems are used to evaluate the effect of these rotator cuff tears on shoulder function, with larger tears receiving poorer functional scores. Unfortunately, current animal models of shoulder injuries involve only one of the rotator cuff tendons and do not examine shoulder function as a result of rotator cuff injury. Animal models are useful for the investigation of rotator cuff injuries as tear size, location, and the length of time from initial injury can be controlled. Therefore, the objective of this study was to develop and utilize an animal model of multiple rotator cuff tendon tears to investigate alterations in shoulder function and the remaining (untorn) tendon mechanical properties. We hypothesized that an increase in the number of tendons torn would result in increased detrimental changes to the remaining (untorn) shoulder tendons. Additionally, we hypothesized that shoulder function parameters, such as rat ambulation and total range of motion, would be reduced as a result of increasing tear size. We created a multiple rotator cuff tendon tear model in the rat in which the detached tendon mechanical properties were decreased, consistent with a lack of loading. Using this model, we found that the remaining (untorn) tendons of the shoulder are damaged and have decreased mechanical properties in the presence of rotator cuff tears. We also identified that functional alterations are present after rotator cuff tendon tears, with larger tears creating larger functional deficits. Therefore, rotator cuff tendon tears may lead to alterations in joint mechanics from compensations and limitations in shoulder function. These alterations can in turn damage the remaining (untorn) tendons of the shoulder