Infraspinatus and supraspinatus tendon strain explained using multiple regression models.

Supraspinatus tendon tears are complex yet common. We have shown that the supraspinatus and infraspinatus tendons interact, indicated by parallel changes in strain in the supraspinatus and infraspinatus with increasing size of supraspinatus tear, load applied to the supraspinatus, and changes in glenohumeral rotation but not abduction angle, suggesting disruption in the interaction between the two tendons with increase in abduction angle. While considering these factors individually is valuable, the contribution of each factor in the context of all others on strain in the supraspinatus, or on the interaction between the two tendons is unknown and has important implications in the management of rotator cuff tears. In this study, regression models using least-square estimation with backward and forward elimination were used to predict strains in the infraspinatus and supraspinatus from joint position, supraspinatus load, and supraspinatus tear size or repair. Interestingly, despite previous findings showing that supraspinatus tear size significantly affects infraspinatus strain, tear size was not a significant predictor of infraspinatus strain, emphasizing the importance of other factors evaluated such as joint position and shoulder loading in management of cuff tears and postoperative care. A better understanding of the loading environment in rotator cuff tendons necessitates multifactorial complex models.