The Fate of the Shoulder Post Rotator Cuff Repair: Biomechanical Properties of the Supraspinatus Tendon and Surrounding Structures.

The study aimed to describe the changes in biomechanical properties of the supraspinatus tendon, deltoid muscle, and humeral head post arthroscopic rotator cuff repair using shear wave elastography. Shear wave velocity of the tendon, deltoid, and humeral head of 48 patients was measured at predetermined sites at 1 week, 6 weeks, 12 weeks, 6 months, and 12 months post repair. One-way ANOVA with Tukey's correction and Spearman's correlation were performed. Mean±SEM healing tendon stiffness, adjacent to tendon footprint, increased from 1 week (6.2±0.2 m/s) to 6 months (7.5±0.3 m/s) and 12 months (7.8±0.3 m/s) (P<0.001). Mean±SEM deltoid muscle stiffness was higher at 12 months (4.1±0.2 m/s) compared to 1 week (3.4±0.1 m/s) and 12 weeks (3.5±0.1 m/s) (P<0.05). Humeral head stiffness did not change. Following arthroscopic rotator cuff repair, supraspinatus tendon stiffness increased in a curvilinear fashion over 6 months. From 6 months, deltoid muscle stiffness increased, corresponding to when patients were instructed to return to normal activities.