Influence of fat infiltration, tear size, and post-operative tendon integrity on muscle contractility of repaired supraspinatus muscle.

Background The purpose of this study was to evaluate the effect of fat infiltration, tear size, and post-operative tendon integrity, on post-operative contractility. Methods Thirty-five patients who underwent rotator cuff repair were included. The fat infiltration, tear size, and post-operative tendon integrity were evaluated by Goutallier stage, Cofield classification, and Sugaya classification, respectively. The muscle elasticity at rest and at contraction was assessed by real-time tissue elastography pre- and one-year post-operatively. We defined the difference in elasticity between at rest and at contraction as the activity value which reflects muscle contractility. Results The activity value in patients with Sugaya Type I tended to increase regardless of Cofield classification, whereas those with Sugaya Type III and IV tended to decrease. While the activity value in the patients classified as stage 1 and Type I tended to increase, patients classified as stage 2 showed decreased or constant in contractility even in those subjects classified as Type I. Stepwise multiple regression analysis showed both pre- (p = 0.004, r = -0.47) and post-operative activity values (p = 0.022, r = -0.39) to be significantly correlated only with the Goutallier stage. Conclusion Multiple regression analysis indicated only the Goutallier stage was a significant independent factor for contractility of the supraspinatus muscle. Supraspinatus muscle contractility in patients classified as Types III and IV based on the Sugaya classification tended to decrease post-operatively, while patients whose contractility increased post-operatively were characterized by having a Type I tendon integrity.