Analysis of Abduction Moment Arms after Rotator Cuff Tear and Acellular Dermal Matrix Allograft Reconstruction.

Abstract

Biomechanical testing of abduction moment arms presents a useful method to assess the contribution of individual rotator cuff muscles to glenohumeral function. This study aimed to investigate the changes in abduction moment arms after a supraspinatus tear treated with Superior Capsule Reconstruction (SCR), Bursal Acromial Reconstruction (BAR), and a combined SCR-plus procedure, all with human dermal allograft. 7 fresh-frozen cadaveric specimens were tested in 6 conditions: (1) intact, (2) 50% supraspinatus tear (partial tear), (3) 100% supraspinatus tear, (4) SCR, (5) SCR+BAR, (6) BAR. In each condition, moment arms for the individual muscles of teres minor, subscapularis, and infraspinatus were calculated throughout 90º of abduction using Optotrak motion capture. ANOVA and post-hoc Tukey testing were performed to determine significance. In teres minor, the moment arms of the SCR (11.92mm), BAR (10.05mm), and SCR+BAR (11.87mm) conditions were greater than those in the intact (8.51mm, p=0.001, p=0.001, p=0.001, respectively), partial tear (9.09mm, p=0.001, p=0.128, p=0.001, respectively), and complete tear (8.75mm, p=0.001, p=0.011, p=0.001, respectively) conditions. Similarly in subscapularis, moment arms in the SCR (13.36mm), BAR (13.84mm), and SCR+BAR (13.53mm) conditions were greater than those in the intact condition (10.59mm, p=0.006, p=0.001, p=0.003, respectively) and partial tear condition (10.43mm, p=0.006, p=0.001, p=0.003, respectively). In teres minor, SCR (11.92mm) and SCR+BAR (11.87mm) were also found to have significantly increased moment arms compared to BAR (10.05mm, p=0.001, p=0.001, respectively). In Infraspinatus, BAR (13.77mm) was found to have a significantly decreased moment arm compared to the partial tear condition (15.78mm, p=0.026), with no other significant findings between conditions. These results suggest that the moment arm contributions from individual muscles comprising the rotator cuff can change after reconstruction to compensate for tears. SCR and SCR+BAR increase moment arms in teres minor and subscapularis, potentially allowing for increased abduction ability.