Restoration of rotator cuff muscle forces in lower trapezius transfer and superior capsular reconstruction in massive rotator cuff tear.

Background: This study aimed to evaluate the biomechanical effects of lower trapezius tendon transfer (LTT), superior capsular reconstruction (SCR), and their combination on rotator cuff muscle force restoration in irreparable massive rotator cuff tears (MRCTs). We hypothesized that combining LTT with SCR would yield superior biomechanical restoration compared to either technique alone. Methods: Eight fresh-frozen cadaveric shoulders were tested under the following 6 sequential conditions: (1) intact control, (2) supraspinatus tear, (3) MRCT (supraspinatus and infraspinatus tear), (4) LTT using an Achilles allograft, (5) LTT combined with SCR, and (6) SCR alone. Muscle forces in the teres minor (TM) and subscapularis (SubS) were measured during humeral abduction using a dynamic shoulder testing system. Results: TM force decreased by 21.6% after a supraspinatus tear and by 49.7% after MRCTs. LTT alone restored 84.5% of intact TM force, LTT with SCR restored 89.8%, and SCR alone restored 65%. SubS force increased by 115% following a supraspinatus tear and by 194% after MRCTs. LTT restored 71% of SubS force, LTT with SCR restored 90%, and SCR alone restored 46%. These differences were statistically significant across conditions (P < .05), particularly between the massive tear and reconstructive states. Conclusions: Combining LTT and SCR demonstrated the most effective restoration of rotator cuff biomechanics, surpassing the results of individual techniques. Statistical analysis confirmed significant improvements in TM and SubS force restoration when using LTT with SCR compared to isolated reconstructions.