Abstract
Background: Posterosuperior massive rotator cuff tears remain challenging to manage. While lower trapezius transfer restores posterior cuff function, it lacks the superior cuff's biomechanical role. Middle trapezius tendon transfer has shown efficacy in addressing superior cuff deficiencies with dynamic joint-centering and spacer effects. This study aimed to compare the biomechanical effects of lower trapezius transfer alone versus combined lower and middle trapezius transfer for posterosuperior massive rotator cuff tears. Methods: Eight cadaveric shoulders were tested under four conditions: intact, posterosuperior cuff tear, lower trapezius transfer, and combined lower and middle trapezius transfer. Superior translation, subacromial contact pressure, and rotational range of motion were measured at multiple abduction and external rotation positions. Statistical analysis was performed using a linear mixed-effects model. Findings: Both lower trapezius and combined lower and middle trapezius transfers significantly reduced superior humeral head translation versus the tear condition (p < .041). The combined transfer restored translation to intact levels and was more effective than lower trapezius transfer alone at 0° and 20° abduction (p < .031). Subacromial contact pressure decreased significantly with both transfers at 20° and 40° abduction (p < .030), and with combined transfer also at 0° abduction and 30° ER (p < .042). Total rotational range of motion was preserved in all conditions. Interpretation: Combined lower and middle trapezius transfer offers superior biomechanical restoration of glenohumeral joint stability compared to lower trapezius transfer alone without compromising range of motion. These findings support the potential of dual tendon transfer in addressing both posterior and superior cuff deficiencies, warranting further clinical evaluation. © 2025