The biomechanical effectiveness of tendon transfers to restore rotation after reverse shoulder arthroplasty: latissimus versus lower trapezius.

BACKGROUND: The purpose of this biomechanical simulator study was primarily to compare latissimus dorsi to lower trapezius tendon transfers for active external rotation and the pectoralis major transfer for internal rotation after reverse shoulder arthroplasty. Secondarily, the role of humeral component lateralization on transfer function was assessed. METHODS: Eight rotator cuff deficient cadavers underwent reverse shoulder arthroplasty with an adjustable lateralization humeral component. Latissimus dorsi and lower trapezius transfers were compared for active external rotation restoration and pectoralis major transfer for internal rotation restoration. Internal rotation/external rotation torques were measured for each lateralization at varying abduction and internal rotation/external rotation ranges-of-motion. RESULTS: The lower trapezius transfer generated, on average, 1.6 ± 0.2 nm more torque than the latissimus dorsi transfer (p < 0.001). The internal rotation/external rotation torques of all tendon transfers decreased as abduction increased (p < 0.01). At 0° elevation, reverse shoulder arthroplasty humeral component lateralization had a significant positive effect on tendon transfer torque at 60° internal rotation and external rotation (p < 0.01). DISCUSSION: Both the lower trapezius and the latissimus dorsi tendon transfers were effective in restoring active external rotation after reverse shoulder arthroplasty; however, the lower trapezius generated significantly more torque. Additionally, the pectoralis major transfer was effective in restoring active internal rotation. All tendon transfers were optimized with greater humeral component lateralization.