LAUSR

BACKGROUND Irreparable posterosuperior rotator cuff tears cause pain and impaired shoulder function. Latissimus dorsi (LD) transfer has been proven to improve shoulder function, but lower trapezius (LT) transfer has recently been proposed as an alternative. This study aimed to compare the biomechanics of LD and LT transfers and how they are affected by different insertion sites. METHODS The Newcastle shoulder model was used to investigate the biomechanics of these 2 tendon transfers. Computed tomography data sets from 10 healthy subjects were used to customize the model, and virtual LD and LT transfers were performed on supraspinatus, infraspinatus, and teres minor insertion sites. Muscle moment arms and lengths were computed for abduction, forward flexion, and external rotation. RESULTS The LT yields greater abduction moment arms compared with the LD when it is transferred to the native supraspinatus and infraspinatus insertion sites. However, they become adductors when transferred to the native teres minor insertion. Both muscles show strong external rotation moment arms, except for the LT with a supraspinatus insertion. Resting muscle strains were 0.21 (±0.03), 0.12 (±0.02), and 0.06 (±0.03) for the LD and 0.70 (±0.15), 0.61 (±0.13), and 0.58 (±0.13) for the LT for the supraspinatus, infraspinatus, and teres minor insertions, respectively. CONCLUSIONS LT provided better abduction and external rotation moment arms when transferred to the infraspinatus insertion. LD performed better when transferred to the supraspinatus insertion. Overall, LT transfer showed a biomechanical advantage compared with LD transfer because of stronger abduction moment arms. However, significantly larger muscle strains after LT transfer necessitate a tendon allograft to prevent muscle overtensioning.