Biomechanical analysis of latissimus dorsi, pectoralis major, and pectoralis minor transfers in subscapularis-deficient shoulders

Irreparable subscapularis (SSc) tears alter the dynamic force coupling of the shoulder, resulting in pain, weakness, and impaired shoulder function. Pectoralis major (Pma), pectoralis minor (Pmi), and latissimus dorsi (LD) transfers are treatment options for irreparable SSc tears, but clinical outcomes vary. The purpose of this study was to compare the biomechanical properties of Pma, Pmi, and LD transfers in an SSc-deficient shoulder using a computational model. A computer shoulder model was used to investigate the moment arms of Pma, Pmi, and LD tendon transfers compared with an intact SSc. Nine computed tomography scans from subjects without osteoarthritis were used. Virtual Pma, Pmi, and LD transfers were performed to the upper border of the SSc insertion site on the lesser tuberosity of the humerus. Muscle moment arms were computed for functional motions of 0°-80° of internal rotation with the arm in 20° and 90° of shoulder abduction and 0°-150° of shoulder abduction. The results were compared with those of the native SSc moment arms. A repeated-measures analysis of variance was then performed to determine significant differences. Internal rotation moment arms of the transferred Pma and Pmi decreased significantly after 30° and 40° of internal rotation compared with the SSc moment arm of the intact shoulder, whereas the moment arm of LD transfer more closely mimicked that of the native SSc through 0°-80° of internal rotation. All 3 tendon transfer configurations demonstrated weak abductive moment arms (7.6-8.0 mm), comparable to the intact SSc (7.8 mm) but significantly lower than the intact adductive moment arms of the native Pma and LD (26.8 mm and 28.2 mm, respectively). LD transfer most closely approximates the native SS regarding internal rotation moment arms. However, LD transfer also showed a reduction in adductive moment arms.