Biomechanical effectiveness of different types of tendon transfers to the shoulder for external rotation

Background: Our purpose was to determine and compare the external rotation moment arm (ERMA) of the latissimus dorsi (LD), teres major (TM), and lower trapezius (LT) when transferred to selected locations on the proximal humerus. We hypothesize that the LT transfer has a higher ERMA compared with LD or TM. Materials and methods: Six fresh frozen cadaveric hemithoraces were used in a novel experimental design. The tendon and joint displacement method was used to calculate ERMA for 6 transfer pairs: LD to superolateral humeral head (SHH), LD to proximal-lateral humeral diaphysis (LHD), TM to SHH, TM to LHD, LT to infraspinatus insertion (ISI), and LT to teres minor insertion (TMI). Results: Tendon transfer pair had a significant effect on ERMA (P < .001), with a significant interaction effect between tendon transfer and position of the humerus (P < .0001). With the humerus at 0° abduction, the ERMAs of the LT-ISI (28.1 mm) or LT-TMI (22.3 mm) transfers were significantly higher than the ERMAs of LD-SHH (10.6 mm; P = .0001, P = .04) or LD-LHD (6.5 mm; P < .0001, P < .001). Also, ERMAs of LT-ISI and LT-TMI transfers were significantly higher than ERMA of TM-LHD (10.4 mm; P = .0001, P = .03). Conclusions: Shoulder external rotation tendon transfers differ in effectiveness and may be affected by arm position. LT potentially results in superior restoration of shoulder external rotation with the arm at the side compared with LD and should be considered as a potential tendon transfer to restore external rotation in selected patients.