Middle Trapezius Tendon Transfer Using Achilles Allograft for Irreparable Isolated Supraspinatus Tendon Tears Effectively Restores the Superior Stability of the Humeral Head without Restricting Range of Motion: A Biomechanical Study

BACKGROUND:Middle trapezius tendon (MTT) transfer has been suggested for promising treatment of irreparable isolated supraspinatus tendon tears (IISTTs). However, there have been no attempts to assess the biomechanical efficacy of MTT transfer. This study aims to evaluate the biomechanical efficacy of MTT transfer in the setting of IISTTs. METHODS:Eight fresh-frozen cadaveric shoulders were tested in three conditions (1) intact rotator cuff, (2) IISTTs, and (3) Middle trapezius tendon transfer (MTT) using Achilles allograft for IISTTs. Total humeral rotational range of motion, superior translation of the humeral head, and subacromial contact characteristics were measured at 0°, 20°, and 40° glenohumeral abduction (representing 0°, 30°, and 60° shoulder abduction). Superior translation and subacromial contact pressures were measured at 0°, 30°, 60° and 90° external rotation (ER). Two different MTT muscle loading conditions were investigated. A linear mixed-effects model and Tukey post hoc test were used for statistical analysis. RESULTS:Total range of motion was significantly increased after IISTT at 20° abduction (P =.037). There were no changes in total ROM following MTT transfer compared to the IISTT condition (P>.625 for all comparisons). The IISTT condition significantly increased superior translation compared to the intact rotator cuff condition in 0° and 20° abduction with all ER angles (P<.001), 40° abduction/30° ER (P=.016), and 40° abduction/60° ER (P=.002). MTT transfer significantly decreased superior translation of the humeral head at all abduction angles compared to the IISTTs condition (P<.026). MTT transfer significantly decreased peak contact pressure by 638.7 kPa (normal loading) and 726.8 kPa (double loading) at 0° abduction/30° ER compared to the IISTTs condition (P<.001). Mean contact pressure was decreased by 102.8 kPa (normal loading) and 118.0 kPa (double loading) at 0° abduction/30° ER (P<.001) and 101.0 kPa (normal loading) and 99.2 kPa (double loading) at 0° abduction/60° ER (P<.001). MTT transfer at 20° abduction/30° ER with 24N loading significantly decreased contact pressure by 91.2 kPa (P=.035). CONCLUSIONS:The MTT transfer biomechanically restored the superior humeral head translation and reduced the subacromial contact pressure in a cadaveric model of IISTT, while not restricting total ROM. These findings suggest that MTT transfer may have potential as a surgical treatment for IISTTs.