Partial Tear at the Musculotendinous Junction of the Teres Major after Anterior Latissimus Dorsi and Teres Major Tendon Transfer: Associated Factors and Clinical Impact in 256 Patients.

INTRODUCTION: Anterior latissimus dorsi and teres major (aLDTM) tendon transfer is an established procedure for isolated irreparable subscapularis tendon tear (IISTT) and anterosuperior irreparable rotator cuff tears (ASIRCTs). However, partial tear at the musculotendinous junction (MTJ) of the teres major (TM) has been observed on postoperative magnetic resonance image (MRI). The associated factors and clinical significance of these lesions remain unclear. This study aimed to identify factors associated with these lesions and to evaluate their impact on clinical outcomes. METHODS: We retrospectively reviewed the consecutive patients who underwent aLDTM tendon transfer for IISTT or ASIRCTs between 2017 and 2023. Potential associated factors were categorized into three domains: patients characteristics, intraoperative variables (operative time, tension of transferred LDTM), and postoperative MRI-based biomechanical parameters (trajectory angle and bending angle). The clinical evaluation included shoulder pain, patient-reported outcome measures (PROMs), active range of motion (aROM), and strength of aROM. RESULTS: 256 consecutive patients were included in this study. Among them, 60 patients (23.4%) demonstrated a partial tear at the MTJ of the TM on postoperative MRI and were classified as the partial tear group, while the remaining patients without a partial tear were classified as the intact group. Of the partial tear group, 43 patients showed evidence of subsequent healing on follow-up MRI and were categorized as the healed group, whereas 16 patients (26.7%) progressed to complete tear and were classified as the unhealed group. On multivariate logistic regression analysis, both intraoperative high tension of the transferred LDTM (odds ratio [OR] =2.89, 95% confidence interval [CI]:1.40-5.98, p=0.004) and lower bending angle at the MTJ of the TM (OR=0.85 per degree increase, 95% CI: 0.81-0.899, p<0.001) were identified as associated factors for partial tear occurrence. The unhealed group demonstrated inferior outcomes in Activities of Daily Living involving Internal Rotation score (75.9±11.6 vs 59.1±10.4, p<0.001), forward elevation strength (28.1±5.6 vs 21.1±5.4, p<0.001) and internal rotation strength (25.6±7.2 vs 22.2±5.7 p<0.001) compared with the intact group and healed groups. CONCLUSION: Partial tear at the MTJ of the TM is a relatively frequent finding after aLDTM tendon transfer. Although most lesions heal spontaneously, persistent tears are associated with inferior functional outcomes. Excessive intraoperative tension and a lower bending angle at the MTJ were identified as associated factors. These findings suggest that optimizing tendon tension and graft configuration during fixation may help reduce the risk of partial tear and preserve the synergistic function of the transferred muscles.