Short-term functional, imaging, and electrodiagnostic outcomes of arthroscopy-assisted lower trapezius transfer.

Background: The purpose of this study was to evaluate the short-term functional outcomes, structural healing, and neuromuscular activity after arthroscopy-assisted lower trapezius transfer for irreparable posterior superior rotator cuff tears.

Methods: All patients who underwent arthroscopy-assisted lower trapezius tendon transfer for an irreparable posterior superior rotator cuff tear between 2017 and 2021 by 2 surgeons with a minimum of 2-year follow-up were identified. Functional outcome scores (American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form [ASES] score, visual analog scale [VAS] for pain), range of motion, shoulder strength, magnetic resonance imaging (MRI) to assess transfer healing, and needle electromyographic (EMG) examination to assess lower trapezius muscle activity were performed at a minimum of 2 years postoperatively. Contralateral nonoperative lower trapezius muscle activity was assessed by EMG. Grafts were defined as completely healed if anatomic graft healing occurred, partial healing if some graft was healed to the proximal humerus, and unhealed if no graft was attached to the proximal humerus on postoperative MRI.

Results: Twenty-four eligible patients (25 shoulders) were identified through chart review. Mean age and follow-up were 54.9 ± 9.5 and 2.9 ± 1.7 years, respectively. Overall, 72% (18/25) clinical follow-up was obtained. All functional outcomes including ASES (preoperative, 48.8 ± 19.6; postoperative, 80.9 ± 15.4; P < .001), VAS pain (4.9 ± 2.3; 1.4 ± 1.5; P < .001), and active forward flexion (110° ± 53.2°; 141.7° ± 40.4°; P = .024) statistically significantly improved. Twelve shoulders (48%) presented for EMG follow-up. All 12 patients demonstrated EMG activity of the lower trapezius in forward elevation, external rotation at the side, and external rotation at 90° of abduction, which was symmetric to the contralateral shoulder. Fifteen shoulders (60%) were available for MRI follow-up. Thirteen patients (87%) demonstrated complete or partial healing of the allograft to the greater tuberosity, whereas 2 (13%) demonstrated a complete tear of the graft.

Conclusions: Arthroscopy-assisted lower trapezius transfer demonstrates improved functional outcomes 2 years postoperatively. Complete retear of the transfer is relatively uncommon (13%). The lower trapezius fired in phase in forward flexion, external rotation at the side, and external rotation in 90° of abduction in all patients who underwent EMG testing, which was consistent with the firing pattern of the contralateral normal lower trapezius muscle. These results may support the theory that active function of the muscle transfer itself, as opposed to a tenodesis effect, is a potential mechanism by which this procedure improves shoulder function as it consistently fires in phase.