Radiological and electrodiagnostic insights into suprascapular nerve dysfunction: a key predictor of poor functional outcomes in shoulder hemiarthroplasty

Background: Suprascapular nerve (SSN) dysfunction has emerged as an underexplored factor influencing functional outcomes after shoulder hemiarthroplasty (SHA) for proximal humerus fractures. Despite achieving optimal tuberosity healing and prosthesis alignment, some patients continue to experience poor functional recovery. This study investigates the role of SSN dysfunction as a key determinant of unfavorable outcomes following SHA. Methods: This retrospective study analyzed 38 patients who underwent SHA for Neer type III or IV proximal humerus fractures. Inclusion criteria included radiographic confirmation of tuberosity healing, absence of pre-existing rotator cuff tears, and sufficient follow-up. Patients were divided into 2 groups based on the Constant Shoulder Score (CSS) at 12 months postoperatively: group G (good outcomes, CSS difference between prosthetic and healthy shoulders <30) and group P (poor outcomes, CSS difference ≥30). Electrophysiologicalassessments were performed bilaterally to evaluate SSN function. Compound muscle action potentials and needle electromyography were used to measure nerve conduction and detect chronic neurogenic changes. Bilateral ultrasound imaging quantified supraspinatus muscle thickness at medial, central, and lateral points. These measurements provided a detailed comparison of prosthetic and healthy shoulders, identifying patterns of nerve dysfunction and muscle atrophy. Results: Group P exhibited significantly lower American Shoulder and Elbow Surgeons scores, higher visual analog scale scores, and reduced shoulder motion (P < .01 for all). Findings revealed significantly lower compound muscle action potential amplitudes in the prosthetic shoulder of group P (2.55 ± 0.42 mV) compared with the prosthetic shoulders of healthy side (4.82 ± 0.67 mV, P < .001) and group G (4.27 ± 0.55 mV, P < .001). Reductions in amplitude exceeded 50% on the prosthetic side for group P. Needle electromyography of prosthetic shoulders in group P demonstrated chronic neurogenic changes, including fibrillation potentials and polyphasic motor unit potentials, in the supraspinatus and infraspinatus muscles. Ultrasound measurements revealed significant supraspinatus muscle atrophy on the prosthetic side in group P, with medial thickness reduction identified as the strongest predictor of poor outcomes (odds ratio = 1.312, 95% confidence interval: 1.042-1.654, P = .021). Healthy shoulders in group P exhibited no significant neurogenic abnormalities, highlighting localized dysfunction in the prosthetic side. Conclusion: SSN dysfunction, evidenced by reduced nerve amplitudes and supraspinatus muscle atrophy, significantly predicts poor functional outcomes following SHA, even when tuberosities are well healed. These findings highlight the importance of perioperative nerve preservation strategies and postoperative neurological assessments. Integrating neurological evaluations into routine clinical practice may improve patient recovery and outcomes after SHA.