Factors affecting outcome of triceps motor branch transfer for isolated axillary nerve injury

Purpose: Triceps motor branch transfer has been used in upper brachial plexus injury and is potentially effective for isolated axillary nerve injury in lieu of sural nerve grafting. We evaluated the functional outcome of this procedure and determined factors that influenced the outcome. Methods: A retrospective chart review was performed of 21 patients (mean age, 38 y; range, 16-79 y) who underwent triceps motor branch transfer for the treatment of isolated axillary nerve injury. Deltoid muscle strength was evaluated using the modified British Medical Research Council grading at the last follow-up (mean, 21 mo; range, 12-41 mo). The following variables were analyzed to determine whether they affected the outcome of the nerve transfer: the age and sex of the patient, delay from injury to surgery, body mass index (BMI), severity of trauma, and presence of rotator cuff lesions. The Spearman correlation coefficient and multiple linear regression were performed for statistical analysis. Results: The average Medical Research Council grade of deltoid muscle strength was 3.5 ± 1.1. Deltoid muscle strength correlated with the age of the patient, delay from injury to surgery, and BMI of the patient. Five patients failed to achieve more than M3 grade. Among them, 4 patients were older than 50 years and 1 was treated 14 months after injury. In the multiple linear regression model, the delay from injury to surgery, age of the patient, and BMI of the patient were the important factors, in that order, that affected the outcome of this procedure. Conclusions: Isolated axillary nerve injury can be treated successfully with triceps motor branch transfer. However, outstanding outcomes are not universal, with one fourth failing to achieve M3 strength. The outcome of this procedure is affected by the delay from injury to surgery and the age and BMI of the patient. Type of study/level of evidence: Therapeutic IV.