A comparison of functional outcomes for triceps motor branch transfer to the anterior division axillary nerve in upper trunk brachial plexus injuries versus non-brachial plexus axillary nerve injuries

OBJECTIVE Triceps motor branch transfer to the anterior division of the axillary nerve (AXN) was originally described for patients with a loss of deltoid function secondary to upper trunk (UT) brachial plexus injuries but has evolved to restore deltoid function in isolated peripheral AXN injuries. The purpose of this study was to compare functional outcomes in patients who had undergone this procedure in the setting of UT brachial plexus injury versus peripheral AXN injury. METHODS The records of patients who had undergone triceps branch to anterior division of the AXN transfer at a single academic institution between 2001 and 2023 were retrospectively reviewed. Patients were included in the study if they had either a UT or an AXN injury and were excluded if their follow-up was less than 2 years. Pre-and postoperative outcomes, including modified British Medical Research Council grade and range of motion, were compared between the two groups. RESULTS Forty-two patients met the criteria for inclusion. Thirty cases were classified as UT injury and 12 cases as AXN injury. The mean postoperative abduction strength was significantly higher in the AXN injury group (3.2 +/- 1.5 vs 1.9 +/- 1.2, p = 0.007), as was the postoperative change in abduction strength (2.8 +/- 1.7 vs 1.6 +/- 1.4, p = 0.01). The mean postoperative forward flexion (136 degrees +/- 57 degrees vs 79 degrees +/- 54 degrees, p = 0.005) and abduction (129 degrees +/- 64 degrees vs 59 degrees +/- 47 degrees, p = 0.004) were significantly better in the AXN group, although postoperative changes in flexion and abduction were not different between the groups. Triceps strength preoperatively was similar to that postoperatively in both groups. CONCLUSIONS Patients with an AXN injury, compared to those with a UT injury, had better postoperative abduction strength and shoulder range of motion after triceps branch transfer to the anterior division of the AXN. Triceps strength was not significantly changed after the procedure in the two groups. The study findings suggest that the outcomes of triceps branch transfer to the anterior division of the AXN are different based on the location and type of injury, providing insight into prognosis while counseling patients.