Is there any clinical significance of axillary nerve electrophysiological changes in the deltoid split approach?

Purpose: The clinical effects of axillary nerve injury in the deltoid splitting approach are controversial. This study investigated the axillary nerve function with clinical and electrophysiologically in proximal humeral fracture patients with internal fixation using the deltoid split approach. We also aimed to investigate the effects of this damage on deltoid muscle volume and discuss the effects of volumetric changes and nerve damage on patients' clinical outcomes. Methods: study designed prospectively with 25 consecutive patients who received open reduction and internal fixation of proximal humerus fracture through a deltoid splitting approach. We performed clinical, electrophysiological, and radiological examinations during minimum follow-up time of 24 months. Electrophysiological examination comprised electromyoneurography (EMNG). Functional results followed by Constant-Murley and Disabilities of the Arm, Shoulder, and Hand scores. Deltoid volumes were evaluated with magnetic resonance imaging. Results: Twenty-five patients operated on with open reduction internal fixation were prospectively observed. In the EMNG measurements of the patients on the 45th postoperative day, partial degeneration was observed in the anterior part of the axillary nerve in all cases (100%). In the control EMNG measurements performed at the 12th month, normal values were obtained for 15 (60%) of the patients, while findings of ongoing regeneration were detected for 10 (40%) of the patients and normal values at all patients at the 24th month. The difference between abnormal and normal EMNG groups' on 12th month Constant-Murley scores was not statistically significant in any period. Only anterior muscle thickness was statistically higher in the normal patient group than with abnormal EMNG results. Conclusions: In proximal humeral fractures treated with the deltoid split approach, there may be iatrogenic damage of the anterior branch of the axillary nerve. Axillary nerve damage does not affect the patients' clinical scores in the early and mid-terms. Level of evidence: LEVEL III.