Anatomical Variations of the Axillary Nerve and Their Impact on Proximal Humerus Fracture Surgery

Abstract

Background: The axillary nerve is associated with the surgical neck of the humerus and is especially susceptible on operative treatment of the proximal humerus fracture. Changes in its location, branching configuration and relation to adjacent structures can increase the risk of intra-operative injury and negatively impact post-operative shoulder function. This study was conducted to find the incidence of specific anatomical variations of the axillary nerve and to assess their relevance to the surgical and functional results in patients who have had surgery for the proximal humerus.

Methodology: This is a prospective observational study that took place between January 2025 and June 2025 at Rawal Institute of Health Sciences, Islamabad. Patients with patients of displaced proximal humerus fractures who were managed by surgery were all included consecutively, total 85 patients. Demographic data, fracture-related and operative data were recorded. The course, branching pattern and relationships of the axillary nerve was determined intraoperatively. Patients were grouped into either a normal or variant axillary nerve anatomy. The neurological status, duration of the operation, blood loss, range of the shoulder, Constant–Murley shoulder score, and complications were assessed postoperatively. Data were analyzed statistically by appropriate comparative tests and multivariable logistic regression and p value < 0.05 was considered statistically significant.

Results: The mean age of the patients was 52.8 ± 13.6 years, and 49 (57.6%) were male. Anatomical variations of the axillary nerve were identified in 26 (30.6%) patients. Multiple branching was the most frequent variation, observed in 10 (11.8%) patients, followed by a low-positioned nerve in 7 (8.2%), a high-positioned nerve in 5 (5.9%) and accessory or communicating branches in 4 (4.7%). The mean nerve-to-acromion distance was significantly shorter in patients with anatomical variations than in those with normal anatomy. Postoperative axillary nerve dysfunction occurred in 11 (12.9%) patients and was significantly more frequent in the variation group than in the normal-anatomy group, 30.8% versus 5.1% (p=0.002). Patients with anatomical variations also had longer operative duration, greater blood loss, more frequent modification of the surgical approach, lower Constant–Murley scores and reduced shoulder abduction. Anatomical nerve variation independently increased the likelihood of postoperative nerve dysfunction.

Conclusion: Anatomical variations of the axillary nerve are common and may significantly influence the complexity and outcome of proximal humerus fracture surgery. Awareness of these variations, careful intraoperative identification and individualized surgical planning may reduce the risk of nerve injury and improve postoperative shoulder function.