The Axillary Nerve Danger Zone in Percutaneous Fixation in the Pediatric Shoulder: The "1-Mountain-3-Valleys" Principle

Adult literature cites an axillary nerve danger zone of 5 to 7 cm distal to the acromion tip for open or percutaneous shoulder surgery, but that may not be valid for younger patients. This study sought to quantify the course of the axillary nerve in adolescent patients with reference to easily identifiable intraoperative anatomic and radiographic parameters.

A single-institution hospital database was reviewed for shoulder magnetic resonance images (MRIs) in patients 10 to 17 years old. One hundred and one MRIs from patients with a mean age of 15.6 ± 1.2 years (range, 10 to 17 years) were included. Axillary nerve branches were identified in the coronal plane as they passed lateral to the proximal humerus and were measured in relation to identifiable intraoperative surface and radiographic landmarks, including the acromion tip, apex of the humeral head, lateral physis, and central apex of the physis. The physeal apex height (i.e., 1 "mountain") was defined as the vertical distance between the most lateral point of the humeral physis (LPHP) and the central intraosseous apex of the physis.

Axillary nerve branches were found in all specimens, adjacent to the lateral cortex of the proximal humerus. A mean of 3.7 branches (range, 2 to 6) were found. The mean distance from the most proximal branch (BR1) to the most distal branch (BR2) was 11.7 mm. The pediatric danger zone for the axillary nerve branches ranged from 6.6 mm proximal to 33.1 mm distal to the LPHP. The danger zone in relation to percent of physeal apex height included from 62% proximal to 242% distal to the LPHP.

All branches were found distal to the apex of the physis (1 "mountain" height proximal to the LPHP). Distal to the LPHP, no branches were found beyond a distance of 3 times the physeal apex height (3 "valleys"). In children and adolescents, percutaneous fixation of the proximal humerus should be performed with cortical penetration outside of this range. These parameters serve as readily identifiable intraoperative radiographic landmarks to minimize iatrogenic nerve injury.

This study provides valuable landmarks for percutaneous approaches to the proximal humerus. The surgical approach for the placement of percutaneous implants should be adjusted accordingly (i.e., performed at least 1 mountain proximal or 3 valleys distal to the LPHP) in order to prevent iatrogenic injury to the axillary nerve.