Is the Axillary Nerve at Risk During a Deltoid-Splitting Approach for Proximal Humerus Fractures?

The strain placed across the axillary nerve during the deltoid-splitting approach could correlate with microtrauma and place the patient at risk of a neuropraxia or more permanent injury. The purposes of this study were to evaluate the change in length and strain exhibited by the axillary nerve during the deltoid-splitting approach and to determine the presence of any microscopic structural damage.

The axillary nerve was identified through a lateral deltoid-splitting approach in 10 fresh-frozen cadaver specimens. Two suture tags were placed near the lateral margins of the incision. The initial distance between the 2 tags was measured and the distance at each retractor click of a Kölbel retractor until full expansion (6 clicks). The retractor was then released for a 1-minute break at 30, 60, 90, and 120 minutes. The strain at each interval was calculated as change in length divided by the initial distance. The section of nerve in the field of exposure was excised for histologic analysis.

The location of the axillary nerve was 6.32 cm (range, 5.20-7.6 cm) from the anterolateral aspect of the acromion. The mean final increase in length was 8.42 mm (range, 6.43-12.26 mm). The strain increased to a final mean of 51% (range, 28%-99%). Histologic analysis confirmed disruption of the myelin sheaths and axonal retraction.

This study demonstrated a progressive, irreversible increase in axillary nerve length and strain, resulting in microscopic damage to the neuronal structure during a deltoid-splitting approach. Prolonged soft tissue retraction can place the axillary nerve at substantial risk for injury.