Mapping the axillary nerve within the deltoid muscle.

Reports place the frequency of axillary nerve injury at 6% for all brachial plexus injuries, emphasizing the importance of an accurate anatomic description of this nerve within the deltoid in order to reduce iatrogenic injury. The aim of the present study was to explore the anatomic variations of the axillary nerve within the deltoid muscle. Fifty human cadavers were dissected, resulting in 100 nerve specimens. The anterior and posterior branches of the axillary nerve were identified and their length measured from their point of origin (split from the axillary nerve) to their termination in the deltoid muscle. In 65% of cases, the axillary nerve split into two branches (anterior and posterior) within the quadrangular space, and in the remaining 35% split within the deltoid muscle. The posterior branch of the deltoid muscle irrespectively of origin gave off a branch to the teres minor and the superior lateral brachial cutaneous nerve in 100% of cases. The branch to the posterior part of the deltoid muscle was present in 90% of cases, and the branch to the middle part of the deltoid was present in 38% of cases. The anterior branch of the deltoid muscle provided a branch to the joint capsule, a branch to the anterior part of the deltoid muscle and the middle part of the deltoid in 100% of cases. In 18% of the cases, the anterior branch of the axillary nerve provided a branch to the posterior part of the deltoid muscle. The middle part of the deltoid muscle received dual innervation in 38% of cases and the posterior part of the deltoid muscle in 8% of the cases.