This is an anatomical study of the anatomy and innervation pattern of the axillary nerve in cadaveric shoulders. The axillary nerve was traced in relationship to the subscapularis muscle, the acromion, and the deltoid. The authors found that the axillary nerve gave no branches to the first segment of the subscapularis muscle in 85% of cases. The mean distance from the posterolateral corner of the acromion to the axillary nerve was 7.8 cm. The authors found the posterior branch and axillary nerve gave its first motor branch to the innervated teres minor. The authors found that the acromial and clavicular portions of the deltoid muscle were innervated from the anterior branch of the axillary nerve in all cases. Posterior deltoid was innervated in three distinct patterns emerging from either the posterior branch of the deltoid or the anterior and posterior branch of the deltoid combined.
The significance of this article is that the lateral approach to the shoulder has been documented to be exceedingly efficacious regarding placement of a plate. There is concern, however, over denervation of the anterior aspect of the deltoid muscle. We can conclude from the results of this study that the anterior deltoid is innervated by the anterior branch in all cases and that the anterior branch contributes in some form or fashion to the posterior deltoid in 30% of cases. The anterior branch of the nerve is responsible for both portions of the deltoid muscle in only 3% of cases.
In addition, this study is significant for the increasing trend towards a medial head of the triceps to deltoid transfer. In this procedure, the medial head of the triceps nerve is transferred to the axillary nerve following the first subdivision of the posterior branch which innervates the teres minor.
Shoulder, Nerve, Axillary, Anatomy, Innervation
J Shoulder and Elbow Surg