Human cadaveric study of subscapularis muscle innervation and guidelines to prevent denervation

The upper and lower subscapular nerves provide innervation to the subscapularis muscle. However, the axillary nerve may provide a significant innervation to the lower portion of the muscle. The prevalence and patterns of anomalous innervation of the subscapularis muscle were studied to determine if these variations increased the risk of muscle denervation during open shoulder surgery. Twenty human cadaveric shoulders were dissected, and the innervation to the subscapularis was defined. The distance from the nerve insertion to the shoulder joint was measured in neutral and maximal external rotation. In the most common variation, the lower subscapular nerve arose from the axillary nerve (5 specimens; 25%). Although external rotation of the shoulder brought the nerve insertion significantly more lateral (35.2 to 16.9 mm, P < .001), the origin of the nerve had no significant effect on nerve proximity to the joint. The closeness of the nerve insertions to the shoulder joint warrants care during an anterior approach to the shoulder and dissections on the anterior surface of the muscle. Subscapularis nerve damage or denervation may cause unexplained joint instability and subscapularis dysfunction.