Relationship of the Subscapular Nerves to the Base of the Coracoid

Abstract

This study was performed to determine the relation of the subscapular nerves to the medial base of the coracoid when using an arthroscopic approach. Twenty human cadaveric shoulder specimens were dissected, and measurements were taken from the medial base of the coracoid to the innervation points of the upper and lower subscapular nerves. Measurements were obtained with the humerus in both neutral and maximal external rotation. The average distance of the upper subscapular nerve from the coracoid base was 31.6 ± 6.6 mm (range, 22 to 45 mm) in neutral rotation and 24.2 ± 7.4 mm (range, 11 to 35 mm) in external rotation. The lower subscapular nerve's insertion point averaged 42.6 ± 7.6 mm (range, 25 to 55 mm) from the coracoid base in neutral rotation and 33.9 ± 6.9 mm (range, 24 to 45 mm) in external rotation. For both nerves, their distance from the coracoid significantly decreased when the humerus was placed in external rotation. The closest that the innervation point of either the upper or lower subscapular nerve came to the medial aspect of the coracoid was 11 mm. Understanding the relationship of the subscapular nerves to the base of the coracoid allows a safe arthroscopic release of a retracted subscapularis muscle that has formed adhesions to the inferior aspect of the coracoid. Use of an arthroscopic elevator to release adhesions between the subscapularis and the inferior aspect of the coracoid does not appear to risk denervation of the subscapularis muscle.