The suprascapular nerve is a peripheral sensory motor nerve arising from the upper brachial plexus that receives contributions from the fifth, sixth, and, occasionally, fourth cervical nerve roots (3). It provides motor innervation to the supraspinatus and infraspinatus muscles as well as sensory innervation around the shoulder (4). From its origin in the superior trunk of the brachial plexus, the nerve passes through the posterior cervical triangle and arises deep to the trapezius and omohyoid muscles where it then follows the suprascapular artery to enter the suprascapular notch. While the artery passes over the transverse scapular ligament (TSL), the nerve passes beneath it before entering the supraspinatus fossa (Fig. 27.1). A superior articular branch arises from the main trunk of the nerve at or near the ligament and travels with the main nerve through the notch. This branch supplies sensory innervation to the coracoclavicular and coracohumeral ligaments, the acromioclavicular joint, and the subacromial bursa. Within 1 cm of passing through the notch, two motor branches arise, which terminate in the supraspinatus muscle. The main nerve then courses inferiorly through the spinoglenoid notch, giving rise to yet another small sensory branch that innervates the posterior glenohumeral joint capsule. The remaining nerve enters the infraspinatus fossa, terminating as multiple motor branches to the infraspinatus muscle (4).

There are two locations of suprascapular nerve entrapment (the suprascapular notch and the spinoglenoid notch). Six types of supra scapula notches have been described (5). The most common types are a wide, a shallow “v”- (type II, 31%), and a “u”-shaped notch (type III, 48%) (Fig. 27.2). Although it has been suggested that entrapment may be associated with a calcified, bifid, trifid, or hypertrophied TSL, no studies have linked nerve entrapment to scapular notch morphology.

In contrast, the spinoglenoid notch is a fibro-osseous tunnel composed of the spinoglenoid ligament and the spine of the scapula. Cadaveric studies have placed the actual occurrence of a spinoglenoid ligament to range from 3% to 80%, but Plancher et al. (6) attributed this variation to be due to errors in specimen preparation and reported the spinoglenoid ligament to be a distinct anatomic structure present in 100% of specimens. This ligament originates from the lateral aspect of the scapular spine and the deep fibers insert distally into the posterior aspect of the glenoid neck, whereas the superficial fibers insert into the posterior glenohumeral joint capsule (Fig. 27.1).