The SSN arises from the upper trunk of the brachial plexus, with contributions from C5 and C6 (rarely also C4). It supplies motor innervation to the supraspinatus and infraspinatus muscles and also, provides sensory fibers to the coracoacromial (CA) ligament, acromioclavicular, and glenohumeral joints. In 15% of population, it contains cutaneous fibers, which innervate the lateral aspect of the shoulder.⁸

The nerve traverses two potential compression points, at the suprascapular notch and spinoglenoid notch (FIG 1), and is accompanied by the suprascapular artery and vein.

As the nerve leaves the brachial plexus, it travels posteriorly to the clavicle to the suprascapular notch. It travels through the suprascapular notch, under the transverse scapular ligament and into the supraspinous fossa where it supplies motor innervation to the supraspinatus muscle.

Its accompanying artery and vein typically course above the ligament; however, in some cases, a branch of the main vessels may accompany the SSN through the suprascapular notch.

The suprascapular notch is a fibro-osseous canal, which lies at the medial base of the coracoid. The notch is approximately 4.5 cm medial to the posterolateral corner of the acromion and 3 cm medial to the glenoid rim (supraglenoid tubercle).⁴ The anatomy of the suprascapular notch may be highly variable.

Continuing on its path to innervate the infraspinatus, the SSN, accompanied by the artery and vein, traverses the spinoglenoid notch to reach the infraspinous fossa.

The spinoglenoid notch is approximately 1.8 cm medial to the glenoid rim and 2.5 cm inferomedial to the supraglenoid tubercle.⁴

Several anatomic studies have described the presence of a spinoglenoid ligament (inferior transverse scapular ligament) at the spinoglenoid notch. The incidence of spinoglenoid ligament has been reported to range from 16% to 100%, and its role in nerve entrapment is controversial.⁶,⁷,¹⁰

Focal nerve entrapment is most common at the suprascapular notch where the nerve is relatively confined and has limited mobility.

The restricted mobility of the nerve at the suprascapular notch predisposes it to various traction injuries, as can be seen with acute trauma or with repetitive overhead activities in throwing athletes, volleyball or tennis players, or with weightlifting.

Compression from labral ganglions can also occur, typically at the spinoglenoid notch.¹,³ These cysts can develop as the result of labral tears that allow fluid extravasation but block backflow, similar to a one-way valve.

More recently, traction injury to the nerve has been described as the result of massive, retracted tears of the posterosuperior rotator cuff.²,¹¹

Direct or indirect trauma leading to SSN neuropathy has been described as the result of shoulder dislocation, proximal humerus fracture, or scapular fracture.

Iatrogenic injury to the SSN can occur during distal clavicle resection, positioning during spine surgery, transglenoid drilling for instability repair, shoulder arthrodesis, or the posterior approach to the glenohumeral joint.

The natural history depends on the presence or absence of a space-occupying lesion as the cause of SSN neuropathy.

The natural history of periarticular ganglion cysts in the shoulder is controversial, but they are thought to persist and enlarge with time.¹⁵ In rare instances, spontaneous resolution of ganglion cysts has been documented.

SSN neuropathy secondary to compression at the suprascapular notch typically presents as a dull pain in the posterior and lateral shoulder, but the pain can also be referred to the anterior chest wall, lateral arm, and ipsilateral neck. Compression at the spinoglenoid notch is often comparatively pain-free and presents with isolated infraspinatus atrophy (FIG 2).

The patient often provides a history of acute or repetitive trauma to the shoulder, such as a fall on the outstretched hand, or repetitive overhead activities, such as throwing, volleyball, tennis, or weightlifting.

There appears to be an increased incidence of isolated infraspinatus atrophy in asymptomatic volleyball players. This typically responds well to conservative measures.

Depending on the chronicity and degree of compression, varying amounts of weakness in abduction and external rotation can be detected on physical examination.

Atrophy, if present, may assist in differentiating compression at the suprascapular notch from that at the spinoglenoid level because supraspinatus atrophy occurs only with the former.

Palpation of the spinoglenoid notch and cross-body adduction may reproduce the patient’s symptoms.

The SSN stretch test may reproduce pain posteriorly. In this test, the clinician laterally rotates the patient’s head away from the affected shoulder while simultaneously gently retracting the affected shoulder.⁹

It is important to exclude other potential sources of pain, such as the cervical spine, acromioclavicular joint, or rotator cuff.¹⁴

History of spinal or shoulder surgery and presence of surgical incisions should raise suspicion for possible iatrogenic injuries of the SSN.

Stryker notch views, or anteroposterior radiographs of the scapula, with a 15- to 30-degrees caudally directed beam, provide visualization of the suprascapular notch. Alternatively, a computed tomography (CT) scan can provide good osseous detail in cases of posttraumatic deformity or ossification of the transverse scapular ligament.

Magnetic resonance imaging (MRI) can reveal labral tears and the presence of a perilabral ganglion in the area of the suprascapular or spinoglenoid notch (FIG 3). Ganglion cysts present as homogeneous masses with low signal intensity
on T1-weighted images and high signal intensity on T2-weighted images.

Electromyography (EMG )and nerve conduction velocity (NCV) studies can often provide a conclusive diagnosis by showing denervation potentials, fibrillations, spontaneous activity, and prolonged motor latencies in the supraspinatus or infraspinatus, depending on the level of entrapment.¹⁷ However, sensitivity and specificity of EMG and NCV are dependent on the operator and interpreter.