Suprascapular Neuropathy

There are many causes of shoulder pain because of the plethora of structures that are involved with passive and active stability and mobility of the glenohumeral joint, clavicle, scapula, and cervical spine. Of the many causes of pain, weakness, or dysfunction in the shoulder, one to consider is a suprascapular nerve compromise or neuropathy. In this blog post, we will go over the path and anatomy of the suprascapular nerve, what can cause problems or injury to it, how to examine or assess for it, and how it is diagnosed.

Path of the Suprascapular Nerve

 The suprascapular nerve predominantly provides motor nerve innervation to the supraspinatus and infraspinatus muscles. Research shows that it also provides sensory innervation for the coracohumeral ligament, the coracoclavicular ligament, the subacromial bursa and the posterior shoulder capsule.³ 

The suprascapular nerve comes off the upper trunk of the brachial plexus with originations from the C5 and C6 ventral rami, with occasional involvement from the C4. It proceeds laterally through the posterior cervical triangle, posterior to the clavicle, across the superior border of the scapula and into the suprascapular notch. As it crosses into the supraspinatus fossa it innervates the supraspinatus muscle and receives sensory branches. It then continues through the spinoglenoid notch, underneath the spinoglenoid ligament, and terminates with the innervation of the infraspinatus.¹ 

Pathogenesis

There are multiple locations and causes of a suprascapular neuropathy. The main sites for the entrapment and compression of the suprascapular nerve include the following²:

1. Suprascapular notch
2. Spinoglenoid notch
3. Superior transverse scapular ligament

Some causes of the nerve compression at these locations include, but are not limited to, the following^1,2: 

1. Variations of the suprascapular notch.⁴
2. Fractures of the scapula and clavicle and associated scar tissue
3. Space occupying lesions⁶
   1. Enlarged spinoglenoid veins
   2. Lipomas
   3. Intraosseous ganglion cysts
   4. Supraglenoid or spinoglenoid cysts 
   5. Paralabral cysts 
4. Retracted rotator cuff muscles from tears⁷
5. Abnormal subscapularis muscle fibers covering the suprascapular notch⁵ 
6. Ligament abnormalities
   1. Anterior coracoscapular ligament⁵
   2. Calcified suprascapular ligament ⁵
   3. Hypertrophied inferior transverse scapular ligament
7. Scapulothoracic dyskinesia, shoulder girdle dysfunction
8. Tension on the suprascapular nerve from lateralization during a supraspinatus and infraspinatus repair⁸ See the image below.

Overhead activities and sports, like volleyball, baseball, tennis, etc, also put stress on the suprascapular nerve through dynamic compression. In a study by Holzgraefe on elite volleyball athletes, they reported having a suprascapular neuropathy in as high as 33% of the athletes in their dominant arm/hand.⁹ Another study found an association between increased shoulder range of motion and isolated infraspinatus weakness.¹⁰ The proposed reason for the cause of the suprascapular neuropathy is that when the shoulder is in throwing motion it goes into extreme external rotation and abduction and causes the supraspinatus and infraspinatus muscles to impinge on the scapular spine, which compresses the motor branch to the infraspinatus.^{11, 12} Another proposed causation for the suprascapular neuropathy with overhead athletes is from damage to the axillary and suprascapular artery and therefore causing microemboli to the suprascapular nerve vasa nervorum.^{1, 13} 

Outside of compressive neuropathies, another condition that often affects the suprascapular nerve is Parsonage-Turner syndrome.

History and Examination

 Patients with a suprascapular nerve will typically present with a dull, aching pain in the superior and posterolateral shoulder and often with radiating symptoms up to the neck or down the arm.^{1,2, 15} However if the problem is at the spinoglenoid notch, the patient may not complain of pain at all.² If the patient is an overhead athlete, there should be a heightened level of suspicion for a suprascapular nerve issue.^1,2  The patient may complain of a loss of function and weakness in the shoulder. Usually, a suprascapular neuropathy usually develops over time, but may also result from a traumatic event in upwards of 40% of patients.¹⁴ 

 With multiple conditions that can present with similar symptoms, a thorough physical exam should be performed on bilateral shoulders as a comparison. The patient should be asked about and inspected for a previous shoulder surgery, any penetrating traumas, or fractures. The shoulder should be assessed for any atrophy in supraspinatus or infraspinatus (image above¹⁹), involve palpation of the AC joint and supraspinatus fossa for tenderness, weakness with shoulder abduction and external rotation, and any signs of instability to the shoulder joint. The neck may also produce similar symptoms, so a thorough neurological screen should also be performed.

Some additional special tests to assess for the suprascapular neuropathy include putting the shoulder into cross-body adduction and internal rotation and performing the suprascapular nerve stretch test. With the patient’s arm placed in cross-body adduction and internal rotation, the test would be considered positive when there is an exacerbation of their pain.¹⁵ The suprascapular nerve stretch test involves the clinician stands behind the patient, gently holds the head of the patient in lateral rotation away from the affected shoulder while retracting the affected shoulder with his other hand (image to the right). A positive test is when pain is reproduced or exacerbated in the posterior aspect of the shoulder.¹⁶  

Diagnosis of a Suprascapular Nerve

The gold standard for diagnosing a suprascapular neuropathy is through electromyography and a nerve conduction study. In testing of patients with weakness, the accuracy of the EMG and NCS for suprascapular nerve pathology was as high as 91%.¹⁷ Findings positive for suprascapular pathology include fibrillation potentials and positive sharp waves, reduction in suprascapular nerve CMAP amplitude²⁰, and increased latency. In the case of compression of the suprascapular nerve at the spinoglenoid notch, there may be a prolonged latency of the suprascapular nerve when recorded from the infraspinatus and/or fibrillation potentials or positive sharp waves only present in the infraspinatus and not the supraspinatus.

Magnetic resonance imaging of the shoulder is also helpful to assess the shoulder to evaluate for suprascapular nerve pathology by assessing for supraspinatus and infraspinatus atrophy. ¹⁸ It can also assess for soft tissue masses around the shoulder and labrum that could cause compression to the supraspinatus and for any rotator cuff pathologies. 

Another way to help differentiate a suprascapular nerve neuropathy from other shoulder pathology can include an injection of anesthetic into the suprascapular and spinoglenoid notch and assess for pain relief in the shoulder and shoulder blade.¹ 

Conclusion

Overall, suprascapular nerve pathology needs to be in the differential diagnosis of patients with shoulder pain and possible radiating symptoms, especially for individuals who are overhead athletes or if they present with pain in the superior and posterolateral shoulder and shoulder blade. In order to properly assess for a possible suprascapular neuropathy, the combination of a thorough physical assessment and neurological screening should be used along with electrodiagnostic (EMG and NCS) testing and MRI to confirm pathology and assess for causation.

Randall Hulet, PT, DPT, ECS

References:

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