The brachial plexus is a large bundle of nerves that supply the arms and upper chest. It is formed from five nerves (C5-T1) that come from the neck (cervical spine) and upper back (thoracic spine), these nerves then combine to form three trunks, the superior, middle, and inferior trunks. It is from the superior trunk that the suprascapular nerve originates and then passes down under the trapezius muscle to the top of the shoulder blade (scapula) in order to supply two of the rotator cuff muscles, the supraspinatus and infraspinatus.
Suprascapular nerve entrapment, also referred to as palsy or impingement, is when there is an injury or compression of the suprascapular nerve in the shoulder. This is not a common condition but can be as the result of trauma, traction, or compression of the nerve by fluid filled swellings (ganglion cyst) or thickening of the ligaments within the suprascapular notch or spinoglenoid notch near the top of the shoulder blade.
Traumatic injuries can include repetitive microtraumas and is more frequent in individuals and athletes that perform a lot of overhead activities (baseball, basketball, swimming), or it can be as a result of more significant trauma such as a rotator cuff tear or scapula fracture.
Symptoms of a suprascapular nerve entrapment or injury can vary depending on where the nerve is compressed, as compression at the suprascapular notch can affect both supraspinatus and infraspinatus, while compression at the spinoglenoid notch generally only affects the infraspinatus.
A common symptom is a deep, dull, burning pain at the posterior (back) aspect of the shoulder. There will be weakness, and occasionally complete paralysis, of the supraspinatus that works to raise the shoulder out to the side (abduction) and the infraspinatus that rotates the shoulder away from the midline (external rotation). Muscle wasting (atrophy) will often be associated with this weakness and can be observed at the upper and middle part of the scapula.
Pain can be exacerbated by stretching the arm across the body (horizontal adduction) or by rotating the arm towards the midline or behind the back (internal rotation). This is due to the suprascapular nerve being placed under increased tension. Pain may refer into the upper back, neck, or chest.
As this is not a common diagnosis, an initial assessment and examination would be conducted by a GP, physiotherapist, or consultant. Should a suprascapular nerve entrapment be suspected; based on the history, symptoms, and observations; then further investigations may be needed to assist in diagnosis.
Xrays, ultrasound scans and MRIs will help to visualise any potential bony or sift tissue components that might be compressing the nerve. They can also help to assess the degree of muscle atrophy or for potential rotator cuff tears.
Imaging is not always able to detect the cause of the suprascapular nerve compression, but if there is a strong suspicion that this is the cause for the symptoms, then a suprascapular nerve block may be considered. This involves injecting a local anaesthetic around the suprascapular or spinoglenoid notches and assessing if this provides any pain relief.
Additionally, electromyography (EMG) or nerve conduction studies (NCS) can be performed to assess the function of the suprascapular nerve. These tests are designed to test the response of the supraspinatus and infraspinatus to the electrical stimulation of the suprascapular nerve.
A majority of suprascapular nerve entrapments can be managed conservatively through physiotherapy. This will incorporate a component of activity modification to reduced overhead and repetitive movements and activities for a period of time. This will allow time for the nerve to attempt to recover, however, it is important to remember that nerve recovery can be an extremely slow process and it may take a long period of time before significant improvements in strength and muscle atrophy are seen.
In combination with activity modification, it is important to begin an individualised and progressive rehabilitation program that will be focused on regaining shoulder movement, as well as strength and co-ordination at the rotator cuff and scapula stabilisers.
If the cause of the entrapment is a ganglion cyst, and there has been minimal improvement through physiotherapy, then this may be drained (aspirated) to release the pressure on the nerve. This would be performed under ultrasound guidance, which allows for accurate identification and drainage of the cyst. While this is a successful procedure the recurrence rate of ganglion cysts is high, and so might only provide temporary relief.
Surgery would be indicated if conservative management over a period of eight to twelve months had failed to improve symptoms, or if there was evidence of a significant mass that was compressing the suprascapular nerve.
Surgery might also be considered if there is a significant rotator cuff tear that could contribute to persistent symptoms. Surgical decompression of the nerve will usually be performed via keyhole surgery (arthroscopically) to limit trauma and facilitate a fast recovery and return to function.