WHAT IS THE SUPRASCAPULAR NERVE NEUROPATHY?
The suprascapular nerve neuropathy is a condition that is caused by the irritation of the suprascapular nerve in the area of the scapula that can lead to pain and weakness. It is a relatively rare peripheral neuropathy that is underdiagnosed until the most common causes of shoulder pain, such as rotator cuff rupture, acromioclavicular joint injury, or even cervical vertebra disc disease are excluded. Often patients undergo surgery for all of these aforementioned conditions, but continue to have pain due to this rare type of suprascapular nerve entrapment.
Patients usually experience a deep and diffuse pain on the top and back of the shoulder.
Some patients exhibit only weakness, without pain, such as volleyball players who injure the nerve from constant tension due to their aerial movements during the race.
ANATOMY – WHAT IS THE SUPRASCAPULAR NERVE?
The nerves on the one hand provide sensation to the joint and the surrounding area, and on the other hand allow the contraction of the muscles by conducting electrical stimulation from the spinal cord. Whereas in the past it was thought that the suprascapular nerve was solely responsible for muscle contraction (motor nerve), it is now known that it provides sensation in the shoulder joint as well as pain sensation.
The suprascapular nerve originates from the spinal cord and more specifically from the A4, A5, and A6 roots of the brachial plexus that come together to form this nerve. It is then directed to the anatomical region of the cervical region (neck), beneath the clavicle and through an incision in the upper part of the scapula. It then continues under the rotator cuff muscles, to which small nerve branches end up in. The suprascapular nerve impulses allow the rotator cuff muscles to contract and thereby allow shoulder movement.
The suprascapular nerve (SSN) passes through a narrow opening in the scapula called the suprascapular notch. This “opening” is usually wide enough for the nerve to pass, but in some cases it may be narrow due to anatomical variation or because the ligaments at the top of the notch are hypertrophic. In both cases, they can cause nerve irritation and trapping.
ETIOLOGY – WHAT CAUSES THE SUPRASCAPULAR NERVE NEUROPATHY?
Muscle pain and weakness can be the result of many different mechanisms. First, the nerve can be compressed by the presence of a local mass as it passes through the scapula or around the scapula. The most common cause is the formation of a cyst as a result of a joint capsule protrusion following injury to the rim cartilage.
The nerve can also be irritated by excessive tension. This can happen in the case of the winged scapula, a pathological condition due to atrophy of the muscles that control the scapula (mainly the serratus anterior muscle), up to a nerve injury that is responsible for the motion of the shoulder muscles (long thoracic nerve).
Finally, the nerve may also be over-stressed in the event of a massive rupture of the rotator cuff. As the tendon is ruptured, it drifts away from its insertion and the nerve, which is attached to the muscle, follows.
In the above figure, after the tendon ruptures, the nerve is dislocated and drifted away from the joint (left image). With surgical repair of the tendon, the nerve is returned to its normal position (upper right and lower).
EPIDEMIOLOGY – HOW FREQUENT IS THE SUPRASCAPULAR NERVE NEUROPATHY?
The suprascapular nerve neuropathy is considered a rare condition. However, it is well-known that anesthetizing the nerve by injection can relieve shoulder pain by thereby confirming that the suprascapular nerve controls the sensation of shoulder pain.
Recent studies have shown that this neuropathy occurs in 4% of patients evaluated with reported shoulder pain within a year. About half of them had an accompanying massive rupture of the rotator cuff.
CLINICAL TEST – WHAT ARE THE FINDINGS OF THE TEST?
Patients with suprascapular nerve neuropathy usually report high shoulder pain and are often accompanied by atrophy of the rotator cuff, which includes inability to abduct and turn outwards. Supraspinatus atrophy can also be observed at the back of the shoulder, accompanied by significant weakness, a sign of chronic nerve dysfunction.
On the left side there is a noticeable atrophy of the supraspinatus muscle (examiner’s hand) compared to the right side, where the muscle is more prominent.
DIAGNOSIS – WHAT OTHER DIAGNOSTIC STUDIES ARE NECESSARY?
Electromyography (EMG / NCV) may be proved useful for studying nerve function. This is a test performed on other peripheral neuropathies as well, such as the carpal tunnel syndrome.
However, this examination is positive only when nerve dysfunction becomes clinically apparent.
For this reason, in some patients while the nerve may be irritated, the test may be negative, especially if there is no significant damage to the nerve. In fact, in only 71-90% of the cases suprascapular nerve dysfunction is electromyographically detected. Therefore, a negative electromyogram (EMG) does not rule out the malfunction of the suprascapular nerve.
Injection under X-ray (or ultrasound) in the area of the nerve, and in particular in the suprascapular notch, can confirm nerve irritation if it significantly reduces pain, albeit temporarily. This is a very sensitive test that can confirm nerve irritation.
Some studies report that 90% of patients who experienced remission of symptoms by this injection had a good outcome with surgical nerve release.
Magnetic resonance imaging is useful not only to rule out the concomitant rupture of the rotator cuff, but to check for the presence of any cyst that may compress the nerve (Figure). In addition, some patients may present atrophy or fatty muscle degeneration as a result of long-term nerve compression.
In this X-ray image we can see the contrast (black) which indicates that the needle is in the suprascapular notch (or cavity). Once the correct position is confirmed, the anesthetic and corticosteroids are injected.
Oblique plane of the rotator cuff muscles – The healthy muscles of the suprascapular (yellow arrow) and the infrascapular (blue arrow) appear evenly, while the infrascapular which is replaced by adipose tissue is highlighted by the red arrow.
Coronary plane of the supraspinatus appearing pale due to adipose degeneration and the suprascapular nerve beneath the muscle
TREATMENT – HOW IS IT TREATED? WHAT WILL HAPPEN IF IT IS NOT TREATED? WHAT ARE THE SIGNS FOR SURGICAL INTERVENTION?
In cases of weakness with no pain, such as in the case of a volleyball player suffering an injury after an over-head overexertion of the upper extremity, a conservative treatment is recommended, including stretching and anti-inflammatory medication.
In case of pain and weakness with a MRI showing a cyst that compresses the nerve, then surgical resection of the cyst and nerve compression are recommended. In these cases where there is nerve compression and weakness, if the nerve is not depressed in time, the damage becomes permanent resulting in muscle atrophy.
In some patients undergoing shoulder surgery without pain relief, infusion of a local anesthetic with corticosteroids under radiological imaging may temporarily relieve the patient’s symptoms. In this case, depressing the nerve is very likely to resolve the patient’s chronic pain.
In patients with massive tendon rupture that report shoulder pain and weakness, if radiologically controlled injection relieves pain, nerve release is recommended along with restoration of rotator cuff rupture. In some of them, rupture may be irreversible, but nerve decompression can greatly relieve patient’s pain.
Traditionally, the nerve was decompressed into the suprascapular notch by making a large incision in the shoulder area. After decompression, the trapezius muscle repair followed (Figure).
Today, a well-known surgical operation makes use of a vertical incision on the suprascapular notch. The incision extends from the anterior side of the shoulder, near the clavicle, to the posterior side, at the acromion. The trapezius muscle (the muscle that allows the shoulder to be lifted) is pulled from the scapula bone. The supraspinatus muscle of the rotator cuff is separated from the nerve while the upper transverse ligament of the shoulder is bisected, paying attention to both the suprascapular nerve and the proximal arteries.
Most patients exhibit significant improvement after surgery in terms of pain and recovery. Studies have shown that improvement of the infraspinatus muscle (outward rotation) is less predictable and only about half of patients presents improvement. Although muscle size can be recovered postoperatively, in some patients, fat infiltration is not expected to subside.
ARTHROSCOPIC DECOMPRESSION OF THE SUPRASCAPULAR NERVE
The arthroscopic method allows the surgeon to locate the nerve and release it from the ligament causing compression through very small incisions.
Through these small incisions, special arthroscopic tools are inserted so that the suprascapular nerve, the artery and the transverse ligament of the shoulder are visible. The nerve can be clearly seen with the arthroscope.