The suprascapular nerve emanates from the brachial plexus nerve trunk composed of C5 and C6 nerve roots, including sensory and motor nerve fibers, and passes parallel to the dorsal scapularis lingualis muscle of the brachial plexus, then crosses the trapezius muscle to the superior border of the scapular gland, and then crosses the suprascapular notch. The motor branch innervates the supraspinatus and infraspinatus muscles, and sends sensory branches to the shoulder joint capsule and the glenohumeral and rostral clavicular joints, but does not innervate the shoulder skin.
Because the suprascapular notch can take many forms, the suprascapular nerve is relatively fixed as it passes through the suprascapular notch, making it vulnerable to damage during repetitive motion. The entrapment of the suprascapular nerve in the suprascapular notch is called suprascapular nerve entrapment syndrome. This syndrome is not common in clinical practice, but it is easily confused with other shoulder conditions including frozen shoulder, rotator cuff injury and cervical spondylosis, and should be carefully differentiated.
Etiology
Chronic trauma: Repetitive movements of the scapula and glenohumeral joint (such as volleyball, basketball, tennis, shoulder strain, etc.) cause the suprascapular nerve to rub at the suprascapular notch and develop neuroinflammatory reaction and edema, which can lead to compression damage; when the shoulder joint is externally rotated, the infraspinatus muscle branch is pulled inward and tense, when the upper limb is abducted, extended forward and the arms are crossed, the scapula is externally rotated, the subscapularis foramen moves outward, and the folding angle of the infraspinatus muscle branch at the inferior foramen In the process of gradual tension, the nerve rubs against the bone surface, causing the nerve to become stuck.
Acute trauma: Acute injury to the suprascapular nerve can occur with a scapular fracture. During the healing process of the fracture, scar formation around the nerve and reduction in the volume of the notch can compress the nerve, which can also cause compression symptoms. The nerve injury is more likely to occur at this time;
(3) Foreign body compression: lipomas, cysts and fibrosis of the suprascapular notch can compress the trunk or branches of the suprascapular nerve and cause compression. Injury to the superior glenoid labrum of the shoulder joint can lead to cysts behind the superior glenoid, which can compress the suprascapular nerve and cause symptoms. In older individuals, osteophytes may narrow the fibrous foramina of the suprascapular foramen and cause compression of the suprascapular nerve trunk.
Clinical manifestations
More males than females, with a predominant hand prevalence. There is often a history of acute/chronic trauma or repetitive motion of the shoulder joint. The main clinical manifestations are diffuse soreness and dull pain in the neck and shoulder, mostly in the posterior and lateral parts of the shoulder joint, with nocturnal pain, which is obvious when the affected side is lying down, and can wake up in severe pain.
The pain mostly occurs when the shoulder is actively moved, but is not obvious when it is passively moved. The pain is also not affected by the neck activity. As the disease progresses, the patient may feel weakness in shoulder abduction and external rotation, limited supination, and atrophy of the muscles around the shoulder. Some patients may have no symptoms other than shoulder pain, and the pain may last for several years.
Physical examination
Pressure pain in the suprascapular notch can be found, and pressure pain in the area between the clavicle and the scapular triangle is most common. There may also be pressure pain in the trapezius muscle. As the suprascapular branch of the scapular nerve innervates the acromioclavicular joint, acromioclavicular joint tenderness may also be present. The supraspinatus and infraspinatus muscles may be atrophied if the disease is prolonged. The strength of the shoulder external rotation muscles may be significantly reduced. Shoulder abduction weakness, especially at the beginning of the 30° or so, is most obvious.
Positive upper arm crossover test: 90° of forward flexion of both arms, crossed in front of the chest, may induce or aggravate shoulder pain. Positive scapular pull test: Make the patient place the affected hand on the contralateral shoulder and put the elbow in horizontal position, so that the affected elbow is pulled toward the healthy side, which can stimulate the stuck suprascapular nerve and induce shoulder pain.
Ancillary tests: electromyography and nerve conduction velocity tests are useful in the diagnosis of suprascapular nerve entrapment syndrome. The motor conduction velocity of the suprascapular nerve is significantly slowed, and there are fibrillation potentials in both supraspinatus and infraspinatus muscles, with no abnormalities in the axillary nerve and deltoid muscle. This can be distinguished from C5 nerve root compression, which also shows abnormal changes in the axillary nerve. x-ray: make the scapula tilt 15° to 30° caudally on the posterior anterior x-ray to check the morphology of the suprascapular notch, which helps in the diagnosis.
MRI: Local soft tissue masses can be detected. It can show the size and morphology of the cyst. MRI examination can also reflect secondary changes in the supraspinatus and infraspinatus muscles after loss of innervation. these changes include muscle atrophy and fatty infiltrative changes; in addition, it can clarify whether there are tears in the articular glenoid lip and rotator cuff tissue.
Diagnostic test: local closure with lidocaine injection: injection of 1% lidocaine at the pressure point of the suprascapular notch can help to diagnose suprascapular nerve entrapment syndrome if the symptoms are rapidly relieved.
Diagnosis and differential diagnosis.
The diagnosis of suprascapular nerve entrapment syndrome can be confirmed by careful history taking and systematic physical examination and electromyographic examination. It should be differentiated from cervical spondylosis, frozen shoulder, impingement syndrome, and rotator cuff injury.
Treatment.
Non-surgical treatment: In the early stage of the disease, conservative treatment can be used, including avoiding movements that damage and strain the suprascapular nerve, such as repeated arm raising over the shoulder; strengthening the muscles around the glenohumeral joint and muscle exercises that help stabilize the scapula. If the pain is severe, oral non-steroidal anti-inflammatory drugs (NSAID) can be taken, and local closure and physiotherapy can also be used. If conservative treatment is ineffective after a period of time or the condition is severe with supraspinatus and infraspinatus muscle atrophy, surgical exploration and release should be performed as early as possible.
Surgical treatment: The surgical treatment is related to the cause and location of nerve entrapment, and there are trans-anterior and posterior approaches for incisional surgery.
With the development of arthroscopic techniques, arthroscopic release of the suprascapular nerve is now being performed. Since synovial cysts are often caused by joint capsule tears and glenoid labral injuries, shoulder arthroscopy can be used to perform both cyst decompression and glenoid labral repair.