Suprascapular Nerve - 1
Suprascapular nerve involvement was first introduced to the applied kinesiology community by Leaf.5 The nerve’s entrapment can be due to shoulder dysfunction or it can cause shoulder dysfunction. It supplies the supraspinatus and infraspinatus muscles. When they fail to function properly shoulder rhythm may be disrupted, resulting in various types of shoulder problems such as impingement syndrome. On the other hand, certain types of shoulder problems cause an improper scapulohumeral rhythm, stretching the suprascapular nerve with consequent neuropathy. Suprascapular nerve entrapment can cause a vicious circle in shoulder dysfunction.
The suprascapular nerve is derived from the upper trunk of the brachial plexus from the roots of C5 and C6.
It passes down behind the brachial plexus parallel to the omohyoid muscle, traverses beneath the upper trapezius muscle to the superior edge of the scapula, and then through the suprascapular notch. The suprascapular notch is roofed by the transverse scapular ligament, creating a foramen. The suprascapular vessels cross above the foramen. Only occasionally the veins or maybe a branch of the suprascapular artery may run through the foramen.8 The nerve then supplies the supraspinatus muscle and provides articular branches to the glenohumeral and acromioclavicular joints. It supplies sensory and sympathetic fibers to two-thirds of the shoulder capsule. Usually there are no sensory fibers to the skin. The nerve then winds around the base of the scapular spine to supply the infraspinatus muscle. In about 50% of people there is another connective tissue band creating a second fibro-osseous opening for the nerve to traverse.8
Suprascapular nerve dysfunction can develop from nerve compression at either fibro-osseous tunnel or from stretching of the nerve. In normal shoulder activity the scapula has a wide range of motion; the nerve must be able to adapt, or entrapment or stretching of the nerve develops. Few nerves are required to have the flexibility to adapt to such a wide range of motion. The most common cause of increased strain on the nerve is poor scapulohumeral rhythm. Occupations that require a lot of overhead work or other activities that place the arm at extremes of abduction and/or external rotation predispose a person to this nerve entrapment. Less common is stenosis at one of the fibro-osseous foramen by a cyst or osseous entrapment.