The Dorsal Scapular Nerve
The dorsal scapular nerve arises from the C5 nerve root. It innervates three muscles: the rhomboids major and minor, and the levator scapulae. The levator scapulae elevates the scapular and tilts the glenoid cavity inferiorly by rotating the scapula.
The rhomboids minor and major muscles connect the medial edge of the scapula to the spinal column. Both rhomboid muscles pull the scapula towards the midline (scapular adduction) and they also pull the scapula superiorly with downward rotation. This is opposite to the serratus anterior, which is supplied by the long thoracic nerve. The dorsal scapular nerve passes dorsally, perforating the middle scalene muscle and then it travels beneath the under surface of the levator scapulae down to reach the rhomboid muscles.
Injury to the dorsal scapular nerve may cause scapular winging. The scapula may become laterally displaced with upward motion.
How do you examine for an injury to the rhomboid muscles?
Have the patient bring the shoulder and scapula together posteriorly. Then palpate the contracted rhomboideus muscles.
Another important topic related to the dorsal scapular nerve, is brachial plexus injuries. The preganglionic injury which is root avulsion has the worst prognosis. It is usually associated with Horner’s Syndrome (ptosis, miosis, and anhidrosis) due to disruption of the sympathetic chain. The patient may have medial winging of the scapula due to involvement of the long thoracic nerve, which innervates the serratus anterior muscle. There may be a loss of the muscle function supplied by the dorsal scapular nerve (C5) and possibly other cervical nerves such as C3 and C4 that supply the levator scapulae.
When you perform an EMG in this situation, you will find a loss of the innervation of the cervical paraspinal muscles. This is very important because it is a sign that there is probably a preganglionic injury and a bad prognosis. Histamine tests will be normal in these conditions.