Anatomic Study of C7 and its Clinical Significance

The authors' preliminary clinical results have shown that ipsilateral C7 transfer is an effective neurotization procedure for treatment of brachial plexus upper trunk injuries. However, there were temporary muscle weakness and sensory disturbance. To provide safety guidelines for this procedure, the topography of the C7 nerve root and the innervating nerve of its indicator muscle, the thoracodorsal nerve, was studied.

Retrograde microdissection was done in 20 embalmed cadaveric brachial plexus specimens. The origin of the thoracodorsal nerve from the brachial plexus and its location in the anterior and posterior divisions of C7 were observed. Another six fresh cadaver brachial plexus specimens were used for AchE staining for identification of sensory and motor fiber components of C7. The area percentage of thoracodorsal nerve originating from C7 and the motor fiber percentage were also calculated.

The thoracodorsal nerve was found to have its origin from all three trunks of the brachial plexus in 17 specimens, accounting for 85%. In one specimen (5%), the thoracodorsal nerve had a fiber contribution from the upper and middle trunks, while in two specimens (10%), the fiber contribution was from the middle and lower trunks. Location of the nerve was seen mostly in the medial portion of the posterior division of C7. Sixty percent of the thoracodorsal nerve was occupied by fibers originating from C7; 16.9% of the motor fibers in the posterior division of C7 went to the thoracodoersal nerve, while 52.7% of the motor fibers of the nerve came from C7.

Under most circumstances, it is safe to harvest the entire ipsilateral C7 for upper or lower trunk injuries. There is a 5% chance of latissimus dorsi muscle weakness when harvesting the ipsilateral C7 for upper trunk injuries and a 10% chance of such weakness in lower trunk injuries. Selective ipsilateral C7 transfer should be considered in these situations. The thoracodorsal component in the medial portion of the C7 posterior division and the sensory fibers in the medial portion of C7 anterior division should be preserved to reduce postoperative sensory impairment and muscle weakness.