The nerve of McKenzie: anatomic study with application to intradural rhizotomy for spasmodic torticollis

Medically recalcitrant spasmodic torticollis may necessitate surgical intervention. One procedure used for this pathologic entity is intradural rhizotomy. However, some patients are symptomatic, perhaps due to an overlooked or underappreciated nerve of McKenzie. The authors' goal was to further elucidate the anatomy of this nerve of the craniocervical junction.

Fifteen adult cadavers (30 sides) underwent microsurgical dissection and observations of the nerve of McKenzie. Morphometrics were performed and anatomic relationships were documented under surgical magnification.

The nerve of McKenzie was found on 70% of sides and was always a single branch. Average length was 5.2 mm for left sides and 6 mm for right sides. Average diameter was 0.9 mm (0.5-1.2 mm). In two specimens, the nerve was found bilaterally. It pierced the first denticulate ligament on 11 sides (52.4%) and travelled through its two prongs on three sides (14.3%) to connect to the anteriorly placed C1 ventral root. On five sides, it was in intimate contact with the adventitia of the vertebral artery. It was more common on right sides and in males, and this was statistically significant.

The authors identified the nerve of McKenzie in most specimens. This nerve, if overlooked during surgical treatment of spasmodic torticollis, may result in continued symptoms. The nerve of McKenzie was often concealed within the denticulate ligament or adventitia of the vertebral artery. The authors hope the data presented here will aid neurosurgeons and decrease complications in patients who undergo neurotomy for spasmodic torticollis.