The Prevalence of the McKenzie Nerve in Cadavers: Its Clinical Application to Intradural Rhizotomy for Spasmodic Torticollis

Introduction Spasmodic torticollis may require surgical intervention, such as intradural rhizotomy, when medical treatments are ineffective. It is important to recognize the nerve of McKenzie, which is a connection between the C1 ventral root and the spinal accessory nerve. It exists in some cases, and if overlooked, it can lead to persistent symptoms. The findings establish a foundation for enhancing outcomes in neurosurgical interventions for spasmodic torticollis by improving understanding of this uncommon neural entity. Methods We included 30 formalin-fixed adult human cadavers (15 female and 15 male) without any previous spinal surgical procedures, pathology of the spinal cord, or non-traumatic pathology. The age range of the cadavers was 60 to 95 years (mean: 77.5 years). Utilizing a posterolateral approach, the craniocervical junction was exposed. The occipital bone and posterior neural arch of the C1-C7 vertebrae were excised, and the meninges were cleaned. The spinal accessory nerve course was traced, and the McKenzie nerve and surrounding vascular relations were identified and documented. Results The McKenzie nerve was observed in six out of 60 sides (10% prevalence). Prevalence was equal between sexes but more frequent on the right side (66.7%). Mean nerve length was greater on the right (5.8 ± 0.61 mm) compared to the left side (5.05 ± 0.07 mm). Bilateral occurrence was noted in two specimens. Two specimens exhibited bilateral absence of C1 dorsal roots. The presence of the McKenzie nerve was statistically significant (p=0.04). Conclusion In our research, we observed that the McKenzie nerve tends to be longer and more frequently found on the right side. In two specimens, it was present bilaterally, highlighting the necessity for a comprehensive bilateral examination due to the possibility of it occurring on both sides. These findings highlight the necessity for meticulous attention during surgical interventions for spasmodic dystonia. Failure to identify the McKenzie nerve could result in incomplete symptom relief. These observations may contribute to improved surgical outcomes.