C2 and Greater Occipital Nerve: The Anatomic and Functional Implications in Spinal Surgery

INTRODUCTION: Posterior C1-C2 fusion is a highly successful treatment for atlantoaxial instability and other pathologies of the cervical spine, with fusion rates approaching 95%-100%. However, poor visualization of the lateral masses of C1 secondary to the course of the C2 nerve root along with blood loss from the venous plexus and compression of the C2 nerve from lateral mass screws are technical obstacles that can arise during surgery. Thus, sacrifice of the C2 nerve root has long since been debated in fusions involving the C1 and C2 vertebral bodies. METHODS: Cadaveric dissections on four adult specimens were performed. Both intradural and extradural courses of C2 were studied in detail. The tentative site of C2 nerve root compression during placement of C1 lateral mass screws was studied in detail. Both the indication as well as the ease of C2 neurectomy were studied in relation to postoperative compression and entrapment. RESULTS: Four-six dorsal rootlets of C2 nerve were observed while studying the intradural course. The extradural course was studied with respect to the lateral mass of C1. The greater occipital nerve (GON) course was fairly consistent in all specimens. Transection of C2 around its ganglion would allow for proper C1 lateral mass screw placement as the course of C2 nerve interferes with proper placement of instrumentation. CONCLUSION: C2 nerve root transection is associated with occipital numbness but this often has no effect on health-related quality of life (HRQOL). The C2 nerve root preservation is often associated with entrapment neuropathy or occipital neuralgia, which greatly affects HRQOL. The C2 nerve root transection helps in better visualization, aids in optimal placement of C1 lateral mass screws, minimizes estimated blood loss and improves surgical outcome with successful fusion.