Anatomic Relationship Between the Greater Occipital Nerve and the Axis: Is It Possible to Safely Insert a Percutaneous C2 Screw Without Causing Occipital Neuralgia?

Background and objectives: Harms' technique is a widely used method for atlantoaxial stabilization. In recent years, minimally invasive surgery (MIS) using various robotic systems for percutaneous C1 to C2 screw insertion has started to be used. However, MIS raises concerns about the precision required to avoid injury to vascular and neural structures. The greater occipital nerve (GON) primarily arises from the C2 spinal root, located between the posterior arch of the C1 vertebra and the lamina of the C2 vertebra. The first bend of the GON could potentially overlay the lateral aspect of the C2 vertebra, specifically between the superior and inferior facets, ie, the interarticular part (IAP), making it susceptible to injury during C2 pedicle screw insertion causing the occipital neuralgia. That is why the aim of our study is to investigate the relationship of the GON to the axis and to assess the risk of its violation during C2 pedicle screw insertion.

Methods: Eight cadaveric specimens, embalmed in classical formaldehyde solution, were dissected to describe the position of the GON in relation to the axis.

Results: The apex of the first GON bend was localized 3.9 ± 2.2 mm from the lateral margin of the C2 IAP, 10.5 ± 2.7 mm caudal from the superior facet joint of the axis. The apex of the first bend was 3.5 ± 2.0 mm above the surface of the C2 IAP. The width of the C2 IAP was 14.2 ± 3.8 mm while the height was 15.9 ± 1.3 mm.

Conclusion: The GON overlaid the cranial two-thirds of the IAP surface and can cross the entry point of the C2 screw. Therefore, we recommend using the most caudal entry point as possible, with steeper cranial angle controlled with navigation, to avoid the GON injury during MIS.