C1–C2 Fusion

Atlantoaxial instability — abnormal movement between C1 and C2 — can arise from trauma (such as certain odontoid fractures), inflammatory conditions such as rheumatoid arthritis, congenital differences, tumour, or ligament failure. Because the spinal cord passes through this region, instability here is potentially serious, and can cause neck pain, neurological symptoms, and a risk to the cord. Where the instability is significant, stabilising C1 on C2 can protect the cord and relieve the mechanical problem.

C1–C2 fusion is carried out from the back of the upper neck. Screws are placed into the strong parts of the first and second vertebrae — commonly into the lateral masses of C1 and the pedicles of C2 (the Goel–Harms technique) — and connected with rods, holding the joint securely. An alternative long-established technique uses transarticular screws passed across the joint. Bone graft is applied so the two vertebrae fuse over the following months. Because the anatomy here is delicate and close to important vessels and the cord, the procedure is planned and carried out with great care and image guidance.

C1–C2 fusion can be considered where there is significant atlantoaxial instability — for example certain odontoid fractures that are unlikely to heal with a screw or brace, instability from rheumatoid disease, or congenital or traumatic ligament failure. The aim is to stabilise the joint and protect the cord. The trade-off is that fusing C1 to C2 removes much of the neck's rotation, so the decision balances the need for stability against this loss of movement, and is individualised to the cause and the person.

The evidence supports modern screw-based techniques as reliable ways to achieve atlantoaxial fusion. Meta-analyses and reviews comparing C1 lateral mass and C2 pedicle screw constructs with transarticular screw techniques report high fusion rates and good stability, and examine the safety and technical factors that influence results. The literature helps guide the choice of technique for a given anatomy. The balanced view is that C1–C2 fusion is a well-established, effective operation for significant atlantoaxial instability, carried out with careful planning at a critical part of the spine.

The operation is performed under general anaesthetic, usually with a hospital stay of several days. The screws provide immediate stability, while the fusion consolidates over the following months. The main expected trade-off is a reduction in the ability to rotate the head, since much of this movement comes from the C1–C2 joint. Rehabilitation supports recovery. As with any operation there are risks, which are discussed fully beforehand. Whether this operation is the right choice for a given person is decided together.

• —Elliott RE, et al. Atlantoaxial fusion with transarticular screws: meta-analysis and review of the literature. World Neurosurg 2013. (PMID 22469527)
• —Elliott RE, et al. Impact of starting point and bicortical purchase of C1 lateral mass screws on atlantoaxial fusion: meta-analysis and review. J Spinal Disord Tech 2013. (PMID 23563339)
• —Elliott RE, et al. Comparison of safety and stability of C2 pars and pedicle screws for atlantoaxial fusion: meta-analysis and review. J Neurosurg Spine 2012. (PMID 23039110)
• —El Masry MA, et al. Two methods of atlantoaxial stabilisation for atlantoaxial instability (Magerl versus Goel-Harms). Acta Orthop Belg 2007. (PMID 18260487)