Odontoid Screw Fixation

The dens can fracture in several patterns. The type II fracture, at the narrow base of the peg, is the most common and the most relevant to screw fixation. Because of the limited blood supply and mechanics at this level, type II fractures can be slow to heal, and some fail to unite if simply braced — particularly in older patients. The choices are therefore between non-operative treatment in a collar or brace, anterior odontoid screw fixation, and posterior C1-C2 fusion. The best option depends on the fracture pattern, the displacement, the bone quality and the individual.

In anterior odontoid screw fixation, a screw is placed through a small approach at the front of the neck, passing up through the body of C2 and across the fracture into the tip of the dens. As it is tightened, it compresses the fracture and holds it firmly. Crucially, it fixes the fracture without fusing the C1-C2 joint, so the normal rotation between the first and second vertebrae — which provides much of the head's turning movement — is preserved. This motion-preserving quality is the main attraction of the technique for suitable fractures.

Anterior odontoid screw fixation is best suited to certain type II fractures with a favourable fracture line and reasonable bone quality, where the fracture can be reduced into a good position. It is less suitable where the fracture line runs in an unfavourable direction, where there is significant comminution, or where the bone is very weak — situations in which a posterior C1-C2 fusion may give a more reliable union. In older patients in particular, the choice between anterior screw and posterior fusion is weighed carefully, because healing can be less predictable. The decision is individualised.

The evidence guides the choice. Meta-analyses comparing anterior odontoid screw fixation with posterior C1-C2 arthrodesis for type II fractures report that both achieve high union rates, with the anterior screw preserving motion and the posterior fusion sometimes offering more reliable union in less favourable fractures. Studies of anterior screw fixation in the elderly, and of the factors influencing union, help identify who is best suited to each approach. This literature underpins a tailored decision for each fracture.

Whether an odontoid fracture is best treated with a brace, an anterior screw or a posterior fusion depends on the fracture pattern, its position, the bone quality and the individual's circumstances. Where an anterior odontoid screw is suitable, it offers fixation that preserves neck rotation; where it is not, a posterior fusion or non-operative care may be the better choice. The options, realistic expectations and risks are discussed individually.

• —Shen Y, et al. Anterior odontoid screw versus posterior C1-C2 arthrodesis for odontoid fractures: a meta-analysis. Eur Spine J 2015. (PMID 25805577)
• —Robinson AL, et al. Fusion rates after anterior odontoid screw versus posterior C1-C2 arthrodesis: a meta-analysis. Global Spine J 2019. (PMID 30877428)
• —Dailey AT, et al. Anterior screw fixation of type II odontoid fractures in the elderly. J Neurosurg Spine 2009. (PMID 19001977)
• —Scheyerer MJ, et al. Odontoid screw placement for type II fractures: factors influencing union. Eur Spine J 2021. (PMID 33007754)