To define how pre-operative evaluation guides surgical planning in patients with atlanto-axial subluxation secondary to rheumatoid arthritis and to measure clinical outcome for the same group.

Prospective evaluation of a consecutive cohort of 26 patients undergoing C1/2 fusion over 5 years (2004-2009).

Pre-operative evaluation of posterior atlanto-dens interval (PADI), C1 lateral mass and C2 pedicle dimensions.

Pre- and post-op Ranawat scores and visual analogue scores for neck and C2 pain

C1/2 instability resulted from rheumatoid arthritis (21), trauma (4) and infection (1).

C1 lateral mass mean height 4.4mm, C2 pedicle mean height 5.1mm and mean width 3.4mm (30% width <3mm).

Ranawat scale improved Grade II to Grade I (p=0.07). Neck pain (pre-op mean 5.5, s.d. 2.8; post-op mean 1.6, s.d. 2.1, t<0.05) and C2 pain (pre-op mean 2.1, s.d. 3.3; post-op mean 0.5, s.d. 1.2, t<0.05) improved.

No instrumentation failure. In the rheumatoid group, 17/21 patients had C1 lateral mass and C1/2 transarticular screws. 1 patient had a cranio-cervical fusion and 3 patients had other constructs.

3 patients had C2 numbness. No other neurological deficit.

In a rheumatoid population, pre-operative evaluation often precludes the use of C2 pedicle screws. Rigid fixation with a C1 lateral mass and C1/2 transarticular polyaxial screw-rod system is associated with good clinical outcomes.