**4. Discussion**

RA is an independent risk factor for increased mortality (Hakoda et al., 2005; Sihvonen et al., 2004). When the cervical spine is involved this risk is increased (Paus et al., 2008; Riise et al., 2001; Shen et al., 2004). In the RA population the estimates of the number of patients with cervical involvement varies from 12% (Naranjo et al., 2004) to 57% (Neva et al., 2006).

Cervical spinal disorders should be diagnosed early and treated actively to prevent severe and potentially fatal complications (Neva et al., 2006). Early surgery corrects AS and prevents further instability (Grob et al., 1999; Hamilton et al., 2001; McRorie et al., 1996). Early surgery may also reduce mortality (Grob, 2000; Paus et al., 2008; Tanaka et al., 2005). Posterior fusion reduces pain and may improve neurological symptoms or signs (Eyres et al., 1998; Matsunaga et al., 2003) as well as preventing progression of existing neural lesions without undue risk for the patient (Kim & Hilibrand, 2005; Santavirta et al., 1988).

When cervical neurological symptoms or signs have developed, the literature agrees that there is indication for operative treatment (Kim & Hilibrand, 2005). In addition to reducing pain, neurological recovery is more consistent with lower grade of preoperative myelopathy (Monsey, 1997). An autopsy study suggests that paralysis may be due to both mechanical neural compression and vascular impairment (Delamarter & Bohlman, 1994).

It is claimed that patients with no clear radiographic evidence of fusion following occipitocervical instrumentation seemed to do just as well as those who have obvious fusion (Moskovich et al., 2000). In our total series of patients (Paus et al., 2008) we came to the same conclusion. However, when we consider the most severely affected patients (i.e. those with neurological symptoms or signs as in the present study), we find a significant better prognosis if ankylosis is achieved. To obtain a higher proportion of bony ankylosis we have changed operative method from Brattstrøm and Granholm (1976) to transarticular screws (Claybrooks et al., 2007; Cornefjord et al., 2003; Haid, Jr. et al., 2001; Henriques et al., 2000; Praveen & Regis, 2005) after this study.

In our minds, based on the present findings, patients with relevant neurology are late for operation, their prognosis being worse, and we advise that operative treatment is initiated prior to the development of neurological symptoms or signs. We disagree with the routine of conservative treatment until neurological complications develop. Residual neurological deficit following operation also resulted in a reduced prognosis in the present study, indicating that delayed treatment may be hazardous.

The high incidence of neurological involvement in patients with SS is well described in the literature (Moskovich et al., 2000; Stirrat & Fyfe, 1993), and we find that this group of patients has a worse prognosis. Our conclusions regarding these patients are more cautious as the operative procedure is more elaborate and carries a higher risk of morbidity, but despite this these patients may benefit from operation prior to the development of neurological complications.

VS can be stopped by AA fixation (Grob, 2000) and patients with neurological symptoms or signs have a significantly more serious settling. In patients with VS, early fixation may reduce the danger of developing neurological complications.

AS is the most frequently occurring dislocation in the spinal neck with an increasing number with increasing severity in both operated groups. However, severe AS is significantly more frequent in the non-neurological group, while SS and VS are overrepresented in the group with relevant neurology. This suggests a weak association between degree of AS per se and neurological phenomena. In the non-neurological group, the majority of patients are operated related to severe AS. As neurological symptoms or signs with indication for surgery may develop before severe AS occurs in patients with SS and VS, this may explain the reduced number with severe AS in the group with relevant neurological findings.
