Incidence and aggravation of cervical spine instabilities in rheumatoid arthritis: A prospective minimum 5-year follow-up study of patients initially without cervical involvement

STUDY DESIGN. A prospective minimum 5-year follow-up study of the cervical spine in patients with rheumatoid arthritis (RA) initially without cervical involvement. OBJECTIVE. To clarify the incidence and aggravation of cervical spine instabilities and their predictive risk factors in patients with RA. SUMMARY OF BACKGROUND DATA. Many reports have shown the progression of cervical spine involvement in RA. However, few articles have described comprehensive evaluation of its prognostic factors. METHODS. A total of 140 patients with "definite" or "classical" RA initially without cervical involvement were prospectively followed for more than 5 years. Radiographical cervical findings were classified into 3 instabilities: atlantoaxial subluxation (AAS: atlantodental interval >3 mm), vertical subluxation (VS: Ranawat value <13 mm), and subaxial subluxation (SAS: irreducible translation ≥2 mm). "Severe" extents were defined as AAS with atlantodental interval 10 mm or more, VS with Ranawat value 10 mm or less, and SAS with translation 4 mm or more or at multiple levels. Incidence of these developments and predictors for "severe" instabilities were investigated. RESULTS. During 6.0 ± 0.5 years, 43.6% of 140 patients developed cervical instabilities: AAS in 32.1%, VS in 11.4%, and SAS in 16.4% with some combinations. "Severe" instabilities were exhibited in 12.9% of patients: AAS in 3.6%, VS in 6.4%, and SAS in 5.0%. Furthermore, 4.3% presented canal stenosis, with 13 mm or less space available for the spinal cord (SAC) due to "severe" AAS or "severe" VS in 2.9% and 12 mm or less SAC due to "severe" SAS in 2.1%. Multivariable logistic regression analysis identified corticosteroid administration, mutilating changes at baseline, and the development of nonmutilating into mutilating changes during the follow-up period correlated with "severe" instabilities (P < 0.05). CONCLUSION. A minimum 5-year follow-up reveals the occurrence of cervical instabilities in 43.6%, "severe" aggravation in 12.9%, and decreased SAC in 4.3% of patients with RA. Characteristics of severe disease activity - established mutilating changes, progressive development into mutilating changes, and potentially concomitant corticosteroid treatment - are indicators for poor prognosis of the cervical spine in RA.