ObjectiveTo clarify the incidence and predictive risk factors of cervical spine instabilities which may induce compression myelopathy in patients with rheumatoid arthritis (RA).MethodsThree types of cervical spine instability were radiographically categorized into “moderate” and “severe” based on atlantoaxial subluxation (AAS: atlantodental interval >3 mm versus ≥10 mm), vertical subluxation (VS: Ranawat value <13 mm versus ≤10 mm), and subaxial subluxation (SAS: irreducible translation ≥2 mm versus ≥4 mm or at multiple). 228 “definite” or “classical” RA patients (140 without instability and 88 with “moderate” instability) were prospectively followed for >5 years. The endpoint incidence of “severe” instabilities and predictors for “severe” instability were determined.ResultsPatients with baseline “moderate” instability, including all sub-groups (AAS+ [VS− SAS−], VS+ [SAS− AAS±], and SAS+ [AAS± VS±]), developed “severe” instabilities more frequently (33.3% with AAS+, 75.0% with VS+, and 42.9% with SAS+) than those initially without instability (12.9%; p<0.003, p<0.003, and p = 0.061, respectively). The incidence of cervical canal stenosis and/or basilar invagination was also higher in patients with initial instability (17.5% with AAS+, 37.5% with VS+, and 14.3% with SAS+) than in those without instability (7.1%; p = 0.028, p<0.003, and p = 0.427, respectively). Multivariable logistic regression analysis identified corticosteroid administration, Steinbrocker stage III or IV at baseline, mutilating changes at baseline, and the development of mutilans during the follow-up period correlated with the progression to “severe” instability (p<0.05).ConclusionsThis prospective cohort study demonstrates accelerated development of cervical spine involvement in RA patients with pre-existing instability—especially VS. Advanced peripheral erosiveness and concomitant corticosteroid treatment are indicators for poor prognosis of the cervical spine in RA.

The incidences of VS and SAS significantly increased during the minimum 5-year follow-up. Prognostic factors of these instabilities were revealed to be the initial radiological findings of VS, SAS, and mutilating changes.

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.

The treatment of patients with severe flexion contracture of the rheumatoid knee, deprived of ambulation for long periods of time, is challenging. Based on three cases, we indicate the potential risks of posterior dislocation of the knee after total knee arthroplasty. In this pathological condition, surgeons must carefully select the type of implant in order to avoid this serious complication. We also emphasize the importance of working on disuse muscle atrophy of trunk (back, abdominal) and lower limbs, both of which play an integral role in ambulation. The personality of each rheumatoid patient should be carefully considered when considering surgical and rehabilitation options.

The treatment of patients with severe flexion contracture of the rheumatoid knee, deprived of ambulation for long periods of time, is challenging. Based on three cases, we indicate the potential risks of posterior dislocation of the knee after total knee arthroplasty. In this pathological condition, surgeons must carefully select the type of implant in order to avoid this serious complication. We also emphasize the importance of working on disuse muscle atrophy of trunk (back, abdominal) and lower limbs, both of which play an integral role in ambulation. The personality of each rheumatoid patient should be carefully considered when considering surgical and rehabilitation options.