Long-term outcomes and duration of outdoor ambulation following primary total knee arthroplasty in patients with rheumatoid arthritis

Abstract

Background: The medical treatment of rheumatoid arthritis (RA) has made remarkable progress with the introduction of methotrexate and biological agents. However, there have been few reports of long-term results of total knee arthroplasty (TKA) for RA since the introduction of these drugs. Ambulation is an important form of exercise for maintaining health. We investigated the long-term outcomes and the ability to walk outdoors following TKA in patients with RA.

Methods: We retrospectively reviewed 142 patients with RA (201 knees) who had undergone primary TKA. The mean follow-up was 10.6 years.

Results: Markers of RA disease activity all improved significantly postoperatively. Mean Japanese Orthopedic Association scores improved from 49.3 points before surgery to 81.8 at follow-up. The mean maximum flexion angle improved from 107.8° to 112.9°. The causes of TKA revision comprised 2 mechanical loosening, 1 late infection, and 1 fracture of the femoral condyle. The survival rate of TKA was 96.6% at 15 years. Fifty-five patients were not able to walk outdoors. The rate of inability to ambulate outdoors was 38.3 per 1000 person-years. The survival rate of ability to ambulate outdoors were 48.8% at 15 years. Preoperative advanced age, low body weight, steroid use and non-use of biologics were identified as risk factors for inability to ambulate outdoors.

Conclusions: Although the cumulative survival rate of TKA implants was as good as 96.6% in 15 years, the cumulative rate of ability to ambulate outdoors was only 48.8%. The reason for the inability to walk outdoors was thought to be mainly due to deterioration of RA, comorbidity or muscular weakness associated with aging, rather than knee dysfunction.