There has been a substantial decline in numbers of patients with rheumatoid arthritis having primary total knee replacement (TKR) in Australia over the last two decades, research shows.

Compared to the use of TKR for osteoarthritis, there has been a significant decline in the proportion of primary TKR for RA, from 2.4% in 2003 to 0.9% in 2016, according to figures from the Australian Orthopaedic Association National Joint Replacement Registry.

Overall numbers were 541,744 TKR procedures, of which 7542 were for RA and 534,202 for OA.

The figures also showed an overall lower revision rate for TKR in RA patients compared to OA patients – particularly for female RA patients –  with the difference becoming apparent after about 9 months.

Revision rates were generally similar for RA and OA patients over the age of 65 undergoing TKR, at around 4% at ten years. However revision rates for TKR were higher for patients under 65, at around 8% for those with OA and 5% among those with RA at ten years.

Revision rates were also noticeably higher for males with RA compared to females (Hazard Ratio 1.66).

The rates of TKR revision rates attributable to infection were significantly higher in the RA patients compared to the OA group of patients, though the difference was only significant for males.

The study, carried out by orthopaedic surgeons in Adelaide in conjunction with researchers at the South Australian Health and Medical Research Institute, also showed that the type of knee implant procedure used (posterior stabilised or minimally stabilised) made little difference in terms of outcomes and revision rates in RA patients.

Study authors Dr Luke Mooney and colleagues from the Wakefield Orthopaedic Clinic said that historically TKR had been an efficacious and often-used treatment for RA patients with severe disease, designed to relieve joint pain whilst correcting deformity and enhancing mobility.

However, improvements in medical therapy had markedly reduced the severity of symptoms in many RA patients and it was notable that a major decline in use of TKR in RA patients had already occurred in the pre-biologics era.

“Contemporary data on standardised mortality ratios in RA is pending within the new paradigm through the Australian Rheumatology Association Database (ARAD),” they wrote in the Australia and NZ Journal of Surgery.