We cross-matched the Swedish Hip and Knee Arthroplasty Registers (SHAR and SKAR) to study the incidence of knee or hip arthroplasty in any of the remaining hip or knee joints.

177835 THR (55.8% females, mean age, SD: 68.5 10.1 years) and 128162 primary TKR (59.8% females, 69.4 9.0 years) procedures in patients with primary osteoarthritis, performed 1992–2014 were studied. Mean and maximum follow up were 7.7 and 23 years.

At the index operation more patients were operated on their right side for both locations (hip and knee). Patients who at the index operation had been operated with a TKR and especially on the left side most frequently (32.5%) received one or several additional TKR or THR. For patients who had a THR at their index operation and underwent a second operation of any of the remaining three joints the mean time to this second procedure was 4.0 years (SD: 3.9). In patients who were operated with a TKR this time period was shorter (3.1, 3.2, p<0.0005).

In patients who had undergone their first (index) operation of either hip the probability of not being subjected to further arthroplasty operations during the following 20 years amounted to 64.0±0.3%. The corresponding probability for patients who at the index operation had received a TKR was somewhat lower (58.4±0.4%). Decreasing age (HR: 1.029, 95% confidence interval: 1.028–1.0292), female gender (1.13 1.12–1.15), TKR at index operation (1.34 1.32–1.36) and left-sided index operation (1.12 1.10–1.13) were associated with higher probability for at least one additional primary joint replacement in the hip or the knee.

During our period of observation 25 to 33 percent of the patients who received their first total hip or knee replacement underwent at least one additional replacement of either the hip or the knee. Knee osteoarthritis more frequently results in staged bilateral joint replacement than in patients who primarily are suffering from osteoarthritis of the hip.