To investigate whether variation exists in the preoperative age, pain, stiffness, and physical function of people undergoing total knee replacement (TKR) and total hip replacement (THR) at several centers in Australia and Europe.


Individual Western Ontario and McMaster Universities Osteoarthritis Index data (range 0–100, where 0 = best and 100 = worst) collected within 6 weeks prior to primary TKR and THR were extracted from 16 centers (n = 2,835) according to specified eligibility criteria. Analysis of covariance was used to evaluate differences in pain, stiffness, and physical function between centers, with adjustment for age and sex.


There was marked variation in the age of people undergoing surgery between the centers (TKR mean age 67–73 years; F[6,1004] = 4.21, P < 0.01, and THR mean age 63–72 years; F[14,1807] = 7.27, P < 0.01). Large differences in preoperative status were observed between centers, most notably for pain (TKR adjusted mean pain 52.5–61.1; F[6,1002] = 4.26, P < 0.01, and THR adjusted mean pain 49.2–65.7; F[14,1802] = 8.44, P < 0.01) and physical function (TKR adjusted mean function 52.7–61.4; F[6,1002] = 5.27, P < 0.01, and THR adjusted mean function 53.3–71.0; F[14,1802] = 6.71, P < 0.01). Large effect sizes (up to 0.98) reflect the magnitude of variation between centers and highlight the clinical relevance of these findings.


The large variations in age and preoperative status indicate substantial differences in the timing of joint replacement across the centers studied, with potential for compromised surgical outcomes due to premature or delayed surgery. Possible contributing factors include patient preferences, the absence of concrete indications for surgery, and the capacity of the health care systems.