Total joint arthroplasty (TJA) is the mainstay of treatment for end-stage arthritis of the hip or knee, a stage loosely defined by unacceptable levels of pain and physical dysfunction despite adequate medical management. Both total hip arthroplasty (THA) and total knee arthroplasty (TKA) have consistently been demonstrated to provide long-lasting pain relief and substantial and sustained improvement in joint functioning and health-related quality of life . In Canada, it is estimated that by 2026 over 6 million Canadians will have arthritis, increased from 4 million in 2000 . In the United States (US), the prevalence of arthritis is projected to increase from 47.8 million in 2005 to nearly 67 million by 2030, an increase of ∼40% over 25 years . In contrast, the rates of TKA in the US and Canada increased by ∼100% and 128% in the period from 1999 to 2008 and from 1994 to 2004, respectively . The trends in the rates of TJA, particularly TKA, are greater than the projected increase in the number of people with end-stage arthritis for the same period, suggesting that the indications for TJA are broadening.

Although TJA was initially designed for older patients (generally defined as >70 years of age) , a recent report from Finland indicated that there has been a sharp increase in the number of TKAs performed for younger patients in that country . This is believed to be secondary to the ageing of the baby boomer cohort (those born in the post-war period from 1946 to 1964). However, the health-care system in Finland is publically funded, with private health care making up <5% of inpatient hospital visits. All health-care personnel including surgeons are compensated with a monthly salary, and patients can only access elective surgical care after referral from a physician . Thus, the degree to which these changes in TJA rates can be generalised to North America is unclear. Canada uses a single-payer health-care insurance system, and all Canadians require referral from a family physician for a surgical consultation. However, Canadian surgeons are paid on a fee-for-service basis, introducing a potential financial incentive to perform surgery. The US uses a combined public (in the case of Medicare and Medicaid) and private health-care insurance system. The payment to orthopaedic surgeons for each elective arthroplasty and the requirement of a physician referral to be seen by a surgeon is not standardised, as it is in Ontario. However, this potential increased access to surgery among those insured is mitigated by factors that may reduce the rates of TJA, including a higher prevalence of individuals who are non-insured or under-insured, and by documented racial disparity .

We set out to estimate and compare the crude and age- and sex-standardised rates of primary TKA and THA over the last decade in the US and Ontario, Canada. In addition, we estimated the age distribution of TJA recipients, and the changes in distribution over time for both areas. We hypothesised a rise in rates of TJA in both countries, with a greater increase in the US. We also hypothesised a shift in the demographic of recipients to younger patients, and once again expected this shift to be more pronounced in the US due to relatively increased access to surgeons.