We read with great interest the article “Role of Obesity on the Risk for Total Hip or Knee Arthroplasty” by Bourne et al. [1] in the December 2007 issue of CORR.

The authors state increasing obesity was associated with increased relative risk for hip or knee arthroplasty. They found almost 75% of total hip arthroplasty recipients and 88% of total knee arthroplasty recipients were overweight or obese whereas the percentage of overweight or obese people for the Canadian population is 51.4%.

These percentages could reflect a relationship between obesity and the risk of hip and knee arthroplasties, but there are no data regarding the etiologic factors leading to obesity in these patients. Arthrosis of the hip or the knee causes pain in the affected joint and typically results in a decline in physical activity; a sedentary lifestyle and physical inactivity lead to obesity [2]. It is unclear whether obesity causes arthrosis or arthrosis leads to physical inactivity and thus to obesity. If the latter is correct, one also would anticipate a higher percentage of obese patients in a population undergoing arthroplasty. Patients complaining of being overweight because of inactivity imposed by their pain is not uncommon. We believe this requires additional research for a definitive answer.