Updated June 20, 2015.

            Obesity and osteoarthritis are closely related medical problems. Obesity has been shown to place additional stress on joints leading to faster wearing away of the joint. Many people with end-stage osteoarthritis and obesity are placed in a difficult situation. While weight loss has been to help alleviate the pain of osteoarthritis in the knee and hip, the significant pain of OA limits activity and makes weight loss difficult.


So can total hip and total knee replacement help people lose weight by allowing them to be more active with less pain?

            A group of researchers from the Hospital for Special Surgery (HSS) set out to answer that question. They looked at over 12,000 patients that underwent total knee and total hip replacements in their registry. Their findings were very interesting. In the total hip replacement group 73% of patients maintained their same body mass index (BMI) two years after their hip replacement. The heavier patients were more likely to lose weight. Out of the patients that had a BMI of over 40 (severe obesity), 35% lost weight at 2 years, 54% maintained their weight, 12%  gained weight at the 2 year follow up.

            In this study female patients were more likely to lose weight than male patients. Another interesting finding was that patients with post-graduate education were less likely to gain weight after hip replacement surgery compared to patients with only a high school education.

Patients that underwent total knee replacement showed similar trends to the total hip replacement patients. Sixty nine percent of patients that underwent a total knee replacement did not have a significant change in weight two years after the surgery. Patients that had a total knee replacement were more likely to lose weight compared to those that underwent total hip arthroplasty.

            Overall 69% of people that had a knee replacement had no change in weight 2 years after their surgery. People that were more obese were more likely to lose weight after a total knee replacement than those of normal weight. Predictors of weight loss after total knee replacement were similar to those after total hip replacement.  The strongest predictor was obesity, patients that had class III obesity (BMI over 40) had a 5 times greater chance of weight loss compared to people that were not obese. Female patients were more likely to lose weight then males. Patients that had a greater improvement in function were more likely to lose weight. People that gained weight reported lower functional scores.

            Setting all the numbers aside, what does this study really mean? The following is my interpretation, and comes with the caveat that this is fact and is only an interpretation of trends from this one study.  This study tells us that most people that undergo total hip or total knee replacement will not lose weight. However, many people that undergo those procedures are not trying to lose weight, and may be happy with their body weight and are simply getting this surgery because they have intolerable pain from end stage arthritis. The people that have the highest likelihood of losing weight are the ones that are at the extreme end of the overweight spectrum. These are the people that are most likely to increase their activity after having a hip or a knee replaced, and therefore end up with greater weight loss.