Contrary to general expectations, patients who have total knee replacement (TKR) surgery gain bodyweight, new research has shown. The study was led by Daniel Riddle, a professor of physical therapy and orthopaedic surgery at Virginia Commonwealth University, and published online in Arthritis Care & Research.
According to the results, nearly a third (30%) of people added 5% or more to their bodyweight within five years of TKR surgery, compared to 20% of people in a control group who had not undergone the surgery. The findings are at odds with the assumption that after the surgery patients would lose weight as a result of their increased mobility and reduced pain.
The weight gain does not seem to influence the outcome of the knee surgery. However, a weight increase of even 5% is “clinically important” as it raises the risk of other health issues such as heart disease and diabetes, according to the study authors.
The study looked at longer-term weight changes involving a patient registry of over 900 people who underwent TKR surgery between 1995 and 2005. The researchers gathered data at the time of surgery and then two and five years after the procedure, comparing the information to a sample of people from the same geographic area who did not have the procedure. Age, weight and gender along with other diseases and conditions were taken into account to ensure these factors would not affect the outcome of the study.
Results further showed that the risk of post-surgery weight increase was particularly high for people who had a second joint replacement procedure, as well as for those below 70 years of age and those with significant weight loss before the surgery.
It is not clear why so many people gain weight after knee replacement, but it is likely that some don’t become very active after the surgery, Riddle said. The results suggest that orthopaedic surgeons need to discuss the issue of weight change with their patients, as undertaking exercise after the procedure involves patients’ willingness as much as their ability to do so. Patients are almost always able to increase their activity after total knee replacement, which restores the knee function and relieves the pain.