Long-Term Effects of Obesity on Knee Joint Replacement

This is the first study to report the long-term results of total knee replacement (TKR) in obese patients after more than 10 years. Other studies have followed patients for shorter periods of time. Researchers compared two groups of patients with TKR. One group had a body mass index greater than 30, which means they were obese. The control group had the same TKR, but these patients were not overweight.

A special computer program was used to match patients from each group. The patients were paired based on gender, age at the time of surgery, type of arthritis, and length of follow-up after surgery. Level of activity after TKR was also measured for each patient.

The researchers reported the following findings:

  • Only 70 percent of the obese group had a successful outcome. This was compared to 90 percent in the control group.
  • Thirty percent of the obese group had their knees revised (a second surgery later). Only 10 percent of the control group needed revisions.
  • There was a trend for obesity to cause loosening of the implant.
  • The control group was more likely to need revision of the plastic spacer between the bone and the implant. Revisions in this group were probably due to higher activity levels.

    The authors conclude that obesity may increase a patient’s chances of implant loosening. Higher loads at the spot where the implant meets the bone can be a problem. Having the patient lose weight before getting a TKR–and keeping it off–may be a good idea.