Many people opt for knee replacement surgery to provide better mobility and eliminate pain. Under those conditions you would expect patients to be more active following the surgery, and therefore to lose weight.
However, a new study suggests it doesn't work out that way in most cases. Researchers Joseph Zeni and Lynn Snyder-Mackler at the University of Delaware found that patients typically drop weight in the first few weeks after total knee arthroplasty (TKA), but then the number on the scale starts creeping upward, with an average weight gain of 14 pounds in two years.
The study, which was sponsored by the National Institutes of Health, is reported in the online edition of Osteoarthritis and Cartilage, the official journal of the Osteoarthritis Research Society International.
The research involved 106 individuals with end-stage osteoarthritis who had knee replacement surgery, and an age-matched, healthy control group of 31 subjects who did not have surgery. Height, weight, quadriceps strength, and self-perceived functional ability were measured during an initial visit to UD's Physical Therapy Clinic, and at a follow-up visit two years later.
"We saw a significant increase in body mass index (BMI) over two years for the surgical group, but not the control group," said Zeni, a research assistant professor at UD. "Sixty-six percent of the people in the surgical group gained weight over the two years -- the average weight gain was 14 pounds."
Those who had the knee replacement surgery started out heavier and ended heavier than the control group. The weaker the surgery patients were, as measured by the strength of the quadriceps, the more weight they gained, Zeni found.
Rethinking assumptions
"These findings are making us re-think the component after total knee surgery and of patients not being in a routine of moving around," said Snyder-Mackler, Alumni Distinguished Professor of Physical Therapy at UD.
She notes that it's critical that people not wait too long to have a knee replaced because their functional level going into surgery typically dictates their functional level after surgery.
Gaining weight after one knee replacement is worrisome because it could jeopardize the patient's other knee. Between 35-50 percent will have surgery on the other side within 10 years, Snyder-Mackler said.
The researchers note that weight gain after a knee replacement needs to be treated as a separate concern and integrated into post-operative care through a combination of approaches, including nutritional counseling to help patients with portion control, and more emphasis on retraining patients with new knees to walk normally.
Why do knee replacement patients tend to put on pounds? Perhaps, the researchers say, because some basic assumptions were wrong.
"For physical therapists and surgeons, the common thinking is that after a patient's knee has been replaced, that patient will be more active," said Snyder-Mackler. "But the practices and habits these patients developed to get around in the years prior to surgery are hard to break, and often they don't take advantage of the functional gain once they get a new knee."
The researchers say the post operative routine needs to include retraining to walk more normally and more systematically. Social habits, as well as physical habits, need to be altered, they say.
"We need to encourage more community participation," Snyder-Mackler said. "If you're not getting out of the house, you won't gain the benefit. We need people with new knees to get out there -- with the help of their family, their friends, and the community at large."
