FRIDAY, March 4, 2005 (HealthDay News) -- After undergoing joint replacement surgery of the knee or hip, many patients with arthritis expect to lose weight, assuming they'll be more active when their new joints work and feel better.
Unfortunately, a new study suggests their obesity isn't driven by painful joints. In fact, the researchers found that patients actually tend to gain weight after knee- or hip-replacement surgery.
Assumptions about links between joint pain and obesity are natural, but it's time for the truth to come out, said study lead author Dr. Thomas Schmalzried, an orthopaedic surgeon and associate director of the Joint Replacement Institute at Orthopaedic Hospital in Los Angeles.
"It's very natural for someone who has a painful hip or knee to be restricted in their activity due to the pain," he said. "When they gain weight, there is a very natural tendency to attribute the weight gain to the fact they have been inactive because of their hip or knee arthritis. What our study shows is that their thinking is incorrect."
The message? "Patients, primary care doctors and surgeons should recognize that obesity [in these patients] is an independent disease process," he said. "Their obesity is not due to the arthritis. I don't think it contributes much at all."
The researchers presented the findings at the annual meeting of the American Academy of Orthopaedic Surgeons in Washington, D. C. last week.
The Los Angeles team recorded changes in body weight after successful joint replacement surgery in 34 men and 66 women, ages 23 to 82. They followed the patients at least one year after the surgery and found that, far from losing weight, the patients gained an average of almost three pounds.
There were no differences in weight gain between the 55 who had hips replaced or the 45 who had knees replaced. Younger patients with arthritis affecting one joint rather than several gained the most weight, the researchers added.
At the study start, 14 patients were normal weight while 31 were overweight (a body mass index of BMI that is above 25) and 55 were obese (a BMI of 30 or higher).
By the end of the study, nine patients had progressed from being overweight to the obese category, the researchers say.
For most of these patients, inactivity doesn't occur as a direct result of the arthritis, Schmalzried said, but is instead "a manifestation of a lifestyle."
Doctors should treat the weight problem as a separate, independent disease and not attribute it only to inactivity from arthritis, he added. Instead, it is probably linked to simple lifestyle factors such as eating too much and exercising too little.
About 500,000 persons in the United States get total hip or knee replacements each year, according to Schmalzried, and many are overweight or obese.
The study is an eye-opener for one expert, Dr. Stuart Miller, an orthopaedic surgeon at Union Memorial Hospital in Baltimore, Md.
"We know the general quality of life index improves after joint replacement," he said. "We assumed people lost weight after the surgery because they were more active."
He agreed with Schmalzried that joint replacement patients need to focus on getting to a healthy weight. Just as excess weight put undue strain on their original joins, the excess weight puts too much strain on the new joint, too, Miller pointed out.
"If they lose weight, the joint will do better and last longer," Miller said. He suggested that many patients may need medical supervision to lose the weight, rather than try to do it on their own.
To find out more about knee replacement, head to the American Academy of Orthopaedic Surgeons.