Not So Happy With the New Knee

Knee replacement surgery delivered function improvements but less satisfaction among obese patients

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) One major consideration when undergoing knee replacement surgery is whether the new knee will actually be an improvement over the original knee.

Obese individuals had the same functional improvements as normal weight individuals after knee replacement surgery, according to a new study.

At the same time, obese patients were less satisfied with the outcomes over the long-term.

Researchers suggested that severely overweight patients who are considering whether to get a new knee be made aware that they may not have the same level of satisfaction, as normal weight patients.

"Research knee replacement surgery risks."

The aim of the study, led by Paul Baker, PhD, associate clinical researcher at the Institute of Cellular Medicine at Newcastle University in the United Kingdom, was to see how body mass index (BMI), a measure of height and weight, impacts knee function, overall health and patient satisfaction three years after having total knee replacement surgery.

The study included more than 1,300 patients who were getting a new knee between July 2004 and August 2008. Patients were part of the Freeman Joint Registry, which monitors hip and knee replacement surgeries.

Patients were divided into groups based on their BMI. Groups were categorized as either normal weight (between 18.5 and 25 kg/m2), overweight (between 25 and 30 kg/m2), obese class I (between 30 and 35 kg/m2) and obese class II (greater than 35 kg/m2).

Patients were surveyed on their how well they could function six weeks before surgery. Researchers then assessed patients’ progress one, two and five years after surgery.

Three years after the operation, patients also completed a questionnaire on their overall knee function, stiffness and pain. Questions asked about their general physical and mental health, as well as their satisfaction with the joint replacement. 

Researchers found that patients in the highest BMI group experienced similar improvements a year after knee surgery as patients with a normal BMI.

Patients with higher BMIs maintained these improvements three years after surgery. Among the higher BMI group, about 85 percent reported feeling satisfied with the operation.

On the other hand, more than 93 percent of the normal BMI group were satisfied with their new knee overall.

When asked if patients would have the operation again, less than 70 percent of the higher BMI patients agreed compared to more than 82 percent in the normal weight group.

"Whilst the absolute post-operative functional scores were lower in patients classified as obese and morbidly obese, the improvements they experienced were comparable to those of patients with lesser BMIs," researchers wrote in their report.

"However, despite similar functional improvements, the obese and morbidly obese patients had the lowest levels of satisfaction, stated their quality of life was poorer and were less likely to undergo similar surgery again."

The authors noted that BMI was calculated based on patients' self-reported height and weight, and researchers did not look into patients' complications after surgery, length of hospital stay or hospital readmission rates. These might have skewed results.

In addition, the data came from a single surgeon and measures of quality of life can differ from one study to another, which might not be representative of other surgeons' work or other populations’ results.

The study, funded by Depuy Orthopaedics Inc, was published online March 19 in the journal PLOS One.

Reviewed by: 
Review Date: 
March 28, 2013
Last Updated:
March 31, 2013