Obesity not a contraindication to knee replacement

Contrary to current perceptions, there is no reason to deny a person knee replacement simply because they are clinically obese, according to a study published recently in the Annals of the Rheumatic Diseases.

The findings show that there is little justification for policies that deny this type of surgery to obese patients on the grounds of their body mass index (BMI). The researchers report that long term improvements in physical functioning in patients who had undergone knee replacement surgery extended to patients who were clinically obese, with a BMI greater than 30.

The new study compares two groups of people, all older than 45, who were followed for six years. The first group of 325 people had all had knee replacement surgery. Their mobility, mental health, and wellbeing were compared with 363 controls matched for age and sex who had not had the procedure.

The results show that the mobility of patients who had knee replacement surgery improved, but it fell in the comparison group. At follow-up, the median physical function score of the patients had improved by six points, but that of the controls had deteriorated by 14 points. However, no evidence showed improvement in vitality or mental health compared with the control group.

When the analysis was restricted to the 108 patients who were obese at the start of the study, results showed that their median physical function score increased from 17 to 20 points during follow-up, but among the 36 controls who were obese at baseline the median score dropped from 61 to 25 points.

The improvement in physical function was smaller in patients who were obese than in patients who were not obese, but the authors argue that it compared favourably with the substantial decline in physical function seen in obese controls.