Weight loss may reduce progression of knee osteoarthritis and help avoid joint replacement surgery – but the amount of weight loss required may be greater than is currently recommended, Australian research suggests

A NSW study that followed up almost 24,000 overweight and obese people over the age of 45 found that those who lost a more than 7.5% of their initial weight had a 30% reduced risk of total knee replacement (TKR) over five years compared to people with stable weight.

People who lost smaller amounts of weight (5-7.5%) did not show any reduced risk of TKR, according to the findings, derived from participants in the 45 and Up Study.

Researchers at the University of NSW and Sydney University analysed weight data collected from 23,916 obese and overweight individuals (BMI >25)  in 2006–2009, of whom 2139 had lost >7.5% weight, 1655 lost 5–7.5% weight, and 4430 gained >5% weight when followed up in 2010.

Hospital admission data showed that 4.2% underwent TKR and 2.0% underwent total hip replacement (THR) during follow up averaging 5.2 years.

Compared to people who were weight-stable, those who had weight loss of >7.5% showed a significantly reduced risk of TKR after adjusting for age, sex, BMI, socioeconomic and lifestyle factors (hazard ratio 0.69, 95%CI 0.54–0.87).

There was a significant linear association between increasing percentage of weight change and TKR in both weight gain  and weight-loss subgroups, but no overall statistically significant increase in risk of TKR among the group who showed weight gain during follow up.

This lack of association might be due to a statistical ‘ceiling effect’, when the variance of weight change was no longer measurable when participants were grouped into different weight gain categories, the researchers said.

They also noted that there was no association between weight loss and risk of THR, though there was a significantly increased risk for THR among people who had weight gain.

They said the findings built on previous research that had shown weight loss was likely to reduce symptoms of OA and improve joint function in individuals with overweight and knee OA.

Furthermore, the effect of weight loss on symptom reduction in knee OA appears to have a dose-response relationship.

The reduced medial cartilage volume loss seen in people with OA after weight loss, suggested there was a disease-modifying effect of weight loss on knee joint structure, the researchers added.

However current OA clinical management guidelines typically advise weight loss of 5% to be efficacious, they noted.

“Setting an evidence-based weight loss target is important for effectively managing knee and hip OA to reduce or delay the need for joint replacement surgery,” they wrote in the International Journal of Obesity.

“The present study suggests a weight loss target of >7.5% to reduce the risk of TKR for OA.”