Media release

From: International Congress on Obesity (ICO)

Small amounts of weight gain can increase odds of knee replacement surgery by up to a third, study finds

• Preventing weight gain in middle age could reduce pain, improve quality of life and reduce need for the costly op, which has the second longest waiting list of any surgical procedure in Australia

Relatively small amounts of weight gain can significantly increase the likelihood of knee osteoarthritis, the most common cause of knee pain, and knee replacement surgery, new research being presented at the International Congress on Obesity in Melbourne (18-22 October) suggests.

A 5kg (11lb) increase in weight was found to increase a woman’s odds of having total knee replacement surgery (TKR, also known as arthroplasty, is the most common type of knee replacement surgery) by a third and a man’s by a quarter.

Knee pain and stiffness also increased with weight gain, while quality of life and function (ability to use the knee) fell.

In osteoarthritis, the most common form of arthritis, the cartilage that cushions the ends of the bones in the joints wears away over time, causing symptoms such as pain, swelling and stiffness.  The knee is commonly affected. In severe cases, shopping, walking, and even getting out of a chair, can become painful and difficult.

Treatments include lifestyle changes, such as weight loss, pain-relieving medicines, and, when symptoms become too severe, knee joint replacement surgery.

“Weight loss can help ease the symptoms of knee osteoarthritis by reducing strain on the joint and lowering levels of harmful inflammation,” explains Professor Anita Wluka, of the School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia, who led the research.

“However, the 10%-plus reduction in total body weight that is required to have even a small effect on knee pain is difficult to achieve and even more difficult to maintain, particularly when osteoarthritis is present, reducing mobility.

“There is evidence that preventing weight gain1 (i.e. weight maintenance) is an easier and more achievable goal for patients than weight loss, so we set out to examine how weight gain was related to the symptoms and progression of osteoarthritis.

“Armed with this information, we may be able to develop new strategies to prevent osteoarthritis and to reduce its progression before it gets too bad.”

To find out more, Dr Wluka and colleagues reviewed existing research into the relationship between weight gain and knee osteoarthritis.

The Medline, Embase and Cochrane Library databases were searched from formation until February 2020 for studies that looked at the relationship between weight gain and the clinical features of osteoarthritis (pain, stiffness, function, quality of life), its structural progression and the need for total knee replacement surgery.

Twenty studies, involving individuals with, or at risk of, osteoarthritis, were included and meta-analyses were carried out where feasible. Study sizes ranged from 72 to 225,908 individuals.

The results tended to show a significant detrimental effect of weight gain on pain, stiffness, function, quality of life and on changes to the joint visible in X-rays.

Weight gain was also associated with more damage to cartilage, bone and other parts of the joint.

“In other words, osteoarthritis was more likely to develop with weight gain and to progress more quickly,” says Dr Wluka.

A meta-analysis of two studies involving more than 250,000 individuals in total, and looking at relationships between weight gain and TKR, found that weight gain significantly increased the odds of having the operation.

A 5kg (11lb) increase in weight increased the odds of TKR by 34% in women and 25% in men.

“This is particularly concerning,” says Dr Wluka.  “Knee replacements are costly and 1 in 5 people are dissatisfied with the results and remain in pain after surgery.

“Those who remain in pain are more likely to require a second surgery, which is more costly and less likely to control their pain.

“The prevention of osteoarthritis and the slowing of its progression would not only reduce the need for surgery, it would also take pressure of the health service which, due to our ageing and increasingly obese population, is facing increasing demand for knee replacement.

“Total knee replacement has the second longest waiting list of any surgical procedure in Australia and costs the health service more than $1 billion per year.”

The study’s authors conclude that weight gain is associated with an increase in symptoms of knee osteoarthritis, in structural changes to the knee and in the likelihood of requiring a total knee replacement.

Dr Wluka adds: “Given the challenges associated with weight loss, attention should also be paid to preventing weight gain, with individuals with osteoarthritis also given advice and support on how to maintain their current weight, something that can be particularly problematic as we get older.

“Weight maintenance in middle age would reduce the risk of knee osteoarthritis occurring and, in those with osteoarthritis, it would reduce worsening of pain, loss of function and the need for costly joint replacement.

“We know that people tend to put on nearly 1kg a year as they get older but the good news is that there is evidence from previous studies2 that it is possible to prevent weight gain.”

Professor John Wilding, Past President of the World Obesity Federation and Professor of Medicine based at Aintree University Hospital, University of Liverpool, UK, comments: “It is recognised that a high body weight puts more strain on joints such as the knee and increases the risk of pain, arthritis and requirement for knee replacement.  This analysis of previously published studies shows that even modest increases in weight (5kg) in middle age increases the risk of structural damage, pain and need for total knee replacement.  More research is needed to show if prevention of weight gain or modest weight loss can prevent or delay this process.”