Many people with obesity believe that knee replacements will help them move more and therefore lose weight. The supporting evidence, however, isn’t good.
You’re heavy and have painful, arthritic knees. A knee replacement will likely reduce your pain, typically within as little as three months. But a knee replacement alone probably won’t help you lose weight.
The cause of your knee pain is probably osteoarthritis. Arthritis breaks down your knee cartilage, a soft flexible tissue that cushions the ball-and-joint socket. Being overweight is a burden on your knees.
That’s one reason obese patients — having a body mass index (BMI) greater than 30 — are more likely to experience pain than slimmer patients and tend to get knee replacements at younger ages, on average 3.5 years earlier.
You can consider alternatives to knee replacement. Whatever you do to calm your knee pain, however, you’ll probably still need other weight-loss strategies.
How being overweight hurts your knees
- Being overweight hurts your knees in three ways.
- Simply carrying more weight makes your joints work harder.
- Your cells do not send out the right signals for normal repair work.
- Fat communicates with your body in ways that work against you.
Do you need to lose weight before surgery?
There’s a debate about the risk of complications for people who have certain BMIs. The American Academy of Orthopaedic Surgeons advises that patients with a BMI above 40 have a greater risk of serious complications, both during and after surgery. In part, that’s because those patients often have other medical problems.
Surgeons, hospitals, and insurance companies may not approve knee replacement surgery if you’re above a certain weight. But you do have options. Some surgeons and hospitals have developed programs specifically to minimize complications.
Regardless of your weight, knee replacements tend to have good outcomes, reducing pain and improving knee function, research suggests. In a study of nearly 500,000 knee replacement patients, people with obesity were only slightly more likely to need a repeat surgery within 10 years.
Smokers can lower their risk of infection or problems healing if they stop smoking at least four weeks before surgery. If you have diabetes, improving your blood sugar control can minimize infection fitness.
Improving your heart and lung fitness also help. Cycling, swimming, water exercises, or using an elliptical machine are excellent low-impact activities.
Will knee surgery help you lose weight?
Many people don’t exercise more with their new knee, even when they have less pain. It’s not uncommon to gain weight.
In one small study, only 7 percent of a group of knee surgery patients lost weight a year later, while 68 percent stayed about the same, and 25 percent gained weight. The average BMI rose slightly after the surgery.
The patients who had been obese, however, were slightly more likely to lose during the next year.
If weight is a longstanding problem for you, you’ll probably find you still need medication to fight your appetite (insurance usually covers the cost of medication if you also have type 2 diabetes). You’ll also probably need motivation strategies to exercise more and eat better. But if you work at it, you can do more if you have less pain.
You might aim to lose about 10 percent of your weight as your first goal. Losing just 10 pounds can relieve 40 pounds of pressure on your knees.
Would losing weight help your knees if you're not obese?
Even people who are just slightly overweight may be more likely to get knee surgery. Losing 11 pounds can lower a woman’s risk of knee osteoarthritis by half. Meanwhile, gaining that much weight can increase your risk by about 28 percent.
Slimmer people also seem to feel less pain, for reasons that aren’t completely clear but are probably related to their overall health.
Your best overall strategy is to address losing weight first, evaluate your pain afterwards, and then talk to your doctor about whether knee replacement surgery is a good option for you.
October 13, 2023
Christopher Nystuen, MD, MBA and Janet O'Dell, RN