Does a knee replacement help you lose weight?

Ross A. Hauser, MD; Danielle R. Steilen-Matias, MMS, PA-C

Many patients are under the assumption that the quickest way to attack their obesity problem is to get a knee replacement. The thinking is that if they eliminate their knee pain with their “new knee,” they can exercise, be more active, and lose weight. Research papers are now recommending to surgeons and other post-replacement specialists that a more realistic expectation of post-knee replacement weight loss should be given and that for many obese patients, knee replacement-generating weight loss is not a reality.

I used to be extremely fit and worked out all the time, but now I am obese

Many patients contact us with knee problems. They tell a story that probably sounds a lot like yours:

I used to be extremely fit and worked out all the time, but now I am obese, I liked being very active. I ran, I hiked, I played sports, I have a home gym. I do not do any of that now. I have two knees that are letting me down. I am stuck in a cycle where I am gaining weight because I can’t exercise, and I can’t exercise because I am gaining weight. My doctors are strongly suggesting knee replacement so I can be active again and work on my weight gain. But one doctor is telling me, “be careful”, the knee replacement may not help me lose weight and I may even gain weight. How is that possible?

Obesity and anxiety after knee replacement

People have successful knee replacements. People can lose weight after knee replacement. People should be made aware that they can also gain weight after knee replacement. Let’s explore the science.

What are we seeing in this image?

This image is a simple demonstration of the development of a bone-on-bone knee. The more weight you have above your knee, that is in your belly and butt and thighs, the more pressure on that small area of cartilage trying to keep you from being bone on bone.

Let’s look at some of the research of the last eight years to help us understand how a successful knee replacement may not lead to weight loss, and in fact, lead to weight gain. Remember, successful knee replacement is the successful replacement of the knee joint. This will be an important fact to remember as you will see in the research.

Increasing weight and anxiety after knee replacement

Let’s start in August 2016 with a study published in the Journal of Rheumatology (1), here, doctors at the University of Texas, MD Anderson Cancer Center, suggested that following knee replacement, increasing BMI (Body Mass Index – Obesity) and rising anxiety levels and decreasing levels of positive social interactions were associated with increased patient costs (the need for continued care) following total knee replacement. The greater the obesity the greater the patient’s need for care (cost) following the knee replacement.

In this study of 212 patients, 66% were women, 71% were white, and the mean age was 65.2 years old, found that some patients following knee replacement gained weight had increased anxiety levels, and had poor psychosocial attributes (social support, locus of control (a patient’s belief that they did not control their own destiny in life), coping, depression, stress, and self-efficacy (their thinking that they would be or not be functional after surgery)). Increased baseline Body Mass Index, anxiety, and poor social support lead to higher total knee replacement-related healthcare needs in patients. The researchers of this study suggested pre-surgery addressing these possible post-surgery problems.

Research: It is unclear whether total knee replacement facilitates weight reduction. Is the surgery a “barrier” to weight loss?

We do understand that some adult children and spouses may implore their loved ones to get a knee replacement because they “have to do something.” They are getting heavier and less mobile. In some instances, people can be “guilted,” into treatment when they perceive that they will be a “burden,” on their loved ones.

But is knee replacement an answer that will make things better or worse?

An earlier study from 2017 from the Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University and the Department of Exercise Science, University of South Carolina published in the journal BioMed Central Musculoskeletal Disorders (2) made these observations:

Most knee replacement patients are overweight/obese, yet are commonly excluded from evidence-based weight loss programs due to mobility limitations and barriers faced around the time of surgery.
The purpose of this study was to identify knee replacement patient preferences for weight loss programs and qualitatively understand previous motives for weight loss attempts as well as strategies used to facilitate behavior changes.

This study focused on patients who were either scheduled to have a knee replacement or had one recently completed within the last 3 months (of the time of the study participation) were recruited to participate. Patients completed a brief weight loss program preference questionnaire assessing preferred components of a weight loss program (i.e. self-monitoring, educational topics, program duration).

Twenty patients (11 pre-operative and 9 post-operative) between 47 and 79 years completed the study (55% male, 90% White, and 85% with a BMI more than 25 (overweight)).
Patients reported a preference for a weight loss program that starts before surgery, is at least 6 months in duration, and focuses both on diet and exercise.
The majority of patients preferred to have a telephone-based program and wanted to track diet and physical activity on a smartphone application.
The most common motive for weight loss mentioned by patients related to physical appearance (including how clothing fit), followed by wanting to lose weight to improve knee symptoms or to prevent or delay knee replacement. Strategies that patients identified as helpful during weight loss attempts included joining a formal weight loss program, watching portion sizes, and self-monitoring their dietary intake, physical activity, or weight.

If you are reading this article, you or a loved one facing knee replacement surgery and if you are like your counterparts in this study, you want to look better than you want to your knee to work better. This would likely not be the dominating motive for someone who is self-employed or still working. As discussed above, this type of weight loss program does require a lot of costs.

Patients who undergo total knee replacement do not lose weight one year after surgery.

A June 2022 study in the journal International orthopaedics (3) followed patients who had a recent total knee replacement to see what effect, if any, the knee replacement had on their weight. In this paper the researchers noted that many patients discuss their obesity problems with their surgeons prior to surgery. The surgeons noted: “Prior to the procedure, most patients perceive that their excessive weight is secondary to the low level of activity due to limiting knee pain.”

Here are the study findings and learning points:

The study included 247 patients who had undergone total knee replacement from January 2018 to January 2019.
Researchers looked for a significant change in weight, that is 5% weight loss or 5% weight gain compared to pre-operative weight.
Results: Among the total study group, 17 (6.9%) lost weight, 168 (68%) did not have a change, and 62 (25.1%) increased weight at one year follow-up.

Obese patients are more likely to require total knee replacement -It is unclear whether total knee replacement facilitates weight reduction

Doctors in the United Kingdom reported these findings in the journal Maturitis: (4)

There is a proven association between obesity and knee osteoarthritis, and obesity is suggested to be the main modifiable risk factor.
Obese patients are more likely to require total knee replacement
It is unclear whether total knee replacement facilitates weight reduction
Surgery in obese patients is more technically challenging.
- This is reflected in the evidence, which suggests
  - higher rates of short- to medium-term complications following total knee replacement, including wound infection and medical complications, resulting in longer hospital stay, and potentially higher rates of malalignment, dislocation, and early revision.

The primary finding of this study is that patients who underwent total knee replacement tend to experience an upward trend in BMI

In September 2023, doctors and surgeons in Chile wrote in the journal Cureus (5) that patients who underwent total knee replacement tend to experience an upward trend in BMI, particularly noticeable in patients under 65 years of age. In fact the trend increased classification of patient from overweight to obese and from obese to severely obese. “This study showed that the nutritional status of patients does not change just by achieving a functional improvement through joint replacement. Patients should be educated to adopt healthier habits, maintain a healthy diet, and perform physical activity, especially those who were overweight or obese before surgery.”

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Research citations:

1 Waimann CA, Fernandez-Mazarambroz RJ, Cantor SB, Lopez-Olivo MA, Barbo AG, Landon GC, Siff SJ, Lin H, Suarez-Almazor ME. Effect of Body Mass Index and Psychosocial Traits on Total Knee Replacement Costs in Patients with Osteoarthritis. The Journal of rheumatology. 2016 Aug 1;43(8):1600-6. [Google Scholar]
2 Pellegrini CA, Ledford G, Hoffman SA, Chang RW, Cameron KA. Preferences and motivation for weight loss among knee replacement patients: implications for a patient-centered weight loss intervention. BMC musculoskeletal disorders. 2017 Dec;18(1):327. [Google Scholar]
3 Coelho A, Leal-Blanquet J, Sánchez-Soler JF, Torres-Claramunt R, Hinarejos P, Monllau JC. Patients lose weight after a total knee arthroplasty: myth or reality?. International Orthopaedics. 2022 Mar 29:1-6. [Google Scholar]
4 Kulkarni K, Karssiens T, Kumar V, Pandit H. Obesity and osteoarthritis. Maturitas. 2016 Jul;89:22-8. doi: 10.1016/j.maturitas.2016.04.006. Epub 2016 Apr 11. Review. [Google Scholar]
5 Barahona M, Barahona MA, Navarro T, Chamorro P, Alegría A, Guzman M, Palet MJ. Increase in Postoperative Body Mass Index in Patients After Total Knee Arthroplasty. Cureus. 2023 Sep 29;15(9). [Google Scholar]