Many total knee replacement patients are overweight or obese. There is a thinking among many that after the knee replacement, their  physical activity levels and weight will improve. This does not appear to be true for some as research points out. In many knee replacement patients, weight loss does not occur even though activity can be increased.

An October 2024 study (18) writes: “Patients expect weight loss post-surgery due to increased mobility, but paradoxically, studies show that weight may not decrease and might even increase postoperatively.”

I recently read a study in the journal Disability and rehabilitation.(1) It was led by Northwestern University. It talked about the weight problems people have after they had total knee replacement and the continued problems the patients had in the inability to losing weight despite the new knee.

This study may come as a surprise to many who think that a knee replacement will help them shed pounds put on by the immobilization caused by their long battle with degenerative knee disease and knee pain.

I want to give some of the learning points here directly from the research so you can get the story directly from the people in the study.

  • “Both before and after total knee replacement, patients reported that knee pain, loss of range of motion, stiffness, swelling (inflammation), inability to stand for a long period of time, loss of strength, fatigue and fear of falling interfered with their ability to be more physically active.”
  • Patients, before their surgery, discussed limitations in physical activity related to knee pain, such as an inability to bend down to do yard work and issues with balance.
  • “One patient discussed how activity led to pain, ultimately making her avoid any activity: “the reality is if I walk for 30 to 45 min, then I have a burning sensation in my knee. I’m also always conscious that my kneecap could be slipping out. I worry about that. Those are definitely limitations that don’t allow me to work out”
  • “Several patients reported difficulty in engaging in physical activity due to having lower levels of fitness, not enough stamina, and getting fatigued quickly. “I still have to get some more muscles in my leg because I knew when I was not walking for two years before the surgery, I was losing a lot of ability to walk and every-thing else. So now it’s hard to walk because I didn’t walk in two years” (This came from a 78 year old male patient after his knee replacement).

The knee replacement did not provide enough motivation to lose weight:

  • “Besides pain and physical limitations, lack of motivation and mood interfered with activity. One patient described her mood after surgery as an obstacle to getting to the gym: “many days where I was just like disgusted with everything and just sat on the sofa all day … ”

  • Another patient mentioned that the biggest challenges with being active were related to, “attitude and knee. Bad knee and attitude where, my depression limits me … If I don’t have a meeting to go to then I have a hard time getting out of bed … ”

It is interesting to note that this research pointed out: The majority of total knee replacement patients are overweight or obese and physical activity levels and weight do not appear to change in a high proportion of patients after knee replacement.

Obesity is one of most discussed factors when assessing prosthetic knee surgery outcomes

A June 2022 study (2) noted that “obesity is one of most discussed factors when assessing prosthetic knee surgery outcomes. Prior to the procedure, most patients perceive that their excessive weight is secondary to the low level of activity due to limiting knee pain.” In this study 247 patients who undergone total knee replacement from January 2018 to January 2019 were followed to see if a significant change in weight was observed. Significant change was considered anything above or below 5% of the pre-operative weight.

  • Three groups were established based on a change in weight:
    • loss of more than 5%,
    • those who did not pass above or below 5% of their initial weight and
    • increase of more than 5%.
  • Follow-up was carried out at 12 months

Among the total population, 17 (6.9%) lost weight, 168 (68%) did not have a change, and 62 (25.1%) increased weight at one year follow-up. Conclusion: Patients who undergo total knee replacement do not lose weight one year after surgery.

People who get knee replacements do not lose any more weight that overweight people with knee osteoarthritis who did not get a knee replacement

A June 2023 study (3) suggested that “the notion that total knee replacement patients lose a considerable amount of weight in comparison to the general population as soon as improved joint function and pain relief have been achieved” is not accurate. This research was a cumulative study following patients over an eight year period.

A December 2022 paper (4) examined the effect of obesity on patient outcome, procedure (surgery) failure rate and osteoarthritis  progression in the tibiofemoral (where the shin bone meets the thigh bone) compartments in a series of isolated patellofemoral arthroplasty (knee cap and thigh bone partial replacement). In examining 120 patellofemoral arthroplasties with an average of almost seven years follow up, the researchers saw “an equal improvement in function after patellofemoral arthroplasty in both obese and nonobese patients; however, the high failure rate due to osteoarthritis progression in the medial tibiofemoral compartment warrants caution when considering patellofemoral arthroplasty in obese patients.” Suggesting that patients did not lose weight and remained obese and the obesity caused further knee breakdown.

Many people who give up sports before the knee replacement do not return to them

This research was supported by a June 2020 paper (5) which concluded: “Most patients who stopped participating in sport activities prior to surgery, however, do not seem to reinitiate their sport activities after surgery. As such, to achieve the full benefits out of knee replacement, clinical guidelines and strategies aimed to keep patients capable and motivated to participate in sport activities until close before and after surgery are warranted.” An April 2020 report (6)  suggested that people with advanced osteoarthritis found it difficult to continue walking or sports with seasonal weather change. Other factors included dislike of gyms, concern of walking on hardwood floors, etc.”

However, a March 2023 paper (7) suggested: “After total knee replacement, patients can be able to return to sporting activity or even perform better than before surgery. Maximum improvement was noted in the first post-operative year. The male and younger groups perform better than the female and older groups. Sports and physical activity do not negatively impact survivorship of the knee prosthesis at mid-term follow-up and all patients are encouraged to take up sports participation after their total knee replacement.”

Not only does knee replacement not help some patients lose weight, it causes them to gain it

This is research from Dr. Daniel Riddle Virginia Commonwealth University in the medical journal Arthritis care and research (8).

“Patients who undergo knee (replacement) are at increased risk of clinically important weight gain following surgery. Future research should develop weight loss/maintenance interventions particularly for younger patients who have lost a substantial amount of weight prior to surgery as they are most at risk for substantial postsurgical weight gain.”

Highlights:

  • Patients are at risk to GAIN weight after knee replacement
  • Patients who lost weight before the knee replacement, especially the younger ones, are at a greater risk to gain substantial weight after the knee replacement.

In the 5 years that separated the two studies, the problem remains. It should also be noted that two of the patients referenced in the first study were young women in regard to knee replacement age 50 and 55 years old.

54% of the patients presented weight gain after knee replacement

Let’s not rely on one study, let’s explore further with researchers in Brazil. Publishing in the Brazilian journal of orthopedics:

Highlights:

  • In this study researchers observed no significant reduction in body mass after knee replacement surgery, and 54% of the patients presented weight gain.
  • Patients who underwent Total Knee replacement did not obtain a significant reduction of Body Mass Index after the surgical procedure. (9)

A higher proportion of patients who gained weight as compared to those who lost weight

A June 2018 paper (10) was the first to evaluate change in Body Mass Index following partial knee replacement. It demonstrated a higher proportion of patients who gained weight as compared to those who lost weight. Post-operative body mass index changes did not appear to affect outcomes of partial knee replacement.”

This is also indirectly acknowledged in a December 2022 paper (11) which suggested obesity increased the risk of the need of a total knee replacement after unicompartimental or partial knee replacement. People continued to suffer from obesity following the partial knee replacement

The second knee replacement surgery in the obese patient

A February 2022 study (12) examined the postoperative outcomes of obesity and morbid obesity patients after revision total knee arthroplasty. An estimated 605,603 revision total knee arthroplasty surgeries were included in this analysis.

Morbidly obese and obese patients were at significantly higher risk for any complication than not obese patients. Patients with morbid obesity were associated with an increased risk of any, hematoma/seroma, wound dehiscence, postoperative infection, pulmonary embolism, and postoperative anemia complications and a lower risk of gastrointestinal complications when compared with not obese patients. Morbidly obese patients had a significantly longer length of stay than both obese and not obese patients, while no significant difference in length of stay was observed between obese and not obese patients.

If weight is a problem before knee replacement, weight will be a problem after knee replacement

We see many patients who struggle with weight. Being obese and overweight is an extraordinary difficult challenge to overcome, especially when you have limited mobility before knee replacement and limited mobility during rehabilitation. Add to the rehabilitation, which is already hard enough on its own, other complications that may arise. All this makes weight loss after knee replacement that much more of a challenge.

Medical engineers in China presented a study that is of concern to the overweight recipient of a total knee replacement. In this research in the Journal of healthcare engineering,(13) they noted that more weight meant a  higher stress on the knee replacement and this indicates an increased risk of femoral component migration and accelerated wear and tear. This means the possibility of a second surgery to fix the hardware and the bone.

Bariatric Surgery before knee replacement

A March 2019 study (14) examined the controversies surrounding the risks of subsequent total joint arthroplasty with and without previous bariatric surgery. In this paper, a total of 9 studies with 38,728 patients were included. Overall, medical comorbidities were higher in the bariatric surgery group compared with the control morbid obesity group before total joint arthroplasty. This paper revealed that bariatric surgery prior to total joint arthroplasty was associated with reduced short-term medical complications, length of stay, and operative time. However, bariatric surgery did not reduce the short-term risks for superficial wound infection or venous thromboembolism, and the long-term risks for dislocation, periprosthetic infection, periprosthetic fracture, and revision. Subgroup analysis identified a significant reduction in the risk of short-term periprosthetic infection in the bariatric surgery group after total knee arthroplasty, but not after total hip arthroplasty.

How do we explain this? Most patients say that they get knee replacement to reduce pain and increase function. Research says patients post-knee replacement likely not to improve activity levels.

The PARADOX:

An April 2018 study in the Journal of orthopaedic translation (15) made this assessment:

“It is well documented that patients with knee osteoarthritis suffer from reduced physical function and that function of the affected knee is improved after knee joint replacement. However, it remains uncertain whether patients with KOA are less physically active than healthy people and whether patients increase their level of physical activity after surgery to a level comparable with that of healthy people. The aim of this study was to examine whether patients with knee osteoarthritis are less physically active than healthy participants and whether patients who have undergone knee joint replacement show an increased activity and achieve the same level of physical activity as healthy participants 5 years postoperatively.”

The results: “Patients with knee osteoarthritis and knee joint replacement showed no significant reduction in number of daily step counts and transfers from sitting to standing position when compared with matched healthy controls. However, the number of short walking bouts was reduced in patients with knee osteoarthritis and by twice as much in patients with knee joint replacement. This indicates that knee osteoarthritis and treatment with knee joint replacement hardly affect health-related general activity but do affect specific physical activity behavior potentially indicative of knee osteoarthritis or post-knee joint replacement functional limitations.”

How can this be? Less activity after knee replacement?

So now we come upon this research published in the World journal of orthopedics. (16)

Here are the highlights:

  • The investigation of physical activity following total knee replacement found several studies that suggest physical activity for patients is at below pre-surgical levels.
  • Daily physical activity for patients following total knee replacement may fall short and does not meet recommended daily amounts for health maintenance and/or improvement.

Following up on this research is a December 2021 paper (17) which found patients after joint replacement tend to be less physically active; however, studies measuring objective physical activity and sedentary behavior in these patients provide conflicting results.  In total, the study assessed 1943 patients with a mean age of 64.9 years.

  • Three to six months after knee or hip arthroplasty, functional performance already exceeded pre-operative levels, yet physical activity levels from this time period remained the same. Although physical activity and functional performance seemed to fully restore and exceed the pre-operation levels at six to nine months, sedentary behavior did not. Moreover, physical activity remained lower compared to healthy individuals even longer than twelve months post-operation.

The take home message

Research tells us that there are no easy answers to losing weight and increasing physical activity, and that patients should not be lead to believe that knee replacement is the easy way to achieve these goals.

With over 27 years experience in regenerative medicine techniques and the treatment of thousands of patients, Dr. Darrow is considered a leading pioneer in the non-surgical treatment of degenerative Musculoskeletal Disorders and sports related injuries. He is one of the busiest Regenerative Medicine doctors in the world. Dr. Darrow has co-authored and continues to co-author leading edge medical research including research on bone marrow derived stem cells. He also comments and writes on research surrounding the treatment of chronic tendon injury, ankle and foot pain, elbow, hand and finger pain.

Marc Darrow MD JD

References

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