What about the Joints? : Weight-inclusive Care for Osteoarthritis

By Louise D. Metz MD

“What about the joints? Isn’t knee arthritis caused by higher weights and doesn’t it improve with weight loss?” 

This is one of the most common questions that I hear when discussing the evidence behind weight-inclusive medical care with healthcare providers, patients, and friends. Many people have a difficult time thinking about joint pain and arthritis outside of the standard weight-focused approach.

How is knee arthritis approached within the typical weight-centric paradigm?

A typical doctor’s visit for a person living in a larger body with knee arthritis often focuses on weight loss as the primary treatment for their condition. A person in a smaller body may have a visit that focuses on treatments such as physical therapy, medications, injections, and surgical referral instead of weight. The very same condition is often managed differently depending on a person’s body size.

 

Is it really the mechanical load on the joints that causes osteoarthritis?

The common thinking about osteoarthritis (OA) is that the mechanical load on the knees due to body size causes arthritis. While mechanical load may be part of the physiology of this condition, there are multiple other factors that contribute to the development of arthritis.

According to the CDC, 16% of people with a “normal” BMI report being diagnosed with arthritis compared with 23%-31% of people with higher BMIs (1). If arthritis was solely caused by the mechanical load on the joints, we might expect that most in a larger body and few in a smaller body would develop arthritis, but this is not the case. There are clearly other factors at play in the onset of OA, including a strong genetic component. Data from twin studies show that genetics account for 40% of the risk for osteoarthritis of the knee (2,3).

We can see from the above statistics, however, that there is a higher incidence of OA in people living in larger bodies compared with smaller bodies. There is an assumption about this condition and others that since it is associated with body size, it must be the body size itself that is causing the condition. This may instead be another case of correlation rather than causation.

Evidence that challenges the assumptions about body size and arthritis: In addition to arthritis of the knees and hips, people in larger bodies are more likely to have arthritis of the hands, which are not weight-bearing joints. Also, if mechanical load was the main cause of osteoarthritis, then we would expect runners to have a higher rate of arthritis, as running puts a force on the knee that is 4-8 times one’s body weight. Surprisingly, studies show that runners do not actually have a higher incidence of OA (4).

If not just mechanical causes, what else may be causing OA?

Inflammatory markers can cause damage to the cartilage, synovium, and bone of the joints that can lead to arthritic changes. Metabolic conditions, including insulin resistance, high blood pressure, high cholesterol, and diabetes, have also been linked to OA. Inflammatory and metabolic factors can be correlated with larger body size, and may be causal mediators between body size and arthritis (4). Though individuals can be genetically predisposed to have inflammatory and metabolic conditions, we also know that internalized weight stigma is independently associated with both inflammation and metabolic conditions (5). It’s important to keep in mind that these factors occur and may contribute to the development of arthritis in people in all size bodies.

Though the research points to genetic, inflammatory, and metabolic causes in addition to mechanical causes for this condition across the weight spectrum, we really don’t have all of the answers about the pathophysiology of osteoarthritis. But let’s suppose for a minute that body weight itself is a significant causal factor of arthritis via mechanical load. Would this change the way we should approach this condition?

Our weight-centric paradigm would suggest that an individual in a larger body is to blame for their arthritis because they should be able to control their weight. In reality, there is a normal diversity of body sizes primarily determined by genetics along with some environmental factors. Our weight is not actually within our control. Though there are some short-term studies showing improvement in symptoms of OA with weight loss interventions (6), we have extensive literature demonstrating that weight loss interventions are ineffective in the long-term and harmful for many health outcomes (7). In addition, it may not be the weight loss itself that leads to the short-term improvements, but could be the behavioral changes, such as physical activity, included in these studies that improves OA symptoms. Even if one’s larger body predisposes them to have arthritis, asking them to shrink their body to treat this condition is not an effective or safe solution. Instead, we can utilize evidence-based treatments for OA irrespective of one’s body size.

What are some evidence-based treatments for OA for all body sizes? 

1. Movement: Physical therapy and low-impact movement (walking, cycling, aquatic exercise, Tai chi) can strengthen the muscles around the joint, and help with pain and function (8).
2. Bracing: Unloader braces are helpful for reducing pain and improving joint function (9).
3. Anti-inflammatory medications: NSAIDs, both oral pills and topical gels, are effective for reducing pain (10,11).
4. Other medications:
   • Topical capsaicin: Made from hot chili peppers and acts on the sensory pain neurons (12)
   • Duloxetine: Works by short-circuiting the central pain pathway (13)
   • Acetaminophen: Provides limited benefit in the short-term (14).
5. Injections: Limited evidence for steroid, hyaluronic acid, and platelet-rich plasma injections (15, 16, 17)
6. Surgery: Total joint replacement when indicated for severe osteoarthritis and persistent symptoms despite non-surgical treatments (18).

That leads us to something that I have been hearing way too often from many of my patients and from many colleagues about their patients:

“The orthopedist said that I have to lose weight before I can have a knee replacement” 

Many people with severe osteoarthritis and associated pain and functional limitations are being denied knee replacement surgery by orthopedists due to their BMI being above a certain threshold. They have instead been advised to lose weight in order to have a knee replacement. Some are even being advised to have bariatric surgery before knee surgery. Patients of mine have traveled over 500 miles to see a surgeon who is willing to operate on them.

Does being in a larger body increase the risk of complications from joint replacement surgery? 

The research demonstrates that postoperative infections are more likely to occur after knee replacement in people in larger bodies. However, the typical infection risk after surgery is low. One meta-analysis found an absolute infection risk of 1% of people with a BMI under 30 and 2% of people with a BMI over 30 (19).  Another study found an increase in infection risk for people with a BMI of over 40, but the absolute risk was very low: 0.5% with “normal” BMI and 1.7% with BMI>40 (20). The research findings are not all in agreement, however, as one study found that people with a higher BMI had no increase in complications and had shorter hospital stays (21). Some literature also shows higher risks of dislocation and revision rates related to body size, though the studies are also inconsistent.

Why might the complication rates be higher? 

Theories in the literature for why the infection rate is higher for people in larger bodies after joint replacement surgery include: lower immune responses, reduced subcutaneous tissue oxygenation, longer operative times, and the technical aspects of the surgeries among people in larger bodies (22, 23). Some of the joint replacement implant devices are cautioned or contraindicated for larger bodies. This means that they are not designed to accommodate the mechanical load of all bodies, thereby increasing failure rates (24).

Do weight loss interventions before joint replacement surgery improve surgical outcomes? 

Though weight loss is constantly being recommended to people in larger bodies before they can undergo joint replacement, the literature does not support this recommendation. According to a meta-analysis, one study found that a weight loss intervention prior to joint replacement surgery was associated with a higher likelihood of deep joint infections, and others found no difference in superficial infections (25).

Why would bariatric surgery, which is a major surgery carrying many significant complication risks, be recommended prior to a less risky joint replacement surgery? This advice is also not supported by research and may cause harm. A review of studies evaluating bariatric surgery prior to joint replacement surgery found that there was no difference in post-operative complications (infections, blood clots, or revision surgeries) between those who had bariatric surgery prior to joint surgery and those who did not (26).  Another study found that having bariatric surgery before joint surgery increased the likelihood of complications (27).

Weight loss interventions through dieting or surgery cause malnutrition, which we know is linked to surgical complications. Malnourished individuals in one research study had a much higher complication rate (12%) after knee replacement compared with those who were not malnourished (2.9%). Of note, 42.9% of the malnourished patients in this study were classified as “obese” (28). Malnutrition carries serious risks and can occur in all body sizes.

What is an ethical, evidence-based approach to body size and joint replacement surgery? 

Instead of excluding many people based on a BMI cutoff from joint replacement surgeries that may significantly improve their quality of life, let’s consider this question from a weight-inclusive and individualized perspective. Though the complication rates of joint replacement surgeries may be higher in the setting of larger body sizes, weight loss interventions before a joint surgery do not change these rates and can be harmful. Compared with people in smaller bodies, research shows that people in larger bodies have the same or better outcomes in terms of improvement in joint pain and joint function after knee replacement. Limiting access to this effective treatment is affecting the lives of many.

Rather than placing blame on people’s bodies for the surgical risk, we could consider whether changes in the surgical intervention might decrease complication rates. Is it possible to develop surgical equipment and surgical techniques to accommodate all body sizes that might decrease operative time, infection risk, and mechanical failure rate? Could an individual be given the option to make an informed decision to have the surgery after considering the potential risks and benefits? Can we shift the focus from surgeons’ complication rates to what is ethical and indicated for each individual’s health and wellness?

Medical and surgical care should be designed to accommodate and benefit all bodies rather than bodies being asked to conform to a certain size for medical treatment. Weight-inclusive care for osteoarthritis and all other health conditions is essential in providing compassionate, ethical, and evidence-based care.

References:

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