October 2016

Role of bariatric surgery in patients with knee OA

10knee-shutterstock_57539299-copyWeight loss following bariatric surgery can have biomechanical and symptomatic benefits for obese patients with knee osteo­arthritis (OA). But it’s less certain whether that weight loss can also reduce the risk of obesity-related complications following total knee arthroplasty.

By Shalmali Pal

During a radio interview, the producer of an online biopic series on Pablo Escobar noted that actor Wagner Moura gained 40 pounds to better embody the Colombian drug lord. While the weight gain may not have put the normally slender, 5’11” Moura, on the obesity spectrum, he did have to maintain his new girth for two years of filming, which had biomechanical consequences.1,2

“[Moura as Escobar] had such a great gait that he found,” explained Narcos series producer Eric Newman in an NPR interview.3 “This walk that was almost like a waddle, and when he put the weight on, it made it even better.” Moura eventually lost the weight, crediting a vegan diet, and has described his time as a heavier person as “horrible.”2

On a small and temporary scale, Moura experienced some of the biomechanical effects associated with obesity (usually defined as a body mass index [BMI] of 30 kg/m2 or higher), which include elevated loads on the knees. Obese patients are 2.63 times more likely to develop knee osteoarthritis (OA) than their normal-weight counterparts, according to a 2010 meta-analysis.4

Many patients with obesity turn to invasive surgery to help them shed that potentially life-threatening weight. In 2015, an estimated 196,000 bariatric surgeries were performed in the US–17,000 cases more than just two years earlier, according to the American Society for Metabolic and Bariatric Surgery. More than half of the 2015 cases (nearly 54%) involved a gastric sleeve, and about 24% involved a Roux-en-Y gastric bypass.5

Postbariatric care too often falls short in emphasizing the importance of exercise, not only to boost and maintain weight loss but to potentially improve knee health.

Bariatric surgery can certainly help with weight loss, but does that weight loss render any positive changes in the knee mechanics and knee OA symptoms? And does bariatric surgery improve total knee arthroplasty (TKA) outcomes in obese patients with end-stage knee OA?

The answer to the first question is a fairly straightforward “yes.”

10knees-istock_87557991-copy“There’s about a one-to-four relationship—for every one pound you gain, you put about four pounds of stress on the knee. Now the reverse is that, for every pound you take off, you lose four pounds of stress on the knee,”6 explained Stephen P. Messier, PhD, director of the J.B. Snow Biomechanics Laboratory and of the Wake Forest University Runners’ Clinic at Wake Forest University in Winston-Salem, NC, who has coauthored numerous studies on the effects of weight loss interventions (diet and exercise) on knee OA symptoms.

The anticipated decrease in stress on the knee—and the decrease in knee pain that typically results—is a great motivator for weight loss, Messier said.

“I wish my [financial] investments had that kind of return,” he joked.

Determining if that weight loss will also pay off in regard to TKA, however, is not as simple. Research has shown that obese patients who undergo TKA can have higher complication rates compared with normal-weight patients for several reasons, including technical challenges during the procedure, comorbidities (such as type 2 dia­betes or vascular disease), or even changes in activity levels (see “TKA in obese patients: Weighing the risks vs the benefits,” February 2014, page 16). But studies of the timing of TKA relative to bariatric surgery have had mixed results, underscoring the complexity of the factors involved.

Loading and beyond

The hazards of excess weight seem to take place on two levels. First, there’s the mechanical component.

“Knee OA is a disease of the whole joint, so the bone, the cartilage, the musculature, the range of motion, and the neuro-inputs to the muscle,” explained Daniel Kenta White, PT, ScD, assistant professor in the Department of Physical Therapy at the University of Delaware in Newark, and a spokesperson for the American Physical Therapy Association. “Excessive weight can certainly contribute to those disease features.”

There’s also an inflammatory component, noted Michael H. Parks, MD, a physician at the Hospital for Special Surgery in New York, NY, and a spokesperson for the American Academy of Ortho­paedic Surgeons.

“Just as heart disease and obesity are linked by inflammation of the vessels…there’s an inflammation that leads to degradation of the cartilage and OA,” he said.

While obese patients are at a much higher risk for developing knee OA,7,8 not all of them do, Parks cautioned. For some, carrying the extra weight may impact the knee cartilage, but it isn’t necessarily detrimental to the point of disease development.

“If that were the case, then everyone who is obese would have OA, but we know that’s not true,” he said. “So there is something else going on there that leads to the development of knee OA.”

Paul DeVita, PhD, a professor in the Department of Kinesiology at East Carolina University in Greenville, NC, concurred.

“No one really understands what causes OA. For a while, biomechanics experts were blaming mechanical load, but now they are backing off a bit on that, and saying the inflammation part is pretty important,” DeVita said. “There’s an idea that if people are obese, they can condition their cartilage to withstand the weight because not every obese person gets OA.”

A 2013 review article9 concluded that “the precise metabolic pathways through which obesity contributes to joint structural damage are currently not known, although thought to involve aberrant adipokine expression with direct and downstream effects leading to the destruction and remodeling of joint tissue.”

Sometimes the problem isn’t so much the extra load on the knee because of the weight itself, but how load is being exerted, and how other knee components respond.

“OA is not just a wear-and-tear disease,” Messier said. “It’s more complicated than that, in the sense that the cartilage is not made to handle that excessive load. So that load is handled by the underlying subchondral bone, which has a lot of space and is a nice shock absorber.”

But when the load becomes excessive on the subchondral bone, and that bone grows thicker to carry that weight, it loses its shock-absorbing ability, he noted, which can lead to OA symptoms, such as pain, stiffness, swelling, loss of range of motion, and difficulty walking.10

Weight loss and knee mechanics

10knee-shutterstock_166817393-copyPatients with OA are most likely looking for a few things when they contemplate TKA: to alleviate the symptoms of OA, improve range of motion and activity level, and boost quality of life (QOL). Both weight loss intervention and TKA have been shown to help patients achieve those goals.

Messier and colleagues (including DeVita) have conducted several trials that have shown success with the diet-and-exercise route. In the Intensive Diet and Exercise for Arthritis (IDEA),11 they tested the hypothesis that intensive weight loss (with or without exercise) would reduce inflammation and joint loads sufficiently to alter disease progression in overweight and obese (BMI, 27-40.5 kg/m2) older adults (55 years and older) with pain and radiographic knee OA.

Almost 90% of the 450 participants completed the 18-month intervention, and the mean weight loss was 10.6 kg for the diet-plus-exercise group, 8.9 kg for the diet-only group, and 1.8 kg for the exercise-only group.

After 18 months, peak knee compressive forces were significantly lower than baseline in all groups, and were significantly lower in diet-only participants than exercise-only participants. Also, the diet-plus-exercise group had less pain, better function, and better QOL scores than the two single-modality groups.

Messier pointed out that, in effect, the diet-plus-exercise regimen decreased the load on the knees, but also strengthened the muscles around the knee. He also noted that in the exercise-only group, loads on the knees went up for the first six of 18 months, partly because participants developed a faster walking speed after weight loss and decreases in peak knee compressive forces.

“They were not accustomed to their new walking speed,” he explained. “So the stress went up initially, but then came back down from months six to eighteen. My feeling is that they were adapting to that new walking speed, so everything got stronger—their muscles got stronger so they started walking better. The exercise offered better [walking] mechanics.”

In a 2016 study, DeVita and colleagues determined the effects of weight loss on knee muscle and joint loads during walking in class III obese adults (BMI, 40-59 kg/m2).12 They enrolled patients who had undergone gastric bypass and used motion capture, force platform measures, and biomechanical modeling to study the impact of that weight loss while patients walked at a controlled velocity and at self-selected velocities. DeVita told LER none of the participants in the study had an official knee OA diagnosis, but “that doesn’t mean they didn’t have knee OA.”

10knee-shutterstock_597906-copyThey reported that weight loss equal to 34% of initial body weight led to a reduction in maximum knee compressive force by 824 N at the controlled velocity, representing a 2:1 reduction in knee force relative to weight loss.

But the unconstrained walking condition, which was more indicative of walking behavior than the standard velocity condition, led to a reduction in compressive knee force of just 392 N, resulting in an approximately 1:1 ratio of reduction in knee force relative to weight loss.

This may reflect gait changes associated with patients’ initial weight loss, including increases in stride length and knee flexion, which would increase load on the knee, DeVita said.

Similar gait changes, along with functional improvement, have also been reported following bariatric surgery.13-17 Although researchers have yet to specifically analyze knee loading in bariatric patients, they have observed decreases in knee adduction and flexion moments, which are associated with knee OA symptoms and progression.15,16

Time for TKA?

Given the risks associated with TKA in obese patients, it makes sense intuitively that the weight loss associated with bariatric surgery could help reduce those risks. Some studies have supported this hypothesis,18-20 but others have not.21-23

In a 2012 study Jasvinder Singh, MD, MPH, a professor of medicine at the University of Alabama at Birmingham, and colleagues compared outcomes—including total operative time, duration of hospital stay, 90-day complication rate, and transfusion rates—of 125 patients with knee OA who underwent bariatric surgery either before or after TKA.24

They found the total operative time differed significantly between patients who had undergone TKA before bariatric surgery (183 minutes), within two years of bariatric surgery (191 minutes), or more than two years after bariatric surgery (144 minutes). The incidence of 90-day complications also differed among the three groups (21%, 4%, and 16%, respectively) but those differences were not statistically significant, and in all three groups the com­plication rate was significantly higher than the overall institutional complication rate.

“Patients who undergo bariatric surgery and TKA experience increased rates of perioperative complications regardless of the temporal relationship between bariatric surgery and TKA,” the authors concluded.

A holistic approach

Parks agreed that there may not be such a thing as an “ideal” time for bariatric surgery patients to undergo TKA. He said that before discussing TKA with a postbariatric patient, he considers their overall health.

“Even if after bariatric surgery, they are still significantly overweight, I want to see that they are managing their weight,” Parks noted. “I tell my patients, ‘You need to show me that you are working on your weight. You don’t have to come in looking like a runway model for me to consider performing TKA.’ But they do have to show me that they are in charge of their weight and their health.”

After bariatric surgery, there is an adjustment in the baseline nutritional status,25 he noted, which can also be an issue. Despite high calorie consumption, obese patients are often deficient in important nutrients, such as antioxidants and fat-soluble vitamins. Bariatric surgery can result in additional nutritional deficiencies, or worsen pre-existing ones. Patients are often put on supplements to address these deficiencies.

“The body needs nutrients to heal,” Parks said. “You don’t want a patient who is nutritionally depleted to undergo [TKA] because that’s going to compromise their recovery.”

He added that he also needs to see that if comorbidites such as diabetes or heart disease are present, those are being medically managed.

Finally, he explained, the way a patient experiences OA can be another marker for whether TKA is appropriate.

“You have to look at OA as a waxing and waning disease—there are days [patients with knee OA] feel good and days they feel bad,” Parks said. “It’s the patients who don’t have the waning aspect anymore that I will consider for TKA, because it’s just painful all the time. With the TKA, we aim to ameliorate those symptoms and give them more good days.”

Messier pointed out that results from the IDEA trial provided “convincing evidence that a 10% weight loss, combined with moderate exercise, results in a 50% reduction in pain in older adults with chronic knee OA,” in turn improving function and QOL.11 Since patients who undergo bariatric surgery are likely to lose more than 10% of their body weight, it’s possible that weight loss could improve their knee OA symptoms enough to delay TKA. But Messier agreed with Parks that a healthful lifestyle must be adopted and maintained.

Messier said he considers TKA a “last resort,” for improving knee health in obese patients, but he acknowledged that when a person is in “excruciating pain and…can’t move, TKA can be effective.”

Given his group’s findings about gait adaptation after weight loss, DeVita suggested that performing TKA soon after bariatric surgery may not be the best route.

“I will hypothesize that it may be better to wait some period of time for these individuals to develop and adapt to their new locomotion biomechanics,” he said. “For example, in our [2016] study, we measured patients at six months and twelve months, but it’s not entirely clear how quickly these adaptations occur. My guess is that postbariatric patients need time to settle into their new health status [before considering TKA].”

Long-term goals

10knee-istock_23610827sil2-copyThe experts interviewed for this article expressed concern that postbariatric care often falls short in emphasizing the importance of exercise—not only to boost and maintain weight loss, but to potentially improve the health of the knees.

This could help explain the findings of a 2016 study of veterans who underwent bariatric surgery, in which patients with OA experienced less weight loss than veterans who did not have OA, as long as five years after the bariatric procedure.26

White expressed concern that bariatric surgery patients may be considered automatic candidates for TKA to manage their knee OA, without their having first made attempts to manage their weight with diet, and seeing if that leads to improvements in their knee OA symptoms. After bariatric surgery, the majority of patients with knee OA aren’t given a prescription for exercise, let alone physical therapy or other nonsurgical modalities, he said.

“After bariatric surgery, the focus is so much on diet, it’s like exercise is just an afterthought,” White said. “The problem with that is that clinicians are missing a ‘teachable moment’ with this patient to get them on a trajectory of long-term health. If you focus solely on diet, that isn’t going to lead to stronger muscles. I think there is a real need to address this gap in exercise prescription, and I think physical therapists can play a major role in calling attention to that in these patients.”

Ensuring that exercise is part of bariatric patients’ overall care continuum is key, he said.

“I like to keep it simple,” he said. “I think the more complex an exercise regimen gets, the less likely people are to follow through long term. So encourage bariatric surgery patients with knee OA to get themselves a [step monitor] and try to reach six thousand steps a day.”

But White acknowledged that nonsurgical methods of symptom management may not work in all patients, including those who have experienced weight loss after a bariatric procedure.

“From a PT perspective,” he said, “if somebody is losing the ability to do the things they enjoy and becoming inactive, it’s probably time to start considering TKA.”

Shalmali Pal is a freelance writer based in Tucson, AZ.

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  2. Narcos’ Actor Wagner Moura On Shedding The Weight Of Pablo Escobar. NPR Morning Edition.. http://www.npr.org/2016/09/02/492234846/narcos-actor-wagner-moura-on-shedding-the-weight-of-pablo-escobar. Aired September 2, 2016. Accessed October 4, 2016.
  3. Narcos’ Producer On The Drug War, Colombia And Escobar’s Son’s Grievances. NPR Fresh Air. http://www.npr.org/2016/09/22/494857817/narcos-producer-on-the-drug-war-colombia-and-escobars-sons-grievances. Aired September 22, 2016. Accessed October 4, 2016.
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  18. McLawhorn AS, Southren D, Wang YC, et al. Cost effectiveness of bariatric surgery prior to total knee arthroplasty in the morbidly obese: A computer model-based evaluation. J Bone Joint Surg Am 2016;98(2):e6.
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