Obesity and Total Hip Replacement: A Poor Combination

Running can help ease the symptoms of hip and knee osteoarthritis.
Running can help ease the symptoms of hip and knee osteoarthritis.. Rick Gomez/Getty Images

The prevalence of obesity in the United States is nothing short of astounding and continues to be an increasing problem. Over one-third of all adults in the U.S. are obese. This poses a number of significant health concerns including heart disease, diabetes, high blood pressure, and development of osteoarthritis.

Excess weight places significant added stress on our joints. For this reason, obesity is a common condition that effects patients that present with osteoarthritis of the hip and knee.

When all conservative measures fail, total hip replacement has been shown to be an effective surgical option for end-stage osteoarthritis of the hip.

Obesity, Hip Arthritis, and Surgery

The problem that obese patients with hip arthritis are faced with is that while surgery may alleviate their symptoms, obese patients have a much higher rate of complications after this surgery. Surgeons, in turn, are faced with a difficult dilemma: should they refuse surgery to obese patients, and if so how big is too big for surgery?

A recent study from the Mayo Clinic shed some light on the issue by providing a large volume of data on the rates of complications based on patients BMI. The body mass index is a crude approximation of how overweight someone is, it is a proportion of height to weight.  BMI over 30 is considered obese.

Researchers at the Mayo Clinic compiled data on all total hip replacements performed between 1985 and 2012.

This totaled 21,000 surgeries in almost 18,000 patients. They looked at the most common complications of total hip replacements as they related to BMI. 

One of the key outcomes that this study looked at was reoperation, meaning a return to the operating room for any reason. The surgeon may need to put in a new component because the original one failed, or simply a washout procedure to treat a superficial infection that does not involve the metal components.

The researchers looked specifically at revision surgery (taking out old components and putting in new ones). Other common complications include dislocation, and infection (both superficial and deep). The trends that the researchers at the Mayo Clinic found were fascinating.

First, it appears that orthopaedic surgeons are operating on more and more obese patients. The frequency of patients with a BMI over 40, which is classified as morbidly obese, was 1.5 percent between 1985 and 1989. That number more than quadrupled to 6.2 percent in the group that underwent surgery between 2000 and 2012.

Increasing BMI was associated with increased risk of reoperation for any reason, revision of implants, early dislocation (within six months of surgery), as well as deep and superficial infections. What is astounding is that the risk of these complications increased in almost a linear fashion with increasing BMI. This means that with each additional pound after a certain optimal BMI, the risk of these complications increases.

The lowest risk was found with relatively low BMI. Risk of reoperation for any reason began to increase after a BMI of 32. Risk of implant revision increased after a BMI of 32 as well. Early dislocation had an increased risk after a BMI of 35, and the risk of infection began to increase after a BMI of only 25.

How Big Is Too Big?

The study does not provide an answer to the question of how big is too big for surgery? At what point does the increased risk of complications outweigh the benefits of a total hip replacement. Hopefully, this is a question that will be answered soon by follow-up studies. 

A number of hospitals have started to enforce weight cutoffs for total joint replacement. A common cut-off that is used is a BMI of 40. This seems harsh, but an argument can be made that it is in the best interest of the patients by decreasing the potential for complications.

This policy can, at times, place patients in a tough situation. Many feel that they can’t lose weight without a pain-free hip, and are unable to undergo surgery to relieve their pain before they lose weight. Dietary modification and nutritional optimization is a common recommendation for those patients.

What Does This Mean for Me?

To put these numbers in perspective, for a 5 foot 9-inch individual a BMI of 25 corresponds to a weight of 169 pounds, a BMI of 32 corresponds to a weight of 216 pounds, and a BMI of 35 corresponds to 236 pounds.

So what can we do with this information? First and foremost this should serve a big motivator to lose weight for people that are considering undergoing a total hip replacement. No one goes into surgery hoping for a complication and this study shows that the best way to avoid them is to shed the extra weight.

The emphasis on weight loss before joint replacement has been brought up before. A study out of Hospital for Special Surgery recently discussed in a previous article, investigated the cost-effectiveness of bariatric surgery before total knee replacements. The researchers found that bariatric surgery in this setting is indeed cost effective. 

This is a somewhat controversial approach and some orthopaedic surgeons remain concerned for the nutritional effects of bariatric surgery. This setting creates a scenario where some patients may become malnourished due to a significantly limited diet. Malnourishment may also result in worse outcomes after total joint replacement.

The Importance of Weight Loss

The data presented by the researchers out of the Mayo Clinic underscores the importance of weight loss before undergoing a total hip replacement. The trend in complication rates suggests that every pound counts. Ideally, this will lead to more patients seeking help from nutritionists and exercise programs to help them lose weight before being operated on. This will likely delay surgery and prolong the overall treatment course, instead of jumping to surgery right away before a patient is given the chance to lose weight, but overall the delay in treatment is worth the better outcomes. If losing weight can prevent a postoperative infection, then every patient should do their best to do so.  

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