October 2013

Total hip arthroplasty: Obesity and outcomes

10THA-iStock23505049-sTotal hip arthroplasty can significantly improve quality of life in obese patients, but high body mass index is also associated with higher rates of complications and re­admissions than in normal-weight patients. The emerging subgroup of super-obese patients poses additional challenges.

By Raghav Rajgopal, MD, and James L. Howard, MD, MSc, FRCSC

Total hip arthroplasty (THA) is a procedure known to significantly improve quality of life. However, complications may arise, resulting in significant morbidity. Risk factors that can increase complication rates following THA include obesity. As world obesity rates rise, demand for joint replacement is increasing, and lower extremity practitioners who are involved in accommodating this demand must subsequently manage the challenging complications.

Approximately 500 million people worldwide are obese.1 The World Health Organization classifies uses body mass index (BMI) as a measure of obesity. BMI is defined as a person’s weight in kilograms divided by the height in meters squared (kg/m2).2 Normal weight patients typically have BMIs between 18.5 and 24.9, overweight patients between 25 and 29.9, class I obese patients between 30 and 34.9, class II obese patients between 35 and 39.9, and class III patients greater than 40.2 More recently, patients with a BMI of greater than 50 have been given a designation of super-obese.3,4

Obesity is associated with adverse health outcomes, including hypertension, coronary artery disease, liver disease, type 2 diabetes, obstructive sleep apnea, and osteoarthritis.5 Morbidly obese (BMI > 40) patients require total hip replacements approximately 8.5 times more often than normal weight patients.6 Furthermore, morbidly obese patients typically need hip replacements approximately 10 years earlier than normal weight patients.7

Obesity and complications after THA

Some previous studies have not demonstrated an increased risk in complications among obese patients undergoing total joint arthroplasty compared with matched normal-weight counterparts.8-12 For example, McLaughlin and Lee in 2006 reviewed 209 THAs utilizing standardized components, and found no difference in outcome or complications at a mean 14.5 year follow up between obese (BMI > 30) and nonobese (BMI < 30) patients.8 Similarly, Andrew et al prospectively demonstrated no difference in Oxford hip score or complications at five-year follow up among nonobese, obese, and morbidly obese (BMI > 40) patients.9

Suleiman et al studied 1731 patients who had received total knee arthroplasty (TKA) or THA and found no significant differences between BMI groups with respect to cardiorespiratory, renal, or systemic complications.10 A large multicenter cohort study performed by Busato et al demonstrated no difference in pain relief among normal weight, overweight, and obese patients who underwent THA.11 Interestingly, however, the same study did find a direct relationship between increased weight and decreased postoperative ambulation.

Other studies have described significant complications secondary to obesity, notably infection, in patients undergoing total joint arthroplasty. A study by Dowsey et al demonstrated infection rates of 2.6% and 9.1% in obese (BMI 30-39.9) and morbidly obese (BMI > 40) patients undergoing THA, respectively, compared with rates of 1% and .9% in normal weight (BMI 18.5-24.9) and overweight (BMI 25-29.9) patients, respectively.13 This study also found a significantly longer operative time in morbidly obese patients compared to the other three groups. In a single-center study of more than 7000 patients, Jamsen et al found infection rates in patients receiving primary THA and TKA were .37% in normal weight patients and 4.66% in morbidly obese (BMI > 40) patients.14

A study by Chee et al pros­pec­tively matched morbidly obese (BMI > 40 or BMI > 35 with one serious comorbidity) patients with nonobese patients scheduled to undergo THA (55 procedures in each group)15 and found a 22% incidence of complications in the morbidly obese group compared with 5% in the nonobese group. Complications included deep infection, superficial infection, and dislocation requiring a total of five revisions in the morbidly obese group compared with zero revisions in the nonobese group. Five-year survival in the morbidly obese group was 90.9%, compared with 100% in the nonobese group.

A study by Lubbeke et al attempted to determine sex-related differences with respect to infection in obese (BMI > 30) patients undergoing THA.16 These authors found a complication incidence rate ratio of 16.1 in obese women compared with nonobese women. There was no significant difference found between obese and nonobese men. Obese patients also had higher risks of dislocation than nonobese patients. Similarly, Davis et al assessed 1617 patients undergoing THA, finding that, at five-year follow up, obese (BMI > 35) patients had a 4.42 times greater risk of dislocation than normal weight (BMI < 25) patients.17

Studies have also demonstrated that obese patients may have an increased incidence of postoperative venous thrombo­embolism.18,19 A study by Mantilla et al demonstrated a 1.5% increase in thromboembolic event for every five-point increase in BMI in obese patients.18 Similarly, a 15-study meta-analysis published by Haverkamp et al found higher rates of venous thromboembolism, dislocation, aseptic loosening, and infection in post-THA obese patients (BMI > 30) than in normal weight patients undergoing THA.

Performing THA in obese patients is technically more demanding than in normal weight patients. Challenges include patient positioning, surgical exposure, blood loss, component positioning, and, as a result, extended intraoperative time. Wang et al reported a significantly longer mean surgical time for obese patients undergoing THA compared with normal weight patients.20 Specifically, average surgical time was 97 minutes in class III obese patients compared with 74 minutes in normal weight patients. There was no difference with respect to anesthesia induction time. Similar findings have been reported by multiple authors.21,22

A 1999 study by Bowditch et al demonstrated significantly greater blood loss in obese patients compared to normal weight patients undergoing THA, with a mean difference of 380 ml.23 Unfortunately, rate of transfusion and perioperative complications were not included in this study and therefore it is difficult to make a clinical correlation to this stated blood loss.

Studies have produced conflicting data with respect to length of hospital stay in obese patients. A study by Dall et al did not find a significant difference in length of hospital stay between BMI groups in 2302 THA patients.24 More recently, however, studies examining complications in super-obese patients undergoing THA demonstrated a significantly longer average hospital stay compared with normal weight patients.3,25

Studies have also investigated the financial implications of obesity and THA. Kim performed a cost analysis of 229,001 THAs in 2006.26 Adjusting for sex, age, race, and healthcare payer, the cost of performing a THA in a morbidly obese patient was 9% higher than for a normal weight patient. However, other studies have suggested the cost of primary THA does not differ between obese and nonobese patients.27,28

Legislative bodies are reforming their healthcare policy as a consequence of increased complications seen in obese patients undergoing THA. For example, some regions in the UK are now mandating that prospective THA patients with BMIs higher than 40 provide evidence that weight loss has been attempted over a defined period of time.29-32 Obesity is not a contraindication to referral, however, and exceptions are made for patients with severely debilitating conditions.

In the US, hospitals and physicians may soon be ranked by the Centers for Medicare and Medicaid Services (CMS) based on arthroplasty-specific outcomes.33,34 These include the risk-standardized complication rate and the risk-standardized 30-day all-cause readmission rate. These outcomes ultimately will affect various institutional funding models as well as hospital ranking systems.

Because morbidly obese patients are associated with increased complications and readmission rates, physicians and administration may be inclined to refuse treatment to these individuals. Based on current evidence, we would recommend that these patients be classified alternately by the CMS to reduce healthcare bias.

Studies have attempted to determine the extent of postoperative weight loss after total joint replacement.35-37 Middleton and Boardman demonstrated that patients actually gain weight in the two years following total hip arthroplasty, irrespective of sex or preoperative BMI.35 In a study by Jain et al, patients who underwent THA had an absolute weight and BMI gain of 2.5% and 2.1%, respectively, at follow up of at least two years.36 Similarly, Aderinto et al found 75% of obese patients gain an average of 6.7 kg following THA while 60% of nonobese patients gain an average 4.2 kg at three-year follow up.37 These study findings suggest the argument that pain-alleviating THA surgery facilitates postoperative weight loss is debatable.

Previous studies have examined the utility of bariatric surgery prior to arthroplasty surgery. Specifically, Kulkarni et al examined the role of bariatric surgery prior to and following joint replacement surgery.38 This study found patients undergoing bariatric surgery prior to total joint arthroplasty had an infection rate 3.5 times lower and 30-day readmission rate seven times lower than patients who underwent arthoplasty prior to bariatric surgery.

The cost effectiveness of treating obesity with a form of bariatric surgery has also been demonstrated.39 However, due to the potential morbidity and mortality (incidence of .28%) associated with bariatric surgery, practitioners should inform patients of the risks and benefits before pursuing this course of treatment.39

Our group has published studies examining the effect of obesity on total hip arthroplasty. McCalden et al retrospectively reviewed 3290 THA patients with respect to outcome.40 Patients were divided into normal weight, overweight, obese, and morbidly obese (BMI > 40). The Harris Hip Score (HHS), Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index, and Short-Form 12 (SF-12) mental and physical scores were used. There was no significant difference among groups with respect to the HHS, WOMAC, or SF-12s change scores.

This study suggested that morbidly obese patients experience benefits after THA that are similar to patients in other weight groups and should not be prevented from obtaining access to THA due to weight alone. These findings have been supported by other studies. For example, Michalka et al demonstrated no significant difference in Oxford score or SF-12 score between nonobese and morbidly obese (BMI > 35) patients.41 However, morbidly obese patients did have a significantly worse six-minute walk test score at six weeks postoperatively compared with nonobese patients. Unfortunately, preoperative baseline six-minute walk tests were unavailable in this study.

Recently, our group published a study on outcomes and complications after THA in the super-obese population (BMI > 50).3 This study demonstrated a significant morbidity associated with super-obese patients undergoing total hip arthroplasty. It also found super-obese patients have a major complication rate seven times higher than normal weight patients as well as a longer average hospital stay. Complications included deep infection, dislocation, periprosthetic fracture, and pulmonary embolus. Despite these complications, there was no significant difference among groups with respect to HHS or WOMAC scores at a mean follow-up of 4.2 years.

Few studies have examined THA in super-obese populations. However, a study by Schwarzkopf et al did investigate complication rates in patients with BMIs higher than 45 undergoing both THA and TKA.25 These patients had significantly higher perioperative complication rates, length of hospital stay, and readmission rates compared with normal weight patients. These variables increased in a linear fashion with every five-unit increase in BMI over 45.

Conclusions

Studies have shown that THA in obese patients greatly improves their quality of life. However, multiple studies have demonstrated increased complication and readmission rates in this patient population. As obesity rates continue to rise, careful planning will be necessary to accommodate the need for primary THA and the ensuing complications. Conflicting data exist with respect to the financial burden of primary THA in obese patients. However, revision surgery for infection and dislocation in obese patients will certainly contribute to increased healthcare costs.

We are also seeing the emergence of super-obese populations who have demonstrated significant morbidity following THA. It is evident that practitioners must employ risk stratification among patient subgroups on the basis of obesity. In other words, the risks quoted to a class I obese patient undergoing THA cannot be extrapolated for a super-obese patient. Although we would not advocate restricting access to care to these patients, we would strongly encourage a multidisciplinary approach to both preoperative and postoperative weight loss. We would also recommend an in-depth preoperative discussion about the risks of surgery and implications of potential complications.

Raghav Rajgopal, MD, is a PGY4 orthopedic resident at Western University in London, Ontario. James Howard, MSc, FRCSC, is assistant professor of orthopaedic surgery and director of the Orthopaedic Residency Program at Western University.

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