Optimization for Total Hip Arthroplasty and Total Knee Arthroplasty

Obesity

Obesity is most commonly defined according to the body mass index (BMI; kg/m ² ). Normal BMI is considered 20 to 25, 26 to 30 is overweight, and greater than 30 is considered obese. The World Health Organization further classifies obesity into Class I (BMI 30–34.9), Class II (35–39.9), and Class III or morbidly obese (>40). Further classification in the bariatric literature considers BMI >50 to be super obese. The prevalence of obesity in patients undergoing total joint arthroplasty (TJA) is increasing. A workgroup of the American Association of Hip and Knee Surgeons (AAHKS) in 2013 conducted a literature review and found that obese patients (BMI >30) who underwent TJA were at increased risk for perioperative complications. In patients undergoing TKA, they found that BMI >40 appeared to be the threshold above which the rates of infection and overall revision increase significantly. The BMI threshold for THA was less clear. They recommended for discussion of these risks with patients prior to surgery and consideration of weight reduction prior to TJA.

This recommendation has been controversial, with concern that BMI thresholds would reduce access to care for patients with obesity. A study published in 2020 followed 158 patients with moderate to severe osteoarthritis (OA) with BMI greater than 40. Of these patients, 51.3% did not return for a second visit and only 42.9% of those who returned for follow-up went on to a TJA. Patients with higher BMI were less likely to return for follow-up. Those patients who eventually underwent surgery had a lower BMI at their initial visit and were more likely to have lost weight than those who did not follow up. When compared with a matched cohort of arthroplasty patients with BMI less than 40, there was not a higher complication rate in the group of obese patients who went on to arthroplasty. Arthroplasty has been shown to be a cost-effective ^, treatment for obese and morbidly obese patients, and significant improvement in both patient-reported and surgeon-reported pain and function scores are seen after arthroplasty surgery. Restricting TJA has not been found to incentivize weight loss. In one study of a cohort of 289 patients with morbid obesity, only 58 went on to arthroplasty surgery and only 23 of those 58 could achieve a BMI of less than 40 at the time of arthroplasty. The average BMI reduction for the 58 patients who underwent TJA was from 45.3 to 42.3.

The risks of arthroplasty for obese patients is well established. What is less clear is the impact that weight reduction can have on those risks. Some obese patients are referred for bariatric surgery prior to TJA. One study in 2019 found that patients who had bariatric surgery prior to TJA had a decreased length of stay, lower rates of thromboembolic disease, and lower 30-day mortality. However, the rate of obesity in the post-bariatric surgery group was unclear. A meta-analysis in 2019 of 9 pooled studies published from 2011 to 2018 found a lower incidence of medical complications in the group that had bariatric surgery prior to TJA. There was a nonsignificant trend favoring bariatric surgery for the rates of thromboembolic disease and periprosthetic infection. The bariatric group members had a significantly better length of stay and shorter operative time for their TJA. There was no difference in long-term complication rate or revision rate between the two groups. Another study in 2018 found that patients undergoing THA at least 6 months after bariatric surgery were less likely to be readmitted within 90 days of their THA, but that there was no association between the time from bariatric surgery to THA or TKA and 90-day complication rates. An analysis of Medicare data for patients who underwent TJA after bariatric surgery found a higher rate of infection in THA patients and higher rate of revision in TKA patients. A study in 2019 found that 20 lbs of weight reduction prior to arthroplasty was associated with shorter length of stay and lower risk of discharge to a facility rather than home. The authors found no changes in operative time or physical function scores.

Recommendations regarding arthroplasty for obese patients require a shared decision-making approach. Making a BMI greater than 40 a hard contraindication to arthroplasty will deprive obese patients of health care services that can provide substantial benefits to pain, physical function, and quality of life. These benefits must be carefully considered against increased risks of delayed wound healing, deep periprosthetic infection, and other complications. Patients should be made fully aware of the implications of these complications when deciding how they would like to proceed.