Body Mass Index and Outcomes of TKA: Insight for Counseling Patients (2017)

Commentary Obesity may be the most common comorbidity that I see as an orthopaedic surgeon specializing in hip and knee arthroplasty. The obesity epidemic has made surgeons acutely aware of the implications of this comorbidity, and there is a substantial amount of literature devoted to the risk of complications among this patient population. Data suggest that the risk of complications is higher for those with obesity, with the risk increasing1 for those with a body mass index (BMI) of >30 kg/m2, with an even greater risk for those with a BMI of >40 kg/m2, and higher still as a patient’s BMI surpasses 50 kg/m2. While it is almost universally agreed upon that the risks of procedures such as total knee arthroplasty are higher among obese patients, the benefits of these same procedures are less well understood for this patient population. One of our main charges as surgeons is to present patients with realistic expectations for recovery, as fulfillment of expectations strongly correlates with patient satisfaction2, and to help them understand the risks and benefits of any proposed intervention. The work by Collins et al. helps us in this regard by providing insight into the effect of obesity on functional recovery following total knee arthroplasty. Specifically, their study suggests that not only do obese patients have outcomes that are similar to those of patients of normal weight, but they actually had an accelerated recovery in the first 3 months postoperatively compared with patients of normal weight. Obese patients started worse off than their normal-weight counterparts, but quickly caught up, having similar functional outcomes at 3 months and throughout the first 2 years. While this is very practical information for us all to know, one of the weaknesses of this study was that the investigators grouped together all of the patients who had a BMI of ≥40 kg/m2, and this subset was only 9% of their sample. Many of us encounter a large number of patients with a BMI of >40 kg/m2, and this study unfortunately provides us with little insight into the super morbidly obese patient with a BMI of >50 kg/m2. In this subset of patients, we know that the risks are very high, but we are still left unsure about the benefits of total knee arthroplasty. One other factor that readers should be mindful of is that patients in this analysis came from randomized controlled trials (RCTs), performed for other reasons. While we all believe in the power of studies conducted using this methodology, my own experience suggests that patients who are willing to participate in RCTs are just a bit different from your average patient. While I have no real data to support my perception, I would suggest that patients who consent to randomized studies are those who are eager to please and possibly more optimistic, and hence, their outcomes may be, on average, better than those of the general population of patients, many of whom will not consent to such a study design. The authors are to be congratulated on tackling a difficult and important question. By helping us to better understand the functional outcomes of total knee arthroplasty in the obese patient, I know that I will be better able to counsel such patients on not only the risks but the benefits of total knee arthroplasty.