The purpose of the study by Wagner et al. was to evaluate the effect of body mass index (BMI) on the risk of complications, reoperations, and implant revision or removal following total knee arthroplasty. Historically, outcomes have been correlated with broad BMI categories. In this assessment, the authors examined obesity as a continuous variable across all BMI categories and sought to determine the presence of thresholds that distinguish those at increased risk for complications. With these results, patients and health-care providers may be better equipped to assess the risks and benefits of elective total knee arthroplasty. Furthermore, the results of this study can provide orthopaedic surgeons and their patients with more information to facilitate discussions on treatment strategies.
In this study, 22,289 primary total knee arthroplasties were analyzed from a large, single-institution total joint registry. Outcomes were associated across the range of all BMI categories depicted on smoothing spline curves, which were used to suggest the inclusion of thresholds. For every BMI unit over 30 kg/m2, there was a 3% increased risk of reoperation and a 5% increased risk of implant revision or removal (p < 0.001 for both). Additionally, for every BMI unit over 35 kg/m2, there was a 7% increased risk of superficial or deep infection and an 8% increased risk of deep periprosthetic joint infection (p < 0.001 for both). Patients’ risks of complications were determined using a BMI of 18 to 24.99 kg/m2 as a control. Compared with this cohort, patients with a BMI of 35 to 39.99 kg/m2 had an increased risk of reoperation and implant revision or removal, whereas patients with a BMI of ≥40 kg/m2 had increased risks in these as well as superficial or deep infection and deep periprosthetic joint infection (p < 0.001 for all).
This study reinforces previously published literature demonstrating the association between BMI and increased complications. However, the study’s increased value is how it may influence access to care and the societal costs of care for these patients. Prior to the introduction of the Affordable Care Act of 2010, the emphasis was on volume, but, more importantly, there was a rationalization that operating on these patients would lead to improved health and minimize lost work days or even disability costs1,2. This overshadowed surgical risk and potential increased health-care costs associated with complications3. Currently, there is a paradigm shift requiring physicians to move away from volume to quality. The current Centers for Medicare & Medicaid Services (CMS) bundled payment models such as the Bundled Payments for Care Improvement (BPCI) initiative or the Comprehensive Care for Joint Replacement (CJR) incentivize physicians to address the patient in a more comprehensive manner. The consequence is to consider risk and the impact on population health when considering surgical procedures. The result is that an arthroplasty may be postponed to permit achievement of weight loss. It is interesting to note that bariatric surgery as one method of weight loss prior to total knee arthroplasty has been suggested to increase the reoperation and revision rate4. Although bariatric surgery may reduce short-term total health-care costs, these are likely to be outweighed by the important long-term societal costs of increased disability and potentially increased labor costs. Bedair et al.2 conducted a Markov analysis to hypothetically calculate the cost to society (lost wages and medical expenses) of delaying total knee arthroplasty in 50-year-old patients with end-stage osteoarthritis. They found that although performing total knee arthroplasty was more expensive than nonoperative treatment in the first 3.5 years, the cost benefit over 30 years was $68,500 in favor of total knee arthroplasty. Mather et al.1 also used a Markov analysis in 60-year-old patients with severe osteoarthritis to examine quality-adjusted life-years (QALYs) in no-delay total knee arthroplasty and total knee arthroplasty after 2 years of nonoperative treatment. The no-delay total knee arthroplasty resulted in greater mean QALYs gained at a lower cost, and the authors proposed that total knee arthroplasty provided greater utility at a lower cost to society. Obviously, this does not consider the increased health-care costs of comorbidities such as obesity, but it suggests that increasing the availability of total knee arthroplasty may actually provide indirect savings to society.
As surgeons, we therefore face difficult decisions on whether or not to operate on obese patients. Obviously, the patient’s best interests are central to the process, but the wider societal implications should be considered. In some cases, younger, more motivated patients without other comorbidities may justify a total knee arthroplasty despite the inherent risks of obesity. Unfortunately, there is a paucity of literature on this topic. More studies similar to those previously described, but applied to patients with high BMI or other high-risk patient groups, are required.
This investigation did have limitations, as with all studies. This was a retrospective study from a singular large database, which may be subject to inaccuracies or misclassifications. Despite this, the authors should be commended for their efforts in attempting to correlate BMI with surgical and postoperative risks.
↵* Disclosure: The authors indicated that no external funding was received for any aspect of this work. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work and “yes” to indicate that the author had other relationships or activities that could be perceived to influence, or have the potential to influence, what was written in this work.
- Copyright © 2016 by The Journal of Bone and Joint Surgery, Incorporated