The two numbers that you’ll want to remember from the computer model-based cost-effectiveness study by McLawhorn et al. in the January 20, 2016 Journal of Bone & Joint Surgery are $13,910 and $100,000. The first number is an incremental cost-effectiveness ratio (ICER). Here, it’s the estimated added cost per quality-adjusted life year (QALY) for morbidly obese patients (BMI ≥35 kg/m2) with end-stage knee osteoarthritis who undergo bariatric surgery two years prior to total knee arthroplasty (TKA), compared with similar patients who undergo immediate TKA.
The $100,000 is the threshold “willingness to pay” (WTP) that the authors used in their evaluation. Willingness to pay reflects the amount society and healthcare payers such as Medicare and private insurers are willing to pay for a patient to accrue one year lived in perfect health.
Here’s another way to view these findings: Morbidly obese patients who undergo TKA are at increased risk for wound-healing problems, superficial and deep infections, early revision, and poor function. The authors estimated that if bariatric surgery reduces the TKA risks in these patients by at least 16%, on average, the combination of bariatric surgery followed by TKA is more cost-effective than immediate TKA alone.
Because the ICER was much less than the WTP in this model, the authors conclude that “bariatric surgery prior to total knee arthroplasty may be a cost-effective option for improving outcomes in motivated patients with a BMI of ≥35 kg/m2 with end-stage knee osteoarthritis.” However, they are quick to add that “decision modeling cannot simulate reality for every clinical situation.” While this rigorously developed model may provide a decision-making framework for surgeons and policymakers, the authors say, “this approach may be impractical for an individual patient…desiring immediate symptomatic relief from knee osteoarthritis.”