Substantial Weight Loss May Not Improve Early Outcomes of Total Knee Arthroplasty in the Morbidly Obese.

Background: Body mass index (BMI) cutoffs for morbidly obese patients otherwise indicated for total knee arthroplasty (TKA) have been widely proposed and implemented, though they remain controversial. Previous studies suggested that a 5% reduction in BMI may be associated with fewer postoperative complications. Thus, the purpose of this study was to determine whether a substantial reduction in preoperative BMI in morbidly obese patients improved 90-day outcomes after TKA.

Methods: There were 1,270 patients who underwent primary TKA at a single institution and had a BMI > 40 recorded during the year prior to surgery. Patients were stratified into three cohorts based on whether their BMI within 3 months to 1 year preoperatively had decreased by ≥ 5% (228 patients [18%]); increased by ≥ 5% (310 [24%]); or remained unchanged (within 5%) (732 [58%]) on the day of surgery. There were several baseline differences between the cohorts with respect to medical comorbidities. The rate of 90-day complications and six-week patient-reported outcome measures were compared via univariate and multivariable analyses.

Results: On univariate analysis, individual and total complication rates were similar between the cohorts (P > .05). On multivariable logistic regression, the risk of complications was similar in patients who had decreased versus unchanged BMI (OR [odds ratio] 1.0; P = .898). However, there was a higher risk of complications in the increased BMI cohort compared to those patients who had an unchanged BMI (OR 1.5; P = .039). The six-week patient-reported outcome measures were similar between the cohorts.

Conclusions: Patients who have a BMI > 40 who achieved a meaningful reduction in BMI prior to TKA did not have a lower rate of 90-day complications than those whose BMI remained unchanged. Furthermore, considering that nearly one in four patients experienced a significant increase in BMI while awaiting surgery, postponing TKA may actually be detrimental.