The Effects of Body Mass Index on Pain Control With Liposomal Bupivacaine in Hip and Knee Arthroplasty.

Background: There is evidence to suggest that liposomal bupivacaine (LB) is an effective component of a multimodal pain regimen for total joint arthroplasty (TJA). Obesity has been associated with chronic pain following TJA. This study assessed whether early postoperative pain is affected by body mass index (BMI), and whether the standard LB dose has similar effects on obese vs nonobese patients.

Methods: A retrospective analysis of 2629 primary TJA over a 12-month period was conducted, with LB used in half of this group. Patients were further classified as nonobese (BMI < 30) or obese (BMI ≥ 30). Pain scores and narcotic use were recorded. Independent-sample t-tests were used for continuous variables and chi-squared analyses for categorical variables. A multivariate regression analysis was performed.

Results: Significantly less narcotic was required on postoperative days (POD) 0 and 1 in patients receiving LB compared to those who did not in both obese and nonobese patient groups. On POD 2, obese and nonobese patients had an increase in narcotic requirement, which was significant in obese patients. A regression analysis found that on POD 0 and POD 1, lack of LB use, obesity, and younger age were independently associated with increased narcotic use.

Conclusion: While narcotic requirement of obese and nonobese patients decreased on POD 0 and POD 1 with initiation of LB at our institution, all patients demonstrated increased narcotic requirement on POD 2 which was statistically and clinically significant in obese patients. Further studies are needed to determine the optimal pain regimen in the growing obese population undergoing TJA.