Knee osteoarthritis outcomes in patients with severe obesity following bariatric surgery or total knee arthroplasty: the swift trial

Abstract

Purpose: High body mass index (BMI, kg/m2) is a modifiable risk factor that has been associated with the development and progression of osteoarthritis (OA) and knee pain. The gold standard for the treatment of end stage knee OA remains total knee arthroplasty (TKA), though patients with morbid obesity (BMI≥40 kg/m2) are increasingly required to lose weight prior to TKA due to increased surgical risk and a higher rate of complications. Conservative weight-loss approaches often fail to help patients lose the recommended weight prior to TKA, potentially making them ineligible for surgery. Recent studies have shown that patients who undergo bariatric surgery experience short-term improvements in knee functionality and decreased pain, either obviating the need for arthroplasty - or at least improving the success of subsequent total knee replacements. Here we present interim data from the trial entitled “Surgical Weight-loss to Improve Functional Status Trajectories following arthroplasty for painful knee osteoarthritis”. This current multi-center, prospective study compares pain and functional outcomes in patients receiving bariatric surgery prior to TKA versus obese patients who go straight to TKA. Methods: We recruited patients with BMI ≥40 kg/m2 and painful knee OA who met the indications for TKA from the bariatrics, orthopedics and rheumatology clinics at the four hospital centers. Patients with a BMI >35 kg/m2 were also recruited if they had a qualifying comorbid condition including obstructive sleep apnea, diabetes, hypertension or hyperlipidemia. Patients were assigned to the bariatric (BAR) or TKA (TKA) arms based on surgical choice (goal n=150 for each arm), with all bariatric patients having anatomy-altering sleeve gastrectomy or gastric bypass, and not laparoscopic gastric banding. At baseline and several time points after surgery (see figure), we documented height, weight, the Knee injury and Osteoarthritis Outcome Score (KOOS), visual analog pain (VAS) scales, and the Western Ontario and McMaster Universities Arthritis Index (WOMAC), and had patients perform functional assessments (Timed-Up and Go, 30-second Chair Stand and 40-meter fast paced walk test). We targeted minimum detectable change (MDC) in outcomes for the VAS for knee pain (33% reduction), Timed Up and Go (decrease by 2 seconds), 30-second Chair Stand (increase by 2 reps), 40-meter fast paced walk (increase by 0.16 m/s), WOMAC score (16% reduction), and the KOOS pain score (10-point improvement). Using a logistic regression to adjust for age and baseline BMI, we compared the percentage of patients in the two arms who achieve an MDC for the various outcomes. Results: For the current analysis, 20 bariatric surgery patients and 22 TKA patients completed their 6-month follow-up visits. Each subcohort had a similar sex distribution (15% vs 14%, p=0.999) but the bariatric group was younger (53 vs 61 years old, p=0.0045) and had a higher baseline BMI (47.1 vs 40.9, p=0.0009). Many bariatric patients achieved significant improvement in knee pain and function as evidenced by the MDC in the various tests, though the percent with MDC consistently tended to be higher in the TKA cohort. These MDC benchmarks included the 30-second Chair Stand (TKA 60% vs BAR 29%, p=0.085), KOOS pain score (TKA 89% vs BAR 65%, p=0.130), the Visual Analog Pain Scale (TKA 50% vs BAR 34%, p=0.390), Timed Up and Go (TKA 45% vs BAR 21%, p=0.205), the 40-meter fast paced walk (TKA 61% vs BAR 42%, p=0.319), and the WOMAC (TKA 81% vs BAR 59%, p=0.225). Many of the bariatric patients have had subsequent arthroplasty, but not enough time has passed to report levels of improvement. Conclusions: In morbidly obese patients who are eligible for TKA, bariatric surgery may result in modest improvements in knee pain and function when compared to TKA at 6 months post operatively. In addition to potentially altering the need for and timing of TKA, surgical weight loss may result in improved TKA outcomes. This study was supported by the Investigator Initiated Study Program of Ethicon-Endo Surgery, Inc. (Grant Number: 14-621).