Morbid Obesity: Increased Risk of Failure After Aseptic Revision TKA.

BACKGROUND: Patients with obesity are known to have a higher risk of complications after primary TKA; however, there is a paucity of data regarding the effects of obesity with revision TKAs. QUESTIONS/PURPOSES: We asked the following questions : (1) Are patients with morbid obesity (BMI≥40 kg/m2) at greater risk for repeat revision, reoperation, or periprosthetic joint infection (PJI) compared with patients without obesity (BMI<30 kg/m2) after an index revision TKA performed for aseptic reasons? (2) Do patients who are not obese achieve higher Knee Society pain and function scores after revision TKA for aseptic reasons?
METHODS: We used a retrospective cohort study with 1:1 matching for sex, age (±3 years) and date of surgery (±1 year) to compare patients with morbid obesity with patients without obesity with respect to repeat revision, reoperation, and PJI. Using our institution's total joint registry, we identified 1291 index both-component (femoral and tibial) aseptic revision TKAs performed during a 15-year period (1992-2007). Of these, 120 revisions were in patients with morbid obesity (BMI≥40 kg/m2) and 624 were in patients with a BMI less than 30 kg/m2. We then considered only patients with a minimum 5-year followup, which was available for 77% of patients with morbid obesity and 76% of patients with a BMI less than 30 kg/m2 (p=0.84). All patients with morbid obesity who met criteria were included (morbid obesity group: n=93; average followup, 7.9 years) and compared with a matched cohort of patients with a BMI less than 30 kg/m2 (nonmorbid obesity group: n=93; average followup, 7.3 years). Medical records were reviewed to gather details regarding complications and clinical outcomes.
RESULTS: Overall, patients with morbid obesity had an increased risk of repeat revision (hazard ratio [HR], 3.8; 95% CI, 1.2-16.5; p<0.02), reoperation (HR, 2.9; 95% CI, 1.3-7.4; p<0.02), and PJI (HR, 6.4; 95% CI, 1.2-119.7; p<0.03). Implant survival rates were 96% (95% CI, 92%-100%) and 100% at 5 years, and 81% (95% CI, 70%-92%) and 93% (95% CI, 86%-100%) at 10 years for the patients with morbid obesity and those without morbid obesity, respectively (p=0.02). At 10 years, The Knee Society pain (90 [95% CI, 88-92] vs 76 [95% CI, 71-81]; p<0.01) and function (61 [95% CI, 53-69] vs 57 [95% CI, 42-52]; p<0.01) scores were higher in patients with a BMI less than 30 kg/m2 compared with patients with morbid obesity.
CONCLUSION: Morbid obesity is associated with increased rates of rerevision, reoperation, and PJI after aseptic revision TKA. As the time-sensitive nature of revision surgery may not always allow for patient or comorbidity optimization, these results emphasize the need for improving our care of patients with morbid obesity earlier on during the osteoarthritic process. Additional studies are needed to risk stratify patients in the morbidly obese population to better guide patient selection and effective optimization. LEVEL OF EVIDENCE: Level III, therapeutic study.