The outcomes of total knee arthroplasty in morbidly obese patients: a systematic review of the literature

IntroductionThe increasing prevalence of obesity has led to an increase in total knee arthroplasties (TKAs) being undertaken in patients with a higher body mass index (BMI). TKA in morbidly obese patients can be technically challenging due to numerousanatomical factors and patient co-morbidities. The long-term outcomes in this patient group are unclear. This systematic review aims to comparethe long-term revision rates, functional outcomes and complication rates of TKAs in morbidly obese versus non-obese patients.MethodsA search of PubMed, EMBASE and PubMed Central was conducted to identify studies that reported revision rates in a cohort of morbidly obese patients (BMI40kg/m(2)) that underwent primary TKA, compared to non-obese patients (BMI30kg/m(2)). Secondary outcomes included Knee Society Objective Scores (KSOS), Knee Society Functional Scores (KSFS), and complication rates between the two groups. The difference in revision rates was assessed using the Chi-squared test. The Wilcoxon signed-rank test was used to compare pre-operative and post-operative functional scores for each group. KSOS and KSFS for morbidly obese and non-obese patients were compared using the Mann-Whitney test. Statistical significance was defined as p0.05.ResultsNine studies were included in this review. There were 624 TKAs in morbidly obese patients and 9,449 TKAs in non-obese patients, average BMI values were 45.0kg/m(2) (range 40-66kg/m(2)) and 26.5kg/m(2) (range 11-30kg/m(2)) respectively. The average follow-up time was 4.8years (range 0.5-14.1) and 5.2years (range 0.5-13.2) respectively, with a revision rate of 7% and 2% (p<0.001) respectively. All functional scores improved after TKA (p<0.001). Pre- and post-operative KSOS and KSFS were poorer in morbidly obese patients, however, mean improvement in KSOS was the same in both groups and comparable between groups for KSFS (p=0.78). Overall complication rates, including infection, were higher in morbidly obese patients.ConclusionsThis review suggests an increased mid to long-termrevision rate following primary TKA in morbidly obese patients, however, these patients have a functional recoverywhich is comparable to non-obese individuals. There is alsoan increased risk of perioperative complications, such assuperficial wound infection. Morbidly obese patients should be fully informed of these issues prior to undergoing primaryTKA.