The influence of body mass index on the outcomes of primary total knee arthroplasty.

PURPOSE: The body mass index (BMI) is widely recognized as a prognostic factor in multiple operations; however, the relationship between the BMI and outcomes following total knee arthroplasty (TKA) is extensively debated. We aimed to evaluate the effect of the BMI at different cutoff values on the outcomes following primary TKA.
METHODS: Electronic databases (PubMed/Medline, CENTRAL, Embase and Web of Science) were systematically searched for studies investigating the association between the BMI and outcomes following primary TKA. Two investigators independently reviewed studies for eligibility, assessed the study quality using the Newcastle-Ottawa Scale and extracted the data. A meta-analysis was performed using Review Manager software.
RESULTS: Twenty-eight articles including a total of 20,988 TKAs were identified. The postoperative Knee Society Score appeared to trend lower in obese (BMI ≥ 30 kg/m(2)) patients than in non-obese (BMI < 30 kg/m(2)) patients. The meta-analysis showed that revision with follow-up ≥5 years, any infection, superficial infection and deep vein thrombosis occurred statistically more frequently in obese patients, whereas a deep infection occurred statistically more frequently in morbidly obese (BMI ≥ 40 kg/m(2)) patients than in non-obese patients. No differences in aseptic loosening with follow-up ≥5 years, pulmonary embolism and perioperative mortality rates were found between obese and non-obese patients.
CONCLUSIONS: Patients with a BMI ≥ 30 kg/m(2) are at a higher risk of lower functional scores and developing complications following primary TKA. It appears reasonable to encourage obese patients to lose weight before selective TKA. LEVEL OF EVIDENCE: Prognostic study, Level III.