To evaluate the pre- and post-operative knee function after total knee arthroplasty among the non-obese patients, overweight patients, obesity patients and morbidly obesity patients.

PubMed, Dutch Excerpta Medica Database (EMBASE), China National Knowledge Infrastructure (CNKI) and Wan Fang database were systematically searched for studies on the function influenced by body mass index after total knee arthroplasty from January 1989 to December 2017. Inclusion criteria: retrospective or prospective longitudinal studies, total knee arthroplasty (TKA) patients grouped according to the World Health Organization’s body mass index (BMI), knee function assessment using the New York Hospital for Special Surgery score (HSS) or American Knee Society Score (KSS), effect indicators were sample size, mean and standard deviation. Exclusion criteria: duplication literatures or similar data, BMI groups not falling within the above group standards, and effect indicators were not sample size, mean or standard deviation. The quality of studies was critically evaluated and the data were extracted by two reviewers independently. Meta-analysis was conducted by Stata 12.0.

Thirteen studies were finally identified. Pooling analysis noted that knee function scores among patients in the non-obese group, the overweight group, the obesity group and the morbidly obesity group were significantly higher post-operatively than the pre-operative ones (P<0.01). The obese patients had a lower score in preoperative knee function than the non-obese patients [SMD =0.32, 95%CI (0.07, 0.58), P=0.012], and had a lower score in postoperative knee function than the overweight patients [SMD =0.18, 95%CI (0.04, 0.32), P=0.013].

The knee function increases in all the patients after total knee arthroplasty, but BMI greater than or equal to 27 and less than 30 may show negative effect on the preoperative and postoperative knee function.