Effect of body mass index on functional outcome in primary total knee arthroplasty——a single institution analysis of 2180 primary total knee replacements

AIM To evaluate the effect of body mass index(BMI) on short-term functional outcome and complications in primary total knee arthroplasty. METHODS All patients undergoing primary total knee arthroplasty at a single institution between 2007 and 2013 were identified from a prospective arthroplasty database. 2180 patients were included in the study. Age, gender, BMI, pre- and post-operative functional scores [Western Ontario and Mc Master University Arthritis Index(WOMAC) and SF-36], complications and revision rate were recorded. Patients were grouped according to the WHO BMI classification. The functional outcome of the normal weight cohort(BMI 25) was compared to the overweight and obese(BMI ≥ 25) cohort. A separate sub-group analysis was performed comparing all five WHO BMI groups; Normal weight, overweight, class 1 obese, class 2 obese and class 3 obese.RESULTS With a mean age of 67.89(28-92), 2180 primary total knee replacements were included. 64.36%(1403) were female. The mean BMI was 31.86(18-52). Ninty-three percent of patients were either overweight or obese. Mean follow-up 19.33 mo(6-60 mo). There was no significant difference in pre or post-operative WOMAC score in the normal weight(BMI 25) cohort compared to patients with a BMI ≥ 25(P 0.05). Sub-group analysis revealed significantly worse WOMAC scores in class 2 obese 30.80 compared to overweight 25.80(P 0.01) and class 1 obese 25.50(P 0.01). Similarly, there were significantly worse SF-36 scores in class 2 obese 58.16 compared to overweight 63.93(P 0.01) and class 1 obese 63.65(P 0.01) There were 32(1.47%) superficial infections, 9(0.41%) deep infections and 19(0.87%) revisions overall with no complications or revisions in the normal weight cohort(BMI 25).CONCLUSION Post-operative functional outcome was not influenced by BMI comparing normal weight individuals with BMI 25. Patients should not be denied total knee arthroplasty based solely on weight alone.

Effect of body mass index on functional outcome in primary total knee arthroplasty - a single institution analysis of 2180 primary total knee replacements