OBESITY AND KNEE ARTHROPLASTY Anette Liljensøe MSc PhD-student, Inger Mechlenburg Associate Professor PhD, Aarhus University Hospital, Jens Ole Laursen MD Hospital Southern Jutland, Denmark Does Overweight and Obesity Influence the clinical Outcome and the Quality of life at five years following primary total knee Arthroplasty? INTRODUCTION In Denmark there is annually performed between 7-8000 primary total knee arthroplasty (TKA) and there seems in all countries, to be a rapid increase in the number of knee replacements. The most frequent indication for TKA is osteoarthritis (80%). Investigations have shown that obesity is a significant factor for the development of arthritis. On the contrary the associations between obesity and outcomes following TKA are ambiguous. The purpose of the study was to investigate whether there is an association between the preoperative BMI in TKA patients and the effect five years postoperative.   METHOD AND MATERIAL 197 patients, who had undergone primary TKA in 2005 and 2006, participated in a three-five years follow-up study. The outcome measures were self-rated health (SF-36), which consists of eight strands and two component scores, “physical component score” and “mental component score” and the Knee Society Rating System (KSS) “knee score” and “function score”, and improvement of the two KSS scores, from baseline to follow-up. RESULTS With Ordinal logistic regression (adjusted for gender, age, basic disease and surgical procedure) were found statistically significant association between BMI and nine of the fourteen outcome measures. For all outcome measures were found OR > 1. With a difference in BMI at 1 kg/m2 increases the risk of lower scores from a minimum of 2% OR 1.02 (0.97-1.07) p = 0.5 (“mental component score”) to maximum 14% OR 1.14 (1.08-1.21) p <0.001 (KSS function score). . Figure 2 Illustrates the estimated difference in self-rated health score (SF-36) 5 years postoperative in two patients with the same gender, age, primary disease and surgical procedure, and with a difference in BMI at 1, 5 and 10 kg/m2. With a difference in BMI at 5 kg/m2 increases the risk of lower scores from a minimum of 9% OR 1.09 (“mental components scores”) to a maximum of 96% OR 1.96 (KSS function scores). With a difference in BMI of 10 kg/m2 rises risk of worse score with minimum 19% OR 1.19 (“mental component score”) to a maximum of 284% OR 3.84 (KSS function score). Figure 3. Illustrates the estimated difference in KSS score 5 years postoperative in two patients with the same gender, age, primary disease and surgical procedure, and with a difference in BMI at 1, 5 and 10 kg/m2. CONCLUSION The association between BMI and the efficacy 5 years following primary TKA is clear. High BMI increases the risk of poor outcome following TKA. More than half of the outcome measures are statistically significant. All the results showed OR> 1 The estimates can be used as a predictor for the expected efficacy of the treatment for each patient. Nothing in the analysis suggests random finds. E-mail: ANETTE.LILJENSOE@KI.AU.DK