OBESITY AND SURGICAL SITE INFECTION IN PRIMARY TOTAL KNEE ARTHROPLASTY

Abstract

Purpose: The aim of this study was to evaluate the rate of surgical site infection (SSI) in all patients undergoing a primary total knee arthroplasty (TKA) and to audit the outcomes for those who were obese.

Methods/Results: We retrospectively reviewed data for 839 primary TKAs done at a National Arthroplasty Centre over one year (April 2007 – March 2008). BMI data was available for 824 (98%) of the patients. SSI data had been collected prospectively by the Infection Control team for up to 30 days post-operatively and was available for all patients. Patients were grouped based on their BMI and the WHO classifications (WHO Technical Report Series 894).

31.2% of the patients were obese class I (BMI 30 – 35), 19.0% were obese class II (BMI 35 – 40) and 8.6% were obese class III (BMI > 40). There were 23 patients with SSIs, 22 having superficial SSI and only one patient with a deep SSI. The overall superficial SSI rate was 2.7%. The superficial SSI rates for each group were as follows: normal (BMI < 25) = 1.3%; overweight (BMI 25 –30) = 2.3%; obese class I = 1.6%; obese class II = 3.2%; obese class III = 8.5%. The Fisher’s Exact Test between all obese patients and those with BMI < 30 showed no significant difference in superficial SSI rates (p = 0.39) but did show a significant difference between superficial SSI rates in the obese class III patients and the rest of the cohort (p = 0.008).

Conclusions: Obese class III (BMI > 40) patients are at an increase risk of superficial SSI as compared to other patients undergoing primary TKA. However, obese class I and II patients do not appear to have an increased likelihood of superficial SSI as compared to patients who have BMI < 30.