OBESITY AND SURGICAL SITE INFECTION IN PRIMARY TOTAL KNEE ARTHROPLASTY

Abstract

Introduction: The prevalence of obesity continues to increase in the United Kingdom leading to a growing burden on the healthcare system. A significant percentage of patients who undergo total knee arthroplasty are obese. A review of the literature reveals that obese patients are at an increased risk of complications including wound problems. The aim of this study was to evaluate the rate of surgical site infection in all patients undergoing a primary total knee arthroplasty and to audit the outcomes for those who were obese.

Methods: We retrospectively reviewed data for 839 primary total knee arthroplasties done at a National Arthroplasty Centre over one year (April 2007 – March 2008). BMI data was available for 824 (98%) of the patients and was obtained from the patients’ clinical records. Surgical site infection data had been collected prospectively by the Infection Control team for inpatient stays and up to 30 days post-operatively. Infection data was available for all patients. Patients were grouped based on their BMI and the WHO classifications (WHO Technical Report Series 894). The infection rates were analysed to establish if there were poorer outcomes for obese patients.

Results: Based on the WHO classifications, 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 infections, 22 having superficial infection and only one patient with a deep infection. The overall superficial surgical site infection rate was 2.7%. The superficial surgical site infection rate for the normal weight group was 1.3%, for the overweight group was 2.3%, obese class I was 1.6%, obese class II was 3.2% but for obese class III was 8.5%. The Fisher’s Exact Test between all obese patients and those with BMI < 30 showed no statistically significant difference in superficial surgical site infection rates (p = 0.39). However, it did show a statistically significant difference between superficial surgical site infection rates in the obese class III patients and the rest of the cohort, p = 0.008.

Conclusion: Obese class III (BMI > 40) patients are at an increase risk of superficial surgical site infection as compared to other patients undergoing primary total knee arthroplasty. However, obese class I and II patients do not appear to have an increased likelihood of superficial surgical site infection as compared to patients who have BMI < 30. It is therefore important that surgeons are aware of the higher risk of surgical site infection in obese class III patients and recommended that patients in this category should be informed of this by their surgeon when considering primary total knee arthroplasty.