KS22: THE IMPACT OF OBESITY AND DIABETES ON PRIMARY TOTAL KNEE ARTHROPLASTY – A REVIEW OF 1214 CONSECUTIVE CASES

Abstract

The number of total knee arthroplasties (TKA) performed each year continues to rise and now outnumbers total hip arthroplasty (THA). Obesity is more predominant amongst TKA patients compared to THA. As such we conducted a review to determine if a relationship existed between obesity and acute prosthetic infection following primary TKA.

A review of 1214 consecutive primary TKA was performed from January 1998 to December 2005 with no exclusions. Pre-operative Body Mass Index (BMI), patient demographics, co-morbidities, and operative data were recorded. Patients were separated into obese (BMI => 30 kg/m2) and non-obese groups (BMI < 30 kg/m2) groups and compared for incidence of acute prosthetic infection in the first 12 months following surgery. The prevalence of obesity in patients who underwent primary (TKA) was 59% (n=715) and more females were obese (63%) than males (48%). The number of patients with multiple co-morbidities was similar for the 2 groups.

Median age was 70 yrs in obese patients and 74 yrs in non-obese patients, (p=< 0.001). Median operative time for obese patients was 105 minutes, compared to non-obese patients 100 minutes, (p=0.02).

The prosthetic infection rate was 1.5% (n=18). The rate was more than double in obese patients (2.0%) compared to non-obese patients, (0.8%), (p=0.16). Of the total, 206 patients had diabetes mellitus (DM) and the incidence of prosthetic infection in this group was 4.9%, compared to patients without DM, 0.8%, (p=< 0.001). However there were no cases of prosthetic infection in diabetic patients with a BMI < 30 kg/m2. Patients with combined DM and obesity had a significantly higher prosthetic infection rate 6.4%, compared to patients who only had one of these conditions or neither; DM only 0%, obesity only 0.7%, neither condition 0.9%, (p=< 0.001).

A post operative drain was used in 1109 patients. The prosthetic infection rate was 3 times higher in patients without a drain 3.8%, compared to patients with a drain, 1.3%. When analyzed together it was the obese group without a postoperative drain, who had the highest infection rate, 6%. This compared to: obese with a drain 1.7%, non-obese with a drain 0.7% and non-obese without a drain 1.8%, (p=0.027).

Obesity was a risk factor for the development of acute prosthetic infection in diabetic patients who underwent primary TKA at our institution. Using a post-operative drain reduced the risk of acute prosthetic infection in our obese patient group.