Abstract
Introduction
Obesity has been associated with higher complication rates and poorer outcomes following joint replacement surgery. Body mass index (BMI) is a simple index of body composition and forms part of preoperative assessment. It does not take into account the proportion of lean mass and body fat and can give a false impression of body composition in healthy manual workers. A more accurate measure of body composition is available using non-invasive bioimpedance methods. This study aims to identify whether BMI provides an accurate measure of body fat composition in patients awaiting lower limb arthroplasty surgery.
Methods
Consecutive patients attending for pre-assessment clinic prior to total knee and hip replacement surgery were examined. All patients had their BMI calculated and underwent bioimpedance testing using a bedside Bodystat 1500 scanner (Bodystat, UK).
Results
83 patients (28 male) were included. Mean age was 68 years (range 16 to 92). All were awaiting lower limb arthroplasty surgery (39 primary total hip replacement, 4 revision total hip replacement, 38 primary total knee replacement, one unicompartmental knee replacement and one patellofemoral joint replacement). Mean BMI was 30.8 (range 20.8 to 48.9). Mean body fat percentage was 37.4% (range 17% to 53.9%). A weak correlation was seen between the calculated BMI and the measured body fat percentage (r=0.42, Pearson's correlation coefficient). Mean body fat percentage in obese patients (BMI > 30; mean BMI 34.9; n=42) was 42% while in the non-obese patients (BMI < 30; mean BMI 26.6; n=41) was 32.8%. This difference was significant (p<0.001).
Conclusion
In patients undergoing lower limb arthroplasty the calculated BMI has a weak correlation with the measured body fat percentage. Bedside, non-invasive bioimpedance analysis provides a quick and accurate measure of body composition and can be used during preoperative assessment. Future correlation of outcome against body composition and BMI will validate the use of body composition in these patients. Care should be taken when relying on BMI alone to assess body fat composition.
