Abstract
Obesity is considered a risk factor to a successful outcome in total knee arthroplasty. The prevalence of obesity is causing concern as risks associated with obesity are well documented and the incidence of obesity is increasing in the Australian population. Previous studies have not reached a consensus on the relationship of BMI and short term outcomes of total knee arthroplasty.
The aims of this study were to evaluate the relationship between BMI and the degree of flexion achieved at discharge and to determine the influence of BMI on pre and postoperaive range of motion, duration of surgery, analgesia requirements and duration of stay.
Obesity is defined as a body mass index (BMI) of greater than 30 KG/m2. 120 consecutive patients were recruited from patients presenting for total knee arthroplasty (TKA) to two hospitals. They were classified into one of four groups based on their BMI. All patients were assessed pre and postoperatively by the surgical team. Data was collected on type of implant used, duration of surgery, type of anaesthetic, analgesia requirements and length of stay. Knee society scores were collected pre and postoperatively. Three to six month follow-up was conducted by the surgical team to record flexion, ROM and KSS. Statistical analysis was performed using statistical software.
120 patients were available for the study with 61 (50.8%) being classified as obese and 6 patients classified as morbidly obese. (BMI > 40). The average preoperative flexion results were 112.1 degrees (BMI 18.5 to 14.9), 114.0 degrees (BMI 25 to 29.9), 107.0 degrees (BMI 30 and above), while the postoperative flexion prior to discharge was 85 (BMI 18.5 to 24.9), 90.3 (BMI 25 29.9) and 88.3 (BMI 30 or above). The obese patients had a lower ROM preoperatively but there was no Significant difference at discharge. Patients with a BMI of 25–29.9 used the least amount of analgesia and had the fastest surgery time. They also spent the least amount of time in hospital. (6.3 days) Patients classified as clinically obese (BMI 30 and above) recorded the lowest KSS. As BMI increases the postoperative functional knee score decreases but there is no Significant difference at discharge and 3–6 months postoperatively.
The increasing prevalence of obesity in the Western world suggests that a Significant proportion of surgical patients will be in the obese or morbidly obese catergory. This studty suggests that BMI alone does not influence the short term outcomes of TKA. The poorer long term outcomes in TKA may be related to other factors. Further research may be appropriate.
The abstracts were prepared by David AF Morgan. Correspondence should be addressed to him at davidafmorgan@aoa.org.au
Declaration of interest: a
