KS49: KNEE ARTHROPLASTY ALIGNMENT AND ITS AFFECTS ON FUNCTION

Abstract

Implant alignment and rotation is important in total knee arthroplasty (TKA). If incorrect it leads to abnormal wear and premature loosening. However, little is known with regard to how these factors influences rehabilitation. Our aim was to identify which aspects of alignment affect functional outcome and Length of Stay. This is an ongoing study with 300 patients results expected by september 2008. Currently 159 patients underwent TKA between May 2003 and July 2004 at Royal Perth Hospital. A Duracon TKA (Stryker Corp) was implanted by multiple surgeons using either computer navigation or conventional jiging. A WOMAC and knee society score (KSS) were calculated on each patient by a physiotherapist at 6 months, 1 year and 2 years. Implant alignment was measured using the Perth CT protocol. A statistician used a combination of independent t-tests and one way analysis of variance to determine significance between groups.

Two groups of alignment were created to allow comparison. These were termed good alignment (< = 2 degrees of mechanical axis) and outlier group (> 2 degrees of mechanical axis). There were no difference between the two groups in terms of age, BMI and preop function. This suggest no confounding variables between the groups. Coronal femoral alignment as well as cumulative error (additive error in all planes of both components) were statistically significant. The p-values are 0.031 and 0.011 respectively. Cumulative error also had an impact on hospital stay, increasing it by 2 days when greater than 6(p=0.006). Trends towards better function at 1 year were seen with regards to sagittal alignment in both the femur and tibia, as well as coronal tibial alignment. It is expected by september 2008 that patient numbers will be double. This should provide the most comprehensive analysis of alignment versus function in the literature to date.

Functional outcome following TKA is multifactorial. However certain aspects of alignment, especially the cumulative error of alignment appear to have significant effects on function.