A1169. KNEE CARTILAGE MOEDELING AND ITS EFFECT ON THE ACCURACY OF SURGICAL LANDMARKS IDENTIFICATION

Abstract

The success of TKAs depends on the restoration of correct knee alignment and proper implant sizing and placement. The mechanical axis is considered a key factor in the restoration of knee alignment along with the transepicondylar axis and the posterior condylar axis as references for external and internal implant rotation. Accurate calculation of the distal resection plane in the femur and proximal resection plane in the tibia is crucial to determine the amount of the bone to be resected. In this study, we developed a model for mapping the thickness of the femoral and tibial articulating cartilage. We also studied the effect of cartilage presence and the absence on the accuracy of calculating the surgical landmarks, implant sizing and placement.

Cartilage models were constructed using fat suppression MRI scans of healthy individuals with different body sizes. The femoral and tibial cartilages were segmented and surface models were generated. The inner and outer surfaces of the cartilage were separated, the inner surfaces were then mapped to the articulating surface of the femur and tibia to establish correspondence between the cortical bone surface and the inner surface of the cartilage. For each vertex on the normalized inner surface of the cartilage, the closest point was found on the outer surface of the cartilage and the normal distances were calculated. These distances were then averaged for each vertex across the population to calculate an average cartilage model. This average cartilage model was then used to grow a cartilage layer on our database of 300 bones from CT scans. Surgical landmarks and implant sizing and placement were then calculated for each bone before and after the cartilage and results were compared.

Some of the landmarks including the mechanical and transepicondylar axes were found to be independent from the presence or absence of knee articulating cartilage, whereas the posterior condylar axis and tibial and femoral resection planes can be affected by the absence or presence of cartilage.