Influence of the distal femoral resection angle on the principal stresses in ceramic total knee components

A certain failure mode using a newly developed cemented ceramic femoral component in total knee replacement was observed in clinical application, i.e. fracture of the femoral component during intraoperative impaction. This may be caused by unintentional deflection of the saw blades during cutting with consecutive higher resection angle of the distal femur than desired, leading to bending of the femoral component during implantation. A finite-element-analysis was carried out to simulate implantation of the femoral component and to evaluate the influence of distal femur preparation on implant stress.

We developed and validated a numerical model of the ceramic femoral component including a contact formulation which allowed calculating the principal stresses of the implant during implantation onto the resected femur. The analysis considered different anterior and posterior resection angles with a total of 17 variations. By increasing the femoral resection angle in the finite-element-model it could be shown that a deviation of three degrees from the intended resection angle can cause critical stress amounts during implantation.

When implanting the ceramic component in total knee arthroplasty, the femoral resection angles should be prepared very precisely, in particular anterior saw blade deflection has to be avoided. The implant manufacturer increased implant safety through an additional resection template. Moreover, the impaction of the ceramic femoral component during cementing was not further recommended by using a hammer.