Can the combination of information from different alignment axis improve rotational alignment of the femoral component in total knee arthroplasty?

Background: There is a strong relationship between rotational alignment of the femoral component in total knee arthroplasty (TKA) and knee joint kinematics, function and prosthetic survival. Excessive internal rotation may lead to pain, patella-femoral instability, failure of the patellar component and flexion laxity. Excessive external rotation may cause laxity in flexion and varus mal-alignment in flexion.

The most widely used secondary reference axes to help navigate the femoral component into rotational alignment corresponding to the CT derived surgical epicondylar axis are the posterior condylar line (PCL), the surgical transepicondylar axis (sTEA) and the antero-posterior axis (APA) (Whiteside's line). More recently the transverse femoral axis (TFA) has been proposed.

Because of the obvious lack of reliability of these secondary alignment axes we started up in 2005 to use a combination of information from three secondary alignment axes in the hope of improving the axial alignment of the femoral component.

Purpose of study: The aim of this study is to estimate the accuracy and precision of the combination technique, and to investigate the degree of patella-femoral joint incongruence as measured by patella-femoral tilt and lateralization that can be expected with this technique for positioning the femoral component in the axial plane.

Materials and methods: At three years follow up 60 consecutive patients will be examined with a very low-dose three dimensional computed tomography for axial and coronal alignment of the prosthetic components. Standard radiographic evaluation with anterio-posterior, sagital, long leg and patella-axial x-rays will also be performed.