Defining distal femoral anatomy for rotational alignment in total knee arthroplasty: a magnetic resonance imaging-based study.

Abstract

The rotational alignment of the femoral component in total knee arthroplasty (TKA) is regarded as being one of the critical factors associated with its long-term success. Traditionally, the femoral component is aligned parallel to the transepicondylar axis (TEA), perpendicular to the Whiteside's line (WL) or at 3 degrees external rotation to the posterior condylar line (PCL). The aim of this study was to use magnetic resonance imaging (MRI) to evaluate the relationship between these anatomical axes used for femoral component rotation (TEA to WL and PCL to TEA) and identify if any of these relationships were influenced by age, sex or coronal axial deformity (mechanical axis). Two hundred and sixty-five patients undergoing preoperative MRI for patient-specific jigs TKA were included in our study. The MRI data were then analysed via preoperative planning software, and values relating to WL, TEA, PCL and coronal axial alignment were generated. The mean age was 66.0 ± 8.7 years. There were 102 men and 163 women. The average mechanical axis (coronal deformity) was 4.2 ± 6.1 degrees of varus. TEA compared with WL was on average 92.6 ± 2.3 degrees. PCL was on average 2.3 ± 1.8 degrees internally rotated to the TEA. The PCL was more internally rotated in women (P < 0.01) and valgus (P < 0.001) knees. There was no significant relationship between age or varus knees when comparing TEA to WL (P > 0.1) and PCL to TEA (P > 0.1). Our study shows that the previously assumed values for rotational alignment of the femoral component may need to be reviewed. The use of advanced preoperative imaging (e.g. MRI) may aid to overcome this variability and assist surgeons in planning femoral component alignment in TKA.