Rotational position of femoral and tibial components in TKA using the femoral transepicondylar axis

Abstract

Proper femoral and tibial component rotational positioning in TKA is critical for outcomes. Several rotational landmarks are frequently used with different advantages and limitations. We wondered whether coronal axes in the tibia and femur based on the transepicondylar axis in the femur would correlate with anteroposterior deformity. We obtained computed tomography scans of 100 patients with arthritis before they underwent TKA. We measured the posterior condylar angle on the femoral side and the angle between Akagi's line and perpendicular to the projection of the femoral transepicondylar axis on the tibial side. On the femoral side, we found a linear relationship between the posterior condylar angle and coronal deformity with valgus knees having a larger angle than varus knees, ie, gradual external rotation increased with increased coronal deformity from varus to valgus. On the tibial side, the angle between Akagi's line and the perpendicular line to the femoral transepicondylar axis was on average approximately 0 degrees , but we observed substantial interindividual variability without any relationship to gender or deformity. A preoperative computed tomography scan was a useful, simple, and relatively inexpensive tool to identify relevant anatomy and to adjust rotational positioning. We do not, however, recommend routine use because on the femoral side, we found a relationship between rotational landmarks and coronal deformity.

Fig. 1

The posterior condylar angle is formed by the posterior condylar line and the surgical transepicondylar axis.

Fig. 2

The condylar twist angle is formed by the posterior condylar line and the clinical transepicondylar axis. This is used when the sulcus is absent on the medial side.

Fig. 3

The Akagi’s anteroposterior line, perpendicular to the projection of the femoral transepicondylar axis (TEA) and passing through the midposterior cruciate ligament attachment, is tangent to the medial patellar tendon attachment. PT = patellar tendon; PCL = posterior cruciate ligament.

Fig. 4

The tibial rotation angle is the angle formed by the line perpendicular to the femoral transepicondylar axis (TEA; dotted line) and the Akagi’s anteroposterior line.

Fig. 5

Scatterplot of posterior condylar angle (PCA) versus frontal plane deformity with men (triangles) and women (boxes). We observed a linear relationship between PCA and preoperative coronal deformity.

Fig. 6

Scatterplot of tibial rotation angle (TRA) versus frontal plane deformity with men (triangles) and women (boxes). We observed no relationship between TRA and preoperative coronal deformity.