Fig 1.
Adjustment of femoral component rotational alignment.
(A) To obtain a rectangular gap in the navigation femoral planning step, the femoral component rotation based on the posterior condylar axis and the varus-valgus angle were adjusted. A difference of <2 mm between the lateral extension/flexion gap and the medial extension/flexion gap was considered acceptable. (B) After distal femoral resection, the AP femoral cutting jig is located using the determined value during the planning step. The rotational position of the AP femoral cutting jig is displayed in real time. The arrow line indicates the actual femoral component rotation.
Fig 2.
Excessive external rotation is needed for valgus knee TKA.
(A) The surgical transepicondylar axis (solid line) connects the medial sulcus to the lateral epicondyle. The posterior condylar axis (dashed line) is the tangent of the posterior part of the medial and lateral condyle. (B) Posterior lateral condylar hypoplasia induces a more internal rotation of the posterior condylar axis relative to the surgical transepicondylar axis. (C) In this case, 10° external rotation of the femoral component from the posterior condylar axis is needed to achieve a rectangular flexion gap.
Fig 3.
(A) The angle between the true mechanical axis of the femur obtained using hip and knee kinematic analysis and distal femoral joint surfaces from the exact 4-point contact with a check plate. (B) The navigation system displays the quantified angle. This angle (arrow line) represents the lateral distal femoral angle from the navigation system (NaviLDFA).
Fig 4.
Measurement of HKA Axis, XrayLDFA, LGVS, and MGVS.
The HKA axis and XrayLDFA were measured using a preoperative whole-leg standing radiograph (A). The HKA axis was measured using intersecting lines from the femoral and tibial mechanical axes. The XrayLDFA was a superolateral angle measured by intersecting the femoral mechanical axis line and distal femoral joint line. LGVS and MGVS were measured from varus (B) and valgus (C) stress radiographs, applying 130 N. The dashed line is the bisector of the angle between the distal femoral and proximal tibial joint lines (black solid lines). LGVS was measured from the lowest point of the lateral femoral condyle to its corresponding point on the tibial joint line (red solid line, drawn perpendicular to the dashed line). MGVS was measured using a similar method.
Fig 5.
(A) The preoperative patellar tilt angle is defined as the angle between the equatorial line of the patella and the line connecting the anterior limits of the femoral condyles in the Merchant view. (B) The postoperative patellar tilt angle is measured using the same method but with a line connecting the anterior limits of the femoral component instead of the femoral condyles.
Table 1.
Correlations between FCR and all potential predictors.
Table 2.
Independent and dependent variables.
Table 3.
Backward multiple regression analysis of factors that affect femoral component rotation (FCR) based on the posterior condylar axis.
NaviLDFA as an independent variable.
Table 4.
Backward multiple regression analysis of factors that affect femoral component rotation (FCR) based on the posterior condylar axis.
XrayLDFA as an independent variable.
Table 5.
Comparison of preoperative and postoperative patellar tilt angles and the HKA axis.