Anatomical landmarks of the distal femoral condyles are not always parallel to the tibial bone cut surface in flexion during total knee arthroplasty

• Soft tissue balancing of the knee is crucial for total knee arthroplasty.
• The flexion joint gap was measured using three measured resection techniques.
• An outlier in the flexion joint gap (> 3.0°) was observed in about 30% of cases with each technique.
• Anatomical landmarks of the distal femur are not always parallel to the tibial bone cut surface in flexion.

BackgroundSoft tissue balancing is crucial to the success of total knee arthroplasty (TKA). To create a rectangular flexion joint gap, the rotation of the femoral component is important. The purpose of this study is to determine whether or not anatomical landmarks of the distal femoral condyles are parallel to the tibial bone cut surface in flexion.MethodsForty-eight patients (three male and 45 female) with a mean age of 74 years were examined. During the operation, we estimated the flexion joint gap with the following three techniques. 1) a three degree external cut to the posterior condylar line (MR1), 2) a parallel cut to the surgical transepicondylar axis (MR2), and 3) a parallel cut to the anatomical transepicondylar axis (MR3).ResultsThe flexion joint gap was 1.1 ± 3.0° (mean ± standard deviation (SD)) in internal rotation in the case of MR1, 0.9 ± 3.4° in internal rotation in the case of MR2, and 2.1 ± 3.4° in external rotation in the case of MR3. An outlier (flexion joint gap > 3.0°) was observed in 12 cases (25%) in MR1, 13 cases (27%) in MR2, and 15 cases (31%) in MR3.ConclusionsThe anatomical landmarks of the distal femoral condyles are not always parallel to the tibial bone cut surface in flexion. To create a rectangular flexion joint gap, the rotation of the femoral component rotation is based not only on the anatomical landmarks but also on the ligament balance.