Is Mediolateral Translation of Femur Caused by Total Knee Arthroplasty Being Ignored?

Purpose This study aims to show the change in overall congruency due to mediolateral translation after total knee arthroplasty compared with normal knee anatomy. Methods This study was performed in two parts. In part 1, the relationship between femur and tibia was defined by new parameters on the antero-posterior radiographs of 84 patients. In part 2, this relationship was evaluated on the postoperative radiographs of 136 total knee arthroplasty patients. Two parallel lines to the tibial anatomical axis were drawn tangent to the most lateral and most medial parts of the tibial plateau. After creating medial and lateral tangential lines, the distance between the most lateral point of the lateral femoral epicondyle and lateral tangential line and the most medial point of the medial femoral epicondyle and medial tangential line was measured. Another new parameter described in the study is epicondylar distance ratio. The ratios between the shortest distance between tibial anatomical axis and lateral femoral epicondyle and the distance between tibial anatomical axis and medial femoral epicondyle were defined. Results It was found that the lateral tangent was not superposed in any measurement to the femoral lateral condyle, the closest tangent was passed, and the mean lateral space distance was 1.8 mm (SD 1.5, 95% CI 0–5.3 mm). The medial tangent was passed from the lateral to the femoral medial epicondyle, and the medial crossing distance was 8.5 mm (SD 5.7, 95% CI 5–14 mm). Epicondylar distance ratio used as the second measurement was 0.8 (0.5–0.9). After total knee arthroplasty measurements showed that the line passing through the lateral tibia crossed the lateral epicondyle of the femur and intersected at an average distance of 4.3 mm (SD 4.1, 95% CI 1–11.2 mm). Conclusions There is a coronal plane congruence between tibia and femur in the healthy knees, which get changed after total knee arthroplasty.