Figure 3. Line 1: the co-tangent of the posterior contours of the medial and lateral tibial condyles. Line 2: the medial tangent of the medial tibial condyle. Line 3: the lateral tangent of the lateral tibial condyle. Line 4: the anterior tangent of the medial tibial condyle. Z-axis: medial/lateral axis. X-axis: anteroposterior axis. Y-axis: vertical axis.