Figure 5.

The calculation of the joint line obliquity (JLO) according to Hsu et al. (51). For a neutral knee with an apex distal JLO, having its mechanical axis (MA) vertical to the ground, involves two angles. The α angle is determined as 90° − lateral distal femoral angle (LDFA), and the β angle is calculated as 90° − medial proximal tibial angle (MPTA). Both α and β angles contribute equally to half of the apex distal JLO. Therefore, the JLO to the ground is calculated as JLO = (α + β)/2, which is equivalent to 90° − (LDFA + MPTA)/2.