Fig. 4. Derotation (γ0>γ1) osteotomy with the rotation axis Y results in varus change (v0>v1) and decreased flexion (β0>β1) of femoral head.
X coordinate is increased (x0<x1), Z coordinate is decreased (z0>z1), and Y coordinate is not changed (y0=y1). Therefore, angle of valgus and anteversion is decreased (v0>v1, γ0>γ1) and flexion angle (β0>β1) is decreased.
H0 and H1: Center of femoral head before and after derotation osteotomy.
v0 and v1: the valgus angle before and after derotation osteotomy.
β0 and β1: the flexion angle before and after derotation osteotomy.
γ0 and γ1: the angle of anteversion before and after derotation osteotomy.