Fig. 1

The zones of the mechanical axis [10] and sketches of the correction velocities of the femur and tibia in different genu angular deformities. The mechanical axis of the lower extremities passing through zone 1 represents normal alignment and includes the middle 2 quadrants (medial: +1; lateral: -1). The mechanical axis of the lower extremities passing through zones − 2 and − 3 represents genu valgum deformity and through + 2 and + 3 represents genu varum deformity. The overall femoral correction velocity (1.28° per month) was significantly faster than the tibial correction velocity (0.83° per month) (P = 0.000). For the femur, the correction velocity for a varus deformity was significantly faster than that for a valgus deformity (1.50° vs. 1.16° per month, P = 0.033). For the tibia, the correction velocity for a valgus deformity was significantly faster than that for a varus deformity (1.03° vs. 0.66° per month, P = 0.010)