In knee osteoarthritis, what is the knee deformity threshold after which the ankle realigns beyond the neutral zone?

Figure 1 Long leg anteroposterior plain radiograph of the hip, knee, and ankle joints, which was used to measure the knee and ankle coronal alignment. The hip to knee to ankle angle (HKAA) in orange is the medial angle between the mechanical axis of the tibia and femur; a neutral HKAA was defined as 180° ± 2°. The tibiotalar angle (TTA) in blue is the medial angle between the distal tibial axis and the line tangential to the upper talar surface; a neutral TTA was defined as 88.9° ± 3°. HKAA: Hip to knee to ankle angle; TTA: Tibiotalar angle.