The effect of varus knee deformities on the ankle alignment in patients with knee osteoarthritis

BACKGROUND: We evaluated the compensatory change in ankle alignment due to knee malalignment and its relationship with varus knee deformities, as well as sex differences in compensation. METHODS: From October 2016 to September 2017, 103 patients with end-stage knee osteoarthritis underwent primary total knee arthroplasty (TKA). Ninety-five knees (78 patients) were included. The hip-knee-ankle angle (HKA) and ankle alignment and tilt were evaluated with full-leg standing anteroposterior radiographs. The ankle alignment was estimated according to the tibiotalar angle, tibial anterior surface angle (TAS), and lateral distal tibial angle. The talar tilt angle (TT), anatomical talocrural angle, angle between the tibial plateau and distal tibial plafond, angles between the ground and distal tibial plafond, and angles between the ground and upper talus were measured to evaluate ankle tilt. The patients were separated into two sex-based groups; correlations between the HKA and ankle parameters were estimated. RESULTS: The mean HKA in men and women was 8.16 ± 4.36° and 7.69 ± 5.93°, respectively. The relative tilt of the talus and distal tibia plafond to the ground was increased when varus knee deformities progressed. In women, there was a positive correlation between the knee alignment and TAS (r = − 0.295, p = 0.016). As the knee mechanical axis became more varus, the distal tibia plafond became more valgus. In women, a negative correlation was observed between the HKA and TT (r = − 0.359, p = 0.003). Compensatory changes in the ankle alignment and TT to knee alignment were not observed in men. CONCLUSION: Compensatory ankle changes should be considered before TKA.