Background: Previous studies focusing on the effects of knee surgery on hindfoot alignment have suggested some degree of compensation between the knee and the hindfoot. However, these studies did not investigate a preoperative relationship in patients without end-stage knee osteoarthritis using 3-dimensional (3D) biometrics. The purpose of this study was to investigate the relationship between knee and hindfoot alignment using 3D weightbearing imaging. Methods: This retrospective comparative study included 95 lower limbs with weightbearing computed tomography and low-dose biplanar radiograph investigations. Cases with a history that may have caused a change in lower limb alignment were excluded. Hindfoot and knee alignments were measured using foot ankle offset (FAO) and hip-knee-ankle (HKA) angle, respectively. Patients were separated into 3 groups according to the knee deformity to investigate the distribution of FAO in each group. Results: The mean (SD) FAO was 2% (7%) for the knee varus group, 1% (6%) for the neutral knee group, and 4% (5%) for the valgus knee group ( P = .12). Fifty-three percent of patients with knee valgus showed a pathological hindfoot valgus ( P = .04). We found a positive but moderate correlation between hindfoot valgus and HKA (ρ = 0.53; P = .01). Female sex was associated with higher FAO (3% ± 4% vs 0.6% ± 6%; P = .009). Conclusion: This feasibility study suggests a new opportunity using 3D biometrics to understand the relationship between knee and hindfoot alignment and to highlight different patterns of combined deformities in further investigations. Level of Evidence: Level III, comparative study.

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