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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Category: Hindfoot Introduction/Purpose: Hindfoot and knee coronal alignments have shown to be related in previous literature suggesting that there might be some degree of compensation between the two. However, previous studies have focused on the effects of knee surgery on hindfoot alignment, not on the preoperative relationship. Recent 3D weight bearing imaging technology may help to investigate this. The objective of this study was to analyse the preoperative relationships between knee and hindfoot coronal alignments using bilateral weight bearing CT (WBCT) and biplanar low dose radiography (BLDR). We hypothesized that hindfoot valgus and varus respectively compensates knee varus and valgus. Methods: Relevant ethical approval was obtained for this retrospective comparative level 3 study including 124 limbs in 62 patients (32 female, 30 male), mean age 56 (23-84). Mean BMI was 27 (20-38). Cases included had been referred continuously according to diagnostic protocols in our institution, for a combined WBCT and BLDR investigation. Age, gender and BMI were recorded. Cases with a history of trauma or surgery, which may have caused a change in lower limb alignment, were excluded. Hindfoot alignment was measured using a semi automatic software (TALAS, Curvebeam, Warrington PA, USA) and given as Foot Ankle Offset (FAO). Knee alignment was measured using the EOS platform (EOS Imaging, Paris, France) and given as HKA. Distribution and demographics of hindfoot alignment in the varus and valgus knee groups were studied. Correlations were investigated using linear regression and Bland and Altman plots. Results: Incidence of Varus hindfeet was 15.8% in the Valgus knee group and 25.5% in the Varus knee group but the difference was not significant (p=0.82). Bland and Altman plots did not yield any additional result. No linear correlation was found between hindfoot and knee coronal alignments in the study population. Conclusion: Our results do not confirm prior findings regarding compensatory valgus in varus knees, and do not confirm the hypothesis according to which linear compensatory mechanisms may relate knee and hindfoot alignments. In practice, these results suggest that in cases where knee and hindfoot misalignments are associated, the causes for each should be analyzed independently before any assumption is made as to hypothetical interactions. Furthermore, subsequent studies are warranted to investigate whether other kinds of non-linear correlations way be found in selected populations.