Foot progression angle (FPA), measuring intoeing and outtoeing gait, has been shown to be related to torsions of the tibia and/or the femur [1,2]. However, it is still unknown how the entire morphology of the pelvis, acetabulum and lower limbs dictate the axial foot orientation during walking. The aim was to evaluate the lower limbs morphological profile in subjects with different foot progression angles.

One hundred and forty-five asymptomatic subjects (70F, age=29.2±11.1years) underwent 3D gait analysis from which FPA was extracted. Subjects then underwent low-dose full-body biplanar radiographs. Pelvis and lower limbs were reconstructed in 3D to calculate: pelvic incidence, sacral slope, pelvic tilt, pelvic axial rotation, neck-shaft angle, femoral torsion (FT), varus/valgus, knee flexion/extension, femoral mechanical angle, tibial mechanical angle, tibial torsion (TT), femorotibial rotation (FTR), vertical center-edge angle, anterior and posterior acetabular sector angles, acetabular coverage over the femoral head (AC), acetabular tilt, abduction and anteversion, and Idelberg and Frank angle (IFA). FPA data was classified using agglomerative hierarchical clustering (AHC) into 3 groups: internal, neutral, external FPA. Demographic data (age, height, weight, sex) was compared between AHC groups using Kruskal–Wallis and Fisher tests. The morphologic parameters were compared between the FPA classes using ANCOVA while controlling for demographic data. Stepwise multiple linear regression (SMLR) was then performed to identify which morphologic parameters determined FPA.

FPA varied from −28.7 to 3.1°. AHC divided FPA data as: external (E) FPA [−17.4±3.6°], neutral (N) FPA [−9.9±1.8°], internal (I) FPA [−2.9±2.5°]. Weight, height and, significantly differed between groups (P<0.0001), and were controlled for in subsequent comparisons. ANCOVA between the 3 groups revealed significant differences for TT (E: 29.3 vs. I: 25.6°, P=0.016), FTR (E: 12.7 vs. I: 8.2°, P<0.0001). SMLR showed that weight (beta=−0.86, P<0.0001), sex (beta=0.19, males as controls, P=0.003), FT (beta=0.24, P=0.002), TT (beta=−0.36, P=0.009), and FTR (beta=−0.31, P<0.0001) significantly influenced FPA.

Subjects with a higher weight and of the male sex tended to walk with a more outtoeing gait. Subjects with an outtoeing gait had a high TT and FTR as well as a low FT, therefore presenting a more outwards rotational profile. However, subjects with a more in toeing gait had a low TT, FTR and a high FT, therefore presenting a more inwards rotational profile. This profile extends over the whole lower limb, and includes FT, FTR, and TT excluding the acetabular morphology. References: [1] Kim, 2011; [2] Hudson, 2016.