The Midfoot Joint Complex (Foot Arch) Contributes to the Upper Body Position in Bipedal Walking and Coordinates With the Lower Limb Joints.

This study estimated the contribution of the midfoot joint complex (MJC) kinematics to the pelvis anterior-posterior positions during the stance phase of walking and investigated whether the MJC is functionally coordinated with the lower limb joints to maintain similar pelvic positions across steps. Hip, knee, ankle, and MJC sagittal angles were measured in 11 nondisabled participants during walking. The joints' contributions to pelvic positions were computed through equations derived from a link-segment model. Functional coordination across steps was identified when the MJC contribution to pelvic position varied and the summed contributions of other joints varied in the opposite direction (strong negative covariations [r ≤ -.7] in stance phase instants). We observed that the MJC plantarflexion (arch raising) during the midstance and late stance leads the pelvis backward, avoiding excessive forward displacement. The MJC was the second joint that contributed most to the pelvis positions (around 18% of all joints' contributions), after the ankle joint. The MJC and ankle were the joints that were most frequently coordinated with the other joints (≅70% of the stance phase duration). The findings suggest that the MJC is part of the kinematic chain that determines pelvis positions during walking and is functionally coordinated with the lower limb joints.

Pelvic Sagittal Torsion Caused by Induced Leg Length Discrepancy: Geometrical Illusion May Influence Measures Based on Superior-iliac Spines Positions.

OBJECTIVE: To investigate whether a common measure of sagittal pelvic torsion based on the superior iliac spines behave similarly to predictions of a rigid (non-torsioned) plane, when leg length discrepancies (LLD) are induced. METHOD: Twenty-four young asymptomatic participants were subjected to pelvic posture measurements that use the anterior-superior iliac spines (ASISs) and posterior-superior iliac spines (PSISs) as references, while standing on level ground and with a one-, two- and three-centimeter lifts under the left foot. A special caliper with digital inclinometers was used. The following angles were measured: angles of the right and left PSIS-to-ASIS lines; right-left relative angle (RLRA), as the angle between the right and left PSIS-to-ASIS lines, which is a traditional lateral-view measure intended to detect sagittal torsions; angle of the inter-ASISs line; angle of the inter-PSISs line; anterior-posterior relative angle (APRA), as the angle between the inter-ASISs and inter-PSISs lines. According to trigonometric predictions based on the geometry given by the lines linking the superior iliac spines (i.e. a trapezoid plane), a pure lateral tilt of the pelvis, without interinnominate sagittal motion, would change RLRA in a specific direction and would not change APRA. RESULTS: Repeated-measures ANOVAs revealed that RLRA (p<0.001) and right and left PSIS-to-ASIS angles (p≤0.001) changed, and APRA did not change (p=0.33), as predicted. CONCLUSIONS: At least part of the sagittal torsion detected by measures that assume the PSIS-to-ASIS angles as the sagittal angles of the innominates is due to pelvic geometry and not to the occurrence of actual torsion, when LLDs are induced.