Check out this interesting article on the effect of rear foot frontal plane position on that of the hip, pelvis and thorax when in single leg stance. A fancy 6-camera Vicon system evaluated the position of the pelvis, and spine when standing on a normal (0 degrees eversion), a 5° calcaneal eversion condition (standing on a wedged platform) and a 10° eversion.
Basically increasing eversion created a significantly (p <0.05) more adducted, internal rotated and flexed hip position, increased anterior pelvic tilt, and the spine rotated towards the stance leg. If you read through the article there are some inconsistencies here which may be associated with a small sample size (n= 28) but the direction of these changes in starting position of the bones in increasingly everted stance is consistent with what we see during walking in the front leg of gait but also illustrates the unity of the body and ‘chain reactive’ effect of changes at the foot all the way through the body.
Between 5 and 10 degrees the frontal plane pelvic position flips the other way, going from more lateral tilt away from the stance leg, to more lateral tilt towards it in the 10 degree eversion situation. This may be a strategy to increase stability by bringing the centre of mass closer to the base of support?
Anyway have a read, it is an interesting study…