Asymmetrical foot pronation has the potential to create a leg length difference of up to 1cm, so obviously this is potentially problematic (this is a functional leg length difference).
However, within podiatry circles there is a common belief that the foot on the side of a structural leg length difference will pronate more as a form of compensation. You can read this in a lot of podiatry books, but do not read about it in any orthopaedic, physical therapy, chiropractic or osteopathy books. I also did not get this as I would see just as many people with a structural leg length difference in which the short leg pronated more. I used to get tired of students coming up to me in clinic when doing a gait analysis and saying things like "Craig, the left leg is longer, but I can't see it pronating more .... "maybe because it wasn't!!!" --- but that’s what they got taught and read in the podiatric literature. Is this just another one of those podiatry myths.
Lets look at some theoretical arguments:
1. When we are walking, when one leg is in the swing phase, how does the body sense the leg on the ground is longer, to make it pronate more?
2. When we are walking, when both legs are on the ground, with one foot in front of the other, how does the body know that one of the legs is longer to make it pronate more?
3. Stand up, try and pronate on foot. Hard work, isn’t it. Now slightly flex the knee. Easy, isn’t it? Would it not be easier for your body to slightly flex the knee to compensate for a LLD rather than pronate the foot?
What does the evidence say:
The 3 studies that have looked at if the long leg pronates more, have all shown no differences in those with a structural leg length difference. Two of them showed we mostly compensated by slightly flexing the knee!
It just does not figure that the myth continues, when ALL the evidence says it does not happen.
Podiatry Arena threads on this.