Why does it hurt?

When functioning properly, your foot forms a tripod, which is a stable foundation for your body. As you take a step, your heel actually moves from side to side. It moves to where it makes the tripod most stable.

When your heel has moved to the pinky toe side of the foot it is said to be in the valgus position. When it has moved to the big toe side it is said to be in the varus position.

In a foot that involves a coalition of the calcaneous (heel bone) with another bone, it is locked into the valgus position. This makes the tripod off center and the arch of the foot collapses. If you have a coalition, you have a flat foot.


In this image, I attempt to illustrate the tripod concept. Remember, my right foot is normal. When someone looks at the image on the left, they may think that the feet are completely normal. But if you look closely, you can see the heel of my right (normal) foot, but not my left (coalition) foot. You can also begin to see how my left (coalition) foot is "rolling" inward which makes my arch disappear. On the right I've drawn some tripods. You can see how the tripod of my right (normal) foot is stable. However, the the heel of my left foot is stuck in the valgus position which causes the point of the tripod to buckle (red arrow).

This instability causes all kinds of trouble. Tendons and other tissues get pulled and twisted abnormally which can cause a burning sensation on the top/outside of your foot. The muscle and tissue along the arch of your foot gets stretched and can spasm. The joint itself takes on a lot more stress than it's intended to.

You may also have some very deep pain, I know I do. That little bony bridge, the coalition, gets a ton of torque on it. The twisting and torquing can cause an bone marrow edema (collection of fluid) to form inside the bones themselves. A recent MRI revealed edema in my left foot.