Pronation of the foot is a normal motion of the ankle bone (talus) on the heel bone (calcaneus) resulting in a slight turning out of the forefoot on the rearfoot. The function of the foot is to transfer the weight of the body to the ground and to propel the body. The function of the talus is to transfer the weight of the tibia and fibula to the calcaneus and the rest of the foot.

Hyperpronation or excessive pronation of the foot is a hereditary condition caused by underdevelopment of the talus and or calcaneus. This condition leads to excessive abnormal motion of the talus on the calcaneus. The result of this excessive motion leads to abnormal closure or obliteration of a naturally occurring space formed by the talus and calcaneus (sinus tarsi).

Normal Sinus Tarsi

Note the space between the ankle bone (talus) and heel bone (calcaneus) in a normal, non-hyperpronated condition.

Obliterated Sinus Tarsi

This image illustrates the collapse of the sinus tarsi between the ankle bone (talus) and heel bone (calcaneus) caused by hyperpronation.

Abnormal Alignment

Note the alignment angle of the ankle bone (talus).

Restored Sinus Tarsi

Angle indicates a misalignment caused by the collapse of the sinus tarsi.

The videos below show what happens when a foot is hyperpronating. These are weight bearing fluoroscopy images. The foot is first placed into "neutral position", which is the normal position the foot should be when standing. Then the person puts full weight on their foot leading to the abnormal closure of the sinus tarsi. The most common thing we do besides breathing is walking. Remember this when you watch the video. The average person takes 10,000 steps a day.

The diagnosis of hyperpronation is actually a structural deformity referred to as: talipes valgus, (pronounced: tal-a-peas, val-gus). Talipes is the relationship of the talus with the rest of the foot (tal-i-pes). In this condition there is a turning inward (varus) of the talus and a turning outward (valgus) of the rest of the foot. The problem with this condition is that the mechanics of the foot are “out-of-alignment”. This deformity is present at birth and will not resolve on its own. With every step taken abnormal forces are occurring to the structures of the foot, and this leads to abnormal motion up the kinetic chain. Therefore, excessive motion in the knee, hip, back, etc. This is an “internal” deformity and results in the abnormal obliteration of the sinus tarsi.