There are many causes for a high arch (cavus) foot. In the United States, the most common cause for a high arch foot is a form of muscular dystrophy called hereditary sensorimotor neuropathy. Most people recognize this by the more commonly used name of Charcot Marie Tooth disease (CMT). This is a disease of the muscles and the nerves of the legs, and occasionally of the hands, in which certain muscles weaken while others retain their strength.
The condition is transmitted as an autosomal dominant condition. This means that 50% of the offspring will statistically inherit the disorder. This is, however, just a statistic. In some families, all the children develop the condition while in others, none inherit it.
Charcot Marie Tooth disease occurs in both children and adults. Once the deformity is present in a child it is going to be progressive. This means that the deformity will slowly get worse as a result of the muscle imbalance and weakness. Although the pattern of muscle and nerve damage may be similar through the generations in a family, this is not always the case. Every cavus foot is unique.
The muscle imbalance around the foot and ankle gives rise to a typical pattern of deformity in addition to the high arch (known as cavus). The bone under the big toe (called the first metatarsal) can become very prominent and the toes can curl or clench like a fist (called claw toes). Excessive amount of weight may be placed on the ball and heel of the foot, which can lead to the ankle weakening and giving way (this is referred to as ankle instability) and soreness.
Calluses and sometimes stress fractures may occur where the foot is exposed to extra friction or pressure, such as on the outer (or lateral) border of the foot.
The deformity of the high arch foot develops because the muscles that pull the foot inward (inversion) remain strong, while those that pull the foot outward (eversion) are weak or absent. The muscle that remains very strong is called the posterior tibial muscle, and the muscle that gets weak is the peroneus brevis muscle.
Another common problem in Charcot Marie Tooth disease is the presence of a foot drop. This means that the muscle that pulls the foot (the anterior tibial muscle) upward is weak or paralyzed, leading to an abnormal dropping of the foot when walking.
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