Charcot-Marie-Tooth disease (CMT) is an inherited neurological condition that affects the nerves that control movement and sensation. Weakness in muscles of the lower leg and foot caused by the disease can lead to foot deformations.
Types of foot deformations in CMT
Two types of foot deformations are commonly found in CMT patients. These are the so-called cavovarus foot and the foot drop.
Foot drop
Foot drop is caused by weakness or paralysis of muscles below the knee that are involved in lifting the front of the foot. The forefoot drags when walking.
Cavovarus foot
Cavovarus foot is the most common foot deformation seen in CMT patients. It is characterized by a high cavus or arch, an inward turned (varus) heel, and toes that are contracted like a claw and called clawed toes.
Because some muscles that stabilize the foot are weaker than they are supposed to be, the foot muscles as a whole do not pull in balance. This results in an abnormal foot shape.
One muscle affected in CMT patients is the peroneus brevis muscle that is located on the outside and above the heel, the function of which is to stabilize the ankle. Another is the tibialis anterior muscle, a long narrow muscle at the front side of the shinbone that works to lift the ankle. These two muscles — and some small muscles — generally keep the toes straight but become weak in CMT patients. Other muscles, such as the one required for pointing the foot and toes, can remain strong, causing an imbalance.
Surgeries to correct foot deformations
Foot drop
Some surgeons recommend an ankle fusion where the bones in the ankle are fused into one piece, but most patients benefit more from a brace that supports the foot and leg.
Cavovarus foot
In mild cases with a slight imbalance, surgery is not necessary, and physiotherapy can help to strengthen weak muscles, correct the foot position and slow further deformation. High-top shoes and simple braces also help to support the foot.
In more advanced cases, surgery is the only option to correct the deformation and to enable painless walking. The aim of surgery is to balance muscle pulls, to preserve motion, and to flatten the foot to the ground. During surgery, a muscle that is involved in pointing the foot (the peroneus longus muscle) is transferred to the weak peroneus brevis muscle to stabilize the ankle. The posterior tibial muscle, usually located at the back of the leg, is also moved to help to lift the ankle. Ligaments and muscles are loosened to relax the bottom of the foot, and to release pressure from the toes so that the foot can flatten and the toes no longer claw Some tendons may also be transferred.
The foot requires rest for a few weeks after surgery, and it may take up to a year before the foot can be used to walk normally and without restrictions. After this time, results are usually very satisfactory.
Another type of surgery, one performed in the past but uncommon today, is the fusion of joints to prevent left-right movements and ankle tilts. This provides stability but also makes the foot rigid and walking difficult. The procedure can lead to arthritis in ankle joints later in life.
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