Charcot-Marie-Tooth (CMT) disease is a condition that commonly produces a high arched foot (Figure 1). It was described independently by Jean-Martin Charcot, Pierre Marie, and Howard Henry Tooth in 1886. It is also known as Hereditary Sensorimotor Neuropathy (HSMN), or Peroneal Muscular Atrophy. CMT is associated with weakness of the lower extremity muscles. It is caused by abnormalities in nerve conduction (too much myelin in the nerve sheath). CMT is usually inherited and therefore a positive family history is common – although up to a quarter of the cases can arise spontaneously. The foot deformities and symptoms related to CMT are typically progressive – they tend to worsen over time. However, the rate at which they worsen can vary greatly. Some patients are able to function at a high level throughout their lives (mild cases) whereas some develop debilitating foot (and sometimes hand) symptoms relatively early (severe cases).
Figure 1: Typical Charcot-Marie-Tooth Foot Deformity
The clinical manifestations of CMT can vary widely. The most common complains are those associated with high arched feet, loose ankles, and muscle weakness. These include a propensity to suffer:
- Recurrent ankle sprains
- Ankle instability
- Jones fractures of the 5th Metatarsal
- Peroneal tendonitis
- Drop foot (in more severe cases), and
- Ankle arthritis (late sequelae)
Physical examination will demonstrate a high arched foot pattern with the heel curved inward. Sometimes the inward curving of the heel can be corrected if the outside aspect of the foot is “propped up” (Coleman block test) and the soft-tissues are still supple. This occurs because one of the main components of the deformity is the downward position of bone that the big toe is attached to (the 1st Metatarsal). In CMT this bone has a tendency to migrate into this position due to muscle imbalance (the peroneus longus is typically much stronger than the tibialis anterior). This in turn serves as a “kickstand” to tip the heel to the inside (varus position).
It is not uncommon to have noticeable claw toe deformities (including the big toe) in patients with CMT.
Muscle testing may reveal subtle (or not so subtle) muscle weakness. Commonly the ability to bring the foot inwards (inversion) is stronger that the ability to move the foot outward (eversion). Also the ability to push the foot down (plantar flexion) is stronger than the ability to lift the foot up (dorsiflexion).
There is a classic set of muscle imbalances that leads to the stereotypical Charcot-Marie-Tooth foot deformities. These four muscle imbalances include:
- The Peroneus Brevis is weaker than the Tibialis Posterior muscle. This leads to a greater inward pull of the foot (inversion).
- The Tibialis anterior muscle is weaker than the Peroneus Longus muscle. This leads to the first metatarsal (the bone that the big toe attaches to) pointing downward and serving as a “kickstand” to drive the heel inward.
- The intrinsic foot muscles (the small muscle in the sole of the foot that help move the toes) are weaker than the extrinsic muscles (the larger muscles in the lower leg that cross the ankle joint and help move the toes). This muscle imbalance leads to clawing of the toes, including clawing of the great toe.
- The Anterior compartment muscles (the muscles at the front of the shin bone (tibia) are weaker than the calf muscles. This in its most pronounced form can lead to a drop foot.
Sensation can be affected in more severe cases but generally it is not a major component of CMT.
Weight-bearing x-rays of the foot and ankle will show evidence of a high arched foot pattern. Classically the heel bone will have an elevated angle to the ground and the 1st metatarsal bone (the bone the big toe is attached to) will be pointed down (Figure 2).
Figure 2: Typical Charot-Marie-Tooth Foot X-rays
Treatment of CMT has focused on addressing the symptoms created by the deformity. To date no treatment has been shown to address the underlying nerve dysfunction. However, significant symptomatic improvement can be achieved with a variety of non-operative and in some cases operative interventions.
Non-operative focuses on controlling/correcting the foot deformities, maintaining muscles strength, preventing ankle sprains, and controlling pain symptoms. Treatments often include:
- Ankle Lacer: This can be an effective device for improving ankle symptoms in patients with mild to moderate foot deformities.
- Ankle-Foot-Orthotic (AFO): An AFO can be used to improve symptoms in patients with more pronounced deformities or more extensive hindfoot arthritis.
- Orthotic insert: An orthotic insert with a recessed first metatarsal head area and/or an elevated lateral forefoot can help to reposition the hindfoot in a more neutral position in patients who still have adequate flexibility in their hindfoot.
- Physical Therapy: Physical Therapy to improve muscle strength and proprioception can help protect against future ankle sprains and serve to improve overall function.
- Anti-inflammatory medications (NSAIDs): For patients with tendnitis or arthritis symptoms NSAIDs can help to decrease their symptoms and improve their overall function, although it typically has no effect on the underlying condition or deformity.
Operative treatment is often performed to help correct the resulting foot deformity. However, it is important to appreciate that the foot deformities occur as a result of the inherent muscle imbalances that affect the foot. Therefore it is often necessary to transfer tendons (and their associated muscles) to help rebalance the foot. Surgery for Charcot-Marie-Tooth foot deformities must be individualized for each patient based on the extent of their deformity, the resulting pathology, the existing muscle function, and the age of the patient. Often a combination of surgical procedures are required – usually performed at the same surgery. Common surgical procedures used to address Charcot-Marie-Tooth foot deformities include:
- Peroneus Longus to Peroneus Brevis tendon transfer
- Release of the tight ligaments on the inside of the foot (talonavicular joint capsule release)
- Release of the tight plantar fascia
- Lengthening of the Achilles Tendon
- Repositioning the 1st metatarsal bone (dorsiflexing 1st metatarsal osteotomy)
- Cutting the heel bone and shifting it to the outside (Lateralizing calcaneal osteotomy)
- Claw toe correction
- Jones procedure to correct a clawed hallux (clawed big toe)
- Peroneal tendon debridement or repair
- Lateral ankle ligament stabilization
- Drop foot correction (Tibialis posterior transfer to the dorsal foot)
- Ankle debridement
- Ankle fusion
Edited November 19th, 2009