Cavovarus Correction in Charcot-Marie-Tooth Disease

Pitfalls

Charcot-Marie-Tooth (CMT) disease includes a wide spectrum of hereditary motor and sensory neuropathies. These diseases are often progressive, which can compromise the long-term results of a surgical reconstruction.
The feet of older adolescents and adults usually require simultaneous osteotomies, tendon transfers, and soft-tissue balancing. Young adolescents and children may benefit from soft-tissue procedures alone, especially in the early stages of the disease.

Indications

Chronic pain or deformity that interferes with activities of daily living
Failure of conservative measures, including bracing, shoe modification, and physical therapy
A relatively flexible deformity without arthritic changes in the involved joints

Indications Controversies

Early surgical intervention may prevent the progression of deformity and minimize impairment. There are no established guidelines, however, that address the appropriate age for surgery. Each case should be dealt with on an individual basis.
In children <14 years of age, it is often preferable to take an incremental approach to surgery, rather than correcting all deformities at once. This chapter examines the surgical options most appropriate for the older adolescents and adults with CMT disease.
Patients with mild to moderate involvement can often be treated successfully with nonoperative care. Cushioned shoes for shock absorption, soft inserts for metatarsalgia, high-topped shoes and lace-up ankle braces for ankle instability, and bracing for foot drop can help avoid surgery. Physical therapy for range of motion, strength, and proprioception can also be helpful.
The overarching goals of surgery are preservation of joint motion, creation of a plantigrade foot, and balance of muscle forces.

Examination/Imaging

Physical Examination

CMT disease can also affect the hips (dysplasia), spine (scoliosis), and upper extremities ( Fig. 34.1 ). Weakness of the first dorsal interosseous muscle in the hand is one of the earliest signs of upper extremity involvement.
A complete orthopedic examination of the lower extremities is required. There is often atrophy of the anterior and lateral compartments of the leg.
Examine the foot from all sides while the patient is standing ( Fig. 34.2 ).
- Closely examine the lateral foot to evaluate the apex of the sagittal deformity ( Fig. 34.3 ).
- Document the calluses on the plantar aspect of the foot ( Fig. 34.4 ).
- Determine if claw toes are passively correctable ( Fig. 34.5 ).
A Coleman block test (Paulos et al., 1980) can be helpful in sorting out forefoot-driven heel varus.
- When the patient stands with a block beneath the lateral border of the foot, the medial column is unsupported and the first metatarsal head drops off the side of the block ( Fig. 34.6A ).
- If the subtalar joint is flexible and there is no fixed varus deformity of the heel, the hindfoot will no longer be in varus when viewed from behind (see Fig. 34.6B ).
Document motor strength, including knee flexion and extension. Measure sensibility.
- Typically, the peroneus longus, long toe extensors, and posterior compartment muscles will maintain strength long after the foot intrinsics, peroneus brevis, and tibialis anterior become weak.
- Evaluate the imbalance between muscle agonists and antagonists (i.e., peroneus longus and tibialis anterior; posterior tibial and peroneus brevis; toe intrinsic flexors and extrinsic extensors).
Overpull of the posterior tibial tendon should be carefully evaluated and often has to be corrected at the time of surgery.
Observe the patient’s gait. A foot drop is often effectively treated with an ankle foot orthosis. The addition of an anterior tibial shelf often provides better balance to the patient. Surgery may still be required if a nonplantigrade foot deformity precludes effective bracing.
A dynamic electromyogram may be particularly helpful when evaluating potential tendon transfers preoperatively.
Multiple incisions are frequently required, which can create problems with skin healing. In patients with previous surgery, make sure that both the dorsalis pedis and posterior tibial pulses are present. If not palpable, a Doppler evaluation is indicated.
Spasticity, asymmetric reflexes, or marked hyperreflexia is not typical of CMT disease. If these symptoms are noted, magnetic resonance imaging of the spine should be obtained.
A neurologic consultation with electromyography/nerve conduction study and genetic testing (Athena Diagnostics, Worcester, MA, USA) is often appropriate. What is often considered idiopathic cavovarus is probably a form of CMT disease.
Document ankle laxity. Although patients often complain of instability during gait, objective ankle laxity is not often present. Extreme varus laxity can masquerade as normal subtalar motion.
Is the foot flexible? During the non–weight-bearing examination, the subtalar, transverse tarsal, and tarsal–metatarsal joints should be reasonably flexible. A fixed deformity will most commonly require a triple arthrodesis, which is not appropriate in a foot that has some preservation of motion in the hindfoot.
Evaluate gastrocnemius and soleus tightness. Typically, both the gastrocnemius and the soleus will have to be surgically lengthened at the level of the Achilles tendon.

Imaging

Standing anteroposterior ( Fig. 34.7A ) and lateral (see Fig. 34.7B ) radiographs of the foot and ankle should be carefully examined to evaluate arthritic changes and determine the need for corrective osteotomies. Standing anteroposterior and lateral images of the foot should be repeated using a Coleman block, which presents a more accurate view of the foot and its true deformity.
The calcaneal pitch angle (normal <30°) and the talus–first metatarsal angle (Meary line; normal = 0°) are particularly useful in preoperative planning. If the calcaneal pitch corrects with the Coleman block in place, a corrective osteotomy of the heel may not be needed.
On the lateral standing radiograph, determine if the apex of the cavus is at the metatarsal–cuneiform joint or the midfoot. The deformity should be surgically corrected through its apex.
A three-dimensional computed tomography reconstruction can be helpful in the assessment of complex deformities and revision surgery ( Fig. 34.8 ).

Treatment Options

Many surgical options are used to address the wide array of deformity and motor imbalance that occurs. This chapter presents one of the most common operative approaches, which includes Achilles lengthening, triplane calcaneal osteotomy, Steindler release of the plantar fascia, peroneus longus-to-peroneus brevis transfer, closing wedge metatarsal or midfoot (Cole) osteotomy, correction of claw toes, interphalangeal fusion of the great toe, and extensor tendon transfers to the metatarsal necks. While often performed at the same time, forefoot reconstruction can be performed during a separate operative procedure.
With the hindfoot held in neutral, evaluate forefoot cavus (valgus) caused by flexion of the medial metatarsals from overpull of the peroneus longus ( Fig. 34.9 ). Commonly, only the first metatarsal is involved, although the second and third may be as well. Involvement of the fourth and fifth metatarsals that requires operative correction is rare. If a plantar-flexed metatarsal is not corrected, the surgical outcome will be poor.