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Cavus Foot Deformity in Children

Schwend, Richard M. MD; Drennan, James C. MD

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Journal of the American Academy of Orthopaedic Surgeons: May 2003 - Volume 11 - Issue 3 - p 201-211
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Abstract

Cavus foot is an abnormal elevation of the medial arch in weight bearing. It results from the development of forefoot equinus relative to the position of the hindfoot. The typical cavus foot also has a component of forefoot pronation, which initially involves first metatarsal plantarflexion relative to the hindfoot. The terms equinus and calcaneus describe the position of the hindfoot. Cavovarus and calcaneocavus deformities are the most common types of cavus foot.

Neurologic assessment is critical in the evaluation of patients with cavus foot because typically there is an underlying spinal cord or neuromuscular etiology. Although the number of neurologic conditions that may lead to cavus foot is extensive, the common factor is muscle imbalance that disturbs the synergy between the intrinsic and extrinsic muscles. Many descriptions of the pathomechanics and treatment of the cavovarus foot have been reported, especially in patients with progressive Charcot-Marie-Tooth (CMT) disease. This disorder combines the typical plantarflexed first ray with tight plantar fascia, atrophy of the intrinsic muscles, and functional paresis of the peroneal and tibialis anterior muscles. However, the natural history and management of cavus foot deformities resulting from relatively nonprogressive conditions, such as poliomyelitis, differ substantially from those of cavus foot deformities resulting from progressive diseases. Management options depend in part on the flexibility of the deformity. Independent of etiology, however, most cavus deformities can be treated successfully without arthrodesis.

Anatomy and Biomechanics

The medial and central portions of the plantar fascia arise from the calcaneal tuberosity at the medial half of the calcaneus and extend via slips to the transverse metatarsal ligaments that attach to the metatarsal heads. The slips continue distally to the base of the toes on both sides of the flexor tendon sheaths.1,2 The fascia covers and is attached to the intrinsic muscles of the foot and protects the plantar neurovascular structures. More than any other structure, the plantar fascia stabilizes the arch and prevents the calcaneus from everting, especially when the fascia is tightened at push-off. The windlass effect is demonstrated at toe-off, when passive dorsiflexion of the metatarsophalangeal joints places the plantar fascia under tension and both stabilizes and elevates the medial arch (Fig. 1).

Figure 1 A,
Figure 1 A,:
Normal foot with normal height of the arch (double arrow) during standing. B, Cavus foot with increased height of the arch (double arrow) as a result of metatarsophalangeal joint hyperextension (curved arrow), such as occurs at toe-off and as seen in the windlass effect of the plantar fascia. (Adapted with permission from Sabir M, Lyttle D: Pathogenesis of pes cavus in Charcot-Marie-Tooth disease. Clin Orthop 1983;175:173-178.)

The arch changes shape during the different segments of the stance phase of the walking and running cycles. Running requires the foot to accept 2.5 times the body weight at heel strike. Eccentric contraction of the quadriceps muscle absorbs much of the initial impact. At heel strike, there is slight supination of the forefoot and inversion of the heel. In midstance, the subtalar joint assumes a valgus position, resulting in unlocking of the midtarsal joints. This increased flexibility results in foot pronation and internal tibial rotation and allows partial stress distribution. At the end of the stance phase, there is metatarsophalangeal dorsiflexion and locking of the midtarsal joints. The elevated arch becomes a rigid lever. The posterior leg muscles permit push-off and provide energy for forward propulsion. With a cavovarus deformity, the foot remains locked in hindfoot inversion and forefoot supination throughout the stance phase, causing less stress dissipation. This increased stress and lack of shock absorption are greatly magnified in running.

Etiology and Differential Diagnosis

Cavus deformity rarely presents in the young child (<3 years) but may develop as the child grows.2 Generally, the etiology can be attributed to the brain, spinal cord, or peripheral nerves, or to muscular or structural problems of the foot. Two thirds of adults with a symptomatic cavus foot have an underlying neurologic condition, most commonly CMT disease.3

Central Nervous System

Patients with cerebral palsy, particularly hemiplegia, may develop an equinovarus foot with a spastic tibialis posterior muscle that may require lengthening at surgery for the deformity. Occasionally, a calcaneocavus deformity may occur in children with spastic diplegia after an excessively lengthened or released heel cord. Children with Friedreich's ataxia may first be diagnosed by the occurrence of cavus feet early in the second decade. The full clinical triad includes ataxia, plantar Babinski response, and areflexia.4 Friedreich's ataxia is autosomal recessive and is caused by an abnormal gene on chromosome 9.

Spinal Abnormalities

Static or progressive cavus foot may be associated with developmental spinal deformities (Fig. 2), although when recognized and treated early, the development of a spinal deformity may be arrested. Myelodysplasia may cause either unilateral or bilateral cavus foot. Calcaneocavus may be seen in children with diastematomyelia or myelodysplasia, especially when the triceps surae muscle is weak and the tibialis anterior muscle is normal. Syringomyelia or split-cord malformations may be associated with a unilateral cavus foot deformity.5 Patients with poliomyelitis may present with calcaneocavus caused by weakness of the triceps surae muscle, with the intrinsic muscles typically spared. Other etiologies include spinal cord tumors, intrathecal lipoma, tethered cord syndrome, and Guillain-Barré syndrome.

Figure 2 A,
Figure 2 A,:
Posteroanterior view of the feet of an 8-year-old girl with scoliosis, a mild, flexible right cavus foot deformity, and a smaller right calf. B, Sagittal T1-weighted MRI scan shows a septated cervical syrinx (arrow) that later underwent decompression.

Peripheral Nerves

Hereditary sensorimotor neuropathy (HSMN) is a common cause of cavovarus foot in children and adults but generally is not diagnosed before age 10 years. Classification is based on motor nerve conduction velocity studies. Types I, II, and III typically are seen in children. HSMN I, the hypertrophic form of CMT disease, is the most common and has spotty peripheral nerve myelin degeneration and decreased motor nerve conduction. The most common form is HSMN IA, caused by duplication of the gene for peripheral myelin protein 22 (PMP-22) on chromosome region 17p11.2. The X-linked form of CMT disease, the second most common form of the disease, is caused by a mutation in the connexin 32 gene.6 HSMN II, the neuronal form of CMT disease, has an intact myelin sheath with wallerian axonal degeneration, which results in mildly abnormal sensory and motor nerve conduction velocities. HSMN types I and II are both autosomal dominant with variable expression. HSMN III, Dejerine-Sottas disease, is autosomal recessive; it has a marked decrease in motor conduction because of demyelination of the peripheral nerves. This condition often presents in infancy; it clinically resembles CMT disease but is more severe and has a worse prognosis. There are associated palpably enlarged peripheral nerves, kyphoscoliosis, ataxia, nystagmus, and myopic pupils. Children with HSMN III may stop walking by maturity. Other peripheral nerve etiologies include polyneuritis, small muscular atrophy, atypical polyneuritis, and neuromuscular choristoma.7

Other Causes

Isolated injuries to nerves, muscles, and tendons can result in cavus foot and may provide insight into how specific muscle imbalance can cause a foot deformity. Cavus deformity may occur after an injection injury to the sciatic nerve. The lateral division of the sciatic nerve is more susceptible than the medial division to injury, which may result in weakness of the peroneal and tibialis anterior muscles. Clawfoot has been described after tibial shaft fracture; the risk of this developing may be lessened by leaving the foot plantarflexed in the cast.8 The cavus deformity is caused by fibrous contracture of the deep posterior compartment resulting from vascular damage, tissue swelling with compartment syndrome, severe muscle laceration, or a combination of these mechanisms. Cavovarus was reported in two children with laceration of the peroneus longus tendon with scarring of the peroneus brevis tendon.9 The involved feet lost eversion strength, thus allowing the tibialis posterior muscle to invert the hindfoot and plantarflex the forefoot. Cavus has been associated with clubfoot or residual clubfoot deformity in 22% of children.10 In clubfoot surgery, placing the navicular in a dorsally subluxated position can lead to postoperative residual cavus foot deformity.11 Despite the diagnostic tools currently available, however, an underlying etiology commonly is not uncovered and the cause is labeled idiopathic.12

Pathomechanics

The pathomechanics of cavus foot, well described for CMT disease, may not apply to cavus foot resulting from nonprogressive causes. Duchenne first stated that cavus foot was caused by weakness or paralysis of the intrinsic muscles of the foot.13 Biopsy specimens of tibialis anterior, peroneus longus, and abductor digiti quinti muscles have shown marked atrophy with collagen replacement. Denervation leads both to an increase in the connective tissue within the thickened epimysium, perimysium, and endomysium of the nerve as well as to fibrillar material deposition into the muscle.14 In the foot with weakened or paralyzed intrinsic muscles, there is overpull by the remaining strong extrinsic toe muscles and the tibialis posterior muscle.

Clinical muscle strength evaluation also has been studied most extensively in CMT disease.15 There is forefoot equinus with weakness of the tibialis anterior, peroneus brevis, and intrinsic muscles. Dorsiflexion of the metatarsophalangeal joint and flexion of the interphalangeal joints of the lesser toes indicates weakness of the lumbrical, dorsal, and interossei volares muscles. The strength of the flexor digitorum longus and flexor hallucis longus muscles is normal. The calcaneus is in a neutral, sagittal-plane position; thus, there is no hindfoot equinus contracture. Although the peroneus brevis muscle is markedly weak, the peroneus longus usually retains its function. Its strength may be better preserved because its relative strength is normally about twice that of the brevis, and thus it has more reserve before showing clinical weakness. In later stages, patients exhibit a so-called stork leg appearance resulting from atrophy of all calf muscles and the distal third of the thigh muscles.

Price et al16 used computed tomography of the legs and feet of 26 patients with CMT disease to show bilateral and symmetric muscle involvement, with early, severe atrophy of the intrinsic muscles of the foot. The interosseous and lumbrical muscles had the highest levels of deterioration, whereas the abductor hallucis was the most frequently spared of the intrinsic muscles. The extrinsic muscles had less involvement, although the peroneus brevis, peroneus longus, and flexor hallucis longus were more often affected than the other leg muscles. Tynan et al12 compared magnetic resonance imaging (MRI) studies of normal patients with those of patients with forefoot equinus from CMT disease, Friedreich's ataxia, cerebral palsy, postpoliomyelitis syndrome, nerve trauma, spinal cord tethering, and idiopathic etiology. In most affected patients, the peroneal compartment was large relative to the anterior compartment, suggesting dominance of the peroneus longus muscle compared with the tibialis anterior.

These studies suggest that, in cavus foot resulting from CMT disease, early degeneration of the intrinsic muscles leads to atrophy and shortening. With the lumbrical muscles not acting to stabilize the metatarsophalangeal joints, the unopposed extensor digitorum longus hyperextends the unstable lesser toe metatarsophalangeal joints, while the functionally unopposed flexor digitorum longus and flexor digitorum brevis flex the phalanges. This causes exaggeration of the windlass effect (Fig. 1).14 Forefoot equinus is magnified by plantarflexion of the metatarsal heads. Plantar fascial shortening, eccentric hallucal muscle activity, and the shorter and more mobile lever arm of the first ray lead to first metatarsal plantarflexion and pronation compared with supination of the lesser rays. Eventually, the flexible plantarflexed first ray becomes fixed in this position. Hindfoot varus is secondary to the forefoot deformity, shortened plantar fascia, and weight bearing on the lateral forefoot. The Achilles tendon becomes a secondary inverter. The tibialis posterior muscle has an enhanced mechanical advantage over the peroneal muscles, which must work against an inverted calcaneus. With heel inversion, the lateral forefoot must supinate, and the peroneus longus muscle further depresses and pronates the first ray to permit the foot to assume a tripod position, in which the lateral and medial columns and heel remain in contact with the ground.

In nonprogressive conditions such as cerebral palsy (typically hemiplegia), spasticity of the tibialis posterior muscle inverts the hindfoot, and the patient bears weight over the lateral margin of the foot. Forefoot equinus also may be secondary to a leg-length discrepancy. Laceration of the peroneus longus tendon can allow overpull of the tibialis anterior and, secondarily, the tibialis posterior muscles, as well as cause progressive hind foot inversion, tightening of the plantar fascia, and rigidity of the hindfoot varus. Loss of even one essential tendon can functionally imbalance the foot over time and lead to structural deformity. In some patients with poliomyelitis and myelodysplasia, and occasionally in some with diastematomyelia, the triceps surae muscle function is weak or absent while the tibialis anterior muscle does function. As a result, there is a shortened, weak posterior lever arm, compromised power of plantarflexion, and a secondary calcaneocavus deformity.

Natural History

Because of the multiple etiologies and varying severity of cavus foot, the natural history may not be predictable. The natural history has most commonly been described for HSMN, which is a group of progressive diseases; thus, expression and prognosis vary depending on the pattern of inheritance. Family members typically show similar patterns of progression, with intrinsic muscles involved initially, then the anterior compartment, the peroneal muscles, and finally the posterior calf muscles.14 Patients with types I and III HSMN tend to develop a cavovarus deformity, whereas those with type II typically develop a calcaneocavus deformity.15 When untreated, the increasing muscle imbalance converts the flexible and correctable foot into one with fixed clawing, forefoot equinus, structural bony changes, restricted tarsal motion, and ultimately a rigid foot with pronounced radiographic changes, dislocated toes, and keratosis.14 When the condition is severe, participation in athletics is difficult, and surgical treatment often becomes necessary.15 Concomitant hip dysplasia and subluxation, either silent or symptomatic, may be increasingly evident.17

Better long-term results can be achieved in the nonprogressive types of cavus foot.18 Runners with a cavus foot configuration can have additional problems, including metatarsalgia, plantar fasciitis, medial longitudinal arch pain, and iliotibial band syndrome.19 Calcaneocavus typically is seen in patients with a lower level of function and activity.20

Evaluation

Clinical

Because the underlying etiology may affect prognosis and outcome, determination, when possible, is important. Birth history, developmental delay, or family history of CMT, as well as hand, hip, foot, bowel, or bladder symptoms, should be noted. Symptoms such as ankle instability (caused by a combination of weakness and malalignment), pain under the metatarsal heads, or sensory changes may be present.2

The physical examination should include the spine, looking for a deformity, hairy patch, sacral dimple, or mass. In children, the presence of a structural spinal condition should be excluded. CMT disease is likely in the patient with toe clawing, cavus foot, thin legs, poor balance, unsteady gait, and intrinsic hand atrophy.3 Occasionally, painful hip dysplasia may be the initial presenting problem in a patient with CMT disease.

Japas21 suggested a series of elements that should be systematically evaluated when assessing a patient with a cavus foot (Table 1). Coleman and Chesnut22 described the cavovarus test, commonly termed the Coleman block test, to evaluate the pronated forefoot. It relies on the tripod effect (Fig. 3), assumes that the initial deformity is in the forefoot, and determines whether the hindfoot deformity is flexible or fixed.23 The examiner places the lateral forefoot on a wooden block with the heel and lateral border on the block, while the first through third metatarsals are suspended off the block (Fig. 4, A and B). The patient is asked to force the first metatarsal head into bearing weight, and the flexibility of the hindfoot is assessed.22 When the hindfoot is flexible, treatment is limited to the forefoot. If the hindfoot deformity is rigid, then surgical correction involves both the forefoot and hindfoot. Examination of the patient lying prone with the heel in a neutral position will show the hindfoot flexibility, plantarflexion of the first ray, and the presence of global forefoot equinus (Fig. 4, C).24

Table 1
Table 1:
Clinical Evaluation of a Cavus Foot
Figure 3 A,
Figure 3 A,:
Posterior and lateral views of a cavus foot in non-weight-bearing position. The long axes of the tibia and the calcaneus are parallel and the first metatarsal is pronated. Dots indicate the three major weight-bearing plantar areas (heel and first and fifth metatarsals). B, Posterior and lateral views of a cavus foot in weight-bearing position. The long axes of the tibia and the calcaneus are not parallel. With weight-bearing, a rigid equinus forefoot deformity forces the flexible hindfoot into varus. This is the tripod effect. (Adapted with permission from Paulos L, Coleman SS, Samuelson KM: Pes cavovarus: Review of a surgical approach using selective soft-tissue procedures. J Bone Joint Surg Am 1980;62:942-953.)
Figure 4
Figure 4:
The cavovarus (Coleman) block test demonstrated in a 12-year-old girl with a flexible left cavovarus deformity. A, Weight bearing causes inversion of the calcaneus. B, With the lateral forefoot and the heel on a wooden block, the heel assumes a neutral position. Therefore, the deformity is limited to the forefoot. C, Examination with the patient lying prone with the heel in a neutral position. Plantarflexion of the first ray and global forefoot equinus are present.

The apex of the cavus should determine the best location for corrective osteotomy and can be confirmed on a lateral radiograph. There may be either no toe deformities2 or clawed hallucal and lesser toe deformities resulting from functional imbalance between the dissociated strong extensor and flexor digitorum longus muscles and the weak intrinsic muscles.15 The rigidity of the deformity will determine the extent to which osteotomies will be required for full correction. The intrinsic muscles are atrophied, often before the patient has noticeable symptoms, whereas calf muscle atrophy develops later.14 Ankle and knee reflexes typically are absent in the hypertrophic form of CMT disease (CMT IA). Patients with severe symptoms may walk with a socalled marionette gait, that is, with pelvic elevation and pelvic shift on the swing side, which are proximal compensations for the foot drop.14 The patient with the neuronal form of CMT disease (CMT IIA) also may walk with a peg-leg gait as a result of a calcaneocavus foot with poor push-off. If hip dysplasia or subluxation is present, a Trendelenburg gait may be observed. Sensory changes include loss of vibration and position sense and vasomotor signs such as flushing, cyanosis, and marbling skin changes.

Radiographic

In addition to anteroposterior and lateral standing foot views, radiographs of the spine should be made to evaluate for scoliosis, spinal dysraphism, or diastematomyelia. In patients with CMT disease, a standing anteroposterior pelvic radiograph also should be made to evaluate for asymptomatic acetabular dysplasia. Coleman and Chesnut22 recommended standing anteroposterior and lateral foot radiographs on the block to document the results of the clinical test. In conditions with forefoot equinus, such as CMT disease, the lateral weight-bearing radiograph shows the calcaneus in neutral dorsiflexion/plantarflexion and the medial forefoot in plantarflexion. In a foot with isolated forefoot equinus, the calcaneus retains a normal relation to the talus. The apex of the deformity can vary. Usually the equinus deformity is located in the midfoot at the transverse tarsal articulation or at the naviculocuneiform joint but does not involve the calcaneus.

Measurement of several radiographic angles is helpful in evaluating a lateral weight-bearing radiograph (Fig. 5). Small differences resulting from radiographic projection errors should not influence treatment decisions. Meary's angle is formed by the two lines connecting the long axis of the talus with the long axis of the first metatarsal. It is usually 0° to 5° in the normal foot but averages 18° in patients with CMT disease.3 The calcaneal pitch angle is measured between a line along the undersurface of the calcaneus and the floor. It is normally about 30° and differentiates a calcaneocavus from a forefoot equinus deformity.4 A calcaneal pitch ≤30° indicates forefoot equinus rather than calcaneocavus. In calcaneocavus, there is marked dorsiflexion of the calcaneus, a normal medial forefoot, and a calcaneal pitch angle ≥30°. Hibbs' angle is formed between a line through the calcaneus and a line through the axis of the first metatarsal.25 It is normally <45° but near 90° in the cavus foot. The weight-bearing tibioplantar angle is measured between the long axis of the tibia and a line from the plantar surface of the calcaneus to the metatarsal heads. It is usually about 90° and is useful when considering a midfoot osteotomy.25

Figure 5
Figure 5:
Radiographic angles for evaluating lateral weight-bearing radiographs. A = Meary's angle. B = Calcaneal pitch angle. C = Hibbs' angle. D = Weight-bearing tibioplantar angle. (Adapted with permission from Alexander IJ, Johnson KA: Assessment and management of pes cavus in Charcot-Marie-Tooth disease. Clin Orthop 1989;246:273-281.)

Disease-Specific

Patients with HSMN may not have obvious clinical findings aside from cavus foot; therefore, a neurologic evaluation including motor nerve conduction and electromyographic studies should be done to establish the diagnosis.25 In HMSN I, there is marked slowing of motor nerve conduction velocities and inconsistent slowing of sensory nerve conduction velocities.3 In type II, there is nearly normal motor nerve conduction but electromyographic evidence of denervation. In type III, there is usually an extreme slowing of motor nerve conduction. Sural nerve biopsy can show demyelinization in HMSN I and III but is rarely needed to make the diagnosis.4 Spinal MRI is recommended in patients with unilateral cavus foot deformity5,12 and is especially useful for progressive deformities in children. Because many mutations in different genes have been identified in HSMN, mutation screening with radioactive singlestranded conformational polymorphism increasingly is being used.

Management

To provide the best chance for functional recovery or prevent deterioration in patients with conditions such as a tethered spinal cord, the first step is identification of a treatable underlying cause. The family will need counseling about the natural history of the deformity, and genetic counseling is mandatory for patients with HSMN. Surgical management is indicated only when the deformity causes functional problems or the patient is asymptomatic and progressive deformity has been observed or can be expected. Progressive neuromuscular conditions worsen and often require repeated surgeries throughout a patient's life. However, it is important whenever possible to avoid a triple arthrodesis in these patients with impaired sensation.

Cavus foot deformity caused by nonprogressive conditions with intact sensation in the foot is more predictable and has a better long-term prognosis. Deformities caused by a tethered spinal cord or lipomeningocele have a less predictable outcome because of varying degrees of sensory involvement and possible changing neurologic involvement. If bony fusion is required, it may be better tolerated and can provide long-term stability in patients with intact sensation.

Nonoperative Management

Nonoperative management is appropriate for the patient with a mild or nonprogressive deformity. In patients with fixed plantarflexion of the first metatarsal and a flexible hindfoot, a shoe insert that supports the lateral forefoot on posts and thus eliminates the hindfoot inversion may be useful.3 Dwyer2 thought that a bar under the metatarsal heads coupled with passive stretching of the plantar fascia was more effective than a shoe insert in controlling dynamic toe deformities. Unloading areas of excessive plantar pressure with foot orthotics and accommodating excessive tarsal or phalangeal height by extra-depth shoes may be needed for advanced cases.25 For runners, activity adjustment, pain management, stretching, quadriceps muscle strengthening, shoe modification, use of flexible orthotics, and replacement of worn jogging shoes may be useful.19 A runner with a cavovarus foot needs more time to recover from injury than does the average runner and may be at greater risk for associated overuse injuries.16

Surgical Management of Cavovarus

The goal of surgical management is to obtain a mobile plantigrade foot with correction of the cavus deformity. 26 The type of procedure depends on patient age, level of activity, nature of the deformity, and etiology of the condition. These procedures may involve the toe and require soft-tissue release, osteotomy, tendon transfers, or arthrodesis.26 Several principles are central to achieving a satisfactory result. (1) It is important to correct the underlying flexible or fixed deformity. Flexible deformities can be treated with soft-tissue procedures, whereas fixed deformities generally require an osteotomy. When the deformity is very severe or has associated arthritis, an arthrodesis may be necessary. Progressive deformities typically require both soft-tissue and bony procedures as well as the use of orthotics after correction. (2) Correction should be obtained at the location of the maximum deformity. (3) Motion should be preserved when possible, particularly in patients with impaired sensation. (4) The underlying muscle imbalance should be corrected by either changing the lever arm that influences the muscle function or by lengthening or transferring a tendon that is causing the deformity. Transferred tendons lose one strength grade, and a muscle should be transferred only when its strength is at least grade 4.27 Transferred tendons should be routed in as straight a line of pull as possible and be secured to bone rather than to tendon. Tendon transfer should not be done until any fixed deformities have been corrected. An early tendon transfer may cause iatrogenic problems if the patient has a changing neurologic status.

Toe Deformities

Flexible or passively correctible claw toes often resolve spontaneously after correction of the midfoot deformity. Dwyer2 thought that postoperative weight bearing on a better balanced foot would gradually flatten the forefoot and toes. Tendon transfers, such as the Girdlestone-Taylor transfer of the flexor digitorum longus muscle to the extensor hood, may be used for flexible deformities. Fixed deformities require dorsal metatarsophalangeal capsulotomies or resection arthroplasty. A modified Jones procedure uses a hallucal interphalangeal joint fusion combined with transfer of the extensor hallucis longus tendon to the first metatarsal neck. This removes the deforming effect of the extensor hallucis longus tendon on the metatarsophalangeal joint and counteracts the windlass effect on the medial arch by helping to dorsiflex the first metatarsal. Tynan and Klenerman28 reported that a modified Jones procedure is useful for relieving problems with clawing in 90% of patients but is less effective in management of metatarsalgia, with only 43% of patients improving. The peroneus longus is 4.6 times stronger than the extensor hallucis longus muscle, and transfer of the extensor hallucis longus to the neck of the first metatarsal may not provide sufficient strength to counteract the pull of the peroneus longus.29 A hallux flexus deformity may occur after a modified Jones procedure as a result of injury to the extensor hallucis brevis tendon.

Soft-Tissue Procedures

Cavus foot in patients with progressive conditions requires early, simple procedures. Subcutaneous plantar fascia release may benefit young children with minimal fixed deformity. A complete release in more involved cases includes release of the plantar fascia and abductor hallucis, flexor digitorum brevis, quadratus plantae, and abductor digiti quinti muscles, as well as occasional release of the flexor digitorum longus muscle.30 This complete release can be done through a lateral or medial incision. Bradley and Coleman20 added capsulotomies of the medial talonavicular and subtalar joints to the plantar release when they noted insufficient correction with the plantar release alone. Minimal cast correction should be attempted the day of the release. Postoperative serial casting is then used to slowly correct the cavus deformity. Superficial pressure sores on insensate feet may develop when excessive pressure is used with cast correction; double-thickness felt placed under the forefoot can help avoid this complication.

Plantar fascia release also is the initial procedure of choice in young children with nonprogressive minimal fixed deformity. There is extensive experience with plantar fascia release in children with poliomyelitis.18 Sherman and Westin31 reported an 83% success rate using plantar release alone through a lateral hindfoot incision for correction of cavus foot in patients with poliomyelitis or clubfoot deformity.

Forefoot Osteotomies

Because the results of soft-tissue procedures and tendon transfers are unpredictable with fixed forefoot deformity, bony correction frequently is needed. A closing-wedge osteotomy of a proximal rigid plantarflexed first metatarsal should be done at the time of the modified Jones procedure. Closing-wedge proximal metatarsal osteotomies require an associated plantar fascia release. In early CMT disease, the functional heel varus is mild and usually corrects after the forefoot osteotomy. Painful calluses generally indicate the need for a metatarsal or more proximal osteotomy. A shortened first metatarsal can be managed by a plantar opening-wedge osteotomy in the skeletally mature foot. If the major deformity is in the midfoot, a large correction through the base of the metatarsals may cause a bayonet-foot appearance; therefore, correction through the midfoot may provide a better result. Generally, forefoot osteotomies are not done as isolated procedures but are part of a more extensive correction of multiple deformities.

Midfoot Osteotomies

Fixed hindfoot varus cannot be corrected by a midfoot osteotomy. Midfoot osteotomies require a concomitant plantar fascia release to achieve correction. When done through the first cuneiform bone, correction of the plantarflexed medial column can be achieved at the apex of the deformity. Osteotomy across the entire midfoot, or a midfoot closing osteotomy, is reserved for children with significant deformity that might otherwise require a triple arthrodesis, and it should be deferred until the second decade to avoid excessive shortening resulting from growth-plate resection. Levitt et al32 reported a 30% rate of pseudarthrosis with a midfoot osteotomy. Further foot stiffness can occur from the procedure.30

A midfoot closing osteotomy is performed proximal to painful forefoot calluses and may be done through painful arthritic joints.25 A rocker-bottom deformity and abnormal weight distribution can occur if the osteotomy is performed too distally. Only 20° to 25° of tarsometatarsal correction can be obtained before a rocker-bottom deformity occurs in the midfoot.25 If the midfoot osteotomy cannot bring the plantar surface to within 10° of plantigrade as measured by the weight-bearing tibioplantar angle, a triple arthrodesis may be required.25 Muscle balancing still will be needed after the fusion because the foot will further deform if muscle balance is not restored.33 However, clinical muscle testing should be done before the triple arthrodesis because motor strength cannot reliably be graded accurately afterward. For progressive conditions, an ankle-foot orthosis is recommended for long-term use after the procedure.

Several types of midfoot osteotomy have been used in children older than 10 years. The Japas V tarsal osteotomy corrects the deformity at the most prominent point, avoids the midtarsal joints, is simple, has acceptable shortening, and readily heals.21 Wilcox and Weiner26 described the Akron midtarsal dome osteotomy for rigid cavus foot or for midfoot cavovarus deformity. Advantages include controlling the forefoot varus and valgus, controlling plantar flexion and dorsiflexion, obtaining correction at the apex of the deformity, and having minimal loss of motion with maximum bony contact for healing. The authors used this procedure frequently for children with residual cavus associated with resistant clubfoot deformities. Most of the poor results occurred in children younger than 8 years. Jahss25 reported a truncated-wedge midfoot osteotomy that corrects the foot but causes shortening. He recommended noting the location of any calluses because the osteotomy should be done proximal to them. For patients with poliomyelitis, Cole18 recommended dorsal closing-wedge resection through the midfoot.

Calcaneal Osteotomies

A calcaneal osteotomy should be included in the correction when the cavovarus block test indicates the presence of fixed hindfoot varus. The two most common calcaneal osteotomies are the lateral closingwedge and the lateral slide. Dwyer34 described the lateral closing-wedge osteotomy to correct heel varus. With subtalar inversion, the Achilles tendon becomes an active secondary inverter, and the forefoot is adducted and pulled closer to the heel as the patient walks on the lateral border of the foot. The medial forefoot has limited weight bearing, and the plantar fascia is not stretched. Dwyer recommended that a plantar release be performed with the calcaneal osteotomy. The Achilles tendon typically is not contracted and requires no treatment. Through a lateral approach, a lateral-based wedge is removed from the calcaneus35 (Fig. 6). The improved calcaneal weight bearing now can exert a corrective influence on the forefoot.

Figure 6
Figure 6:
Lateral closing-wedge calcaneal osteotomy. A, Calcaneus in varus with osteotomy cuts performed through a lateral approach. B, The wedge of bone is removed and the correction secured with a bone staple. (Adapted with permission from Gould N: Surgery in advanced Charcot-Marie-Tooth disease. Foot Ankle 1984;4:267-273.)

Dwyer2 also recommended an associated tarsometatarsal dorsal wedge osteotomy for a fixed deformity in this location. In this procedure, the calcaneal slide osteotomy is done through a lateral approach and involves a single cut with a large osteotome across the tuberosity. The heel segment is slid laterally, may be combined with a closing-wedge osteotomy, and is temporarily fixed with a threaded pin that can be removed 3 to 4 weeks postoperatively.

Tendon Transfers

Tendon transfers or lengthenings can be used when there is an identifiable muscle imbalance, especially in younger patients with a flexible deformity.27 Principles of tendon transfer should be followed, particularly in correcting the fixed deformity first and transferring only those tendons having adequate motor strength. In progressive conditions, transfer of the tibialis posterior tendon through the interosseous membrane to the lateral cuneiform augments dorsiflexion and may prevent recurrence of the heel varus.25 In HSMN II, the hindfoot may be in dorsiflexion, and the Achilles tendon should not be lengthened.34 In equinocavus associated with spastic hemiplegia, the triceps surae muscle may need surgical lengthening, and tendons, such as the tibialis posterior, may need to be transferred, either in whole or as a split transfer to the peroneus brevis tendon.

Arthrodesis

Triple arthrodesis (Fig. 7) is considered a salvage procedure for a fixed cavus deformity in adolescents for whom other types of treatment have failed.27 Because the foot growth spurt occurs early in puberty and is completed by bone age 12 years in girls and 14 years in boys, arthrodesis can be performed at these times without affecting further growth. The long-term results are better for nonprogressive motor conditions than for progressive diseases with sensory involvement. Alternative salvage techniques include talectomy and tarsal medullostomy.

Figure 7
Figure 7:
Lateral weight-bearing radiographs in a 37-year-old man with bilateral CMT disease who developed severe degenerative disease of the ankle joint and anterior subluxation of the talus in the ankle mortise after a triple arthrodesis of the right foot (A). The left foot (B), which was not operated on, has retained a normal configuration of the ankle. (Adapted with permission from Wetmore RS, Drennan JC: Longterm results of triple arthrodesis in Charcot-Marie-Tooth disease. J Bone Joint Surg Am 1989;71:417-422.)

The triple arthrodesis is done proximal to the apex of the cavus and may thus leave a residual midfoot deformity.26 If subtalar motion already is diminished in the severe deformity, a triple arthrodesis will not make the cavus foot significantly stiffer.27 Tendon transfers may be needed when the arthrodesis has healed. However, motor testing should be done before the fusion because preoperative examination gives the most accurate assessment of motor imbalance. In nonprogressive conditions such as cerebral palsy, tight plantar structures also may need to be released, and the Achilles tendon may need lengthening. Although runners have difficulty with a triple arthrodesis, low-demand patients can be expected to function adequately.

Surgical Treatment of Calcaneocavus

Many of the surgical procedures for calcaneocavus were developed for patients with poliomyelitis. Calcaneocavus should be treated aggressively because, with growth, it may progress rapidly as the tuber calcanei becomes horizontally aligned under the calcaneus. Transfer of the tibialis anterior and flexor digitorum longus tendons through the interosseous membrane to the calcaneus should be done in children younger than 8 years. A crescentic posterior displacement calcaneal osteotomy can be used in children aged 8 to 12 years with fixed deformities. For children older than 12 years, a one- or two-stage Elmslie triple arthrodesis may be necessary. In the two-stage arthrodesis, the forefoot is first fused to the hindfoot, as described for poliomyelitis.20 This is followed in 6 weeks by fusion of the subtalar joint, combined with tendon transfers. Regardless of age, tendon balancing procedures are necessary. With adequate surgical correction, the triceps surae muscle lever arm function improves, although not to normal.20 In patients with a calcaneocavus foot associated with poliomyelitis or clubfoot, Sherman and Westin31 advised against a plantar fascia release, which worked well for isolated cavus but not for calcaneus hindfoot deformity. When the dorsiflexor muscles are nonfunctional, all available functional muscles should be transferred to the calcaneus.27 To prevent a secondary dorsal bunion, the tibialis anterior muscle should be moved to the calcaneus whenever the peroneal muscles and flexor digitorum longus muscles are transferred to the calcaneus.

Outcome

Long-term follow-up studies are not yet available of patients with progressive diseases who have had soft-tissue procedures and osteotomies. The worst prognosis occurs in those with early disease onset. Although these procedures can delay the progression of the deformity and provide a less deformed foot, further surgery often is required.

Patients with progressive diseases who undergo triple arthrodesis have not done well in long-term studies. Twenty-two patients with CMT disease who underwent a triple arthrodesis for cavovarus were reviewed at intermediate (12-year) follow-up.36 The authors reported 32% good results by objective criteria, although 88% of patients had good or excellent clinical function and 86% were satisfied. A total of 24% of ankles and 62% of feet had evidence of degenerative joint disease. Approximately 60% of the feet were either undercorrected or overcorrected; the poorest results were related to technical problems at surgery. The authors' recommendation for the mature foot with CMT disease was to perform a triple arthrodesis to restore hindfoot stability, followed by a staged tibialis posterior tendon transfer to prevent later deformity.

Wetmore and Drennan33 evaluated 16 patients with CMT disease who underwent a total of 30 triple arthrodeses. The mean age at surgery was 15 years (range, 12 to 30 years); mean follow-up was 21 years. Fourteen of the 30 feet (47%) had poor results (undercorrected or overcorrected; unstable; required orthotics; had moderate or severe pain, calluses, limited function, or arthritis). Osteoarthritis was seen in 23 feet (77%), which the authors thought may have been accelerated by the arthrodesis (Fig. 7). They concluded that the longer the follow-up, the worse the clinical outcome. Triple arthrodesis is a salvage procedure for fixed osseous deformity if the patient is willing to use an orthosis. To decrease the possibility of overuse injuries, the patient should be aware of the limitations on future vocational and recreational activities. Most patients who underwent a hindfoot arthrodesis during their teenage years experienced significant foot problems by their midthirties.33

Outcomes are better in nonprogressive conditions with no sensory loss. Stable muscle balance can be achieved, and with retained normal proprioception, the articular surfaces are less likely to be abused. However, certain types of deformities, such as equinovarus, are less well tolerated.

Summary

A cavus foot deformity in a child may indicate an underlying neuromuscular condition. The most frequent type of cavus foot is cavovarus, which has an elevated arch, first ray plantarflexion, and, if longstanding, a fixed heel varus. Initially, the deformity is flexible, but if left untreated, the foot gradually develops a fixed bony deformity. Evaluation includes reviewing for other neurologic symptoms, assessment with a cavovarus block test, and performing a neurologic examination. Treatment principles are to create a plantigrade, mobile, pain-free, stable, motorbalanced foot. Surgical options include plantar fascia release for a flexible deformity, tendon transfers to restore muscle balance, and osteotomies for fixed deformities. Triple arthrodesis is acceptable for conditions with intact sensation, such as poliomyelitis, but should be used with caution in sensory-impaired feet.

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