Cavovarus Deformity
A. Holly Johnson, MD
Dr. Johnson or an immediate family member serves as a paid consultant to or is an employee of Synthes and Wright Medical Technology Inc. and serves as a board member, owner, officer, or committee member of the American Orthopaedic Foot and Ankle Society.
ABSTRACT
The cavovarus foot is characterized by hindfoot varus, a high medial longitudinal arch, a plantarflexed first ray, and clawing of the toes. Although the etiology is often linked to hereditary motor sensory neuropathies or other systemic causes of muscle imbalance, idiopathic cases are not uncommon. Clinical findings vary depending on the etiology and the severity of the deformity. Treatment is based on the physical findings, flexibility of the deformities, and patient goals and typically combines procedures including soft-tissue releases, tendon transfers, osteotomies, and sometimes fusion.
Introduction
The cavovarus foot involves a complex array of deformities of the hindfoot, midfoot, and forefoot. The elevated medial longitudinal arch is caused by hyperplantar flexion of the first ray (forefoot equinus) and relative dorsiflexion of the calcaneus (calcaneocavus). The hindfoot is in varus, and the forefoot is pronated. Claw toes develop, and the plantar metatarsal fat pad migrates distally. These characteristic deformities result from muscle imbalance secondary to a neurologic, traumatic, or other cause. Altered foot and ankle mechanics and the resulting abnormal gait cause a multitude of issues, including lateral instability, bony overload and stress fracture, loss of motion, and possibly a fixed arthritic limb. Treatment is guided by the relative flexibility of the foot and the extent of deformity.
Etiology
Cavovarus foot deformities have several etiologies. In the past, approximately one-third of incidences were classified as idiopathic, but improved diagnostic methods have determined that many of these incidences are attributable to a neurologic disease.1 Charcot-Marie-Tooth (CMT) disease is the most common cause of pes cavovarus, but other etiologies also have been identified2,3 (Table 1).
The most common neurologic causes of pes cavus are hereditary motor sensory neuropathies, which are responsible for CMT disease as well as other, less common syndromes and diseases. CMT disease encompasses several genetically varied syndromes with similar clinical manifestations. Jean-Martin Charcot, a French neurologist and anatomist, described the disease with Pierre Marie in 1886. Also in 1886, Howard Tooth, an English physician, described the same disorder as peroneal muscular atrophy.4
The CMT neuropathies result from a mutation in one of more than 40 genes that affect Schwann cells and neurons. The disease has demyelinating (CMT1 and CMT4), axonal (CMT2 and CMT4), and intermediate (CMTX, CMT2E, and CMT) forms.5,6,7 The classic phenotype of the most common form, CMT1, emanates from an abnormality in the peripheral myelin protein-22 (PMP22) gene and is characterized by axonal demyelination that causes distal sensory loss, weakness, and skeletal deformity.5 Patients with CMT disease typically have abnormalities before they reach age 20 years and often before age 10 years. The peripheral neuropathy leads to distal muscle weakness, with intrinsic muscle degeneration that over time selectively spreads proximally to larger muscle groups, leading to imbalances in forces around the foot and ankle and eventually to cavovarus deformity.8
Neurologic conditions including other hereditary motor sensory neuropathies unrelated to CMT disease, amyotrophic lateral sclerosis, Huntington disease, cerebral palsy, spinal cord lesions, and other cerebral injuries also can lead to pes cavovarus.3 In a child with pes cavus, the clinician must consider a spinal cord anomaly, especially if the deformities are unilateral.9 Congenital causes of pes cavovarus, such as congenital talipes equinovarus (clubfoot) and arthrogryposis, can be identified from birth. Arthrogryposis typically causes early rigid deformity, but other causes of rigid cavovarus in adolescence or young adulthood can be avoided if they are treated effectively during childhood.10 In the past, poliomyelitis, which affects the anterior horn cells of the spinal cord, was a common cause of foot and ankle deformity.
TABLE 1 Causes of Adult Cavovarus Foot | ||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||||||||||||
Trauma to the lower extremity can cause cavovarus deformity. Malunion of a talar neck fracture leads to shortening of the medial column and a fixed varus position of the talonavicular joint and the hindfoot. An untreated calcaneus fracture can heal in a varus malunion. Superficial peroneal nerve injury can cause footdrop and posterior tibial tendon overdrive. Any isolated tendon injury can leave the strength of the opposing tendon unchecked, causing deformity over time. A burn injury or a compartment syndrome causing muscle contraction and neurologic injury can lead to cavovarus deformity. Some incidences of cavovarus deformity have no obvious etiology and may be the result of an as-yet undetected peripheral neuropathy.
Anatomy and Pathomechanics
Pes cavovarus can be seen as the product of any of several different etiologies arising in an imbalance of both the intrinsic and extrinsic musculature of the foot.11 Depending on the muscles involved and the etiology of the disorder, the appearance of the deformity varies. Many deformities continue to progress over time.
In the normal foot, proper function is maintained by pairs of muscles working in opposition to each other. These agonist-antagonist pairs keep the foot balanced. If one muscle is disturbed, relative overdrive of the opposing muscle results and a deformity develops. Understanding the normal anatomy and function of the muscle groups is essential to comprehending the pathologic cavovarus foot (Table 2).
The tibialis anterior, which inserts on the navicular and medial cuneiform, acts as a primary dorsiflexor and secondary inverter of the ankle. The antagonist of the tibialis anterior is the peroneus longus, which acts as a plantar flexor and weak evertor; it inserts on the plantar aspect of the medial cuneiform and the first metatarsal base. The tibialis posterior, with its wide insertion along the medial and plantarmedial aspect of the medial column, inverts the foot primarily and plantar flexes secondarily. The tibialis posterior is opposed by the peroneus brevis, a strong evertor that inserts at the base of the fifth metatarsal.
The intrinsic muscles, including the lumbricals and the interossei, insert into the extensor mechanism at the proximal phalanx; they flex the metatarsophalangeal (MTP) joints and extend the proximal and distal interphalangeal joints. The extrinsic extensor muscles, including the extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis, and extensor hallucis brevis, extend the toes through the MTP, proximal interphalangeal, and distal interphalangeal joints. The extrinsic long flexors (including the flexor digitorum longus and flexor hallucis longus [FHL]) and the short flexors (including the flexor digitorum brevis and flexor hallucis brevis) flex the toes at the proximal and distal interphalangeal joints.
CMT disease is the most commonly used template for cavovarus deformity. In the most widely accepted etiology, weakness in the peroneus brevis and tibialis anterior is primarily responsible for the deformity. As these two muscle groups deteriorate, the peroneus longus and tibialis posterior initially are spared and demonstrate a relative increase in strength. Dorsiflexion through the tibialis anterior and long toe extensors and eversion through the peroneus brevis are compromised. The opposing muscles are left unrestrained. The overpull of the tibialis posterior leads to medial displacement of the talonavicular and calcaneal cuboid joints and locks the subtalar joint in supination.4 The peroneus longus pulls the first ray into plantar flexion. As the tibialis anterior becomes unable to dorsiflex the ankle, the long toe extensors attempt to act as a substitute, and they hyperextend the toes at the MTP joints. Weakness of the intrinsic muscles contributes to the clawing of the toes and distal migration of the plantar fat pad. Forefoot equinus and plantar flexion of the first ray cause forefoot pronation. As the forefoot deformity becomes fixed, the hindfoot becomes fixed in varus to keep the foot plantigrade10,12 (Figure 1).
TABLE 2 Muscles of the Foot and Ankle | ||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
The mechanism of development may be different in cavovarus stemming from other etiologies. In poliomyelitis, triceps surae involvement causes weak push-off strength. The long toe flexors are recruited, leading to forefoot plantar flexion and the development of cavus. A deep posterior compartment syndrome with subsequent muscle contracture can lead to tibialis posterior overpull with equinus and cavovarus. Identification of the etiology of the disorder and the affected nerves and muscles allows further understanding of the pathomechanics manifested by the patient over time.
 FIGURE 1 Photographs show a cavovarus foot in a patient with Charcot-Marie-Tooth disease. A, Anterolateral view shows the high medial longitudinal arch and clawing of the toes. B, Posterior view shows the varus position of the hindfoot. (Reproduced with permission from Johnson AH, May CJ: Adult cavovarus foot. Orthop Knowl Online J 2012;10[4]. https://www.aaos.org/OKOJ/vol10/issue4/FOO042/?ssopc=1. Accessed January 18, 2019.) |
Diagnosis
Patients typically present with foot pain and/or lateral instability in the ankle. Lateral foot pain from bony overload at the base of the fifth metatarsal may result in a stress reaction or fracture at the fifth metatarsal base; recurrent stress fracture can occur in a subtle cavovarus foot or with a fixed deformity.13 Forefoot pain at the sesamoids with hyperplantar flexion of the first ray may also be a presenting symptom. Pain beneath the metatarsal heads may be caused by distal migration of the plantar fat pad associated with subluxated or dislocated MTP joints and claw toes. Late in the disease, when the deformities are fixed, the cause of pain may be secondary to degenerative changes in the joints (particularly the subtalar, midfoot, and ankle joints). Lateral ankle and subtalar instability typically results from eversion
weakness and the mechanical contribution of hindfoot varus. The patient may have frequent ankle sprains and damage to the collateral ligaments.
weakness and the mechanical contribution of hindfoot varus. The patient may have frequent ankle sprains and damage to the collateral ligaments.
History and Physical Examination
A careful history is an important first step in diagnosing the cause of a cavovarus deformity. The family history can be useful because the patient often describes a sibling or parent with similar physical characteristics. Identification of a family member with pes cavovarus suggests a hereditary neuropathy. A unilateral deformity, especially if it is severe or accompanied by other neurologic abnormalities, may indicate a spinal cord abnormality.9 Children with minimal symptoms of pes cavus are often referred for evaluation. The presence of clinical features such as weakness, unsteady gait, family history, or other neurologic deficits can obviate the need for further testing if the diagnosis of CMT seems clear.14
The patient should be examined standing and walking, with the limbs unclothed. During the swing phase of gait, footdrop or recruitment of the toe extensors indicates tibialis anterior weakness. The lower extremities should be compared while the patient is standing. From behind, the position of the heel is noted relative to the midfoot and forefoot; hindfoot varus is more apparent from this viewpoint. The Coleman block test is critical to understanding whether the hindfoot deformity is rigid and whether the deformity is driven by the forefoot. If the heel is corrected to neutral or a few degrees of valgus, the hindfoot is considered flexible, and correction of the forefoot deformity should correct the hindfoot deformity. If the hindfoot remains in varus, the deformity is considered rigid, and a hindfoot and forefoot procedure probably will be necessary for deformity correction15 (Figure 2).
Joint motion is examined to identify an equinus contracture. If the contracture is not corrected with the knee flexed, the cause may be a tight soleus and/or gastrocnemius, or it may be a mechanical block to dorsiflexion, such as a tibial or talar bone spur or a medialized talus. If dorsiflexion increases when the knee is bent, the gastrocnemius is contracted. A thorough neurologic examination is critical. Vibration, position, sensation, and reflexes should be checked, and any muscle atrophy or weakness, noted. A child should be examined to detect spinal skin dimples, a hair patch, or another sign of occult spinal disease.
Any patient presenting with lateral instability or weakness, frequent sprains, peroneal tendon tear or pain, or fifth metatarsal fracture must be evaluated for a cavovarus deformity. Even a subtle hindfoot varus deformity can lead to lateral overload and further deformity. Overall alignment must always be considered in addition to the acute diagnosis.16
 FIGURE 2 Posterior photographs show a cavovarus deformity before (A) and during (B) the Coleman block test. With the Coleman block in place, the hindfoot is corrected to neutral, and the hindfoot deformity is found to be flexible. |
The diagnosis of CMT disease is based on physical examination findings, neurologic testing, family history, and genetic testing. A physician may be alerted to the presence of pes cavus by physical examination findings consistent with the disorder, such as a high arch, weak extensors, claw toes, and even footdrop. Electromyography and nerve conduction studies can be used to identify patterns of deficiency often seen with CMT disease. If a familial link appears to be present, genetic testing is indicated for purposes of determining the prognosis, a need for family planning, and eligibility for a clinical study.14,17 Algorithms for neurologic and genetic testing have been developed and published.18 Nerve biopsies typically are unnecessary for diagnosis.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
