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.
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
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
Talipes equinovarus (clubfoot)
Cerebrovascular accident (stroke)
Charcot-Marie-Tooth disease (hereditary motor sensory neuropathy)
Spinal cord lesion (eg, myelomeningocele, syringomyelia, tumor)
Spinal muscular atrophy
Peroneal nerve injury
Peroneal tendon insufficiency, severe chronic ankle instability
Talus fracture nonunion
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
TABLE 2 Muscles of the Foot and Ankle
Navicular, medial cuneiform
Strong dorsiflexion, weak inversion
Medial column (wide insertion at medial and plantar midfoot and forefoot)
Strong inversion, weak plantar flexion
First metatarsal base, medial cuneiform
Strong plantar flexion of the first metatarsal, weak eversion
Fifth metatarsal base
Intrinsics (lumbricals, interossei)
Proximal phalanges (extensor expansions)
Flexion of metatarsophalangeal joints, extension of proximal and distal interphalangeal joints
Extrinsic long extensors and flexors
Extrinsic long extensors (extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis, extensor hallucis brevis)
Extensor hood at metatarsophalangeal joint, distal phalanges
Extension of metatarsophalangeal joints, proximal and distal interphalangeal joints
Intrinsics, extrinsic long flexors
Extrinsic long flexors (flexor digitorum longus, flexor hallucis longus, flexor digitorum brevis, flexor hallucis brevis)
Flexor sheath, plantar aspect of distal phalanges
Toe flexion at proximal and distal interphalangeal joints
Extrinsic long extensors
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. https://www.aaos.org/OKOJ/vol10/issue4/FOO042/?ssopc=1. Accessed January 18, 2019.)