A cavus foot is characterized by increased height of the longitudinal arch and is associated with clawing of the toes and heel varus. Cavus is most often physiological. It is simply the extreme end of the spectrum of normal variability of the shape of the longitudinal arch. This physiologic form is often familial. Pathologic forms of cavus deformity are usually neurogenic or myopathic.
This deformity falls outside the normal range of ±2 SD in arch height. Often a parent’s feet have a high arch. The parent often volunteers that they have a “good” (high) arch. The cavus is usually bilateral, with an onset in infancy. They may also have calluses under the metatarsal heads. The child’s musculoskeletal and neurologic screening examinations are normal, and clawing of the toes is absent. This is a diagnosis of exclusion. Occasionally, the teenager will complain of metatarsal pain. This is best managed by shock-absorbing shoeware and, if necessary, a soft shoe insert to unload the metatarsal heads.
Pathologic cavus is usually secondary to a neuromuscular disorder causing muscle imbalance. A major objective of management is to determine the underlying cause of the deformity.
Evaluation The neuromuscular disorders causing cavus deformities are often familial, so the family history is important. Look at the parents’ feet. Sometimes they may claim their feet are normal when they are clearly deformed. Perform a careful screening examination of the child. Examine the musculoskeletal system for other problems. Look for midline skin lesions over the spine. A careful neurologic examination is essential. Check muscle strength. Examine the foot, noting the severity of the cavus, degree of rigidity, and presence of clawing of the toes and skin changes under the metatarsal heads. Standing radiographs of the feet are useful in documenting the type and severity of the deformity. Special studies such as spine radiographs for spinal dysraphism, electromyography (EMG), DNA blood tests for Charcot–Marie–Tooth (CMT) disease, nerve conduction velocity measurements, and CPK determination for muscular dystrophy assessment may be necessary. Consultation with a neurologist may be appropriate. Establish the etiology of the cavus deformity.
Natural history Because of the reduced area of plantar contact, deformity, and rigidity, cavus feet often cause considerable disability.
Types of Cavus Deformities
Congenital cavus is a rare deformity that may be due to intrauterine constraint or fixed deformity. Assess the effect of growth.
Calcaneocavus results from weakness of the triceps. There is an increase in the calcaneal pitch, and a cavus deformity. Correct muscle imbalance, if possible. This deformity is seen in poliomyelitis, in spina bifida, and following overlengthening of the triceps.
Cavovarus is the most common form. Muscle imbalance results in plantarflexion of the forefoot, inversion of the hindfoot, and a mild increase in the calcaneal pitch. This deformity is seen in CMT disease. Clawing of the toes is often seen.
Follow a flowchart to manage. The teenager will often complain of difficulty in fitting shoes, calluses over the claw toes and under the metatarsal heads, pain, and instability causing recurrent ankle sprains.
Mild deformity Order shock-absorbing footwear and soft molded shoe inserts to broaden the load-bearing area of the foot.
Moderate or severe deformity This requires operative correction. Operations improve muscle balance, flatten the arch to broaden the weight-bearing surface, and correct toe deformity.
Flexible deformities or those in young children are best managed by a plantar medial release and appropriate tendon transfers. If performed during childhood, recurrence can occur.
Fixed deformities require correction in two stages. First, perform a soft tissue release, as described above. Follow this by osteotomies to correct bony deformity and tendon transfers to balance the foot. In most cases, perform a calcaneal osteotomy for calacaneocavus deformity and a dorsi flexion medial cuneiform osteotomy for cavovarus correction. Avoid arthrodesis whenever possible to maintain mobility and reduce the risk of degenerative arthritis of adjacent joints.