- Pes cavus is an abnormal elevation of the medial longitudinal arch of the foot.
- Idiopathic cavus foot should be a diagnosis of exclusion as greater than two-thirds of such deformities are caused by an underlying neurological diagnosis causing a muscle imbalance.
- The Coleman block test differentiates flexible from rigid hindfoot varus. This distinction is important in planning surgical treatment
- The goal of treatment of a cavus foot deformity is to achieve a painless, plantigrade, mobile foot with improved muscle balance.
Description:The hallmark feature of a cavus foot is elevation of the longitudinal arch. Arch elevation may be due to a plantar-flexion deformity of the forefoot (forefoot equinus) or due to dorsiflexion of the calcaneus. Although the hindfoot is more commonly in varus, it may at times be in valgus alignment. The first ray is typically plantar-flexed and the forefoot is typically in pronation.
Epidemiology:The incidence of cavus foot deformity is variable as it is typically related to an underlying neuromuscular disorder or neurological injury.
Clinical Findings:Cavus deformities are frequently more symptomatic than planovalgus feet as the shock absorption function during gait is lost as a result of the inability of the hindfoot to assume a valgus alignment. The normal tripod weight-bearing structure of the foot becomes unbalanced in a cavus foot leading to frequent episodes of ankle instability or painful calluses on the sole of the foot. A varus hindfoot will lead to calluses on the lateral border of the foot, usually at the base of the fifth metatarsal. Plantar flexion of the forefoot leads to increased pressure on the metatarsal heads. Clawing of the toes may cause calluses on the dorsum of the flexed proximal interphalangeal joints of the toes due to friction in the shoe (Kasser, 2006).
A detailed neurological examination of the extremities is important, as is a full examination of the spine for deformity or signs of spinal dysraphism. As mentioned above, the clinical progression of a cavus foot deformity entails a transition from a flexible to a rigid deformity. In the most common variety, a cavovarus foot, the forefoot is rigidly pronated relative to the hindfoot and the subtalar joint is inverted into varus. The hindfoot deformity is initially flexible but eventually becomes rigid. The Coleman block test is used to evaluate the flexibility of the hindfoot (Coleman, 1977). For the test, the patient stands with a rigid block under the lateral border of the foot, allowing the first metatarsal to plantar-flex. A flexible hindfoot varus deformity will correct to valgus alignment indicating the presence of a forefoot-driven flexible hindfoot varus whereas a rigid hindfoot deformity will not correct with this maneuver.
A history of progressive changes in foot shape and function must be sought. A sudden worsening of the deformity in a child with myelomeningocele could represent the effects of a tethered spinal cord. Examination of family members for subtle or not so subtle cavus foot deformity may help reveal the underlying diagnosis. Long standing cavovarus deformities can be associated with patellar instability and recurrent ankle sprains.
Imaging Studies:Initial evaluation should include weight-bearing anteroposterior (AP) and lateral radiographs of the feet. Meary’s angle, the Hibbs angle and calcaneal pitch are measured on the lateral view. Meary’s angle is the angle between the axis of the talus and the axis of the first metatarsal on the lateral view (Meary, 1967). It is normally a straight-line relationship but in cavus feet will be angulated apex dorsally. The Hibbs angle is the angle between the first metatarsal and the long axis of the calcaneus on the lateral view. In normal feet it is 150 degrees and it decreases as the cavus deformity worsens and the longitudinal arch becomes more elevated. Calcaneal pitch is also measured on the lateral view and values greater than 30 degrees are consistent with cavus deformity. On the AP radiograph, the angle between the axis of the talus and the calcaneus is normally approximately 30 degrees; this angle lessens and the talus and calcaneus become increasingly parallel with increased hindfoot varus (Mosca, 2014).
As Charcot-Marie-Tooth disease is associated with progressive hip subluxation and dysplasia, an AP pelvis radiograph is indicated in those with suspected Charcot-Marie-Tooth disease. As part of the work-up of possible spinal dysraphism or tumor, spine radiographs and/or MRI may be indicated. Complete neurological evaluation by a pediatric neurologist is often appropriate and electromyography or muscle biopsy may be part of the work-up of an underlying neuromuscular disorder.
Treatment:Treatment of a cavus foot deformity must be considered in the context of the underlying diagnosis. If the etiology of the deformity is treatable (such as a spinal cord tumor or tethered spinal cord) it should be the first focus of treatment even though the resultant foot deformity may still be progressive. The goal of treatment of a patient with a cavus foot deformity is to achieve a painfree, plantigrade, mobile foot with improved muscle balance.
Non-operative management options should be attempted when appropriate before advancing to surgical options. Associated tightness in the heel cord and plantar fascia may be managed with a stretching program. Weakness in dorsiflexion and eversion may be addressed with an exercise program. Orthotic management including a lateral heel wedge for the flexible hindfoot or a well molded supramalleolar orthosis (SMO) or ankle foot orthosis (AFO) may improve balance and help prevent recurrent ankle instability. Symptoms of plantar callosities may be improved with appropriate arch support or metatarsal pads (Kasser, 2006).
Indications for operative intervention include progressive deformity, painful callosities and hindfoot or ankle instability. Many operative procedures have been described to correct the individual deformities and balance the muscle forces in a cavus foot (a full description of these is beyond the scope of this discussion). An important classification that should guide treatment is the flexibility of the segmental deformities. Soft tissue and plantar fascia releases may be used for a flexible deformity whereas an osteotomy or multiple osteotomies are required for a fixed deformity. Plantar fascia release is a standard component of cavus foot procedures. Open release rather than percutaneous release is preferable and should include release of the intrinsic muscles of the foot and the origin of the abductor hallucis. Muscle balancing procedures to help the first ray imbalance are typically considered next, including the peroneus longus to brevis transfer and the transfer of the extensor hallucis longus to the first metatarsal head with interphalangeal joint fusion of the great toe (Jones transfer). Lesser toe imbalance may be addressed by transfer of the extensor digitorum longus tendons to the metatarsal necks (Hibbs transfer) with proximal interphalangeal joint fusion, with or without flexor tenotomy. Correction of the claw toe deformities frequently requires dorsal capsulotomy of the metatarsophalangeal joint in addition to the described tendon transfers and interphalangeal joint fusion.
A rigid plantar flexion deformity of the first ray requires a corrective osteotomy. Advantages of a plantar-based opening-wedge osteotomy of the medial cuneiform are its stability and its location at the apex of the cavus deformity. An osteotomy of the first metatarsal places the physis at risk for arrest and is less stable. Midfoot osteotomies remove a dorsally based wedge from the tarsal bones, preserving the talonavicular joint and calcaneal cuboid joints. This approach results in a short foot and does not address hindfoot varus. A lateral closing wedge (Dwyer type) osteotomy of the calcaneus or a calcaneus lateral slide (Koutsougiannis-Pridie type) will correct an associated varus deformity of the hindfoot. Calcaneo-cuboid-cuneiform osteotomies have been advocated for correction of the deformity as well. Triple arthrodesis should be reserved as a salvage procedure for feet near or at skeletal maturity with advanced rigid deformity with associated degenerative changes. It has been associated with poor long-term results, particularly in patients with progressive deformity and sensory impairment (Schwend, 2003).
Complications:Given that cavus foot deformities are typically the result of a neurologic disorder, recurrence is common. Revision surgical intervention is often required. The healing of medially based incisions may be tenuous given the stretching that occurs as part of the correction of the cavus deformity. Excessive scar formation medially may also impair revision correction of recurrent cavus deformity.
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- Coleman SS, Chesnut WJ. A simple test for hindfoot flexibility in the cavovarus foot. Clin Orthop Relat Res. 1977; 123:60-62.
- Herring JA. (2008). Disorders of the foot. In Tachdjian’s Pediatric Orthopaedics, Fourth Edition, Ed. Herring, JA. Saunders Elsevier, Philadelphia, PA.
- Kasser JR. (2006). The Foot. In Lovell & Winter’s Pediatric Orthopaedics, Sixth Edition, Ed. Morrissy RT and Weinstein SL; Lippincott Williams & Wilkins, Philadelphia, PA
- Meary R. On the measurement of the angle between the talus and the first metatarsal. Symposium: Le Pied Creux Essential. Rev Chir Orthop. 1967; 53: 389.
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- Mosca VS. (2014). The Foot. In Lovell & Winter’s Pediatric Orthopaedics, Seventh Edition, Ed. Weinstein SL and Flynn JM; Lippincott Williams & Wilkins, Philadelphia, PA.
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