What Is Congenital Vertical Talus?
The congenital vertical talus (CVT), also known as the rocker-bottom foot, is a rare foot deformity at birth in which the child’s feet flex abnormally convex due to dislocation of the talus bone at the ankle joint. The foot appears flat at birth owing to the extra fat pad, but as the child grows, a natural concavity develops. In CVT children, the foot curves in the opposite direction, with the middle sole touching the floor while the toes and heel curve upwards and even touch the shin. A less severe form of the condition, called oblique talus, occurs when the talus bone is wrongly positioned in the ankle while bearing weight but self-aligns when the foot is pointed down. The severity is between the flat foot and vertical talus.
Anatomy of the Ankle
The talus is a small bone lodged between the heel bone (calcaneus) and the two lower leg bones (tibia and fibula). The tibia and fibula sit over the top and sides of the talus bone to formulate the ankle joint. The talus holds a special place in the anatomy of the foot as it helps transfer weight across the ankle joint.
How Common Is Congenital Vertical Talus?
Congenital vertical talus is a rare congenital anomaly occurring once in about 10,000 live births. According to some comparative estimates, the incidence of CVT is about a tenth of the incidence of congenital clubfoot deformity. The condition is bilaterally presented in about half of the cases with no gender predilection.
What Is the Cause of Congenital Vertical Talus?
The exact etiology of CVT is still unknown as more than 50 percent of the cases are of idiopathic onset, while the remaining are associated with other conditions. Ogata et al. proposed a classification to categorize CVT cases based on the association or etiology.
The three groups are:
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Idiopathic (a disease with an unknown cause or mechanism of origin).
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Genetic or syndromic.
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Neuromuscular.
What Is the Pathophysiology of Congenital Vertical Talus?
CVT occurs when there is a flexion of the talus bone and calcaneum bone. This is a dislocation between the talus and navicular bone near the ankle joint. The dislocation is rigid and irreducible, which results in the prominence of the talus head (the part that articulates with the navicular bone) and ultimately results in the characteristic rocker bottom sole.
The valgus (outward angled joint) and equinus deformity (limited upwards movement of the foot), seen in CVT, are due to the contracture of the subtalar joint capsule, Achilles tendon, and the posterolateral part of the ankle. The dorsiflexion (backward bending and contracting of the ankle) and abduction (away from the midline of the body) of the foot are by the contracture of the peroneus tertius, extensor digitorum longus, tibialis anterior, extensor hallucis longus tendon, extensor hallucis brevis, and the talonavicular capsule.
Dorsiflexion of the ankle joint is due to the subluxation of the peroneus longus and tibialis posterior tendon. All of these changes result in hypoplastic navicular bone, abnormally shaped talus, and dislocation of the calcaneocuboid joint.
What Are the Signs and Symptoms of Congenital Vertical Talus?
The clinical features of congenital vertical talus include,
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Valgus at the hindfoot.
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Equinus at the hindfoot.
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Forefoot abduction.
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Forefoot dorsiflexion at the midtarsal joint.
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Vertically positioned talus.
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Weak spring ligament.
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Convexity of the sole.
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Deep creasing on the foot top.
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Bony prominence in the midfoot (the talar head).
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Callosities at the talar head.
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Rigidity.
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The heel cannot touch the ground.
How to Diagnose Congenital Vertical Talus?
The evaluation studies, apart from the clinical examination of the lower limbs, include roentgenogram images (radiographs). Anteroposterior and lateral X-rays are taken of the foot in neutral positions (for infants) and standing (for weight-bearing children). Early diagnosis is difficult due to the lack of ossification in multiple bones. Also, it is essential to establish the relationship between the talus and calcaneum relative to the tibia and metatarsals of the hindfoot. This is critical from a diagnostic point of view.
1. The X-ray findings include
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An increased angle between the talus and calcaneum bones.
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The long axis of the talus is vertical and parallel to the longitudinal axis of the tibia.
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Decreased tibia-calcaneum angle in forced dorsiflexion.
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Malalignment of the talus with navicular bone.
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Malalignment of the talus to the first metatarsal on forced plantar flexion.
2. Magnetic resonance imaging (MRI) studies may be ordered in case of spinal anomalies like spina bifida, lipomeningocele. This should be supported with posterior and lateral spinal radiographs. Ultrasonography can be implemented to differentiate between irreducible talonavicular dorsal dislocation (CVT) and reducible talonavicular dorsal dislocation (oblique talus).
3. Histopathological samples from the abductor hallucis muscle have shown abnormalities like variations in muscle fiber size, type I muscle fiber smallness, and predominance of abnormal fiber type.
How to Treat Congenital Vertical Talus?
The aim of CVT management is to restore the normal functionality of the foot by achieving the correct anatomic alignment between the talus, calcaneum, and navicular bone. Non-surgical techniques require manipulation, followed by serial casting. In case of failed conservative approaches, surgical interventions may be opted for. Some surgeons opt for conservative treatment until the reduction of the talonavicular joint and the follow-up with surgery.
Toddlers’ CVT is appropriately managed by open reduction of the talonavicular joint, either in a single or two-stage procedure. In a two-stage approach, the first stage requires the reduction of the talonavicular joint and the lengthening of the extensor tendons, the tibialis anterior tendon. In the next stage, peroneal tendons are lengthened, and equinus contracture is corrected, lengthening of an Achilles tendon and release of the posterior ankle and subtalar soft tissues.
The benefit of the single-stage approach is fewer complications like avascular necrosis of the talus bone. The three steps of the single-stage surgery include reduction of the talonavicular joint, lengthening of the peroneals and toe extensors, and the final step includes equinus contracture of the ankle by lengthening the Achilles tendon and releasing the subtalar and ankle joint capsules.
What Is the Differential Diagnosis of Congenital Vertical Talus?
The differential diagnosis of congenital vertical talus includes:
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Congenital talipes equinovarus.
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Calcaneovalgus foot.
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Posterior medial bowing of the tibia.
Complications of Congenital Vertical Talus
The complication of congenital vertical talus include:
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Multiple bony deformities.
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Callosities formation.
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Difficulty in wearing shoes.
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Post-operative complications like avascular necrosis.
Conclusion
Most children with CVT have favorable outcomes and may require orthotic devices for proper alignment through the growth ages. Bracing and stretching must be done to prevent relapse after manipulation and serial casting. Bracing for at least 23 hours a day for three months and more than half a day per day for the next couple of years. CVT associated with syndromes or neuromuscular disorders requires lifelong care and follow-up with concerned specialists.
