Pretest

Introduction

In 1914, Henken was the first surgeon to describe congenital vertical talus (CVT).¹ Since then, numerous terms have been proposed to define this pathology. Some of those historical terms are congenital (rigid) rocker-bottom foot, rocker-bottom flatfoot, congenital rigid flatfoot, congenital flatfoot with talonavicular dislocation, rocker-foot due to congenital subluxation of the talus, Persian slipper foot, teratologic dislocation of talocalcaneonavicular joint, and congenital convex pes valgus. Although it draws attention to only one facet of this severe deformity, the condition is now referred to as CVT or, simply, vertical talus. Oblique talus (physiologic flatfoot) should be differentiated from vertical talus.

Definition

Congenital vertical talus is a complex of deformities, rather than a single talar deformity. The primary deformity is the dislocation of the talonavicular joint, which causes the navicular to articulate with the dorsal aspect of the talus. Associated findings include subluxation of the calcaneocuboid joint, eversion of the subtalar joint, and a fixed dorsiflexion of the midfoot on the hindfoot.^1,2

Epidemiology

Congenital vertical talus is a rare condition. The incidence in the general population is unknown. Incidence of CVT accompanying arthrogryposis is reported between 2% and 12%.³ Congenital vertical talus occurs as an isolated abnormality in half of the cases (idiopathic CVT) or associated with neuromuscular disorders (such as arthrogryposis and myelomeningocele), and genetic disorders in the rest (teratologic CVT).^2,6-9 There is no predilection for either gender.^2,7 Approximately one-half of cases are bilateral.^2,4,7

Etiology

Congenital vertical talus is a teratologic anomaly of unknown etiology.¹ Several theories exist, including an arrest of prenatal development, decreased intrauterine space, neuromuscular imbalance, and genetic causes.¹⁰

Genetics

Familial incidence has been observed,^8,11 and CVT was reported in identical twins.¹

Clinical Features (Slide 1 and Slide 2)

Clinically, CVT presents as a rigid flatfoot with a rocker-bottom appearance of the foot. The convex sole of the foot is present at birth.^1,2 Walking is not delayed, and an untreated child does not have pain until callous forms over the talar head later in adolescence.¹ The heel does not touch the ground while weight-bearing, and the Achilles tendon is tight. The hindfoot also is in valgus. The talar head is found medially in the sole, which can be palpable. In ambulatory children, callosities develop under the head of the talus, which is prominent along the plantar-medial foot. The forefoot is abducted and dorsiflexed. The foot is generally stiff.¹² The contralateral foot should be examined carefully, and a complete perinatal and family history should be obtained. A meticulous physical examination should also be performed to find any associated signs.

SLIDE 1		SLIDE 2

Pathophysiology

Contractures occur on the dorsolateral and posterolateral aspect of the foot and ankle. The triceps surae, tibialis anterior, long-toe extensors, and peronei are contracted. The tibialis posterior tendon may be subluxated anteriorly at the medial malleolus. The peroneus longus and brevis may subluxate anteriorly, as well, at the lateral malleolus, and bowstring across the midfoot. Hence, these two muscle groups are converted to act as dorsiflexors.¹³ The intrinsic musculature of the foot does not prevent the midfoot from the pull of the dorsiflexors, which subsequently displace the talonavicular joint by pulling the midfoot dorsally and laterally, leaving the talar head to dislocate inferomedially.^14,15 The navicular is displaced laterally.⁶ Adaptive changes occur at the ligamentous and cartilaginous structures; for example the calcaneonavicular (spring) ligament is elongated.⁶

Associated Conditions

Neuromuscular disorders constitute nearly half of the cases. Examples of those disorders are arthrogryposis, myelomeningocele, sacral agenesis, muscular dystrophy, cerebral palsy, and ischiocalcaneus band. Some skeletal dysplasias and other genetic disorders like multiple pterygium syndrome, Larsen syndrome, Patau syndrome, Edwards syndrome, and Pierre Robin syndrome may also accompany CVT.^1-3,13

Imaging and Radiographic Measurements

Plain radiographs reveal the pathology satisfactorily. Evaluation should consist of anteroposterior (AP), and lateral (preferably simulated weight-bearing) views, and a maximum plantarflexion lateral (the so-called Eyre-Brook) view.¹⁶ A maximum dorsiflexion view might help, at times, to establish the degree of the posterior soft tissue contractures.¹⁶ In a normal foot with maximum dorsiflexion view the talus dorsiflexes to a right angle with the tibia, and the calcaneus dorsiflexes more than 20° past a right angle with the tibia, whereas in CVT there would be fixed plantarflexion of the talus and calcaneus, caused by the contracture of the Achilles tendon and posterolateral joint capsules.²

Congenital vertical talus can be classified radiologically according to Coleman.¹⁷ According to this classification, type I CVT has a disruption of only the talonavicular joint with an intact calcaneocuboid articulation, whereas a type II deformity has a dislocation of the calcaneocuboid and talonavicular joint complexes, with significant separation between the calcaneus and cuboid. Talus and anatomic axis of tibia would show parallelism.^6,18 There are several angles that can be used in objective evaluation, which include the talocalcaneal on both AP and lateral views, talo-first metatarsal, tibiocalcaneal, talohorizontal, and tibiotalar angles on the lateral view.¹⁸ There are also the talar axis-first metatarsal base angle (TAMBA) and the calcaneal axis-first metatarsal base angle (CAMBA) measured on the lateral view. They describe not only the degree of verticality of the talus and calcaneus but also the severity of the dislocation of the talonavicular joint and the contracture of the Achilles tendon.⁹ TAMBA and CAMBA are both established by a line extending perpendicularly from a point originating on the base of the first metatarsal bone, which is the midpoint of the ossified metaphysis. The first metatarsal is identified on the lateral view by locating the widest and most distal metatarsal bone. The talar and calcaneal axes pass through the midpoints of the anterior curvatures of their respective ossified heads. Intersection of the talar axis with the line originating from the first metatarsal base creates the TAMBA, and the calcaneal axis intersection corresponds with formation of the CAMBA.¹⁸ The talocalcaneal angle on the AP (Kite's angle) is increased. On the lateral, talocalcaneal and tibiocalcaneal angles are increased as well. Due to the verticality of the talus, the talohorizontal and tibiotalar angles reach 90° and 180°, respectively.² In a newborn with mild CVT, ultrasonography might be helpful to demonstrate the dislocated talonavicular joint that is not reduced in maximum plantarflexion.¹⁹

Differential Diagnosis

Positional calcaneovalgus should be differentiated from CVT. It is characterized by marked dorsiflexion of the entire foot at the ankle joint with mild and flexible eversion of the subtalar joint. The soft tissue contractures are not rigid and generally do not prevent the plantarflexion and inversion of the foot.² Moreover the foot does not have a rocker-bottom appearance, and on radiograph the talonavicular relationship is normal.⁶ The child will grow out of it by 3 to 6 months of age.⁷ The other important conditions to keep in mind when making a differential diagnosis are congenital posteromedial bowing of the tibia and the equinovalgus deformity associated with fibular hemimelia. In all of those conditions, the feet are flexible and the arch can be demonstrated by manipulation. Oblique talus is considered a milder and more flexible form of CVT, which is a variation of flexible flatfoot with a short Achilles tendon.² Oblique talus can be differentiated from CVT by physical examination or by a lateral radiograph taken in maximal plantarflexion, which shows that the navicular can be reduced on the talus.³ In other words, the articulation of the talonavicular joint is maintained although it is dorsally subluxated in dorsiflexion or weight bearing, and is reducible with plantarflexion of the forefoot.¹⁸ In patients whose radiographs do not show an ossified navicular, the malalignment of the talo-first metatarsal axis can be used to establish the diagnosis.³ The navicular bone is usually not ossified until 3 years of age.¹ The distinction from the more flexible oblique talus to the rigid CVT is a TAMBA of about 60° and CAMBA of 20°.⁹

Natural History

Because CVT does not delay walking, it may be apparent for the first time when a child starts to walk.²⁰ As a child walks, a callosity forms on the sole of the foot right where the talus touches the ground. If this is left untreated, it can lead to a severe flat foot and pain by the time a child reaches adolescence or early adulthood. At this point, walking and wearing shoes becomes awkward. The patient bears all of the weight on the protruding talus without being able to touch the heel to the ground. The forefoot also does not touch the ground to any considerable extent, therefore not allowing the patient to push off the forefoot to prepare the transfer of weight to the other side of the body.²¹ The gait simulates that of someone with a Syme amputation but without the well-cushioned heel pad under the weight-bearing bone.²

Treatment

The goal of surgery is to correct hindfoot equinus, and to restore talonavicular congruity and the functional anatomy.⁶ Manipulation to reduce the navicular followed by percutaneous pin fixation is successful within the first year of life.⁶ Manipulation and serial casting should be started soon after birth for every 2 weeks to elongate the contracted dorsolateral tendons, joint capsules, and skin.^2,3,22 The forces applied are in the opposite direction of those applied in the management of clubfoot.² The foot is casted every other week in equinus, supination, and forefoot adduction.³ Once the alignment of the forefoot and hindfoot are achieved by casting, the talonavicular joint is reduced manually and fixed percutaneously.

Numerous surgical procedures are described for the treatment of CVT if a child is too old for reduction and percutaneous pinning, or if this fails.¹ These include staged or unstaged release (circumferential or dorsal), naviculectomy, subtalar arthrodesis, triple arthrodesis, lateral column lengthening, and talectomy.² Currently, most surgeons recommend a one-stage procedure.^2,4,10,20 Reduction of the talonavicular joint, release of the ankle subtalar and calcaneocuboid joint, peroneal tendons, and Achilles tendon lengthening can be performed. The simplest approach is a dorsolateral incision with open reduction and pin fixation of the talonavicular joint and lengthening of the associated tight tendons. After the reduction of the talonavicular joint, it is fixed by means of a K-wire or a Steinman pin.⁵ Postoperatively, the foot is held in a long-leg cast for a period of 8 weeks after which a molded ankle-foot orthosis is worn for 1 year.³

Another approach is posteromedial, through a transverse circumferential incision, the so-called Cincinnati incision. This incision was first used by Giannestras for the one-stage correction of a congenital vertical talus before it was described by Crawford. Although not proven to be beneficial, the split transfer of tibialis anterior to the talar neck or head can be applied, additionally.² The age of the patient and the severity of the deformity determine treatment. The upper age limit of the procedures are not clear, although children 1 to 4 years old are best treated by means of open reduction and realignment of the talonavicular and subtalar joints.²² Children with CVT are usually operated upon between 6 and 12 months. Reduction should be done before 2 years of age to obtain best results.⁷ Children 3 years of age and older require navicular excision at the time of open reduction, occasionally. Children 4 to 8 years of age and older are treated by open reduction and soft tissue procedures combined with extra-articular subtalar arthrodesis (Grice-Green subtalar fusion); as described by Coleman^17,22 Children older than 12 years into adolescence should undergo triple arthrodesis.²² Naviculectomy allows a satisfactory medial column shortening when combined with a posterolateral release. Other options would include a lateral column lengthening or a calcaneal osteotomy.⁶ Complications include wound infection or avascular necrosis of the talus, stiffness, pain, recurrence, overcorrection, cavus deformity, and degenerative arthritis.^2,6,10

In cases of oblique talus, where there is only a subluxation of the talonavicular joint that reduces on maximum plantarflexion, surgery is not necessary.^2,12

References

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