Congenital Vertical Talus

Congenital vertical talus (congenital convex pes valgus, rocker bottom foot) is a rigid foot deformity present at birth. The talus is fixed in plantar flexion and the navicular is dislocated dorsally onto the talar neck. The hindfoot is in equinus and valgus, and the forefoot is dorsiflexed and abducted.

It is rare, with an incidence of about 1 in 10 000 live births, and is bilateral in about half. Over half of patients have an associated condition: neuromuscular disease (myelomeningocele, arthrogryposis, spinal dysraphism, sacral agenesis, cerebral palsy) or a genetic syndrome (trisomy 13, 15 or 18, Costello syndrome, Larsen syndrome, mutations such as HOXD10). The idiopathic form accounts for the remaining 20 to 50%, and a family history is found in some.

Complications of untreated deformity are pain, calluses and ulcers beneath the prominent talar head, a rigid, painful flat foot, difficulty with shoes, and gait abnormalities. Treatment gives good function in most children, but may lead to stiffness, recurrence and avascular necrosis of the talus after extensive surgery.

Pathophysiology.

The talus, calcaneus and navicular are malaligned, and the posterior structures (Achilles tendon, posterior ankle and subtalar capsule, peroneals, tibialis anterior and extensor tendons) contract, while the talonavicular joint is dislocated and the navicular is locked on the dorsal talar neck. The cause is thought to be a neuromuscular imbalance or intrauterine disturbance in the first trimester, and the deformity fixes the calcaneus in equinus.

A rigid, convex plantar surface (rocker bottom), with a prominent talar head in the sole, a fixed heel in equinus and valgus, a dorsiflexed and abducted forefoot, and a deep crease on the dorsolateral ankle. The foot does not correct with plantar flexion. In the older child, there are callosities, pain and gait problems.

Examine the foot flexibility, ankle and hindfoot range, hips, spine (dimples, tufts, spinal defects), neurological state (tone, reflexes, power, sensation), and the other joints for arthrogryposis or other anomalies.

• Weight bearing or simulated weight bearing lateral radiographs of the foot in maximal plantar flexion: the long axis of the talus stays parallel with the tibia.
• The first metatarsal axis does not realign with the talus even when the foot is forced into plantar flexion (the talonavicular joint stays dislocated), which separates it from oblique talus (flexible).
• The calcaneus is in equinus, and the navicular is not ossified until age 3 to 4 years, so the first metatarsal axis is used.
• Anteroposterior views show increased talocalcaneal angle.
• Neurological assessment, MRI of the spine, and genetic or chromosomal tests (microarray, gene panel) in all affected children, since many have an underlying condition.
• Ultrasound or MRI in infants when radiographs are not definitive. Hip assessment and echocardiography when a syndrome is suspected.

Differential diagnosis.

• Oblique talus (flexible flatfoot that corrects with plantar flexion).
• Calcaneovalgus foot and clubfoot.
• Flexible flatfoot and tarsal coalition.
• Arthrogryposis and myelomeningocele related foot deformities.

The aim is to reduce the talonavicular joint and correct hindfoot equinus early, ideally in the first year, with minimal surgery.

Reverse Ponseti (Dobbs) method (preferred in infants and young children).

• Serial manipulation and casting weekly for 4 to 6 casts, stretching the dorsal structures and pulling the forefoot and navicular into plantar flexion and inversion to reduce the navicular on the talus.
• Then a minimally invasive procedure under anaesthesia: percutaneous Achilles tendon tenotomy, with a Kirschner wire fixing the talonavicular joint reduction (through the navicular into the talus).
• Limited dorsal release when needed, and tibialis anterior transfer to the talar neck in older children with a dynamic deformity.
• Long leg cast for 6 weeks, with wire removal, then a short leg cast for 2 to 4 weeks and an ankle foot orthosis, worn full time for a few months and then at night until age 2 to 4.

Open surgery. A single stage extensive soft tissue release (dorsal and lateral release, posterior release with Achilles and peroneal lengthening, talonavicular reduction and pinning, and tendon transfer) is used for older children, failed casting or syndromic feet. Risks are stiffness, avascular necrosis of the talus, wound problems and recurrence. In children over 5 years with a rigid residual deformity, talar resection or triple arthrodesis is considered.

Operative antibiotic prophylaxis. Cefazolin 30 mg/kg to a maximum of 2 g intravenously (2 g in adolescents; 3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose.

With severe penicillin allergy: clindamycin 10 mg/kg (maximum 900 mg) intravenously or vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.

Analgesia.

• Children: paracetamol 15 mg/kg orally every 4 to 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily) and ibuprofen 10 mg/kg orally every 6 to 8 hours with food (maximum 40 mg/kg daily and not exceeding 2400 mg daily), for up to 5 days.
• Avoid ibuprofen in infants under 3 months, with kidney impairment, dehydration or active bleeding.
• After open surgery, oral morphine 0.1 to 0.2 mg/kg every 4 hours as needed for severe pain for up to 2 to 3 days (maximum 10 mg a dose); monitor sedation and respiration.

Monitoring. Cast changes and skin checks every week during casting. After correction, clinic review at 2 weeks, 6 weeks, 3 months, 6 months and 12 months, then yearly to skeletal maturity, with radiographs to confirm talonavicular alignment. Orthosis wear and recurrence at each visit. Neurological and developmental follow up.

Referral and escalation. Refer every infant with a rigid rocker bottom foot to paediatric orthopaedics in the first weeks of life, and to neurology or genetics for underlying disease. Urgent referral for neurological signs, spinal dysraphism, or multiple congenital contractures.

Special groups.

• Infants: start casting early for the best results with minimal surgery.
• Syndromic and neuromuscular disease: higher failure rates, more recurrence and need for open surgery; coordinate care with the primary condition.
• Older children with untreated deformity: soft tissue release with fusion, depending on age and symptoms.
• Families: genetic counselling, since a minority are inherited.