Metatarsus Adductus

Metatarsus adductus is a common paediatric foot deformity in which the forefoot (the metatarsals) is deviated medially (adducted) in relation to the midfoot and hindfoot, with a normal or neutral hindfoot, and a convex lateral border of the foot ("kidney shaped" foot).

It occurs in about 1 to 2 in 1000 live births (some series higher), with equal frequency in each sex, and is bilateral in about half. It is attributed to intrauterine packaging and abnormal positioning in the last trimester, and is more frequent in first pregnancies, oligohydramnios, breech presentation and multiple births. A positive family history is found in some.

Over 85 to 90% resolve spontaneously by 12 to 18 months. About 1 to 5% have associated developmental dysplasia of the hip (the hips are screened), and a few have torticollis or other packaging deformities. Complications of persistent deformity are in toeing, difficulty with shoe wear, and rarely pain and callosities in older children.

Pathophysiology.

Soft tissue contracture of the medial structures (abductor hallucis, tibialis anterior insertion, medial tarsometatarsal ligaments) with an abnormal medial cuneiform and first metatarsal alignment holds the forefoot in adduction. The hindfoot stays in neutral or slight valgus, which distinguishes the condition from clubfoot (hindfoot equinus and varus) and from skew foot (hindfoot valgus with forefoot adduction).

Medial deviation of the forefoot with a concave medial border, a convex lateral border with a prominent base of the fifth metatarsal, a deep medial skin crease, and a wide gap between the first and second toes. The heel is neutral and ankle dorsiflexion is normal. Parents notice in toeing when the child begins to walk.

Examine the flexibility by stabilising the heel and abducting the forefoot: flexible (the forefoot corrects past the midline), partly flexible (corrects to the midline), or rigid (does not correct). The heel bisector line (a line through the centre of the heel and along the long axis of the foot should pass through the second toe web; in adductus it falls lateral to the third toe) is used for grading (Bleck classification). Examine the hips, spine, neck and the other foot.

• The diagnosis is clinical; radiographs are not needed for typical cases.
• Weight bearing anteroposterior and lateral radiographs of the foot when the child is over 4 to 5 years old, with a rigid deformity or when surgery is planned: increased metatarso adductus angle (over 15 degrees), a normal talocalcaneal angle, and the first metatarsal medial deviation.
• Hip ultrasound (under 4 to 6 months) or pelvic radiograph (after 4 to 6 months) when risk factors for hip dysplasia exist or the examination is abnormal.

Differential diagnosis.

• Clubfoot (congenital talipes equinovarus) and skew foot (serpentine foot).
• Isolated adducted great toe (hallux varus) and congenital vertical talus.
• Tibial torsion and femoral anteversion causing in toeing.
• Cavus foot and neuromuscular disease.

Most cases need no treatment, and the aim is to correct persistent, rigid deformity early to avoid surgery.

Observation and stretching.

• Flexible deformity (most cases): reassure the family; teach passive stretching at nappy changes (stabilise the heel, abduct the forefoot, hold for 5 to 10 seconds, repeated at each change). Check at 6 and 12 months. Avoid prolonged sleeping in the prone position with the feet turned in.
• Corrective shoes and splints are of no proven benefit.

Serial casting.

• Indication: rigid or partly flexible deformity persisting at 6 to 8 months of age (best between 6 and 12 months; can be used to 2 years or later).
• Method: weekly long leg casts (knee flexed to 90 degrees), 4 to 6 casts, moulding the forefoot into abduction while holding the heel in neutral, followed by a straight last shoe or night splint for a few months. Success is over 90% when started early.
• Check skin and cast fit, and avoid pressure over the base of the fifth metatarsal.

Surgery (rare; for persistent rigid deformity after 4 years of age, or after failed casting).

• Soft tissue release of the tarsometatarsal joints (Heyman-Herndon-Strong capsulotomy, usually at 2 to 8 years).
• Medial cuneiform opening wedge osteotomy with a cuboid closing wedge osteotomy (or metatarsal osteotomies) in children older than 6 to 8 years.
• Abductor hallucis release for a dynamic component.
• Cast for 6 to 8 weeks after surgery.

Operative antibiotic prophylaxis (surgery). Cefazolin 30 mg/kg to a maximum of 2 g intravenously (2 g in adolescents and adults; 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 (casting and surgery).

• 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 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. Foot position, flexibility and gait at 3, 6 and 12 months, then yearly until the age of 4 to 5 years. Skin and circulation at each cast change. Hip examination and ultrasound as indicated. After surgery, radiographs at 6 weeks and 6 months.

Referral and escalation. Refer to paediatric orthopaedics for rigid deformity, failure to correct by 6 to 8 months, associated hip dysplasia, or a deformity that is not typical. Urgent referral for a deformity with a stiff hindfoot (suspect clubfoot or vertical talus), neurological signs, or an infant with multiple joint contractures.

Special groups.

• Infants with a rigid foot: start casting between 6 and 12 months.
• Older children (over 4 years) with in toeing: check for other causes (tibial torsion, femoral anteversion) before treating the foot.
• Neuromuscular disease: needs a full neurological assessment.
• Parents: provide reassurance and teach stretching; most feet become normal without treatment.