Metatarsus Adductus (Pediatric)

INTRODUCTION

Definition

Adduction/medial deviation of the forefoot (the metatarsals on the cuneiform) with normal alignment of the hindfoot.

Epidemiology

• Usually seen in the first year of life.
• The condition occurs in up to 12 % of the newborns, making it the most common congenital foot deformity.
  • Occurs in approximately 1 in 1,000 births.
  • Equal frequency in males and females.
  • Bilateral approximately 50% of cases.
• There is an increased incidence in:
  • Late pregnancy.
  • First pregnancies.
  • Twin pregnancies.
  • Oligohydramnios.

Etiology

The cause is unknown. One possible cause may be ntrauterine positioning of the foot.

Classification

Based on the heel bisector line. The classification grades the severity of the deformity based on flexibility.

• Flexible forefoot: Could be abducted beyond the midline heel-bisector angle
• Partially flexible forefoot: Could be abducted to the midline.
• Rigid forefoot: Could not be abducted to the midline.

Bleck classification
Normal foot	The heel bisector line bisects the 2nd and 3rd toes or 2nd and 3rd toe webspace.
Valgus foot	The heel bisector line bisects the great and 2nd toes.
Mild MTA	The heel bisector line bisects the 3rd toe.
Moderate MTA	The heel bisector line bisects the 3rd and 4th toes or toe webspace.
Severe MTA	The heel bisector line bisects 4th and 5th toes or toe webspace.

Divides the condition into four subtypes:

• Simple MTA: MTA.
• Complex MTA: MTA, lateral shift of midfoot.
• Skew foot: MTA, valgus hindfoot.
• Complex skew foot (serpentine foot): MTA, lateral shift, valgus hindfoot.

Differential diagnosis

Foot deformities:

• Clubfoot.
• Skewfoot: It may not always be possible to different the disorders in infants.
• Atavistic great toe (congenital hallux varus).
• Metatarsus primus varus: The lateral border of the foot is normal, but a medial crease is present secondary to isolated varus alignment of the first ray. This deformity is typically rigid, requires early casting, and may result in hallux valgus.

CLINICAL FEATURES

Symptoms

The parents may complain of intoeing, usually seen in the first year of life.

Signs

Inspection:

• The foot has a kidney-bean shape, because there is a convex lateral border (instead of being straight).
• Forefoot is adducted (at tarsal-metatarsal joint).
• The hindfoot is in a neutral position.
• A medial crease indicates a more rigid deformity.

Palpation:

• The amount of active correction of the deformity can be assessed by tickling the foot.

Motion: There is a normal hindfoot and subtalar motion.

Associated Conditions

Metatarsus adductus can be associated with:

• DDH (in 10-20 %).
• Torticollis.

DIAGNOSIS

Conventional Radiography

Indication: Indicated in older children and children undergoing surgery.
Findings: The mid-tarsal axis will hit the base of the first metatarsal or be lateral to it.

TREATMENT

Overview

Metatarsus adductus is a benign condition that resolves spontaneously in majority of cases.

Nonoperative Treatment

Indication: Deformity that has a passively corrected or rigid component.
Method:

• Flexible deformity:
  • If actively corrected to midline: No treatment required.
  • If passively corrected to midline: Serial (passive) stretching by parents at home.
    
    • The condition usually responds to stretching if peroneal muscle stimulation corrects the deformity.
• Rigid deformity with medial crease: Serial casting between 6 and 12 months of age with the goal of obtaining a straight lateral border of foot.
  • Casting is most effective if started before child reaches one year of age, but casting can be effective in children up to age of 4-5 years.
  • Persistent or rigid forefoot adductus can be readily corrected with cast.

Casting: 

• The cast should extend above knee with knee flexed 20-25° because it allows the child to walk.
• The casts are changed weekly or every second week. Correction is usually achieved after two to three changes.

Operative Treatment

Indication: Severe residual deformity (refractory cases) that produces problems with shoe wear and pain. Indicated only in children older than 7 years.
Method: 

• Lateral column shortening (closing wedge osteotomies) of the calcaneus or cuboid combined with a medial column lengthening (opening wedge osteotomy of the medial cuneiform).
• Abductor hallucis longus recession (for an atavistic frst toe).
• Calcaneal osteotomy for hindfoot valgus in skewfoot.

Operation Methods

• Indication:
  
  • Resistant cases that fail nonoperative treatment (usually with medial skin crease).
  • Severe deformity produces difficulty with shoeware and pain.
• Method:
  • Lateral column shortening done with cuboid closing wedge osteotomy.
  • Medial column lengthening includes a cuneiform opening wedge osteotomy with medial capsular release and abductor hallucis longus recession (for atavistic first toe).

COMPLICATIONS AND PROGNOSIS

Complications

Metatarsus adductus may be associated with late medial cuneiform obliquity but not hallux valgus.

Prognosis

• Spontaneous resolution occurs in 85-90% of children by age 4 years.
• Another 5% resolve in the early walking years (age 1-4 years).
• Residual metatarsus adductus is not related to pain or decreased foot function.