Metatarsus adductus is the most common foot disorder in infants. It is characterized by a convexity of the lateral foot and is caused by in utero positioning. It is bilateral in half of the cases. Occurring equally in boys and girls, it is more common in first-born children due to the smaller primigravid uterus. Two percent of infants with metatarsus adductus have developmental dysplasia of the hip.
The forefoot is adducted and sometimes supinated, but the midfoot and hind foot are normal. The lateral border of the foot is convex, while the medial border is concave. Ankle dorsiflexion and plantar flexion are normal. With the midfoot and hindfoot stabilized, the deformity can be pushed beyond a neutral position (into abduction). Older children may present with an in-toeing gait.
True metatarsus adductus resolves spontaneously over 90% of the time without treatment, so reassurance is all that is needed. Metatarsus adductus that does not improve within 2 years needs evaluation by a pediatric orthopedist. Persistent cases may benefit from serial casting or bracing, and potentially surgery. Many feel that it is acceptable to live with the deformity because it is not associated with a disability.
It is important to differentiate between metatarsus adductus, metatarsus varus, and skewfoot. Metatarsus varus looks like metatarsus adductus, but it is an uncommon rigid deformity that will need serial casting. Skewfoot is an uncommon deformity that is characterized by hindfoot plantar flexion, midfoot abduction, and forefoot adduction, giving the foot a Z or serpentine appearance. This needs to be managed very carefully with serial casting and surgery to help reduce the risk of disability in adulthood.