Metatarsus adductus

What is metatarsus adductus, and how common is it?

Metatarsus adductus (also called metatarsus varus or forefoot adductus) is a foot shape in which the front half of the foot turns inward at the tarsometatarsal joint (a joint in the middle of the foot), while the heel and ankle sit normally¹. Seen from above or from the sole, the foot looks C-shaped or bean-shaped². It can affect one foot or both³.

It is the most common foot deformity present at birth⁴. How often it occurs depends on the estimate: about 1 to 2 in every 1000 births⁴, or 0.1% to 1% of births². In the past it was reported more often in girls².

Most cases are flexible, which means the foot can be gently guided back toward a normal position⁵.

What causes it, and who gets it?

It's thought to be related to the position the baby lay in during pregnancy³. Often it results from cramped space in the womb, and the shape is evident from birth⁶. It can be positional (flexible) or structural (fixed)⁷. Beyond womb position and the past tendency in girls, it isn't clear yet who is more likely to have it.

How is it noticed and diagnosed, and what can make it serious?

It's usually noticed by a parent or midwife soon after birth, or when the feet are checked at the newborn examination⁸. The front of the foot turns in, the heel looks normal, and there may be a gap between the big toe and the second toe⁹. A very mild case may not be noticed until a child starts walking and toes in¹⁰.

Diagnosis is made by looking at and moving the foot. The key step is judging how flexible the forefoot is. It's flexible if it can be moved past straight, semiflexible if it can only be brought to straight, and rigid if it can't reach straight². The whole leg (hip, knee and foot) and the way a child walks are also checked².

Some features make it more significant:

• A rigid foot that can't be brought to the middle suggests a fixed (structural) deformity rather than a positional one⁷⁵. It may call for orthopaedic (bone and joint) care, which in selected cases includes casts or a surgical opinion⁵.
• A stiff foot that isn't fully correctable, is painful, or isn't improving within a few months can also mean a fixed deformity³. Pain, or a foot that isn't working normally, also makes it more significant².
• The hips. Hip dysplasia (a hip joint that hasn't formed properly) can occur alongside metatarsus adductus or on its own², so a careful hip examination is advised for a baby with it¹¹. A hip ultrasound scan at around six weeks is sometimes arranged³.
• Skewfoot. Long-standing untreated or undertreated adductus can worsen into skewfoot, with more marked symptoms and deformity¹². In rare uncorrected cases the foot can become Z-shaped¹³.

A few other problems can look similar or occur with it:

• Clubfoot also involves the ankle pointing down (equinus). Metatarsus adductus doesn't².
• Internal tibial torsion is a twisted shin bone that turns the foot in while the kneecaps point forwards⁶.
• Residual clubfoot can come back, usually in children over three, looking like metatarsus adductus¹³.

What helps first?

For flexible feet, watching is the usual first step. Treating flexible metatarsus adductus isn't needed, and the evidence for treating semi-rigid feet is limited⁴. Most cases are managed by watching the foot and reassuring the family². Flexible feet begin to correct within the first 3 months².

Milder cases are managed with follow-up or stretching of the foot¹⁴. Special shoes, orthotics (shoe inserts), braces and physiotherapy are kept for feet that aren't improving², and there's little to show that orthotics or braces help¹⁵.

Sleeping on the tummy and W-sitting (sitting with the knees bent and feet out beside the hips) don't make it worse. That idea is a myth².

What helps if that isn't enough?

Serial casting is the usual next step for a rigid or severe foot, or one that isn't starting to correct on its own²¹⁴. The casts help move the foot into position, and they're usually changed weekly, guided by a physiotherapist¹⁶. For a moderate or severe stiff foot in a baby, treatment with a below-knee plaster cast can take around 6–8 weeks¹⁷. Skewfoot needs about twice as long in casts as simple metatarsus adductus¹⁸.

The evidence for casting is limited, and it isn't clear yet exactly when to move from stretching to casting.

What is the outlook, and can it come back?

The outlook is generally good, because most flexible feet correct without treatment. About 90% of cases have corrected by 1 year of age². Most babies' feet settle over the first two to three years without treatment¹¹, fully by around age three¹⁰, and by age four in 95% of cases³. A flexible foot is expected to have settled by age 2, and if it lingers it typically causes no symptoms².

Flexibility is the main thing that shapes the outlook. If a severe deformity doesn't go away, it can lead to foot problems such as bunions or hammertoes later in life¹⁶.

It isn't clear yet whether any footwear, positioning or stretching programme stops it coming back.