Tarsal coalition

A tarsal coalition is an abnormal connection between two or more of the small bones at the back of your foot, called the tarsal bones, which can make part of your foot stiff. It is present from birth, but often isn't noticed until the bones harden in later childhood or the teenage years, which is when it can start to cause pain.

What are the symptoms of tarsal coalition?

Many people with a tarsal coalition have no symptoms at all and the condition is only picked up by chance, for example on an X-ray taken for something else. When symptoms do develop, they can include:

• pain below the ankle, around the middle or back of the foot, which often gets worse with activity
• a stiff, flat foot that doesn't form an arch even when you stand on your tiptoes
• difficulty walking on uneven ground
• frequent ankle sprains
• cramping or spasms in the muscles of your lower leg

Both feet are affected in around half of people with the condition, though symptoms often only show up on one side.

What causes tarsal coalition and who is at risk?

In most cases, a tarsal coalition happens because two or more bones in the foot fail to separate properly before birth. This is usually genetic and can run in families.

Less often, a coalition can develop later in life, caused by an injury, an infection, or arthritis in the joint.

It's thought to affect around 1 in 100 people, though estimates go up to about 1 in 20, since many cases cause no symptoms and are never diagnosed.

Are there different types of tarsal coalition?

Yes. Coalitions are usually described in two ways: by which bones are joined, and by the type of tissue connecting them.

The two most common locations are:

• a calcaneonavicular coalition, between the heel bone and the navicular bone (a bone at the front of the heel bone); this is the most common type, and tends to start causing symptoms earlier, typically between the ages of 8 and 12
• a talocalcaneal (subtalar) coalition, between the heel bone and the talus (the bone that sits on top of it); this tends to cause symptoms a little later, typically between the ages of 12 and 15

A connection between the talus and navicular bones is also possible, but is much rarer.

The connecting tissue itself can be made of bone, cartilage, or fibrous tissue (similar to scar tissue). As you grow, this tissue can gradually harden into solid bone, in a process called ossification. This is often when symptoms first appear, because the joint becomes stiffer.

How is tarsal coalition diagnosed?

Your doctor will examine your foot, checking how well the joints move and how your foot looks when you stand normally and on your tiptoes. In tarsal coalition, the arch typically stays flat even when you rise onto your toes, which helps tell it apart from other causes of flat feet.

To confirm the diagnosis, you'll usually need imaging tests, which may include:

• an X-ray, which can often show the coalition, especially if it's made of bone
• a CT scan, which gives a more detailed, three-dimensional picture and is often the best test for planning treatment
• an MRI scan, which is better at showing coalitions made of cartilage or fibrous tissue that don't always show up on X-rays or CT scans

How is tarsal coalition treated?

Most people try non-surgical treatment first. Options include:

• resting from high-impact activities for a few weeks (typically 3–6 weeks) to let inflammation settle
• physiotherapy to stretch and strengthen the muscles around the foot
• orthotics, such as arch supports, insoles or an ankle brace, to support the foot
• a boot or cast worn for a few weeks to rest the joint
• pain relief, such as anti-inflammatory medicine or a steroid injection

If non-surgical treatment doesn't ease your symptoms, or your pain and mobility are significantly affecting your daily life, surgery may be considered. The main options are:

• resection, where the coalition is removed and a small graft of fat or muscle is placed in the gap to help stop it growing back; this usually preserves more movement in the foot and is often used when there is little or no arthritis
• fusion (arthrodesis), where the affected joint is fixed in place with screws, pins or plates; this is more often used for larger coalitions or when arthritis is already present, and trades some movement for pain relief

If your foot is very flat, a separate procedure to realign it may be carried out at the same time as the resection. Afterwards, you'll usually need a period in a cast or boot while the foot heals. It's worth knowing that surgery won't make the foot completely normal, as the joints were never entirely normal to begin with, so some stiffness is likely to remain.

When should I see a doctor?

See your (or your child's) doctor if you notice:

• foot or ankle pain that does not go away, particularly around the middle or back of the foot
• ongoing stiffness in the foot
• repeated ankle sprains, especially without an obvious cause
• growing difficulty walking on uneven ground, or increasing pain with activity

Your doctor can examine the foot and arrange further tests if needed, and work out a management plan suited to your symptoms.