Ankle pain is a common complaint among athletes. The vast majority of cases are related to direct trauma – most commonly ankle sprains or simple avulsion fractures. It is however important to recognise that there are other potential causes of ankle pain. One of these is a tarsal coalition.

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Patients presenting with a tarsal coalition generally present with an insidious onset of foot and ankle pain. The patient may relate the onset of their pain to trauma – however, this is generally fairly minor. A history of recurring ‘ankle sprains’ may also be given. Tarsal coalitions generally present when the patient is in their mid to late teens. This is because the coalition starts to become symptomatic when it starts to ossify. The key examination finding is of stiffness of the sub-talar joint.

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While a tarsal coalition can potentially affect any bones in the foot the most common are calcaneo-navicular and talo-calcaneal coalitions. It is important to remember when you are treating this problem that they can be bilateral.

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While a CT scan or MRI is generally needed to define this injury, they can often be shown on a simple x-ray. An oblique view of the mid-foot or a Harris-Beath view may be helpful. The following x-ray findings may help to diagnose a tarsal coalition.

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Calcaneo-navicular coalition

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This should be suspected whenever there is elongation or squaring of the anterior process of calcaneus (quite subtle on this image).  This is usually best appreciated on a lateral or oblique view.

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Talo-calcaneal Coalition

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This condition involves fusion across the middle subtalar joint at the level of the sustentaculum tali.  This should be suspected when one observes prominent beaking of the talar head on a lateral view.  A ‘C-sign’ can also usually be seen (a continuous cortical line running from the talar dome to the under surface of the sustentaculum tali) on the lateral view. This represents bridging between the middle subtalar joint.

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If you suspect that your patient may have a tarsal coalition they should generally be referred for a specialist opinion (with a view to obtaining further imaging). Appropriate treatment is needed to make sure that the patient’s symptoms resolve – and to minimise the risk of future joint disease.

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