Your foot and ankle contain 26 bones, and seven of these bones are in a group called the tarsal bones. These are located towards the back of the foot, including the heel area. If two or more bones in this area are joined together, it is called a tarsal coalition. The two most common sites affected are between the calcaneus and the talus and between the calcaneus and the navicular. Usually, this condition happens in the womb when the feet are forming. An abnormal band of tissue will form between these two bones.
Although this is generally believed to happen while a baby is growing in the womb, the condition is not usually identified until the child is older. A child still has a lot of cartilage and their bones are still forming. As the cartilage hardens, the bands of tissue connecting the two foot bones may also harden, leading to pain and stiffness. Children between the ages of eight and 16 are most often diagnosed with tarsal coalition. It’s estimated that the rate of occurrence is about one in 100 people, but many are never formally diagnosed as the coalition is too small to cause a problem.
If the coalition is small, there may never be any symptoms. A large band of tissue that has hardened can cause stiffness in the foot. The stiffness also leads to pain. The pain will be felt below the ankle and towards the back of the foot. This condition is a type of flatfoot, so you will notice that the foot is flat to the ground, instead of having a natural arch. The foot is also more rigid than a normal foot. The rigidity and flatness make walking more difficult on uneven surfaces. Someone who has a tarsal coalition may subconsciously roll their ankle more while walking, which can lead to frequent ankle sprains.
A physical examination of the foot may be all the doctor needs to make a diagnosis. The flatness of the foot is one clue, as well as any stiffness while walking. The doctor will check for arches in the feet, especially while the patient is standing on their tiptoes. Even though a physical examination may be enough to diagnose tarsal coalition, a CT scan may also be ordered. This test gives a better view of all of the bones in the foot and will help the doctor see which bones are affected and how large the band is that is connecting the bones. Regular x-rays may also be used. MRIs are less likely to be ordered.