A tarsal coalition is an abnormal connection between two bones in the midfoot and/or rearfoot. The term tarsal refers to the name used for the group of bones in the mid and rear portions of the foot. The term coalition refers to the abnormal connection, union, or bridge between two of the bones.
The most common tarsal bones affected are the heel bone (calcaneus) and the bones near the ankle (talus and navicular). The two most common coalitions are the talocalcaneal (between the talus and calcaneus) and the calcaneonavicular (between the calcaneus and navicular). Although tarsal coalitions can occur between any two or more bones, all are far rarer than the talocalcaneal and calcaneonavicular coalitions. Coalitions may involve an abnormal connection that is bony (synostosis), cartilaginous (synchondrosis), fibrous (syndesmosis), or combinations of these types. The extent of the abnormal the abnormal connection can be minimal to extensive, and can even replace the usual location of a joint.
Tarsal coalitions occur congenitally (present since birth) in about 1% of all people and may effect only one foot or both feet. However, the pain from a tarsal coalition may not arise until adolescence or later. Some individuals with tarsal coalition do not experience any pain. The abnormal connection between two bones in a tarsal coalition prevents what would otherwise be normal movement between the two bones. As consequence, the hindfoot and/or midfoot usually are stiff and immobile in a foot affected by a tarsal coalition. As a person ages, the abnormal connection becomes more bony and stiffer, which is why the pain from a tarsal coalition usually arises in adolescence (when the bones of the foot complete their bone formation) or later. Because of the restricted movement between two bones affected by a tarsal coalition, the joints around the coalition are functionally impaired and can develop painful degenerative arthritis as the person ages. In some cases, an injury can disrupt and aggravate a previously non-painful tarsal coalition.
A person affected by a tarsal coalition is often flat-footed on the foot in which the tarsal coalition exists. Pain is usually present just below the ankle area and made worse with weight bearing activities. In some cases, the muscles on the outside of the leg will spasm. Tarsal coalitions can often be diagnosed simply with an examination and standard radiographs (x-rays). However, special imaging techniques (CT scan or MRI) are also used to confirm the diagnosis and determine both, the extent of the coalition (abnormal connection) and whether degenerative joint disease is present in the nearby joints.
Non-surgical treatment is directed at allowing the person affected by a tarsal coalition to live a painfree life, but does not correct existing malalignment of the foot. Surgery to remove the abnormal connection can be performed, but its success depends on a number of factors, including the person’s age, the extent of the abnormal connection, and whether there is degenerative arthritis in the nearby joints. When the predicted outcome of removal of the abnormal connection (resection of the coalition) is poor, then surgical fusion of the two involved bones is performed.