A tarsal coalition is when two tarsal bones (the bones of the mid- and rear-foot) become fused. This can cause pain and a loss of motion at the effected joint, as well as other biomechanical symptoms.
The most common joint to be effected by a tarsal coalition is the subtalar joint, which is a joint formed by the articulation between the talus and the calcaneus. There are actually three facets between the two bones that help to form the joint – the anterior, middle, and posterior facets. Most commonly, a talocalcalcaneal coalition is formed between the middle facets. When a coalition exists between the talus and the calcaneus, it may present as a rigid flatfoot deformity with considerable decrease in range of motion.
Other tarsal coalitions that are occasionally seen include calcaneo-navicular and talo-navicular coalitions, though these are much less common than talocalcaneal coalitions. Overall, the incidence of tarsal coalitions is about 1% of the population. There is a familial inheritance that is often seen with tarsal coalition, though it is not thoroughly understood.
The cause of congenital tarsal coalition has been an area of interest for quite some time. It was first proposed in 1897 that they were caused by the incorporation of accessory bones within the joint, but was later postulated that the bones actually failed to separate in the fetus. The latter of the two explanations is the more commonly accepted situation.
Tarsal coalitions may also be acquired from trauma to the joint, degenerative changes to the joint such as what is seen in osteoarthritis, and fractures through the joint space.
Diagnosis of tarsal coalition comes from a combination of clinical findings, as well as x-ray, CT, and MRI imaging. Imaging techniques allow a doctor to visualize the joints to evaluate for fusion.
Clinical findings include pain, stiffness and decreased range of motion at the joint, rigid flatfoot deformity, and local tenderness and possibly swelling.
Conservative treatment is usually initiated once the diagnosis is made. This most commonly includes custom-made orthotic devices that prevent the effected joint from moving too much. The movement of the fused joint is what causes much of the pain. Immobilization may be required with an ankle brace or other device. Physical therapy can help in some cases, as well as shoe modifications to accommodate the coalition.
Surgical treatment can include either removal of the coalition or a fusion of the joint to prevent movement altogether. There are several different ways of performing each of these types of procedures, depending on the individual patient and situation.
