A calcaneonavicular coalition is a condition where two of the bones in the midfoot, the calcaneus and the navicular, are abnormally connected. This condition is one of the most frequent forms of a broader diagnosis called tarsal coalition, which refers to any irregular connection between the seven tarsal bones of the foot. This abnormal union often leads to chronic foot pain and stiffness. While the condition is present from birth, symptoms generally do not become noticeable until adolescence when the connecting tissue begins to harden.
Defining the Calcaneonavicular Coalition
The calcaneonavicular coalition involves an irregular bridge forming between the calcaneus, which is the large heel bone, and the navicular bone, located in the arch of the foot. This coalition represents a failure of the two bones to properly separate during the early stages of fetal development. The connection, often referred to as a “bar,” can be composed of three different tissue types: bone (osseous), cartilage (cartilaginous), or fibrous tissue.
The presence of the coalition limits the normal movement between these tarsal bones, particularly the subtalar joint motion necessary for walking on uneven surfaces. Symptoms typically start between the ages of 8 and 12 years because the initial cartilaginous or fibrous bridge begins to ossify, or turn into solid bone. This process of hardening greatly restricts the foot’s flexibility, leading to pain and other noticeable issues. Calcaneonavicular coalitions are the most common type of tarsal coalition.
Recognizing the Signs and Confirming Diagnosis
The primary symptom is chronic, recurring foot pain that usually worsens with physical activity. This pain is often felt around the outside of the ankle and foot, in an area known as the sinus tarsi. The restricted motion of the subtalar joint can also cause a characteristic issue known as peroneal spastic flatfoot, where the foot is held in a stiff, outward-pointing position.
During a physical examination, a doctor will often observe a limited ability to invert or evert the foot, which are the motions that allow the sole to turn inward and outward. The foot may appear to have a rigid flatfoot deformity, and the arch will not reconstitute when the patient stands on their toes. The initial diagnostic step typically involves standard X-rays of the foot, especially an oblique view, which is considered the best angle for visualizing the calcaneonavicular bar.
While X-rays may reveal a direct bony connection, they may also show indirect signs of the coalition, such as the “anteater sign,” which describes an elongated appearance of the anterior process of the calcaneus. For a more definitive diagnosis and to characterize the tissue type of the bar, advanced imaging is often required. A Computed Tomography (CT) scan is highly effective for determining the size and extent of the coalition, while Magnetic Resonance Imaging (MRI) is particularly helpful for visualizing non-osseous connections.
Treatment Options for Tarsal Coalition
Initial management for a symptomatic calcaneonavicular coalition focuses on conservative, non-surgical methods. This often begins with a period of rest and may include the temporary use of immobilization, such as a cast or walking boot, for several weeks. Over-the-counter anti-inflammatory medications are frequently used.
Long-term non-surgical treatment typically involves the use of custom orthotics designed to support the foot’s arch and limit the painful motion of the affected joints. If symptoms persist despite these conservative efforts, surgical intervention may be considered to restore function and eliminate pain. The two main surgical approaches are coalition resection and joint fusion.
Coalition Resection
Coalition resection involves surgically removing the abnormal bridge of tissue. Material, such as a fat graft or muscle tissue, is then placed into the gap to prevent the bones from reconnecting. This procedure is generally preferred for younger patients with smaller coalitions that do not involve significant joint damage.
Joint Fusion (Arthrodesis)
A procedure called arthrodesis, or joint fusion, eliminates movement by permanently joining the affected bones together. Arthrodesis is typically reserved for cases where an initial resection surgery has failed. It is also used if the coalition is very large and has already led to extensive degenerative changes within the joint.