Tarsal coalition is an abnormal connection between two or more bones in the midfoot or hindfoot. This union, which can be composed of bone, cartilage, or fibrous tissue, restricts the natural movement of the foot. It is a common underlying cause of a rigid flatfoot deformity, where the arch does not reappear when the person stands on their toes. While the condition is present from birth, symptoms often emerge later in life, typically during the adolescent years.
Understanding the Fusion and Its Origins
The foot is a complex structure containing seven tarsal bones, with the talus, calcaneus (heel bone), and navicular being the most commonly involved in this condition. Tarsal coalition represents a failure of these bones to properly form separate joints during fetal development. This developmental error is congenital, often due to an inherited genetic abnormality.
The abnormal bridge between the bones can take one of three forms: a bony fusion (synostosis), a cartilaginous connection (synchondrosis), or a fibrous tissue link (syndesmosis). Regardless of the composition, this bridge acts as a bar that prevents the smooth gliding and rotation necessary for normal foot mechanics. The condition often progresses as a child grows, becoming symptomatic when the initially soft cartilage or fibrous tissue begins to harden and transform into bone.
Signs and Symptoms of Tarsal Coalition
Although present from birth, the foot remains asymptomatic while the connecting bar is soft cartilage. Symptoms typically begin to appear in late childhood or early adolescence, usually between the ages of 8 and 16, a period when the coalition starts to ossify. This hardening process removes the last bit of flexibility, leading to pain and stiffness.
The most noticeable sign is often a rigid flatfoot, which contrasts with a flexible flatfoot where the arch appears when the foot is non-weightbearing. Pain is commonly felt in the midfoot or hindfoot, often worsening with increased physical activity and sometimes radiating into the lower leg. The foot’s restricted motion can cause the peroneal tendons on the outside of the ankle to spasm and tighten, a condition sometimes called peroneal spastic flatfoot. This muscle spasm can cause the foot to turn outward when walking, leading to a noticeable limp or an awkward gait.
How Doctors Confirm the Diagnosis
Diagnosis typically begins with a thorough physical examination, where a doctor assesses the range of motion in the foot and ankle, especially the subtalar joint. The inability to invert or evert the foot, or the persistence of a flat arch when the patient stands on their toes, often raises suspicion for a tarsal coalition. Tenderness is frequently noted over the specific location of the coalition.
Initial screening often involves standard X-rays, which are useful for identifying bony fusions, particularly the calcaneonavicular type, which may show a characteristic “anteater nose” sign. However, X-rays can easily miss coalitions composed primarily of cartilage or fibrous tissue, leading to the need for more advanced imaging. A Computed Tomography (CT) scan provides high-resolution, three-dimensional images, making it the most reliable method for confirming bony coalitions and determining their size and location for surgical planning. Magnetic Resonance Imaging (MRI) is particularly helpful for visualizing soft tissue bridges, such as fibrous or cartilaginous connections, which X-rays or CT scans may miss.
Treatment and Management Strategies
The primary goal of treatment is to relieve pain and restore foot function, beginning almost always with non-operative conservative management aimed at reducing inflammation and limiting painful motion. These methods include a temporary period of rest and activity modification, often involving the use of a walking boot or a cast for three to six weeks to fully immobilize the foot.
Custom-made orthotic inserts are frequently prescribed to stabilize the foot, provide arch support, and redistribute pressure away from the painful area. Non-steroidal anti-inflammatory drugs (NSAIDs) can help manage pain and reduce localized swelling. For persistent pain, a doctor may recommend a corticosteroid injection directly into the affected joint to deliver a powerful anti-inflammatory effect.
If conservative treatments fail to provide lasting relief, surgical intervention may be considered to address the underlying structural problem. The choice of procedure depends mainly on the size of the coalition and whether arthritis has developed in the surrounding joints. For smaller coalitions, resection is performed, where the abnormal connection is removed to restore foot motion. After resection, a barrier of muscle or fat tissue is often placed in the gap to prevent the bones from fusing together again.
If the coalition is extensive, involves a large portion of the joint surface, or if significant arthritis has already developed, a joint fusion, known as arthrodesis, may be necessary. This procedure permanently unites the involved bones, sacrificing motion to create a stable, pain-free foot. While arthrodesis results in a stiffer foot, it is often the most effective option for severe cases, providing long-term pain relief.