Tarsal coalition is an abnormal connection between two or more bones in the back and middle of the foot. Instead of separate bones gliding against each other, the affected bones are bridged by bone, cartilage, or fibrous tissue, which restricts normal foot motion. Most people are born with the condition, but symptoms typically don’t appear until late childhood or the teen years, when the connection gradually hardens into bone.
Which Bones Are Involved
The foot contains seven tarsal bones that work together to absorb impact and adapt to uneven ground. Two pairings account for the vast majority of coalitions. The calcaneonavicular type connects the heel bone to the navicular bone on the inner midfoot. The talocalcaneal type bridges the talus (the bone that sits between the shin and heel) to the calcaneus (heel bone) at the subtalar joint. Less common coalitions can occur between other tarsal bones, but these two types dominate clinical practice.
Why Symptoms Appear in Adolescence
Babies born with a tarsal coalition often have no symptoms at all because the bridge between bones starts out as flexible cartilage or fibrous tissue. As a child grows, that bridge slowly ossifies, turning into rigid bone. Calcaneonavicular coalitions typically ossify between ages 8 and 12, while talocalcaneal coalitions harden later, usually between 12 and 15. Once the bridge becomes bony, it locks the affected joints in place, and the foot can no longer move the way it needs to. That’s when pain and stiffness show up, often during sports or growth spurts.
What It Feels Like
The hallmark of tarsal coalition is a rigid flat foot. Unlike a flexible flat foot (where the arch disappears when standing but reappears on tiptoe), a foot with a coalition stays flat even when you push up on your toes and lift the heel. That rigidity creates a cascade of problems.
Walking on uneven surfaces like trails, grass, or gravel becomes difficult because the foot can’t adjust to the terrain. To compensate, the ankle often rolls inward more than normal, which can lead to repeated ankle sprains. Deep, aching pain around the outer ankle or the top of the foot is common, especially after activity. Some people also notice muscle fatigue or cramping in the lower leg because the calf and shin muscles work harder to make up for the foot’s lost motion.
How It Runs in Families
Tarsal coalition has a genetic component. A related condition called tarsal-carpal coalition syndrome follows an autosomal dominant inheritance pattern, meaning a child needs only one copy of the altered gene from one parent to develop the condition. Mutations in the NOG gene, which produces a protein called noggin, are responsible. Noggin normally acts as a brake on bone growth signals in joint areas. When it’s reduced, those signals go unchecked and stimulate bone to form where it shouldn’t, fusing joints together. Not all isolated tarsal coalitions trace to this specific gene, but the condition clearly clusters in families, and bilateral involvement (both feet affected) is common.
How It’s Diagnosed
Diagnosis often starts with a standard X-ray of the foot. Two classic signs help radiologists spot a coalition even on plain film. The “anteater sign” appears when the front portion of the heel bone looks elongated and broad, resembling an anteater’s snout, rather than its normal triangular shape. This points to a calcaneonavicular coalition. The “C sign” shows up as a continuous curved line on a side-view X-ray, arcing from the inner edge of the talus down to a small shelf on the heel bone called the sustentaculum tali. This suggests a talocalcaneal coalition.
When X-rays are suggestive but not definitive, CT scans and MRI provide much higher accuracy. CT is especially good at visualizing bony coalitions, while MRI can detect cartilaginous and fibrous bridges that haven’t yet turned to bone. These advanced scans also help surgeons measure the size and exact location of the coalition if surgery becomes an option.
Non-Surgical Treatment
Initial treatment is almost always conservative: activity modification, supportive shoe inserts, and sometimes a period of immobilization in a walking boot or cast to calm inflammation. The goal is to reduce pain enough to return to normal activity.
For some people, this approach works well enough to manage symptoms long term. But the data on orthotics and activity modification paint a more sobering picture for active individuals. In one study published in the Journal of the American Podiatric Medical Association, patients who did not have surgery were statistically far less likely to return to their desired activity level (P < .001). Use of foot orthotics alone had a moderate correlation with lower-than-desired activity levels. That doesn't mean orthotics are ineffective for pain relief, but it does suggest they may not be enough for people who want to stay active in sports or physically demanding work.
When Surgery Makes Sense
Surgery enters the conversation when conservative measures fail to control pain or when the coalition significantly limits function. The two main surgical approaches are resection (removing the abnormal bridge) and arthrodesis (fusing the affected joints permanently).
Resection is the preferred option for younger patients and smaller coalitions. For calcaneonavicular coalitions, resection has long been considered the standard. For talocalcaneal coalitions, a traditional guideline recommended resection only if the coalition occupied less than half the width of the subtalar joint surface on a CT scan. If the coalition was larger, surgeons historically turned to triple arthrodesis, which fuses three joints in the hindfoot.
More recent thinking has shifted the decision-making framework. Rather than focusing solely on coalition size, many pediatric orthopedic surgeons now evaluate the health of the surrounding joint cartilage, particularly the posterior facet of the subtalar joint. A coalition that’s relatively large but sits next to healthy cartilage may still respond well to resection. When the nearby cartilage is already damaged or thinned, fusion becomes more appropriate regardless of the coalition’s size.
Recovery After Resection Surgery
A large retrospective study of 97 resections in 78 patients offers a detailed picture of what recovery looks like. Patients are typically non-weight-bearing for two weeks after surgery, either in a walking boot or a below-knee cast. After suture removal, range-of-motion exercises begin. A walking boot continues for another two weeks, and formal physical therapy starts around the four-week mark, focusing on balance, strengthening, and flexibility.
If additional procedures were performed alongside the resection (such as a bone realignment to correct flatfoot), the timeline stretches. Weight-bearing may not begin until four to six weeks, with a transition to an ankle brace around eight to ten weeks.
On average, patients returned to their desired activity level about 18 weeks after surgery. Calcaneonavicular resections recovered slightly faster, at roughly 15 weeks, while talocalcaneal resections averaged closer to 19 weeks. The overall results were favorable: most patients reported little to no pain once back in sports, and only 4% experienced a lasting decrease in their desired activity level after surgery. About 12% showed signs of degenerative joint changes on follow-up X-rays, though in many of those cases the degeneration had already been present before or during the operation.
Long-Term Outlook
Left untreated, a symptomatic tarsal coalition forces the surrounding joints to absorb extra stress year after year. Over time, this can accelerate wear and tear in the subtalar joint, the ankle, and the midfoot, leading to early-onset arthritis. For people whose symptoms are mild or who aren’t very active, monitoring and supportive measures may be perfectly reasonable. But for young athletes or anyone whose pain limits daily life, early surgical resection offers the best chance of preserving joint health and returning to full activity. The condition itself isn’t dangerous, but ignoring persistent foot pain and stiffness through the adolescent years can shape how the foot functions for decades.