Tarsal Coalition: Fused Foot Bones, Symptoms & Treatment

Quick answer

A tarsal coalition is an abnormal connection between two of the bones in the back of the foot, present from birth. The connection can be made of bone, cartilage, or fibrous tissue. Many coalitions are silent in childhood and only become symptomatic in adolescence, when they begin to ossify (turn into solid bone) and the limited motion becomes apparent. The classic patient: a teenager with persistent foot pain, frequent “sprains,” or a stiff flatfoot.

The two main types

Two coalitions account for the great majority of cases:

• Calcaneonavicular coalition — between the calcaneus (heel bone) and navicular. Roughly 50% of cases. Symptoms typically begin around ages 8–12.
• Talocalcaneal coalition — between the talus and calcaneus, usually at the middle subtalar facet. Roughly 40% of cases. Symptoms typically begin around ages 12–16.

Other less common types involve the navicular-cuneiform joint, the calcaneocuboid joint, and others.

Why coalitions become painful when they do

Coalitions develop in fetal life — the joint that “should” form between two bones doesn’t form, leaving them connected. In childhood, the connection is typically cartilaginous or fibrous, allowing some flexibility. Symptoms are usually absent.

As the patient enters adolescence:

• The cartilage ossifies (turns to solid bone)
• Motion at the affected joint decreases sharply
• Adjacent joints have to compensate, often with pain
• Repeated minor injuries (ankle sprains) become common because the foot can’t accommodate uneven ground
• The peroneal muscles can spasm in response to abnormal mechanics — historically called “peroneal spastic flatfoot”

This is why the diagnosis is most often made in teenagers, even though the coalition has been there since birth.

How to recognize it

• Persistent foot or ankle pain in an adolescent, often without clear injury
• Frequent ankle sprains with minimal mechanism
• Stiff flatfoot — the arch doesn’t reform when the patient stands on tiptoe (a classic exam finding)
• Pain with running, jumping, walking on uneven ground
• Vague aching in the hindfoot, lateral foot, or just below the ankle
• Limited subtalar motion on exam — the heel doesn’t tilt side-to-side normally
• Sometimes muscle spasm in the peroneal tendons

About 50% of patients have bilateral coalitions, though they may not be symptomatic on both sides at the same time.

Diagnosis

• Physical exam — limited subtalar motion is the key finding; stiff flatfoot is suggestive
• X-rays — can show calcaneonavicular coalitions well; may miss talocalcaneal coalitions, which often require additional imaging
• CT scan — gold standard for bony coalitions; shows the location and completeness of the connection
• MRI — best for fibrous and cartilaginous coalitions before ossification, and for evaluating cartilage and surrounding tissues
• Sometimes both CT and MRI for surgical planning

Standardized X-ray views (oblique view for calcaneonavicular, axial Harris view for talocalcaneal) help when initial X-rays are unrevealing.

Treatment

Conservative care (first-line)

Many coalitions can be managed without surgery:

• Activity modification — reduce high-impact activities during flares
• Walking boot or short-leg cast for 4–6 weeks during acute pain — often dramatically helpful
• Custom orthotics with hindfoot support and motion control
• NSAIDs for inflammation
• Physical therapy — strengthening, flexibility, peroneal tendon work
• Cortisone injection in selected cases

A meaningful percentage of patients become asymptomatic with these measures and avoid surgery long-term.

Surgery

For coalitions that don’t respond to conservative care:

• Coalition resection — the abnormal bony bridge is surgically removed and the resulting gap filled with fat or muscle to prevent recurrence. Best results in young patients with small coalitions and minimal arthritis.
• Subtalar fusion — for large talocalcaneal coalitions or when arthritis has developed in adjacent joints
• Triple arthrodesis — for advanced cases with extensive arthritis
• Recovery typically 8–12 weeks, with a long return to full activity

The choice between resection and fusion depends on coalition size, the patient’s age, and the status of surrounding joints. Younger patients with smaller coalitions and healthy adjacent joints do best with resection.

Bottom line

Tarsal coalition is the underdiagnosed cause of “ankle problems” in many teenagers — a stiff flatfoot, frequent sprains, or persistent ankle pain that doesn’t fit normal sprain biology. CT imaging usually clinches the diagnosis. Conservative care helps a meaningful fraction of patients; surgery is well-established and effective for those who need it. Catching it early gives the best surgical options before secondary arthritis develops.