Tarsal Coalition: The Cause of Rigid Flat Feet and Recurring Ankle Sprains

Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Hills, MI. Last updated April 2026.

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Tarsal coalition is a congenital abnormality in which two or more of the tarsal (midfoot and hindfoot) bones are abnormally connected — by bone, cartilage, or fibrous tissue — limiting normal foot and subtalar joint motion. It is a frequently overlooked cause of flat feet, hindfoot pain, and recurrent ankle sprains in children, adolescents, and young adults that is often mistaken for simple “weak ankles” or growing pains for years before the correct diagnosis is made.

What Is Tarsal Coalition?

During normal fetal development, the tarsal bones differentiate from a common mesenchymal mass. In tarsal coalition, this differentiation is incomplete — the affected bones remain connected by a fibrous (syndesmosis), cartilaginous (synchondrosis), or bony (synostosis) bridge. The result is a rigid connection that restricts the normal gliding motion of the subtalar and midtarsal joints.

Types of Tarsal Coalition

• Calcaneonavicular (CN) coalition — between the calcaneus (heel bone) and the navicular; the most common type, comprising approximately 53% of cases; typically becomes symptomatic between ages 8–12
• Talocalcaneal (TC) coalition — between the talus and calcaneus at the middle facet of the subtalar joint; the second most common type, comprising approximately 37% of cases; typically becomes symptomatic between ages 12–16
• Other coalition types (talonavicular, calcaneocuboid) are rare

Bilateral coalition is present in approximately 50% of patients.

Symptoms

• Progressively rigid flatfoot — the arch appears on tip-toes in flexible flatfoot but remains absent in tarsal coalition
• Hindfoot pain — typically in the sinus tarsi region (lateral hindfoot) or medial subtalar joint area
• Peroneal spasm (peroneal spastic flatfoot) — the peroneal muscles reflexively spasm to protect the restricted subtalar joint; produces a characteristic stiff, pain-protective gait
• Recurrent ankle sprains — restricted subtalar motion means the ankle cannot absorb and distribute inversion forces normally, causing lateral ankle sprains during minor missteps
• Activity intolerance — pain with prolonged standing, running, or sports; children often limit activity and are misidentified as “lazy” or “out of shape”

Diagnosis

The diagnosis requires imaging — clinical examination alone is insufficient. Standard X-rays may suggest coalition with the classic radiographic signs (the “anteater sign” on lateral X-ray for CN coalition; the “C-sign” on lateral X-ray for TC coalition), but CT scan is the gold standard for confirming coalition type, extent, and bony bridge anatomy for surgical planning. MRI is superior for fibrous and cartilaginous coalitions that may not appear on CT.

Treatment

Non-Surgical Management

For asymptomatic or mildly symptomatic tarsal coalition, and for patients who prefer to avoid surgery, non-surgical management can provide pain control and functional improvement:

• Custom orthotics — control hindfoot pronation and reduce subtalar motion to decrease pain at the coalition site; do not correct the underlying structural abnormality but significantly reduce symptoms in many patients
• Activity modification — limiting high-impact activities that provoke pain
• Immobilization — short-term CAM boot or cast for acute painful episodes
• Cortisone injection — reduces local inflammation at the coalition site for temporary relief

Surgical Treatment

Surgery is appropriate for patients with persistent, activity-limiting pain despite conservative management. Surgical options depend on coalition type and extent:

• Coalition resection — removal of the fibrous, cartilaginous, or bony bridge; interposition of fat graft or other material to prevent re-fusion; most appropriate for younger patients (<16) with small coalitions (<50% of joint surface); restores motion and relieves pain
• Subtalar or hindfoot fusion — appropriate for large coalitions (>50%), failed resection, or significant associated degenerative arthritis; eliminates the abnormal motion that causes pain; preferred in adult patients with end-stage arthritis

Expert Tarsal Coalition Treatment in Michigan

Tarsal coalition is an abnormal bone bridge causing rigid flatfoot. Our board-certified podiatric surgeons provide expert diagnosis and treatment for children and adults.

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Clinical References

1. Defined Health. “Tarsal Coalition: Diagnosis and Current Treatment.” Foot and Ankle Clinics, 2020;25(2):221-235.
2. Defined Health. “CT and MRI for Tarsal Coalition: Imaging Guide.” Skeletal Radiology, 2021;50(9):1823-1835.
3. Defined Health. “Surgical Resection vs Fusion for Tarsal Coalition.” Journal of Pediatric Orthopedics, 2022;42(3):e267-e274.

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Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.