Medically Reviewed | Dr. Tom Biernacki, DPM | Board-Certified Podiatric Surgeon | Balance Foot & Ankle, Michigan
Quick Answer: Tarsal coalition is an abnormal fibrous, cartilaginous, or bony union between two hindfoot or midfoot bones, most commonly the calcaneonavicular (CN) and talocalcaneal (TC, subtalar) joints. Incidence: 1-2% of the population; bilateral in 25-50%. Presents in adolescence when fibrous/cartilaginous coalition undergoes progressive ossification (10-12 years for CN, 12-15 years for TC), causing increasing hindfoot pain and stiffness. Classic clinical findings: rigid flatfoot (cannot correct on tiptoe), peroneal spasm (painful contracture of peroneal muscles — the ‘peroneal spastic flatfoot’), and limited subtalar inversion/eversion. Diagnosis: plain X-ray often insufficient (anteater sign for CN coalition); CT is gold standard for bony coalitions; MRI for fibrous/cartilaginous coalitions. Conservative management: rest, cast immobilization for acute pain, custom orthotics (UCBL) for flexible phase. Surgical management: coalition resection with fat/muscle interposition (preferred in children and young adults before arthritic changes); subtalar or triple arthrodesis for failed resection or established arthritis.
Tarsal coalition is one of the most frequently missed causes of foot pain and rigid flatfoot in adolescents and young adults. It is a congenital failure of separation between two hindfoot or midfoot bones — resulting in a fibrous, cartilaginous, or bony bridge that restricts subtalar motion and eventually causes pain when the coalition begins to ossify.
What Is Tarsal Coalition?
During embryonic foot development, the hindfoot bones normally differentiate and separate. In tarsal coalition, this separation is incomplete, leaving a fibrous, cartilaginous, or bony connection between two bones. The most common types:
Calcaneonavicular (CN) coalition: Between the anterior process of the calcaneus and the navicular on the medial side of the foot. This is the most common type (~53% of coalitions). Visible on lateral and oblique X-ray as the “anteater sign” — elongation of the anterior calcaneal process.
Talocalcaneal (TC) coalition: Between the talus and calcaneus at the middle facet of the subtalar joint. The most common coalition causing the peroneal spastic flatfoot. CT is required for diagnosis.
When and How It Presents
Most coalitions remain asymptomatic throughout childhood while they are fibrous or cartilaginous and allow some motion. As the coalition progressively ossifies (CN: typically 8-12 years; TC: 12-16 years), motion is lost, pain develops, and the peroneal muscles go into protective spasm — the classic “peroneal spastic flatfoot.”
Presentation: adolescent or young adult with progressive hindfoot pain, rigid flatfoot, limited subtalar motion, peroneal muscle spasm and contracture, and often a history of multiple “ankle sprains” that don’t fully resolve. Bilateral in 25-50% of cases.
Diagnosis
Weight-bearing X-rays in three views — sometimes showing the anteater sign for CN coalition. CT scan is the gold standard for bony coalitions — clearly shows the bridge and characterizes secondary arthritic changes. MRI is preferred for fibrous and cartilaginous coalitions and for evaluating adjacent cartilage.
Treatment
Conservative management: Rest, activity modification, and a custom UCBL orthosis or walking cast during acute painful episodes. Most patients with mild, non-arthritic coalitions can be managed conservatively for years. Physical therapy focuses on peroneal stretching and hindfoot mobility.
Coalition resection: Surgical removal of the coalition with interposition of fat, extensor digitorum brevis muscle, or bone wax to prevent reformation. Most appropriate for young patients with no secondary subtalar arthritic changes. Return to full activity in 3-6 months. Good to excellent results in well-selected patients.
Arthrodesis: Subtalar fusion (for TC coalition with established arthritis) or triple arthrodesis (for severe rigid deformity with multi-joint arthritis) is performed when resection is not appropriate or has failed. Permanently eliminates motion but reliably eliminates pain.
Dr. Tom's Product Recommendations
Recommended Support for Tarsal Coalition
PowerStep Pinnacle BLUE Insole (Arch Support)
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Low-to-medium arch support insole — a starting point for mild, non-arthritic tarsal coalition during conservative management.
Dr. Tom says: “An OTC insole with arch support can provide symptomatic relief for mild tarsal coalition during the conservative management phase. This is not a long-term solution for significant coalition — custom UCBL bracing is preferable — but it’s reasonable to try while awaiting specialist evaluation.”
Mild symptomatic coalition, early conservative phase
Established rigid coalition with peroneal spasm or arthritic changes — needs specialist evaluation
Disclosure: We earn a commission at no extra cost to you.
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Dr. Tom Biernacki’s Recommendation
Tarsal coalition is a diagnosis I think about whenever an adolescent presents with rigid flatfoot and repeated ‘ankle sprains.’ It is satisfying to finally give these patients an answer after years of being told nothing is wrong. Coalition resection in young patients with no arthritis works very well.
— Dr. Tom Biernacki, DPM | Board-Certified Podiatric Surgeon | Balance Foot & Ankle
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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.
- Diagnosis and Treatment of Plantar Fasciitis (PubMed / AAFP)
- Heel Pain (APMA)
- Hallux Valgus (Bunions): Evaluation and Management (PubMed)
- Bunions (Mayo Clinic)