Tarsal coalition is an abnormal connection between two or more of the tarsal bones of the hindfoot or midfoot, formed through bone, cartilage, or fibrous tissue. It is a congenital condition — present from birth — resulting from incomplete segmentation of the developing foot bones. While often silent in childhood, it typically becomes painful in adolescence as the bridge ossifies and restricts normal subtalar motion.
Tarsal coalition is an important cause of rigid flatfoot and chronic hindfoot pain in adolescents and young adults. Its symptoms overlap significantly with sinus tarsi syndrome and plantar fasciitis, and it can predispose to ankle ligament sprains due to compensatory gait mechanics and restricted subtalar motion.
Causes
Tarsal coalition is a congenital condition caused by a failure of normal mesenchymal segmentation during fetal development. Rather than separating into distinct bones, two or more tarsal bones remain connected by an abnormal bridge of bone (synostosis), cartilage (synchondrosis), or fibrous tissue (syndesmosis).
- Calcaneonavicular coalition: The most common type, occurring between the anterior calcaneus and the navicular. Typically becomes symptomatic between ages 8–12 as the fibrocartilaginous bridge begins to ossify.
- Talocalcaneal coalition: The second most common type, involving the middle facet of the subtalar joint between the talus and calcaneus. Usually presents between ages 12–16, often with more severe subtalar stiffness and pain than calcaneonavicular coalition.
- Other coalitions: Talonavicular and calcaneocuboid coalitions are less common and may be associated with more complex foot deformities.
- Genetic inheritance: Tarsal coalition is inherited in an autosomal dominant pattern with variable penetrance. It is bilateral in approximately 50% of cases, though often asymptomatic on one side.
Symptoms
- Hindfoot pain: Pain localized to the back and outer side of the foot, worsened by activity and prolonged standing. Pain onset typically correlates with ossification of the coalition in adolescence.
- Rigid flatfoot: A characteristic finding — the arch fails to reform when the patient rises onto their toes (the "Jack test"). This distinguishes coalition from flexible flatfoot, which is usually asymptomatic.
- Limited subtalar motion: Stiffness in the inward/outward rocking motion of the hindfoot (inversion/eversion) is the defining clinical finding. In severe cases, subtalar motion may be completely absent.
- Peroneal muscle spasm: Involuntary spasm of the peroneal muscles ("peroneal spastic flatfoot") occurs as a protective response to subtalar stiffness and can be a presenting complaint.
- Recurrent ankle sprains: Restricted subtalar motion forces compensatory motion through the ankle, increasing ankle ligament stress and sprain frequency.
- Swelling: Localized swelling over the sinus tarsi or medial hindfoot, worsening with activity.
- Abnormal gait: A stiff, flat-footed walking pattern with reduced push-off is characteristic.
Diagnosis
Physical examination reveals the hallmark combination of rigid flatfoot, restricted or absent subtalar inversion/eversion, and hindfoot tenderness. The single-leg heel rise test demonstrates inability to reconstitute the arch. Peroneal spasm may be visible or palpable.
X-rays may identify osseous coalitions in later stages — the "anteater sign" on lateral X-ray is classic for calcaneonavicular coalition — but fibrous and cartilaginous coalitions are invisible on plain films. MRI is the definitive imaging modality for tarsal coalition. It identifies all three tissue types (bone, cartilage, and fibrous), precisely defines the coalition's location, size, and extent, and evaluates for secondary degenerative changes in adjacent joints that influence surgical planning. CT scan provides superior bony detail for surgical planning of excision procedures but does not characterize soft tissue or cartilaginous coalitions as well as MRI. For most patients, MRI is the single most valuable study — it confirms the diagnosis, characterizes the coalition type, and guides treatment decisions in one examination.
Classification
Tarsal coalitions are classified by tissue type and location:
- By tissue type: Synostosis (bone-to-bone), synchondrosis (cartilage bridge), or syndesmosis (fibrous tissue). Bony coalitions are fully rigid; fibrous and cartilaginous coalitions allow some motion and are more likely to respond to conservative treatment.
- By location: Calcaneonavicular (most common), talocalcaneal (middle facet, second most common), talonavicular, calcaneocuboid.
- By associated deformity: The presence and severity of secondary flatfoot deformity and subtalar arthritis significantly affects prognosis and surgical planning.
Treatments
Conservative treatment (fibrous or cartilaginous coalitions, mild symptoms):
Activity modification to reduce provocative loading, NSAIDs for pain and inflammation, and immobilization in a walking boot for 4–6 weeks to allow acute flares to settle. Custom orthotics with medial arch support and hindfoot posting improve biomechanics and reduce subtalar stress. Physical therapy targets peroneal flexibility and hindfoot stabilization. Many patients with fibrous coalitions achieve adequate symptom control with these measures, particularly those with less than complete subtalar restriction.
Surgical treatment — coalition excision (young patients without arthritis):
Resection of the coalition is the preferred surgical option for skeletally immature patients and young adults without significant secondary arthritis. The abnormal bridge is excised and the space filled with fat, muscle, or extensor digitorum brevis (EDB) interposition to prevent re-fusion. Calcaneonavicular coalition excision has excellent results with high rates of motion restoration. Talocalcaneal coalition excision outcomes depend on the size of the coalition — lesions involving less than 50% of the posterior facet surface area generally do well; larger coalitions have higher recurrence and failure rates.
Surgical treatment — hindfoot fusion (older patients or significant arthritis):
When secondary degenerative arthritis has developed in the subtalar or adjacent joints, or when excision has failed, subtalar or triple arthrodesis (fusion of the subtalar, talonavicular, and calcaneocuboid joints) is performed. Fusion reliably eliminates pain by eliminating motion across the arthritic joints, accepting the trade-off of permanent hindfoot stiffness. Results are generally good for pain relief and functional recovery, though recovery is prolonged (3–6 months non-weight-bearing).
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Foot and Ankle MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.