Tarsal Coalition Stiff Flat Foot 2026 | DPM

Coalition Type	Bones Involved	Tissue Type	Prevalence	Age of Symptom Onset	Radiographic Finding
Talocalcaneal Coalition	Talus + calcaneus (middle facet most common)	Osseous, cartilaginous, or fibrous	~48% of coalitions	12–16 years (as fibrocartilage ossifies)	Axial CT: bony bar middle facet; “C-sign” on lateral X-ray; anteater sign
Calcaneonavicular Coalition	Calcaneus + navicular	Osseous or cartilaginous	~43% of coalitions	8–12 years (earlier ossification)	Lateral oblique X-ray: “anteater sign” (elongated anterior calcaneal process); CT confirms
Talonavicular Coalition	Talus + navicular	Osseous	~~5%	Variable	AP X-ray: bony bridge; CT confirms
Calcaneocuboid Coalition	Calcaneus + cuboid	Osseous	Rare (<2%)	Variable	Lateral X-ray; CT confirms
Multiple Coalitions	Two or more joint pairs	Variable	~20% of coalition cases	Variable	CT mandatory to identify all coalitions before surgery

Treatment	Indication	Details	Success Rate	Recovery
Conservative (orthotics + boot)	First-line; any coalition; initial symptom management	Custom orthotics for arch support; boot immobilization during acute flares; activity modification	Symptom control in 40–50%; does not correct coalition	Ongoing; use between flares
Calcaneonavicular Bar Resection	CN coalition; <50% of CN joint involved; <16 years; minimal subtalar arthrosis	Excise bony/fibrous bar; interpose fat graft or extensor digitorum brevis to prevent re-fusion	75–85% good-to-excellent; best in younger patients before arthrosis develops	4–6 weeks NWB; 3–4 months full activity; good long-term outcomes in children
Talocalcaneal Bar Resection (Middle Facet)	TC coalition; <50% posterior facet involved; minimal subtalar arthrosis	Resect middle facet bar; fat graft interposition; tibialis posterior lengthening if equinus	60–75% good-to-excellent; lower than CN resection; patient selection critical	6–8 weeks NWB; 4–6 months full activity
Subtalar Arthrodesis	TC coalition >50% facet involved; subtalar arthrosis; failed resection; adult patient	Fuse subtalar joint in corrected position; eliminates coalition pain by fusing the joint	85–90% pain relief; sacrifices subtalar motion (already limited by coalition)	8–10 weeks NWB; 6 months full recovery
Triple Arthrodesis	Multiple coalitions; severe rigid flatfoot with subtalar + midfoot arthrosis	Fuse subtalar, talonavicular, calcaneocuboid joints; addresses all hindfoot pathology	High satisfaction for pain; significant motion loss	10–12 weeks NWB; 6–9 months full recovery

Tarsal coalition is one of the most important—and frequently missed—causes of progressive foot stiffness and pain in adolescents. When a teenager presents with a painfully flat, rigid foot that doesn’t respond to typical treatments, tarsal coalition should be high on the differential. Understanding this condition is the first step to effective treatment and preventing unnecessary years of diagnostic delay.

What Is Tarsal Coalition?

Tarsal coalition is an abnormal connection between two or more of the seven tarsal bones in the hindfoot and midfoot. This connection—called a coalition or bar—can be composed of fibrous tissue (syndesmosis), cartilage (synchondrosis), or bone (synostosis). The more rigid the coalition material, the more motion it restricts and the more symptoms it tends to produce.

The two most common types are: calcaneonavicular coalition (between the calcaneus/heel bone and the navicular), accounting for approximately 45–60% of cases; and talocalcaneal coalition (between the talus and calcaneus/subtalar joint), accounting for approximately 35–45%. Rarer coalitions involve the naviculocuneiform, talonavicular, and calcaneocuboid joints. Tarsal coalition is bilateral in approximately 50–60% of cases—meaning if a patient has coalition on one foot, there is a meaningful chance of involvement on the other side as well.

The condition has an autosomal dominant inheritance pattern with variable penetrance—meaning it runs in families but doesn’t affect every family member equally. The overall prevalence is approximately 1–2% of the general population, though many individuals with coalition remain asymptomatic throughout their lives.

Why Does Tarsal Coalition Become Painful During Adolescence?

Tarsal coalitions are present from birth as a developmental variant, but symptoms typically emerge during adolescence—usually between ages 8–12 for calcaneonavicular coalitions and 12–16 for talocalcaneal coalitions. The timing corresponds to skeletal maturation: as the fibrous or cartilaginous coalition begins to ossify (turn to bone) during adolescence, it becomes increasingly rigid, restricting subtalar and midtarsal joint motion. This loss of hindfoot mobility transfers stress to adjacent joints, causing secondary impingement, peroneal spasm, and pain.

The characteristic “peroneal spastic flatfoot” presentation—in which the peroneal muscles reflexively contract to stabilize the increasingly rigid hindfoot—is one of the hallmarks of tarsal coalition in clinical practice. The spasm is not actually a neurological problem; it’s the body’s protective response to the mechanical instability created by the coalition.

Clinical Presentation and Examination

The typical patient is an adolescent who presents with progressively worsening flatfoot pain that is aggravated by walking on uneven surfaces, sports, and prolonged activity. The foot appears pronated (rolled in) with loss of the medial arch, and the hindfoot is in valgus (leaning outward) when viewed from behind. Critically, subtalar (hindfoot) motion is significantly restricted—the examiner can invert and evert the heel only a few degrees, compared to the normal 15–30 degrees of combined motion. This restricted hindfoot motion in the context of a flat, painful foot strongly suggests tarsal coalition.

Peroneal muscle spasm may be evident on exam—the peroneal tendons appear tight and prominent on the outer ankle, and the patient guards against hindfoot inversion. In severe cases, a fixed valgus deformity that cannot be corrected passively indicates a rigid coalition with secondary structural changes.

Imaging Diagnosis

Weight-bearing foot and ankle X-rays are the starting point. Calcaneonavicular coalitions are often visible on 45-degree oblique foot views as a bony bar between the anterior calcaneus and the navicular—sometimes described as the “anteater sign” (the anterior calcaneal process elongates toward the navicular, resembling the snout of an anteater). Talocalcaneal coalitions are harder to identify on plain X-ray; secondary changes including talar beaking (bony spur on the dorsal talar head) and rounding of the lateral process of the talus suggest coalition.

CT scanning is the gold standard for characterizing coalition anatomy, coalition size, and the extent of secondary degenerative changes. This information is essential for surgical planning. MRI is superior for identifying fibrous coalitions not visible on CT and for evaluating articular cartilage health in adjacent joints—important for determining whether resection or fusion is more appropriate.

Treatment of Tarsal Coalition

Conservative management is appropriate for mild or minimally symptomatic cases. Custom orthotics with medial arch support and rearfoot posting can reduce stress on the coalition and improve patient comfort. Activity modification—avoiding high-impact sports during symptomatic episodes—combined with anti-inflammatory medications and physical therapy reduces pain and maintains function. A short-leg walking cast or CAM boot can break a cycle of acute peroneal spasm and inflammation.

Surgical resection is indicated when conservative management fails and the coalition is amenable to resection. Calcaneonavicular coalition resection involves removing the bony or fibrous bar and interposing fat or extensor digitorum brevis muscle to prevent re-ossification. Results for calcaneonavicular resection are excellent: studies report 75–85% good-to-excellent outcomes, with significant improvement in hindfoot motion and pain. Resection is most successful when performed before significant secondary arthritis develops.

Subtalar or triple arthrodesis (fusion) is reserved for patients with large coalitions, extensive secondary degeneration, or failed prior resection. Fusion eliminates subtalar motion entirely but reliably resolves pain in patients with advanced disease. Modern techniques allow adjacent joint-sparing fusion approaches that preserve more foot flexibility than traditional triple arthrodesis.

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