Tarsal Coalition

Aetiology

Prevalence: Found in ~1% of the population, potentially more.
Inheritance: Autosomal dominant.
Pathogenesis: Failure of mesenchymal differentiation in peritalar joints.
- Results in a fibro-osseus bar instead of a joint.
- 20% have multiple coalitions in the same foot.
- 50% are bilateral.

Common Locations:
- Calcaneonavicular: Most common site.
- Talocalcaneal: Second most common, often in the medial facet.
- Other Coalitions: Rare, can occur between any peritalar joints.

Symptoms typically appear once the coalition ossifies and becomes painful.
- Calcaneonavicular coalitions present earlier than talocalcaneal (age 8-15 years).
- Symptoms: Recurrent ankle sprains, difficulty on uneven terrain.

Feature	Description
Rigid Planovalgus Deformity	Fixed flatfoot with heel valgus
Sinus Tarsi Pain	Pain due to impingement

By Anatomy of Coalition:
- Based on location and involved joints.
By Nature of Bar:
- Fibrous, Cartilaginous, or Osseous bar types.

X-Ray Findings:
- Negative Meary’s Angle: Indicates planovalgus deformity.
- Anteater Sign: Suggestive of calcaneonavicular coalition.
- C-Sign: Seen in talocalcaneal coalitions; forms a “C” shape between talus and calcaneus.
- Dorsal Talar Beaking: Non-specific finding, common with coalition.
Advanced Imaging:
- CT Scan: Gold standard for evaluating osseous coalitions.
- MRI: Confirms fibrous or cartilaginous coalitions.

Indications: Failed non-operative management, arthritis, rigid deformity.
- Resection: Preferred for calcaneonavicular and <50% talocalcaneal coalitions.
  - Advantages: Preserves motion but may have recurrence.
- Fusion: Recommended if >50% of the medial facet is involved.
  - Types: Subtalar fusion preferred; may require triple fusion in severe cases.
  - Indications: Late presentation with osteoarthritis.
- Additional Procedures: Corrective osteotomies for fixed valgus deformity.