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Coalition by MSKMRI JEE EUN LEE.pdf
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Tarsal coalition is strongly linked to hindfoot valgus, the key driver of rigid pes planovalgus (peroneal spastic flatfoot). Restricted subtalar motion alters biomechanics and leads to progressive deformity.
Pathophysiology
- Restricted Subtalar Motion → abnormal biomechanics, rigid flatfoot, early OA.
- Peroneal Shortening/Spasm → protective contraction of peroneal muscles during inversion attempts.
- Progressive Flatfoot → collapse of medial arch, heel valgus, forefoot abduction, worsening after ossification.
Clinical & Surgical Implications
- Pain often arises from pes planovalgus itself. Severe heel valgus (>16–21°) predicts poor outcome after simple coalition resection.
- Simple resection is inadequate → does not correct valgus deformity.
- Combined approach recommended: coalition resection + flatfoot reconstruction (e.g., medializing calcaneal osteotomy, Evans, Achilles lengthening).
Secondary Pathologies
- Lateral Hindfoot Impingement (from valgus malalignment):
• Talocalcaneal impingement at lateral talar process and calcaneus.
• Subfibular impingement from calcaneus–fibula contact in severe valgus.
• MRI: subcortical edema, cysts, sclerosis at impingement sites. - Peroneal Tendon Instability: Subluxation/dislocation from valgus malalignment and overactive peroneus brevis.
Imaging Clues
- Radiographs:
• C-sign (continuous arc of medial talus + sustentaculum tali) – more a marker of valgus than coalition.
• Broad lateral talar process from valgus stress. - CT/MRI: Define coalition type, assess valgus angle, detect impingement. MRI may underestimate valgus due to non–weight-bearing position.
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