Ro-Woon Lee

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1. Introduction Posterior ankle impingement (PAI) is a common cause of posterior ankle pain during plantar flexion. It is caused by overuse, repetitive plantarflexion, or a traumatic event, often in combination with congenital anatomic anomalies [1]. Moreover, the essential cause of PAI is the presence of an os trigonum. It is a separate ossicle located posterior to the lateral tubercle of the posterior process of the talus (Stieda’s process), just lateral to the flexor hallucis longus groove [2].

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