Posterior Ankle Impingement Due to Hypertrophic Low-Lying Flexor Hallucis Longus Muscle: A Case Series and Literature Review.

Posterior ankle impingement syndrome (PAIS) is a clinical disorder with pain elicited when the foot is placed into a forced plantarflexion position, resulting in compression of bony and/or soft tissue structures located within the posterior ankle region. Numerous soft tissue structures exist in close proximity to the posterior ankle joint which can also result in impingement, with flexor hallucis tendinitis being associated in 63% to 85% of cases. The purpose of this study is to present 3 cases of both open and endoscopic surgical approaches for the treatment of PAIS caused by a hypertrophied and low-lying flexor hallucis longus (FHL) muscle. While there remains a paucity of high-level research with regards to treatment outcomes for PAIS, our report demonstrates that surgical excision can lead to significant improvements in patient symptomatology and function. We hope that this report will shed light on the importance of identifying alternative and uncommon causes of PAIS as well as aid in the workup and treatment of such cases.Level of Evidence: Level 4.