False FHL: A Normal Variant Posing Risks in Posterior Hindfoot Endoscopy

Posterior hindfoot endoscopy has been more commonly used in the treatment of various pathologies by surgeons with different arthroscopic experience. The flexor hallucis longus is usually the initial and most important landmark serving as a medial boundary for the arthroscope and instruments to avoid inadvertent injury to the tibial nerve and vessels. We report 2 cases in which the presence of the peroneocalcaneus internus muscle, “false FHL,” imitated the flexor hallucis longus, risking imminent neurovascular injury during the initial endoscopic exposure. Awareness of this rare anatomic variation, preoperative magnetic resonance imaging studies, and intraoperative differentiation techniques were found helpful to avoid devastating complications.