Anterior fibulocalcaneus muscle: a must-see when performing arthroscopic Brostrom

Abstract

Accessory muscles of the ankle and hindfoot are rare anatomical variants that are typically asymptomatic but may become clinically significant following trauma or surgery. The anterior fibulocalcaneus muscle (AFCM) is a rare accessory muscle, with limited documentation in the literature and no previously reported symptomatic cases requiring surgical intervention. The authors present the case of a 32-year-old man with persistent lateral ankle pain and instability following high-energy trauma and surgical fixation of a medial malleolar fracture. Despite appropriate bone healing, the patient’s symptoms persisted until MRI identified an accessory muscle tendon consistent with the AFCM, originating from the distal fibula and inserting onto the anterolateral calcaneus. Its superficial trajectory over the anterior talofibular ligament (ATFL) risked intraoperative misidentification as part of the lateral ligament complex, potentially leading to inadvertent preservation or tensioning during repair. Surgical excision of the AFCM tendon, combined with lateral ligament repair, resulted in complete resolution of symptoms and full functional recovery. This case highlights the importance of considering accessory musculature that can mimic or obscure native ligaments and complicate surgical management of chronic post-traumatic ankle pain, and demonstrates that surgical excision can be effective when such variants are implicated.