AIM: Posterior ankle pain is a nonspecific symptom that can result from various pathologies. Rare accessory muscle variants, including the accessory soleus muscle, may cause overlapping clinical conditions due to mass effect, dynamic impingement, chronic compartment syndrome, or tibial nerve compression. Limited familiarity with this anatomical variant often leads to diagnostic delay, misdiagnosis, or inappropriate treatment. The authors report three cases of chronic posterior ankle pain in athletes caused by the accessory soleus muscle with the aim to highlight the importance of considering the accessory soleus muscle (ASM) as a possible cause of this symptomatology. The diagnostic and therapeutic management, and clinical-functional outcomes are analysed.

CASE PRESENTATION: All patients reported posterior ankle pain for more than one year, exacerbated by sports activity and forced plantar flexion, with relief at rest. Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) demonstrated the presence of ectopic muscle tissue compatible with an accessory soleus muscle. Clinical data, imaging findings, treatment modalities, and clinical-functional outcomes were retrospectively collected for each case. Preoperative, one year postoperative, and final follow-up assessments included the Visual Analog Scale (VAS) for pain evaluation, 17-Item Italian Foot Function Index (17-IFFI), and the American Orthopaedic Foot and Ankle Society (AOFAS) ankle–hindfoot score validated in Italian. All patients underwent surgical excision of the accessory soleus muscle through a posteromedial approach.

RESULTS: Surgical excision was the definitive treatment for each patient, resulting in pain relief, clinical and functional improvement, and return to sports activity. No complications or recurrences were observed.

CONCLUSIONS: The accessory soleus muscle is a potential cause of chronic posterior ankle pain and must be considered in the differential diagnosis to avoid diagnostic delays or misdiagnosis. Surgical excision has represented the effective and definitive treatment of the three reported cases.