The Accessory Soleus Muscle: A Narrative Review of the Literature

Although the accessory soleus muscle is a rare supernumerary muscle of the leg, its presence has been well discussed in the literature. This rare anatomic variation has been described mainly in the anatomic, surgical, and radiology literature. Awareness of the muscle's presence and its clinical presentation can help with diagnosis without surgical exploration. This narrative review summarizes the available data describing the anatomy, clinical presentation, diagnosis, associated pathologies, and treatment options of this accessory muscle.A literature review was performed to provide a comprehensive report of the existing data regarding the accessory soleus muscle. PubMed, Heal Link, and Google Scholar were searched for articles in English reporting on the accessory soleus muscle. The search was conducted using the following key words: "soleus muscle" and "accessory soleus muscle". PubMed was searched primarily, and then cross-referenced articles were found via Heal Link and Google Scholar. Results from non-English studies were excluded.A total of 148 articles were reviewed. The majority of the articles was composed of case reports along with a review of the literature. After the initial screening, 33 irrelevant studies, 47 duplicates, and 9 non-English articles were excluded; thus, 59 studies were eligible for analysis.Although the accessory soleus muscle is a rare anatomic variation, many cases have been reported in the literature. Nonetheless, the results reported in this literature review are still inconclusive regarding why some patients are symptomatic and others are not, and the recommendation of therapy protocols. Recognizing this anomaly is important in deciding the right diagnosis and planning the appropriate treatment. However, further research is needed to investigate the symptoms' presentations and propose specific treatment protocols.