Accessory Soleus
Leg & Ankle
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The accessory soleus is an extra calf muscle found in only a small percentage of people. Because it often creates a soft bulge along the inner ankle, it can be mistaken for a tumour or other abnormal mass.
Function
Assists the normal soleus with plantarflexion of the ankle, contributing to standing on the toes, walking, running, and pushing off the ground. Its exact mechanical contribution depends on its size and attachment pattern.
Origin
Variable. Most commonly arises from the anterior/deep surface of the soleus, but it may also originate from the tibia, fibula, or adjacent deep fascia.
Insertion
Variable. Usually inserts onto the medial or superior surface of the calcaneus by a muscular or tendinous attachment; some variants blend with or insert near the calcaneal (Achilles) tendon.
Innervation
Tibial nerve, typically associated with the S1–S2 nerve roots, like the normal soleus.