Accessory soleus muscle

The accessory soleus muscle is an anatomical variant characterized by an additional distinct muscle encountered along a normal soleus muscle. It is uncommon with a prevalence of ~3% (range 0.7-5.5%).

Summary

• origin: fibula, soleal line of the tibia, or the anterior surface of the soleus muscle
• insertion:  calcaneus, at either the upper surface or the medial cortex
  • into the Achilles tendon distally
  • fleshy insertion into the upper surface of the calcaneus
  • fleshy insertion into the medial cortex of the calcaneus
  • tendinous insertion into the upper calcaneal surface
  • tendinous insertion into the medial surface of the calcaneus
• arterial supply: posterior tibial artery
• innervation: tibial nerve

Gross anatomy

The accessory soleus muscle arises from the deep surface of the soleus or from the fibula and descends anteriorly to the calcaneal (Achilles) tendon. Its insertion may occur into the calcaneal tendon, the upper surface of the calcaneus, or in the medial aspect of the calcaneus.

Radiographic features

Plain radiograph 

The Kager fat pad is obliterated by a well-defined area of increased soft-tissue attenuation. 

Related pathology

Associated exertional pain can occur, especially in athletes ¹.