Anatomy and Location
The soleus muscle lies on the posterior aspect of the leg deep to the gastrocnemius muscle (m. gastrocnemius). Together, they form the triceps surae muscle (m. triceps surae).
- Origin: Muscle fibers originate from the posterior aspect of the fibular head and proximal third of the fibula, as well as the soleal line (linea m. solei) on the tibia.
- Insertion: The muscle fibers merge into the calcaneal tendon (tendo calcanei), which inserts onto the calcaneal tuberosity.
The groove separating the soleus and the fibular (peroneal) muscles serves as the lateral boundary of the leg.
Topography and Related Structures
The soleus muscle contributes to the formation of key topographical spaces in the lower limb:
- Crural-popliteal canal (canalis cruropopliteus): This canal lies between the gastrocnemius and soleus muscles. The entrance to this canal is formed by the tendinous arch of the soleus muscle (arcus tendineus m. solei).
- Contents of the canal: The deep neurovascular bundle travels through the crural-popliteal canal. It consists of the tibial nerve (n. tibialis), which occupies the most superficial position, along with the posterior tibial artery and veins (a. et vv. tibiales posteriores).
Blood Supply and Innervation
- Blood supply: Provided by the posterior tibial artery (a. tibialis posterior) and the fibular (peroneal) artery (a. fibularis).
- Innervation: Supplied by the tibial nerve (n. tibialis), whose fibers arise from spinal segments L₄–S₂.
Function
The soleus muscle performs two primary functions:
- Acts as a powerful plantarflexor of the foot.
- Stabilizes the body in an upright posture.
Clinical Significance
- Radicular syndromes: Compression of the S1 nerve root causes weakness in the soleus, gastrocnemius, and fibular muscles. This is accompanied by pain in the S1 dermatome and loss of the Achilles tendon reflex.
- Nerve function assessment: To objectively evaluate motor deficits in tibial nerve mononeuropathies, testing the muscle strength of both the soleus and gastrocnemius is recommended.
- Surgical infections: In purulent knee joint infections (gonitis), deep fascial collections can extend into the leg. A posteroinferior intermuscular collection is located between the gastrocnemius and soleus muscles, while another lies between the soleus and the deep fascia of the leg.
- Traumatology: The calcaneal (Achilles) tendon, into which the soleus inserts, can rupture during jumping or landing heavily on the heel.