Location and anatomy
The soleus muscle lies on the posterior surface of the leg beneath the gastrocnemius muscle (m. gastrocnemius). Together, they form the triceps surae muscle (m. triceps surae).
- Origin: muscle fibers originate from the posterior surface of the head and proximal third of the fibula, as well as from the soleus line (linea m. solei) on the tibia.
- Insertion: the muscle merges with the Achilles tendon (tendo calcanei), which inserts into the calcaneal tuberosity.
The groove separating the soleus muscle from the fibular (peroneal) muscles serves as the lateral boundary of the leg.
Topography and adjacent structures
The soleus muscle participates in the formation of important topographical spaces of the lower limb:
- Cruropopliteal canal (canalis cruropopliteus). The cruropopliteal canal runs 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).
- Canal contents: the deep neurovascular bundle lies within the cruropopliteal canal. It includes the tibial nerve (n. tibialis), which occupies the most superficial position, as well as the posterior tibial artery and veins (a. et vv. tibiales posteriores).
Blood supply and innervation
- Blood supply: supplied by the posterior tibial artery (a. tibialis posterior) and fibular artery (a. peronea / fibularis).
- Innervation: supplied by the tibial nerve (n. tibialis), fibers of which originate from spinal segments L₄–S₂.
Function
The soleus muscle performs two main functions:
- Acts as a powerful plantarflexor of the foot.
- Stabilizes the body in an upright position.
Clinical significance
- Radicular syndromes: compression of the S1 nerve root leads to weakness of the soleus, gastrocnemius, and fibular muscles. This is accompanied by pain in the S1 dermatome and loss of the Achilles reflex.
- Nerve function assessment: to objectify motor impairments in tibial nerve mononeuropathies, assessing the muscle strength of the soleus and gastrocnemius muscles is recommended.
- Surgical infection: in purulent gonitis, fluid collections (abscesses) spreading down the leg have been described. The posterior-inferior intermuscular collection is located between the gastrocnemius and soleus muscles, while the intermuscular collection is located between the soleus muscle and the deep fascia of the leg.
- Traumatology: the Achilles tendon, with which the soleus muscle merges, can rupture during jumping or when striking the heel against a hard surface.
Class and exam questions
Which structure includes the soleus muscle?
It is part of the triceps surae (m. triceps surae), uniting with the gastrocnemius muscle (m. gastrocnemius), which has two heads. The soleus muscle merges with the Achilles tendon, which inserts into the calcaneal tuberosity.
What passes beneath the tendinous arch of the soleus muscle?
The tendinous arch of the soleus muscle (arcus tendineus m. solei) serves as the entrance to the cruropopliteal canal. The tibial nerve and posterior tibial vessels pass through the canal.
How does S1 nerve root lesion affect the soleus muscle?
Compression of the S1 nerve root causes weakness of the soleus muscle and loss of the Achilles reflex. Pain with paresthesias or hypalgesia also occurs in the S1 dermatome area.
What else to study on this topic
- Triceps surae muscle (m. triceps surae)
- Cruropopliteal canal (canalis cruropopliteus)
- Tibial nerve (n. tibialis)
- Posterior tibial artery (a. tibialis posterior)
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