Triceps surae muscle
Anatomy and Supply
The triceps surae muscle is a three-headed muscle at the dorsal lower leg. It lies within the superficial posterior compartment. Its heads and body determine the surface anatomy of the calf. Its insertion, the Achilles tendon, is easily visible and palpable at the heel.
The triceps surae muscle is innervated by the tibial nerve. It is made up by:
- Soleus muscle - originates at the upper fibula, tibia and the tendinous arch of soleus which stretches between the tibia and fibula.
- Gastrocnemius muscle - has its origins at the medial epicondyle (medial head) and lateral epicondyle (lateral head) of the femur. It overlaps the soleus muscle almost completely.
At the distal third of the lower leg both the soleus and gastrocnemius muscles merge into a common tendon, the Achilles tendon (tendo calcaneus), which inserts at the posterior calcaneus. The neurovascular bundle coming from the hollow of the knee (posterior tibial artery and vein and tibial nerve) runs under the tendinous arch of soleus after which it courses between the superficial and deep flexor muscles.
The triceps surae muscle crosses multiple joints. Its most important function is the plantar flexion in the upper ankle joint enabling the lifting of the heel against gravity when walking or jumping. The maximal jumping power is achieved by adequate stretching of the muscle, i.e. stretching of the knee joint. The plantar flexion fixes the lower leg when standing and thus prevents the upper body from falling forward. Furthermore the muscle is the strongest supinator of the lower ankle joint. The gastrocnemius muscle contributes to a small extent to the bending of the knee.