Triceps surae muscle
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 calcaneal tendon, is easily visible and palpable at the heel.
Origins: Lateral head: Posterolateral surface of lateral femoral condyle; Medial head: Posterior surface of medial femoral condyle, Popliteal surface of femoral shaft
Insertion -Posterior surface of calcaneus (via calcaneal tendon)
Function -Talocrural joint: Foot plantar flexion; Knee joint: Leg flexion
Origin: Soleal line, Medial border of tibia, Head of fibula, Posterior border of fibula
Insertion - Posterior surface of calcaneus (via calcaneal tendon)
Function - Talocrural joint: Foot plantar flexion
|Innervation||Tibial nerve (S1, S2)|
|Vascularization||Posterior tibial artery|
Anatomy and supply
The triceps surae muscle is innervated by the tibial nerve. It is made up by:
- The gastrocnemius muscle is a large and strong plantar flexor of the ankle and flexor of the knee. It has two heads: medial and lateral. The medial head originates from the posterior surface of the medial condyle of the femur, whereas the lateral head originates from the superior part of the posterolateral surface of the lateral femoral condyle. Both heads insert at the posterior surface of the calcaneus, via the calcaneal tendon.
- The soleus muscle is deep to the gastrocnemius and is another plantar flexor. It arises from the soleal line on the dorsal surface of the tibia, medial border of the tibia and the posterior border of the fibular head. Just as the gastrocnemius muscle, it inserts onto the posterior surface of the calcaneus.
Both the gastrocnemius and soleus muscles are innervated by the tibial nerve and vascularized by the posterior tibial artery.
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. As the body's centre of gravity is anterior to the ankle joint, the body has a natural tendency to lean forward. This is counteracted by a continuous state of plantar flexion produced mainly by the soleus when standing. The gastrocnemius muscle contributes to a small extent to the flexion of the knee.
Clinically the triceps surae muscle is the reference muscle for the nerve root S1. It can be compressed due to a herniated disk or vertebral fracture. Classic symptoms are irritations and pain along the buttock and posterior lower leg and a weak or absent Achilles tendon reflex. Additionally the triceps surae muscle is often functionally restricted. The affected patients present with a so-called talipes calcaneus caused by the overbalance of the anterior muscles of the lower leg. Both walking on toes as well as rolling the foot from the heel becomes practically impossible.
The Achilles tendon is the strongest tendon of the human body. Its load bearing capacity amounts up to one tonne, which is why its rupture goes along with a loud “whipping” sound. It is usually associated with previous damages due to chronic false strain. The microtraumas disturb the blood supply of the tendon leading to a decrease of its strength. The region about 3 to 5 centimeters proximal to the tendon insertion is particularly vulnerable as it is relatively poorly supplied already. In adolescents, the Achilles tendon rupture often comes along with an osseous fracture of the calcaneus bone.