Gastrocnemius is a large muscle located in the posterior leg. Posteriorly, is the most superficial of the muscles of the leg, and forms the bulk of the calf. It takes its name from the Greek words γαστήρ (gaster) meaning stomach or belly, and κνήμη (kneme) meaning leg; the combination of the two words means the “belly of the leg” or in other words the bulk of the calf.
In conjunction with the soleus muscle, it is a component of a composite, three-headed group of muscles referred to as triceps surae. Together, they act in many basic activities, such as walking, running and leaping. This article will outline the morphology of the gastrocnemius muscle, as well as its functional and clinical anatomy.
Lateral head: Posterolateral aspect of lateral condyle of the femur
Medial head: Posterior surface of medial femoral condyle, popliteal surface of femoral shaft
|Insertion||Posterior surface of the calcaneus via the calcaneal tendon|
|Innervation||Tibial nerve (S1, S2)|
Talocrural joint: Foot plantar flexion
Knee joint: Leg flexion
In this article we will discuss the anatomy of the gastrocnemius muscle, together with the clinical relevance of this muscle.
- Anatomical relations
- Innervation and blood supply
- Clinical notes
- Related diagrams and images
Gastrocnemius originates as two heads from the femur. The medial head originates from the popliteal surface of the femoral shaft, and the posterior surface of the medial condyle.
The lateral head originates from a facet on the upper lateral surface of the lateral condyle of the femur, where it joins the lateral supracondylar line. Both heads also take origin from the capsule of the knee joint. The tendinous attachments of the medial and lateral head expand, covering the posterior aspect of each head with an aponeurosis. The muscle fibres arise from the anterior aspect of this aponeurosis.
At the inferior margin of the popliteal fossa, the two heads come together and join to form a single, elongated, muscle belly. This forms most of the bulge of soft tissue on the posterior leg, referred to as the calf.
The fleshy part of the muscle extends to approximately the midpoint of the calf. In the lower leg, the muscle fibres of gastrocnemius gradually form a broad aponeurosis. The aponeurosis gradually narrows, and fuses with the fibres of another deeper muscle, the soleus, to form a large tendon called the calcaneal (Achilles) tendon. The calcaneal tendon attaches to the posterior surface of the calcaneus in the foot.
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Proximally, the lateral and medial heads of gastrocnemius form the inferior boundaries of the popliteal fossa. The tendon of biceps femoris partially covers the lateral head, and semimembranosus partially covers the medial head. For the remainder of its length, the muscle is superficial, with both bellies visible beneath the skin.
The small saphenous vein and accompanying sural nerve run along the superficial surface of the muscle, separated from it by the deep fascia. The common fibular nerve crosses the lateral head of the muscle, between it and biceps femoris. Deep to gastrocnemius are the soleus, popliteus and plantaris muscles, the popliteal vessels and the tibial nerve. The deep flexor muscles, flexor digitorum longus, flexor hallucis longus and tibialis posterior, also lie deep to gastrocnemius.
Learn more about the leg and knee structures here.
Innervation and blood supply
The gastrocnemius is innervated by the ventral rami of S1 and S2 spinal nerves, carried by the tibial nerve into the posterior compartment of the leg. Both medial and lateral heads of gastrocnemius are supplied by the lateral and medial sural arteries, which are direct branches of the popliteal artery.
The arteries arise in the popliteal fossa, although the level at which these arteries arise is variable, with the medial sural artery usually arising more proximally and the lateral more distally. Minor accessory sural arteries may also branch off the popliteal and superior genicular arteries. Venous drainage is through corresponding medial and lateral sural veins into the popliteal vein.
The gastrocnemius is a powerful plantar flexor of the foot at the talocrural joint. It also flexes the leg at the knee. The actions of gastrocnemius are usually considered along with soleus, as the triceps surae group. They are the chief plantar flexors of the foot. The muscles are usually large and powerful. Gastrocnemius provides the force behind propulsion for walking, running and jumping.
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Tennis leg is an injury that commonly occurs in tennis and squash players. It presents as a sudden, sharp pain at the back of the calf that usually follows rupture of the myotendinous junction of the medial head of gastrocnemius. Less commonly, it entails the rupture of the plantaris muscle. It is caused by overstretching the muscle by fully extending the knee and dorsiflexing the ankle.
Achilles tendon tendonitis
Achilles tendon tendonitis involves pain induced by thickening of the calcaneal (Achilles) tendon at its insertion. It most commonly occurs in middle to older age people. It is caused by repetitive strain of the muscle, resulting in cartilaginous and bony metaplasia. Symptoms usually include pain in the back of the heel, with a bony enlargement at the insertion of the tendon onto the calcaneus.
Achilles tendon rupture
Rupture of the calcaneal (Achilles) tendon is common among people playing recreational sports. The rupture may be complete or more frequently partial and usually occurs 4-6cm above the calcaneal insertion of the tendon, which is relatively avascular. The patient may recall a pop sound upon rupturing of the tendon, and the feeling of the muscle rolling up their leg. Complete rupture of the tendon causes excessive passive dorsiflexion, and loss of plantar flexion against resistance.
Calcaneal bursitis involves inflammation of the bursa that separates the calcaneal tendon from a process of the calcaneus called the calcaneal tuberosity. It can cause pain in the posterior part of the heel. It is commonly the result of long distance running, basketball and tennis, where excessive friction caused by the movement of the tendon leads to inflammation.