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Gastrocnemius muscle

The gastrocnemius muscle is a large, superficial muscle of the posterior compartment of the leg. It forms the bulk of the calf and, along with the soleus, contributes to the triceps surae. It consists of two distinct heads — medial and lateral — that arise from the posterior aspect of the femur just above the knee joint. Both heads unite to form a thick belly that narrows into the Achilles tendon, inserting on the calcaneus.

The gastrocnemius is a biarticular muscle, acting across both the knee and ankle joints. It is primarily responsible for powerful plantarflexion of the foot, and also assists in knee flexion. Due to its superficial location, it is prone to injuries such as strains (“tennis leg”) and tears.

Synonyms

  • Calf muscle (superficial head)

  • Gastrocnemius portion of triceps surae

  • Medial and lateral heads of gastrocnemius

Origin and Insertion

  • Medial head: Posterior surface of femur just superior to medial condyle

  • Lateral head: Posterior surface of femur just superior to lateral condyle

  • Course:

    • Both heads arise separately, forming two bellies separated by a central groove

    • Bellies unite mid-leg to form a thick tendon, blending with soleus to form the Achilles tendon

  • Insertion:

    • Posterior surface of calcaneus via the calcaneal (Achilles) tendon

Nerve Supply

  • Tibial nerve (S1–S2)

Arterial Supply

  • Sural branches of the popliteal artery

  • Posterior tibial artery (minor contributions)

Venous Drainage

  • Sural veins → Popliteal vein

  • Posterior tibial venous system

Function

  • Powerful plantarflexion of the ankle joint (with soleus)

  • Flexion of the knee joint (due to crossing above knee)

  • Provides propulsive force in running, jumping, and walking

  • Stabilizes the ankle and knee during locomotion

MRI Appearance

T1-weighted images:

  • Normal muscle shows low-to-intermediate signal intensity

  • Intramuscular fat or septa appear as bright signal lines

  • Chronic atrophy or fatty degeneration appears hyperintense

T2-weighted images:

  • Normal muscle shows low-to-intermediate signal intensity

  • Muscle strain, tear, or edema shows bright hyperintense signal

  • Hematomas may appear variable depending on stage

STIR (Short Tau Inversion Recovery):

  • Normal muscle shows low-to-intermediate signal

  • Acute injuries, strains, or inflammation show bright hyperintensity

Proton Density Fat-Saturated (PD FS):

  • Normal gastrocnemius shows low-to-intermediate signal

  • Tears, tendinopathy, or edema show bright hyperintensity within the muscle belly or myotendinous junction

T1 Fat-Sat Post-Contrast:

  • Normal muscle shows mild, uniform enhancement

  • Strains or myositis: diffuse or patchy enhancement

  • Abscess or large hematoma: peripheral rim enhancement with non-enhancing core

  • Tumors: heterogeneous or nodular enhancement

CT Appearance

Non-Contrast CT:

  • Muscle appears as homogeneous soft tissue density in the posterior compartment

  • Hematomas: hyperdense acutely, becoming hypodense over time

  • Fatty infiltration: seen as areas of low attenuation

Post-Contrast CT:

  • Normal gastrocnemius enhances mildly and homogeneously

  • Inflammatory changes: diffuse enhancement with surrounding fat stranding

  • Abscess: rim-enhancing collection with central hypodensity

  • Tumors: irregular or heterogeneous enhancement

MRI image

gastrocnemius muscle axial cross sectional anatomy 3T radiology anatomy image-img-00000-00000

MRI image

gastrocnemius muscle coronal cross sectional anatomy 3T radiology anatomy image-img-00000-00000

MRI image

gastrocnemius muscle sag cross sectional anatomy 3T radiology anatomy image-img-00000-00000

CT image

gastrocnemius muscle CT axial image

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gastrocnemius muscle ct coronal image

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gastrocnemius muscle ct sag image