Gastrocnemius (inner head) !

The inner head of the gastrocnemius is the larger part of the calf muscle; it crosses the back of the knee and points the foot.

Official name: Medial head of gastrocnemius

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What it is

The calf muscle (gastrocnemius). Its two heads start on the back of the femur and join the Achilles tendon.

What it does

Points the foot (pushing off when walking or jumping) and helps bend the knee.

Key facts

Origin: Posterior femur just above medial condyle
Insertion: Posterior calcaneus via calcaneal (Achilles) tendon
Action: Plantar flexes ankle; flexes knee
Nerve: Tibial nerve (S1–S2)
Blood supply: Medial sural artery (from popliteal artery)

Relations

Above: Its origin above the medial femoral condyle lies against the back of the knee capsule; between it and the semimembranosus tendon sits the gastrocnemius–semimembranosus bursa, which often opens into the knee joint
Lateral: The lateral head, separated by a midline groove that carries the small saphenous vein; deep in the gap between the heads, the popliteal vessels and tibial nerve pass down into the calf
Deep: Plantaris tendon and soleus; higher up, popliteus and the back of the knee capsule
Medial: Semimembranosus and the pes anserinus tendons at the knee; lower down, the great saphenous vein and saphenous nerve in the subcutaneous tissue of the medial leg
Superficial: Deep fascia and skin; the medial sural cutaneous nerve runs down over the heads and joins a branch of the common fibular nerve to form the sural nerve

How to find it

Standing on tiptoe, the medial head stands out as the larger, rounder bulge of the inner calf, its lower edge clearly lower than that of the lateral head. Lying prone with the knee bent against resistance, it is felt as the lower medial border of the popliteal fossa.

Examination

Silfverskiöld test: ankle dorsiflexion is measured with the knee straight and then bent; if it is limited only with the knee straight the tightness is in the gastrocnemius, if limited in both positions the soleus or Achilles tendon is also tight
Repeated single-leg heel raises: fewer or lower raises than on the other side point to calf weakness from a tear, a tibial nerve lesion or an S1 root problem
Ankle reflex: a reduced or absent jerk suggests an S1 root or tibial nerve lesion (it is also often reduced in older people and in peripheral neuropathy)

On imaging

Ultrasound is the usual first test for tennis leg: a tear at the lower end of the medial head, where it meets the soleus, with fluid or haematoma between the two muscles. The same scan rules out a deep vein thrombosis, the main differential. A Baker's cyst bulges from the knee between this head and the semimembranosus tendon. MRI grades unclear tears.

Common problems

Calf strain or tear, often in the inner head during a sudden push-off ('tennis leg').
Cramps.

How it is diagnosed

Physical exam; ultrasound. Calf pain and swelling should also be checked for a blood clot.

Treatment

Rest, ice, compression, then gradual stretching and strengthening.

Clinical notes

Tennis leg typically follows a push-off with the knee straight and the ankle dorsiflexed; ultrasound shows the tear at the medial head with fluid between it and the soleus
Popliteal artery entrapment: an abnormal course of the artery medial to or under the medial head, or an abnormal muscle slip, compresses it in young active people and causes exertional calf claudication
Calf muscle pump: contraction squeezes the deep veins and the venous sinuses inside the calf muscles, driving blood upward through the valves; long immobility removes this pump and favours deep vein thrombosis
A popliteal (Baker's) cyst bulges from the gastrocnemius–semimembranosus bursa; if it ruptures, fluid tracks down the calf and can mimic a deep vein thrombosis
The medial head is the standard local muscle flap for exposed bone or hardware over the knee and upper third of the tibia; gastrocnemius recession lengthens an isolated gastrocnemius contracture

Anatomical variants

A third head (gastrocnemius tertius) or an extra slip from the femur may be present and is one cause of popliteal artery entrapment

Development

The calf muscles come from the ventral (flexor) muscle mass of the leg, so the whole superficial posterior compartment is supplied by the tibial nerve.

Test yourself

Think of the answer, then tap the question to see it.

What is «tennis leg» and which muscle is usually torn?

A calf tear on push-off with the knee straight and ankle dorsiflexed; it is usually the medial head of the gastrocnemius, where it joins the soleus aponeurosis.

What does the Silfverskiöld test show?

If dorsiflexion is limited only with the knee straight the tightness is in the gastrocnemius; if limited with the knee straight and bent, the soleus or Achilles tendon is also tight.

Which nerve supplies the gastrocnemius, and which reflex tests it with the soleus?

The tibial nerve (S1–S2); the ankle jerk (S1) is the stretch reflex of the triceps surae (gastrocnemius and soleus).

Which border of the popliteal fossa does the medial head of the gastrocnemius form?

The inferomedial border; the lateral head and plantaris form the inferolateral border.

How does the medial head of the gastrocnemius cause popliteal artery entrapment?

An abnormal course of the artery medial to or under the medial head compresses it in young active people, causing exertional calf claudication.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): caput mediale musculi gastrocnemii TA2 2659
Official Spanish (DeCS): Cabeza medial del músculo gastrocnemio
English (TA2): Medial head of gastrocnemius
Also called: caput tibiale musculi gastrocnemii

Sources: Terminologia Anatomica (TA2); Anatomy, Bony Pelvis and Lower Limb: Gastrocnemius Muscle.

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Representative model, for educational purposes only.

Gastrocnemius (inner head) highlighted on the Durgical 3D model