Gastrocnemius (outer head) !
The outer head of the gastrocnemius is the smaller part of the calf muscle; it crosses the back of the knee and points the foot.
Official name: Lateral head of gastrocnemius
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What it is
The outer head of the calf muscle (gastrocnemius), starting on the back of the femur.
What it does
Points the foot (pushing off when walking or jumping) and helps bend the knee.
Key facts
- Origin
- Lateral surface of lateral femoral condyle
- Insertion
- Posterior calcaneus via calcaneal (Achilles) tendon
- Action
- Plantar flexes ankle; flexes knee
- Nerve
- Tibial nerve (S1–S2)
- Blood supply
- Lateral sural artery (from popliteal artery)
Relations
- Above
- Arises from the lateral femoral condyle, above and behind the attachments of the lateral collateral ligament and the popliteus tendon
- Lateral
- Biceps femoris tendon, with the common fibular nerve lying in the angle between that tendon and the lateral head
- Deep
- Plantaris belly, the back of the knee capsule and popliteus; lower down, the soleus
- Medial
- The medial head; the popliteal vessels and tibial nerve pass between the two heads into the calf
- Superficial
- Deep fascia and skin, supplied here by the lateral sural cutaneous nerve from the common fibular nerve
How to find it
Standing on tiptoe, the lateral head forms the smaller, higher bulge of the outer calf. Lying prone with the knee bent against resistance, it is felt just below and medial to the biceps femoris tendon at the lower lateral edge of the popliteal fossa.
Examination
- Silfverskiöld test (as for the medial head): dorsiflexion limited only with the knee straight points to gastrocnemius tightness rather than soleus tightness
On imaging
On a lateral knee radiograph a fabella appears as a small, smooth, rounded ossicle behind the lateral femoral condyle; its well-defined cortex and typical position help tell it from a loose body or an osteophyte.
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
- Fabella syndrome: posterolateral knee pain where the fabella rubs on the lateral femoral condyle; compression of the common fibular nerve by a fabella has also been reported
- The common fibular nerve is at risk next to the lateral head in posterolateral knee approaches and from tight casts or bandages around the fibular head
- The lateral head can serve as a local muscle flap for the upper lateral tibia and knee, but its reach is shorter than the medial head's and the fibular nerve limits its arc
Anatomical variants
- Absence of one gastrocnemius head is rare and, when it occurs, usually affects the lateral head
- How often a fabella is present varies widely between populations and studies
Development
Like the medial head, a ventral (flexor) muscle mass derivative supplied by the tibial nerve; a fabella, when present, develops as a sesamoid within its tendon of origin.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Which small sesamoid bone may sit in the tendon of origin of the lateral head of the gastrocnemius?
The fabella, behind the lateral femoral condyle; on a lateral radiograph it is a smooth, rounded ossicle, not a loose body.
Which nerve runs between the biceps femoris tendon and the lateral head of the gastrocnemius?
The common fibular nerve, before winding round the fibular neck; it is at risk there in posterolateral approaches and from tight casts.
Which artery supplies the lateral head of the gastrocnemius?
The lateral sural artery, a branch of the popliteal artery.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- caput laterale musculi gastrocnemii TA2 2658
- Official Spanish (DeCS)
- Cabeza lateral del músculo gastrocnemio
- English (TA2)
- Lateral head of gastrocnemius
- Also called
- caput fibulare musculi gastrocnemii
Related
- Gastrocnemius (inner head)
- Tibial nerve
- Popliteal artery
- Gastrocnemius tendon (outer head)
- Femur
- Achilles tendon
Sources: Terminologia Anatomica (TA2); Anatomy, Bony Pelvis and Lower Limb: Gastrocnemius Muscle.
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Representative model, for educational purposes only.
