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# 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](https://durgical.com/en/anatomy/femur/).

## What it does

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

## Key points

- Smaller than the medial head and ends higher on the calf; with plantaris it forms the inferolateral border of the popliteal fossa
- A fabella, a small sesamoid bone, sits in its tendon of origin behind the lateral femoral condyle in some people
- The common fibular nerve runs between the biceps femoris tendon and the lateral head before winding round the fibular neck

## Key facts

**Origin**
Lateral surface of lateral femoral condyle

**Insertion**
Posterior [calcaneus](https://durgical.com/en/anatomy/calcaneus/) via calcaneal (Achilles) tendon

**Action**
Plantar flexes ankle; flexes knee

**Nerve**
Tibial nerve (S1–S2)

**Blood supply**
Lateral sural artery (from [popliteal artery](https://durgical.com/en/anatomy/popliteal-artery/))

## Relations

**Above**
Arises from the lateral femoral condyle, above and behind the attachments of the lateral collateral ligament and the [popliteus tendon](https://durgical.com/en/anatomy/tendon-of-popliteus/)

**Lateral**
[Biceps femoris tendon](https://durgical.com/en/anatomy/tendon-of-biceps-femoris/), with the [common fibular nerve](https://durgical.com/en/anatomy/common-fibular-nerve/) lying in the angle between that tendon and the lateral head

**Deep**
[Plantaris](https://durgical.com/en/anatomy/plantaris-muscle/) belly, the back of the knee capsule and [popliteus](https://durgical.com/en/anatomy/popliteus-muscle/); lower down, the [soleus](https://durgical.com/en/anatomy/soleus-muscle/)

**Medial**
The medial head; the popliteal vessels and [tibial nerve](https://durgical.com/en/anatomy/tibial-nerve/) pass between the two heads into the calf

**Superficial**
Deep fascia and [skin](https://durgical.com/en/anatomy/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](https://durgical.com/en/anatomy/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

- [Duchenne muscular dystrophy](https://durgical.com/en/conditions/duchenne-muscular-dystrophy/)
- [Achilles tendon rupture](https://durgical.com/en/conditions/achilles-tendon-rupture/)
- [Sarcopenia](https://durgical.com/en/conditions/sarcopenia/)

## 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.

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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)](https://durgical.com/en/anatomy/medial-head-of-gastrocnemius/)
- [Tibial nerve](https://durgical.com/en/anatomy/tibial-nerve/)
- [Popliteal artery](https://durgical.com/en/anatomy/popliteal-artery/)
- [Gastrocnemius tendon (outer head)](https://durgical.com/en/anatomy/tendon-of-lateral-head-of-gastrocnemius/)
- [Femur](https://durgical.com/en/anatomy/femur/)
- [Achilles tendon](https://durgical.com/en/anatomy/calcaneal-tendon/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Bony Pelvis and Lower Limb: Gastrocnemius Muscle](https://www.ncbi.nlm.nih.gov/books/NBK532946/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/lateral-head-of-gastrocnemius/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/lateral-head-of-gastrocnemius/