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# Gastrocnemius tendon (outer head)

The outer gastrocnemius tendon anchors the outer head of the calf muscle to the back of the [femur](https://durgical.com/en/anatomy/femur/), just above the knee.

Official name: Tendon of lateral head of gastrocnemius

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## What it is

The upper tendon of the outer calf muscle head, on the back of the femur.

## What it does

Anchors the calf muscle above the knee.

## Key points

- A fabella, when present, sits inside this tendon behind the lateral femoral condyle; it is a normal sesamoid, not a loose body or a fracture
- The fabellofibular ligament runs from the fabella (or this tendon) to the tip of the fibular head, as part of the posterolateral corner
- The common fibular nerve runs superficial to the lateral head, along the biceps femoris, before winding round the fibular neck

## Key facts

**Attaches**
Origin tendon of the lateral head on the lateral surface of the lateral femoral condyle; may hold a fabella (sesamoid bone)

**Function**
Anchors the lateral head above the knee (knee flexion and ankle plantarflexion); forms the inferolateral border of the popliteal fossa

**Tight in**
Knee extension with ankle dorsiflexion

## Relations

**Superficial**
[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/) between them

**Medial**
[Plantaris](https://durgical.com/en/anatomy/plantaris-muscle/), which arises just above it, then the [popliteal artery](https://durgical.com/en/anatomy/popliteal-artery/) and vein between the two heads

**Deep**
Posterolateral knee [joint capsule](https://durgical.com/en/anatomy/articular-capsule-of-knee-joint/), with the [popliteus tendon](https://durgical.com/en/anatomy/tendon-of-popliteus/) inside the joint beneath it

## How to find it

Hard to feel; the lateral head forms the outer lower border of the popliteal fossa, under the biceps femoris tendon.

## On imaging

On a lateral knee radiograph a fabella is a small, smooth, round bone behind the lateral condyle, often on both sides; MRI shows it embedded in the tendon, which separates it from a loose body.

## Clinical notes

- Fabella pain syndrome and fabella fractures are rare causes of pain at the back outer knee
- In rare cases a fabella presses on the common fibular nerve
- After knee replacement, a fabella rubbing on the metal femoral condyle is a recognised cause of posterolateral pain and clicking; removing it usually relieves the symptoms

## Anatomical variants

- A fabella is present in a variable share of people, with rates that differ widely between populations
- Absence of a gastrocnemius head is rare and, when seen, usually affects the lateral head

## Test yourself

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

## What is a fabella, and where does it lie?

A normal sesamoid inside the lateral head of gastrocnemius tendon, behind the lateral femoral condyle; not a loose body or a fracture.

## Which ligament runs from the fabella to the fibular head?

The fabellofibular ligament, part of the posterolateral corner.

## Which border of the popliteal fossa does the lateral head of gastrocnemius form?

The inferolateral border.

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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)**
Tendón del gemelo externo DeCS D013710

**English (TA2)**
Tendon of lateral head of gastrocnemius

**Also called**
caput fibulare musculi gastrocnemii

## Related

- [Gastrocnemius (outer head)](https://durgical.com/en/anatomy/lateral-head-of-gastrocnemius/)
- [Femur](https://durgical.com/en/anatomy/femur/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=14088); [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/tendon-of-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/tendon-of-lateral-head-of-gastrocnemius/