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# Biceps femoris tendon

The biceps femoris tendon is the outer hamstring tendon at the back of the knee, attaching to the head of the fibula.

Official name: Tendon of biceps femoris

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## What it is

The outer hamstring tendon, ending on the head of the fibula.

## What it does

Bends the knee and turns the shin outward; supports the outer knee.

## Key points

- The common fibular nerve runs along its back inner edge down to the fibular neck, so the nerve is found and protected first in lateral and posterolateral knee surgery
- A bone fragment pulled off the fibular head by the biceps and LCL, or off its tip by the arcuate complex ('arcuate sign'), marks a posterolateral corner injury, often with cruciate tears
- The prominent [lateral cord](https://durgical.com/en/anatomy/lateral-cord-of-the-brachial-plexus/) at the back of the knee; the iliotibial band (IT band) runs in front of it toward Gerdy's tubercle

## Key facts

**Attaches**
Common tendon of both heads of biceps femoris to the head of the fibula, splitting around the fibular attachment of the LCL; slips to the lateral tibial condyle and [crural fascia](https://durgical.com/en/anatomy/crural-fascia/)

**Function**
Knee flexion and lateral rotation of the leg; part of the posterolateral corner; the common fibular nerve runs along its posteromedial border

**Tight in**
Hip flexion with the knee extended

## Relations

**Course**
Down the back and outer side of the thigh, forming the upper lateral border of the popliteal fossa, to the head of the [fibula](https://durgical.com/en/anatomy/fibula/)

**Medial**
[Common fibular nerve](https://durgical.com/en/anatomy/common-fibular-nerve/), then the [lateral head of gastrocnemius](https://durgical.com/en/anatomy/lateral-head-of-gastrocnemius/) and the [plantaris](https://durgical.com/en/anatomy/plantaris-muscle/)

**In front**
[IT band](https://durgical.com/en/anatomy/iliotibial-tract/) and the lateral femoral condyle

**Deep**
LCL, around which its insertion splits, with a small bursa between them

## How to find it

Prone or seated with the knee bent against resistance, the cord at the outer back of the knee is followed down to the fibular head; the common fibular nerve can be rolled under the fingers just behind and inside it, then around the fibular neck.

## Examination

- Resisted knee flexion with the leg turned outward loads the biceps; pain or a gap near the fibular head suggests a distal tendon injury

## On imaging

Knee radiographs show avulsed fragments from the fibular head; MRI shows the shared biceps–LCL attachment, tears, bone oedema and injury to the other posterolateral corner structures.

## Common problems

- Strains, tendinitis, and less often a pull-off injury at the fibula with severe knee injuries.

## How it is diagnosed

Physical exam; ultrasound or MRI if needed.

## Treatment

- Rest and physical therapy; surgical repair for a pulled-off tendon.

## Clinical notes

- Foot drop from a stretched common fibular nerve can accompany distal biceps avulsions and posterolateral corner injuries
- The tendon can snap over the fibular head, a rare cause of lateral knee snapping

## Related conditions

- [Hamstring Strain](https://durgical.com/en/conditions/hamstring-strain/)

## Test yourself

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

## Where does the biceps femoris tendon insert, and how does it relate to the LCL?

On the head of the fibula, splitting around the fibular attachment of the LCL.

## Which nerve runs along the posteromedial border of the biceps femoris tendon?

The common fibular nerve, down to the fibular neck; it is found and protected first in lateral knee surgery.

## What does a bone fragment pulled off the fibular head by the biceps and LCL indicate?

A posterolateral corner injury, often with cruciate tears.

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

## Its names

**Official Latin (TA2)**
caput longum musculi bicipitis femoris TA2 2639

**Official Spanish (DeCS)**
Tendón del bíceps femoral DeCS D013710

**English (TA2)**
Tendon of biceps femoris

## Related

- [LCL](https://durgical.com/en/anatomy/fibular-collateral-ligament/)
- [Common fibular nerve](https://durgical.com/en/anatomy/common-fibular-nerve/)
- [Biceps femoris (long head)](https://durgical.com/en/anatomy/long-head-of-biceps-femoris/)
- [Fibula](https://durgical.com/en/anatomy/fibula/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=14088); [Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle](https://www.ncbi.nlm.nih.gov/books/NBK546688/); [Anatomy, Bony Pelvis and Lower Limb: Posterior Thigh Muscles](https://www.ncbi.nlm.nih.gov/books/NBK542215/).

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Representative model, for educational purposes only.

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