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# Big toe flexor tendon

The big toe flexor tendon runs behind the ankle and under the sole to the tip of the big toe, which it curls; it helps push off.

Official name: Tendon of flexor hallucis longus

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## What it is

The tendon of the long big-toe flexor. It runs in a groove behind the talus and under the sole to the tip of the big toe.

## What it does

Curls the big toe and helps push off. It is sometimes moved to the heel to reinforce a damaged [Achilles tendon](https://durgical.com/en/anatomy/calcaneal-tendon/).

## Key points

- The most posterior tendon behind the medial ankle; the tibial nerve and posterior tibial artery lie just medial to it, so in posterior ankle arthroscopy work stays lateral to the [flexor hallucis longus](https://durgical.com/en/anatomy/flexor-hallucis-longus/)
- In ballet dancers it can thicken and catch in its tunnel behind the [talus](https://durgical.com/en/anatomy/talus/), making the big toe lock and then release (hallux saltans)
- Often coexists with posterior ankle impingement from an os trigonum or a large lateral talar tubercle, which sit right beside its groove

## Key facts

**Attaches**
In a groove on the back of the talus between its two tubercles, under the sustentaculum tali, crossed by the FDL in the sole, then between the two hallux [sesamoids](https://durgical.com/en/anatomy/sesamoid-bones-of-foot/) to the base of the distal phalanx of the big toe

**Function**
Flexes the big toe for push-off; supports the medial arch; tendinopathy in dancers; used as a transfer to the calcaneus in chronic Achilles rupture

**Tight in**
Big toe extension with ankle dorsiflexion

## Relations

**Course**
From the lower [fibula](https://durgical.com/en/anatomy/fibula/) it passes behind the lower [tibia](https://durgical.com/en/anatomy/tibia/) into the groove between the talar tubercles, under the sustentaculum tali, across the sole and on to the [big toe](https://durgical.com/en/anatomy/great-toe/)

**Medial**
[Posterior tibial artery](https://durgical.com/en/anatomy/posterior-tibial-artery/) and veins and the [tibial nerve](https://durgical.com/en/anatomy/tibial-nerve/); further medial, the [flexor digitorum longus](https://durgical.com/en/anatomy/flexor-digitorum-longus/) and [tibialis posterior](https://durgical.com/en/anatomy/tibialis-posterior-muscle/) tendons

**Lateral**
Lateral talar tubercle and, when present, an os trigonum

**Above**
Sustentaculum tali of the [calcaneus](https://durgical.com/en/anatomy/calcaneus/), which acts as a pulley above it

## How to find it

Bending the big toe against resistance makes it move deep behind the medial ankle, behind the neurovascular bundle; it is easier to feel under the [first metatarsal](https://durgical.com/en/anatomy/first/) head, between the sesamoids.

## Examination

- Big-toe extension tested with the ankle pointed down and then pulled up: less extension with the ankle up suggests the tendon is tethered or narrowed behind the ankle

## On imaging

Its sheath often connects with the ankle joint, so a little fluid around it is normal; disproportionate fluid, thickening or a split on MRI or ultrasound points to tenosynovitis; a lateral radiograph shows an os trigonum.

## Common problems

- Tendinitis behind the inner ankle, common in ballet dancers ('dancer's tendinitis').

## Clinical notes

- Transferred to the calcaneus to reconstruct chronic Achilles tendon ruptures and severe insertional Achilles disease: it is strong, works in phase with the calf and lies close by
- Releasing its tunnel behind the talus, often with removal of an os trigonum, treats stenosing tenosynovitis in dancers
- The posterolateral approach to posterior malleolus fractures uses the interval between the fibular tendons and the flexor hallucis longus, whose belly is lifted off the back of the tibia

## Anatomical variants

- A slip joining it to the flexor digitorum longus in the sole is common
- A rare accessory muscle (peroneocalcaneus internus) can run beside it behind the ankle and be mistaken for it

## Memory aid

'Harry' comes last in 'Tom, Dick And Very Nervous Harry': the flexor hallucis longus is the most posterior structure behind the medial malleolus.

## Test yourself

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

## Which tendon is the most posterior structure behind the medial malleolus?

The flexor hallucis longus ('Harry' in 'Tom, Dick And Very Nervous Harry').

## Why does posterior ankle arthroscopy work stay lateral to the flexor hallucis longus?

The tibial nerve and posterior tibial artery lie just medial to it.

## What is hallux saltans in ballet dancers?

The thickened flexor hallucis longus catches in its tunnel behind the talus, making the big toe lock and then release.

## Which tendon is transferred to the calcaneus in chronic Achilles tendon ruptures?

The flexor hallucis longus: it is strong, works in phase with the calf and lies close by.

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

## Its names

**Official Latin (TA2)**
flexor longus hallucis TA2 2668

**Official Spanish (DeCS)**
Tendón del flexor largo del dedo gordo DeCS D013710

**English (TA2)**
Tendon of flexor hallucis longus

**Also called**
flexor hallucis longus muscle

## Related

- [Sesamoids](https://durgical.com/en/anatomy/sesamoid-bones-of-foot/)
- [Flexor retinaculum](https://durgical.com/en/anatomy/flexor-retinaculum-of-ankle/)
- [Flexor hallucis longus](https://durgical.com/en/anatomy/flexor-hallucis-longus/)
- [Calcaneus](https://durgical.com/en/anatomy/calcaneus/)
- [Fibula](https://durgical.com/en/anatomy/fibula/)
- [Talus](https://durgical.com/en/anatomy/talus/)
- [Tibia](https://durgical.com/en/anatomy/tibia/)
- [Big toe](https://durgical.com/en/anatomy/great-toe/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=14088); [Anatomy, Bony Pelvis and Lower Limb: Calf Flexor Hallucis Longus Muscle](https://www.ncbi.nlm.nih.gov/books/NBK539776/).

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Representative model, for educational purposes only.

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