Muscular system · Lower limb

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.

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 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 it passes behind the lower tibia into the groove between the talar tubercles, under the sustentaculum tali, across the sole and on to the big toe

Medial

Posterior tibial artery and veins and the tibial nerve; further medial, the flexor digitorum longus and tibialis posterior tendons

Lateral

Lateral talar tubercle and, when present, an os trigonum

Above

Sustentaculum tali of the 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 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.

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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
• Flexor retinaculum
• Flexor hallucis longus
• Calcaneus
• Fibula
• Talus
• Tibia
• Big toe

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Bony Pelvis and Lower Limb: Calf Flexor Hallucis Longus Muscle.

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Representative model, for educational purposes only.