[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) › Flexor digitorum longus [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Lower limb](https://durgical.com/en/anatomy/region/lower-limb/) # Flexor digitorum longus The flexor digitorum longus is a deep calf muscle that curls the four smaller toes; its tendon runs behind the inner ankle. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=lower_limb&select=flex_digitorum_longus&side=r) Opens in the Durgical app, no sign-up needed. ## What it is A deep calf muscle. ## What it does Curls the toes. ## Key points - Second structure behind the medial malleolus, between the [tibialis posterior tendon](https://durgical.com/en/anatomy/tendon-of-tibialis-posterior/) in front and the posterior tibial vessels behind - It crosses twice: superficial to tibialis posterior above the ankle, and superficial (plantar) to flexor hallucis longus in the sole at the master knot of Henry - In the second layer of the sole its tendon receives [quadratus plantae](https://durgical.com/en/anatomy/quadratus-plantae-muscle/) and gives origin to the four lumbricals - Its tendons pass through the split tendons of [flexor digitorum brevis](https://durgical.com/en/anatomy/flexor-digitorum-brevis/) to reach the distal phalanges ## Key facts **Origin** Medial part of posterior tibia below soleal line **Insertion** Bases of distal phalanges of lateral four toes **Action** Flexes lateral four toes; plantar flexes ankle; supports longitudinal arch **Nerve** Tibial nerve (S2–S3) (some texts: L5–S2) **Blood supply** [Posterior tibial artery](https://durgical.com/en/anatomy/posterior-tibial-artery/) ## Relations **Course** From the back of the [tibia](https://durgical.com/en/anatomy/tibia/) it runs down behind the medial malleolus and under the flexor retinaculum into the sole, where it crosses the [flexor hallucis longus](https://durgical.com/en/anatomy/flexor-hallucis-longus/) tendon and divides into four tendons for toes 2–5 **Deep** Back of the tibia and [tibialis posterior](https://durgical.com/en/anatomy/tibialis-posterior-muscle/) **Superficial** Deep transverse fascia and [soleus](https://durgical.com/en/anatomy/soleus-muscle/); the posterior tibial vessels and [tibial nerve](https://durgical.com/en/anatomy/tibial-nerve/) lie between it and flexor hallucis longus **Lateral** Tibialis posterior high in the leg, flexor hallucis longus further out ## How to find it Its tendon is felt just behind the tibialis posterior tendon, behind the medial malleolus, when the lesser toes are curled against resistance. ## Examination - Resisted flexion of the tip of a lesser toe while the middle phalanx is held: weakness points to a flexor digitorum longus or tibial nerve lesion (the short flexor acts only up to the middle phalanx) - Passive extension of the toes is painful in deep posterior compartment syndrome ## On imaging Axial MRI shows it in the deep posterior compartment, on the back of the tibia medial to the tibialis posterior; lower down it crosses superficial to that muscle (crural chiasm). Denervation oedema in it, the tibialis posterior and the flexor hallucis longus points to a tibial nerve lesion. Its tendon is assessed behind the medial malleolus with ultrasound or MRI. ## Clinical notes - Its tendon is the usual replacement for tibialis posterior in reconstruction of flexible adult-acquired flatfoot - Flexible hammer and claw toes can be treated by moving its tendon slip to the top of the toe (flexor-to-extensor transfer) - Deep posterior compartment syndrome involves it with tibialis posterior, flexor hallucis longus and the tibial nerve ## Anatomical variants - A tendinous slip linking it with flexor hallucis longus in the sole is common ## Development Its cells gather in the ventral (flexor) muscle mass of the leg bud, which the tibial nerve supplies; the 90° medial turn of the [lower limb](https://durgical.com/en/anatomy/region/lower-limb/) in week 7 carries this flexor mass round to the back of the leg. ## Related conditions - [Plantar Fasciitis](https://durgical.com/en/conditions/plantar-fasciitis/) - [Tarsal tunnel syndrome](https://durgical.com/en/conditions/tarsal-tunnel-syndrome/) - [Medial tibial stress syndrome (shin splints)](https://durgical.com/en/conditions/medial-tibial-stress-syndrome/) - [Flatfoot (pes planus)](https://durgical.com/en/conditions/flatfoot/) ## Test yourself Think of the answer, then tap the question to see it. ## Where does the flexor digitorum longus tendon lie behind the medial malleolus? Second, between the tibialis posterior tendon in front and the posterior tibial vessels behind. ## Which tendon is the usual replacement for the tibialis posterior in flexible adult-acquired flatfoot? The flexor digitorum longus tendon, transferred to the navicular. ## Which sole muscles attach to the flexor digitorum longus tendon? The quadratus plantae inserts into it and the four lumbricals arise from it, in the second layer of the sole. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/flexor-digitorum-longus/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** flexor longus digitorum TA2 2667 **Official Spanish (DeCS)** Músculo flexor largo de los dedos **English (TA2)** Flexor digitorum longus **Also called** flexor digitorum longus muscle ## Related - [Tibial nerve](https://durgical.com/en/anatomy/tibial-nerve/) - [Posterior tibial artery](https://durgical.com/en/anatomy/posterior-tibial-artery/) - [Toe flexor tendon](https://durgical.com/en/anatomy/tendon-of-flexor-digitorum-longus/) - [Tibia](https://durgical.com/en/anatomy/tibia/) Sources: Terminologia Anatomica (TA2); [Anatomy, Bony Pelvis and Lower Limb: Leg Posterior Compartment](https://www.ncbi.nlm.nih.gov/books/NBK537340/); [8.5 Development of the Appendicular Skeleton](https://openstax.org/books/anatomy-and-physiology-2e/pages/8-5-development-of-the-appendicular-skeleton) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/flexor-digitorum-longus/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/flexor-digitorum-longus/