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Flexor Digitorum Longus

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Flexor Digitorum Longus

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Flexor Digitorum Longus muscle is one of the deep group muscles of the posterior compartment of the leg. It’s smaller than the flexor hallucis longus muscle, even though it moves four digits.

Four muscles make up the deep group in the posterior compartment of the leg:

  1. Popliteus,
  2. Flexor digitorum longus,
  3. Flexor hallucis longus,
  4. Tibialis posterior.
See Also: Flexor Hallucis Longus Muscle
See Also: Tibialis posterior Muscle
Flexor Digitorum Longus muscle

Flexor Digitorum Longus Muscle Anatomy

Flexor Digitorum Longus passes diagonally into the sole of the foot, superficial to the tendon of the Flexor hallucis longus (FHL). However, its direction of pull is realigned by the quadratus plantae muscle, which is attached to the posterolateral aspect of the flexor digitorum longus tendon as it divides into four tendons, which in turn pass to the distal phalanges of the lateral four digits.

Flexor Digitorum Longus anatomy

Origin

The Flexor Digitorum Longus originates from the posterior surface of tibia distal to popliteal line, medial to the tibial origin of the tibialis posterior muscle. It also arises from the fascia covering the tibialis posterior muscle.

Insertion

The FDL tendon passes behind the medial malleolus and the tibialis posterior tendon , in a groove. Then, it splits into four slips after passing through medial intermuscular septum of plantar surface of foot; these slips then insert on plantar surface of bases of 2nd – 5th distal phalanges.

FDL tendon

Innervation

The FDL is innervated by the tibial nerve (S2, S3) (S2, S3).

Blood Supply

It takes its blood supply from the muscular branch of posterior tibial artery.

Action

The flexor digitorum longus acts to flex second to fifth toes; it also helps in plantar flexion of ankle joint.

OriginPosterior surface of tibia distal to popliteal line
InsertionSplits into four slips after passing through medial intermuscular septum of plantar surface of foot;
These slips then insert on plantar surface of bases of 2nd – 5th distal phalanges
InnervationTibial nerve (S2, S3) (S2, S3)
Blood SupplyMuscular branch of posterior tibial artery
ActionFlexes toes 2 – 5;
It also helps in plantar flexion of ankle joint

Clinically

The flexor digitorum longus tendon is susceptible to injury along its entire course, and lacerations, ruptures, longitudinal tears, and stenosing tenosynovitis have all been reported. Moreover, the FDL tendon is commonly used for reconstruction of dysfunctional posterior tibial and Achilles tendons.

To test the FDL, the distal phalanges of the lateral four toes are flexed against resistance; if they are acting normally, the tendons of the toes can be seen and palpated.

See Also: Achilles Tendon Repair Technique

References & More

  1. Murdock CJ, Munjal A, Agyeman K. Anatomy, Bony Pelvis and Lower Limb: Calf Flexor Hallucis Longus Muscle. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539776/
  2. Lui TH. Flexor digitorum longus tendoscopy. J Foot Ankle Surg. 2012 Sep-Oct;51(5):690-2. doi: 10.1053/j.jfas.2012.05.005. Epub 2012 Jun 21. PMID: 22727339. Pubmed7Wei B, Yao R, Amendola A. Anatomy of the Distal End of Flexor Digitorum Longus Tendon and Percutaneous Release Technique: A Cadaveric Study. Foot Ankle Orthop. 2019 Nov 7;4(4):2473011419884274. doi: 10.1177/2473011419884274. PMID: 35097346; PMCID: PMC8697276. Pubmed
  3. Clinically Oriented Anatomy – 8th Edition
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