Flexor digitorum longus

Original Editor - George Prudden

Top Contributors - George Prudden, Kim Jackson and Evan Thomas;



The muscle belly is located at the medial and posterior of the calf where is travels down to form a tendon about 3 fingers breath above the medial malleous. The tendon then passes laterally to tibialis posterior tendon where it then situated deep to the flexor retinaculum lying in its own synovial sheath along the medial aspect of the sustentaculum tali. Beyond this point it is difficult to palpate as it enters the sole of the foot deep to the abductor hallucis where is crosses forwards and laterally on the plantar aspect. Halfway along the sole, on the lateral side the tendon merges with flexor accessorius and divides into 4 individual tendons for the second to fifth toes. The lumbricals arise distal to the attachment of the flexor accessorius.[1]

Distal to the metatarsophalangeal join the tendons enter fibrous sheaths with the respective flexor digitorum tendon which lie superficial. The brevis tendon then splits allowing the longus tendon to pass through and reach its insertion at the base of the distal phalanx. Both tendons share a synovial sheath.[1]


Medial and posterior surface of the tibia.


On the plantar surface at the base of the distal phalanges of the second, third, fourth and fifth toes.


Tibial nerve (root L5, S1 and S2).

Cutaneous supply on the medial and posterior aspect of the calf and sole from L4, L5 and S1.


Posterior tibial artery[2]


Flexes the second to fifth toes first at the distal interphalangeal joint, then the proximal interphalangeal joint and finally the metarsophalangesl joint. Aids with plantarflexion of the foot at the ankle. 

When the ankle is plantarflexed, the muscle is unable to perform its flexion action of the toes[1]

Clinical relevance

During the propulsion phase of walking, running or jumping, flexor digitorum longus pulls the toes downwards towards the ground to attain maximal grip and thrust during toe-off. During standing the muscle aids with balance by gripping the ground.[1]

Fractures of the sustentaculum tali can cause entrapment of the flexor hallucis longus or flexor digitorum longus tendons amongst other abnormalities that may indicate reconstructive surgery. Post-operative management includes the use of a lower leg splint for 5-7 days, partial weight-bearing with 20 kg for 6-8 weeks in the patient's own footwear, early range of motion exercises of the ankle, subtalar and mid-tarsal joints. Outcomes are generally good with those sustaining isolated fractures performing better.[3]



It is near impossible to locate the origin due to it's depth to the soleus muscle. The insertional tendon is also deep but can be identified as it passes alongside the sustentaculum tali.


Resisted flexion of second to fifth toes with the foot in neutral or dorsiflexion.


In supine or seated, with ankle in dorsiflexed position. Stabilise proximal bone of joint to be measured. Extend the joint to be measured through available ROM.[4]



A common exercise for foot strength is performed using a towel. Ask the patient to sit and place a towel under their foot, then ask the patient to grip the towel with their toes thereby moving the towel along the floor.

The muscle can be strengthened by utilising its role in balance. Providing a patient with a suitably challenging balance exercise such as using wobble board makes exercise more functional. 

Further in rehabilitation, walking or running on different surfaces such as grass or sand will further challenge the function of flexor digitorum longus.


A stretch can be performed by pulling the toes into a extended position and the ankle into a dorsiflexed position. Similar to strengthening, a towel may be useful if the patient is struggling to reach forward. It can be wrapped around the toes and ball of the foot.


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See also


  1. 1.0 1.1 1.2 1.3 Palastanga N, Soames R. Anatomy and Human Movement: Structure and Function. 6th ed. London, United Kingdom: Churchill Livingstone; 2012.
  2. Saladin K. Anatomy & physiology: The Unity of Form and Function. 5th ed. New York: McGraw-Hill; 2010.
  3. Dürr C, Zwipp H, Rammelt S. Fractures of the sustentaculum tali. Operative Orthopädie und Traumatologie. 2013 Dec;25(6):569–78.
  4. Reese NB, Bandy WD, B WD, Y MM. Joint range of motion and muscle length testing. Philadelphia: Saunders (W.B.) Co; 2002 Jan 15. ISBN: 9780721689425.