Location and structure
In the forearm, the flexor pollicis longus muscle is located in the third muscle layer. It lies laterally, while the deep digital flexor (m. flexor digitorum profundus) is located medially to it.
- Origin (Origo): anterior surface of the radius and the interosseous membrane (membrana interossea) at the border between the upper and middle thirds of the forearm.
- Insertion (Insertio): base of the distal phalanx of the thumb.
Topography of the tendon in the hand
The tendon of the muscle is enclosed in a synovial sheath and follows this topographical course:
- The proximal blind end of the sheath is located in the Pirogov-Parona space, 2 cm proximal to the flexor retinaculum (retinaculum mm. flexorum).
- The tendon passes through the carpal tunnel.
- It emerges into the proximal part of the midpalmar space.
- It perforates the lateral intermuscular septum.
- It passes through the thenar fat pad between the heads of the short flexor of digit I (m. flexor pollicis brevis).
- It inserts into the base of the distal phalanx.
The medial compartment of the thenar fascial space communicates laterally with the synovial sheath of the tendon of m. flexor pollicis longus.
Blood supply and innervation
- Innervation: median nerve (n. medianus), segments C6–C8.
- Blood supply: anterior interosseous artery (a. interossea anterior), radial (a. radialis) and ulnar (a. ulnaris) arteries. In the forearm, the anterior interosseous artery lies on the interosseous membrane deep to m. flexor pollicis longus and m. flexor digitorum profundus. In the hand, the princeps pollicis artery (a. princeps pollicis) runs along the tendon, passing between m. adductor pollicis and m. flexor pollicis brevis.
Function
The muscle flexes the distal phalanx of the thumb. It also flexes the thumb and the wrist.
Do not confuse with: flexor hallucis longus
In lower limb anatomy, there is a similarly named muscle — flexor hallucis longus (m. flexor hallucis longus).
- Location: deep layer of the posterior leg muscles; the muscle lies laterally, closer to the fibula. It originates from the posterior surface of the fibula and the interosseous membrane.
- Topography: the synovial sheath of the flexor hallucis longus is located in the medial retromalleolar region.
- Function: flexes the big toe, participates in flexion and stabilization of the foot, and supports the medial longitudinal arch.
- Innervation and blood supply: tibial nerve (n. tibialis, L4–S2), posterior tibial and fibular arteries.
Class and exam questions
Where is the blind end of the synovial sheath of this muscle's tendon located?
The proximal blind end of the sheath is located in the Pirogov-Parona space, 2 cm proximal to the flexor retinaculum (retinaculum mm. flexorum).
Between which structures does the tendon pass in the thenar region?
In the hand, the tendon passes through the thenar fascial space between the heads of the short flexor of digit I (m. flexor pollicis brevis).
Which artery runs along the tendon in the hand?
Along the tendon, between the adductor pollicis and the flexor pollicis brevis, runs the princeps pollicis artery (a. princeps pollicis).
What else to study on this topic
- Parona's space (Pirogov's space)
- Thenar spaces
- Median nerve (n. medianus)
- Synovial sheaths of the hand
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