Flexor digitorum profundus muscle
The flexor digitorum profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm.
|Flexor digitorum profundus muscle|
Ventral view of the deep muscles of the forearm. FDP is shown in blue.
|Origin||upper 3/4 of the anterior and medial surfaces of the body of the ulna, interosseous membrane and deep fascia of the forearm|
|Insertion||base of the distal phalanges of the fingers|
|Artery||anterior interosseous artery|
|Nerve||median (anterior interosseous), muscular branches of ulnar|
|Actions||flex hand and both interphalangeal joints|
|Antagonist||Extensor digitorum muscle|
|Latin||Musculus flexor digitorum profundus|
|Anatomical terms of muscle|
Together the flexor pollicis longus, pronator quadratus, and flexor digitorum profundus form the deep layer of ventral forearm muscles. The muscle is named from Latin, meaning 'deep bender of the fingers'.
Flexor digitorum profundus originates in the upper 3/4 of the anterior and medial surfaces of the ulna, interosseous membrane and deep fascia of the forearm. The muscle fans out into four tendons (one to each of the second to fifth fingers) to the palmar base of the distal phalanx.
Flexor digitorum profundus lies deep to the superficialis, but it attaches more distally. Therefore, profundus's tendons go through the tendons of superficialis, and end up attaching to the distal phalanx. For this reason profundus is also called the perforating muscle.
- The medial aspect of the muscle (which flexes the 4th and 5th digit) is supplied by the ulnar nerve (C8, T1)
- The lateral aspect (which flexes the 2nd and 3rd digit) is innervated by the median nerve specifically the anterior interosseous branch (C8, T1).
It is one of two flexor muscles that is not exclusively supplied by the median nerve (the other is flexor carpi ulnaris).
The tendon of the index finger often has a separate muscle belly.
Flexor digitorum profundus is a flexor of the wrist (midcarpal), metacarpophalangeal and interphalangeal joints. The lumbricals, intrinsic muscles of the hand, attach to the tendon of flexor digitorum profundus. Thus, the flexor muscle is used to aid the lumbrical muscles in their role as extensors of the interphalangeal joints. As the lumbrical muscles originate on the palmar side of the hand and attach on the dorsal aponeurosis, power is transferred from the flexor digitorum profundus muscle to fully extend the fingers as well as flex the metacarpophalangeal joints.
The tension generated by flexor digitorum profundus at the more distal joints is determined by wrist position. Flexion of the wrist causes muscle shortening at that point, reducing tension that can be generated more distally. Fingers cannot be fully flexed if the wrist is fully flexed.
In many primates, the FDP is fused with the flexor pollicis longus (FPL). In great apes the belly of the FDP has a separate tendon for the FDP. In lesser apes, both muscles have separate bellies in the forearm, but in Old World monkeys they separate in the carpal tunnel. The lack of differentiation in the FDP musculature in baboons makes it unlikely that this monkey can control individual fingers independently. 
Cross-section through the middle of the forearm.
- Platzer 2004, p 162
- Lutsky KF, Giang EL, Matzon JL (January 2015). "Flexor tendon injury, repair and rehabilitation". Orthopedic Clinics of North America. 46 (1): 67–76. doi:10.1016/j.ocl.2014.09.004. PMID 25435036.
- Levangie, Pamela K; Norkin, Cynthia C (2011). Joint Structure and Function: A Comprehensive Analysis (5 ed.). F.A. Davis. p. 326. ISBN 0803626347.
- Tocheri et al. 2008, pp 556-7
- Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1.
- Tocheri, MW; Orr, CM; Jacofsky, MC; Marzke, MW. (April 2008). "The evolutionary history of the hominin hand since the last common ancestor of Pan and Homo". J. Anat. 212 (4): 544–62. doi:10.1111/j.1469-7580.2008.00865.x. PMC 2409097. PMID 18380869. (Abstract, PubMed) (PDF, Smithsonian)
- Illustration: upper-body/flexor-digitorum-profundus from The Department of Radiology at the University of Washington