The Flexor Digitorum Profundus Muscle (FDP) is an extrinsic hand muscle that flexes the metacarpophalangeal and distal interphalangeal joints of the index, middle, ring, and little fingers. The flexor digitorum profundus lies in the deep volar compartment of the forearm and originates from the upper three-fourths of the volar and medial surfaces of the ulna, interosseous membrane, and deep fascia of the forearm. The tendons of the flexor digitorum profundus insert into the base of the distal phalanges of the index, middle, ring, and little fingers. The tendons of the flexor digitorum profundus lie deep to the tendons of the flexor digitorum superficialis, and the tendon to the index finger is usually separate from the other three partially attached flexor digitorum profundus tendons as they pass through the carpal tunnel.[rx] Since the tendons of the flexor digitorum profundus arise at or below the wrist joint, contraction of the muscle produces mass action movement in all four tendons and allows for a power grip.
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.
Together the flexor pollicis longus, pronator quadratus, and flexor digitorum profundus form the deep layer of ventral forearm muscles.[rx] The muscle is named from Latin, meaning ‘deep bender of the fingers’.
Structure of Flexor Digitorum Profundus Muscle
The flexor digitorum profundus is a flexor of the midcarpal (wrist), metacarpophalangeal, and interphalangeal joints of the index, middle, ring, and little fingers. Since the lumbricals arise from the flexor digitorum profundus tendons and insert into the dorsal extensor expansions of the proximal phalanges, the flexor digitorum profundus muscle aids the lumbricals in fully extending the fingers at the interphalangeal joints and flexing the fingers at the metacarpophalangeal joints. Flexion at the distal interphalangeal joints depends on wrist positioning and the tension generated at the distal joints is reduced when the wrist is fully flexed.
Flexor digitorum profundus
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Origin: ulna and interosseous membrane
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Insertion: base of phalanges
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Action: flexion DIP joints of digits
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Innervation: digits 2-3: median nerve; digits 4-5: ulnar nerve
Origin and Insertion of Flexor Digitorum Profundus Muscle
Flexor digitorum profundus originates from four sites; the superior three-quarters of the anterior surface of the ulna, the adjacent part of the interosseous membrane, the coronoid process of ulna and the aponeurosis of the flexor carpi ulnaris muscle. From this broad origin, the muscle takes an inferior course towards the hand.
At the level of the distal third of the forearm, it gives off a broad tendon. This crosses the superficial surface of the pronator quadratus and enters the hand by passing beneath the flexor retinaculum. Upon entering the hand, the tendon splits into four slips that attach to the palmar surfaces of the bases of the distal phalanges of digits 2-5. The muscle fibers are arranged in a way that the medial part of the muscle inserts into digits 4 and 5, while the lateral part inserts to digits 2 and 3.
Nerve Supply of Flexor Digitorum Profundus Muscle
Flexor digitorum profundus is a composite muscle innervated by the anterior interosseous nerve and ulnar nerves.
- The medial aspect of the muscle (which flexes the 4th and 5th digit) is supplied by the ulnar nerve (C8, T1)[rx]
- The lateral aspect (which flexes the 2nd and 3rd digit) is innervated by the median nerve[rx] 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).
Blood Supply of Flexor Digitorum Profundus Muscle
Flexor digitorum profundus is supplied by the inferior ulnar collateral and ulnar recurrent arteries at its origin. The superior part of the muscle belly is supplied either by the ulnar artery or by its branch; the common interosseous artery. The rest of the muscle is vascularized by branches of the ulnar, anterior interosseous and median arteries.
Function of Flexor Digitorum Profundus Muscle
Flexor digitorum profundus is a flexor of the wrist (midcarpal), metacarpophalangeal and interphalangeal joints.[rx] The lubricants, 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.[rx]
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