Flexor Digitorum Profundus
Forearm · Upper Limb
The flexor digitorum profundus is the deep flexor of the fingers, lying against the ulna and interosseous membrane from which it arises. Its four tendons pass through the splits in the superficialis tendons to reach the bases of the distal phalanges of digits 2 to 5. It is the only muscle able to flex the distal interphalangeal (DIP) joints, and it also assists at the PIP joints and wrist. Its innervation is split: the medial half (to the ring and little fingers) is supplied by the ulnar nerve (C8, T1) and the lateral half (to the index and middle fingers) by the anterior interosseous branch of the median nerve (C8, T1).
Origin, Insertion, Action & Nerve
Origin
Anterior and medial surfaces of proximal ulna and interosseous membrane
Insertion
Bases of distal phalanges of digits 2–5
Action
Flexion of distal interphalangeal (DIP) joints of digits 2–5; assists wrist flexion
Nerve
Medial part: ulnar nerve (C8, T1); Lateral part: anterior interosseous branch of median nerve (C8, T1)
Attachments explained
The Flexor Digitorum Profundus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Anterior and medial surfaces of proximal ulna and interosseous membrane
Insertion
Bases of distal phalanges of digits 2–5
Action & function
When the Flexor Digitorum Profundus contracts, it produces the following movements: Flexion of distal interphalangeal (DIP) joints of digits 2–5; assists wrist flexion.
As part of the Forearm group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Flexor Digitorum Profundus receives its nerve supply from the Medial part: ulnar nerve (C8, T1); Lateral part: anterior interosseous branch of median nerve (C8, T1). This nerve carries fibres from spinal segment(s) C8, T1.
Because a muscle can only contract when its nerve is intact, injury to the Medial part: ulnar nerve or to its spinal roots (C8, T1) can weaken or paralyse the Flexor Digitorum Profundus, impairing the movements it normally produces (flexion of distal interphalangeal (DIP) joints of digits 2–5). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Flexor Digitorum Profundus (the OIANS method)
The single most testable fact is that flexor digitorum profundus is the only muscle that can bend the distal interphalangeal joints, because its tendons alone reach the distal phalanges. Everything else about the muscle can be reasoned from that deep, fingertip-bound course.
Master its split nerve supply with a rule of halves: the lateral half (index and middle fingers) follows the median nerve through its anterior interosseous branch, while the medial half (ring and little fingers) follows the ulnar nerve. This dual innervation is a favourite exam theme, so learn it deliberately alongside the muscle's action.
Frequently asked questions
Where is the Flexor Digitorum Profundus located?
The Flexor Digitorum Profundus is a muscle of the Forearm group, located in the Upper Limb.
What is the origin of the Flexor Digitorum Profundus?
Anterior and medial surfaces of proximal ulna and interosseous membrane
What is the insertion of the Flexor Digitorum Profundus?
Bases of distal phalanges of digits 2–5
What movements does the Flexor Digitorum Profundus produce?
Flexion of distal interphalangeal (DIP) joints of digits 2–5; assists wrist flexion
What nerve supplies the Flexor Digitorum Profundus?
Medial part: ulnar nerve (C8, T1); Lateral part: anterior interosseous branch of median nerve (C8, T1)
Is the Flexor Digitorum Profundus free to study in OIANS?
Yes. The Flexor Digitorum Profundus is free in OIANS: its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory, and because it belongs to the Upper Limb it is also covered by the free Quiz and Flashcard decks. The other regions, the "All Muscles" deck, and the Progress and Explore tools are unlocked with a one-time Lifetime purchase.
Related muscles
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