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Flexor digitorum profundusMusculus flexor digitorum profundus

Deep forearm muscle lying on the ulna that bends the fingertips and is the only muscle able to flex the end joints of the four fingers.

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LatinMusculus flexor digitorum profundus
Origin
  • Upper three-quarters of the front and inner (medial) surfaces of the ulna
  • Interosseous membrane
  • Deep fascia of the forearm
Insertion
  • Front of the bases of the distal phalanges of the four fingers
Action
  • Flexes the fingers at the distal interphalangeal (fingertip) joints
  • Assists flexion of the middle and knuckle joints of the fingers
  • Assists wrist flexion
NerveInner half (ring and little fingers): ulnar nerve; outer half (index and middle fingers): anterior interosseous branch of the median nerve (C8–T1)
GroupWrist flexors
NameLatin: the 'deep bender of the fingers (digits)'.

Palpation

  1. Client supine with the forearm palm up, or seated with the forearm resting on a table.
  2. Run your fingers from the olecranon down the sharp back border of the ulna, which lies just under the skin.
  3. Roll your fingers just off this border towards the palm side, onto the inner forearm.
  4. Hold the client's middle phalanges straight and ask them to bend only the fingertips; feel the contraction under your fingers.

Landmarks: Olecranon

Flexor digitorum profundus is the deepest of the Wrist flexors. Most of it lies under the other flexors, but the part on the inner edge of the ulna can be reached from the side. Sustained Compression or slow Stripping along the ulna, starting near the Olecranon, reaches it better than broad kneading.

It is unusual because two nerves supply it: the ulnar nerve for the ring and little fingers, and a branch of the median nerve for the index and middle fingers. Its partner, Flexor digitorum superficialis, bends the middle joints; profundus is the one that curls the fingertips.

Techniques

  • Compression — Pressing straight down into a muscle with the palm, fist or forearm, holding briefly, then releasing and moving on.
  • Stripping — A slow, deep, narrow glide along the length of a single muscle with the thumb, knuckle or elbow, pausing over tight bands on the way.
  • Trigger point pressure release — Sustained thumb or finger pressure on a tender spot within a taut band of muscle, held until the client reports the discomfort easing, then slowly released.
  • Passive stretching — The therapist gently moves a relaxed limb to lengthen a muscle to a point of mild stretch and holds it there, with no effort from the client.

Works with

  • Flexor digitorum superficialis — Large middle-layer forearm muscle that bends the four fingers at their middle joints and helps bend the knuckles and wrist.

Opposes

  • Extensor digitorum — Muscle in the middle of the back of the forearm whose four tendons straighten the fingers and help extend the wrist.

Same group

  • Flexor carpi radialis — Superficial forearm muscle that runs from the medial epicondyle to the index and middle finger metacarpals, bending the wrist and tilting it towards the thumb.
  • Flexor carpi ulnaris — Superficial muscle along the inner (little-finger) border of the forearm that bends the wrist and tilts it towards the little finger.
  • Flexor digitorum superficialis — Large middle-layer forearm muscle that bends the four fingers at their middle joints and helps bend the knuckles and wrist.
  • Palmaris longus — Small, slender forearm muscle with a long tendon that tightens the fascia of the palm and weakly bends the wrist; missing in some people.

Sources

  1. Wikipedia: Flexor digitorum profundus muscle
  2. Gray's Anatomy of the Human Body (1918), Myology 7e: The Muscles and Fasciae of the Forearm (Public domain. Nerve roots C8 and T1 agree with Wikipedia.)