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MuscleForearm & handsuperficialBeyond Cert IVDraft

Extensor digitorumMusculus extensor digitorum

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

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LatinMusculus extensor digitorum
Origin
  • Lateral epicondyle of the humerus (common extensor tendon)
Insertion
  • Extensor expansions (hoods) of the four fingers, reaching the middle and distal phalanges
Action
  • Extends the four fingers, mainly at the metacarpophalangeal (knuckle) joints
  • Assists wrist extension
  • Tends to spread the fingers as it extends them
NervePosterior interosseous nerve (deep branch of the radial nerve) (C7–C8)
GroupWrist extensors
NameLatin: the 'straightener of the fingers (digits)'.

Palpation

  1. Client supine or seated with the forearm palm down and resting on the table.
  2. Place your fingers in the middle of the back of the forearm, between extensor carpi radialis brevis (thumb side) and extensor carpi ulnaris (little-finger side).
  3. Ask the client to lift the fingers one at a time, as if playing a piano; feel the belly move under your fingers.
  4. On the back of the hand, trace the four tendons fanning out to the fingers as the client straightens them.

Landmarks: Lateral epicondyle of humerus

Extensor digitorum sits in the middle of the back of the forearm, between the radial wrist extensors and Extensor carpi ulnaris. It is part of the Wrist extensors and starts from the common extensor tendon on the Lateral epicondyle of humerus. The “piano fingers” test is the easiest way to find it, because only this muscle moves when the fingers lift one at a time.

On the back of the hand its tendons are joined by small bands, which is why it is hard to lift the ring finger on its own. Gentle Stripping between the tendons on the back of the hand is a pleasant finish to forearm work.

It opposes the finger flexors, Flexor digitorum superficialis and Flexor digitorum profundus. Kenhub gives roots C7–C8 (used here); Gray’s (1918) gives C7 only.

Techniques

  • Petrissage — Kneading strokes that compress, lift and squeeze the muscle away from the bone, working the tissue between the hands.
  • 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.
  • Cross-fibre friction — Deep, specific friction applied back and forth across the direction of a tendon, ligament or muscle's fibres, with the fingers and skin moving together as one.
  • 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

  • Extensor carpi radialis brevis — Wrist extensor lying just under its longer partner, running from the lateral epicondyle to the middle finger metacarpal and lifting the back of the hand.
  • Extensor carpi ulnaris — Long muscle on the back of the forearm next to the ulna that extends the wrist and tilts it towards the little finger.

Opposes

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

Same group

  • Extensor carpi radialis brevis — Wrist extensor lying just under its longer partner, running from the lateral epicondyle to the middle finger metacarpal and lifting the back of the hand.
  • Extensor carpi radialis longus — Outer forearm muscle running from above the lateral epicondyle to the index finger metacarpal, extending the wrist and tilting it towards the thumb.
  • Extensor carpi ulnaris — Long muscle on the back of the forearm next to the ulna that extends the wrist and tilts it towards the little finger.

Sources

  1. Wikipedia: Extensor digitorum muscle
  2. Kenhub: Extensor digitorum muscle (Used for nerve root levels (C7–C8), which the Wikipedia article does not give.)
  3. Gray's Anatomy of the Human Body (1918), Myology 7e: The Muscles and Fasciae of the Forearm (Public domain. Used for actions; gives the seventh cervical nerve only.)