Extensor digitorum brevis manus

Dr Henry Knipe and Dr Yuranga Weerakkody et al.

The extensor digitorum brevis manus (EDBM) muscle is an accessory muscle in the hand and is a normal anatomical variant. 

  • origin: distal radius and posterior radiocarpal ligament
  • insertion: extensor hood of 2nd or 3rd digits (variable)
  • innervation: posterior interosseous nerve
  • action: extension of the digits

It is thought to be present in ~3% of the population 1. It is often painless, although rarely it can present as a painful mass over the dorsal aspect of the hand. It can be bilateral in up to half of cases.

The EDBM muscle lies along the ulnar side of the extensor tendon of the 2nd digit (usually fourth wrist compartment 5). It commonly arises at the distal end of the radius and posterior radiocarpal ligament to insert most commonly on the 2nd digit. However, insertion can also be seen on the 3rd, 4th, or 5th digits, as well as multiple insertions on more than one digit. 

The muscle is usually painless but may occasionally be associated with exercise-induced pain or tenosynovitis of the extensor tendons.

Plain radiograph

Can be normal.

Ultrasound

Sonography may reveal a soft-tissue mass with muscle echotexture; in real time, it usually undergoes morphologic changes during active finger extension.

MRI

Signal characteristics include:

  • T1/T2/PD: isointense to muscle on all sequences
  • C+ (Gd): no enhancement in uncomplicated cases (e.g. unless there is inflammation)
Upper limb anatomy
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Article information

rID: 9948
Section: Anatomy
Synonyms or Alternate Spellings:
  • Extensor digitorum brevis manus (EDBM)
  • EDBM

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