Extensor digitorum brevis manus

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 ligmanet
  • insertion: extensor hood of index or middle fingers (variable)
  • innervation: posterior interosseous nerve
  • action: extension of the fingers

It is thought to be present in ~ 3% of the population 1. It is often painless although rarely 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 index finger (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 index finger. 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 a musclelike echo texture, on real time this usually undergoes morphologic changes during active finger extension.

MRI

Signal characteristics include

  • T1/T2/PD - Iso dense to muscle on all sequences
  • C+ (Gd) - no enhancement in uncomplicated cases (e.g. unless there is any inflammation etc)

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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