Extensor digitorum brevis manus muscle

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

Summary

• origin: distal radius and posterior radiocarpal ligament

• insertion: extensor hood of 2^nd or 3^rd digits (variable)

• innervation: posterior interosseous nerve

• action: extension of the digits

Epidemiology

ItFirst described by Albinus in 1734, it is thought to be present in ~3% of the population ¹. It can be bilateral in up to half of cases.

Gross anatomy

The EDBM muscle lies along the ulnar side of the extensor tendon of the 2^nd 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 2^nd digit. However, insertion can also be seen on the 3^rd, 4^th, or 5^th digits, as well as multiple insertions on more than one digit. 

Arterial supply

• anterior interosseous artery ⁷

Innervation

• posterior interosseous nerve ⁷

Clinical presentation

The muscle is usually painless although rarely it can present as a painful mass over the dorsal aspect of the hand. Occasionally it may be associated with exercise-induced pain or tenosynovitis of the extensor tendons.

Radiographic features

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)

History and etymology

The muscle was first described by Bernhard Albinus (1697-1770), German-born Dutch anatomist, who discovered the muscle in 1734 and initially named it the extensor brevis digiti indicis vel medii ^8,9.