OVERVIEW
Other Name: Extensor digitorum.
Muscle Test Group: Extensor digitorum communis, extensor indicis proprius, and extensor digiti minimi.
Key Points:
• Extensor digitorum communis is tested in a muscle group with extensor indicis proprius and extensor digiti minimi/quinti.
• Extensor digitorum communis extends the fingers.
• Additional small and index finger extensors (extensor indicis proprius and extensor digiti minimi) that contribute and attach to the extensor digitorum communis tendons. These tendons lie on the ulnar aspect of the corresponding finger.
• Extrinsic muscle.
• Extensor digitorum communis and extensor indicis proprius are located in the forth dorsal/extensor compartment, Extensor digiti minimi is located in the fifth extensor compartment. (Note: extensor indicis proprius has the most distal muscle belly of the extensors).
EXAMINATION
Extensor digitorum communis (EDC) is examined and tested with extensor indicis and extensor digiti minimi as a muscle group.EDC is the primary contributor to this group.
Muscle Function:
• Primary: Extends the metacarpal-phalangeal joints of the index, long, ring and small fingers.
• Secondary: Assists the lumbricals and interossei to extend interphalangeal joints. Assists in wrist extension. Assists in abduction of the index, ring, and small fingers away from the long finger.
Palpation: Palpate all tendons together at the wrist or individual tendons proximal to the metacarpal-phalangeal joint.
Strength Testing: Position – wrist at neutral and interphalangeal joint relaxed into flexion. Stabilize – at the wrist. Resist – finger extension by applying force over dorsal proximal phalanges (in the direction of flexion).
Possible Substitutions: Careful to avoid interpreting tenodesis effect (active wrist flexion with subsequent finger extension) as active extension via the extensor digitorum communis.
Relevant Anatomy:
Key Points:
• Additional small and index finger extensors (extensor indicis proprius and extensor digiti minimi) that contribute and attach to the extensor digitorum communis tendons. These tendons lie on the ulnar aspect of the corresponding finger.
• Extensor digitorum communis and extensor indicis proprius are located in the forth dorsal/extensor compartment. Extensor digiti minimi is located in the fifth extensor compartment. (Note: extensor indicis proprius has the most distal muscle belly of the extensors).
Innervation:
• Roots: C6, C7, C8.
• Nerve: Radial nerve, posterior interosseous nerve.
• Innervation Route: C6, C7, C8 → radial nerve → posterior interosseous nerve → extensor digitorum communis branch.
Origin: Lateral epicondyle of the humerus (common origin with other extensors), intermuscular septum, and antebrachial fascia.
Insertion: By four tendons and insert into the extensor apparatus of the middle and distal phalanx of the index, long, ring and small finger by the following manner:
• Each tendon divides into a central and two lateral bands over the proximal phalanx. The medial band inserts into the base of the middle phalanx. The lateral bands reunite over the middle phalanx and insert into the base of the distal phalanx.
• In addition, the intrinsic musculature (interossei and lumbricals) provide a significant contribution to the central and lateral bands.
• Some tendon fibers insert into the sagittal bands.
• A tendon slip may insert into the dorsal base of the proximal phalanx for each finger.
• Tendon to the index finger is accompanied by the extensor indicis on its ulnar side.
• Tendon to the small finger is accompanied by the extensor digiti minimi on its ulnar side.
Variation: Extensor digitorum to the small finger may be very small or absent.