Where is the muscle located and how is it structured?
- Origin: the muscle originates from the lateral epicondyle of the humerus (epicondylus lateralis) as part of the common extensor tendon.
- Topography on the forearm: belongs to the superficial layer of the posterior forearm. In a cross-section of the middle third of the forearm, it is located posteriorly together with the extensor carpi ulnaris (m. extensor carpi ulnaris).
- Insertion: the tendons pass to all digits except the thumb. They run to the 2nd–5th digits via the dorsal aponeuroses (aponeurosis dorsalis).
- Tendinous slips: the central slip attaches to the base of the middle phalanx, and the lateral slips attach to the base of the distal phalanx. The extensor digiti minimi (m. extensor digiti minimi) joins the extensor digitorum tendon.
How do the tendons pass through the wrist region?
The tendons of the muscle pass through the tendinous compartment of the common extensor digitorum and extensor indicis.
- Synovial sheath: the content of the compartment is the triangular synovial sheath of the tendons of the extensor digitorum and extensor indicis (vagina tendinum mm. extensoris digitorum et extensoris indicis).
- Boundaries of the sheath: the base of the triangle faces the digits. Proximally, the sheath extends 10 mm above the extensor retinaculum (retinaculum mm. extensorum), and distally it ends blindly at the mid-metacarpal level.
Blood supply and innervation
- Blood supply: posterior interosseous artery (a. interossea posterior).
- Innervation: radial nerve (n. radialis), C7–C8.
What is its function?
- Extends the 2nd–5th digits at the metacarpophalangeal and interphalangeal joints.
- Participates in extension of the hand.
- Participates in abduction of the digits.
Clinical significance
- Tendon injuries: rupture of the central slip leads to a boutonnière deformity. Rupture of the lateral slips causes a mallet finger deformity.
- Neurological diagnostics: in mononeuropathies, needle electromyography of the extensor digitorum is performed to assess denervation and reinnervation changes. It is also recommended to examine the extensor digitorum when assessing motor function and trophism.
Do not confuse: extensor digitorum longus of the foot
There is a similarly named muscle in the lower extremity — the extensor digitorum longus (m. extensor digitorum longus). It originates from the lateral condyle of the tibia, the anterior surface of the fibula, the interosseous membrane, and the crural fascia; it is innervated by the deep fibular nerve (n. peroneus profundus) and extends the 2nd–5th digits of the foot. Its tendons divide on the foot: the intermediate parts attach to the bases of the middle phalanges, and the lateral parts to the bases of the distal phalanges.
Class and exam questions
Where exactly do the extensor digitorum tendons insert?
Via the dorsal aponeuroses, the tendons divide into slips: the central slip attaches to the base of the middle phalanx, and the lateral slips attach to the base of the distal phalanx of the 2nd–5th digits.
Do the tendons of this muscle go to the thumb?
No, the extensor digitorum tendons pass to all digits of the hand except the thumb.
What happens when the extensor digitorum tendons rupture?
Rupture of the central slip causes a boutonnière deformity, and rupture of the lateral slips leads to the formation of a mallet finger.
What else to study on this topic
- Radial nerve (n. radialis)
- Extensor retinaculum (retinaculum mm. extensorum)
- Extensor digiti minimi (m. extensor digiti minimi)
- Posterior interosseous artery (a. interossea posterior)
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