Extensor digitorum longus

The extensor digitorum longus (EDL) is a penniform muscle situated in the anterior compartment of the leg, occupying the lateral part of its anterior surface.

Origin

• Lateral condyle of the tibia

• Proximal three-fourths of the anterior surface of the fibula

• Proximal three-fourths of the adjacent interosseous membrane

• Deep surface of the fascia cruris (deep fascia of the leg)

• Intermuscular septa between:

  • Tibialis anterior (medially)

  • Fibularis (peroneal) muscles (laterally)

Course and insertion

• The muscle forms a common tendon that passes beneath both the superior (transverse) and inferior (cruciate) extensor retinacula, accompanied laterally by the fibularis tertius tendon.

• On the dorsum of the foot, the tendon divides into four slips (for digits 2 to 5).

• Each tendinous slip contributes to the dorsal digital expansion (extensor hood) of its corresponding toe, which splits into a central and two collateral slips.

  • Central slip inserts onto the base of the middle phalanx

  • The two collateral slips unite distally to insert onto the base of the distal phalanx

The EDL tendons to the 2nd, 3rd, and 4th toes are each joined on their lateral side by a slip from the extensor digitorum brevis. While, each extensor hood (dorsal digital expansion) also receives attachments from the tendons of the lumbrical and interosseous muscles. All of these contribute to the formation of the extensor apparatus on the dorsum of the foot.

Nerve Supply

• Deep fibular (peroneal) nerve (L5–S1 nerve roots)

Blood Supply

• Anterior tibial artery and its muscular branches

Actions

• Extension of the lateral four toes at metatarsophalangeal and interphalangeal joints

• Dorsiflexion of the foot at the ankle joint

• Weak eversion of the foot