Extensor Hallucis Longus Muscle/The extensor hallucis longus muscle is one of four muscles in the anterior compartment of the lower limb. The three other muscles in the anterior compartment are the tibialis anterior, extensor digitorum longus and fibularis tertius muscles. The anterior compartment receives innervation from the deep fibular nerve, supplied by the anterior tibial artery, and is important in the dorsiflexion of the ankle and extension of the toes. The extensor hallucis longus specifically extends the hallux, dorsiflexes the foot at the ankle and inverts the foot. The extensor hallucis longus muscle is susceptible to several pathologies including nerve injury resulting in foot drop, tendonitis, tendon rupture, and anterior compartment syndrome.
Structure of Extensor Hallucis Longus Muscle
The extensor hallucis longus arises from the anterior surface of the fibula and inserts at the base and dorsal center of the distal phalanx of the hallux. Its location is between the tibialis anterior and extensor digitorum longus muscles on the anterior side of the lower limb coursing inferiorly and medially to its insertion point at the base of the distal phalanx of the great toe. The anterior tibial artery and vein and deep peroneal nerve run between the extensor hallucis longus and the tibialis anterior muscles. The muscle fibers of the extensor hallucis longus course inferiorly and medially, ending in a tendon that passes under the inferior extensor retinaculum, which prevents the muscle from bowstringing or subluxation.[rx]
The principal function of the extensor hallucis longus is to extend the hallux and dorsiflex the foot at the ankle. Due to its origination on the fibula—the lateral bone of the anterior leg—and insertion on the tendon of the distal phalanx of the hallux, muscle contraction lifts the foot and the big toe upward toward the shin (dorsiflexion). This movement is critical to gait because it allows clearance of the foot off the ground during the swing phase. Consequently, damage or loss to the muscles or deep peroneal nerve, the innervation of the anterior compartment, can result in foot drop—loss of dorsiflexion—and a characteristic high-stepping gait.[rx]
In addition to extending the hallux and dorsiflexing the foot at the ankle, the extensor hallucis longus has a role in weakly inverting the foot due to its insertion on the distal phalanx of the hallux—the most medial toe. Consequently, loss of the extensor hallucis longus can also result in weakness in foot inversion, although typically not clinically significant due to the strong action of the tibialis anterior in inverting the foot.
Anatomy of Extensor Hallucis Longus Muscle
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Origin: Lateral tibial condyle and continues distally to split into four tendons after the level of the extensor retinaculum
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Insertion: Dorsum of the middle and distal phalanges
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Action: Extend the second through fifth digits and dorsiflex the ankle
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Blood Supply: anterior tibial artery
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Innervation: deep peroneal nerve
Blood Supply of Extensor Hallucis Longus Muscle
The anterior tibial artery supplies the extensor hallucis longus muscle. The anterior tibial artery arises from the popliteal artery, which originates from the superficial femoral artery, a branch of the common femoral artery off of the external iliac artery. As the superficial femoral artery passes through the adductor hiatus into the popliteal fossa, it becomes the popliteal artery. The popliteal artery then divides toward the distal end of the popliteal fossa to give rise to the anterior and posterior tibial arteries. The anterior tibial artery passes from the posterior popliteal fossa to the anterior leg through the interosseous membrane between the tibia and fibula. It continues down the anterior portion of the leg to supply all of the muscles of the anterior compartment including the extensor hallucis longus before terminating as the dorsalis pedis artery as it passes into the foot.
The lymphatic vessels of the lower limb divide into two major groups—superficial and deep vessels. The superficial lymph vessels of the lower limb further subdivide into two groups: a medial group, which follows the greater saphenous vein, and a lateral group, which follows the small saphenous vein. There are also deep lymph vessels including the anterior tibial, posterior tibial and peroneal vessels that follow the course of the corresponding arteries and veins. The lymph vessels of the lower limb drain into the popliteal, superficial inguinal, deep inguinal, external iliac and lumbar or aortic lymph nodes.
Nerves Supply of Extensor Hallucis Longus Muscle
The tibial nerve, composed of spinal roots L4, L5, S1, S2, and S3, innervates the flexor hallucis longus; it receives the majority of its nerve supply from the S1 and S2, but also receives innervation from L5 as well via the muscular branch of the tibial nerve.[rx]
The deep peroneal nerve innervates the extensor hallucis longus. The deep peroneal nerve is one of the terminal branches of the common peroneal nerve, which originates from the sciatic nerve. The sciatic nerve branches at the apex of the popliteal fossa into the tibial and common peroneal nerves. The tibial nerve continues its course down the leg, posterior to the tibia supplying the deep muscles of the posterior leg. It terminates by dividing into two sensory branches, medial and lateral plantar nerves.[rx] The common peroneal artery follows the medial border of the biceps femoris, running in a lateral and inferior direction continuing over the head of the gastrocnemius.[rx] The common peroneal nerve wraps around the neck of the fibula passing between the attachments of the fibularis longus muscle to supply the lateral compartment of the leg.[rx] It then divides and terminates into the superficial peroneal, which will supply the lateral compartment of the leg and the deep peroneal which will supply the anterior compartment of the leg including the extensor hallucis longus.[rx] The nerve roots of the deep peroneal artery are L4 to S1. Injury to the deep peroneal nerve can result in foot drop and consequently gait difficulty and a characteristic high step gait.
Functions of Extensor Hallucis Longus Muscle
The primary action of the extensor digitorum longus is to extend the lateral four toes at the metatarsophalangeal joint. This means that when acting independently, it is unable to extend the entire length of the toes, extending only at metatarsophalangeal, while at the interphalangeal joints the toes remain flexed. However, contracting together with lubricants which are the main extensors of the interphalangeal joints, this muscle contributes to extension at every joint between the bones of the lateral four toes.
Acting in synergy with tibialis anterior, extensor hallucis longus and fibularis tertius, this muscle participates in dorsiflexion of the foot when their proximal attachments are fixed. When the distal attachments are fixed and the body is in the anatomical position, all four muscles bring the trunk and lower limb to the front. This action moves the body weight-bearing point from the proximal to the distal part of the foot.
All of these actions are important for the gait cycle; the dorsiflexion angulates and lifts the foot above the walking surface, while the toe extension keeps the toes extended until the heel hits the ground.
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