The extensor digitorum longus is a muscle located in the anterior (front) compartment of the leg. It originates from the lateral condyle of the tibia, the upper three-fourths of the anterior surface of the fibula, and from the interosseous membrane. It extends down the front of the leg and inserts into the middle and distal phalanges of the four lesser toes (the second to fifth toes). This muscle is situated lateral to the tibialis anterior and medial to the fibularis (peroneus) muscles.
Anatomy
The extensor digitorum longus (EDL) muscle is a significant structure in the anterior compartment of the lower leg, primarily involved in extending the toes and dorsiflexing the foot.
Origin
The EDL originates from several points in the lower leg, including:
- The lateral condyle of the tibia, which is a protrusion on the outer side of the lower end of the tibia.
- The upper three-fourths of the anterior (front) surface of the fibula, which is the thinner of the two bones in the lower leg.
- The anterior surface of the interosseous membrane, which is a fibrous sheet connecting the tibia and fibula.
Course
From its origin points, the muscle travels down the front of the leg. In its descent, it is positioned lateral to the tibialis anterior muscle and medial to the fibularis (peroneus) muscles. The EDL lies within the anterior compartment of the leg, an area bounded by fascia (connective tissue).
Structure
As the EDL approaches the ankle, it divides into four tendons, each corresponding to one of the four lesser toes (from the second to the fifth). These tendons pass under the extensor retinaculum, a band of fascia that holds the tendons close to the ankle, and then travel across the dorsum (top) of the foot.
Insertion
The tendons of the EDL split into two slips before they insert into the toes. Each tendon inserts into the middle and distal phalanges of the respective toes. The division of the tendon allows for the extension of both the proximal and distal interphalangeal joints (the joints in the toes).
Blood Supply
The EDL receives blood from branches of the anterior tibial artery, which supplies the anterior compartment of the leg.
Innervation
The muscle is innervated by the deep peroneal (fibular) nerve, which arises from the sciatic nerve. This nerve supplies both motor impulses to the muscle and sensory information from the area.
Functional Compartment
The EDL is part of the anterior compartment of the leg, which also contains muscles responsible for dorsiflexion of the foot and extension of the toes. This compartment is characterized by muscles that help lift the foot and spread the toes, playing a crucial role in normal walking and balance.
Function
The extensor digitorum longus (EDL) muscle has several important functions related to movement of the foot and toes:
- Toe Extension: The primary function of the EDL is to extend the second to fifth toes at the metatarsophalangeal joints (the joints where the toes join the foot) and the interphalangeal joints (the joints between the segments of the toes). This action is crucial for activities like walking, running, and balancing, particularly during the push-off phase when the body’s weight is transferred over the toes.
- Dorsiflexion of the Foot: In addition to extending the toes, the EDL also assists in dorsiflexing the foot at the ankle joint. Dorsiflexion is the action of lifting the front part of the foot off the ground while keeping the heel in place. This movement is essential for the swing phase of walking, allowing the foot to clear the ground.
- Supporting the Longitudinal Arches of the Foot: By maintaining tension in the tendons across the top of the foot, the EDL helps to support the longitudinal arches of the foot. This contributes to the foot’s structural integrity and its ability to absorb shock during movement.
Clinical significance
The extensor digitorum longus (EDL) muscle is clinically significant for several reasons, particularly in the context of foot and ankle disorders:
Injuries and Strains: The EDL is susceptible to strains and injuries, particularly in athletes or individuals engaging in activities involving repetitive foot movements or sudden changes in direction. Injuries to this muscle can lead to pain, swelling, and a decrease in the ability to extend the toes or dorsiflex the foot, affecting gait and mobility.
Tendonitis and Tendinopathy: Overuse or excessive strain can lead to inflammation or degeneration of the EDL tendons, known as tendonitis or tendinopathy. This condition is characterized by pain on the top of the foot or around the ankle, especially during activity, and can significantly impact daily activities and athletic performance.
Foot and Ankle Disorders: The EDL plays a role in conditions such as drop foot, where there is difficulty lifting the front part of the foot due to muscle weakness or nerve damage. The muscle’s function is also important in the context of flat feet or fallen arches, where altered biomechanics can lead to additional strain on the EDL.
Surgical Considerations: In certain surgical procedures involving the foot or lower leg, care must be taken to preserve the function of the EDL and its tendons. The muscle may also be involved in reconstructive surgeries, such as tendon transfers, to restore function or correct deformities.
Rehabilitation and Physical Therapy: Rehabilitation programs for foot and ankle injuries often include exercises to strengthen the EDL and improve flexibility. Proper function of the EDL is essential for restoring normal gait patterns and ensuring the stability and mobility of the foot and ankle.
