The Extensor hallucis longus (EHL) muscle is a thin skeletal muscle located in the lower leg, part of the anterior compartment of leg muscles. It plays a significant role in foot and toe movement. Its primary function is to extend the big toe and assist in the dorsiflexion of the foot. The EHL originates from the middle portion of the fibula and the interosseous membrane and extends down the front of the leg.
Location
The Extensor hallucis longus muscle is situated in the anterior compartment of the lower leg. It lies between the Extensor digitorum longus muscle, which is located laterally, and the Tibialis anterior muscle, which is medially positioned. The EHL extends from its origin points on the fibula and interosseous membrane, running down the length of the leg, and inserts into the distal phalanx (the tip) of the big toe.
Anatomy
- Origin: The EHL originates from the middle portion of the anterior surface of the fibula, which is one of the two bones in the lower leg. It also arises from the adjoining part of the interosseous membrane, which is a fibrous sheet separating the tibia (shin bone) and fibula.
- Course: The muscle travels downward along the leg, transitioning from a muscular to a tendinous form as it descends. It is positioned between the Extensor Digitorum Longus (EDL) on the lateral side and the Tibialis Anterior on the medial side. This linear arrangement in the anterior compartment helps facilitate its movement and function.
- Insertion: The tendon of the EHL muscle passes over the ankle joint and continues along the top of the foot. It inserts into the base of the distal phalanx of the big toe (hallux). As it crosses the ankle and instep, the tendon is held in place by a series of fibrous loops known as retinacula which prevent bowstringing during toe extension.
- Innervation: The EHL is innervated by the deep peroneal nerve (also known as the deep fibular nerve), which arises from the lumbar plexus. This nerve supplies the muscle with the necessary motor commands required for its function.
- Blood Supply: The muscle receives its blood supply from the anterior tibial artery, which accompanies the deep peroneal nerve. The artery provides the necessary nutrients and oxygen for the muscle’s metabolic needs.
- Functional Anatomy: Within its compartment, the EHL lies deep to the Extensor Digitorum Longus and is often enveloped by its fascia. The unique positioning of the EHL allows it to act effectively in extending the big toe and assisting in the dorsiflexion of the foot, contributing to the fine control of foot movements, particularly in activities like walking, running, and climbing.
Function
The Extensor Hallucis Longus (EHL) muscle has several key functions that are crucial for the movement and stability of the foot and toe.
Here are some of it’s main functions:
Extension of the Big Toe
The primary function of the EHL is to extend the big toe (hallux). This action is vital for the ‘push-off’ phase of the gait cycle, which is the last part of the step that propels the body forward. During this phase, the extension of the big toe provides leverage and helps in the efficient transfer of energy necessary for the next step. This is particularly important during activities such as running, walking, or climbing, where precise movement and force exertion of the big toe are required.
Dorsiflexion of the Foot
In addition to extending the big toe, the EHL assists in dorsiflexing the foot at the ankle joint. Dorsiflexion refers to the action of lifting the foot upwards towards the shin. This function is essential for clearing the foot off the ground during the swing phase of walking or running, preventing the toes from dragging and ensuring a smooth step. The EHL works in coordination with other muscles of the anterior compartment, such as the Tibialis Anterior, to perform this action.
Contribution to Foot Supination
While the EHL is primarily involved in toe extension and foot dorsiflexion, it also contributes to supination of the foot. Supination involves the inward rolling of the foot, which helps to stabilize the foot during the stance phase of walking or running. Although not the primary muscle for this action, the EHL aids in this movement through its position and the tension it creates across the foot.
Stabilizing the Metatarsophalangeal (MTP) Joint
The EHL plays a role in stabilizing the metatarsophalangeal joint of the big toe by extending the toe. When the EHL contracts, it not only lifts the toe but also helps to maintain the alignment and stability of this joint. This stabilization is crucial for maintaining balance and effective foot mechanics during various activities.
Facilitating Postural Balance
By controlling the actions of the big toe and aiding in foot dorsiflexion, the EHL contributes to overall postural balance and stability. Proper functioning of the EHL helps maintain an even and effective distribution of body weight over the feet, which is essential for standing, walking, and other upright activities.
Clinical Significance
- Foot and Ankle Pathologies: Dysfunction or injuries of the EHL can lead to various foot and ankle pathologies, including hallux rigidus (stiffness or arthritis of the big toe), drop foot (difficulty in lifting the front part of the foot), and other gait abnormalities. Understanding the EHL’s role helps clinicians in diagnosing and treating these conditions effectively.
- Surgical Considerations: The EHL is an important landmark in foot and ankle surgeries. Knowledge of its anatomy and function is crucial during surgical procedures to avoid inadvertent damage, which can result in postoperative complications such as loss of big toe extension or foot drop.
- Rehabilitation and Physical Therapy: In cases of injury or surgery affecting the lower limb, targeted rehabilitation exercises focusing on the EHL can aid in recovery and restoration of normal foot functions. Physical therapists often design specific exercises to strengthen the EHL and improve foot dorsiflexion and toe extension.
- Biomechanical Assessments: The EHL is an important muscle for biomechanical evaluations, especially for athletes and individuals with gait abnormalities. Assessing its strength and functionality can help identify issues related to balance, coordination, and walking or running efficiency.
- Neurological Evaluations: Since the EHL is innervated by the deep peroneal nerve, weakness or paralysis of this muscle can indicate nerve damage or neurological disorders. Clinicians use the function of the EHL as a marker to diagnose and assess the severity of neurological conditions.
