The muscles in the anterior compartment of the leg are a group of four muscles that act to dorsiflex and invert the foot.
These muscles are collectively innervated by the deep fibular nerve (L4-S2). The arterial supply is through the anterior tibial artery.
In this article, we shall look at the anatomy of the anterior leg muscles – their attachments, actions and clinical correlations.
Tibialis Anterior
The tibialis anterior muscle is located alongside the lateral surface of the tibia. It is the strongest dorsiflexor of the foot.
- Attachments: Originates from the lateral surface of the tibia and attaches to the medial cuneiform and the base of metatarsal I.
- Actions: Dorsiflexion and inversion of the foot.
- Innervation: Deep fibular nerve.
Extensor Digitorum Longus
The extensor digitorum longus lies laterally and deep to the tibialis anterior. Its four tendons can be palpated on the dorsal surface of the foot.
- Attachments:
- Originates from the lateral condyle of the tibia and the medial surface of the fibula.
- The fibres converge into a tendon, which travels onto the dorsal surface of the foot.
- The tendon splits into four and each tendon inserts onto a toe.
- Actions: Extension of the lateral four toes, and dorsiflexion of the foot.
- Innervation: Deep fibular nerve.
Extensor Hallucis Longus
The extensor hallucis longus is positioned deep to tibialis anterior and extensor digitorum longus. Its tendon emerges from between the two muscles to insert onto the big toe.
- Attachments: Originates from the medial surface of the fibular shaft. The tendon crosses anterior to the ankle joint and attaches to the base of the distal phalanx of the great toe.
- Action: Extension of the great toe and dorsiflexion of the foot.
- Innervation: Deep fibular nerve.
Fibularis Tertius
The fibularis tertius muscle is thought to arise from the most distal part of the extensor digitorum longus. It is not present in all individuals.
- Attachments: Originates with the extensor digitorum longus from the medial surface of the fibula. Its tendon descends onto the dorsal surface of the foot and attaches to the fifth metatarsal.
- Actions: Eversion and dorsiflexion of the foot.
- Innervation: Deep fibular nerve.
Clinical Relevance: Footdrop
Footdrop is a clinical sign that refers to an inability to dorsiflex the foot at the ankle joint – resulting in the foot “dropping” under the influence of gravity.
It indicates paralysis or weakness of the muscles in the anterior compartment of the leg, and typically occurs as a consequence of damage to the common fibular nerve (from which the deep fibular nerve arises)
The inability to dorsiflex the foot can interfere with walking – as the affected foot drags along the ground. To circumvent this, the patient can flick the foot outwards while walking – known as an ‘eversion flick‘.
Fig 3 – Left footdrop. This can occur following common fibular or deep fibular nerve palsy.
