The anterior muscles of the lower leg
When studying the muscles of the leg, we can examine them by four primary groupings, which are the anterior, fibular/lateral, superficial posterior and deep posterior compartments. These are defined by intermuscular septa and surrounded by the deep fascia of the leg.
The muscles of the anterior leg are a group of muscles which lie within the anterior compartment of the leg, located in the anterolateral region of the leg. They are also known as the dorsiflexors of the leg.
Anatomy and supplyThe muscles of the anterior comparment of the leg are all palpeable along the anterolateral surface of the leg. Their tendons are also are particularly prominent on the dorsum of the foot. All anterior muscles are innervated by the deep fibular nerve (L4-S1) which is a branch of the common fibular nerve.
Tibialis anterior muscle
The tibialis anterior is the larger and most superficial of the anterior muscles and runs medioinferiorly from the lateral tibia, interosseous membrane and crural fascia. At the level of the lower tibia it becomes tendinous and is led by both extensor retinacula of the foot before inserting at the plantar side of the medial cuneiform and base of the first metatarsal bone.
The tibialis anterior muscle serves as the leading muscle for the neurovascular pathway running towards the ankle (deep fibular nerve, anterior tibial artery and vein).
Extensor digitorum longus muscle
The EDL originates at the lateral tibial condyle, anterior/ventral side of the fibula and interosseous membrane and merges into a tendon above the superior extensor retinaculum. Below the inferior extensor retinaculum it now divides into four tendons inserting at the dorsal aponeurosis and the distal phalanges of the second through fifth toes.
About 90% of the people have an additional fifth tendon running towards the lateral foot edge and inserting into the base of the fifth metatarsal bone (fibularis tertius muscle).
Extensor hallucis longus muscle
The EHL has its origin at the medial side of the fibula and interosseous membrane. It merges into a tendon above the superior extensor retinaculum as well. Its insertion is the distal phalanx of the big toe.
Extensor retinacula of the foot
The canal-like extensor retinacula are thickenings of the crural fascia anchoring and leading the tendons of the anterior muscles. The superior extensor retinaculum (transverse crural ligament) runs between fibula and tibia proximal to the malleoli. The Y-shaped inferior extensor retinaculum (cruciate crural ligament) lies more distally and stretches between calcaneus, medial malleolus and plantar aponeurosis.
The common task of the anterior muscles of the lower leg is dorsiflexion of the foot, which occurs at ankle joint.
- In addition, due to the course of it's tendon, the tibialis anterior also contributes to the movement of the subtalar joint, by means of inversion or supination of the foot. It also works to support the medial longitudinal arch of the foot.
- The extensor digitorum longus is involved in extension of the second to fifth digits, occuring at both the metatarsophalangeal and interphalangeal joints
- Similary, the extensor hallucis longus extends the great/big toe at both the metatarsophalangeal and interphalangeal joints of the same digit.
The anterior muscles are indispensable for a natural gait. When paralyzed, a dorsal extension of the foot and toe-lifting become practically impossible. In order to prevent the toes from dragging on the floor the affected patients lift up their legs unusually high and place their toes first (steppage gait).
Because of its relatively rigid and inflexible structure, the anterior compartment of the lower leg is extraordinarily vulnerable to critical increases of pressure, e.g. due to bleeding or edemas (compartment syndrome).
Often they occur after a heavy strain (e.g. a long hike) or trauma. Hereby the muscles swell compromising the nerves and vessels within the compartment which may quickly lead to ischemic muscle necrosis. In this emergency case the muscle compartment has to be immediately decompressed by a surgical incision of the fascias (fasciotomy).