Leg muscles: Overview

Muscles

This compartment contains the tibialis anterior, extensor digitorum longus, extensor hallucis longus and fibularis tertius.

• The tibialis anterior muscle originates from the lateral surface of tibial condyle and proximal shaft, and inserts into the medial cuneiform bone and the base of the first metatarsal of the foot. Its action is inversion of the foot at the subtalar joint, dorsiflexion of the foot at the talocrural joint, as well as the dynamic support of the medial arch of the foot.

• The extensor digitorum longus muscle originates from the proximal half of the medial surface of fibula and interosseus membrane, and the anterior surface of the lateral tibial condyle. It inserts onto the dorsal surface of the middle and distal phalanges of the lateral four toes. Its action is to extend the 2nd to 5th toes and dorsiflexion of the foot. It also assists with inversion of the foot at the subtalar joint.
• The extensor hallucis longus muscle arises from the middle portion of the medial surface of the fibula and adjacent portion of the interosseus membrane and inserts onto the base of the distal phalanx of the hallux. Its action is to extend the hallux and to dorsiflex the foot.

• The fibularis tertius muscle arises from the distal aspect of the medial fibular surface and inserts onto the base of the fifth metatarsal. Its action is to dorsiflex the ankle and to evert the foot.

Motor innervation

The motor innervation to the anterior compartment comes from the deep branch of the common fibular nerve (ventral rami of L4-S2).

Blood supply

The blood supply of the anterior compartment is from the anterior tibial artery, a branch of the popliteal artery.

Superficial muscle group

This compartment is divided into a deep and superficial group. The superficial group contains the gastrocnemius and soleus muscles. They are also known as the ‘calf muscle pump’, which assists venous return to the heart as the veins of the leg run through the leg.

• The gastrocnemius muscle is a large and strong plantar flexor of the ankle and flexor of the knee. It has two heads: medial and lateral. The medial head originates from the posterior surface of the medial condyle of the femur, whereas the lateral head originates from the superior part of the posterolateral surface of the lateral femoral condyle. Both heads insert at the posterior surface of the calcaneus, via the calcaneal tendon.

• The soleus muscle is deep to the gastrocnemius and is another plantar flexor. It arises from the soleal line on the dorsal surface of the tibia, medial border of the tibia and the posterior border of the fibular head. Just as the gastrocnemius muscle, it inserts onto the posterior surface of the calcaneus.

Both the gastrocnemius and soleus muscles are innervated by the tibial nerve and vascularized by the posterior tibial artery.

Deep muscle group

The deep group consists of the popliteus, flexor digitorum longus, flexor hallucis longus and the tibialis posterior.

• The popliteus muscle arises from the posterolateral surface of the lateral femoral condyle, and lateral meniscus of the knee joint, before it inserts onto the posterior shaft of the tibia above the soleal line. It causes lateral rotation of the tibia with respect to the femur (unlocks the knee), as the tibia undergoes medial rotation in terminal extension and the anterior cruciate ligament and extrinsic ligaments of the knee (medial collateral, lateral collateral) become taut. 
  Recommended video: Functions of the popliteus muscle

  Functions and anatomy of the popliteus muscle shown with 3D model animation.
• The flexor digitorum longus muscle arises from the medial side of the posterior surface of the tibia, inferior to the soleal line, and inserts onto the plantar surface of the bases of the distal phalanges of the lateral four toes. It causes the flexion of the lateral four toes, in addition to plantarflexion and inversion of the foot. 

• The Flexor hallucis longus muscle arises from the distal two thirds of the posterior surface of the fibula and inserts onto the plantar surface of the base of the distal phalanx of the hallux. It flexes the hallux, and assists in plantar flexion and inversion of the foot. 

• The tibialis posterior muscle arises from posterior surface of the interosseous membrane and adjacent surfaces of the tibia and fibula. It inserts onto the tuberosity of the navicular bone, the cuneiform bones, the bases of the second-fourth metatarsal bones, and variably the cuboid bone. It plantarflexes the ankle and inverts the subtalar joint. It also provides support to the medial longitudinal arch of the foot.

Motor innervation

The motor innervation to the posterior compartment comes from the tibial branch of the sciatic nerve (ventral rami of L4-S3). The muscles of this compartment cause plantar flexion. The tibialis posterior also acts to invert the subtalar joint.

Blood supply

The blood supply to the posterior compartment is from the posterior tibial artery, a branch of the popliteal artery.

Muscles

This compartment consists of the fibularis longus and fibularis brevis muscles.

• The fibularis longus muscle arises from superior lateral shaft of the fibula. Its tendon runs around the lateral aspect of the cuboid bone, runs in a tunnel formed by the long plantar ligament against the inferior surface of the cuboid bone, and eventually inserts onto the first metatarsal and medial cuneiform bones. It supports the lateral longitudinal and transverse arches of the foot in this regard, in addition to plantarflexing and inverting the foot.

• The fibularis brevis muscle arises from lower two thirds on the lateral surface of the fibula and inserts onto the tuberosity at the base of the fifth metatarsal.

Both these muscles evert the subtalar joint, and plantar flex the ankle (talocrural joint). Inversion and eversion of the ankle is important for our adjustment when walking on uneven surfaces.

Motor innervation

The motor innervation to the lateral compartment comes from the superficial fibular nerve (a.k.a superficial peroneal nerve).

Blood supply

The blood supply to the lateral compartment is from the fibular artery, a branch of the posterior tibial artery.