Leg Muscles: an overview
The muscles of the leg are important for movements of the ankle, and for adjustments to changing surfaces we are walking on.
There are three distinct groups i.e. an anterior group, a posterior group, and a lateral group.
The function of these compartments helps us in activities such as walking, kicking, running and dancing. It is important to consider muscle groups as functional units. The individual muscles in each compartment may have additional functions, but the primary function of each compartment is the most important thing to remember.
|Anterior (dorsiflexor) compartment||Tibialis anterior
Extensor digitorum longus
Extensor hallucis longus
|Posterior (plantar flexor) compartment||
Superficial muscle group:
Deep muscle group:
- flexor digitorum longus
- flexor hallucis longus
- tibialis posterior
|Lateral (fibular) compartment||Fibularis longus
|Vascularization||Anterior compartment: anterior tibial artery
Posterior compartment: posterior tibial artery
Lateral compartment: fibular artery
|Innervation||Anterior compartment: deep fibular nerve
Posterior compartment: tibial nerve
Lateral compartment: superficial fibular nerve
|Clinical relations||Acute compartment syndrome, medial tibial stress syndrome, common fibular nerve palsy|
In this article, we will discuss the gross anatomy, functional anatomy and clinical relevance of the leg muscles.
- Anatomy of the leg
- Anterior (Dorsiflexor) compartment
- Posterior (Plantarflexor) compartment
- Lateral (Fibular) compartment
- Clinical Points
- Related diagrams and images
Anatomy of the leg
Anatomically the leg is defined as the region of the lower limb below the knee. It consists of the posterior, anterior and lateral compartment. There is no medial compartment of the leg (unlike the thigh). The leg is innervated by branches of the sciatic nerve, and receives its blood supply from branches of the popliteal artery. Drainage also occurs from the popliteal vein, and superficial drainage from the small and great saphenous veins.
Anterior (Dorsiflexor) compartment
This compartment contains the tibialis anterior, extensor digitorum longus, extensor hallucis longus and fibularis tertius.
Origin: Lateral tibial condyle, proximal half of lateral tibial shaft, Interosseous membrane
Insertion: Medial cuneiform bone, Base of metatarsal bone 1
Function: Talocrural Joint: Foot dorsiflexion; Subtalar joint: Foot inversion; Supports medial longitudinal arch of foot
|Extensor digitorum longus||
Origin: (Proximal half of) Medial surface of fibula, Lateral tibial condyle, Interosseus membrane
Insertion: Distal and middle phalanges of digits 2-5
Function:Metatarsophalangeal and interphalangeal joints 2-5: Toe extension; Talocrural joint: Foot dorsiflexion; Subtalar joint: Foot inversion
|Extensor hallucis longus||
Origin: (Middle third of ) Medial surface of fibula, Interosseous membrane
Insertion: Base of distal phalanx of great toe
Function: Metatarsophalangeal and interphalangeal joint 1: Toe extension; Talocrural joint: Foot dorsiflexion
Origin: (Inferior third of) Anterior surface of fibula
Insertion: Dorsal surface of base of metatarsal bone 5
Function: Talocrural joint: Foot dorsiflexion; Subtalar joint: Foot eversion
|Vascularization||Anterior tibial artery|
|Innervation||Deep fibular nerve (L4-S1)|
- 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.
The motor innervation to the anterior compartment comes from the deep branch of the common fibular nerve (ventral rami of L4-S2).
The blood supply of the anterior compartment is from the anterior tibial artery, a branch of the popliteal artery.
Posterior (Plantarflexor) compartment
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.
- Lateral head: Posterolateral surface of lateral femoral condyle
Function -Talocrural joint: Foot plantar flexion; Knee joint: Leg flexion
Soleal line, Medial border of tibia, Head of fibula, Posterior border of fibulaInsertion - Posterior surface of calcaneus (via calcaneal tendon)
Function - Talocrural joint: Foot plantar flexion
|Vascularization||Posterior tibial artery|
Tibial nerve (S1, S2)
- 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.
Origin - Lateral femoral condyle, Posterior horn of lateral meniscus of knee joint
Insertion -Posterior surface of proximal tibia
Function - Unlocks knee joint; Knee joint stabilization
|Flexor digitorum longus||
Origin -Posterior surface of tibia, (inferior to soleal line)
Insertion -Bases of distal phalanges of digits 2-5
Function -Metatarsophalangeal and interphalangeal joints 2-5: Toe flexion; Talocrural joint: Foot plantar flexion; Subtalar joint: Foot inversion
|Flexor hallucis longus||
Origin - (Distal 2/3 of) Posterior surface of fibula, Interosseous membrane
Insertion -Base of distal phalanx of great toe
Function -Metatarsophalangeal and interphalangeal joint 1: Toe flexion; Talocrural joint: Foot plantar flexion; Subtalar joint: Foot inversion
Origin -Posterior surface of tibia, Posterior surface of fibula, Interosseous membrane
Supports medial longitudinal arch of foot
|Vascularization||Posterior tibial artery|
|Innervation||Tibial nerve (L4- S2)|
- 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.
- 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.
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.
The blood supply to the posterior compartment is from the posterior tibial artery, a branch of the popliteal artery.
Lateral (Fibular) compartment
This compartment consists of the fibularis longus and fibularis brevis muscles.
Origin -Head of fibula, Superior 2/3 of lateral surface of fibula, Intermuscular septa
Insertion - Medial cuneiform bone, Metatarsal bone 1
Function -Talocrural joint: Foot plantar flexion; Subtalar joint: Foot eversion; Supports longitudinal and transverse arches of foot
Origin - Inferior 2/3 of lateral surface of fibula
Insertion - Tuberosity of metatarsal bone 5
Function -Talocrural joint: Foot plantar flexion; Subtalar joint: Foot eversion
Superficial fibular nerve (L5, S1)
- 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.
The motor innervation to the lateral compartment comes from the superficial fibular nerve (a.k.a superficial peroneal nerve).
The blood supply to the lateral compartment is from the fibular artery, a branch of the posterior tibial artery.
Acute compartment syndrome: This is a condition in which the pressure in a closed compartment increases to such extent that the microcirculation of the tissues in that compartment is diminished. The resulting inadequate perfusion and oxygenation leads to soft tissue ischemia, anoxia and cell death, especially in skeletal muscle. The most common site of compartment syndrome is the leg. Risk factors include the following:
- trauma, especially the type and site
- revascularization after acute arterial injury or obstruction
- incorrect limb positioning during prolonged surgical procedures
- excessive exercise
Shin Splints/Medial tibial stress syndrome: If the anterior compartment of the leg is repetitively used, the anterior shin adjacent to the tibia becomes painful. This condition is known as shin splints, and commonly affects athletes who engage in running or jumping. It usually affects the middle or lower third of the medial side of the tibia.
Common Fibular Nerve palsy: The common fibular nerve (L4-S2) winds around the neck of the fibula, and divides into the deep and superficial fibular nerves. The nerve runs close to the skin as it winds around the neck of the fibula, and is hence vulnerable to compression from tight clothing or casts on the leg. Symptoms of this nerve palsy include:
- foot drop
- loss of sensation over the anterior and lateral surface of the leg, and the dorsum of the foot.