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The leg, ankle, and foot

Last updated: May 7, 2021

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The lower extremity consists of the hip, thigh, knee, and popliteal fossa, as well as the leg (crus), ankle, and foot. The leg (crus) extends from the knee to the ankle and contains the tibia and fibula. The tarsal bones include the calcaneus, talus, cuboid, navicular bones, and the medial, middle, and lateral cuneiform bones. The ankle joint (talocrural joint) is formed by the articulation of the talus with the tibia and fibula. The talus also articulates with the calcaneus inferiorly forming the subtalar joint and with the navicular anteriorly forming the talonavicular joint. The foot consists of 5 metatarsal bones, the phalanges, metatarsophalangeal (MTP), and interphalangeal (IP) joints. The foot has one transverse and two longitudinal arches that help distribute body weight. The leg (crus) has an anterior, posterior, and lateral compartment. The anterior compartment (extensor compartment), which is innervated by the peroneal nerve, contains muscles involved in ankle dorsiflexion and foot eversion. The posterior compartment (flexor compartment), which is innervated by the tibial nerve, contains muscles involved in ankle plantarflexion, foot inversion, and knee flexion. The lateral compartment (peroneal or fibular compartment), which is innervated by the superficial peroneal nerve, contains muscles involved in foot eversion and ankle plantarflexion. The intrinsic muscles of the foot are responsible for fine movements of the foot, which include flexion and extension at the MTP and IP joints as well as abduction and adduction of toes. The leg, ankle, and foot are perfused by the anterior and posterior tibial arteries, fibular artery, and their branches. These are drained by superficial (great saphenous vein, small saphenous vein) and deep veins (anterior tibial vein, posterior tibial vein, fibular vein).

Bones of the leg

Tibia

Medial bone of the leg

  • Important landmarks
  • Function
    • Weight-bearing bone
    • Articulates superiorly with the femoral condyles to form the knee joint
    • Articulates with the talus to form a portion of the ankle joint
    • Articulates with the fibula proximally and distally
    • Site of attachment of lower extremity muscles

Fibula

Lateral bone of the leg; non-weight bearing

Joints of the leg

Tibiofibular joints

Interosseous membrane of the leg

Fibrous connective tissue that extends between the medial border of the fibula and the lateral border of the tibia

Bones of the ankle (tarsal bones)

Seven tarsal bones make up the ankle joint

Characteristics of tarsal bones
Tarsal bones Anatomy Function
Talus
  • Transmits bodyweight from the tibia to the calcaneus
  • Forms part of the medial longitudinal arch of the foot
Calcaneus
  • Forms the heel of the foot and transmits bodyweight from the talus to the ground
  • Site of attachment for the Achilles tendon
Navicular
Cuneiform
  • Forms part of the proximal transverse and medial longitudinal arches of the foot
Cuboid
  • Forms part of the lateral longitudinal arch of the foot

Ankle joint

Bones and joints of the foot

Arches of the foot

There are 3 arches in the foot: two longitudinal and one transverse.

  • Function
    • Distribute the body weight
    • Act like springs and shock absorbers while running and walking
  • Clinical significance
Characteristics of foot arches
Arch Formed by Supporting structures
Medial longitudinal arch
Lateral longitudinal arch
Transverse arch

Fascia and retinacula of the foot

Overview of foot retinacula

Retinacula

Characteristics

Anterior retinacula (extensor retinacula)

Medial retinaculum (flexor retinaculum of the foot; flexor retinaculum)

Lateral retinacula
Tarsal tunnel

Muscles of the leg

Anterior compartment of the leg (extensor compartment)

Characteristics of the anterior leg compartment
Muscle Origin Insertion Innervation Function

Testing

Tibialis anterior
  • Lateral tibial condyle, proximal 2/3rd of the lateral surface of the tibial shaft, and the adjacent interosseous membrane
Extensor hallucis longus (EHL)
  • Middle 1/3rd of the medial surface of the fibula and the adjacent interosseous membrane
  • Hallux extension against resistance
Extensor digitorum longus (EDL)
  • Divides into 4 tendons that insert into the bases of the middle and distal phalanges of the 2nd–5th toes
  • Extension of the lateral 4 toes against resistance
Peroneus tertius
  • Cannot be tested in isolation

Posterior compartment of the leg (flexor compartment)

Characteristics of the posterior leg compartment
Group Muscle Origin Insertion Innervation Function Testing
Superficial flexor group Triceps surae Gastrocnemius
Soleus
Plantaris
  • Cannot be tested in isolation
Deep flexor group Tibialis posterior
  • Posterior surfaces of the upper parts of the fibula and tibia and the adjacent interosseous membrane
  • Inversion of the plantarflexed foot against resistance
Flexor digitorum longus
(FDL)
Flexor hallucis longus
(FHL)
Popliteus
  • Cannot be tested in isolation

Lateral compartment of the leg (peroneal or fibular compartment)

Characteristics of the lateral leg compartment
Muscle Origin Insertion Innervation Function Testing

Peroneus longus (fibularis longus)

  • Tested together by everting the foot against resistance

Peroneus brevis (fibularis brevis)

Muscles of the foot

Characteristics of muscles of the foot
Layer of the foot Muscle Origin Insertion Innervation Function
Muscles of the dorsum of the foot Extensor digitorum brevis
Extensor hallucis brevis
Muscles of the sole of the foot (superficial to deep) First layer Abductor hallucis
Flexor digitorum brevis
Abductor digiti minimi

Second layer

Quadratus plantae
Lumbricals
  • Extensor expansion of the lateral 4 toes
Third layer Flexor hallucis brevis
Adductor hallucis
Flexor digiti minimi brevis
Fourth layer

Plantar interossei (3)

Dorsal interossei (4)

Arteries of the leg

Characteristics of arteries of the leg [1]
Characteristic

Anterior tibial artery

Posterior tibial artery

Fibular artery (peroneal artery)

Origin
Course
Branches
  • Muscular branches
Supply
  • Lateral and deep flexor compartments of the leg
Important relations
  • N/A

Arteries of the foot [1]

Dorsum of the foot

Dorsalis pedis artery

Sole of the foot

Veins of the leg [1]

Superficial veins

The superficial veins lie within the subcutaneous tissue. There are two main superficial veins of the leg:

Great saphenous vein (GSV)

Small saphenous vein (SSV)

Deep veins of the leg

Veins of the foot [1]

Motor and sensory innervation of the lower extremity

Characteristics of motor and sensory innervation of the leg
Nerves Origin Motor supply Sensory supply Clinical significance
Mixed motor and sensory nerves Tibial nerve
Common peroneal nerve
(common fibular nerve)
  • None
Deep peroneal nerve
  • 1st web space of the foot (i.e., the sandal gap)
Superficial peroneal nerve
  • Distal part of the anterior aspect of the leg and the dorsum of the foot (except the 1st web space)
Pure sensory nerves Saphenous nerve
  • None
Sural nerve
  • Formed by the union of sural branches from the tibial and common peroneal nerves
  • None
  • Skin over the posterolateral aspect of the distal 1/3rd of the leg and the lateral border of the foot

TIPPED = tibial nerve versus peroneal nerve
TIP = Tibial nerve Inverts and Plantarflexes the foot → cannot walk on TIPtoes when injured
PED = Peroneal nerve Everts and Dorsiflexes the foot → foot drop when injured

Dermatomal distribution of the leg and foot

  1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences ; 2016