The leg, ankle, and foot

Summary

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 and joints

Bones of the leg

Tibia

Medial bone of the leg

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

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

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

Fascia and retinacula of the foot

Retinacula

Characteristics

Anterior retinacula

(Extensor retinacula)

Medial retinaculum

(Flexor retinaculum)

Lateral retinacula

Muscles

Muscles of the leg

Anterior compartment of the leg (extensor compartment)

Muscle Origin Insertion Innervation Function

Testing

Tibialis anterior
  • Lateral tibial condyle, proximal 2/3rd of lateral surface of 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
  • Extend the hallux 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
  • Extend the lateral 4 toes against resistance
Peroneus tertius

Posterior compartment of the leg (flexor compartment)

Group Muscle Origin Insertion Innervation Function Testing
Superficial flexor group Triceps surae Gastrocnemius
Soleus
Plantaris
Deep flexor group Tibialis posterior
  • Posterior surfaces of the upper parts of the fibula and tibia and the adjacent interosseous membrane
  • Invert a plantarflexed foot against resistance
Flexor digitorum longus
(FDL)
  • Flex the lateral 4 toes against resistance
Flexor hallucis longus
(FHL)
  • Distal 2/3rd of the posterior aspect and the adjacent interosseous membrane
  • Flex the hallux against resistance
Popliteus

Lateral compartment of the leg (peroneal or fibular 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

Layer of the foot Muscle Origin Insertion Innervation Function
Muscles of the dorsum of the foot Extensor digitorum brevis
Extensor hallucis brevis
  • Hallux: extension at the MTP and IP joints
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)

Vasculature

Arteries of the leg

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

Arteries of the foot

Dorsum of the foot

Dorsalis pedis artery

Sole of the foot

Veins of the leg

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

References:[1][2][3][4]

Innervation

Motor and sensory innervation

Nerve 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

Clinical significance