The leg, ankle, and foot

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
  • Tibial condyles: horizontal upper surface of the tibia with medial and lateral depressions that articulate with the femoral condyles
  • Tibial tuberosity
    • A rough triangular area on the anterior aspect of the tibia, where the condyles merge
    • Site of attachment of the patellar tendon
    • Clinical significance: Osgood Schlatter disease
  • Shaft: has 3 surfaces (anterior, lateral, and posterior)
  • Medial malleolus: inferomedial projection of the distal end of the tibia
• 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

• Important landmarks
  • Head
    • Site of attachment of the lateral collateral ligament of the knee and the biceps femoris muscle
    • A component of the proximal tibiofibular joint
  • Neck
    • A constriction between the head and the shaft of the fibula
    • Common peroneal nerve wraps around on the neck of the fibula
  • Shaft: has 3 surfaces (anterior, lateral, and posterior)
  • Lateral malleolus: inferolateral projection of the distal end of the fibula
• Function
  • Articulates with the talus to form a portion of the ankle joint
  • Site of attachment of lower extremity muscles

Joints of the leg

Tibiofibular joints

• Proximal tibiofibular joint: synovial joint between the head of the fibula and the lateral tibial condyle
• Distal tibiofibular joint: fibrous joint (syndesmosis) between the distal ends of the tibia and fibula

Interosseous membrane of the leg

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

• Important landmark: A notch at the superior end permits the anterior tibial vessels to enter the anterior compartment of the leg.
• Function
  • Stabilizes the tibiofibular joints
  • Site of attachment of numerous leg muscles

Bones of the ankle (tarsal bones)

Seven tarsal bones make up the ankle joint

Ankle joint

• Type: synovial hinge joint
• Components: the talus with the tibia and fibula
• Ligaments
  • Medial ligament (deltoid ligament)
    • Extends from the medial malleolus to the medial tarsal bones
    • Composed by the anterior tibiotalar ligament, tibiocalcaneal ligament, posterior tibiotalar ligament, and tibionavicular ligament
    • Prevents excessive ankle eversion
  • Lateral ligament
    • Extends from the lateral malleolus to the talus and calcaneus
    • Composed by the anterior talofibular ligament, posterior talofibular ligament, and calcaneofibular ligament
    • Prevents excessive ankle inversion
    • Commonly injured in sports injuries (inversion injury)
• Movements (uniaxial)
  • Flexion (plantarflexion)
  • Extension (dorsiflexion)

Bones and joints of the foot

• Metatarsal bones
  • There are five metatarsal bones that are located distal to the tarsal bones.
  • Each has a base that articulates with the tarsal bones (tarsometatarsal joints), a head that articulates with the proximal phalanges (metatarsophalangeal joints), and a shaft in between.
• Phalanges
  • Small long bones of the toes
  • Each toe has three phalanges, except the hallux, which only has two.
• Metatarsophalangeal joints (MTP joints)
  • Medial 3 tarsophalangeal joints: between the medial 3 proximal phalanges and the 3 cuneiform bones
  • Lateral 2 tarsophalangeal joints: between the lateral 2 proximal phalanges and the cuboid
• Interphalangeal joints
  • The lateral 4 toes have proximal and distal interphalangeal joints.
  • The hallux only has one interphalangeal joint.

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
  • Pes cavus
  • Pes planus

Fascia and retinacula of the foot

• Plantar fascia (plantar aponeurosis)
  • A thick band of connective tissue that extends from the calcaneal tuberosity to the plantar aspect of the proximal phalanges of the toes
  • Supports the bony arches of the foot
  • Plays an important role in the dynamics of the foot
  • Clinical significance: plantar fasciitis
• There are three main retinacula of the foot.

Muscles of the leg

• The muscles of the leg exert their action on the ankle, foot, and toes
• The deep fascia of the leg divides these muscles into three compartments
  • Anterior compartment
    • Common nerve supply: deep peroneal nerve
    • Common function: dorsiflexion of the ankle (extension)
  • Posterior compartment (superficial and deep group)
    • Common nerve supply: tibial nerve
    • Common function: plantarflexion of the ankle (flexion)
  • Lateral compartment
    • Common nerve supply: superficial peroneal nerve
    • Common function: eversion of the foot

Anterior compartment of the leg (extensor compartment)

Posterior compartment of the leg (flexor compartment)

Lateral compartment of the leg (peroneal or fibular compartment)

Muscles of the foot

• The muscles of the foot are divided into two groups based on where the muscle belly is located.
• Extrinsic muscles of the foot: muscle bellies are located in the leg (see “Muscles of the leg” above)
• Intrinsic muscles of the foot: muscle bellies are located within the foot
  • Dorsal intrinsic muscles: innervated by the deep fibular nerve
  • Plantar intrinsic muscles: innervated by branches of the tibial nerve (medial and lateral plantar nerves)
  • Tested by asking the examinee to perform the action of the muscle against resistance

Arteries of the leg

Arteries of the foot ^[1]

Dorsum of the foot

Dorsalis pedis artery

• Origin: continuation of the anterior tibial artery beyond the ankle joint
• Course
  • Travels in the 1^st intermetatarsal space, lateral to the tendon of the EHL
  • Passes through the 1^st dorsal interosseus muscle and enters the sole
  • Ends by anastomosing with the lateral plantar artery and giving off the 1^st dorsal metatarsal artery
  • The dorsalis pedis artery is often aberrant or absent.
• Branches
  • Tarsal arteries
  • Arcuate artery: gives rise to the lateral 3 dorsal metatarsal arteries, from which the digital arteries arise

Sole of the foot

• Branches of the posterior tibial artery
  • Medial plantar branch: supplies the medial side of the sole
  • Lateral plantar branch: supplies the lateral side of the sole and anastomosis with the dorsalis pedis
• Plantar arterial arch
  • Formed by the anastomosis between the dorsalis pedis and lateral plantar arteries
  • Located on the plantar aspect of the bases of the lateral 4 metatarsal bones
  • Branches: 4 plantar metatarsal arteries

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)

• Origin: continuation of the medial marginal vein of the foot (medial end of the dorsal venous arch)
• Course
  • At the ankle: passes in front of the medial malleolus
  • In the leg: ascends along the medial aspect of the shin
  • At the knee: behind the medial condyles of the femur and tibia
  • Thigh: medial aspect of the thigh
• Termination: saphenofemoral junction (SFJ)
  • The site at which the GSV passes through the saphenous opening in the deep fascia of the thigh to meet the femoral vein.
  • The position is fairly constant at 4 cm inferolateral to the pubic tubercle.
• Main tributaries
  • Short saphenous vein
  • Superficial external pudendal vein
  • Superficial epigastric veins
  • Superficial circumflex iliac vein
  • Lateral femoral cutaneous vein
• Drains: the anteromedial aspect of the sole, leg, and thigh
• Important relations: saphenous nerve accompanies the GSV below the knee
• Clinical significance
  • Varicose veins
  • Thrombophlebitis
  • Can be harvested for vein grafts for peripheral or coronary arterial surgery

Small saphenous vein (SSV)

• Origin: continuation of the lateral marginal vein of the foot (lateral end of the dorsal venous arch)
• Course:
  • At the ankle: passes behind the lateral malleolus
  • In the leg: ascends in the midline of the calf towards the popliteal fossa
• Termination: saphenopopliteal junction (SPJ)
  • The site at which the SSV drains into the popliteal vein
  • Unlike the SFJ, the location of the SPJ is variable, lying within, proximal, or distal to the popliteal fossa.
• Important relations: Sural nerve accompanies the SSV through most of its course.

Deep veins of the leg

• The deep veins lie deep to the deep fascia.
• They accompany the arteries of the leg:
  • Anterior tibial veins
  • Posterior tibial veins
  • Fibular veins (peroneal veins)
• These deep veins join at the inferior border of the popliteus muscle to form the popliteal vein.
• Clinical significance: deep vein thrombosis

Veins of the foot ^[1]

• Digital veins (on the sides of the toes) → metatarsal veins (in the intermetatarsal spaces) → deep plantar venous arch (plantar aspect of the lateral 4 metatarsal bones) → medial and lateral plantar veins → GSV and SSV

Motor and sensory innervation of the lower extremity

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

• Anterior leg
  • Medial third: L4
  • Middle third: L5
  • Lateral third: S1
• Posterior leg
  • Medial third: L4
  • Middle third: S2
  • Lateral third: S1
• Dorsal and plantar aspects of the foot
  • Medial half: L5
  • Lateral half: S1

• Tibial fracture
• Medial tibial stress syndrome
• Fibular fracture
• Ankle sprain
• Ankle fracture
• Peripheral arterial disease
• Deep vein thrombosis
• Varicose veins
• Peripheral nerve injuries
• Plantar fasciitis
• Thromboangiitis obliterans