Lower leg; calf

Tibia

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  Proximal tibiofibular joint

  
  
  
  
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    Head of fibula and lateral condyle tibia joined by synovial-lined fibrous capsule

    
    
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    May communicate with knee joint (10%)

    
    
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    Posterolaterally located

    
    
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    Synovial joint, so can be affected by any synovial inflammatory process

  
  
  
  
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  Anterolateral tibia: Origin of anterior muscles of leg

  
  
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  Anterior border (shin): Sharp ridge running from tibial tuberosity proximally to anterior margin of medial malleolus

  
  
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  Medial tibial surface

  
  
  
  
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    Wide and flat

    
    
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    Proximally, covered by pes anserinus

    
    
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    Remainder is subcutaneous

  
  
  
  
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  Medial border of tibia: Saphenous nerve and great saphenous vein run along it

  
  
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  Posterior tibia: Origin of deep posterior muscles of leg

  
  
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  Lateral border of tibia: Ridge for attachment of interosseous membrane

  
  
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  Medial malleolus: 2 colliculi, anterior longer than posterior

  
  
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  Distal tibiofibular joint

  
  
  
  
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    Fibula articulates with tibia at fibular notch; joined by interosseous ligament

    
    
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    Strengthened by anterior and posterior tibiofibular ligaments

    
    
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    Posterolaterally located

  
  

Fibula

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  Anterior fibula

  
  
  
  
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    Origin of lateral muscles of leg

  
  
  
  
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  Medial fibula

  
  
  
  
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    Origin of deep posterior muscles of leg

  
  
  
  
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  Posterolateral fibula

  
  
  
  
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    Origin of posterior muscles of leg

  
  
  
  
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  Lateral malleolus: 1 cm longer than medial malleolus

Stretches across interval between tibia and fibula

Greatly extends surface for origin of muscles

Strong, oblique fibers run downward and laterally from tibia to fibula

In upper part, below lateral condyle of tibia, there is opening for passage of anterior tibial vessels

Distally, opening allows passage of perforating branch of peroneal artery

Tibialis posterior and flexor hallucis longus take partial origin from back of membrane

Tibialis anterior, long extensors of toes, and peroneus tertius take partial origin from front of membrane

Compartments separated by deep fascia, which give partial origin to several muscles

Posterior compartment: Superficial muscles

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  Gastrocnemius

  
  
  
  
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    Origin: Medial from posterior femoral metaphysis; lateral from posterior edge of lateral epicondyle

    
    
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    Heads separated from posterior capsule by bursa

    
    
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    2 heads unite to form main bulk of muscle

    
    
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    Join in thin aponeurotic tendon near midleg

    
    
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    Joins soleus aponeurosis to form Achilles tendon; concave in cross section; musculotendinous junction is 5 cm above calcaneal insertion

    
    
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    Nerve supply: Tibial nerve

    
    
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    Action: Plantar flexor of ankle and flexor of knee

  
  
  
  
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  Plantaris

  
  
  
  
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    Origin: Superior and medial to lateral head of gastrocnemius origin, as well as from oblique popliteal ligament

    
    
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    Continues deep to lateral head of gastrocnemius

    
    
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    Myotendinous junction at level of origin of soleus (muscle is 5-10 cm long)

    
    
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    Tendon then lies between medial head of gastrocnemius and soleus

    
    
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    Follows medial side of Achilles to insert either anteromedially on Achilles or on calcaneus

    
    
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    Plantaris absent in 7-10% of general population

    
    
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    Nerve supply: Tibial nerve

    
    
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    Action: Acts with gastrocnemius

  
  
  
  
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  Soleus

  
  
  
  
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    Origin: Extensive, from back of fibular head and upper 1/3 of posterior surface of shaft of fibula, from soleal line and middle 1/3 of medial border of tibia, and from tendinous arch joining these across popliteal vessels

    
    
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    Flat, thick, powerful muscle that ends in strong tendon

    
    
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    Joins with tendon of gastrocnemius to form Achilles tendon

    
    
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    Nerve supply: Tibial nerve

    
    
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    Action: Stabilizes ankle in standing, plantarflexes ankle

    
    
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    Accessory soleus: Rare variant, arises from anterior surface of soleus or from fibula and soleal line of tibia; inserts into Achilles or onto calcaneus anteromedially to Achilles; presents as mass

  
  

Posterior compartment: Deep muscles

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  Popliteus

  
  
  
  
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    Origin: Tendon from popliteal groove of lateral femoral condyle

    
    
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    Passes through popliteal hiatus posteriorly and medially, pierces posterior capsule of knee

    
    
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    Muscle fibers directed medially and downward to insert on posterior surface of tibia above soleal line

    
    
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    Nerve supply: Tibial nerve

    
    
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    Action: Flexes knee and medially rotates tibia with respect to femur at onset of flexion (unlocking extension “screwing home” mechanism)

  
  
  
  
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  Tibialis posterior

  
  
  
  
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    Origin: Interosseous membrane and adjoining parts of posterior surfaces of tibia and fibula

    
    
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    Superior end bifid; anterior tibial vessels pass forward between 2 attachments

    
    
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    Distally, it inclines medially, under flexor digitorum longus

    
    
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    Grooves and curves around medial malleolus

    
    
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    Nerve supply: Tibial nerve

    
    
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    Action: Plantarflexes and inverts foot

  
  
  
  
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  Flexor digitorum longus

  
  
  
  
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    Origin: Posterior surface of tibia, below popliteus, and medial to vertical ridge

    
    
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    Crosses superficial to distal part of tibialis posterior

    
    
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    Tendon grooves lower end of tibia lateral to that of tibialis posterior, passes around medial malleolus to foot

    
    
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    Nerve supply: Tibial nerve

    
    
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    Action: Flexes interphalangeal and metatarsophalangeal joints of lateral 4 toes; plantarflexes and inverts foot

  
  
  
  
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  Flexor hallucis longus

  
  
  
  
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    Origin: Posterior surface of fibula, below origin of soleus

    
    
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    Passes medially, descends down posterior to midtibia

    
    
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    Associated with os trigonum posterior to talus

    
    
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    Tendon occupies deep groove on posterior surface of talus, passes around medial malleolus, under sustentaculum tali, to great toe

    
    
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    Nerve supply: Tibial nerves

    
    
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    Action: Flexes interphalangeal and metatarsophalangeal joints of great toe; plantarflexes foot

  
  

Lateral compartment

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  Peroneals separated from extensors by anterior intermuscular septum and from posterior muscles by posterior septum

  
  
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  Peroneus longus

  
  
  
  
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    Origin: Upper 2/3 lateral surface of fibula and intermuscular septa and adjacent muscular fascia

    
    
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    Becomes tendinous a few cm above lateral malleolus

    
    
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    Curves forward behind lateral malleolus, posterior to peroneus brevis

    
    
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    Nerve supply: Superficial peroneal

    
    
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    Action: Everts foot and secondarily plantarflexes foot

  
  
  
  
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  Peroneus brevis

  
  
  
  
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    Origin: Lower 2/3 lateral surface of fibula and intermuscular septa and adjacent muscular fascia

    
    
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    Muscle is medial to peroneus longus at origin but overlaps peroneus longus in middle 1/3

    
    
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    Tendon curves forward behind lateral malleolus, in front of peroneus longus tendon

    
    
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    Nerve supply: Superficial peroneal

    
    
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    Action: Everts foot and secondarily plantarflexes foot

  
  
  
  
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  Synovial sheath for peroneals begins 5 cm above tip of lateral malleolus and envelops both tendons; divides into 2 sheaths at the level of calcaneus

  
  
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  Peroneus quartus

  
  
  
  
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    Accessory muscle with prevalence of 10%

    
    
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    Originates from distal leg, frequently from peroneal muscles, with variable insertion sites at foot

    
    
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    At level of malleolus, located medial or posterior to both peroneal tendons

  
  
  
  
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  Peroneus digiti minimi

  
  
  
  
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    Accessory with prevalence of 15-36%

    
    
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    Extends from peroneus brevis muscle around medial malleolus to foot

    
    
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    Tiny tendinous slip

  
  

Anterior compartment

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  Tibialis anterior

  
  
  
  
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    Origin: Upper 1/2 of lateral surface of tibia and interosseous membrane

    
    
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    Tendon originates in distal 1/3; passes deep to retinaculum

    
    
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    Nerve supply: Deep peroneal and recurrent genicular

    
    
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    Action: Dorsiflexor and invertor of foot

  
  
  
  
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  Extensor digitorum longus

  
  
  
  
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    Origin: From upper 3/4 of anterior surface fibula

    
    
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    Descends behind extensor retinacula to ankle

    
    
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    Nerve supply: Deep peroneal

    
    
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    Action: Extends interphalangeal and metatarsophalangeal joints of lateral 4 toes, dorsiflexes foot

  
  
  
  
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  Peroneus tertius

  
  
  
  
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    Small, not always present

    
    
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    Origin: Continuous with extensor digitorum longus, arising from distal 1/4 of anterior surface of fibula and interosseous membrane

    
    
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    Inserts into dorsal surface at base of 5th metatarsal

    
    
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    Nerve supply: Deep peroneal

    
    
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    Action: Dorsiflexes ankle and everts foot

  
  
  
  
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  Extensor hallucis

  
  
  
  
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    Thin muscle hidden between tibialis anterior and extensor digitorum longus

    
    
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    Origin: Middle 1/2 of anterior surface of fibula and interosseous membrane

    
    
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    Tendon passes deep to retinacula to great toe

    
    
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    Nerve supply: Deep peroneal

    
    
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    Action: Extends phalanges of great toe and dorsiflexes foot

  
  

Leg muscles and vessels are well demonstrated by ultrasound throughout their course and depth

Start imaging at the ankle and move proximally to identify “hard to find” structures or ones that change course (i.e., plantaris)

Gastrocnemius muscle tears at the myofascial junction and deep venous thrombosis in the leg are common

Deep structures of posterior compartment, such as peroneal vessels and tibialis posterior muscle, may be difficult to visualize in very muscular patients

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  Attempt scanning anteriorly through anterior compartment using the gap between the tibia and fibula as a window

Intramuscular veins of the leg have variable anatomy

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  May be duplicated &/or asymmetric to the contralateral side

  
  
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  Any thrombus in a vein that is intramuscular (deep to a muscular fascia) is a deep venous thrombosis