Anatomy of Leg

Review: (527)

Deep Fascia:

• In the thigh = Fascia Lata
• Same layer in the leg = Crural Fascia

Superficial structures:

• In posterior perspective see the short saphenous vein.
• Subcutaneous Sural nerve runs with short saphenous vein for most of its length in calf.
• Popliteal fossa:
  • Biceps has short / long head on lateral aspect
  • semimembranous / semitendinous muscles on medial aspect
  • Gastrocnemius forms inferior lateral / medial border.
• Femoral artery gives off profundus femorus.
• It then continues through adductor hiatus to go onto the posterior aspect into popliteal fossa.

(504) Compartments: 3 in leg based on interosseus membrane and posterior / anterior lateral septae. Crural fascia invests all.

• Anterior compartment- dorsiflexion
• Lateral compartment- eversion (turn lateral side of foot upward)
• Largest posterior compartment- all are plantar flexors

Posterior divided into:

• Superficial part
• Deep part

Superficial part:

• Sciatic comes into popliteal fossa and divides into
  • Tibial nerve– continues into posterior leg
  • Common fibular nerve– courses laterally
  • both branches give cuteaneous branches that supply calf (sensory) and run with saphenous vein (after the branches unite to form Sural nerve)
• Soleus muscle: Deep to gastrocnemius
  • Is powerful plantar flexor of ankle joint
  • Hypertrophy of this makes gastrocnemius more prominent
  • Becomes tendinous and unites with gastrocnemius = tendons form the calcaneal tendon (Achilles)
  • Does not act on the knee joint (doesn’t cross knee0
• Plantaris
  • Tendon called “freshman nerve”
  • Becomes very small and resembles a nerve
  • Is great source for transplants
  • Some say it is just a proprioreceptive organ monitoring other leg muscles

(523) Sciatic nerve

• See division in the popliteal fossa
• Tibial nerve passes deep to gastrocnemius and soleus (all muscles of superficial posterior compartment)
  • All of these muscles get nerve supply from tibial nerve
  • Branches to these nerves come off in the popliteal fossa, not in the leg.
  • Tibial then descends down into the midregion of the leg.

1. 1. • When it passes deep to soleus, it lies deep to transverse intermuscular septum
      • thus lies in the deep part of the posterior compartment.

• • • Superficial compartment only has short saphenous and sural nerve (no artery)

Deep posterior compartment

4 muscles:

• Flexor Hallucis longus
  • Most lateral muscle is associated with great toe
  • Terminal attachment is on base of distal phalanx on great toe
  • Origin is fibula, some from interosseus membrane
  • Is most well developed (toe is last to leave floor in walking)
• Tibialis posterior
• Flexor Digitorum longus
  • Flexes the toes
  • Most medial
• These 3 deviate toward ankle and cross the ankle on medial aspect
• Popliteous muscle:
  • Origin from lateral chondyle of femur
  • Supplied by Tibial nerve / popliteal artery
  • Is oblique in course across posterior of knee joint
  • Attaches proximal end of Tibia just above soleal line (where soleus takes origin)
  • Can flex the knee joint (weak flexor of knee)
  • Initiates flexion of the knee
  • Knee also has small amount of rotation near full extension (locks the knee)
  • From this position, popliteous “unlocks” the knee joint with a small amount of rotation.

1. 1. • Limb free – tibia rotates
      • Limb planted- femur rotates

• Tibia and Fibula- w/ ankle joint
  • Both have distal portions that participate in ankle joint
  • These are the medial (tibia) and lateral (fibula) malleolus
  • Little tissue between these and skin
  • Muscles in posterior compartment have tendons that past over medial malleolus and use it as fulcrum to change direction from vertical out of leg to go onto sole of foot. They are held there by 2 retinaculum.
• All innervated by tibial nerve
  • Nerve deviates with tendons
  • goes posterior to medial malleolus
• Popliteal artery courses across knee joint
  • When reach the inferior border of fossa it divides into terminal branches

• • • Posterior tibial artery
      1. Stays in posterior compartment
      2. Runs with tibial nerve
      3. Will give off large branch: Fibular artery
         1. Courses laterally
         2. Runs parallel with fibula
         3. May go into Flexor Hallucis longus
         4. Supplies ankle joint on lateral side
    • Anterior tibial artery
      1. Goes deep and passes between tibia and fibula
      2. Goes through hole in interosseus membrane to enter anterior compartment
      3. Is primary vessel for anterior compartment

Medial malleolus:  many structures

• When structures pass they have an order
• Tom (tibialis posterior), Dick (Flexor Digitorum longus), And (posterior tibial artery / nerve), Harry (Flexor Hallucis longus) From medial to lateral
• Bound to posterior side of medial malleolus
• The artery and nerve divide into terminal branches in foot
• Tibial nerve: supplies all of superficial / deep of posterior leg and plantar surface of foot.
• Posterior tibial artery:
  • All muscles of deep / superficial / plantar surface
  • Supplies posterior and lateral compartments of the leg
  • Will continue on to the foot to supply the plantar surface as the medial and lateral plantar arteries

Posterior deep compartment: General comments

• Origins of these muscles:
  • Flexor Hallucis longus- most lateral = from fibula.
  • Tibialis posterior- in middle = from interosseus membrane.
  • Flexor digitorum longus- Most medial  = from tibia.
• Attachments:
  • Flexor Hallucis longus- base of distal phalanx on great toe.
  • Flexor digitorum longus – 4 toes at base of distal phalanx.
  • Tibialis posterior- complex insertion in plantar foot.

Anterior compartment

Superficial structures: (526)

• Great saphenous vein
  • Runs length of medial thigh
  • Origins is venous network at dorsum of foot

1. 1. • Forms from 2 veins- merge to become Great saphenous
      • When it leaves the foot and crosses the ankle joint, Great saphenous is just anterior to the medial malleolus

1. • Is joined by saphenous nerve (terminal branch of femoral)

1. 1. • Only branch of femoral nerve to extend beyond the knee
      • All other branches distribute on thigh

• • • Does not go into popliteal fossa

• Another vein originates from network in foot: Short Saphenous
  • Ascends up leg in posterior compartment
  • In the subcutaneous tissues of calf
  • Travels with the Sural nerve

Muscles:

• Tibialis anterior
  • Right on the shaft of the tibia (just lateral of shin)
  • Takes origin from Tibia
  • In the lower 1/3 of leg, it becomes tendinous
  • Crosses leg and deviates medially, crosses ankle and goes to medial aspect of foot and inserts onto bones of the foot
• Extensor Hallucis longus
  • Comes out of anterior compartment
  • Extends onto foot
  • Buried beneath Tibialis anterior
  • Attaches distal phalanx on great toe
• Extensor Digitorum longus
  • Goes to 4 toes
  • Also difficult to locate beneath Tibialis anterior
  • Broadens and forms hood on dorsal side of toe

1. 1. • Forms extensor hood, tendon extends to middle and distal phalanx
      • Not much significance in foot

1. • Lowest fibers: form their own tendon that comes out and does not extend to toes

1. 1. • Attaches the base of 5^th metatarsal
      • Called Fibularis Tertius– goes onto dorsum of foot.

• • • Absent 20% of time

Anterior compartment: General comments

• Innervation for all muscles is Deep fibular nerve
• Blood supply is mainly from Anterior Tibial Artery
• Main action is Dorsiflexion / toe extension
• Origins of these muscles:
  • Extensor Hallucis longus- most lateral = from fibula.
  • Extensor digitorum longus- in middle = from interosseus membrane.
  • Tibialis anterior- Most medial  = from tibia.
• Attachments:
  • Extensor Hallucis longus- base of distal phalanx on great toe.
  • Extensor  digitorum longus – 4 toes at base of middle and distal phalanx.
  • Tibialis anterior- medial cuneiform / base of 1^st metatarsal

• All these extensor have securing retinaculum

1. • Superior extensor retinaculum
   • Inferior extensor retinaculum
   • Bands that secure tendons onto ankle

Nerves / Vessels of anterior compartment: (502)

• Sciatic nerve divided into tibial and common fibular nerve
  • Tibial nerve remains in straight line
  • Common fibular deviates laterally and becomes subcutaneous

1. 1. • Lies on the neck of fibula (right beneath skin)
      • Because it is subcutaneous and lateral, it is very vulnerable (same level as bumpers)

• • • A tibial fracture requires cast below knee: must ensure cast isn’t compressing fibular nerve.

• • • Comes anteriorly around leg and splits:
      1. Deep fibular nerve– extends into anterior compartment and runs with the anterior tibial artery (which arrived there via interosseus membrane). This bundle crosses ankle joint and goes onto to dorsum of foot.
      2. Superficial fibular nerve– is the nerve of the lateral compartment. Innervates both muscles in that compartment.
    • Injury to common fibular will demonstrate plantar flexion (foot drop). Have a high stepping gait.

Lateral compartment

Muscles

• Fibularis longus
  • Origin: from fibula
  • Enters plantar surface and goes across diagonally to medial side of foot to insert 1^st metatarsal (great toe).
  • Is most superficial and most powerful
  • Midleg, it becomes tendinous

1. 1. • Passes posterior to lateral malleolus
      • Uses lateral malleolus as pivot to enter the foot

• Fibularis brevis
  • Origin: from fibula
  • Also becomes tendinous
  • Tendon take same course. They both lie together behind lateral malleolus.
  • Inserts base of 5^th metatarsal (little toe)
• Both muscles innervated by superficial fibular nerve
• Blood supply from branches of fibular artery (stays in posterior compartment)
• Action: curls the lateral margin upward = Eversion of the foot.  Are Everters.
  • Opposite is inversion- Tibialis anterior is most powerful inverter.
  • Fibularis longus is most powerful Evertor
  • There is no named artery here.

Leg: Clinical

• Crural fascia in the leg binds muscles into their respective compartments
• This is not true in the thigh (lose packing in thigh)
• Anterior compartment is most compact
  • Between bone and thick crural fascia on anterior surface
  • Has very little room for expansion of structures
  • If muscles here accumulate edemaà pain = anterior compartment syndrome.  AKA shin splint.

1. 1. • May be tearing of fibers that are used w/o proper warm up
      • Due to running / working out on hard surface

• • • Tight fitting shoes

• • • May be edema putting so much pressure that it is cutting off blood supply leading to ischemic pain in nerves / muscles.

• Posterior compartment:
  • Subject to atherosclerosis
  • Usually in sedentary individuals who participate in sudden exercise
  • Intermittent claudication (pain) in the calf region due to ischemia.

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