Popliteal Fossa Anatomy

Popliteal Fossa Overview

• A diamond-shaped region posterior to the knee joint acting as a gateway to the leg
• All neurovascular structures pass deep here
• Anterior bony protection and posterior soft tissue protection are afforded

Popliteal Fossa Walls and Borders

• There are 4 oblique walls:
  • Superomedial: Semimembranosus
  • Superolateral: Biceps femoris
  • Inferomedial: Medial head of gastrocnemius
  • Inferolateral: Lateral head of gastrocnemius (and plantaris, if present)
• Floor is composed of the femur superiorly and the popliteus inferiorly
• Roof includes muscle, popliteal fascia, and skin

Popliteal Fascia and Space

• Strong fascial covering limits space expansion
• Popliteal abscesses, tumors, aneurysms in this region generate significant pain, especially in full extension, spreading superiorly/inferiorly

Nerves of Popliteal Fossa

• The sciatic nerve typically splits at the fossa's superior angle

Tibial Nerve Details

• Central components are most superficial
• It crosses the knee joint at the fossa's midline and runs distally within the deep posterior compartment, below the transverse intermuscular septum
• Branches include articular branches to the knee, muscular branches, and the cutaneous medial sural nerve

Common Fibular Nerve Facts

• A branch of the Sciatic Nerve
• Follows superolateral wall, emerging from the popliteal fossa superficial to the inferolateral wall
• Curves superficially to fibular neck, splitting into superficial and deep branches
• Gives off a lateral sural nerve branch in the popliteal fossa

Popliteal Artery Aspects

• Extension of the femoral artery past the adductor hiatus
• Located as the deepest component of the fossa, closely related to the tibial nerve
• Aneurysms can cause palpable pulsations and referred pain
• There are 4 genicular branches that anastomose around the knee
• Blood flow is maintained when the knee is bent and the popliteal artery is occluded
• The anastomosis encircles the patella, protecting it from blunt force trauma
• Supplies muscular branches to the surrounding muscles
• It passes through the tendinous arch of the soleus to enter the posterior compartment of the leg
• Bifurcates distal to the popliteus muscle, forming the anterior and posterior tibial arteries

Popliteal Vein Characteristics

• It runs in close proximity and superficially to the popliteal artery
• Has numerous valves
• Receives the small saphenous vein in addition to muscular and articular branches

Lymphatics in Popliteal Fossa

• Superficial popliteal lymph nodes lie superficial to the popliteal fossa and drain cutaneous tissue
• Deep popliteal lymph nodes lie deep in the fossa, surrounding vessels, draining muscle compartments and the knee joint capsule
• They drain proximally to deep inguinal lymphatics

Posterior Leg Overview

• Area posterior to the tibia, fibula, and posterior intermuscular septum
• Subdivided into superficial and deep muscular compartments with muscles for plantar/digital flexion
• Crucial for developing thrust during walking/running

Superficial Compartment Explained

• Known as the calf
• Loosely packed between crural fascia and transverse intermuscular septum, allowing expansion of the dense gastrocnemius muscles
• Contains the triceps surae muscle group
• Muscles insert on the calcaneal tendon which is the thickest and strongest in the body
• High mechanical load can lead to microtrauma, tendinitis, and Achilles tendon ruptures
• Innervated by tibial nerve muscular branches and supplied by the posterior tibial artery

Gastrocnemius Properties

• The compartment's most superficial muscle
• Recognisable due to its large size and abrupt border
• A two-joint muscle that crosses both knee and ankle
• Two heads originate off the lateral and medial condyles of the femur
• Both heads merge into an aponeurotic tendon that narrows/thickens distally, forming the calcaneal tendon
• More active during forceful contractions like sprinting and jumping

Soleus Details

• A broad, flat muscle deep to the gastrocnemius
• Originates in a horseshoe shape off the posterosuperior surfaces of the tibia and fibula, arch pierced by the popliteal artery/vein/nerve
• The distal half fuses with the gastrocnemius aponeurosis, contributing to the calcaneal tendon
• Considered the workhorse of plantar flexion, continuously active during standing and walking

Plantaris Features

• A minor muscle that contributes to the popliteal fossa's posteroinferior wall
• Originates off the supracondylar ridge superior to the lateral gastrocnemius
• Its exceptionally long tendon fuses inferiorly with the calcaneal tendon
• Thought to be more proprioceptive, having a high density of muscle spindles

Deep Posterior Compartment Characteristics

• Located deep to the transverse intermuscular septum and tibia/fibula/interosseus membrane
• The transverse intermuscular septum narrows inferiorly to form the flexor retinaculum
• Tightly packed, with little room for expansion
• Swelling can lead to posterior compartment syndrome
• Contains the tibial neurovascular compartment and fibular vessels
• Four muscles are housed here, with three contributing to plantar and digital flexion

Popliteus Muscle Action

• A triangular muscle crossing the knee joint
• Originates off the lateral epicondyle and meniscus and it inserts on the posterolateral surface of the proximal Tibia
• It is essential to "unlock" the knee from full extension by medially rotating the tibia on the fibula
• The popliteal tendinitis is an inflammation of the popliteus tendon due to excessive wear

Tibialis Posterior Muscle Information

• Originates off the surfaces of the tibia/fibula, interosseus membrane
• Crosses posterior to the medial malleolus inserting onto navicular, cuneiform, and medial metatarsals
• Responsible for plantar flexion and inversion, playing a role in maintaining the foot's longitudinal arch during standing and walking

Flexor Digitorum Longus Attributes

• Originates medially to the tibialis posterior on the middle third of the posterior tibial shaft
• It extends over the tibialis posterior and crosses posterior to the tendon behind the medial malleolus to insert on digits 2-5
• Primarily a flexor of distal phalanges 2-5

Flexor Hallucis Longus Summary

• Originates off half the surface of the fibula
• The tendon is more medially positioned than tibialis posterior and flexor digitorum longus
• Plantar flexion of the big toe is achieved

Posterior Tibial Artery Details

• It is one of the popliteal's divisions
• Begins along the posterior compartment's midline and gives way to Fibular artery
• Continues medially, lying just deep to the transverse intermuscular septum, between tibialis posterior and flexor digitorum longus
• Supplies superficial, deep posterior compartment muscles, continuing into the foot as medial/lateral arteries

Fibular Artery Characteristics

• Positioned close to the Fibula in the deep posterior compartment's lateral part
• Terminates at the lateral malleolus
• Supplies muscles to the deep/lateral compartments

Tibial Nerve Aspects

• Direct continuation from the popliteal fossa alongside the tibial artery/vein as a neurovascular bundle
• Innervates all posterior compartment muscles
• Branches to the superficial muscle emerge in the popliteal fossa
• Injury is uncommon but can cause loss of Plantar Flexion
• Continues into the foot

Anterolateral Leg Overview

• Area containing the anterior and lateral compartments.
• Anterior compartment contains ankle and digital extensors.
• Lateral compartment contains ankle everters.

Anterior Compartment Muscles Aspects

• Aids with dorsiflexion and vascular supply by the anterior tibial artery is observed
• Deep fibular nerve innervates

Tibialis Anterior Specifics

• It is located superficially and medially in the compartment
• Insertion occurs on the medial cuneiform's inferior surface and the 1st metatarsal base
• The ankle is inverted along with dorsiflexion effects

Extensor Digitorum Longus Characteristics

• Runs lateral and superficial in the compartment
• Insert on the dorsal surface of the phalanges which forms an extensor hood that is the digital extensor

Extensor Hallucis Longus Traits

• Found in the deep and central compartment of the leg
• The tendon runs between tibialis anterior and extensor digitorum longus and inserts at the distal phalanx of the great toe
• Extends the 1st digit

Fibularis Tertius Muscle Breakdown

• A vestigial muscle not always present
• Inserts on the dorsal surface of the 5th metatarsal
• It is a weak dorsiflexor and evertor of the ankle

Lateral Compartment Details

• Composed of evertors, plantar flexors of the ankle
• Superficial fibular nerve innervates the muscles

Fibularis Longus Specifics

• Shaft of fibula gives origin to a proximally and laterally positioned fibularis longus
• Medial cuneiform and 1st metatarsal insertion

Fibularis Brevis Facts

• It originates distally and laterally on the fibular shaft
• Insertion is on the 5th metatarsal base

Lower Leg Vascular Aspects

• Almost entirely supplied by the popliteal artery, which also runs posterior to the knee joint
• Supply to Anterolateral Portion
  • Anterior Tibial Artery: Passes between the tibia, fibula and courses along the anterior interosseous membrane, supplying the anterior compartment
• Posterior Tibial Artery
  • Passes posterior to the medial malleolus to supply the foot
  • Gives off the fibular artery; supplying the posterior, lateral compartments

Lower Leg Innervation Details

• Sciatic nerve controls most motor and sensory information of the leg
• Tibial Nerve
  • Passes behind the knee, separating superficial and deep posterior compartments and supplies both compartments
  • Then passes posterior to the medial malleolus for the foot's intrinsic muscle supply
• Common Fibular Nerve
  • Courses superficially around the fibular head, making easy to injure. Injury results in loss of dorsiflexion and eversion
  • Supplies the lateral compartment of the leg
• Deep Fibular Nerve supplies the anterior compartment of the leg

Ankle Joint Overview

• Hinge joint with mortise formed by the lower surface of the tibia and facets on tarsal bones
• The surfaces are encased in cartilage
• Thickened bands surround the enclosure: Limits are set by medial, lateral, posterior ligaments

Medial Collateral Ligament (Deltoid)

• Originates at the medial malleolus and is stronger and more fracture-resistant than the other ligaments
• Tibionavicular, tibiocalcaneal, and anterior/posterior tibiotalar are included

Lateral Collateral Ligament

• Anterior talofibular, which stabilizes anterior translocation of the talus on the tibia, is most often sprained
• Calcaneofibular and Posterior talofibular

Ankle Joint Movements

• Primary movements such as flexion and extension can be observed
• Eversion and inversion are allowed during bending of the shaft

Talocalcaneal Joint Properties

• Characterized by its 2 articulations, 2 synovial joints-anterior and posterior
• Also supported by a Medial talocalcaneal from talus toward sustentaculum tali

Gliding Joints Actions

• Permits inversion and eversion of the joint

Calcaneo-Cuboid Joint

• Calcaneo-Cuboid joint has 4 ligaments that allow the bones to be joined
• Minor gliding is observed for Movement

Spring Ligament

• The spring ligament supports the head of talus and provides elastic fiber concentration

Naviculocuneiform joint

• Movements are restricted to slight gliding