Popliteal Fossa

The popliteal fossa or the “knee pit” is a diamond-shaped, fat-filled, shallow depression on the posterior aspect of the knee joint. The popliteal fossa is located at the dorsal aspect of the knee and contains an increased number of lymph nodes as well as structures of the neurovascular system that travel from the thigh to the lower leg. The boundaries are formed by various muscles of the thigh and leg.

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Boundaries of the Popliteal Fossa

Popliteal fossa

  • Also known as the “knee pit” or “hough” 
  • Diamond-shaped depression on the posterior aspect of the knee joint
  • The leg analog of the cubital fossa

Boundaries

Multiple muscles of the dorsal thigh and lower leg form the majority of the boundaries of the popliteal fossa.

Boundaries Structures
Superolaterally
  • Biceps femoris muscle
Superomedially
  • Semimembranosus muscle
  • Semitendinosus muscle
Inferolaterally
  • Lateral head of the gastrocnemius muscle
  • Plantaris muscle
Inferomedially
  • Medial head of the gastrocnemius muscle
Roof
  • Skin
  • Popliteal fascia (continuous with the fascia lata superiorly and the fascia cruris inferiorly)
Floor
  • Capsule of the knee joint
  • Distal femur
  • Proximal tibia
  • Popliteus muscle

The boundaries of the popliteal fossa

Image by BioDigital, edited by Lecturio.

Muscles of the Popliteal Region

MuscleOriginInsertionInnervationFunction
Semimembranosus
  • Ischial tuberosity
Medial condyle of the tibia Tibial nerve
  • Extension of the hip
  • Flexion and internal rotation of the knee
Semitendinosus Superomedial surface of the tibia
Biceps femoris
  • Long head: ischial tuberosity
  • Short head: upper supracondylar line and the linea aspera
Head of the fibula and the lateral tibial condyle
  • Extension of the hip
  • Flexion and external rotation of the knee
Gastrocnemius
  • Lateral head: lateral femoral condyle
  • Medial head: medial femoral condyle
Helps form the calcaneal or Achilles tendon, inserted into the posterior aspect of the calcaneus bone
  • Plantar flexion of the ankle
  • Flexion of the knee
Popliteus
  • Lateral femoral condyle
Tibia, below the medial tibial condyle
  • Internal rotation of the tibia

Contents of the Popliteal Fossa

The popliteal fossa is the location of many important nerves and vessels of the lower extremity and is the main channel for the neurovascular system between the thigh and the lower leg.

Contents of the popliteal fossa

Image by BioDigital, edited by Lecturio.

Mnemonic

To recall the contents of the popliteal fossa from medial to lateral, remember to Serve and Volley Next Ball

  • Semimembranosus/Semitendinosus
  • Artery
  • Vein
  • Nerve
  • Biceps femoris

Vessels

Popliteal artery: 

  • Continuation of the femoral artery, beginning at the level of the adductor hiatus in the adductor magnus muscle of the thigh
  • Popliteal artery gives off 5 branches that anastomose around the knee joint:
    • Superior medial and lateral genicular arteries
    • Middle genicular artery
    • Inferior medial and lateral genicular arteries
  • The deepest vessel within the popliteal fossa
  • Enters the posterior compartment of the leg and bifurcates into the anterior and posterior tibial arteries

Popliteal vein:

  • Continuation of the posterior tibial vein
  • Becomes the femoral vein proximally to the popliteal fossa
  • Found between the popliteal artery (deeply) and tibial nerve (superficially)
  • The tributaries of the popliteal vein are the deep veins of the leg: the posterior and anterior tibial veins, the common fibular veins, and the small saphenous vein.
  • The small saphenous vein enters the fossa through the popliteal fascia and drains into the popliteal vein between the 2 heads of the gastrocnemius muscle.

Nerves

The main nerves of the popliteal fossa are the 2 branches of the sciatic nerve, which is the largest branch of the lumbosacral plexus and bifurcates at the superior angle of the popliteal fossa into the following: 

  1. Tibial nerve: 
    • More medial and larger of the 2 branches
    • Runs deeply through the fossa and into the posterior compartment of the leg
    • Gives off motor branches to the muscles of the popliteal region
    • Gives off a cutaneous branch that joins a branch from the common fibular nerve to form the sural nerve
  2. Common fibular (peroneal) nerve: 
    • More lateral and smaller of the 2 branches
    • Runs along the medial border of the biceps femoris muscle before exiting the fossa superficially

Innervation of the popliteal fossa

Image by BioDigital, edited by Lecturio.

Lymph nodes

  • There are 6–8 lymph nodes embedded in the fat of the popliteal fossa.
  • They are divided into superficial and deep popliteal lymph nodes:
    • Superficial group: receive lymph from the accompanying nodes of the small saphenous vein
    • Deep group: receive lymph from the superficial nodes, the leg, and the foot

Clinical Relevance

The following is an important clinical concept related to the structures found within the popliteal fossa:

  • Popliteal pulse: The palpation of the popliteal artery pulse is usually performed with the knee in slight flexion, which relaxes the popliteal fascia and the muscles of the posterior thigh (semimembranosus, semitendinosus, and biceps femoris). The pulse is best felt in the inferior part of the fossa but may be difficult to palpate due to the deep location of the popliteal artery. 

The following conditions are of clinical significance regarding the popliteal fossa:

  • Popliteal cyst (Baker’s cyst): a synovial cyst that is the most common mass that occurs in the popliteal space. A popliteal cyst is a fluid-filled sac usually associated with knee joint arthritis that develops in the semimembranosus bursa. A popliteal cyst may resolve without treatment but occasionally will require aspiration or may rupture leading to swelling that resembles deep vein thrombosis.
  • Popliteal artery aneurysm: an abnormal dilatation of the popliteal artery more than 50% of the artery’s diameter that can lead to compression of the tibial nerve with diminished plantar flexion and paresthesia of the foot and posterolateral aspect of the leg. Diagnosis is based on palpation of a pulsatile mass or auscultation of a bruit.
  • Knee dislocation: generally secondary to high-impact trauma, such as a fall from height or a motor vehicle collision. Dislocations are most commonly anterior or posterior, depending on the mechanism of injury. Treatment is an immediate reduction and evaluation of the vascular system, specifically the popliteal artery. Vascular evaluation includes serial exams and may include surgical exploration. Interruption of the blood supply can lead to acute ischemia, gangrene, and even amputation of the foot and/or leg. 
  • Tibial nerve damage: Posterior dislocation of the knee joint or lacerations of the popliteal region may damage the tibial nerve. Injury results in weakness in plantar flexion of the calf and the intrinsic muscles of the foot.

References

  1. Drake, R.L., Vogl, A.W., Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.
  2. Chummy, S.S. (2011) Last’s Anatomy (12th ed.). Edinburgh: Churchill Livingstone.

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