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Popliteal fossa is a shallow depression located posterior to the knee joint. This area is often referred to as the knee “pit” and may develop vascular, nervous, lymphatic, and adipose tissues as well as swelling and masses.[rx] The fossa houses several important structures that are essential for lower extremity function.
Anatomic boundaries of the popliteal fossa include the following
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Superomedially – the semimembranosus, and semitendinosus muscles
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Superolaterally – the biceps femoris muscle (short and long heads)
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Inferomedial and inferolateral – the medial and lateral heads of the gastrocnemius muscle contribute to the lower border, respectively.
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The plantaris muscle – also runs deep to the gastrocnemius to form the inferolateral border.
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The roof of the fossa – proceeding from most superficial to deep, consists of the skin, superficial fascia, and deep (popliteal) fascia.
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The floor of the fossa – includes the popliteal surface of the femur, the capsule of the knee joint, popliteal ligament, and fascia encasing the popliteus muscle.
Blood Supply and Lymphatics
Popliteal Artery
- The predominant arterial supply in the popliteal fossa is the popliteal artery. The artery represents the distal continuation of the femoral artery after passing through the adductor hiatus of the adductor Magnus’s muscle. The popliteal artery then ends at the lower border of the popliteus muscle before further dividing into the anterior tibial artery and the common trunk of the posterior tibial and peroneal arteries.[rx]
- Five genicular branches of the popliteal artery provide blood to the capsular structures and ligaments of the knee: superior lateral, superior medial, middle, inferior lateral, and inferior medial genicular arteries. The genicular arteries form a collateral network between the femoral artery and the popliteal artery.
This dense vascular network allows for an alternative pathway for blood to flow from the femoral to popliteal arteries. [rx]
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Medial superior genicular artery – branch of the popliteal artery that runs anterior to the semimembranosus and semitendinosus. Anastomoses with lateral superior genicular artery.
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Lateral superior genicular artery – branch of the popliteal artery that passes above lateral femoral condyle. Anastomoses with medial superior genicular artery, lateral femoral circumflex, and lateral inferior genicular arteries.
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Medial inferior genicular artery – arises from the popliteal artery and descends with popliteus muscle, then passes the medial tibial condyle. Anastomoses with lateral inferior and medial superior genicular arteries.
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Lateral inferior genicular artery – arises from the popliteal artery and passes under the gastrocnemius. Anastomoses with inferior medial genicular, superior lateral genicular, and anterior recurrent tibial artery.
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Middle genicular artery – branch of the popliteal artery that supplies the ligaments and synovial membrane of the knee joint. [6]
Popliteal Vein
- The popliteal vein is superficial to the popliteal artery in the fossa. The popliteal vein receives venous circulation from several tributaries. The anterior tibial vein, posterior tibial vein, and the peroneal vein merge at the popliteus muscle to make the popliteal vein. Within the popliteal fossa, the small saphenous vein feeds into the popliteal vein and is located more superficially, but transverses the deep fascia in between both gastrocnemius heads. Similarly to the popliteal artery, the popliteal vein extends superiorly through the adductor hiatus before transitioning into the femoral vein.[7]
Nerves
- The sciatic nerve branches into the tibial and common peroneal nerve just anterior to the popliteal fossa. The tibial nerve then enters the posterior legs between the heads of the gastrocnemius. The common peroneal nerve passes around the neck of the fibula.
Tibial Nerve
- The tibial nerve is a branch of the sciatic nerve consisting of nerve roots L4-S3. It is superficial to the popliteal vessels and travels laterally to medially from the superior angle to the inferior angle of the popliteal fossa, respectively. The tibial nerve contains muscular, articular, and cutaneous branches. Muscular branches in the distal portion of the fossa supply the medial and lateral heads of the gastrocnemius, soleus, plantaris, and popliteal muscles.
- The sural nerve is the cutaneous branch of the tibial nerve and extends from the middle of the popliteal fossa, providing innervation of the lower posterior half of the lower leg and lateral foot. The three articular branches arise from the superior portion of the fossa. The superior medial genicular is found at the medial femoral condyle, and the middle genicular nerve pierces the posterior capsule of the knee joint innervating intercondylar structures and the inferior genicular nerve which travels to the medial tibial condyle.[rx][rx]
Common Peroneal Nerve
- The common peroneal nerve also referred to as the common fibular nerve, consists of nerve roots L4-S2 and arises from the sciatic nerve as well. It branches approximately at the superior angle of the popliteal fossa and travels to the lateral angle where it wraps around the fibular head, splitting off into the deep and superficial peroneal nerves and innervating the anterior and lateral compartments of the lower leg, respectively
Muscles
The musculoskeletal structures found in the popliteal fossa form its boundaries. The fossa has the shape of a rhombus or diamond and is made up of the following musculoskeletal structures.
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Superomedial – The semimembranosus and semitendinosus muscles from the superomedial aspect of the fossa. The semimembranosus is the most medial of the hamstring muscles and functions to extend the hip and flex the knee as well as assist in medial rotation of the knee. The semitendinosus muscle is superficial to the semimembranosus and is the middle of the three hamstring muscles. Not surprisingly, it gets its name because of the long tendinous nature of its structure and assists in the same mechanism as the semimembranosus muscle.[rx]
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Superolateral – The biceps femoris forms the superolateral portion of the popliteal fossa and has two functioning heads. The long head is part of the hamstring muscles while the short head is not included in this description. Both structures participate in knee flexion, while the long head additionally assists in hip extension.[rx]
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Inferomedial – The medial head of the gastrocnemius forms the anteromedial border of the fossa. It assists the lower leg in plantar flexion at the ankle and knee flexion when contracted. Along with the lateral head of the gastrocnemius and soleus, it forms the calf muscle.[rx]
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Inferolateral – The lateral head of the gastrocnemius and the plantaris muscle forms the inferolateral border of the popliteal fossa. Both contribute to plantarflexion of the ankle. The lateral gastrocnemius head also contributes to knee flexion. The plantaris muscle is notably the longest tendon in the body and is not found in every human being.[rx]
Function
- The function of the popliteal fossa is closely associated with the critical anatomic structures it contains. The fossa is a diamond-shaped region directly posterior to the knee and clinically appears as a soft impression behind the knee. It is an important area serving as a transition point/conduit for nerve tissue, vasculature, lymphatic tissue, and musculoskeletal structures, which are discussed at length below.
