The popliteal fossa is a diamond-shaped depression located posterior to the knee joint. Important nerves and vessels pass from the thigh to the leg by traversing through this fossa and the muscles of the thigh and the leg form its boundaries. This article will discuss the anatomical structure and the contents of the popliteal fossa, followed by any relevant clinical pathology.
Inferiorly, the medial and lateral heads of the gastrocnemius form the medial and lateral borders. The capsule of the knee joint, the distal femur and the proximal tibia form the floor of the popliteal fossa. More inferiorly, the popliteus muscle also forms the floor.
The popliteal fascia, which is continuous with the fascia lata superiorly and the fascia crusis inferiorly, forms the roof of the fossa. This dense fascia is reinforced by transverse fibres and forms a protective sheath for the structures passing through the fossa.
The short saphenous vein and the sural nerve often pierce the fascia and are both important landmarks in surgery involving the posterior aspect of the knee joint.
NervesThe popliteal fossa is 2.5 cm wide and mainly consists of fat tissue. There are many important neurovascular structures, however, which pass through the fossa. The nerves are the most superficial of these structures and include:
The sciatic nerve bifurcates into the tibial and common fibular nerves at the superior angle of the popliteal fossa. The larger medial branch, the tibial nerve, passes through the fossa inferiorly, before it exits deep to the plantaris muscle and enters the posterior compartment of the leg. While in the fossa, the tibial nerve and its branches supply the soleus, gastrocnemius, plantaris and popliteus muscles. One of its branches, the medial sural cutaneous nerve, joins with the sural communicating branch of the common fibular nerve to form the sural nerve.
Common Fibular Nerve
The other branch of the sciatic nerve, the common fibular nerve, traverses the fossa close to the medial border of the biceps femoris muscle before it exits the fossa superficial to the lateral head of the gastrocnemius muscle. It then crosses the posterior aspect of the head of the fibula before it winds around the neck of the fibula and divides into its terminal branches.
Blood vessels are located deep to the nerves within the fossa and include the popliteal artery, the popliteal vein and the short saphenous vein. The short saphenous vein is located within the popliteal fascia and the popliteal vessels are held together by dense areolar tissue.
Popliteal ArteryThe popliteal artery, a branch of the femoral artery, enters the popliteal fossa by passing under the semimembranosus muscle. It travels through the fossa inferolaterally before entering the posterior compartment of the leg. The popliteal artery branches off to form five genicular arteries, which supply the ligaments and capsule of the knee joint. These arteries include:
- superior medial
- superior lateral
- inferior medial
- inferior lateral
These arteries anastomose to form the genicular anastomosis, a collateral circulation surrounding the knee joint. The popliteal artery also gives off muscular branches, which supply the soleus, gastrocnemius, plantaris and hamstring muscles.
The popliteal vein, a continuation of the posterior tibial vein, lies superficial to the popliteal artery within the same fibrous sheath. After it exits the fossa superiorly, it becomes the femoral vein as it passes through the adductor hiatus.
Short Saphenous Vein
The short saphenous vein travels superiorly in the posterior aspect of the leg from the lateral part of the dorsal venous arch, before entering the popliteal fossa. It travels within the popliteal fascia before penetrating it and anastomosing with the popliteal vein.
There are two main groups of lymph nodes located within the popliteal fossa: the superficial popliteal and the deep popliteal. The superficial popliteal lymph nodes lie within the subcutaneous tissue and receive lymph from the lymphatic vessels accompanying the short saphenous vein.
The deep popliteal lymph nodes surround the popliteal vessels and receive lymph from the superficial popliteal lymph nodes as well as from the leg and the foot. The lymph from these nodes then drains into the deep inguinal lymph nodes.
Palpation of the popliteal pulse is usually performed with the knee flexed in order to relax the hamstrings and popliteal fascia. The pulse is best felt in the inferior part of the fossa but may be difficult to find because of the deep location of the popliteal artery. A loss of the popliteal pulse can indicate femoral artery obstruction.
An abscess, or tumour, located within the popliteal fossa usually results in severe pain due to the strength and resistance of the popliteal fascia. Because of this, popliteal abscesses usually spread superiorly and inferiorly from the popliteal fossa.
Pain in the popliteal fossa can also be due to a popliteal aneurysm, an abnormal dilation of the popliteal artery. This may produce a palpable pulsation, a thrill, or an abnormal arterial sound, a bruit. Popliteal aneurysms can compress surrounding nerves, resulting in referred pain to the medial aspect of the calf, ankle and foot.
Dislocations of the knee joint or fractures of the distal femur can cause haemorrhage from the popliteal artery. If prompt action is not taken, it can result in the loss of the leg and the foot. Any injuries to the popliteal artery or vein can result in an arteriovenous fistula, an abnormal connection between an artery and a vein.
Tibial Nerve Damage
Posterior dislocation of the knee joint or laceration to the popliteal fossa may damage the tibial nerve. Injury to this nerve results in paralysis of the leg flexors and the intrinsic muscles of the foot. Individuals with tibial nerve damage are unable to flex their toes or plantar flex their ankle and can lose sensation on the sole of their foot.