The popliteal fossa [sometimes called knee pit] is a diamond-shaped depression lying behind the knee joint, covering the lower part of the femur, and the upper part of the tibia.
Boundaries of Popliteal Fossa
It becomes easier to understand the landmarks when we visualize looking at the fossa from behind.
The boundaries or borders of the popliteal fossa are as follows of the fossa are as follows.
Semitendinosus and the semimembranosus, supplemented by the gracilis, the Sartorius and the adductor magnus.
Lateral head of the gastrocnemius supplemented by the plantaris.
Medial head of the gastrocnemius.
Posteriorly, deep popliteal fascia forms the roof of the popliteal fossa. It is further covered by superficial fascia which contains
- Short saphenous vein
- Three cutaneous nerves
- Branches and the terminal part of the posterior cutaneous nerve of the thigh
- Posterior division of the medial cutaneous nerve of the thigh
- Peroneal (sural) communicating nerve.
Anteriorly, the floor of the popliteal fascia is formed from above downwards by
- The popliteal surface of the femur
- The capsule of the knee joint and the oblique popliteal ligament
- Popliteal fascia covering the popliteus muscle.
Contents of Popliteal Fossa
The main contents of the fossa are:
- Popliteal artery and its branches.
- Popliteal vein and is tributaries.
- Tibial nerve and its branches.
- Common peroneal nerve and its branches.
- Posterior cutaneous nerve of the thigh.
- Genicular branch of the obturator nerve.
- Popliteal lymph nodes.
The popliteal vessels and the tibial nerve cross the fossa vertically and are arranged one over the other. The tibial nerve is most superficial; the popliteal vein lies deep (anterior) to tibial nerve, and the popliteal artery is deepest [anteriormost] of all. The artery is crossed posteriorly by the vein and by the nerve.
- In the upper part of the fossa, from medial to lateral side: artery, vein, and nerve.
- In the middle part, from behind forwards: nerve, vein, and artery.
- In the lower part, from medial to lateral: nerve, vein, and artery.
The common peroneal nerve crosses the fossa obliquely from a superior angle to the lateral angle, along with the medial border of the biceps femoris. It lies in the same superficial plane as the tibial nerve/
The politeal artery is the continuation of the femoral artery. It begins at the opening in the adductor magnus (hiatus magnus) in the thigh at the junction of the middle one third with the lower one-third of the thigh. It runs downwards and slightly laterally, to reach the lower border of the popliteus, where it terminates by dividing into the anterior and posterior tibial arteries.
The popliteal artery is the deepest structure in the popliteal fossa. It has the following relations.
Anterior (or deep) to the artery, from above downwards
- Popliteal surface of the femur
- Back of the knee joint
- Fascia covering the popliteus muscle.
Posteriorly or superficially
- Popliteal vein, and further posteriorly tibial nerve [Nerve is separated from the artery by the vein.]a
- The popliteal vein and the tibial nerve cross the artery from lateral to medial side. At the upper end, vein and tibial nerve are lateral to the artery whereas at the lower end they become medial.
- The popliteal artery is overlapped by semimembranosus over the lower part at the medial margin. The artery is also covered by skin and fascia.
- Upper part
- Biceps femoris
- Tibial nerve
- Popliteal vein
- Lateral condyle of the femur.
- Lower part
- Lateral head of the gastrocnemius.
- Upper part
- Medial condyle of the femur
- Lower part
- Tibial nerve
- Popliteal vein
- Medial head of the gastrocnemius.
- Muscular branches
- Cutaneous branches
- Genicular branches
Genicular branches take part in forming the anastomosis around the knee.
Read more details about popliteal artery and its course
Popliteal vein begins at the lower border of the popliteus by the union of veins accompanying the anterior and posterior tibial arteries. It lies medial to the popliteal artery in the lower part of the fossa, posterior to the artery in the middle and posterolateral in the upper part of the fossa.
The vein continues as the femoral vein at the opening in the adductor magnus. It receives the small saphenous vein, and and the veins corresponding to the branches of the popliteal artery.
The tibial nerve is the larger terminal branch of the sciatic nerve which lies posterior to popliteal vessels.
It extends from the superior angle to the inferior angle of the popliteal fossa, crossing the popliteal vessels from the lateral to the medial side.
It gives muscular branches, a cutaneous branch, the sural nerve and three genicular branches which arteries the genicular arteries
Common Peroneal Nerve
It is the smaller terminal branch of the sciatic nerve and lies in the same superficial plane as the tibial nerve. It extends from the superior angle of the fossa to the lateral angle, along with the medial border of the biceps femoris.
From there, it continuous downwards and forwards to wind round neck of the fibula and continue further.
The common peroneal nerve can be palpated against the neck of the fibula.
Posterior Cutaneous Nerve of Thigh
It is a content of the upper half of the popliteal fossa. It pierces the deep fascia about the middle of the fossa and supplies the skin up to the middle of the back of the leg.
Genicular Branch of Obturator Nerve
This is the continuation of the posterior division of the obturator nerve. It runs on the posterior surface of the popliteal artery, pierces the oblique popliteal ligament, and supplies the capsule of the knee joint.
Popliteal Lymph Nodes
These lies deep to the deep fascia near the termination of the small saphenous vein.
Clinical Significance of Popliteal Fossa
Blood pressure can be measured in the popliteal artery. In coarctation of the aorta, the popliteal pressure is lower than the brachial pressure.
Popliteal cyst is due to the inflammation and swelling of the semimembranosus bursa. The usually arise in conjunction with arthritis of the knee (rheumatoid or osteoarthritis).
It presents as swelling in the popliteal fossa.
An aneurysm is a dilation of an artery, which is greater than 50% of the normal diameter. As the popliteal fascia is tough and non-flexible, the aneurysm can result in compression of other structures in the fossa, particularly tibial nerve.
Other causes of popliteal mass are deep vein thrombosis, adventitial cyst of the popliteal artery and malignancy.