Anatomy of the popliteal fossa

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Introduction0:00–0:18

The popliteal fossa is the space behind your knee; and even though it may not look like much from the outside, it’s actually a complex region, delimited by muscles and fascia, and it contains a lot of vessels and nerves that pass from the thigh to the leg.
So first, let’s look at the popliteal fossa, which, superficially, resembles a diamond-shaped cavity when the knee is slightly flexed.

Borders0:18–1:51

This means the popliteal fossa has two superior borders and two inferior borders. So, lets go over these borders; The two superior ones are the superolateral border, delimited by the biceps femoris; and the superomedial border, delimited by the semimembranosus and semitendinosus muscles.
The two inferior borders are the inferomedial border, represented by the medial head of the gastrocnemius muscle, and the inferolateral border, delimited by the lateral head of the gastrocnemius muscle.
The popliteal fossa also has a floor and a roof. The roof consists of two layers: the popliteal fascia and skin.
However, things get a bit more complicated with the floor, which has three sections: the bony popliteal surface of the femur superiorly, the posterior aspect of the joint capsule of the knee joint centrally, and the popliteus muscle and fascia covering the popliteus muscle inferiorly.
The popliteal fossa contains the small saphenous vein; the posterior cutaneous nerve of the thigh; the sciatic nerve, which divides into the tibial and common fibular nerves at the superior border; the popliteal arteries and veins along with their branches and tributaries; and the popliteal lymph nodes and lymphatic vessels.
Ok, so now let’s dive in with a little bit more detail, layer by layer. First, there’s the subcutaneous or superficial fascia, which contains the small saphenous vein, the terminal branch of the posterior cutaneous nerve of the thigh, and the medial and lateral sural cutaneous nerves.

Fasciae1:51–2:20

Then comes the deep fascia, also called the popliteal fascia which covers and protects the neurovascular structures within the popliteal fossa.
Next there are the neurovascular structures that traverse the popliteal fossa to pass from the thigh to the leg. When dissecting from superficial to deep within the fossa, first are the nerves, then the veins and finally the arteries, which lie deep, directly on top of the floor of the fossa.

Nerves2:20–5:18

So let's start with the nerves. You might have already heard about the sciatic nerve, which begins in the lower part of the sacral plexus and ends at the superior angle of the popliteal fossa, where it divides into the tibial and common fibular nerves.
The tibial nerve is the medial and larger terminal branch and it derives from the anterior divisions of the anterior rami of the L4 to S3 spinal nerves.
From its origin at the apex of the popliteal fossa, it divides the fossa into two equal parts as it passes from its superior to its inferior angle.
Within the fossa, it gives muscular branches to the soleus, gastrocnemius, plantaris and popliteus muscles. The tibial nerve eventually passes deep to the plantaris and gastrocnemius muscles at the inferior border of the popliteal fossa, then it enters the foot beneath the flexor retinaculum and finally divides into the medial and lateral plantar nerves.
The tibial nerve also gives off the medial sural cutaneous branch that contributes to the sural nerve. The sural nerve mainly provides cutaneous innervation for the leg.
Now let’s look at the common fibular nerve which is the lateral terminal branch of the sciatic nerve, and derives from the posterior divisions of the anterior rami of the L4 to S2 spinal nerves.
It begins in the same place as the tibial nerve, and it follows closely to the medial border of the biceps femoris and its tendon along the superolateral boundary of the fossa.
It then leaves the fossa by passing superficial to the lateral head of the gastrocnemius, it reaches the posterior aspect of the head of the fibula, where it winds around the fibular neck and divides into its terminal branches: the deep and superficial fibular nerves.
It also gives off a branch called the lateral sural cutaneous nerve, which contributes to forming the sural nerve. After the sural nerve receives branches from both the tibial and common fibular nerve, it descends between the two heads of gastrocnemius and becomes superficial in the middle leg.
It then descends with the small saphenous vein and passes inferior to the lateral malleolus to reach the lateral part of the foot.
Ultimately, the sural nerve supplies the posterior and lateral part of the inferior third of the leg and the lateral side of the foot.

Arteries5:18–6:57

Next up let's look at the arteries of the popliteal fossa, the starring role in this short movie belongs to the popliteal artery.
This artery continues the femoral artery after it passes through the adductor hiatus. The popliteal artery is the deepest structure in the popliteal fossa, and it crosses it inferolaterally and ends at the inferior border of the popliteus, where it divides into the anterior tibial artery, which supplies the anterior compartment of the leg, and the posterior tibial artery, which supplies the lateral and posterior compartments.
The popliteal artery also gives off branches to the hamstrings, gastrocnemius, soleus, and plantaris muscles. Ok, so, the popliteal artery also sends five branches that supply the capsule and ligaments of the knee joint - the superior lateral, superior medial, middle, inferior lateral, and inferior medial genicular arteries.
These form the periarticular genicular anastomosis, a network of vessels surrounding the knee that provides collateral circulation when the popliteal artery is compressed or blood flow is reduced.
Other arteries also contribute to the genicular anastomosis. For example, superomedially, there’s the descending genicular branch of the femoral artery; superolaterally, there’s the descending branch of the lateral femoral circumflex artery; and inferolaterally, there’s the anterior tibial recurrent artery, a branch of the anterior tibial artery.

Veins6:57–7:52

Moving on, there are the veins. The popliteal vein begins at the distal border of the popliteus as a continuation of the posterior tibial vein.
It ascends, and becomes superficial in the same fibrous sheath as the popliteal artery, but it lies superficial to the artery.
The popliteal vein terminates at the adductor hiatus, which is an osseo-aponeurotic opening in the adductor magnus at the junction of middle one-third and lower one-third of the thigh.
After traversing the hiatus, it becomes the femoral vein. Now, there are also several veins that drain into this structure.
The most important ones are the veins corresponding to the branches of the popliteal artery and the small saphenous vein, which passes from the posterior aspect of the lateral malleolus to the popliteal fossa, where it pierces the deep popliteal fascia and enters the popliteal vein.

Lymphatic drainage7:52–8:21

And finally, lymphatic drainage is divided into superficial and deep lymph nodes. Superficial popliteal lymph nodes are typically small and are found in the subcutaneous tissue.
The deep popliteal lymph nodes, on the other hand, surround the popliteal vessels and receive lymph from the joint capsule and the lymphatic vessels that accompany the deep veins of the leg.
These lymphatic vessels and nodes then follow the femoral vessels to the deep inguinal lymph nodes. Ok, now, before we wrap up, let’s see if you can identify the contents of the popliteal fossa.

Quiz8:21–8:33

All right, as a quick recap, the popliteal fossa is bounded superolaterally by the biceps femoris, superomedially by the semimembranosus and semitendinosus muscles, and inferolaterally and inferomedially it is bounded by the lateral and medial heads of the gastrocnemius.

Review8:33–9:47

The roof is made of the popliteal fascia and skin, whereas the floor is made by the popliteal surface of the femur superiorly, the posterior aspect of the knee joint capsule centrally, and the popliteus fascia inferiorly.
The fossa also contains structures like the sciatic nerve, the tibial nerve, the common fibular nerve, and the sural nerve which ultimately supplies the posterior and lateral side of the leg and the lateral side of the foot.
The deepest neurovascular structure is the popliteal artery, which continues the femoral artery after it passes through the adductor hiatus.
Then there is the popliteal vein, a continuation of the posterior tibial vein that terminates at the adductor hiatus, where it becomes the femoral vein.
Finally, the popliteal fossa has superficial lymph nodes in the subcutaneous tissue, and deep nodes around the popliteal vessels.