Boundaries and contents
The popliteal fossa is bounded by four muscles, two above and two below, with bone and capsule in its floor.
| Boundary | Structure |
|---|---|
| Superolateral | Biceps femoris |
| Superomedial | Semimembranosus, with semitendinosus lying on it |
| Inferolateral | Lateral head of gastrocnemius, with plantaris |
| Inferomedial | Medial head of gastrocnemius |
| Roof | Skin, superficial fascia and the popliteal fascia, pierced by the small saphenous vein |
| Floor | Popliteal surface of the femur, capsule with the oblique popliteal ligament, fascia over popliteus |
The contents are embedded in fat. From deep to superficial lie the popliteal artery, the popliteal vein and the tibial nerve. The common fibular (peroneal) nerve runs separately along the medial edge of biceps femoris. The small saphenous vein enters through the roof to join the popliteal vein, and a few popliteal lymph nodes lie around its termination.
Nerves of the popliteal fossa
The sciatic nerve usually divides at the upper angle of the fossa into the tibial and common fibular nerves, though the split can occur anywhere higher in the thigh.
- Tibial nerve: the larger branch, running straight down the middle to pass deep to the tendinous arch of soleus. In the fossa it gives motor branches to both heads of gastrocnemius, plantaris, soleus and popliteus; the medial sural cutaneous nerve; and articular branches to the knee.
- Common fibular nerve: follows biceps femoris to the lateral angle, crosses the lateral head of gastrocnemius, and winds round the fibular neck. It gives the lateral sural cutaneous nerve and a sural communicating branch.
- Sural nerve: usually formed below the fossa by the medial sural cutaneous nerve and the communicating branch. It runs down the back of the calf with the small saphenous vein to the lateral border of the foot.
Popliteal artery and genicular branches
The popliteal artery continues the femoral artery from the adductor hiatus and ends at the lower border of popliteus by dividing into the anterior and posterior tibial arteries. It lies deepest of all the contents, directly against the femur and the back of the capsule.
| Branch | Course |
|---|---|
| Sural arteries | To gastrocnemius, soleus and plantaris |
| Superior lateral genicular | Winds laterally above the lateral femoral condyle, deep to biceps femoris |
| Superior medial genicular | Winds medially above the medial femoral condyle |
| Middle genicular | Pierces the capsule to supply the cruciate ligaments |
| Inferior lateral genicular | Runs laterally above the fibular head, deep to the lateral collateral ligament |
| Inferior medial genicular | Runs medially below the medial tibial condyle, deep to the medial collateral ligament |
The genicular arteries form an anastomosis around the knee with branches of the femoral and anterior tibial arteries, but it is too small to keep the leg alive if the popliteal artery is suddenly occluded.
The popliteal vein lies superficial to the artery, crossing from its lateral side above to its medial side below, and continues as the femoral vein at the adductor hiatus.
Clinical relevance
Because the popliteal artery is tethered and deep, most disease here is vascular or compressive.
- Knee dislocation: the artery is fixed at the adductor hiatus and under the soleal arch, so it is stretched or torn. Pulses and the ankle-brachial index are documented before and after reduction, and any abnormality needs urgent vascular imaging or surgery.
- Popliteal aneurysm: the commonest peripheral arterial aneurysm, often bilateral and associated with an abdominal aortic aneurysm. It presents as a pulsatile mass or with distal emboli.
- Baker's (popliteal) cyst: a swollen bursa between the medial head of gastrocnemius and semimembranosus that communicates with the knee. When it ruptures, calf pain and swelling mimic a deep vein thrombosis.
- Common fibular nerve injury: at the fibular neck, from fractures, plaster casts or prolonged leg crossing, causing foot drop.
- Popliteal artery entrapment: an abnormal relation to the medial head of gastrocnemius causes calf claudication in young athletes.
- Popliteal pulse: felt deep in the fossa with the knee slightly flexed to relax the fascia.
On the specimen
The station shows the fossa opened from behind with its borders and neurovascular contents displayed. Name the borders first: the tendon going to the lateral side is biceps femoris; the thick muscle medially is semimembranosus, and the round tendon lying on it is semitendinosus; the two fleshy heads below are gastrocnemius.
The thickest nerve in the midline is the tibial nerve; the nerve hugging the biceps tendon is the common fibular nerve. A short twig from the tibial nerve into the medial head of gastrocnemius is the nerve to that head. The thin nerve heading down the calf midline is the sural nerve. The two small arteries on the lateral side are genicular branches: the upper one above the lateral femoral condyle is the superior lateral, and the lower one above the fibular head is the inferior lateral.