Anatomy & Function

The arteries to the knee joint and surrounding structures are supplied by the large femoral and popliteal arteries. The femoral artery enters the lower limb by passing deep to the inguinal ligament and into the femoral triangle. The artery then sends off the large profunda femoris branch which dives deep into the thigh. The femoral artery continues more superficially giving off more muscular branches to the quadriceps muscle. The profunda femoris also gives off muscular branches and contributes to the circulation around the knee joint.

The femoral artery proceeds through the adductor hiatus in the distal thigh (where it becomes the popliteal artery). Before entering the adductor canal the femoral artery gives rise to the descending genicular artery which contributes to the anastomosis and blood supply around the knee.

As the femoral artery leaves the adductor canal it enters the popliteal space and becomes known as the popliteal artery. It descends in the popliteal space and is separated from the intercondylar fossa of the femur by fat, the posterior oblique ligament and the popliteus fascia distal to the joint line from above downwards. The popliteal artery is the deepest of the vascular structures in the popliteal fossa lying deep to the popliteal vein and the tibial nerve, the latter of which is most superficial. During its course through the popliteal fossa, it gives multiple branches that supply the knee joint and musculature. Opposite the lower border of the popliteus muscle the popliteal artery ends by dividing into the anterior tibia and posterior tibial artery.

The blood vessels around the knee form an extensive anastomosis linking the femoral artery above with the popliteal and tibial arteries below. During its course, the popliteal artery gives off the medial and lateral superior genicular artery, the middle genicular artery, the sural artery and the lateral inferior and medial inferior genicular arteries. All these vessels together supply the muscles, tendons, ligaments and bone of the knee joint as well as the synovial membrane lining the knee joint and capsular structures.

At a variable level in the popliteal fossa the anterior tibia vein and the posterior tibial vein together with the peroneal vein join together to form the popliteal vein. The popliteal vein ascends through the popliteal fossa superficial to the popliteal artery and deep to the tibial nerve. The popliteal vein becomes continuous with the femoral vein at the adductor canal.

The popliteal vein is a common site of deep venous thrombosis (DVT) especially in total knee replacement patients.

Although considerable individual variation exists, predominant patterns of nerve supply about the knee have been described. Two distinct groups of nerve have been identified. The first a posterior group includes the posterior articular branch of the tibial nerve and obturator nerves. The second group is the anterior group and includes the articular branches of the femoral, common peroneal and saphenous nerves.

The obturator nerve arises from the lumbar spine (L2,3,4). The obturator nerve supplies the adductor thigh muscles on the inner side of the thigh.

The femoral nerve arises from the lumbar spine (L2,3,4). It enters the leg passing under the inguinal ligament and supplies the quadriceps muscles as well as the knee joint. The saphenous nerve is a terminal branch of the femoral nerve which runs down the inner aspect of the leg into the foot.

The sciatic nerve is derived from the sacral plexus (L4,5, S1,2,3) and is made up of the tibial (medial) and common peroneal (lateral) nerves contained within a common connective tissue sheath. The sciatic nerve enters the leg posteriorily and runs down the back of the thigh. It splits into the tibial and common peroneal nerve above the knee. The tibial nerve supplies the superficial and deep hamstring muscles as well as the muscles of the posterior compartment of the leg including the gastrocnemius and soleus muscles. The common peroneal nerve supplies the anterior and lateral compartments of the leg including the peroneal muscles.

The tibial nerve is the larger of the two divisions of the sciatic nerve. It runs vertically through the popliteal fossa directly underneath the fascia and is the most superficial of the neurovascular structures behind the knee. The common peroneal nerve separates from the tibial portion of the sciatic nerve at the apex of the popliteal fossa and then follows the tendon of the biceps femoris along the upper lateral margin of the popliteal fossa to the back of the head of the fibula. The nerve then winds round the neck of the fibula and passes deep to the peroneus longus muscles and divides into the superficial and deep peroneal nerves.

All these nerves give off branches to the knee joint during their passage down the leg.

Not only do these nerves supply the knee joint but they also supply the skin of the knee (cutaneous innovation). The nerve supply to the skin of the knee comes primarily from the femoral nerve, obturator nerve, tibial nerve and common peroneal nerves.

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