Nerves and Blood Supply

For Young Learners

Structure and Location

Behind your knee is a soft hollow. Feel gently and you may notice a pulse. That is the popliteal artery, the main blood supply to everything below the knee.

Two large nerves pass nearby. One continues down the back of the calf. The other winds around the outside of the shin bone, just below the knee, where it lies very close to the surface.

If you have ever banged the outside of your knee and felt a strange electric tingle down to your foot, that was that nerve.

Function

The artery carries blood to the lower leg and foot. The nerves carry signals both ways: instructions out to the muscles, and sensation back from the skin.

Because the artery is tethered at the back of the knee, a severe injury can damage it, and the lower leg can lose its blood supply quickly. That is why a knee that looks badly out of shape after an accident is treated as an emergency rather than something to watch.

For Patients

Structure and Location

The popliteal artery is the continuation of the femoral artery as it passes behind the knee. It gives off a network of smaller branches, the geniculate arteries, which supply the joint itself, before dividing below the knee into the vessels that supply the lower leg and foot.

The sciatic nerve divides above the knee into the tibial nerve, which continues down the back of the calf, and the common fibular nerve, which winds around the neck of the fibula on the outer side of the knee, where it lies just under the skin.

Function

The geniculate network supplies the joint capsule, the lining, the ligaments and the outer parts of the menisci. The limited reach of these vessels into the cartilage and the inner meniscus explains why those tissues heal so poorly.

The nerves carry movement signals to the lower leg muscles and sensation back from the skin. They also supply the joint itself, which is how you know where your knee is without looking.

Clinical Relevance

The popliteal artery is relatively tethered behind the knee, so a severe injury such as a dislocation can tear or block it. The lower leg tolerates loss of blood supply for only a few hours, which is why such injuries are assessed urgently and why pulses and foot colour are always checked.

The common fibular nerve lies very superficially at the outer knee, so it is vulnerable to direct blows, to tight casts and to prolonged pressure. Damage causes difficulty lifting the foot, known as foot drop, and numbness over the top of the foot.

Surgical neurovascular anatomy and the management of these injuries are covered elsewhere.

For Medical Students

Structure and Location

The femoral artery continues as the popliteal artery behind the knee and divides below the joint into the vessels supplying the lower leg and foot. A network of smaller branches arises from it to supply the joint itself.

The sciatic nerve divides in the distal thigh into a tibial component, which passes vertically behind the knee, and a common fibular component, which winds around the neck of the fibula where it lies subcutaneously.

The surgical anatomy of this region, including the named branches and the order of structures in the popliteal fossa, belongs to the Anatomy Academy and to the surgery section.

Blood Supply and Innervation

The periarticular network supplies the capsule, the synovium, the ligaments and the peripheral portions of the menisci. Penetration into articular cartilage and into the inner meniscal zones is negligible, which determines the healing capacity of each tissue.

Articular innervation follows Hilton's law, arising from the nerves that supply the muscles acting on the joint. Mechanoreceptors within capsule and ligament provide the proprioceptive afferents.

Clinical Relevance

The popliteal artery is relatively fixed above and below the joint, so knee dislocation carries a recognised risk of arterial injury. Vascular assessment is mandatory, palpable pulses alone do not exclude it, and the limb tolerates warm ischaemia for only a few hours.

The subcutaneous course of the common fibular nerve at the fibular neck makes it the most frequently injured peripheral nerve around the knee, whether from direct trauma, from traction, or from external compression. The deficit is weakness of ankle dorsiflexion and eversion with sensory loss over the dorsum of the foot.

A small sensory nerve crosses the front of the knee and is commonly injured during anterior incisions, producing a numb patch beside the scar.

Management of neurovascular injury is covered in the surgery section.