The knee joint is a complex structure that enables mobility and supports the body’s weight, relying on an intricate network of nerves to transmit signals between the brain and the lower limb. These nerve pathways are essential for controlling movement and perceiving sensations in the lower leg and foot.
The Major Nerve Pathways
The main nerve that runs behind the knee is the sciatic nerve, which branches into two primary nerves just above or within the popliteal fossa, the diamond-shaped space located at the back of the knee. These two major branches are the tibial nerve and the common fibular (peroneal) nerve. Both originate from the larger sciatic nerve, which itself descends from the lower back.
The tibial nerve continues straight down the back of the leg, passing through the popliteal fossa. It is generally the larger of the two main branches. The common fibular nerve, in contrast, branches off laterally and wraps around the head of the fibula, a bone on the outer side of the lower leg, just below the knee. These nerves are the principal conductors of signals for motor control and sensation in the lower leg and foot.
Functions of These Nerves
The tibial nerve plays a significant role in controlling several movements of the foot and toes. It primarily facilitates plantarflexion, which is the action of pointing the foot downwards. This nerve also enables the flexion of the toes, allowing them to curl downwards. Beyond movement, the tibial nerve provides sensory input to the sole of the foot, transmitting feelings such as touch, temperature, and pain.
The common fibular nerve, after branching, divides further into two main parts: the superficial fibular nerve and the deep fibular nerve. The deep fibular nerve is responsible for dorsiflexion, the action of lifting the foot upwards towards the shin. The superficial fibular nerve controls eversion, which is the movement of turning the sole of the foot outwards. Both branches contribute to sensation; the deep fibular nerve provides feeling to the web space between the first and second toes, while the superficial fibular nerve supplies sensation to the top of the foot and the outer part of the lower shin.
When Nerves Are Affected: Common Symptoms
When the nerves behind the knee are irritated, compressed, or injured, individuals may experience a range of symptoms that reflect their disrupted function. Pain is a frequent symptom, which can manifest as sharp, burning, or radiating sensations that travel along the nerve’s path. This discomfort might extend down the leg or into the foot, depending on which nerve is affected.
Numbness or a diminished sense of touch is another common indicator of nerve involvement, particularly in the areas where these nerves provide sensation. Tingling, often described as “pins and needles,” can also occur, indicating abnormal nerve activity. Muscle weakness may develop, making it difficult to perform specific movements, such as pointing the foot down or lifting it upwards, depending on the nerve.