The knee joint is a complex intersection of bone, ligaments, and muscle, serving as a major pathway for the nervous system to the lower leg and foot. While small nerves provide local sensation to the joint itself, one large nerve passes closely around the knee’s structure, making it uniquely exposed to injury. Due to its superficial course near the joint, this nerve is the most frequently damaged nerve in the lower extremity.
The Primary Nerve Near the Knee
The major nerve that runs past the knee joint is the Common Fibular Nerve, also known as the Common Peroneal Nerve. This structure is a terminal branch of the sciatic nerve, which originates in the lower back. The sciatic nerve travels down the back of the thigh before splitting into two main divisions near the popliteal fossa (the space behind the knee). One division continues as the Tibial Nerve, and the other becomes the Common Fibular Nerve.
Where the Nerve is Most Vulnerable
The Common Fibular Nerve is vulnerable due to its anatomical course around a specific bony point on the outer side of the leg. After separating from the sciatic nerve behind the knee, it moves laterally toward the fibular head, the prominent bony knob just below the knee joint. The nerve winds around the neck of the fibula before diving deeper into the leg muscles.
This location is highly exposed, covered only by a thin layer of skin, fascia, and subcutaneous fat, offering minimal natural protection. This superficial position makes the nerve susceptible to external pressure or direct trauma, unlike most major nerves shielded by muscle. Any force directed at the outer side of the leg can easily squeeze the nerve against the unyielding bone underneath. It is at this tethered point that the nerve is most frequently injured.
What Happens When the Nerve is Working Properly
When functioning normally, the Common Fibular Nerve enables both motor control and sensory perception. Its main motor roles are carried out by its two branches, the deep and superficial fibular nerves. These branches control the muscles responsible for lifting the foot at the ankle (dorsiflexion) and turning the sole of the foot outward (eversion).
The nerve also provides sensation to the skin over the front and outer portions of the lower leg. It supplies feeling to the top surface, or dorsum, of the foot. These functions coordinate foot lift and position, allowing for a smooth, natural gait.
Causes of Nerve Damage Near the Knee
Causes of Injury
Damage to the Common Fibular Nerve results from acute trauma, chronic compression, or medical procedures near the fibular neck. Acute injuries include a direct blow to the outer knee, a fibula fracture, or a severe knee dislocation. A knee dislocation can damage the nerve in up to 40% of cases due to intense stretching and tearing.
Chronic compression is a substantial cause, particularly relevant to the general population. Pressure can result from habitually sitting with legs crossed, prolonged squatting or kneeling, or the use of tight casts, splints, or knee braces. Weight loss can inadvertently increase risk by reducing the protective fat layer around the nerve. Injury can also occur as a complication of surgery, such as total knee replacement or ligament repairs.
Symptoms of Damage
When the nerve is damaged, the most noticeable effect is often “foot drop,” the inability to properly lift the front of the foot due to loss of dorsiflexion control. This motor deficit is frequently accompanied by numbness or a tingling sensation along the outer shin and the top of the foot. Anyone experiencing sudden weakness or sensory changes in the lower leg should consult a medical professional for an evaluation.