Nerve pain in the knee, known as neuropathic pain, is distinctly different from the mechanical ache of arthritis or a muscle strain. This pain is characterized by sensations often described as sharp, burning, electric-like, shooting, or a persistent tingling, sometimes accompanied by numbness or heightened sensitivity to touch. Neuropathic pain arises from damage or irritation to the nerves that transmit signals from the knee to the brain. Understanding that the source of the pain is the nerve pathway, rather than the cartilage or bone, is crucial for diagnosis and treatment.
Key Nerves Supplying the Knee
The knee joint and the surrounding skin are innervated by a complex network of sensory nerves branching from larger nerves in the thigh. The largest is the sciatic nerve, which splits above the knee into the tibial nerve and the common peroneal nerve. The common peroneal nerve travels along the outer side of the knee, wrapping around the head of the fibula.
The femoral nerve, which runs down the front of the thigh, gives rise to the saphenous nerve, a purely sensory branch. The saphenous nerve continues down the inner side of the knee and lower leg, providing sensation to the skin in that region. Other smaller branches from the femoral and obturator nerves also provide deep sensation to the joint structures.
Causes Stemming from Local Injury or Surgery
Direct physical trauma to the knee can damage the peripheral nerves that supply the area. A severe contusion, laceration, or fracture involving the joint can cause nerves to be stretched, crushed, or severed. This direct injury disrupts the nerve’s ability to transmit signals, leading to chronic pain sensations.
Surgical procedures, particularly total knee replacement or ligament repair, are also a recognized cause of localized nerve pain. The infrapatellar branch of the saphenous nerve is frequently affected during the incision and manipulation required for these operations. Damage to this small sensory nerve can lead to numbness or burning sensations post-surgery.
When a nerve is cut or damaged, the healing process can sometimes result in the formation of a neuroma, a tangled, non-cancerous growth of nerve tissue. These neuromas become extremely sensitive, firing off chronic pain signals that manifest as sharp or electric-like pain at the site of the incision. This persistent, localized pain often requires targeted treatment to desensitize or remove the neuroma.
Causes Resulting from Entrapment and Compression
Nerve pain can arise from mechanical restriction where a nerve is trapped or squeezed by surrounding tissues, known as entrapment neuropathy. The common peroneal nerve is vulnerable as it winds around the fibular head on the outer side of the knee. Compression can result from prolonged external pressure, such as habitually crossing the legs, or from internal causes like a Baker’s cyst putting pressure on the nerve.
The saphenous nerve is prone to entrapment as it passes through the adductor canal in the inner thigh and near the inner knee. Tight fascia, scar tissue, or muscle hypertrophy can reduce the space the nerve occupies, causing irritation. This often leads to a burning or aching pain along the inner knee, which may worsen with activities that tense the surrounding muscles.
Severe swelling within the joint, or effusion, can also increase pressure on nerves that travel close to the joint capsule. Any mass, such as a ganglion cyst or a tumor near a nerve, can similarly cause external compression. This sustained pressure interferes with the nerve’s blood supply and signal transmission, resulting in neuropathic pain symptoms.
Referred Pain and Systemic Neuropathy
Sometimes, the source of the knee nerve pain is not the knee itself, but the lower spine, a phenomenon called referred pain or lumbar radiculopathy. The nerves that eventually supply the knee originate in the lumbar region of the lower back, specifically the L3 and L4 nerve roots. Compression of these roots, often due to a herniated disc or spinal stenosis, can send pain signals that are felt entirely in the thigh and knee area.
This referred pain is often described as shooting down the front of the thigh to the inner knee. It may also be accompanied by quadriceps muscle weakness or a diminished knee-jerk reflex. Because the problem is in the spine, treatment focused only on the knee joint will fail to resolve the symptoms.
Systemic conditions, such as diabetic neuropathy, can cause generalized nerve damage that manifests as pain in the legs and feet, potentially involving the knees. Chronically high blood sugar levels damage the small blood vessels supplying the nerves, affecting the longest nerves first. This type of pain is felt as a bilateral burning, tingling, or pins-and-needles sensation that can affect the knee area.