The relationship between chronic knee problems and nerve damage, known as neuropathy, is often misunderstood. Knee pain typically arises from structural issues like worn cartilage or torn ligaments, while neuropathy stems from damage to the nerves themselves. However, major nerves pass closely by the knee joint’s bone and soft tissue, creating opportunities for mechanical injury or compression. Understanding this connection requires separating localized effects of a “bad knee” from other common sources of nerve issues that manifest near the knee.
Understanding Neuropathy and Knee Pain
Peripheral neuropathy involves damage to the peripheral nervous system (all nerves outside the brain and spinal cord). Symptoms often appear as tingling, burning pain, numbness, or “pins and needles” (paresthesia), typically in the hands and feet. Motor nerves can also be affected, potentially leading to muscle weakness.
Knee pain is usually mechanical or structural, caused by degeneration or injury within the joint itself. Common sources include osteoarthritis (wearing down of cartilage) or internal damage like meniscal tears. These structural problems can lead to inflammation and fluid accumulation (effusion), which disrupts the joint’s function.
The Direct Link: How Knee Pathology Affects Local Nerves
A damaged knee can directly cause neuropathy when structural abnormalities compress or entrap nearby nerves, resulting in a localized nerve injury. Two nerves are particularly vulnerable to this compression.
Common Peroneal Nerve
The common peroneal nerve wraps around the outside of the knee near the head of the fibula. It is susceptible to injury from trauma, fracture, or direct pressure from a tight brace or cast. Damage to this nerve can cause “foot drop” (inability to lift the front of the foot) and numbness on the top of the foot and outer leg.
Saphenous Nerve
The saphenous nerve and its infrapatellar branch run along the inside of the knee and can be entrapped by scar tissue. This localized nerve irritation is common following knee surgery, such as total knee replacement, where incisions or internal scarring tether the nerve. Symptoms include sharp, burning pain or hypersensitivity along the inner side of the joint.
Baker’s Cysts
Significant fluid accumulation, such as a large Baker’s cyst, can exert pressure on structures in the popliteal space behind the knee. Baker’s cysts are fluid-filled sacs resulting from underlying knee issues like arthritis. If a cyst grows large enough, it can compress the tibial or common peroneal nerves, causing calf pain, numbness, or weakness in the lower leg and foot.
Distinguishing Causes: When Leg Neuropathy Originates Elsewhere
While knee pathology causes localized nerve issues, many cases of leg neuropathy felt near the knee originate from a more proximal location, typically the lower back or a systemic condition.
Spinal Compression (Radiculopathy)
The most frequent source of radiating leg symptoms is nerve root compression in the lumbar spine. When a herniated disc or spinal stenosis pinches a nerve root (L4, L5, or S1), the resulting pain, numbness, or tingling can travel down the entire nerve pathway. For instance, L4 nerve root compression can cause pain in the thigh and weakness in the muscles that straighten the knee. This referred pain, known as radiculopathy, is often mistaken for a joint problem. Spinal symptoms are often aggravated by positions like sitting or bending, which increase pressure on the nerve root.
Systemic Conditions (Diabetes)
Another major cause is diabetic peripheral neuropathy, a systemic condition that damages nerves due to prolonged high blood sugar. This condition typically affects the longest nerves first, causing symmetrical numbness, tingling, and burning in both feet and lower legs. Symptoms may slowly ascend toward the knee as the disease progresses. Bilateral knee-level neuropathy is often a sign of a systemic disease rather than a localized knee problem.
Seeking Clarity: Diagnosis and Treatment Approach
Differentiating the source of neuropathy—local to the knee, stemming from the spine, or systemic—requires a thorough medical evaluation.
Diagnosis
Diagnostic imaging is the first step. X-rays assess bone structure, while Magnetic Resonance Imaging (MRI) visualizes soft tissues, including spinal discs, nerve roots, and cysts around the knee. An MRI can show a disc herniation or a Baker’s cyst compressing a nerve.
Specialized electrodiagnostic tests confirm nerve involvement and pinpoint the exact location of the damage.
- Nerve Conduction Studies (NCS) measure the speed and strength of electrical signals through peripheral nerves.
- Electromyography (EMG) assesses muscle electrical activity, helping distinguish between nerve root compression in the spine and localized nerve entrapment at the knee.
Treatment
Treatment depends entirely on the identified root cause. If knee pathology is the culprit, addressing the structural issue resolves nerve symptoms. This may involve draining a cyst, removing scar tissue, or joint replacement. If the neuropathy is systemic (e.g., diabetes), treatment focuses on managing the underlying condition through strict blood sugar control. For spinal causes, physical therapy, injections, or surgery to decompress the nerve root may be necessary.