The sensation of burning pain in the knee is a distinct and often alarming symptom, suggesting a specific type of irritation within the complex joint structure. This feeling, which can range from persistent warmth to an intense, fire-like sensation, frequently signals either nerve involvement or a high degree of localized inflammation. The knee contains bone, cartilage, ligaments, and a dense network of nerves, and a burning complaint typically indicates that one of these systems is sending an abnormal pain signal. Identifying the precise source of this irritation is the first step toward finding relief.
Causes Originating from Nerve Irritation
The most direct reason for a burning sensation is a disruption in how nerve fibers transmit signals, known as neuropathic pain. This often manifests as generalized peripheral neuropathy, where damage to small sensory nerves, frequently linked to uncontrolled diabetes, causes chronic paresthesia and a burning feeling in the knee and lower extremities. The mechanism involves nerves misfiring or becoming hypersensitive, interpreting normal sensory input as a painful, hot stimulus.
Burning pain can also result from a nerve becoming physically compressed or entrapped along its course. The saphenous nerve, the largest sensory branch of the femoral nerve, is particularly susceptible to entrapment as it passes down the inner side of the knee. Irritation of this nerve, known as saphenous neuritis, results in a sharp, electric, or burning pain focused specifically on the inner knee and sometimes the calf. This type of localized nerve compression can occur after trauma, surgery, or due to pressure from adjacent anatomical structures.
The pain may also be referred from the lumbar spine. Conditions like sciatica, caused by a herniated disc or spinal stenosis in the lower back, cause pain that radiates down the leg along the affected nerve root. This referred pain is often described as a deep, burning discomfort that travels to the knee. The nervous system misinterprets the origin of the signal due to the shared pathway of the sensory fibers, even though the structural problem originates in the spine.
Severe Inflammation and Autoimmune Conditions
Systemic diseases that trigger intense joint inflammation can lead to a burning sensation as a direct result of the body’s immune response. Inflammatory arthritis, such as Rheumatoid Arthritis (RA) or Psoriatic Arthritis, causes the immune system to mistakenly attack the joint lining. This leads to tissue breakdown and the accumulation of inflammatory cells. The resulting heat, swelling, and pain are often perceived as a deep, persistent burn within the joint capsule.
A sudden and excruciating burning pain can indicate crystal-induced arthritis, most commonly Gout. Gout is caused by a buildup of uric acid, which forms needle-like crystals that deposit in the joint space. This deposition triggers an acute, rapid inflammatory response, making the knee joint feel intensely hot and swollen. A similar, less common condition is Pseudogout, where calcium pyrophosphate crystals cause comparable inflammatory episodes.
A concerning cause of severe, burning inflammation is Septic Arthritis, an infection within the knee joint. Bacteria enter the joint space, causing a rapid and destructive inflammatory cascade. This condition presents with extreme pain, marked swelling, and the joint feeling hot and red, often accompanied by systemic symptoms like fever and chills. Septic Arthritis is a medical emergency requiring immediate attention to prevent permanent joint damage.
Localized Soft Tissue and Overuse Injuries
Mechanical issues resulting from repetitive strain or friction can generate enough localized inflammation to produce a burning feeling. Patellofemoral Pain Syndrome (PFPS), frequently called runner’s knee, occurs when the cartilage beneath the kneecap becomes irritated. This irritation is often due to maltracking or muscle imbalance, leading to increased friction and a burning sensation felt primarily around or under the kneecap, especially when climbing stairs or squatting.
Bursitis, the inflammation of the small, fluid-filled sacs (bursae) that cushion the knee, is another frequent source. Bursae become inflamed due to repetitive pressure, such as excessive kneeling, or direct trauma. Prepatellar bursitis causes burning and swelling at the front of the knee, while pes anserine bursitis causes pain on the inner side of the joint where the hamstring tendons attach. The burning sensation arises from the inflamed sac rubbing against surrounding tissues during movement.
Tendinitis, or inflammation of a tendon, is also a common cause of localized burning pain, especially in athletes. Patellar tendinitis, often called jumper’s knee, involves inflammation of the tendon connecting the kneecap to the shinbone, producing discomfort just below the kneecap. Another element is Iliotibial Band Syndrome (ITBS), which causes a distinctive burning pain on the outside of the knee when the thick band of connective tissue rubs against the outer femur during repetitive knee movement, creating friction and inflammation.
Determining the Severity and Next Steps
Recognizing symptoms that indicate a potentially serious problem is important when experiencing a burning sensation in the knee. While many cases are due to treatable overuse injuries, certain “red flag” symptoms warrant immediate medical evaluation.
When to Seek Immediate Medical Attention
These symptoms include:
- Sudden onset of severe pain.
- Inability to bear any weight on the affected leg.
- Visible deformity of the joint.
- A systemic reaction, such as fever or chills.
- A knee that is significantly hot, red, and swollen (signaling a possible infection like Septic Arthritis).
- Pain that persists or worsens at night.
- Pain accompanied by numbness or tingling that extends into the foot.
For milder cases of burning pain linked to activity, initial self-care may involve rest and the application of ice to reduce inflammation. However, because a burning sensation points toward nerve irritation or intense inflammation, a definitive diagnosis from a healthcare professional is necessary. A medical provider can determine if the pain is mechanical, inflammatory, or neuropathic, ensuring the treatment plan targets the underlying cause.