The sensation of heat and burning in the knee signals irritation within the joint or surrounding tissues. This discomfort is usually a direct manifestation of inflammation, the body’s natural response to injury or disease. Understanding the source of the heat is the first step toward finding relief, as causes range from chronic joint diseases and acute mechanical injuries to serious infections or neurological issues.
Causes Stemming from Joint Inflammation
Chronic inflammation within the knee joint frequently causes persistent warmth and discomfort. The most common cause is Osteoarthritis (OA), often called “wear-and-tear” arthritis, involving the progressive breakdown of articular cartilage. As cartilage erodes, bone surfaces rub together, and the joint lining, the synovium, becomes chronically inflamed. This synovial inflammation contributes significantly to the pain and sensation of heat in OA.
Rheumatoid Arthritis (RA) is another inflammatory cause, an autoimmune condition where the immune system attacks the synovial membranes. This systemic attack thickens the synovium and produces excess fluid, causing swelling, stiffness, and heat, often affecting both knees. Unlike OA, RA symptoms typically worsen after periods of rest, such as in the morning. Gout is caused by a buildup of uric acid that forms sharp crystals in the joint fluid. These crystals trigger a rapid and severe inflammatory response, making the knee joint feel intensely hot, swollen, and painful during a flare.
Overuse Injuries and Local Tissue Irritation
When heat and burning relate to physical activity, the cause often lies in the soft tissues outside the main joint structure. These injuries typically arise from repetitive strain, sudden increases in exercise, or improper mechanics.
One common condition is Bursitis, the inflammation of the bursa, a small, fluid-filled sac that cushions tendons and bones. When the prepatellar bursa, located in front of the kneecap, becomes irritated from kneeling or repetitive friction, it swells and generates localized heat and burning.
Tendinitis, such as patellar tendinitis (“Jumper’s Knee”), involves inflammation and micro-tears in the tendons connecting muscle to bone. This causes a distinct burning pain just below the kneecap, especially during activities like running or climbing stairs. Patellofemoral Pain Syndrome (PFPS), known as “Runner’s Knee,” causes a diffuse burning sensation around or under the kneecap. This irritation results from the kneecap tracking incorrectly in its groove, which increases friction and leads to localized inflammation.
Critical Causes: Infection and Nerve Involvement
While most causes of a hot knee are manageable, some conditions require immediate medical evaluation due to their potential for rapid joint destruction. Septic Arthritis, or infectious arthritis, is a medical emergency occurring when pathogens enter the joint space. This condition causes rapid, severe cartilage damage and presents with intense symptoms.
Symptoms include extreme pain, rapid swelling, and a markedly hot joint, usually affecting only one knee. Infectious arthritis is often accompanied by systemic signs of illness, such as a high fever, chills, and an inability to bear weight.
Separately, the burning sensation may be neurological rather than inflammatory. Peripheral Neuropathy, a condition of damaged nerves, can cause persistent, non-inflammatory burning, tingling, or electric pain in the extremities. The sensation could also be referred pain, where a pinched nerve in the lower back or hip is mistakenly perceived as a burning issue in the knee.
Immediate Steps and When to See a Doctor
For a hot knee resulting from a known injury or overuse, initial home care should focus on reducing inflammation and providing rest. The RICE protocol—Rest, Ice, Compression, and Elevation—is the standard first response to calm irritated tissues. Applying a cold pack wrapped in a towel for 10 to 20 minutes several times a day helps constrict blood vessels, minimizing swelling and the sensation of heat.
Over-the-counter Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), such as ibuprofen, can also be used to help reduce both the pain and the inflammatory response, provided there are no contraindications.
If symptoms are persistent, lasting more than a week, or if the pain interferes with daily activities or sleep, scheduling an appointment with a primary care physician or orthopedist is appropriate. However, certain “red flag” symptoms demand an immediate trip to the emergency room:
- A high fever or chills.
- Rapid and extreme swelling of the joint.
- A sudden inability to put any weight on the leg.