The common cause of heat and pain in the knee joint is inflammation of the knee joint, mainly due to the following causes: 1. gouty arthritis, because of abnormally high uric acid leading to the deposition of gout crystals in the knee joint, invading cartilage and synovial membrane, with obvious redness, swelling, heat and pain during acute attacks. 2. wear and tear of joint cartilage, most commonly patellofemoral joint wear, because of aseptic inflammation after cartilage wear, which leads to 3. sprains or strains that cause damage to the intra-articular structures, which can then produce synovial inflammation, resulting in fever and pain. 4. rheumatoid arthritis or arthritis caused by other pathologies, such as tuberculosis, can cause fever and pain in the knee joint.