The possible cause of knee pain during fever is hematogenous synovitis. Inflammation or bacteria in the body during fever can spread through the blood into the synovial membrane of the knee, and cause a sterile inflammatory reaction or even bacterial synovitis in the synovial membrane of the knee. If the patient’s symptoms are more pronounced and localized redness, swelling, heat and pain are very obvious, he or she should promptly go to the hospital to see an orthopedic surgeon or joint surgeon for further diagnosis. X-rays, MRI, etc. can be used to clarify whether there is synovitis or joint effusion in the local knee joint, and only after an accurate diagnosis is clear can symptomatic treatment be given.