Soreness and swelling in the knee may be caused by fluid inside the knee joint, or synovitis or synovial hyperplasia. If the knee joint is examined, it can be found to be swollen and thicker than the other side. This is caused by chronic strain on the knee joint, or by the knee joint catching cold. Another condition is the compression of the nerve by a herniated lumbar disc, which can also radiate pain to this area, and some patients also have numbness and weakness. In the last case, osteoarthritis of the knee joint is characterized by soreness and pain in the knee area, which can seriously affect squatting and pain in going up and down stairs. Therefore, if the knee joint is sore and swollen, you need to reduce activities, pay attention to joint warmth, and put some joint pain relief cream.