The specific causes of knee pain when walking up and down the stairs are as follows: 1. Knee degeneration: mostly occurs in middle-aged and elderly patients, because when going up and down the stairs, the load on the knee is equivalent to 3-4 times the weight, so in the case of knee degeneration, articular cartilage defects, the joint is prone to stress concentration, prone to increased joint pain in the case of such weight-bearing activities, when resting after this 2. Synovitis of the knee: This condition occurs in younger patients, probably due to the recent intense and extensive physical activity, which itself has a state of chronic synovitis of the knee, so in the case of weight-bearing activities such as going up and down stairs, the degree of synovial stimulation will increase, and therefore will show the symptoms of knee pain.