There are several reasons for knee pain when climbing stairs: First, meniscal damage. When the posterior horn of the meniscus is torn, the knee joint can be flexed when climbing stairs, resulting in pain due to compression of the posterior horn of the meniscus, and MRI of the meniscus should be examined for diagnosis and early treatment. Secondly, osteoarthritis of the knee joint. In severe cases, osteoarthritis of the knee joint can involve the soft tissues around the knee joint, meniscus and cartilage, resulting in pain in the knee joint when climbing stairs. Third, patellofemoral arthritis, patellofemoral arthritis is an injury to the cartilage of the patellofemoral joint, resulting in pain due to friction between the patella and the femur when flexing and extending the knee joint. Fourth, injury to the ligaments around the knee joint, when the patellar ligament, quadriceps tendon and goose foot are injured, it can lead to pain when climbing stairs, then MRI of the ligaments and physical examination should be checked for early diagnosis and treatment.