Knee pain is one of the most common complaints in orthopedic clinics, with a predominance of women. Common causes include 1. meniscal injury in younger patients, and 2. knee wear and tear. With meniscal injuries, most have a history of sports or trauma. The main manifestations, knee pain, playing soft leg, inability to straighten or flex (extension pain or flexion pain) joint space pressure pain. The treatment is based on minimally invasive arthroscopic surgery. Knee wear and tear is medically known as osteoarthritis of the knee joint. The early manifestations are normal walking on flat ground and painful walking up and down stairs or squatting. The treatment is mainly non-surgical: avoid walking up and down stairs or squatting, and take oral non-steroidal anti-inflammatory painkillers. Physical therapy, straight leg raising to exercise the quadriceps, and terminal 30 degree resistance knee extension training. As the lesion progresses, pain appears on the medial side of the knee and progresses to total knee pain in advanced stages, where the patient is unable to straighten the knee, has decreased knee mobility, and has an inversion deformity of the knee (O-leg). Treatment varies at different stages. I do not recommend joint cavity injection treatment.