I. Early 0 to 2 weeks 1. Quadriceps isometric stretching exercises: repeated contraction and relaxation between maximum intensity contraction and complete relaxation, continuous exercises for as long as possible when no other exercises are performed. 2.Weight-bearing and balancing exercises: stand with your feet shoulder-width apart; or stand in front of and behind each other. Move the center of gravity, so that the feet alternate weight-bearing, and gradually transition to the affected leg to stand on one foot, 5 minutes each time, 2 to 3 times no day. In the second week, flexion exercises will be performed as appropriate, and the exercise angle will be as prescribed by the doctor. Second, the middle 3 to 6 weeks 1, quadriceps isometric contraction to maximum strength contraction, and hold 5 seconds, relax 1 second for 1 time, 50 to 100 times each group, 2 to 3 groups per day. 2.To 4 weeks, flexion up to 60 degrees. 3.Full 4 weeks, you can start straight leg raise exercise. Wearing an external fixation brace, lift the leg straight to 30 degrees, hold for 10 to 15 seconds for 1 rep, 10 to 15 reps per set, 2 to 4 sets per day. 4.Start active knee flexion exercises, sitting or lying down, the posterior thigh muscle force, so that the knee flexion to the maximum angle, hold 2 to 5 seconds for 1 time, 30 times to group, 2 groups to day, straight by the healthy leg help or with the help of rubber band, the affected leg should never force. 5, to 6 weeks, flexion up to 100 degrees. Third, the late 6 to 12 weeks 1, eight weeks 110 degrees. 2.Strengthen all strength exercises. 3, Twelve weeks, the angle of flexion is basically the same as the healthy side.