Tuan, female, 79 years old. Osteoarthritis of both knees. Before surgery, both knees were in severe pain, unable to fully straighten and walk slowly with flexed knees. Knee surface replacement surgery was adopted. After the operation, she resumed normal walking without pain after standardized rehabilitation exercises under the guidance of Prof. Kang. Pre-operative X-ray of both lower limbs Pre-operative X-ray of both knees shows inversion deformity of the knee joint Intra-operative X-ray of both lower limbs shows severe degeneration and exfoliation of the knee joint surface Post-operative X-ray shows recovery of the force line of both lower limbs