Cartilage are special tissues that do not re-grow or repair themselves after injury. But with advancement in medical science, a new surgical technique has evolved called Autologous Chondrocyte Implantation (ACI surgery). With this method, cartilages can be re-grown on areas where they are badly damaged. The surgery is performed in situations where patients with multiple knee injuries , due to reduced cartilage in the injured joints, may experience severe pain, crippling their normal activities.ACI means same-site cartilage cell implantation. The procedure involves two surgeries. In the first , cartilage cells are removed from the patient ?s knee. They are cultured and grown in lab. In the second surgery, these cells are re-implanted in the area of damaged cartilage. The recovery process may take 12 months. Rehabilitative exercises that restore full range motion on the knee and regaining full weight on the knee , must be done regularly.