Management of a complete ACL tear depends on certain factors such as age, level of physical activity and feeling / symptoms of instability ,i.e feeling of giving away at the knee joint.Therefore if you are young playing sports/ physically active and with a feeling that the knee is going to give away or buckle then you certainly need surgery. However prior to surgery you have to ensure your knee has complete range of movement,i.e it can bend and straighten completely, no swelling should be present and your quadriceps,i.e the front thigh muscle should be well exercised for a successful out come of surgery.I recommend 6 weeks physiotherapy prior to undergoing ACL reconstruction in cases adiviced surgery.If you are middle aged with not much physical activities like sports and there are no symptoms of buckling then a conservative approach/ physiotherapy is recommended