Comparison Between Adjuvants Added to Bupivacaine in Adductor Canal Block

Adult patients undergoing anterior cruciate ligament repair under Spinal Anaesthesia will be randomly assigned into one of the following groups (The Four study groups will receive the standard treatment in the form of spinal anesthesia and adductor canal block), using computer generated codes and opaque sealed envelopes: 1. Group DX(DEXAMETHASONE): The patients receive 20ml plain bupivacaine (0.5%) + 8 mg dexamethasone (2ml) in adductor canal block after spinal anaetthesia. 2. Group DM (dexmedetomidine)The patients receive 20 ml plain bupivacaine(0.5)+25 microgram dexmedetomidine( diluted in 2 ml normal saline) in adductor canal block after spinal anaetthesia. 3. Group M (magnesium sulphate):The patients receive 20 ml plain bupivacaine(0.5)+200 milligram magnesium sulphate (2 ml of magnesium 10%) in adductor canal block after spinal anaetthesia. 4. Group C(CONTROL): The patients receive 20ml plain bupivacaine (0.5%) + 2 ml of Normal saline in adductor canal block after spinal anaetthesia.