Performing on both side is bilateral procedure (modifier 50 or RT,LT depending on payer) Modifier 76 would mean for instance Left knee, patient returns later that day and the left knee is done again (repeat = redo). 76 is not to be used in place of anatomical modifiers (RT, LT, 50, E1-E4, FA, F1-F9, TA, and T1-T9)