Group T: Tramadol 37.5mg / acetaminophen 325mg: 1 tablet 3 times daily orally Group P: Acetaminophen 500mg 3 times daily A computer-generated random sequence will decide the allocation order. The appearance of acetaminophen looks similar to the tramadol/acetaminophen combination. Both pain team members and patients will be blinded to the study medications. The study medications will be used for 48 hours after operation.