Randomization
A list of computer-generated random numbers (Excel; Microsoft Corporation, Redmond, WA, USA) was used to divide patients into two groups. Subsequently, such random numbers were sealed in opaque envelopes by Investigator A, who was blinded to the group allocation and study design. Investigator A asked each patient to choose an envelope on the morning of the operation. The patients were assigned by Investigator B to the magnesium sulfate or control group, following the number in the chosen envelope. Before surgery, Investigator B ensured that anesthesiologists who did not participate in the study prepared the appropriate analgesic cocktail. The surgeon and outcome assessor (Investigator C) were blinded to the treatment group. Another investigator (Investigator D), who was also blinded to the group assignment, performed statistical analysis. By the end of the test (3 months after the operation), the patients were informed of the group to which they belonged.