Magnesium sulphate attenuates acute postoperative pain and increased pain intensity after surgical injury in staged bilateral total knee arthroplasty: a randomized, double-blinded, placebo-controlled trial

Background: We evaluated the effect of magnesium sulphate on increased pain in 44 patients undergoing staged bilateral total knee arthroplasty (TKA). Methods: The magnesium group (n=22) and the control group (n=22) received magnesium sulphate and isotonic saline, respectively, throughout the surgery. Postoperative pain (visual analogue scale, VAS) at rest and the amounts of patient controlled analgesia (PCA, fentanyl) and rescue analgesia (ketoprofen) administered during the first 48 h were compared between the two groups and within each group between the first and second TKA. Results: The VAS scores were significantly higher in the control group than in the magnesium group not only after the first TKA [29 (11) vs 19 (9) at 24 h and 33 (8) us 24 (10) at 48 h; P=0.001] but also after the second TKA [44 (17) us 20 (10) at 24 h and 43 (14) vs 25 (10) at 48 h; P<0.0011. In the control group, VAS scores were significantly higher for the second than for the first operated knee [44 (17) us 29 (11) at 24 h and 43 (14) us 33 (8) at 48 h; P<0.001 and P=0.006, respectively]. In the magnesium group, there were no significant differences in VAS scores between the first and second TKA. Magnesium significantly reduced the amounts of rescue analgesics and fentanyl administered over the first 48 h postoperatively. Conclusions: Magnesium sulphate administration significantly reduced postoperative pain and minimized the difference in pain intensity between the first and second operations.