Intra-articular magnesium is effective for postoperative analgesia in arthroscopic knee surgery

Background. Several medications are commonly injected intra-articularly for postoperative analgesia after arthroscopic knee surgery. Among the potentially efficient substances, magnesium could be of particular interest through its NMDA-receptor blocking properties. Methods. A total of 60 patients undergoing arthroscopic knee surgery were randomly and double-blindly assigned to two groups to receive intra-articular injection of either 10 ml of magnesium sulphate (MgSO4) (50 mg ml(-1)) (Group M) or 10 ml of normal saline (Group C). Analgesic effect was evaluated by measuring pain intensity (visual analogue scale; VAS) 1, 2, 6, 8, 12, 18 and 24 h after operation and the time delay between MgSO4 or saline administration and the first requirement of supplementary analgesic medication by the patient (diclofenac). Results. Intra-articular magnesium administration resulted in a significant reduction in pain scores in Group M compared with Group C 1, 2, 6 and 8 h after the end of surgery [1.7 (0.59), 2.2 (0.69), 2.8 (1.01) and 3.5 (1.10) in Group M; 8.0 (1.25), 5.9 (1.12), 4.4 (0.67) and 4.5 (1.13) in Group C, respectively]. A longer delay between intra-articular injection of the study medication and first administration of diclofenac was observed in Group M [667 (198) min] as compared with Group C [49 (13) min]. Total diclofenac consumption was significantly lower in Group M [37.5 (38.14) mg] than in Group C [117.5 (46.95) mg]. No early side-effects were noted. Conclusion. Intra-articular magnesium is effective for postoperative analgesia in arthroscopic knee surgery.