A comparison of intra-articular magnesium and/or morphine with bupivacaine for postoperative analgesia after arthroscopic knee surgery

Purpose Both magnesium and morphine provide enhanced patient analgesia after arthroscopic knee surgery when administered separately via the intra-articular route. Magnesium sulfate amplifies the analgesic effect of morphine. This study was designed to compare the analgesic effects of intra-articular magnesium and morphine, with bupivacaine, when used separately and in combination.
Methods Eighty patients undergoing arthroscopic menisectomy were randomized blindly into four intra-articular groups: group B+Mor+Mg received 20 ml 0.25% bupivacaine, morphine 2 mg, and magnesium 150 mg; group B+Mor received 20 ml 0.25% bupivacaine and morphine 2 mg; group B+Mg received 20 ml 0.25% bupivacaine and magnesium 150 mg; and group B received 20 ml 0.25% bupivacaine. Pain scores at rest and during movement, analgesic duration, and total analgesic consumption were recorded.
Results Group B+Mor and group B+Mg patients had equally effective postoperative analgesia. Group B+Mor+Mg patients had significantly reduced visual analogue scale (VAS) values both at rest and during movement and significantly increased time to first postoperative analgesic request, as well as significantly reduced total analgesic consumption, compared with the other groups.
Conclusion Intra-articular administration of magnesium sulfate or morphine, with bupivacaine, had comparable analgesic effects in the doses used. Their combination provided more effective postoperative analgesia than either drug alone.