Intra-articular versus intravenous magnesium-sulfate as adjuvant to femoral nerve block in arthroscopic knee surgery under general anesthesia: Randomized controlled trial

Background
The combined use of intra-articular (IA) or intravenous (IV) magnesium-sulfate (mgso4) with femoral nerve block might be associated with additive effects on the duration and quality of postoperative analgesia in arthroscopic knee surgery.
Patients and methods
This randomized controlled double-blind study included 90 patients. Femoral nerve block was performed in all patients using 20 ml 0.25% bupivacaine before induction of general anesthesia. At the end of surgery patients were randomly allocated into: Group-IA (intra-articular 1 g MgSO in 20 ml), Group-IV (intravenous 1 g MgSO in 20 ml), and Group-P (20 ml intra-articular and 20 ml intravenous normal saline). 20 ml normal saline was given IV in IA group and IA in IV group. Visual analogue pain score (VAS) at rest, with movement, time to first postoperative rescue analgesia, total postoperative diclofenac consumption, and the number of meperidine rescue doses during the first 24 h postoperatively were measured.
Results
Pain scores were comparable in the three groups at 2 and 4 h and were significantly higher in the control group at 6 h and over 24 h. Group IA had the lowest pain scores. Duration of analgesia was significantly higher [11.6 (4.5) h] in IA group compared to [7.5 (3.6) h] in IV group and [5.2 (2.3) h] in control group ( < 0.01). Total Diclofenac over 24 h was significantly lower in IA group [73.8 (50.9) mg] versus [138.4 (51.6) mg] in IV group and [186.0 (43.9) mg] in the control group ( < 0.01).
Conclusion
The combined use of femoral nerve block with IA or IV MgSO is associated with significant reduction of the intensity and duration of postoperative pain and postoperative analgesic requirements in patients undergoing arthroscopic knee surgery with the IA MgSO being superior to IV route of administration.