Efficacy of intra-articular magnesium for postoperative analgesia in total hip arthroplasty.

The aim of the present study was to compare the efficacy of intra-articular magnesium sulphate and a saline placebo for postoperative pain control following total hip arthroplasty (THA). Sixty patients underwent THA and were randomly allocated into two groups to receive intra-articular injections of either 10 ml magnesium sulphate (100 mg/ml; magnesium group, n=30) or 10 ml normal saline solution (control group, n=30). Postoperative analgesia was maintained by intravenous morphine injection. The outcome measurements were visual analogue score (VAS), morphine consumption and Harris hip score (HHS). The two groups were well matched. The outcome of VAS at rest was significantly lower at postoperative hours 6 and 12 in the magnesium group as compared with the control group, although the difference was insignificant preoperatively and at postoperative hours 2, 4, 24 and 48, and days 3, 7 and 14. This indicator during activity was also lower in the magnesium group at postoperative hour 24 than that of the control group, although the difference was insignificant preoperatively and at hour 48, and days 7 and 14. The consumption of morphine (the total quantity) at 0-6, 6-12 and 0-48 h in the magnesium group was significantly lower than in the control group, although no significant differences were observed at 12-24 and 24-48 h between the groups. The improvements of HHS from preoperative to postoperative scores were statistically significant, however, no significant differences were identified between groups. Thus, the findings indicate that intra-articular magnesium sulphate injections provided improved pain control and reduced the need for morphine when compared with a saline placebo following THA.