Effect of saphenous nerve block for postoperative pain on knee surgery: a meta-analysis

Early post-operative mobilization is important both to reduce immobility-related complications and to get the best functional result following surgery on knee. We hypothesized that saphenous nerve block would reduce pain in this patient category compared with placebo injection. In this study, two reviewers independently searched the databases of PubMed, EMBASE, and Cochrane Library (last performed on 12 October, 2014) to retrieve eligible randomized controlled clinical trials. The primary outcomes were visual analog scale (VAS) pain scores within 24 hours after operation when at rest and at an active flexion of knee. Mean difference (MD) or odds ratio (OR) with 95% confidence intervals (CIs) was calculated for each end point. Subgroup analysis was calculated to evaluate potential sources of heterogeneity. Nine randomized controlled trials were retrieved and analyzed. We found that VAS pain scores at rest within postoperative 24 hours were significantly decreased in saphenous nerve block group than that in placebo group (MD = -0.79; 95% CI -1.35 to -0.22; P = 0.007), as well as VAS pain scores at an active flexion of knee within postoperative 24 hours (MD = -0.92; 95% CI -1.61 to -0.22; P = 0.010). In addition, compared to placebo injection group, saphenous nerve block resulted in significantly less morphine consumption during the first postoperative 24 hours (MD = -6.56; 95% CI -11.26 to -1.86; P = 0.006). To conclude, this meta-analysis suggests that saphenous nerve block has an advantage in pain relief both at an active flexion of knee and at rest after knee surgery. Further studies are still wanted to validate these conclusions.