Prospective, double-blind, randomized controlled trial of electrophysiologically guided femoral nerve block in total knee arthroplasty

BACKGROUND: The purpose of this study was to compare electrophysiologically guided and traditional nerve stimulator analgesia femoral nerve block after total knee arthroplasty. METHODS: Patients scheduled for unilateral total knee arthroplasty were randomized to electrophysiologically guided or traditional nerve stimulator analgesia by pre-emptive single injection femoral nerve block with corresponding assistance. We assessed pain scores using a visual analog scale (VAS, 0 = no pain, 100 = the worst pain) and the volumes of morphine consumed at 4, 24, 48, and 72 hours after total knee arthroplasty. RESULTS: Of the 60 patients enrolled, eight withdrew from the study. The remaining 52 patients were randomized to the electrophysiologically guided group (n = 27) or traditional nerve stimulator analgesia (n = 25) group. Four hours after total knee arthroplasty, VAS scores were significantly lower in the electrophysiologically guided group than in the traditional nerve stimulator group at rest (4.8 ± 1.4 versus 5.9 ± 0.8, P < 0.01) and while moving (6.2 ± 1.1 versus 6.9 ± 0.9, P < 0.01). The total volumes of morphine injected at 24, 48, and 72 hours were significantly decreased in the electrophysiologically guided group (P < 0.05 each). Variable × time interaction of VAS was significant in the electrophysiologically guided group (P < 0.05), with each VAS score at 24, 48, and 72 hours being significantly lower than the baseline score (P < 0.05). VAS scores at every time point were significantly lower in the electrophysiologically group guided than in the traditional nerve stimulator group (P < 0.05). CONCLUSION: Electrophysiologically guided single injection femoral nerve block may provide better postoperative analgesia and a greater reduction in the demand for pain killers than femoral nerve block using traditional nerve stimulator analgesia.