The analgesic effects of proximal, distal, or no sciatic nerve block on posterior knee pain after total knee arthroplasty: a double-blind placebo-controlled randomized trial.

Background: The analgesic efficacy of sciatic nerve block (SNB) after total knee arthroplasty (TKA) is unclear. Proximal and distal SNB are each reported to provide posterior knee analgesia, whereas others suggest that posterior knee pain is not important after TKA. This prospective, randomized, double-blind, parallel-arm, placebo-controlled trial examined whether proximal or distal SNB provides superior analgesia in the posterior knee compared with no SNB after TKA.

Methods: Sixty patients undergoing TKA were randomized to single-shot SNB using either the infragluteal (Proximal group) or popliteal (Distal group) technique, or no SNB (Placebo group). All patients received spinal anesthesia and continuous-femoral nerve blockade. A blinded observer assessed posterior and anterior knee pain at 2, 4, 6, 8, 12, and 24 h postoperatively. The primary outcome was moderate-to-severe posterior knee pain at 4 h postoperatively; secondary outcomes included SNB procedural time, needle passes, and discomfort.

Results: Fifty-three patients were analyzed. The proportion of patients (Proximal:Distal:Placebo) who experienced moderate-to-severe posterior knee pain was 18%:22%:89% (P<0.00001) at 2 h, 24%:28%:72% (P<0.01) at 4 h, and 12%:17%:78% (P=0.00003) at 6 h postoperatively. For the anterior knee, the proportion of patients reporting moderate-to-severe pain was 6%:11%:44% (P=0.02) at 2 h, 6%:6%:39% (P=0.012) at 4 h, and 12%:6%:44% (P=0.017) at 6 h postoperatively. Moderate-to-severe pain did not differ between groups beyond 6 h. Both proximal and distal SNB reduced rest pain in the posterior and anterior knee up to 8 h postoperatively compared with no SNB. The popliteal technique required shorter procedural time, fewer needle passes, and produced less discomfort.

Conclusion: Proximal and distal SNB each reduce posterior and anterior knee pain after TKA compared with no SNB.