Pain control after primary total knee replacement. A prospective randomised controlled trial of local infiltration versus single shot femoral nerve block.

Background: We report a prospective blinded randomised trial of local infiltration versus femoral nerve block in patients undergoing primary total knee replacement (TKR), in accordance with the CONSORT statement 2010.

Methods: Fifty patients in a teaching hospital were consented for the study. The study arms were intraoperative local anaesthesia (150ml 0.2% ropivacaine/1ml 1:1000 adrenaline/30mg ketolorac) and femoral nerve block (30ml 0.2% ropivacaine) with a primary outcome of pain score at 4h post operatively. Secondary outcomes were pain at 2h, pain scores before and after physiotherapy on day one, total opiate administered, time to physiotherapy goals and length of stay. Randomisation was by sealed envelope. The assessor was blinded and the patients partially blinded to the intervention.

Results: Ten patients were excluded, eight before randomisation. The trial is complete. Forty patients were analysed for the primary outcome measure. The local infiltration group had significantly lower pain scores at 4h post-operatively; mean [SD] score 2.1 [2.6] versus 6.8 [3.2], p<0.00001 and on post-operative day one prior to physiotherapy; mean score 2.4 [2.3] versus 4.4 [2.3], p<0.05. Total opiate use was also significantly lower in the local infiltration group; mean total 115 [50.3]mg versus 176.5 [103.5]mg, p<0.01. There was no difference in any other outcome. There were no harms as a result of either intervention.

Conclusion: Intraoperative local infiltration gives superior pain relief compared to single shot femoral nerve block over the first 24h following primary TKR and minimises post-operative opiate use.