Analgesic efficacy of subcutaneous local anaesthetic wound infiltration in bilateral knee arthroplasty: a randomised, placebo-controlled, double-blind trial.

BACKGROUND: High-volume wound local infiltration analgesia is effective in knee arthroplasty, but the analgesic efficacy of subcutaneous wound infiltration has not been evaluated.

METHODS: In a randomised, double-blind, placebo-controlled trial in 16 patients undergoing bilateral knee arthroplasty with high-volume local infiltration analgesia in the deeper layers, saline or ropivacaine 2 mg/ml was infiltrated into the subcutaneous part of the wound in each knee along with the placement of multi-fenestrated catheters in the subcutaneous wound layers in both knees. Pain was assessed for 6 h post-operatively and for 3 h after a bolus injection given through the catheter 24 h post-operatively.

RESULTS: Visual analogue scale (VAS) pain scores were significantly lower from the knee infiltrated with ropivacaine compared with the knee infiltrated with saline in the subcutaneous layer of the wound, at rest (P<0.02), with flexion of the knee (P<0.04) and when the leg was straight and elevated (P<0.04). Twenty-four hours post-operatively, a decline in the VAS pain scores was observed in both groups, with no statistically significant difference between injection of ropivacaine or saline in the subcutaneously placed catheters (P>0.05).

CONCLUSION: As part of a total wound infiltration analgesia intraoperative subcutaneous infiltration with ropivacaine in bilateral total knee arthroplasty is effective in early post-operative pain management, while a post-operative subcutaneous bolus administration through a multiholed catheter 24 h post-operatively did not show improved analgesia compared with the administration of saline.