Alkalinization of local anaesthetic for intra-articular instillation during arthroscopy

Intra-articular instillation of a local anaesthetic agent for pain relief after arthroscopy has not been shown consistently to be beneficial. Alkalinization of a local anaesthetic agent may be expected to improve onset time, quality and duration of the block. In a prospective, double-blind, randomized, placebo-controlled study, we have examined the effect of 1% prilocaine 20 ml, plain or alkalinized, or saline, instilled into the knee joint after arthroscopy. Linear analogue scale (LAS) pain scores were assessed at six times after operation and time to first request for analgesia, total analgesic consumption and times to walking unaided and normal activities were recorded. There were no differences in any of these measurements at any time between the groups, except that the group which received intraarticular saline had significantly lower pain scores 8 h after operation than the groups which had alkalinized or plain prilocaine. We conclude that prilocaine, at both pH values, is ineffective in producing postoperative analgesia but as there were patients who received no analgesic agents and who had very little pain, we may also conclude that arthroscopy is not a consistently painful procedure and is not a good model for assessing the efficacy of local anaesthetic agents.