We read with interest the letter by O’Donnell on our study on the antiinflammatory effect of peripheral nerve block after total knee arthroplasty.1We clearly stated that the mechanisms underlying the observed antiedematous effect of peripheral nerve block is unknown. We agree that this study was powered to demonstrate a 50% reduction in IL-6 24 h after surgery and not the clinical criteria as its primary outcome. We clearly identified in our discussion the absence of sham as a limitation. The putative vasoconstriction as a result of ropivacaine has been in fact demonstrated for terminal vessels, which is not the case in our study. We already discussed in our manuscript the impact of increased mobility on inflammation. We agree that mobility might have influenced edema, but associated reduced temperature suggests an antiinflammatory effect. We never suggested that this observed antiedematous effect of peripheral nerve block might translate into long-term patient benefit, but we still think that it probably contributes to the observed improvement in functional recovery.

*Hôpital Raymond Poincaré, Garches, France. dominique.fletcher@rpc.aphp.fr

Martin F, Martinez V, Mazoit JX, Bouhassira D, Cherif K, Gentili ME, Piriou P, Chauvin M, Fletcher D: Antiinflammatory effect of peripheral nerve blocks after knee surgery: Clinical and biologic evaluation. Anesthesiology 2008; 109:484–90