We read with interest Martin et al. ’s1study on the antiinflammatory effect of peripheral nerve block after total knee arthroplasty. We would be delighted to see such an outcome; however, we wish to raise the following questions on the conclusion drawn that peripheral nerve blocks have a clinical antiinflammatory effect, especially when there was no change in inflammatory mediator levels. This study’s primary outcome measure was IL-6 at 24 hours. Statistically it was powered to demonstrate a 50% reduction in IL-6 at 24 hours, with 20 patients per treatment arm. This study was not powered to demonstrate the clinical outcome measures for inflammation–knew circumference and temperature. Therefore we cannot draw any definitive conclusions regarding peripheral nerve blocks and any potential anti-inflammatory effects until further work is done. Second, the absence of sham blocks here can lead to observer bias. Third, the use of 20 ml of 0.75% Ropivicaine for each femoral and sciatic nerve block could have contributed towards reduced temperature and edema, given that studies have shown that Ropivicaine’s vasoactive properties cause a reduction in blood flow.2,3Lastly, and most importantly, the reduced circumference and temperature seen may merely be the result of improved pain control and mobility. The conclusions drawn were based only on findings from postoperative days 1 to 7, with no significant differences seen between groups at a later follow-up.

We therefore feel that further investigation is required before concluding that peripheral nerve blocks reduce clinical or biochemical inflammation, and if it does so, whether it actually translates into long-term patient benefit.

*Toronto Western Hospital, University of Toronto, Toronto, Canada. dod00@hotmail.com

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. Anesthesiology 2008; 109:484–90
Burke D, Joypaul V, Thomson MF: Circumcision supplemented by dorsal penile nerve block with 0.75% ropivacaine: A complication. Reg Anesth Pain Med 2000; 25:424–7
Wienzek H, Freise H, Giesler I, Van Aken HK, Sielenkaemper AW: Altered blood flow in terminal vessels after local application of ropivacaine and prilocaine. Reg Anesth Pain Med 2007; 32:233–9