Paul etal.  1should be congratulated for examining the body of evidence on the comparison of patient-controlled analgesia opioid or epidural analgesia with femoral nerve blockade for analgesia after a common operation, total knee arthroplasty. A meta-analysis, by pooling and analyzing statistically the results from several combinable studies, can increase the statistical power to detect small but clinically important treatment harms and effects. Paul et al.  clearly demonstrated that femoral nerve blockade improved analgesia and reduced opioid consumption compared with intravenous patient-controlled analgesia techniques.

The quality of the systematic review performed by Paul et al . is high, as evidenced by the comprehensive and systematic search of the literature and explanation of statistical tests and models used for their analyses. Furthermore, the authors (and the accompanying editorial2) clearly emphasize the limitations of their meta-analysis regarding comparison of single shot femoral nerve blockade (SSFNB) with continuous femoral nerve block, including that:

  1. Most of the data come from indirect comparisons, which are subject to the same biases as observational studies.

  2. Only two trials with a total of 69 patients directly compared the two techniques, and they came to conflicting conclusions.3,4 

  3. The different conclusions may be explained by the different local anesthetics used in these two studies (ropivacaine vs.  bupivacaine), so we question the appropriateness of combining these studies in a meta-analysis in which the type and dosage of local anesthetics are not considered a source of heterogeneity (as in this meta-analysis).

  4. Other studies exist, not included in this meta-analysis (for correct reasons), that contribute to the evidence base comparing SSFNB with continuous femoral nerve block. These and other studies support the use of continuous techniques.5 

In reality there was only one study4comparing SSFNB with continuous femoral nerve block that used a technique considered clinically appropriate in 2010. In view of this and the above points, we were somewhat mystified by the contents of the highlighted box on the first page of the article, which stated “these studies do not demonstrate further improvement with continuous compared with single-shot femoral nerve block.” This finding, one of only two key findings in the highlighted box, is based on data which, by the authors' own admission, are “subject to the same biases as observational studies.” This is inconsistent with the subtitle of the article, “A Meta-analysis of Randomized Controlled Trials,” which suggests that the key results will be of the highest level of evidence.

We believe that this key message contained within the highlighted box is misleading and unsupported by the data, discussion, and accompanying editorial. This falls below the standard expected of a scientifically informed and scholarly process and does not do justice to the excellent meta-analysis and editorial.

On the issue of comparison of SSFNB and continuous femoral nerve block, the meta-analysis could come to only one conclusion: that there is conflicting evidence and more studies are required to determine which techniques are most appropriate for femoral nerve blockade for total knee arthroplasty. Anesthesiology appears to be promoting SSFNB in preference to continuous techniques for total knee arthroplasty. This is not an accurate reflection of current evidence and may influence practitioner's opinions, including those of surgeons, which may inhibit both appropriate clinical practice and innovation in this area.

We would strongly agree with the editorial2that continuous catheter techniques provide the ability to control the dosage of local anesthetic used and are preferred to SSFNB, where the inevitable tendency is to increase the initial dose, potentially impairing motor function. Analgesia is not the only goal of femoral nerve blockade, and early mobilization is a realistic goal when dilute concentrations of local anesthetic are used in a controlled fashion. Readers should be reminded that lack of evidence is not the same as evidence of lack of effect, and the commonsense approach outlined in the editorial should be strongly considered.

*St. Vincent's Hospital, Melbourne, Australia.

Paul JE, Arya A, Hurlburt L, Cheng J, Thabane L, Tidy A, Murthy Y: Femoral nerve block improves analgesia outcomes after total knee arthroplasty: A meta-analysis of randomized controlled trials. Anesthesiology 2010; 113:1144–62
Hadzic A, Houle TT, Capdevila X, Ilfeld BM: Femoral nerve block for analgesia in patients having knee arthroplasty. Anesthesiology 2010; 113:1014–5
Hirst GC, Lang SA, Dust WN, Cassidy JD, Yip RW: Femoral nerve block. Single injection versus  continuous infusion for total knee arthroplasty. Reg Anesth 1996; 21:292–7
Salinas FV, Liu SS, Mulroy MF: The effect of single-injection femoral nerve block versus  continuous femoral nerve block after total knee arthroplasty on hospital length of stay and long-term functional recovery within an established clinical pathway. Anesth Analg 2006; 102:1234–9
Ilfeld BM, Mariano ER, Girard PJ, Loland VJ, Meyer RS, Donovan JF, Pugh GA, Le LT, Sessler DI, Shuster JJ, Theriaque DW, Ball ST: A multicenter, randomized, triple-masked, placebo-controlled trial of the effect of ambulatory continuous femoral nerve blocks on discharge-readiness following total knee arthroplasty in patients on general orthopaedic wards. Pain 2010; 150:477–84