To The Editor: We read with interest the article "Continuous
Infusion of Local Anesthetic at Iliac Crest Bone-Graft Sites for Postoperative
Pain Relief. A Randomized, Double-Blind Study" (2006;88:2606-12) by
Morgan et al., which demonstrated the ineffectiveness of continuous local
anesthetic infusion to the iliac crest bone-graft site. This result is
surprising and not in accordance with that found in a quite similar, recent
investigation1. Several methodological concerns have to be
discussed.
The analgesic regimen of continuous infusion of 0.5% bupivacaine at a rate
of 2 mL/hr might be insufficient because of a limited spread of this small
volume. A continuous infusion of 0.2% ropivacaine at a rate of 5 mL/hr over
forty-eight hours was successfully used in this surgical context1.
The volume may be more important than the concentration in this setting. This
may explain the differences observed between the two studies, but additional
studies will be needed to clarify this issue.
The results of the study by Morgan et al. may have been compromised by the
influence of the pain from the surgical recipient site. This can influence the
pain perception at the iliac bone graft site. This factor also may have been
influenced by the heterogeneous surgical locations, including various graft
harvest and recipient sites. Additionally, the lack of a precise explanation
of whether pain at rest or pain in motion had been assessed is important in an
analysis showing the limited potency of narcotics to treat activity-induced
pain2,3.
The authors calculated that sixty patients would have been necessary to
achieve power, so, with fifty-eight complete data sets, the study was
underpowered.
Finally, regarding the repetitive pain assessment, the statistical tests
were not correct since no correction for repeated measurement had been
made.