We read with great interest the article by Brixel et al. entitled “Posterior Quadratus Lumborum Block in Total Hip Arthroplasty” published in May 2021 in Anesthesiology. We appreciate the authors’ great work; however, after reading the article carefully, we also found some worthwhile issues that we would like to raise to the investigators.

First, the authors mentioned that this study was a double-blind trial. Contrary to the authors’ claim, the patients were not blinded. Since the authors graphically mapped cutaneous sensory loss in figure 4 in the article, patients in the ropivacaine group were aware that they had been injected with a local anesthetic.

Second, the authors indicated that the anesthesiologist recorded the final solution spread on an anatomical diagram. However, the article did not mention when it was recorded. In our opinion, the diffusion of the local anesthetic varied over time, and when the anesthesiologist documented that...

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