We read with great interest the article by Brixel et al.1  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 it was quadratus lumbar block 2, after a while, it may have spread to quadratus lumbar block 1 + 2 + 3.

Third, the authors have assessed the extent of sensory blockade in the nine hip areas with a cold glass vial. However, the authors did not measure whether there was sensory loss over a wider range, including the areas of femoral and obturator innervation. Next, the authors suggested that obturator and femoral nerves were not blocked after posterior quadratus lumborum block, which may contribute to the lack of analgesia. However, the innervation of the hip joint is primarily provided by the articular branches of obturator and femoral nerves,2  which could not be measured by cutaneous sensation.

This letter was supported by the National Natural Science Foundation of China (grant No. NSFC 81772130) and the National Key R&D Program of China (grant No. 2018YFC2001800).

The authors declare no competing interests.

1.
Brixel
SM
,
Biboulet
P
,
Swisser
F
,
Choquet
O
,
Aarab
Y
,
Nguyen
H
,
Bringuier
S
,
Capdevila
X
:
Posterior quadratus lumborum block in total hip arthroplasty: A randomized controlled trial.
Anesthesiology
.
2021
;
134
:
722
33
2.
Tinnirello
A
,
Todeschini
M
,
Pezzola
D
,
Barbieri
S
:
Pulsed radiofrequency application on femoral and obturator nerves for hip joint pain: Retrospective analysis with 12-month follow-up results.
Pain Physician
.
2018
;
21
:
407
14