Background: This study aimed to investigate the analgesic efficacy and motor block profile of single-shot transmuscular quadratus lumborum block (QLB) in comparison with those of suprainguinal fascia iliaca block (FIB) in patients undergoing hip arthroplasty. Methods: This randomized, double-blinded, controlled trial included adult patients undergoing hip arthroplasty under spinal anesthesia. Patients were allocated to one of two groups according to the regional block received: FIB group (n=19) or QLB group (n=17). Both study groups were compared with regard to the duration of analgesia (primary outcome), block performance time, pain during positioning for spinal anesthesia, total morphine consumption in the first postoperative 24-h period, quadriceps muscle power, and static and dynamic visual analog scale. Results: Thirty-six patients were included in the final analysis. Both study groups had comparable durations of analgesia. Postoperative visual analog scale (static and dynamic) values were comparable between the two groups in most readings. The block performance time was shorter in the FIB group. The number of patients with pain during positioning for the subarachnoid block was lower in the QLB group. The total morphine requirement during the first 24 h was marginally lower in the FIB group, whereas the quadriceps motor grade was higher in the FIB group than in the QLB group at 4 h and 6 h after surgery. Conclusion: Both single-shot blocks, namely the suprainguinal FIB and transmuscular QLB, provide effective postoperative analgesia after hip arthroplasty. FIB showed slightly lower 24-h morphine consumption, while QLB showed better quadriceps motor power. Clinical Trial Registration: The study was registered at clinical trials registry system before enrollment of the first participant (NCT04005326; initial release date, 2 July 2019; https://clinicaltrials.gov/ct2/show/NCT04005326).

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