No quadriceps muscle weakness following anterior quadratus lumborum block compared with placebo: a randomized, non-inferiority, blinded, volunteer trial

Background and aims Anterior quadratus lumborum block is a truncal block, applied in close proximity to the lumbar plexus, potentially causing lower limb weakness. This trial aimed to evaluate whether a unilateral anterior quadratus lumborum block caused quadriceps muscle weakness compared with placebo. Methods In this randomized, non-inferiority, triple-blind trial, 20 healthy volunteers received an active unilateral anterior quadratus lumborum block with 30 mL ropivacaine 0.75% and a placebo block on the contralateral side. Primary outcome was change in maximal quadriceps muscle strength from baseline to 60 min postblock compared with placebo. Secondary outcomes were change in single-leg 6 m timed hop test, change in Timed-Up and Go test, change in mean arterial pressure from baseline to 30 min postblock and dermatomal affection. Results There was no statistically significant difference in changes in maximal quadriceps muscle strength between active and placebo block; 15.88 N (95% CI −12.19 to +43.94), p non-inf =0.003, indicating non-inferiority. Timed-Up and Go test was performed significantly faster 60 min postblock; −0.23 s (95% CI −0.38 to −0.08, p=0.005). Mean change in mean arterial pressure from baseline to 30 min postblock was 4.25 mm Hg (95% CI 0.24 to 8.26, p=0.04). Dermatome testing revealed an affection primarily of the lower abdomen (Th10-L1) with the active block. Conclusion In this randomized controlled trial including healthy volunteers a unilateral anterior quadratus lumborum block does not cause statistical or clinical significant motor block of the quadriceps muscle compared with placebo. When administered correctly, the block can be used for procedures where early postoperative mobilization is essential. Trial registration number NCT05023343 .