Impact of ropivacaine volume and concentration on functional recovery following surgical treatment of hip fractures: a randomized, observer-masked, controlled trial

Abstract Background: The pericapsular nerve group (PENG) block is a novel regional anaesthesia technique aiming to provide better hip analgesia without hampering motor function . However, the factor of pain on muscle strength cannot be ruled out and unexpected motor block has still been observed clinically. So it is unknown whether the motor-reservation is partly due to the effect of pain reduction and it is unknown whether this unexpected motor block is caused by the inappropriate dose of ropivacaine.Methods: We investigated the ropivacaine volume and concentration effect on muscle strength and analgesia. With ethical committee approval, 90 consenting patients undergoing surgical treatment of hip fractures were randomly allocated to receive one of three volume/concentration combinations of ropivacaine (20 ml/0.5%, 20 ml/0.25% and 10 ml/0.5%). The primary outcome measure was postoperative quadriceps strength using the knee extension test and Oxford muscle strength grading 12, with grouped scores of intact (5/5), reduced (1-4/5) and absent (0/5) measured at 6 and 12 hours postoperatively. Secondary outcomes included postoperative pain scores (0-10 numeric rating scale), blood pressure, patient movement assessments, patient satisfaction and side effects.Results: Overall, 10 ml of 0.5% ropivacaine resulted in a lower incidence of quadriceps motor block at 6 hours (76.7% vs. 40.0% vs. 46.7%; p<0.05), 12 hours (86.7% vs. 53.3% vs. 53.3%; p<0.05). No intergroup differences were found in terms of postoperative pain scores at any interval (p>0.05). Similarly, we found no significant differences in resting pain or exercise pain among the three groups . Conclusions: As for the PENG block, the effect of pain on muscle strength can be ruled out. Unexpected motor block of PENG block may be caused by inappropriate dose of ropivacaine. We found that 10 ml 0.5% ropivacaine resulted in better muscle strength, considering the significance of rapid rehabilitation, we recommend performing PENG block with 10 ml 0.5%Trial registration: ChiCTR2100052511 . Register Date 2021/10/30