Refining evidence on motor‐sparing regional analgesia for hip arthroplasty: a reply

We wish to thank Drs Li and Guo for their correspondence [1] and thoughtful consideration of our work [2]. We appreciate their comments regarding our methodology and suggestions for future studies and would like to address them. We acknowledge that our standardised protocol of spinal anaesthesia with a posterolateral surgical approach to total hip arthroplasty limits the generalisability of our findings. The effectiveness of the erector spinae plane (ESP) block is influenced inherently by the diffusion of local anaesthetic to relevant muscles and nerves and spreads preferentially to posterior structures [3]. In contrast, the pericapsular nerve group (PENG) block targets the distal sensory branches of the lumbar plexus, supplying the anterior hip joint and capsule [4]. Intuitively, the PENG block may have advantages for total hip arthroplasty using an anterior approach but, so far, the evidence available shows limited benefit over placebo [5] and there is a lack of studies comparing PENG and ESP in this surgical subpopulation. Early pain scores were low in patients who underwent spinal anaesthesia for total hip arthroplasty and were included in randomised clinical trials [6]; it is possible that the low opioid usage in both groups in our study validates these findings. Our study did not include patients with baseline chronic pain or opioid therapy as they may exhibit altered pain perception and different patterns of peri-operative analgesic use compared with patients who are opioid-naïve. We agree with Drs Li and Guo that this population should be included in future studies as the relative effectiveness of specific regional analgesic interventions may be elucidated more clearly when pain is not as well-controlled with conventional multimodal analgesia. We also agree that our primary outcome of opioid consumption in the first 24 h after surgery gives very limited assessment of postoperative recovery. Effective opioid-sparing analgesia is a crucial component of enhanced recovery protocols and represents a necessary initial intervention that affects other outcomes, such as early mobility and the prevention of postoperative complications. Research involving regional anaesthesia and peri-operative analgesia will benefit from the collection and reporting of more patient-reported outcomes including satisfaction, pain interference and quality of recovery, as these measures may help differentiate interventions even when pain intensity and opioid usage are similar in the setting of multimodal pain management. We reported no difference in the incidence of chronic postsurgical pain (CPSP) at 3 months postoperatively, but this was a secondary outcome and underpowered. The transition from acute to chronic pain after surgery has a multifactorial aetiology, and it is unlikely that a single, short-lived intervention such as a single-injection block would prevent it. However, given that poorly controlled postoperative pain is a known risk factor for CPSP, the combination of low opioid use in the immediate postoperative period and low incidence of CPSP in our study is encouraging. Finally, we recognise that block selection should consider cost-effectiveness and resource availability. We do not believe that the performance of ESP or PENG block differs significantly in terms of equipment or time, but there are differences in patient positioning, sono-anatomy and familiarity with each technique. We believe that block selection is ultimately a medical decision based on the specific clinical scenario that should be guided by input from anaesthetists, surgeons, patients, caregivers and other peri-operative staff.