Defining the optimal spread of local anesthetic during pericapsular nerve group (PENG) block may help to avoid short-term motor block (reply to Aliste et al)

Abstract

Dear Editor We congratulate with Aliste et al, as we read with great interest their study showing a comparable efficacy between pericapsular nerve group (PENG) block and suprainguinal fascia iliaca block in terms of postoperative analgesia and opioid consumption after hip arthroplasty, although the first was associated with a faster motor recovery. These results reinforce those highlighted by a previous study conducted by our group, which already suggested the PENG block as a valid analgesic and motorsparing regional anesthesia technique to manage postoperative pain following total hip replacement. However, Aliste et al reported several patients with postoperative shortterm motor weakness following PENG block regarding both knee and hip motion (45%–50% at 3 hours and 25%–50% at 6 hours, respectively). One could speculate that motor weakness may result from local anesthetic (LA) spread to femoral nerve (FN), as noted by the authors. The femoral nerve involvement after PENG block has already been reported by Yu et al in two patients with hip fractures. The possible mechanisms of femoral nerve involvement during PENG block performance may be explained by three hypothesis: ► Medial injection: the injection is performed medial to iliopubic eminence (IPE) rather than lateral. In this case, LA may rise along the medial margin of iliopsoas muscle (IPM) reaching FN. ► High volume: an elevated volume of LA, even if the needle is correctly placed, may spread through the abovementioned anatomical planes toward FN. ► Intramuscular injection: the needle does not pierce the IPM epimysium, thus the periosteum is not reached. This may result in an inadvertent intramuscular injection with LA spreading through the muscle to femoral nerve; a similar mechanism has already been described for other regional anesthesia techniques. 5 We would be curious to get Aliste et al opinion on strategies to potentially avoid the femoral nerve. In our practice, once the needle tip has been placed between the iliopsoas tendon (IPT) and periosteum, lateral to IPE, we find it helpful to inject 1–2 mL of saline solution in order to observe an ovalshaped spread under the IPM with the IPT lifted up; it is only then will we complete the injection with a total volume of 20 mL of LA.