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Reply to Dr Pascarella and colleagues

To the Editor We thank Dr Pascarella and colleagues for their interest in our recent trial investigating pericapsular nerve group (PENG) block for total hip arthroplasty. The authors highlight the possibility of inadvertent local anesthetic (LA) spread to the femoral nerve and solicit our opinion to prevent such occurrence. In our humble opinion, unintended femoral blockade after PENG block stems from excessive LA injectate rather than suboptimal technique. In GirónArango et al’s original description of PENG block, LA can be seen to diffuse ventrally towards the femoral nerve. Presumably, GirónArango et al possessed perfect technique since they devised the latter. Although most published reports employ a 20 mLvolume, the optimal (motorsparing) injectate for PENG block has yet to be validated with robust dosefinding methodology. From a scientific standpoint, such investigation would present an interesting challenge. Since PENG blocks target the articular branches of the femoral and accessory obturator nerves, their success cannot be evaluated with sensorimotor blockade. Furthermore, because the hip joint also receives innervation from the sacral plexus, postoperative pain cannot be used to infer block failure. One possible solution, reminiscent of the recent strategy adopted for suprainguinal fascia iliaca blocks, would be to inject and dissect cadaveric specimens. Block success would be therefore defined as spread of methylene blue over the pubic ramus (between the anteroinferior iliac spine and iliopubic eminence) accompanied by absent staining of the femoral nerve. Once their motorsparing volume elucidated, PENG blocks could perhaps become the analgesic gold standard for ambulatory hip arthroplasty.