Anatomical and Radiological Assessments of Injectate Spread Stratified by the Volume of the Pericapsular Nerve Group Block

Abstract

BACKGROUND:The pericapsular nerve group (PENG) block was recently suggested as a regional technique for managing acute pain after hip surgery. However, few anatomical studies have confirmed the spread of injectate during the PENG block. This cadaver study aimed to analyze injectate spread to the target nerves during single-injection ultrasound-guided PENG block. METHODS: Ultrasound-guided PENG block with 3 different injectate volumes (10, 20, or 30 mL) was performed in 18 cadavers. Injectate spread by the volume was first evaluated on computed tomography, followed by cadaver dissection. The spread of the dye over the pelvis and lower limb was evaluated. RESULTS: The articular branches of the femoral nerve were stained nearly sufficiently with 20and 30-mL specimens. The femoral nerve itself was stained simultaneously in six of 12 (50%) 20-mL specimens and 12 of 12 (100%) 30-mL specimens. The accessory obturator nerve was observed only in three (9%) of 36 specimens. The articular branches of the obturator nerve were rarely affected, regardless of injectate volume (1/12, 10 mL specimens; 2/12, 20 mL specimens; 1/12, 30 mL specimens; P > .999). Rather, the obturator nerve was affected. However, the obturator nerve was not stained consistently even with 30 mL of injectate (50%). CONCLUSIONS: After combining the dissection and radiological findings, the single-injection ultrasound-guided PENG blocks with volumes of 10, 20, and 30 mL do not support motor sparing or selective anterior hip capsule innervation in a clinical setting. If early rehabilitation is needed, high-volume PENG block might not be the ideal option, and persisting pain after PENG block might be attributed in part to the lack of obturator nerve articular branches blockade.

Effect of Pericapsular Nerve Group Block with Different Concentrations and Volumes of Ropivacaine on Functional Recovery in Total Hip Arthroplasty: A Randomized, Observer-Masked, Controlled Trial

“…And a recent cadaveric study 16 indicated that for PENG block, the maximum effective volume of dye in 90% of cases (MEV90) of methylene blue required to spare the FN is 13.2 mL, which indicates that motor weakness may result from high volume of ropivacaine spread to FN. Furthermore, Kim JY 23 reported the anatomical spread of injectate during PENG block and found that the articular branches of the FN were stained with dye in nearly all 20 mL and 30 mL specimens, which was consistent with the quadriceps weakness observed clinically after PENG block. In addition, theoretically, if PENG block only blocks the sensory fibres, the change in concentration will not lead to a change in postoperative muscle strength but will only affect the postoperative sensation at most.…”

Effects of Different Volumes of Ropivacaine for Pericapsular Nerve Group Block on Incidence of Quadriceps Weakness and Analgesic Efficacy Following Hip Arthroplasty: A Randomized Controlled Trial

“…For example, Ahiskalioglu et al determined that injecting a 30 ml volume of local anesthetic when performing a PENG block can result in the upward diffusion of the anesthetic, potentially resulting in a lumbar plexus block-like effect [ 15 ]. In a recent anatomical study, simultaneous staining of the femoral nerve was observed in 6/12 (50%) 20 ml specimens and 12/12 (100%) 30 ml specimens [ 16 ]. Additional randomized controlled clinical studies will be necessary to clarify whether high-volume PENG block can replace lumbar plexus block.…”

Comparing the Pericapsular Nerve Group Block and the Lumbar Plexus Block for Hip Fracture Surgery: A Single-Center Randomized Double-Blinded Study

“…Regarding the LA volume used in our study, the 20 mL administered for the PENG block reflects the volume recommended by Girón-Arango et al [ 11 ]. A high-volume PENG block might not be an ideal option, and persistent postoperative pain may be partially attributed to the lack of an obturator nerve articular branch blockade [ 24 ]. In a 2015 LPB dose-finding trial, Sauter et al [ 25 ] concluded that the minimum effective volume of 0.5% ropivacaine in 95% of patients (ED95) was 36 mL.…”

“…The superior performance of the PENG block may be due to the patient’s posture during the procedure (a supine versus a lateral decubitus). The time to analgesic requirement indicates that the PENG block may result in shorter analgesia and reduced total intravenous fentanyl consumption over 24 h. We speculate that the reduced block duration is a result of the injected LA spreading around the pericapsule, causing a dispersion effect [ 24 ], and that the concentration of the LA in one large muscle affects the duration of the pain block [ 17 ]. Our results were limited to single-injection blocks and further studies are needed to confirm our findings regarding continuous PENG blocks and LPBs.…”