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Background and Aims PENG block is routinely implemented as a part of multi-modal analgesia for hip surgical procedures. However, a recent cadaver dissection suggest it is not a true pericapsular block. We in 2 cadavers executed cross-sections after PENG injection with methylene blue dye.

Methods In 2 fresh (4 sides) cadavers (76 and 86 years), ultrasound guided PENG block (0 mL 0.1% methylene blue dye) was administered with linear probe (sonosite 3-12mHz) in real time. The cadavers were cross-sectioned at the level of ASIS and below the inguinal ligament. The spread of the dye was noted.

Results In 4 specimens, the spread of dye was noted in following areas table 1. Intra-osseous spread was noted in 2 specimens. Figure 1 In all specimens the dye was dorsal and lateral to iliacus muscle.

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Abstract OP073 Figure 1

Methylene blue dye is observed dorsal and lateral to iliacus muscle after right injection and an intra-osseus spread in the left PENG injection. The orange asterix depicts the site of PENG injection. LFCN-lateral femoral cutaneous nerve; TFL-tensor fascia lata; VL-vastus lateralis; IPE-ilio-pectineal eminence; PT-psoas tendon; GLmax-gluteus maximus

Conclusions Cross-sections reveal a more deeper tissue plane diffusion. In our study, the intra-osseous identification in 2 specimens was a revelation. To our knowledge, this is the first occasion where dye spread from an inter-fascial plane is recognized inside the marrow. We recommend applying colour mode for PENG injection to be scrutinize abnormal vasculature.