Anatomic evaluation to compare the dye spread with ultrasound-guided pericapsular nerve group (PENG) injection with or without an additional suprainguinal fascia iliaca (SIFI) injection in soft embalmed cadavers

Novel interfascial plane blocks like PEricapsular Nerve Group (PENG) and SupraInguinal Fascia Iliaca (SIFI) blocks are effective for management of hip fracture pain. We compared the difference in the distribution of the dye injected and nerves stained by the addition of the SIFI block to the PENG block.

A total of 24 designated dye injections were performed in eight soft-embalmed cadavers. Under ultrasound guidance 20 ml green ink injected bilaterally in PENG block and 30 ml methylene blue dye was injected in the SIFI block on the right side. The cadavers were dissected 24 h later to assess the extent of dye spread.

Extensive spread of dyes was seen on both side of iliacus muscle on the right side, but blue dye was not visible medial to the psoas tendon. The subcostal and iliohypogastric nerves were stained green in the infra-inguinal region. On the left side (PENG alone), the anterior division of the obturator, femoral and saphenous nerve (7/8) and iliohypogastric nerves (3/8) were stained in the infrainguinal region. In the suprainguinal region, the femoral nerve (5/8), accessory obturator nerve (3/8), lateral femoral cutaneous (1/8) and nerve to rectus femoris (4/8) were stained. The main obturator nerve trunk was spared with both injections while its anterior branch and accessory obturator nerve were stained with the PENG injection.

The study findings indicate that combined PENG + SIFI injections lead to an extensive craniocaudal and longitudinal spread along the iliacus muscle. We perceive that the combination of these two injections will have a superior clinical outcome.