Injectate spread following posterior hip pericapsular block: a preliminary single-case anatomical observation in a formalin-fixed cadaver.

Background: Pericapsular nerve group (PENG) block may not reliably address posterior capsular innervation, potentially contributing to residual pain after hip surgery. The posterior hip pericapsular block (PHPB) was developed as a posterior periarticular injection to complement anterior approaches, but its anatomical spread has not been well characterized. Methods: In a formalin-fixed cadaver, ultrasound-guided PHPB was performed with injectate deposited in the fascial plane between the piriformis muscle and the ischiofemoral ligament adjacent to the posterior hip capsule. A total of 15 mL injectate, consisting of 13 mL of 0.25% ropivacaine mixed with 2 mL of 1% methylene blue, was administered. Layer-by-layer anatomical dissection was subsequently performed to assess injectate distribution along the posterior hip capsule and surrounding neural structures, including the sciatic nerve. Results: Dissection demonstrated dye distribution along the posterior hip capsule and the ischiofemoral ligament, with staining of small neural structures grossly consistent with previously described posterior articular branches. No macroscopic dye spread was observed on the superficial surface of the piriformis muscle or along the exposed sciatic nerve trunk. Conclusion: This preliminary single-case cadaveric observation demonstrated posterior pericapsular dye distribution after ultrasound-guided PHPB. The findings are descriptive and specimen-specific, and do not establish anatomical reproducibility, clinical efficacy, safety, or sciatic nerve sparing. Further validation in fresh-frozen cadavers with standardized injection protocols is warranted.