FRONT block: a cadaveric study of a dual-plane injection block targeting femoral rami and obturator nerve trunk for anterior hip joint analgesia

Background The quest for a single nerve block to anesthetize all anterior hip articular nerve branches has long been a challenge for anesthetists, particularly in targeting the obturator nerve (ON). The FRONT block (Femoral Rami Obturator Nerve Trunk) is a newly developed dual-injection technique providing comprehensive anesthetic coverage of the anterior hip joint by targeting both the sensory femoral rami and the ON trunk. Methods 15 intact cadaveric sides from eight embalmed cadavers were dissected after FRONT block administration with one injection and two dye deposits in the iliopsoas plane and in the subpectineal compartment under dynamic ultrasonography. The primary outcome was dye spread to the sensory hip articular branches of the femoral nerve (FN) and the ON trunk evaluated during the gross anatomical dissection. Secondary outcomes included identifying landmarks for accurate injection of dye and measuring the distance from the needle trajectory to the femoral and the lateral femoral cutaneous nerves (LFCN). Results In 86.7% of cadaver sides, the FRONT block successfully covered both the sensory femoral rami and the ON trunk. The injection was performed 6.7 cm (SD 1.6) distal to the anterior superior iliac spine with a medial deviation of 1.8 cm (SD 2.1). The average distance from the needle trajectory to the FN was 0.8 cm (SD 0.4) and 3.7 (SD 2.1) cm to the LFCN. Conclusion The FRONT block offers reliable coverage of the anterior hip joint and capsule. Proficiency in ultrasound-guided regional anesthesia is important during clinical applications.