Anatomical spread of the novel transversus abdominis–rectus abdominis aponeurotic (TARAA) block: a cadaveric comparison with lateral transversus abdominis plane (TAP) and combined TAP-rectus sheath blocks

Effective analgesia of the abdominal wall remains a clinical challenge. The transversus abdominis plane (TAP) block and rectus sheath (RS) block are widely applied for postoperative analgesia, yet their differing dermatomal coverage often necessitates combined techniques for comprehensive pain control. Such combinations, however, require multiple injections, which may increase procedural time and complexity. The current cadaveric study aimed to describe and evaluate a novel ultrasound-guided block, the Transversus Abdominis–Rectus Abdominis Aponeurotic (TARAA) block, hypothesized to achieve broad and continuous spread of injectate across both the rectus sheath and transversus abdominis compartments using a single injection. A comparative cadaveric study was performed in accordance with the Quality Appraisal for Cadaveric Studies (QUACS) principles. Fifteen fresh-frozen adult cadavers were used, and thirty hemi-abdomens were randomly assigned to receive one of three techniques with injections of 20 mL of dye-labeled ropivacaine under ultrasound guidance: lateral TAP block, combined TAP + RS (10 mL each), or the novel TARAA block. Following a 30-minute diffusion period, blinded anatomical dissections were carried out to measure the cranio-caudal and medio-lateral spread of the dye. Each technique was performed in 10 hemi-abdomens. Because the rectus sheath and TAP components of the combined technique produced anatomically separate stains, they were measured separately, yielding four analysed groups (TARAA 20 mL, TAP 20 mL, RS 10 mL and TAP 10 mL; n = 10 each). Groups were compared using a linear mixed-effects model with cadaver as a random effect to account for the correlation of observations obtained from the same cadaver. The TARAA block produced greater cranio-caudal spread (mean 9.4 ± 1.58 cm) than the lateral TAP block with 20 mL (6.5 ± 1.65 cm; p < 0.001) and the 10-mL TAP component of the combined technique (4.7 ± 1.42 cm; p < 0.001), and did not differ significantly from the 10-mL RS component of the combined technique (8.2 ± 1.32 cm; p = 0.49). Medio-lateral spread was also greatest after TARAA (11.6 ± 1.07 cm) compared with TAP 20 mL (8.2 ± 2.15 cm) and the 10-mL TAP component (6.3 ± 1.16 cm) ( p < 0.001 for both). A single 20-mL TARAA injection produced greater anatomical spread than a lateral TAP block of the same volume, and cranio-caudal spread not significantly different from that of the RS component of a combined TAP + RS technique, while requiring only one injection. Nerve involvement, sensory blockade and analgesic efficacy were not assessed; whether this anatomical spread translates into effective abdominal wall analgesia is a hypothesis that requires clinical investigation.