Posterior Component Separation (PCS) with Transversus Abdominis Release (TAR) is an intraoperative surgical technique performed by the surgeon when a standard retromuscular repair, such as the Rives-Stoppa technique, does not allow for tension-free midline closure. In such cases, additional myofascial release is required, and PCS with TAR is subsequently performed to achieve adequate medial advancement of the abdominal wall components and enable secure, tension-free closure of the midline defect.

Changes in preoperative radiological indices following Botulinum Toxin A (BTA) injection will be assessed using abdominal computed tomography (CT) scans. The Rectus-to-Defect Ratio (RDR) will be calculated on pre- and post-injection CT imaging; each 0.5-point increase in RDR is associated with an approximate 20% linear reduction in the need for anterior myofascial release (AMR). The Component Separation Index (CSI) will be determined on axial CT images using the aorta as a fixed reference point and the medial borders of the rectus abdominis muscles. Abdominal cavity volume will be estimated using the ellipsoid volume formula based on craniocaudal, transverse, and anteroposterior diameters measured on CT imaging. Pre- and post-BTA values will be compared to evaluate improvement in abdominal wall compliance and anatomical reconstruction parameters.

Two surgical strategies will be considered based on abdominal wall reconstruction requirements: (A) Posterior Component Separation (PCS) with Transversus Abdominis Release (TAR), and (B) Rives-Stoppa repair, performed when no myofascial release is required. For PCS with TAR procedures, the Posterior Bridging Ratio (PBR) and Anterior Bridging Ratio (ABR) will be assessed as the proportion of the peritoneal sac used as a bridge to achieve tension-free closure of the posterior and anterior fascial layers, respectively. The extent of ABR and PBR will be analyzed in relation to the preoperative effect of Botulinum Toxin A (BTA) injection. In particular, higher percentages (>50%) of PBR and ABR will be considered indicative of poor BTA efficacy, intermediate values (25-50%) of partial efficacy, and low values (0-25%) of good to very good BTA efficacy. The relationship between changes in preoperative indices after BTA administration and the selected surgical approach will be evaluated.