Purpose: 
To evaluate whether the ratio of rectus abdominis muscle to surgical pelvic defect (M:P ratio) calculated using preoperative imaging correlates with postoperative outcomes in patients undergoing vertical rectus myocutaneous (VRAM) muscle flap pelvic reconstruction.

Methods:
A single centre retrospective review was performed on patients who underwent abdominoperineal resection (APR) or pelvic exenteration (PEx) with immediate VRAM reconstruction. Preoperative CT abdomen/pelvis was used to calculate rectus muscle volume and MRI pelvis was used to calculate planned surgical pelvic defect volume. M:P ratios were compared to outcomes using independent t-tests. Outcomes extracted from electronic medical records included major complications (wound dehiscence, complete flap loss, surgical drainage), minor complications (partial flap loss or dehiscence, small hematoma/seroma, local infection), and time to wound healing. 

Results:
Of 31 patients, 25 underwent APR and 6 PEx. 26 of 31 patients had complete wound healing. There were 3 major and 14 minor complications. The average M:P ratio was 0.3 (STD 0.2) and had no significant impact on major or minor complication rates (p=0.84 and p=0.90). Regression analyses demonstrated a negative correlation of M:P ratio and time to wound healing.

Conclusions:
The lack of association of M:P ratios with postoperative complications suggests limited utility of M:P ratios as a preoperative index of surgical outcomes. Conversely, lower M:P ratios were associated with longer time to complete wound healing, supporting current theories that pelvic defect obliteration contributes to improved outcomes. It additionally supports the value of preoperative imaging in identification of patient characteristics as possible prognostic markers.

Pelvic Reconstruction with the VRAM Flap: Does Preoperative Muscle-to-Surgical Pelvic Defect Ratio Affect Postoperative Outcomes?