This comparative study evaluates the short- and long-term outcomes of Quadrant-based Intersphincteric Resection (Q-ISR) versus traditional subtotal ISR (Sub-ISR) and conventional/total ISR (t-ISR) in patients with ultra-low rectal cancer undergoing sphincter-preserving surgery, with short-term endpoints focusing on perioperative safety (operative time, blood loss, length of stay, and postoperative complications such as Clavien-Dindo grade ≥II, anastomotic leakage/stricture, and stoma reversal) and long-term endpoints assessing anorectal function recovery (LARS and Wexner scores after stoma closure) and oncologic efficacy (R0 resection, recurrence patterns, and survival outcomes), aiming to determine whether a quadrant-tailored resection strategy can better balance tumor control with anal function preservation.