A 46-year-old man presents to your office with rectal bleeding associated with bowel movements and prolapse of tissue from his anus that spontaneously reduces. Recent colonoscopy demonstrated moderate internal hemorrhoids and a 3-mm tubular adenoma in the sigmoid colon removed with cold forceps. A single rubber band ligation was performed during this procedure. Two days later, he presents to the emergency department with a fever of 102°C, pelvic pain, and urinary retention. The most definitive treatment is