A 54-year-old healthy woman, gravida 3, para 3, with morbid obesity is seen in the clinic for a recurrent rectal prolapse 1 year after posterior suture rectopexy. She reports a bulge in the vagina for many years that has not changed with the rectopexy. Colonoscopy shows a redundant sigmoid colon. Which of the following most likely contributed to the recurrence of rectal prolapse?