Background: Pelvic organ prolapse is one of the most common benign gynecological disorders in middle-aged and elderly women, and it has a significant negative impact on women's social, physical, and psychological health. Sacrospinous ligament fixation (SSLF) is one of the main surgical procedures for reconstructing pelvic floor defects. In previous studies, the ischial spine fascia fixation (ISFF) technique developed by our team has been shown to be a safe and effective alternative to SSLF. However, both procedures have inadequate support for the anterior vaginal wall. Therefore, based on the traditional ISFF, we fix the anterior vaginal wall to the ipsilateral ischial spine fascia to enhance support for the anterior vaginal wall. This modified procedure is called modified ISFF. This trial aims to compare the subjective and objective therapeutic effects, recurrence rates, quality of life, perioperative parameters, and complications of modified ISFF and SSLF in the treatment of patients with pelvic organ prolapse of degrees II-IV.

Methods: This trial is a randomized controlled multicenter non-inferiority trial. The primary outcome measure is the composite surgical success rate at one-year follow-up, defined as the absence of subjective vaginal bulge symptoms, no need for retreatment, and absence of POP-Q points at or beyond the hymen or vaginal introitus, i.e., Aa, Ba, C, Ap, Bp all < 0 cm. The secondary outcomes include anatomical outcomes of each vaginal segment based on the POP-Q score, subjective improvement in quality of life evaluated by questionnaires (PFIQ-7, PFDI-20, PISQ-12, and PGI-I), perioperative parameters (operation time, blood loss, length of hospital stay, pain VAS score, hospital costs), and complications. Data analysis will be conducted according to the intention-to-treat principle. Based on a composite success rate of 88% and a non-inferiority margin of -10% (one-sided α = 0.025, β = 0.2), 370 patients will be recruited from 9 centers, including a 10% dropout rate. The purpose of this study is to investigate whether modified ISFF is non-inferior to SSLF in terms of clinical efficacy and complications.

Discussion: This multicenter non-inferiority trial will evaluate the effectiveness and safety of modified ISFF compared to SSLF in symptomatic patients with degrees II-IV uterovaginal prolapse. If modified ISFF is proven to be non-inferior to SSLF, it would be a preferable alternative for patients with a shorter vaginal length and those who have difficulties with SSLF due to anatomical factors.

Inclusion Criteria:

• Patients with symptomatic mid-pelvic organ prolapse (POP-Q stage ≥ II) who may concurrently have anterior and/or posterior pelvic organ prolapse.
• Patients willing to undergo long-term follow-up for at least one year.
• Patients willing to sign an informed consent form and participate in this study.

Exclusion Criteria:

• Patients who have undergone previous POP or urinary incontinence surgery with the use of implant materials.
• Patients who require simultaneous anti-urinary incontinence surgery for the current procedure.
• Contraindications for general anesthesia and surgical intervention, such as severe medical comorbidities that render the patient unable to tolerate surgery.
• Patients who wish to preserve the uterus.
• Patients in the active phase of genital, urinary, or systemic infections.
• Patients who, for other reasons (such as having genital malignancies), choose not to undergo SSLF/modified ISFF surgical intervention at the moment.
• Patients who are unable or unwilling to attend follow-up visits (excluding those who may be willing to participate in telephone follow-up).