Clinical Evaluation of the Pelvic Floor Fatigue Index (PFFI)

Overview

Background: Ureteral stent-related symptoms vary considerably among patients despite similar surgical procedures and stent characteristics. Although several mechanisms have been proposed, the reasons for this interindividual variability remain incompletely understood. Pelvic floor muscle endurance may represent one of the patient-related factors contributing to symptom severity. The Pelvic Floor Fatigue Index (PFFI) is a novel ultrasound-based index developed to quantify pelvic floor muscle endurance by measuring the percentage decline in bladder base elevation during a sustained maximum voluntary pelvic floor contraction using suprapubic transverse B-mode ultrasonography. This prospective observational study aims to clinically evaluate the PFFI by investigating the association between preoperative PFFI measurements and postoperative ureteral stent-related symptoms assessed using the Ureteral Stent Symptom Questionnaire (USSQ). In addition, the study will evaluate the test-retest reliability of the PFFI measurement method and explore its potential role as an objective functional assessment tool for pelvic floor muscle endurance. The findings of this study are expected to provide the first clinical evaluation of the PFFI and establish the methodological basis for future validation studies and broader clinical applications.

Background Ureteral stent-related symptoms are common following ureteroscopy (URS) and retrograde intrarenal surgery (RIRS). Despite similar surgical procedures, stent characteristics, and postoperative management, symptom severity varies considerably among patients. Although trigonal irritation, local inflammation, vesicoureteral reflux, and the mechanical effects of the distal stent have been proposed as contributing mechanisms, these factors do not fully explain the observed interindividual variability. Pelvic floor muscle function may represent an additional patient-related factor influencing symptom severity. While current assessment methods primarily evaluate maximal voluntary contraction or anatomical movement, no standardized ultrasound-based method is currently available to objectively quantify pelvic floor muscle endurance. Study Rationale The Pelvic Floor Fatigue Index (PFFI) was developed to provide an objective, non-invasive, and reproducible ultrasound-based assessment of pelvic floor muscle endurance. The index quantifies the percentage decline in bladder base elevation during a sustained maximum voluntary pelvic floor contraction using suprapubic transverse B-mode ultrasonography. Unlike conventional pelvic floor assessments that primarily measure maximal contraction, PFFI evaluates the ability to maintain that contraction over time, providing complementary information regarding pelvic floor functional performance. Study Objectives The primary objective of this study is to clinically evaluate the Pelvic Floor Fatigue Index (PFFI) by investigating the association between preoperative PFFI measurements and postoperative ureteral stent-related symptoms assessed using the Ureteral Stent Symptom Questionnaire (USSQ). Secondary objectives include evaluating the reliability of the PFFI measurement method using test-retest analysis and assessing the influence of selected clinical variables on PFFI measurements.