A loss of pelvic organ support has been identified as a contributing factor in stress urinary incontinence (SUI) (1) and the excursion of pelvic landmarks is used to infer pelvic floor muscle contraction performance or tissue strain. Bladder neck height is often used to evaluate bladder/urethral support while anorectal junction height and levator plate angle reflect posterior compartment support. These variables can be challenging to measure using ultrasound imaging (USI) because there is only one static, non-deformable landmark visible within the image frame, the pubic symphysis. To overcome this, the position of landmarks and their excursion can be determined through creating a local co-ordinate system based on the short (y) and long (x) axis of pubic symphysis (2). Unfortunately, in many females, particularly those with large body mass index or large levator hiatus, it can be difficult if not impossible to capture enough of the pubic symphysis while keeping the anorectal junction within the imaging frame. Further, when using USI in clinic, for example, for real-time biofeedback, this method is inaccessible as it requires post-processing. Some authors have therefore measured the position of landmarks relative to a reference line estimating either the horizontal axis or the levator plate (Figure 1). The aim of this study was to compare measurements of the bladder neck height, levator plate angle and anorectal junction height and cranio-caudal excursion when computed using the more rigorous co-ordinate system approach to the more clinically accessible approach.

This was a secondary analysis of data collected for the purpose of a cross-sectional study which received prior approval from the local institutional research ethics board.  Participants were adult females without pelvic organ prolapse> stage 2 or dyspareunia, with and without urinary incontinence. Participants provided written informed consent prior to engaging in any study activities.  Two-dimensional transperineal imaging (Voluson S6, RAB 3.5-7 3D curvilinear probe, GE , Toronto, Canada) was performed with participants at rest and while they performed three maximum voluntary contractions in supine and in standing. The median value of each variable was retained for statistical analysis. Linear regression and Bland-Altman analyses were used to compare bladder neck height, levator plate angle and anorectal junction height between the two methods under investigation. The methods were compared when analyzing participants at rest, at the peak of a pelvic floor muscle contraction, and when evaluating cranio-caudal excursion from rest to peak.

Ultrasound datasets from 34 participants were included in the analysis; poor image quality resulted in the exclusion of one participant’s data recorded in standing. The results of the Bland-Altman analysis and the linear regressions (all p<0.05) are presented in Table 1.

The bias between methods was quite high and the limits of agreement were quite broad when measuring landmark cranio-caudal position using the different measurement methods, yet overall, the linear regressions were strong, particularly for imaging performed in standing where the slope was close to one and the model explained the vast majority of variance in the data (R2). Landmark excursion was minimally impacted by the measurement method, intercepts very close to zero, presumably because errors in landmark position were consistent between rest and peak excursion.

While the anatomic position of the bladder neck and anorectal junction relative to the public symphysis is best measured using a local coordinate system created using the pubic symphysis, changes in bladder neck height, anorectal junction height and levator plate angle can be visualized and measured in a clinical setting through a simpler approach using the levator plate line or an estimate of the horizontal.

Falah-Hassani, K., Reeves, J., Shiri, R., Hickling, D., & McLean, L. (2021). The pathophysiology of stress urinary incontinence: a systematic review and meta-analysis. International Urogynecology Journal, 32(3), 501-552.
Kalayeh, K., Fowlkes, J. B., Daignault-Newton, S., Schmidt, P., Ashton-Miller, J. A., & DeLancey, J. O. (2026). Automated Ultrasound-Based Analysis of Urethral Kinematics in Stress Urinary Incontinence: A Pilot Study. Neurourology and Urodynamics.
Dietz, H. P., & Wilson, P. D. (1998). Anatomical assessment of the bladder outlet and proximal urethra using ultrasound and videocystourethrography. International Urogynecology Journal, 9(6), 365-369.