We hypothesized that functional alterations of the puborectalis muscle, assessed by dynamic ultrasonography, are associated with constipation and may be more relevant than static measurements. The aim of this study was to investigate the association between functional pelvic floor ultrasonographic parameters, particularly puborectalis dynamics, and constipation, as well as to evaluate their predictive performance.

A cross-sectional study was conducted between July and December 2024, including volunteers aged 18–40 years. The following variables were assessed: age, gender, presence of constipation, and ultrasonographic parameters obtained at rest and during voluntary contraction of the ischiocavernosus, bulbospongiosus, puborectalis, internal anal sphincter, and external anal sphincter. Additionally, anal area, anal circumference, and anorectal angle were measured. Pelvic floor assessment was performed using a Mindray ultrasound system, with convex and linear transducers operating at frequencies ranging from 2.5 to 10 MHz.Data were expressed as mean and standard deviation or median and interquartile range, according to data distribution, as well as absolute and relative frequencies. Normality and homogeneity of variances were assessed using the Shapiro–Wilk and Levene tests, respectively. Effect size was calculated using Cohen’s d (moderate effect size: 0.39). For inferential analysis, delta values (difference between contraction and resting conditions) were calculated for all ultrasonographic variables. Binary logistic regression was performed to identify predictors of constipation, with variable selection based on physiological relevance. Model fit was assessed using the Hosmer–Lemeshow test, and results were presented as odds ratios (OR) with 95% confidence intervals. Predictive accuracy was evaluated using receiver operating characteristic (ROC) curves and the area under the curve (AUC).

A total of 45 volunteers were included, of whom 12 (26.6%) had constipation. The mean age in the non-constipation group was 23.0 ± 2.48 years, while in the constipation group it was 22.5 ± 2.61 years. Among constipated individuals, 1 (8.3%) was male and 11 (91.7%) were female. Normality analysis revealed that only baseline puborectalis muscle, baseline anal area, and anal area during contraction did not follow a normal distribution. All variables showed homogeneity of variances, as confirmed by Levene’s test. The effect size was 0.39, indicating a moderate effect. The logistic regression model demonstrated adequate goodness-of-fit, as indicated by the Hosmer–Lemeshow test (χ²=4.733; p=0.692), suggesting good agreement between predicted and observed outcomes. Logistic regression analysis demonstrated a trend toward an association between puborectalis functional variation and constipation (OR=3.92; 95% CI: 0.82–18.75; p=0.088). Gender also showed a trend toward association with constipation (OR=10.32; p=0.064). Despite the association observed in logistic regression, ROC curve analysis demonstrated low discriminatory ability for puborectalis functional variation (AUC=0.43), suggesting that isolated ultrasonographic parameters have limited predictive performance for constipation.

Constipation may be more closely related to functional alterations of the puborectalis muscle than to static measurements.
Furthermore, the trend toward association observed in the logistic regression suggests that puborectalis contractile dynamics may play a relevant role in the pathophysiology of constipation, even in the absence of robust statistical significance, possibly due to the sample size.
The low diagnostic accuracy observed in the ROC curve analysis indicates that isolated ultrasonographic parameters may not be sufficient to identify constipation, reinforcing the need for a multimodal approach integrating clinical, functional, and behavioral data.

Functional puborectalis dynamics appear to be more relevant than static measures in constipation; however, isolated ultrasonographic parameters show limited diagnostic performance, supporting the need for a multimodal assessment approach.