Changes in Vaginal and Pelvic Support Biomechanics Following Pelvic Organ Prolapse Surgery Assessed by Vaginal Tactile Imaging: A Prospective Exploratory Observational Cohort Study

1. Introduction

Pelvic organ prolapse (POP) is a common pelvic floor disorder characterized by descent of the bladder, uterus, vaginal walls, or rectum into or beyond the vaginal canal due to weakening of the muscular and connective tissue support [1]. POP may be associated with vaginal, urinary, bowel, and sexual symptoms, which can substantially affect patients’ quality of life [2]. The prevalence of POP increases with age, although estimates vary considerably depending on the population studied and the method of assessment, with examination-based prevalence reported to be as high as 50% [3]. More recently, a systematic review and meta-analysis reported an overall global prevalence of 30.9%, rising to 41.8% in studies that used physical examination for POP assessment [4]. The lifetime risk of undergoing surgery for POP has been estimated at 12–19%, while approximately 11% of surgically treated women undergo reoperation within 5 years [5]. Long-term evaluation after POP surgery should therefore extend beyond anatomical durability and the need for reoperation to include symptom burden and patient-reported functional outcomes, which can be assessed using validated pelvic floor–specific instruments [5,6].

Three distinct concepts are relevant to POP evaluation and should not be conflated: (i) anatomical support, quantified by the Pelvic Organ Prolapse Quantification (POP-Q) system; (ii) tissue biomechanical properties, such as the elasticity, resistance, and stiffness of the vaginal walls and adjacent connective tissue; and (iii) neuromuscular function, reflected in the voluntary and reflex contractile activity of the pelvic floor muscles [7]. The POP-Q system primarily characterizes anatomical support, whereas complementary imaging modalities provide additional structural and functional information. Translabial 3D/4D ultrasound enables dynamic assessment of pelvic organ support and levator anatomy and function [8], while shear-wave elastography has emerged as a non-invasive approach for quantifying pelvic floor muscle stiffness [9].

Vaginal Tactile Imaging (VTI) is a non-invasive technique in which a vaginal probe fitted with high-resolution pressure sensors records tissue responses to controlled deformation, producing three-dimensional tactile maps and derived parameters spanning vaginal wall elasticity, tissue resistance, pelvic floor muscle contractile strength, ligamentous support, and inter-compartmental asymmetry [10,11,12]. Cross-sectional studies have described characteristic patterns of tissue weakening in POP [13,14,15]. However, several important knowledge gaps remain. Prospective, paired preoperative–postoperative VTI data are limited, and compartment-specific patterns of biomechanical change after reconstructive surgery are incompletely defined. Furthermore, it remains unclear whether the differences observed between POP patients and non-prolapse comparators reflect prolapse itself or coexisting demographic factors such as age, parity, and menopausal status.

Building on this gap, the present study was designed as a prospective, exploratory, physiological proof-of-concept investigation. The primary objective was to test the hypothesis that reconstructive POP surgery induces a significant change in a prespecified VTI-derived integral pressure parameter (P1_I) at 6 months. The secondary objectives were (i) to describe changes in five additional prespecified support-structure parameters; (ii) to compare VTI parameters with those of a non-prolapse reference group, with strict adjustment for age, parity, BMI, and menopausal status; and (iii) to descriptively explore patterns of change according to surgical category. Because the primary aim was to establish the sensitivity of VTI to surgical intervention at the tissue level, subjective clinical questionnaires and postoperative anatomical gradings were intentionally omitted at this stage to isolate biomechanical responses. Consequently, no confirmatory claims regarding clinical utility are made.

2. Materials and Methods

2.1. Study Design and Ethics

This was a single-center, prospective, observational cohort study conducted at the Department of Obstetrics and Gynecology, Alanya Alaaddin Keykubat University School of Medicine Education and Research Hospital, between December 2022 and December 2023. The study was conducted in accordance with the Declaration of Helsinki and was approved by the Alanya Alaaddin Keykubat University School of Medicine Clinical Research Ethics Committee (protocol code 14-05; date of approval: 14 December 2022). Written informed consent was obtained from all participants.

2.2. Participants and Setting

Two groups were prospectively enrolled by consecutive sampling among women attending the urogynecology outpatient clinic during the study period: the patient group, comprising women with POP-Q stage I–IV prolapse scheduled for pelvic floor reconstructive surgery, and the reference (non-prolapse) group, comprising women presenting for routine gynecologic examination with POP-Q stage 0 and no prolapse symptoms. Because POP is intrinsically associated with age, parity, and menopausal status, demographic matching was not attempted at recruitment; the resulting between-group imbalance is addressed statistically (Section 2.8) and discussed in the Limitations (Section 4.5).

2.3. Eligibility Criteria

Inclusion criteria were age 18–80 years and provision of written informed consent. Exclusion criteria were pregnancy; previous POP or vaginal reconstructive surgery; active vaginal infection or ulceration; vaginal septum; pelvic malignancy; ongoing pelvic radiotherapy; significant pelvic pain syndromes; severe vaginismus or vulvodynia; advanced hemorrhoidal disease; and significant cardiovascular disease precluding examination.

2.4. Clinical Assessment and Variables

For all participants, we recorded age, BMI, gravidity, parity, menopausal status, current systemic or local hormone therapy, comorbidities, smoking status, medications, and prior surgical history. Patients underwent standardized POP-Q examination, transvaginal ultrasonography, and a clinical stress test for urinary incontinence. POP-Q stage was recorded per compartment. Patient-reported outcome measures (PFDI-20, PFIQ-7, and PISQ-12) and postoperative POP-Q measurements were not collected, as the study focused on changes in VTI-derived biomechanical parameters.

2.5. Surgical Procedures

Surgery was performed by two experienced pelvic floor surgeons using standardized techniques. Procedures were pre-classified into three categories to facilitate transparency and exploratory subgroup analysis: Category A — compartment repair only (anterior colporrhaphy, posterior colporrhaphy, or combined anterior–posterior colporrhaphy [CAP]); Category B — compartment repair plus midurethral sling (CAP + transobturator tape [TOT]); and Category C — compartment repair plus apical procedure (vaginal hysterectomy [VH] with uterosacral ligament suspension, VH + CAP, or VH + CAP + sacrospinous fixation [SSF]). Absorbable sutures were used for fascial plication. No transvaginal synthetic mesh was used.

2.6. Vaginal Tactile Imaging Protocol

VTI (Model 2S, Advanced Tactile Imaging Inc., Trenton, NJ, USA) recordings were obtained with subjects in the dorsal lithotomy position by a single trained investigator. Device calibration was verified before each session according to the manufacturer’s specifications. The probe was advanced at a constant rate of 5 mm/s, and the anterior and posterior walls were evaluated separately. Blinding and standardization: the investigator who extracted and calculated the parameters offline was fully blinded to whether the recordings corresponded to the preoperative or 6-month postoperative time point. Although the operator performing the VTI examination could not be fully blinded to the patient’s surgical status (as postoperative anatomy is visually evident), standardized visual and verbal instructions for the Valsalva maneuver and pelvic floor contractions were strictly followed to minimize operator-induced bias. The examination consisted of eight standardized tests yielding 46 biomechanical parameters per subject [11]:

• Test 1 (probe insertion): pressure pattern, gradients, and anatomical dimensions.

• Test 2 (probe elevation): pressure generated as the probe is elevated toward the vaginal apex, used as an index of apical/uterosacral–cardinal ligament support (referenced in the exploratory subgroup analysis of apical-fixation procedures, Section 3.4).

• Test 3 (probe rotation): tactile image of the left and right vaginal walls.

• Test 4 (Valsalva maneuver): pressure dynamics.

• Test 5 (voluntary contraction, anteroposterior): static and contraction amplitudes.

• Test 6 (voluntary contraction, left–right): static and contraction amplitudes.

• Test 7 (involuntary relaxation): pressure dynamics and relaxation slope.

• Test 8 (involuntary contraction, cough): resting tone and reflex amplitudes.

Postoperative measurements were repeated at 6 months using an identical protocol.

2.7. Prespecified Endpoint Hierarchy

To manage the multiplicity introduced by the 46 candidate parameters, a prespecified endpoint hierarchy was applied. Primary endpoint: the within-patient change from the preoperative to the 6-month postoperative measurement of the integral pressure parameter P1_I. This parameter was selected a priori because it represents an integrated index of pelvic support pressure at the mid-vaginal level and has previously been reported to show good test–retest and inter-observer reproducibility in independent VTI cohorts [11,12,14]; formal reliability testing was not repeated within the present cohort (see Section 4.5.6). Secondary endpoints: within-patient changes in five complementary parameters — P2max_a, P2max_p, dF_p (Test 6), dF_p (Test 8), and dPmax_r. Exploratory outcomes: all remaining VTI parameters, between-group comparisons, and subgroup analyses.

2.8. Statistical Analysis

Descriptive statistics, normality testing (Shapiro–Wilk), paired-samples t-tests/Wilcoxon signed-rank tests, and chi-square/Fisher’s exact tests were performed in IBM SPSS Statistics v22.0 (IBM Corp., Armonk, NY, USA). ANCOVA models, collinearity diagnostics, and effect-size (Cohen’s d) calculations were performed in R v4.3.0 (R Foundation for Statistical Computing, Vienna, Austria). No formal a priori sample-size calculation was performed, as the study was designed to be exploratory; the implications of this for statistical power are addressed in Section 4.5.3. Continuous variables are reported as mean ± SD; non-normally distributed variables are reported as median (IQR). Categorical variables are reported as n (%).

Because of substantial between-group differences in age, parity, and menopausal status, ANCOVA adjusted for age, parity, BMI, and menopausal status (treated as a binary covariate) was prespecified as the primary approach for between-group inference. Because age and menopausal status are inherently correlated, variance inflation factors (VIFs) were calculated for all covariates in each ANCOVA model; VIF values remained below 3 for all models, arguing against severe multicollinearity, although residual confounding from the strong age–menopause association cannot be fully excluded given the modest sample size (see Section 4.5.2). The primary endpoint (change in P1_I) was evaluated at α = 0.05 without multiplicity adjustment, consistent with its prespecified, single-hypothesis status. For the remaining 45 secondary and exploratory VTI parameters, a Bonferroni-adjusted significance threshold of 0.05/45 (≈0.0011) was applied. Raw and adjusted p-values are reported, together with Cohen’s d and 95% CIs for significant comparisons.

3. Results

3.1. Participants

32 POP patients and 30 non-prolapse reference subjects were enrolled and completed the study. There was no loss to follow-up in the patient group. The patient group was substantially older (55.8 ± 11.5 vs. 36.6 ± 8.5 years; p < 0.001) and had higher gravidity (4.2 ± 2.1 vs. 0.4 ± 0.8; p < 0.001) and parity (3.6 ± 1.2 vs. 2.0 ± 0.7; p < 0.001) than the reference group. Postmenopausal status was significantly more common among patients (24 [75.0%] vs. 6 [20.0%]; p < 0.001), and 8 patients (25.0%) were using local vaginal estrogen. The POP-Q stage distribution in the patient group was as follows: stage I, 2 (6.3%); stage II, 13 (40.6%); stage III, 14 (43.8%); and stage IV, 3 (9.4%).

Table 1. Demographic and clinical characteristics of the patient and reference groups.

Variable	Patient Group (n = 32)	Reference Group (n = 30)	p-value
Age (years), mean ± SD	55.8 ± 11.5	36.6 ± 8.5	<0.001 *
BMI (kg/m²), mean ± SD	28.9 ± 5.4	26.6 ± 4.5	0.079
Gravidity, mean ± SD	4.2 ± 2.1	0.4 ± 0.8	<0.001 *
Parity, mean ± SD	3.6 ± 1.2	2.0 ± 0.7	<0.001 *
Postmenopausal, n (%)	24 (75.0)	6 (20.0)	<0.001 *
Local estrogen therapy, n (%)	8 (25.0)	0 (0.0)	0.004 *
Smoking, n (%)	5 (15.6)	4 (13.3)	0.642

¹ SD, standard deviation; BMI, body mass index; POP-Q, Pelvic Organ Prolapse Quantification.

Table 1. Demographic and clinical characteristics of the patient and reference groups.

Variable	Patient Group (n = 32)	Reference Group (n = 30)	p-value
Age (years), mean ± SD	55.8 ± 11.5	36.6 ± 8.5	<0.001 *
BMI (kg/m²), mean ± SD	28.9 ± 5.4	26.6 ± 4.5	0.079
Gravidity, mean ± SD	4.2 ± 2.1	0.4 ± 0.8	<0.001 *
Parity, mean ± SD	3.6 ± 1.2	2.0 ± 0.7	<0.001 *
Postmenopausal, n (%)	24 (75.0)	6 (20.0)	<0.001 *
Local estrogen therapy, n (%)	8 (25.0)	0 (0.0)	0.004 *
Smoking, n (%)	5 (15.6)	4 (13.3)	0.642

¹ SD, standard deviation; BMI, body mass index; POP-Q, Pelvic Organ Prolapse Quantification.

3.2. Surgical Procedures

By surgical category, 16 patients (50.0%) underwent Category A procedures (compartment repair only), 5 (15.6%) underwent Category B procedures (compartment repair plus midurethral sling), and 11 (34.4%) underwent Category C procedures (compartment repair plus apical procedure).

3.3. Preoperative Comparison Between the Patient and Reference Groups

In unadjusted analyses, anterior compartment resistance and global vaginal wall integrity (Pmax, Fmax_ap, Fmax_s, P1_I, P3_r) were markedly lower in patients (all raw p < 0.001). Posterior pressures P1max_p and P2max_p were lower, whereas P3max_p (distal posterior pressure) was unexpectedly higher in patients. Notably, after comprehensive ANCOVA adjustment for age, parity, BMI, and menopausal status, between-group differences remained statistically significant for the tissue integrity and stiffness parameters (Pmax, P1_I, P3_r). In contrast, between-group differences in muscle function and innervation indices (Pmax_r, Pmax_I, dp/dt_a) were completely attenuated (adjusted p > 0.10). This indicates that the diminished levator function observed in the POP group is heavily confounded by advancing age and postmenopausal estrogen deficiency, rather than being solely a consequence of the prolapse itself.

Table 2. Preoperative VTI parameters: patient versus reference group (unadjusted and adjusted analyses).

Parameter	Description	Patient (n = 32) mean ± SD	Reference (n = 30) mean ± SD	Raw p	Adjusted p	Cohen’s d (95% CI)
Pmax_a	Anterior vaginal resistance	19.4 ± 6.8	31.0 ± 8.2	0.002 *	0.014 *	1.54 (0.98–2.10)
P1max_a	Anterior pressure, level 1	11.3 ± 4.9	31.7 ± 9.4	<0.001 **	0.002 *	2.75 (2.05–3.44)
P2max_a	Anterior pressure, level 2	6.2 ± 3.1	11.8 ± 4.5	<0.001 *	0.021 *	1.46 (0.90–2.01)
P1max_p	Posterior pressure, level 1	8.7 ± 3.6	14.4 ± 4.8	<0.001 *	0.018 *	1.35 (0.80–1.90)
P2max_p	Posterior pressure, level 2	8.0 ± 3.3	11.7 ± 4.1	0.001 *	0.045 *	0.99 (0.46–1.52)
P3max_p	Posterior pressure, level 3 ‡	9.5 ± 4.2	6.3 ± 2.9	0.001 *	0.038 *	0.88 (0.36–1.40)
Pmax	Global vaginal integrity	14.0 ± 5.1	33.9 ± 9.7	<0.001 **	<0.001 **	2.60 (1.92–3.28)
Fmax_ap	Anteroposterior force	2.9 ± 1.1	4.4 ± 1.4	<0.001 **	0.001 **	1.20 (0.66–1.73)
Fmax_s	Lateral force	1.7 ± 0.6	2.6 ± 0.8	<0.001 **	0.002 *	1.28 (0.74–1.82)
P1_I	Integral pressure, level 1	5.3 ± 2.0	10.8 ± 3.4	<0.001 **	<0.001 **	1.99 (1.38–2.59)
P2_I	Integral pressure, level 2	4.1 ± 1.6	6.4 ± 2.1	<0.001 *	0.003 *	1.24 (0.70–1.77)
P3_r	Tissue stiffness, level 3	6.6 ± 2.5	12.0 ± 3.8	<0.001 **	<0.001 **	1.69 (1.11–2.26)
dPmax_p	Posterior Valsalva response	3.2 ± 1.4	4.7 ± 1.8	0.038 *	0.082	0.94 (0.42–1.46)
Pmax_I	Puborectal contraction	9.0 ± 3.2	13.0 ± 4.1	0.007 *	0.098	1.09 (0.55–1.62)
dp/dt_a	Levator innervation, anterior	−1.0 ± 0.8	−3.5 ± 1.6	0.002 *	0.062	2.01 (1.40–2.61)
dp/dt_p	Levator innervation, posterior	−0.5 ± 0.6	−0.2 ± 0.4	0.045 *	0.211	0.59 (0.08–1.10)
2 VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval. † ANCOVA adjusted for age, parity, and BMI. * Raw p < 0.05. ** Bonferroni-significant (p < 0.0011). Data are presented as mean ± SD. † Adjusted p-values were obtained using ANCOVA with adjustment for age, parity, BMI, and menopausal status. Adjusted p-values represent covariate-adjusted ANCOVA results and not multiplicity-adjusted p-values. The Bonferroni-adjusted significance threshold for exploratory comparisons was p< 0.0011. ‡ P3max_p was higher in the POP group than in the reference group, in contrast to the direction observed for the other pressure parameters. Abbreviations: VTI, vaginal tactile imaging; POP, pelvic organ prolapse; ANCOVA, analysis of covariance; BMI, body mass index; SD, standard deviation; CI, confidence interval; Pmax, maximum pressure; Fmax, maximum tissue force; dPmax, differential maximum pressure; dp/dt, rate of pressure change over time; _a, anterior; _p, posterior; _s, side/lateral; _I, integral; _ap, anteroposterior.

Table 2. Preoperative VTI parameters: patient versus reference group (unadjusted and adjusted analyses).

Parameter	Description	Patient (n = 32) mean ± SD	Reference (n = 30) mean ± SD	Raw p	Adjusted p	Cohen’s d (95% CI)
Pmax_a	Anterior vaginal resistance	19.4 ± 6.8	31.0 ± 8.2	0.002 *	0.014 *	1.54 (0.98–2.10)
P1max_a	Anterior pressure, level 1	11.3 ± 4.9	31.7 ± 9.4	<0.001 **	0.002 *	2.75 (2.05–3.44)
P2max_a	Anterior pressure, level 2	6.2 ± 3.1	11.8 ± 4.5	<0.001 *	0.021 *	1.46 (0.90–2.01)
P1max_p	Posterior pressure, level 1	8.7 ± 3.6	14.4 ± 4.8	<0.001 *	0.018 *	1.35 (0.80–1.90)
P2max_p	Posterior pressure, level 2	8.0 ± 3.3	11.7 ± 4.1	0.001 *	0.045 *	0.99 (0.46–1.52)
P3max_p	Posterior pressure, level 3 ‡	9.5 ± 4.2	6.3 ± 2.9	0.001 *	0.038 *	0.88 (0.36–1.40)
Pmax	Global vaginal integrity	14.0 ± 5.1	33.9 ± 9.7	<0.001 **	<0.001 **	2.60 (1.92–3.28)
Fmax_ap	Anteroposterior force	2.9 ± 1.1	4.4 ± 1.4	<0.001 **	0.001 **	1.20 (0.66–1.73)
Fmax_s	Lateral force	1.7 ± 0.6	2.6 ± 0.8	<0.001 **	0.002 *	1.28 (0.74–1.82)
P1_I	Integral pressure, level 1	5.3 ± 2.0	10.8 ± 3.4	<0.001 **	<0.001 **	1.99 (1.38–2.59)
P2_I	Integral pressure, level 2	4.1 ± 1.6	6.4 ± 2.1	<0.001 *	0.003 *	1.24 (0.70–1.77)
P3_r	Tissue stiffness, level 3	6.6 ± 2.5	12.0 ± 3.8	<0.001 **	<0.001 **	1.69 (1.11–2.26)
dPmax_p	Posterior Valsalva response	3.2 ± 1.4	4.7 ± 1.8	0.038 *	0.082	0.94 (0.42–1.46)
Pmax_I	Puborectal contraction	9.0 ± 3.2	13.0 ± 4.1	0.007 *	0.098	1.09 (0.55–1.62)
dp/dt_a	Levator innervation, anterior	−1.0 ± 0.8	−3.5 ± 1.6	0.002 *	0.062	2.01 (1.40–2.61)
dp/dt_p	Levator innervation, posterior	−0.5 ± 0.6	−0.2 ± 0.4	0.045 *	0.211	0.59 (0.08–1.10)
2 VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval. † ANCOVA adjusted for age, parity, and BMI. * Raw p < 0.05. ** Bonferroni-significant (p < 0.0011). Data are presented as mean ± SD. † Adjusted p-values were obtained using ANCOVA with adjustment for age, parity, BMI, and menopausal status. Adjusted p-values represent covariate-adjusted ANCOVA results and not multiplicity-adjusted p-values. The Bonferroni-adjusted significance threshold for exploratory comparisons was p< 0.0011. ‡ P3max_p was higher in the POP group than in the reference group, in contrast to the direction observed for the other pressure parameters. Abbreviations: VTI, vaginal tactile imaging; POP, pelvic organ prolapse; ANCOVA, analysis of covariance; BMI, body mass index; SD, standard deviation; CI, confidence interval; Pmax, maximum pressure; Fmax, maximum tissue force; dPmax, differential maximum pressure; dp/dt, rate of pressure change over time; _a, anterior; _p, posterior; _s, side/lateral; _I, integral; _ap, anteroposterior.

3.4. Preoperative Versus Postoperative Comparison

Primary endpoint: the prespecified primary outcome, change in P1_I, demonstrated a statistically significant within-patient increase at 6 months (Δ +1.2; 95% CI 0.4–2.0; p = 0.006; Cohen’s d = 0.55).

Secondary endpoints: all five prespecified secondary endpoints showed nominal increases at the conventional p < 0.05 level: P2max_a (Δ +2.9; raw p = 0.021; d = 0.48), P2max_p (Δ +2.0; raw p = 0.033; d = 0.42), dF_p (Test 6) (Δ +0.5; raw p = 0.012; d = 0.51), dPmax_r (Δ +1.4; raw p = 0.023; d = 0.46), and dF_p (Test 8) (Δ +0.5; raw p = 0.002; d = 0.68). However, none met the rigorous Bonferroni-adjusted threshold of p < 0.0011; therefore, these secondary changes should be interpreted strictly as hypothesis-generating.

Exploratory subgroup analysis: although statistically underpowered, visual scatterplot analysis revealed that patients undergoing apical fixation (Category C) exhibited numerically distinct improvements in Test 2 (apical support gradients) compared with those undergoing anterior/posterior repair alone.

Table 3. Preoperative versus 6-month postoperative VTI parameters (patient group, n = 32).

Endpoint level	Parameter	Preop mean ± SD	Postop (6 mo) mean ± SD	Δ (postop − preop) (95% CI)	Raw p	Adjusted p †	Cohen’s d
Primary	P1_I	5.3 ± 2.0	6.5 ± 2.3	+1.2 (0.4 to 2.0)	0.006 *	0.276	0.55
Secondary	P2max_a	6.2 ± 3.1	9.1 ± 3.6	+2.9 (0.5 to 5.3)	0.021 *	0.966	0.48
Secondary	P2max_p	8.0 ± 3.3	10.0 ± 3.9	+2.0 (0.2 to 3.8)	0.033 *	1.000	0.42
Secondary	dF_p (Test 6)	2.4 ± 1.1	2.9 ± 1.2	+0.5 (0.1 to 0.9)	0.012 *	0.552	0.51
Secondary	dPmax_r	6.7 ± 3.0	8.1 ± 3.4	+1.4 (0.2 to 2.6)	0.023 *	1.000	0.46
Secondary	dF_p (Test 8)	1.6 ± 0.7	2.1 ± 0.8	+0.5 (0.2 to 0.8)	0.002 *	0.092	0.68
3VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval. Δ, postoperative minus preoperative change (positive value indicates postoperative increase). Paired-samples t-test or Wilcoxon signed-rank test, as appropriate. † Bonferroni-adjusted p-value for exploratory family of 46 parameters (α = 0.05/46 ≈ 0.0011). * Raw p < 0.05. VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval. Δ, postoperative minus preoperative change (positive value indicates postoperative increase). Paired-samples t-test or Wilcoxon signed-rank test, as appropriate. † Bonferroni-adjusted p-value for exploratory family of 46 parameters (α = 0.05/46 ≈ 0.0011). * Raw p < 0.05. Post-hoc power. For the observed effect sizes (Cohen’s d = 0.42–0.68) with n = 32 paired observations, achieved statistical power ranged from 0.62 to 0.94 at α = 0.05 (two-sided) and from 0.14 to 0.53 at the Bonferroni-adjusted α. Post-hoc power should be interpreted cautiously and is provided only to indicate the sensitivity of the observed findings to sample size. Exploratory subgroup analysis. Patients undergoing procedures with apical fixation (Category C; n = 11) showed numerically larger changes in P1_I (Δ +1.6 vs. +1.0) and dF_p Test 6 (Δ +0.7 vs. +0.4) than those in Categories A + B combined (n = 21), but no between-subgroup comparison reached statistical significance (all raw p > 0.10; Supplementary Table S3). Given the small subgroup sizes, these observations should be regarded as descriptive. Data are presented as mean ± SD. Mean change represents postoperative minus preoperative values; positive values indicate an increase at 6 months. Within-patient comparisons were performed using paired-samples t-tests or Wilcoxon signed-rank tests, as appropriate. The prespecified primary endpoint (P1_I) was evaluated at α = 0.05 without multiplicity adjustment. † Bonferroni correction was applied to the remaining 45 secondary and exploratory VTI parameters (α = 0.05/45 ≈ 0.0011). Accordingly, the five secondary endpoints showing nominal significance at the conventional α = 0.05 level did not meet the Bonferroni-adjusted significance threshold and should be considered hypothesis-generating. VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval; dF_p, integral pelvic floor contraction force (posterior); dPmax, differential maximum pressure.

Table 3. Preoperative versus 6-month postoperative VTI parameters (patient group, n = 32).

Endpoint level	Parameter	Preop mean ± SD	Postop (6 mo) mean ± SD	Δ (postop − preop) (95% CI)	Raw p	Adjusted p †	Cohen’s d
Primary	P1_I	5.3 ± 2.0	6.5 ± 2.3	+1.2 (0.4 to 2.0)	0.006 *	0.276	0.55
Secondary	P2max_a	6.2 ± 3.1	9.1 ± 3.6	+2.9 (0.5 to 5.3)	0.021 *	0.966	0.48
Secondary	P2max_p	8.0 ± 3.3	10.0 ± 3.9	+2.0 (0.2 to 3.8)	0.033 *	1.000	0.42
Secondary	dF_p (Test 6)	2.4 ± 1.1	2.9 ± 1.2	+0.5 (0.1 to 0.9)	0.012 *	0.552	0.51
Secondary	dPmax_r	6.7 ± 3.0	8.1 ± 3.4	+1.4 (0.2 to 2.6)	0.023 *	1.000	0.46
Secondary	dF_p (Test 8)	1.6 ± 0.7	2.1 ± 0.8	+0.5 (0.2 to 0.8)	0.002 *	0.092	0.68
3VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval. Δ, postoperative minus preoperative change (positive value indicates postoperative increase). Paired-samples t-test or Wilcoxon signed-rank test, as appropriate. † Bonferroni-adjusted p-value for exploratory family of 46 parameters (α = 0.05/46 ≈ 0.0011). * Raw p < 0.05. VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval. Δ, postoperative minus preoperative change (positive value indicates postoperative increase). Paired-samples t-test or Wilcoxon signed-rank test, as appropriate. † Bonferroni-adjusted p-value for exploratory family of 46 parameters (α = 0.05/46 ≈ 0.0011). * Raw p < 0.05. Post-hoc power. For the observed effect sizes (Cohen’s d = 0.42–0.68) with n = 32 paired observations, achieved statistical power ranged from 0.62 to 0.94 at α = 0.05 (two-sided) and from 0.14 to 0.53 at the Bonferroni-adjusted α. Post-hoc power should be interpreted cautiously and is provided only to indicate the sensitivity of the observed findings to sample size. Exploratory subgroup analysis. Patients undergoing procedures with apical fixation (Category C; n = 11) showed numerically larger changes in P1_I (Δ +1.6 vs. +1.0) and dF_p Test 6 (Δ +0.7 vs. +0.4) than those in Categories A + B combined (n = 21), but no between-subgroup comparison reached statistical significance (all raw p > 0.10; Supplementary Table S3). Given the small subgroup sizes, these observations should be regarded as descriptive. Data are presented as mean ± SD. Mean change represents postoperative minus preoperative values; positive values indicate an increase at 6 months. Within-patient comparisons were performed using paired-samples t-tests or Wilcoxon signed-rank tests, as appropriate. The prespecified primary endpoint (P1_I) was evaluated at α = 0.05 without multiplicity adjustment. † Bonferroni correction was applied to the remaining 45 secondary and exploratory VTI parameters (α = 0.05/45 ≈ 0.0011). Accordingly, the five secondary endpoints showing nominal significance at the conventional α = 0.05 level did not meet the Bonferroni-adjusted significance threshold and should be considered hypothesis-generating. VTI, vaginal tactile imaging; SD, standard deviation; CI, confidence interval; dF_p, integral pelvic floor contraction force (posterior); dPmax, differential maximum pressure.

3.5. Postoperative Versus Reference Group Comparison

At 6 months, most VTI parameters remained lower in patients than in the reference group. Vaginal wall resistance and elasticity indicators (Pmax, Fmax_ap, Fmax_s, P1_I, P3_r) remained lower. However, after ANCOVA adjustment for age, parity, BMI, and menopausal status, P2max_a and P2max_p were no longer significantly different from the reference group (adjusted p > 0.05), suggesting partial restoration of periurethral and mid-vaginal support.

4. Discussion

4.1. Main Findings

In this prospective cohort study, reconstructive POP surgery resulted in a statistically significant improvement in the primary biomechanical endpoint (P1_I) at 6 months postoperatively. Furthermore, VTI identified substantial preoperative biomechanical differences between women with POP and a non-prolapse reference group. Notably, after adjustment for age, parity, and menopausal status, differences in vaginal elasticity remained significant, whereas differences in muscle contractile function were heavily attenuated.

4.2. Interpretation and Comparison with Prior Work

The higher distal posterior pressure (P3max_p) observed in women with POP, despite lower proximal posterior pressures, was unexpected and warrants cautious interpretation given the exploratory nature of this comparison. Several non-mutually-exclusive mechanisms may plausibly contribute: (i) compensatory hypertonicity of the distal perineal/bulbocavernosus complex in response to proximal and mid-vaginal support loss, a pattern described in other compartment-specific pelvic floor dysfunction models; (ii) altered distal vaginal geometry secondary to concomitant rectocele or perineal descent, which could increase probe–tissue contact pressure independent of true tissue stiffness; and (iii) a measurement artifact related to probe positioning in a distorted vaginal axis. Because this was not a prespecified hypothesis and the comparison did not survive Bonferroni correction (Table 2), it should be regarded as a descriptive observation to be tested prospectively, ideally alongside imaging of the perineal body, rather than as an established biomechanical feature of POP. After adjustment for age, parity, BMI, and menopausal status, differences in several muscle-related parameters were attenuated, suggesting that demographic factors may account for part of the observed differences in pelvic floor muscle function between groups. Postoperative increases in P2max_a and P2max_p were consistent with previous observations [11,15]. However, most parameters did not reach reference-group levels within 6 months.

4.3. Research and Potential Clinical Implications

Because the secondary within-patient changes did not meet the Bonferroni-adjusted threshold and clinical endpoints were not collected, no immediate clinical decision-making application is proposed. VTI may provide a quantitative research complement to POP-Q for investigating tissue biomechanics after reconstructive surgery, but confirmation of its clinical utility, diagnostic accuracy, and prognostic value requires dedicated studies.

4.4. Exploratory Procedure-Related Observations

The exploratory subgroup analysis suggested numerically larger increases in P1_I and apical-support-related parameters among patients undergoing apical fixation (Category C) than among those undergoing compartment repair alone (Categories A and B). Because the primary analysis pooled all three surgical categories into a single patient group, the overall between-group effect size reported for P1_I should be interpreted as a weighted average across a heterogeneous set of procedures; if apical fixation genuinely confers a larger biomechanical benefit, pooling may have diluted the true effect size in the categories where apical support was not addressed, and conversely may have overestimated the expected benefit for compartment-only repairs. This heterogeneity therefore limits the generalizability of the pooled primary-endpoint estimate to any single procedure and should be considered when applying these findings to clinical decision-making. Given the small subgroup sizes (n = 11 vs. n = 21) and the absence of a statistically significant between-subgroup comparison, these observations do not support inference regarding procedure-specific superiority but provide an empirical basis for the design, endpoint selection, and sample-size calculations of future, adequately powered, procedure-stratified studies.

4.5. Limitations

4.5.1. Absence of Clinical and Anatomical Outcomes

As a physiological proof-of-concept study, postoperative POP-Q gradings and quality-of-life questionnaires (PFDI-20, PFIQ-7) were purposefully omitted to isolate tissue biomechanics. Consequently, we cannot determine whether the significant increase in P1_I translates into subjective patient satisfaction or anatomical cure.

4.5.2. Reference Group Mismatch

The patient and reference groups differed substantially in age, parity, and menopausal status, and demographic matching was not performed at recruitment. Although ANCOVA adjustment was applied and collinearity diagnostics (VIF < 3) did not indicate severe multicollinearity among covariates, age and menopausal status remain strongly biologically correlated, and with only 62 participants in total the model’s ability to fully partition their independent contributions is limited. Residual confounding therefore cannot be excluded, and the adjusted between-group estimates in Table 2 should be regarded as approximate rather than definitive. Future studies should employ age- and estrogen-matched, or ideally propensity-matched, control groups to strengthen causal inference.

4.5.3. Sample Size and Multiplicity

With 32 patients and 46 parameters, the risks of both false-negative and false-positive findings are non-trivial. Although the significance of our primary endpoint was preserved, the failure of the secondary parameters to meet the adjusted threshold requires confirmation in larger studies.

4.5.4. Surgical Heterogeneity

Seven different procedures, grouped into three categories, were included, limiting procedure-specific conclusions.

4.5.5. Single-Operator Acquisition and Blinding

All VTI recordings were acquired by a single trained investigator. While this maximized acquisition consistency, it precluded assessment of inter-observer variability within the present cohort and means the reported changes reflect the performance of one operator. Although data extraction and analysis were blinded to timepoint, the operator performing the physical VTI examination could not be fully blinded to surgical status, since postoperative anatomy is visually evident. Standardized visual and verbal instructions were used to minimize operator-induced bias, but residual bias cannot be entirely excluded.

4.5.6. Reliability Not Independently Established in This Cohort

Formal test–retest and inter-observer reliability assessments were not repeated in this cohort; the reproducibility of P1_I and related parameters relies on data from prior independent VTI studies [11,12,14]. Site- and operator-specific reliability should be established before VTI-derived parameters are used as trial endpoints in future, larger studies.

4.6. Future Directions

Priorities for future research include (i) larger, multicenter cohorts with age-, parity-, and menopause-matched controls; (ii) integration of validated patient-reported outcomes and anatomical (POP-Q) endpoints; (iii) formal establishment of the intra- and inter-observer reliability of VTI; (iv) longitudinal follow-up of at least 12 months; and (v) procedure-stratified analyses.

5. Conclusions

In this exploratory cohort, reconstructive POP surgery was associated with a statistically significant increase in the prespecified primary biomechanical endpoint, P1_I, at 6 months, while changes in the five secondary biomechanical parameters were smaller and did not survive correction for multiple comparisons. After adjustment for age, parity, BMI, and menopausal status — covariates that were unevenly distributed between groups — differences in vaginal wall elasticity relative to the non-prolapse reference group remained significant, whereas differences in muscle contractility were substantially attenuated. These findings support VTI as a physiologically sensitive research tool for characterizing tissue-level biomechanical change after POP surgery, but they do not, on their own, establish VTI as a validated clinical outcome measure. Confirmation of its diagnostic accuracy, reliability across operators and sites, and clinical relevance will require larger, adequately powered, matched-control studies that incorporate postoperative anatomical (POP-Q) and patient-reported outcomes.