Chronic vulvar pain or vulvodynia is a frequent chronic pain condition with a population prevalence rate as high as 7% to 16% by the age of 40.  Provoked vestibulodynia (PVD), the most common type of vulvodynia, is characterized by a sharp, burning pain located at the entry of the vagina when applying pressure or attempting vaginal penetration.  Alterations in pelvic floor muscle (PFM) function have been suggested to play a key role in the pathophysiology of PVD [1].  More notably, heightened PFM tone was demonstrated in women with PVD compared to asymptomatic controls using dynamometry and transperineal 3D/4D ultrasound [1].  Increased PFM tone is suspected to be a contributing factor in the development of vestibular pain as well as a perpetuating factor, which may exacerbate pain even further, due to increasing alterations of muscle tone.  Primarily targeting PFM alterations, pelvic floor physiotherapy is recommended as an effective first line treatment for PVD.  This highlights the relevance of PFM tone assessment in understanding the pathophysiology of PVD and evaluating the effects of treatment.

Most physiotherapists in clinical practice rely on digital palpation to assess PFM tone because it is easy to use and requires no equipment.  Among the several scales available, the Reissing scale, consisting of a 7-level grade ranging from -3 (hypotonic) to +3 (hypertonic), was reported to have a good inter-rater reliability [2].  Despite the widespread use of this gradation system, the concurrent validity, evaluated by comparing the scale with other validated and objective instruments, has never been assessed.  An in vitro study done recently has suggested that digital palpation may lack sensitivity amongst physiotherapists in assigning stiffness values to the tested 7-point Reissing scale [3].  While using an electromechanical instrument that aimed to replicate the stiffness perceived by the clinician, they found large variability and overlap in stiffness values on the 7-point scale.  The study emphasized the relevance to carry out an in vivo study to examine the ability of physiotherapists to assess PFM tone using the Reissing palpation scale.  The aim of the present study was to assess the validity of digital palpation in assessing tone using the Reissing Scale by 1) examining the association of palpation scores with dynamometry and 3D/4D transperineal ultrasound imaging in women with PVD; and 2) evaluating whether the palpation grade scale can be discriminated against dynamometry and ultrasound imaging.

This cross-sectional study involved 208 nulliparous women, all having a confirmed diagnosis of PVD by a gynecologist on our team.  Participants were included if they had a mean pain intensity during intercourse of ≥ 5 on the numerical rating scale for a period over 6 months.  Participants were convened to an assessment session carried out by experienced physiotherapists.  PFM tone was assessed intra-vaginally with one finger using the Reissing scale after participants were instructed to relax their pelvic floor musculature.  The physiotherapist palpated the levator ani muscle toward the posterior fourchette (6 o’clock) and designated a score from -3 to +3, representing no resistance to very firm resistance respectively.  ‘0’ found at the centre of the scale would represent normal resting muscle tone.  Thereafter, an intravaginal dynamometric speculum was used to assess PFM tone according to a validated methodology.  More specifically, passive forces at a vaginal aperture of 15 mm,  followed by flexibility measures (maximal tolerated aperture obtained while separating the speculum branches) were recorded.  And finally, PFM morphometry was assessed at rest using transperineal 3D/4D ultrasound (GE voluson e8 equipped with a convex transducer 5-9MHz) to assess the levator hiatus area.
The associations between digital palpation, dynamometric, and ultrasound assessments were investigated using Spearman correlation coefficients.  The correlations were interpreted as follows:  little or no relation (r=0–0.25); fair (r=0.25–0.50); moderate to good (r=0.50–0.75); and good to excellent relation (r≥ 0.75).  Differences between palpation scores, dynamometry and ultrasound imaging were assessed using one-way ANOVA followed by the post hoc Scheffe tests.

Participants had a mean age of 23 years (SD=4) with a mean pain intensity of 7.3/10 (SD=1.5) during intercourse for an average duration of 4 years (SD=3.3).  For PFM tone assessed using digital palpation, the Reissing scale scores obtained were as follows:  0=45 (21%); 1=58 (28%); 2=80 (39%); 3=25 (12%).  None of participants had scores of -1, -2, or -3.

As for the association between palpation and dynamometry, a weak association was found for the passive forces (tone) (R= 0.16; p <0.05).  The ANOVAs indicated that passive resistance at the 15mm aperture significantly differed across palpation score categories (F= 4.878, P< 0.01).  As shown in Figure 1, there was a significant difference between passive forces at palpation scores 0-3; 1-3; and 2-3 (posthoc p<0.05). Moreover, there was a fair association between palpation and flexibility (measurement of maximal vaginal aperture obtained with the speculum) (R= 0.36; p<0.05).  The ANOVAs indicated that flexibility significantly differed across palpation score categories (F=14.021, P< 0.05).  The values were significantly different for scores 0-1; 0-2; 0-3; and 1-3 (posthoc p <0.05) as illustrated in Figure 2.

Regarding the association between palpation and ultrasound imaging, a weak association was found with the levator hiatus area (R=-0.19; p<0.05).  The ANOVAs indicated that the levator hiatus area differed across palpation categories (F= 3.121, P< 0.05) and that a significant difference was found only for the score 0-3 (posthoc p<0.05).

The results of the correlation analyses showed weak to fair associations between the Reissing scale and both dynamometry and ultrasound imaging.  With the ANOVA tests, it was shown that although mean values of dynamometry and ultrasound imaging increased or decreased across subsequent scores of digital palpation, they did not consistently differ between adjacent scales.  It should however be highlighted that given the population understudied (i.e. women with pain), only the increased tone spectrum of the scale was investigated.  Although several assessors were involved in the study, this should have a negligible impact on our results given that good inter-rater reliability has been shown for the Reissing scale [2].

Findings of this study showed that PFM tone assessed with digital palpation was weakly or fairly associated with dynamometry and ultrasound imaging.  Our results also showed limited ability of the physiotherapist to discriminate between palpation scores against dynamometry and ultrasound measures. Therefore, it is important to understand that although palpation is easy, inexpensive, and widely used, it is subject to overlap in adjacent or closely related scores.  For that reason, changes in muscle tone may not be captured by digital palpation.  This study suggests that assessors/clinicians/researchers should be conscious of these limitations when relying solely on digital palpation as an assessment and outcome measure tool.

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Reissing ED, Brown C, Lord MJ, Binik YM, Khalifé S. Pelvic floor muscle functioning in women with vulvar vestibulitis syndrome. J Psychosom Obstet Gynaecol. 2005 Jun;26(2):107-13.
Davidson MJ, Nielsen PMF, Taberner AJ, Kruger JA. Is it time to rethink using digital palpation for assessment of muscle stiffness? Neurourol Urodyn. 2020 Jan;39(1):279-285.