Levator Plate Upward Lift on Dynamic Sonography and Levator Muscle Strength

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1 ORIGINAL RESEARCH Levator Plate Upward Lift on Dynamic Sonography and Levator Muscle Strength Ghazaleh Rostaminia, MD, Jennifer Peck, PhD, Lieschen Quiroz, MD, S. Abbas Shobeiri, MD Received December 4, 2014, from the Department of Obstetrics and Gynecology, Inova Fairfax Hospital, Falls Church, Virginia USA (G.R.); and Departments of Obstetrics and Gynecology and Biostatistics and Epidemiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma USA (J.P., L.Q., S.A.S.). Revision requested December 7, Revised manuscript accepted for publication January 8, This research was supported in part by the National Institutes of Health, National Institute of General Medical Sciences (grant 1 U54 GM A1). Address correspondence to S. Abbas Shobeiri, MD, Department of Obstetrics and Gynecology, Section of Female Pelvic Medicine and Reconstructive Surgery, University of Oklahoma Health Sciences Center, 920 Stanton L. Young Blvd, PO Box 26901, WP2410, Oklahoma City, OK USA. abbas-shobeiri@ ouhsc.edu doi: /ultra Objectives To compare digital palpation with levator plate lift measured by endovaginal and transperineal dynamic sonography. Methods Dynamic transperineal and endovaginal sonographic examinations were performed as part of multicompartmental pelvic floor functional assessment. Patients were instructed to perform Kegel contractions while a probe captured a video clip of levator plate movement at rest and during contraction in a 2-dimensional midsagittal posterior view. We measured the distance between the levator plate and the probe on endovaginal sonography as well as the distance between the levator plate and the gothic arch of the pubis on transperineal sonography. The change in diameter (lift) and levator plate lift ratio (lift/rest 100) were calculated. Pelvic floor muscle strength was assessed by digital palpation and divided into functional and nonfunctional groups according to the Modified Oxford Scale. Mean differences in levator plate upward lift were compared by Modified Oxford Scale scores using Student t tests and analysis of variance. Results Seventy-four women were available for analysis. The mean age was 55 (SD, 11.9) years. When measured by vaginal dynamic sonography, mean lift and lift/rest ratio values increased with increasing Modified Oxford Scale score (analysis of variance, P =.09 and.04, respectively). When scores were categorized to represent nonfunctional (0 1) and functional (2 5) muscle strength groups, the mean lift (3.2 versus 4.6 mm; P =.03) and lift/rest ratio (13% versus 20%; P =.01) values were significantly higher in women with functional muscle strength. All patients with lift of 30% or greater detected by vaginal sonography had functional muscle strength. Conclusions A greater levator plate lift ratio detected by dynamic endovaginal sonography was associated with higher muscle strength as determined by the Modified Oxford Scale. This novel measurement can be incorporated into sonographic evaluation of levator ani function. Key Words endovaginal sonography; genitourinary ultrasound; levator function; modified Oxford Scale A ccording to the International Urogynecology/International Continence Society joint report, voluntary pelvic floor muscle contraction and relaxation may be assessed by visual inspection, digital palpation, electromyography, dynamometry, perineometry, or sonography. 1 Vaginal pressure is a key measure of the strength of the pelvic floor muscles. Kegel 2,3 was the first to use a pneumatic resistance chamber to measure vaginal pressure and perform biofeedback therapy using this device to improve the strength of pelvic floor muscles. Digital palpation, which is the basic form of functional assessment of the levator ani muscle, has limited 2015 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2015; 34:

2 repeatability. 1 Messelink et al 1 recommended quantifying contractions by using the Modified Oxford Scale to classify digital pelvic muscle strength into 6 categories ranging from absent to strong. The Modified Oxford Scale is widely used in clinical practice, as it is easy to perform, is inexpensive, and requires no special equipment. Furthermore, vaginal palpation is an effective aid in providing feedback to patients when they perform a pelvic floor muscle contraction. 4 With the advent of magnetic resonance imaging 5 7 and dynamic sonographic technology, 8,9 there have been recent advances in the understanding of the anatomic changes occurring in pelvic floor architecture as a consequence of pelvic floor contraction. A good levator contraction will substantially shorten minimal levator hiatus diameters, effect a change in angle between the levator plate and symphysis pubis, and shift the bladder neck cranioventrally. 8,10,11 In seeking an effective method to evaluate pelvic muscle function, transperineal sonography has been used. More recently, endovaginal sonography has provided new indices for pelvic floor measurement. The vaginal ultrasound probe has the advantage of providing higher resolution and also helps patients contract the pelvic floor muscles against the probe, mimicking the digital examination. Upward lift of the levator plate as a result of pelvic floor contraction was used as indicator of levator muscle function in our study. The aim of our study was to compare pelvic floor strength assessed by digital palpation with the amount of levator plate lift on endovaginal and transperineal dynamic sonography for pelvic muscle function evaluation. Materials and Methods The study was approved by the Institutional Review Board at our institution. This cross-sectional study included 74 women who were referred to our urogynecology clinic because of different pelvic floor dysfunction symptoms and received dynamic pelvic floor sonographic assessment and documented digital pelvic floor palpation based on the Modified Oxford Scale between January 2013 and January Patients signed an informed consent form, completed a standardized interview, and received an examination using the pelvic organ prolapse quantification staging system, assessment of the pelvic floor by dynamic 3-dimensional endovaginal automatic acquisition sonography and dynamic transperineal sonography, and digital assessment of pelvic floor function using the Modified Oxford Scale. Patients with a history of pelvic floor reconstructive surgery and central nervous system or peripheral neurologic diseases were excluded. Sonographic Protocol Imaging was performed at the time of the primary visit with an Ultrafocus ultrasound system (BK Medical, Peabody, MA) and an MHz transducer and convex transperineal probe. All sonographic examinations were performed in the office setting, with the patient in the dorsal lithotomy position, with hips flexed and abducted. No preparation was required, and the patient was recommended to have a comfortable volume of urine in the bladder. No rectal or vaginal contrast agent was used. To avoid excessive pressure on surrounding structures that might distort the anatomy, the probe was inserted into the vagina in a neutral position. The 360 endovaginal sonographic volumes were digitally stored for further analysis. Dynamic transperineal and endovaginal sonographic examinations were performed as part of multicompartmental pelvic floor assessment in an office setting. Patients were instructed to perform a Kegel contraction while the probe captured a video clip of the levator plate movement in a 2-dimensional midsagittal posterior view. Sonographic volumes were evaluated by the senior investigator, who was blinded to the digital palpation score by the Modified Oxford Scale. The distance from the levator plate to the probe on endovaginal sonography (Figure 1) and the distance from the levator plate to the gothic arch of the pubis on transperineal sonography (Figure 2) were measured in millimeters in rest and contraction modes. The absolute change in diameter (lift) was calculated by subtracting the contraction measurement from the resting measurement. The relative change was calculated as the levator plate lift ratio (lift/rest 100) and expressed as a percentage. To calibrate the technique, initially 10 endovaginal levator plate resting and squeeze movements were obtained by 2 operators. The measurements were obtained live during the scanning by freezing the screen and using the ultrasound machine software to obtain the measurements. Complete agreement was found between the operators. Digital Palpation Based on the Modified Oxford Scale Protocol Pelvic floor muscle function was assessed subjectively by digital palpation while inserting a lubricated gloved index finger approximately 4 cm into the vagina. 12,13 All women were instructed to squeeze their levator ani muscles without activation of other groups of muscles: abdominal, gluteal, and adductor muscles. Muscle strength was graded on a 6-point Modified Oxford Scale: 0, no contraction; 1, minor muscle flicker; 2, weak muscle contraction; 3, moderate muscle contraction, 4; good; and 5, strong muscle contraction against resistance by the examining finger. 1, J Ultrasound Med 2015; 34:

3 Scores were recorded for both left and right sides, and the lower score was used for analysis. Statistical Methods Statistical analysis was performed with SAS version 9.2 software (SAS Institute, Inc, Cary, NC). Descriptive statistics were used to summarize the distribution of patient characteristics; t tests and analysis of variance were used to evaluate differences in absolute and relative mean measurements by pelvic floor muscle function (Modified Oxford Scale scores). Mean lift and lift/rest ratio measurements were compared by Modified Oxford Scale scores (0 5), combining scores 4 and 5 into a single category because of the small number (n = 3) of women with a score of 5. Figure 1. Distance between the levator plate and endovaginal probe on dynamic endovaginal sonography at rest (A) and during a Kegel contractions (B). A indicates anterior; AR, anorectum; C, cephalad; EVP, endovaginal probe; LP, levator plate; and P, posterior. Figure 2. Distance between the levator plate and pubis on dynamic transperineal sonography at rest (A) and during a Kegel contraction (B). A indicates anterior; AR, anorectum; B, bladder; C, cephalad; LP, levator plate; P, posterior; PS, pubic symphysis; and TPP, transperineal probe. J Ultrasound Med 2015; 34:

4 Due to the limited sample size within each group defined by Modified Oxford Scale scores, mean comparisons were also examined after categorizing Modified Oxford Scale scores to reflect nonfunctional (scores 0 1) and functional (scores 2 5) pelvic floor muscles. Results Seventy-four women were available for analysis. The mean age and body mass index were 55 (SD, 11.9) years and 28.6 (SD, 6.3) kg/m 2, respectively; median parity was 3 (range, 1 6); 95.4% of patients were white; and 70.4% had prior hysterectomy. Means, medians, and ranges of perineal and vaginal sonographic measurements are summarized in Tables 1 and 2. On endovaginal sonography, the mean levator plate lift and mean lift ratio increased with increasing Modified Oxford Scale score (Figure 3; analysis of variance, P =.09 and.04, respectively). Although mean levator plate lift increased from 2.1 mm in those with a Modified Oxford Scale score of 0 to 5.2 mm in those with a score of 4 or 5, this difference was marginal but did not achieve statistical significance. The mean lift ratio, however, significantly increased from 10% to 24% in those with Modified Oxford Scale scores of 0 and 4 or 5. When Modified Oxford Scale categories were collapsed by functional status to improve precision, the mean levator plate lift and mean lift ratio were 3.2 (SD, 2.1) mm and 13.0% (SD, 8.2%), respectively, in women with nonfunctional muscle strength; however, the lift and lift/rest ratio were 4.6 (SD, 2.8) mm and 20.1% (SD, 11.2%) in women with functional muscle strength (Figure 4). The position of the levator plate at rest relative to the vaginal probe was lower in women with nonfunctional muscle strength than in those with functional muscle strength (24.1 versus 22.5 mm), which may be attributed to loss of resting muscle tone. Only when measured by vaginal dynamic sonography were the mean lift and lift/rest ratio values significantly different between nonfunctional and functional muscle strength groups as assessed by Modified Oxford Scale digital palpation (P =.03 and.01, respectively). All 8 patients with lift of 30% or greater detected by vaginal sonography had good muscle strength on their Modified Oxford Scale digital palpation (Figure 3). In contrast, the lift and lift/rest ratio differences observed on perineal sonography were not statistically significant when compared across each Modified Oxford Scale score (P =.53 and.37) or when compared by nonfunctional versus functional muscle strength (P =.23 and.17). Discussion Our study shows that the levator plate lift ratio as detected by dynamic endovaginal sonography is a good predictor of levator ani muscle function as measured by the Modified Oxford Scale. All women who could elevate their levator plate to greater than 30% of its rest position had functional levator muscle strength (Modified Oxford Scale score of 2 5). On average, patients with nonfunctional muscle strength (Modified Oxford Scale score of 0 1) had a mean lift/rest ratio of 13%, and those with functional muscle strength (Modified Oxford Scale score of 2 5) had a mean lift/rest ratio of 20%. Additionally, when muscle strength was scored 0 1 on the Modified Oxford Scale, endovaginal sonography could still detect levator plate lift in most women. That is, 20% with Modified Oxford Scale scores of 0 1 had lift/rest ratios of greater than 10%. As shown in Table 1, the mean resting position of the levator plate in the nonfunctional group was lower than that in the functional group, and although the nonfunctional group could lift their levator plate, this lift brought the mean levator plate lift of the nonfunc- Figure 3. Distribution of dynamic vaginal sonographic measurements of levator plate lift and the lift ratio by Modified Oxford Scale digital palpation J Ultrasound Med 2015; 34:

5 tional group during Kegel contractions barely to the resting position of the functional group. This finding indicates that, although these muscles move, their movement is ineffective and in some cases below the threshold of a human digit s sensitivity. In a study of the correlation between digital palpation (Modified Oxford Scale) and dynamic transperineal sonography for muscle function evaluation, 14 the authors used bladder neck displacement as their index of muscle strength and found correlations ranging from 0.52 to 0.62 with dynamic transperineal sonography. In another study of 31 Figure 4. Distribution of dynamic vaginal sonographic measurements of the levator plate lift ratio by Modified Oxford Scale digital palpation. women, the change in anorectal angle on transperineal sonography was used as an index of pelvic floor muscle contraction. 15 These authors reported that pelvic floor muscle responses of healthy participants and those with stress urinary incontinence were significantly different. In another study of 446 nulligravid women in their first pregnancy and after their delivery, muscle function was evaluated with digital palpation based on the Modified Oxford Scale and dynamic transperineal sonography. 16 Pelvic floor muscle function on transperineal sonography was determined as the amount of bladder neck lift in the midsagittal plane, shortening of the midsagittal hiatal diameter, and change in anorectal angle. The study showed that levator avulsion was associated with reduced contractile function of the pelvic floor. This effect was more easily detected by palpation than by sonographic indices of levator function. Steensma et al 17 studied the prevalence of major levator abnormalities in symptomatic patients with underactive pelvic floor contractions. The quality of pelvic floor contractions was evaluated on transperineal sonography as a reduction in the levator hiatus dimensions. The study showed that underactive pelvic floor muscles were associated with an increased prevalence of levator ani avulsion and fecal incontinence; however, the study did not compare different methods of muscle function evaluation. Our study showed that dynamic endovaginal sonography is a useful tool for predicting levator muscle function, but the associations observed when using endovaginal sonographic Table 1. Levator Plate Lift Detected by Endovaginal Sonographic Measurements and Levator Strength Detected by the Modified Oxford Scale Modified Vaginal Sonographic 25th 75th Oxford Scale n Measurements Mean (SD) Median Percentile Percentile Min Max Poor 22 Rest, mm (5.58) (nonfunctional) Lift, mm 3.15 (2.05) Lift/rest ratio, % (8.21) Good 43 Rest, mm (5.72) (functional) Lift, mm 4.64 (2.80) Lift/rest ratio, % (11.23) Table 2. Levator Plate Lift Detected by Perineal Sonographic Measurements and Levator Strength Detected by the Modified Oxford Scale Modified Perineal Sonographic 25th 75th Oxford Scale n Measurements Mean (SD) Median Percentile Percentile Min Max Poor 22 Rest, mm (8.66) (nonfunctional) Lift, mm 6.81 (4.21) Lift/rest ratio, % (7.61) Good 52 Rest, mm (9.50) (functional) Lift, mm 8.28 (5.02) Lift/rest ratio, % (7.38) J Ultrasound Med 2015; 34:

6 measurements were not replicated when using transperineal sonography. In addition, endovaginal sonography could visualize levator plate movements not palpated during Modified Oxford Scale palpation. Our study had certain limitations. A larger study population would be beneficial to achieve greater statistical power and improved precision. This factor will be addressed in our future projects. The method of Modified Oxford Scale digital palpation performed by our 3 physicians has intermediate inter-rater reliability; however, all evaluators were trained under the senior author s supervision to enhance the reliability of the method. Categorization of muscle strength evaluated by the Modified Oxford Scale as functional and nonfunctional is based on the definition of scores and not a validated term in the literature. Measurement of levator plate lift using endovaginal sonography seems more strongly associated with digital Modified Oxford Scale palpation rather than bladder neck lift, the change in anorectal angle, or the change in hiatal dimensions. Lift of the levator plate as well as the strength and duration of a contraction are 3 parameters evaluated while performing digital palpation; therefore, our study s use of the digital palpation method is consistent with standard techniques that are common in most practices. Additionally, the vaginal probe helps patients contract the pelvic floor muscles against the probe, mimicking the digital examination. In summary, our technique creates a feasible method for muscle function evaluation in the field. Studies are needed to replicate these findings in larger samples. In addition, comparison of levator plate lift to perineometric measurements may provide further evidence in favor of the effectiveness of endovaginal sonographic measurement as a method for evaluation of pelvic floor function. References 6. Miller JM, Perucchini D, Carchidi LT, DeLancey JO, Ashton-Miller J. Pelvic floor muscle contraction during a cough and decreased vesical neck mobility. Obstet Gynecol 2001; 97: Miller JM, Sampselle C, Ashton-Miller J, Hong GR, DeLancey JO. Clarification and confirmation of the Knack maneuver: the effect of volitional pelvic floor muscle contraction to preempt expected stress incontinence. Int Urogynecol J Pelvic Floor Dysfunct 2008; 19: Dietz HP, Tekle H, Williams G. Pelvic floor structure and function in women with vesicovaginal fistula. J Urol 2012; 188: Kruger JA, Dietz HP, Murphy BA. Pelvic floor function in elite nulliparous athletes. Ultrasound Obstet Gynecol 2007; 30: Dietz HP, Shek KL. Levator function and voluntary augmentation of maximum urethral closure pressure. Int Urogynecol J 2012; 23: Dietz HP. Female pelvic floor dysfunction: an imaging perspective. Nat Rev Gastroenterol Hepatol 2011; 9: van Delft K, Shobeiri SA, Thakar R, Schwertner-Tiepelmann N, Sultan AH. Intra- and interobserver reliability of levator ani muscle biometry and avulsion using three-dimensional endovaginal ultrasonography. Ultrasound Obstet Gynecol 2014; 43: Laycock J. Clinical evaluation of the pelvic floor. In: Schussler B, Laycock J, Norton P, Stanton S (eds). Pelvic Floor Re-education: Principles and Practice. Berlin, Germany: Springer-Verlag; 1994: Dietz HP, Jarvis SK, Vancaillie TG. The assessment of levator muscle strength: a validation of three ultrasound techniques. Int Urogynecol J Pelvic Floor Dysfunct 2002; 13: Peng Q, Jones R, Shishido K, Constantinou CE. Ultrasound evaluation of dynamic responses of female pelvic floor muscles. Ultrasound Med Biol 2007; 33: Guzman Rojas R, Wong V, Shek KL, Dietz HP. Impact of levator trauma on pelvic floor muscle function. Int Urogynecol J 2014; 25: Steensma AB, Konstantinovic ML, Burger CW, de Ridder D, Timmerman D, Deprest J. Prevalence of major levator abnormalities in symptomatic patients with an underactive pelvic floor contraction. Int Urogynecol J2010; 21: Messelink B, Benson T, Berghmans B, et al. Standardization of terminology of pelvic floor muscle function and dysfunction: report from the pelvic floor clinical assessment group of the International Continence Society. Neurourol Urodyn 2005; 24: Kegel AH. Progressive resistance exercise in the functional restoration of the perineal muscles. Am J Obstet Gynecol 1948; 56: Kegel AH. Physiologic therapy for urinary stress incontinence. J Am Med Assoc 1951; 146: Bo K, Finckenhagen HB. Vaginal palpation of pelvic floor muscle strength: inter-test reproducibility and comparison between palpation and vaginal squeeze pressure. Acta Obstet Gynecol Scand 2001; 80: DeLancey JO, Morgan DM, Fenner DE, et al. Comparison of levator ani muscle defects and function in women with and without pelvic organ prolapse. Obstet Gynecol 2007; 109: J Ultrasound Med 2015; 34: