Chronic pelvic pain (CPP) is an umbrella diagnosis consisting of any pain in or around the pelvis lasting longer than 3-6 months that is non-malignant and non-cyclical. [1, 2] Chronic pelvic pain affects roughly 15% of women ages 18-50 and 10-40% of women presenting to their primary care providers, having a similar incidence to low back pain and asthma.[3,4] Overlapping impairments from a number of body systems make diagnosis difficult and delays treatment on average 6-8 years in the in the United States.[5,6] Imaging is often used to rule out malignancy or anatomical abnormalities, but is not effective in guiding care.[2,7,8]

Pelvic health physical therapists (PHPTs) are a part of the multidisciplinary team tasked with treating this patient population. They routinely perform intravaginal and intrarectal assessments of the pelvic floor muscles as they are thought to contribute to pain and dysfunction. [9, 10] However, this type of evaluation is not always available or appropriate, such as for people with vagnismus or for those who have experienced sexual trauma. Although their contribution to CPP is not well known, extra pelvic symptoms and impairments such as low back pain, altered posture (increased kyphosis, sway back, posterior pelvic tilt, rounded shoulders), decreased hip range of motion and increased muscle stiffness have been identified in approximately 85% of individuals with CPP.[11-14] Therefore, a routine orthopedic assessment of extra pelvic muscles and joints are usually performed in addition to or in lieu of an intravaginal assessment in these patients.

Although some studies suggest extra pelvic muscle and joint impairments may contribute to CPP, other studies question the clinical relevance of such findings. Several studies have shown areas of increased tenderness in muscles of the abdomen, hips, and lumbar spine refer pain to the pelvis.[14-18] another study showed that women with CPP present with increased muscle stiffness in the rectus femoris, adductor longus, lumbar par spinals at the level of L1/L2 and L4/L5 and the piriformis.19 However, the increased stiffness was not correlated to pain sensitivity, decreased pain pressure threshold (PPT), as has previously been hypothesized.[14-15, 17-19]  Moreover, it is currently unknown whether extra pelvic muscle stiffness is associated with common symptoms of CPP such as urological function, pain with intercourse, or birth and medical history thought to contribute to CPP. If extra pelvic muscle stiffness is associated with CPP symptoms, these relationships may help categorize impairments into sub classifications and improve efficiency of treatment of CPP. Therefore, the purpose of this study was to assess the association of extra pelvic muscular stiffness measures with pelvic symptoms and other clinical impairments in a cohort of women with CPP. In addition to bivariate correlations, exploratory factor analysis (EFA) was used to identify multivariate clinical presentation patterns that might suggest the existence of clinical subgroups of women with CPP.

Participants

One-hundred and forty-nine women with CPP were recruited and enrolled via phone call, print, and in-person advertising within San Antonio Military Medical Center between December 2017 and February 2019 for a one-time data collection appointment. Inclusion criteria were Department of Defense beneficiaries (active-duty military or civilian dependents) between the ages of 18 and 50 assigned female at birth and currently identifying as such, and able to read and understand English. Specific pain inclusion criteria included current non-cyclical “abdominal-lumbopelvic” pain with a duration of 3 months or longer. The location of the pain was defined as below the umbilicus, between the two ilia and above the pubic symphysis to include the vulva, but not the legs or thighs.

 Exclusion criteria were followed to ensure the reliability and validity of instrumentation such as the inability to lie prone, supine or side lying, or body mass index (BMI) over 33. [20] Additional exclusion criteria were followed to ensure pelvic pain was neuromuscular skeletal and not due to a more serious medical cause. Exclusion criteria included recent history of abdominal pelvic surgery, known pregnancy or postpartum within the last 6 months, current infection, neoplasm or history of radiation to the pelvic floor tissue or the tissues being measured for stiffness. [21,22] Participants were also excluded if they received any intervention aimed at decreasing muscle stiffness and pain such as dry needling, injections, or soft tissue intervention of any kind within the last 4 weeks. All data were collected in a private office in the uro gynecology department at San Antonio Military Medical Center. The study protocol was approved by the Central Regional Health Command Institutional Review Board. All participants provided consent prior to enrollment and the rights of the participant were protected.

Procedures

Outcome Measures and Questionnaires: All participants completed health history and demographic questionnaires, including uro gynecologic, obstetric, and trauma history. Questionnaires for psychosocial status, pain, and pelvic floor function, were also answered, via a computer tablet. 

The Beck Depression Index-II (BDI-II) consists of 21 items, assessing the intensity of depression in clinical and non-clinical populations. Each item is a list of four statements rated 0 to 3 resulting in a total score of 0 to 63. Higher scores indicate greater severity of symptoms. [9, 23] A score of 0-13 is considered no to minimal depression, 14-19 is mild, 20-28 is moderate and 29-63 is severe. [23] The Central Sensitization Inventory (CSI) is a two-part questionnaire intended to identify individuals with central sensitization syndrome (CSS) or multiple somatic symptoms and psychopathology that have been shown to predict poorer outcomes and higher healthcare utilization. Only the first section was used in this study, which consists of 25 items, each with a 5-point scale from 0 (never) to 4 (always) with a total possible score of 100. A cutoff of 40 was found to have good sensitivity (81%) and specificity (79%) for identifying those with CSS compared to healthy counterparts. [24, 25]

The Numeric Pain Rating Scale (NPRS) is a reliable, generalizable, and internally consistent measure of clinical and experimental pain intensity in individuals with musculoskeletal disorders. [26, 27] Participants rated their current pain on a scale of 0 to 10 with 0 being no pain at all and 10 being the worst pain imaginable. To assess variability and intensity of pain, participants also rated their worst pain within the past week and their lowest level of pain within the last week. All pain measurements were averaged to use for statistical analysis.

Pelvic floor dysfunction was assessed through the use of the Pelvic Floor Impact Questionnaire-7 (PFIQ-7), a shortened version of the PFIQ. [28] Consisting of 21 total questions, the PFIQ-7 assesses the impact of pelvic floor related disorders on day-to-day function via 3 subscales made up of seven questions in each. Responses may be not at all (0), a little (1), moderately (2) or a lot (3). The three subscales focus on the impact of colorectal-anal, pelvic organ prolapse, and urinary incontinence symptoms on activities of daily living. The final score is calculated by multiplying subscale scores by 33.3 so the total score varies from 0 to 300. The higher the final score, the greater the symptoms impact quality of life. [28] This short form has been found to have excellent test-retest reliability and a change of 12% or 36 points was found to be the minimal clinically important change (MCID).[28]            

Muscle Stiffness Measurement: Tissue stiffness or elasticity is most commonly quantified as Young’s modulus, defined as the slope of the stress-strain curve of a material in the elastic deformation region of interest. [29, 30] Biomechanical elasticity measurements were obtained using the Myoton Pro (Myoton AS, Tallinn, Estonia). The Myoton Pro applies a mechanical impulse to the skin, which is transmitted to the underlying soft tissue and muscle (0.58 N for 15 ms). [31, 32] The muscle responds to the external mechanical impulse by a damped natural oscillation. The oscillation of the muscle is recorded by an accelerometer in the form of an acceleration signal. The recorded tissue stiffness is a combined measure of both neuromuscular activity and viscoelasticity of the muscle at rest and calculated from the acceleration signal. The dynamic stiffness (S) in Myoton Pro is expressed as S = mp/d, where m is the mass of the probe (18 g), p is the maximum amplitude of the oscillation in the acceleration signal, and d is the amplitude of the displacement signal at the end of the impulse time. [33]

The device was gently placed against the skin, perpendicular to the muscle being tested, in compliance with usage instructions from the manufacturer. One measurement was taken from each muscle.³⁴ Measurement location within each muscle was standardized based on ease of accessibility to superficial muscle tissue and standardized procedures from muscular electromyography (EMG) measurement locations, due to the hypothesis that these areas will have most neuromuscular activity and therefore stiffness. [20, 33, 35] Each measurement was taken with the muscle at rest and supported.

Stiffness measurements were taken in the same order for every participant due to time at rest affecting muscle stiffness measurements. [36] Measurements were taken in the order of: (1) rectus femoris, (2) rectus abdomens, (3) tensor fascia latae, (4) gluteus medius, (5) quadratus labarum, (6) iliac us, (7) adductor longus, (8) adductor magnus, (9) L1/L2 paraspinal, (10) L4/L5 para spinal, and (11) piriformis. These muscles were selected based on anatomical or biomechanical link to the presentation of CPP as shown in Appendix A. Muscles were chosen based on three different criteria; (1) if they have been identified as facilitators of pelvic floor activation (2) they limit hip internal or external rotation, or (3) they surround the tract of peripheral pelvic nerves thought to contribute to CPP. [37-42] all selected muscles were also consistent with myofascial pain referral maps of the abdominopelvic and perineal region. [43] Participants' muscle stiffness was measured unilaterally by one tester. When a participant had pain on both sides, they were asked to identify the most painful side. If they could not identify a more painful side, then they were assigned a side based on predetermined randomization. A full description of measurement positioning, location and palpation can be found in the Appendix B.

Data Analysis

All statistics were performed using IBM SPSS Statistics (Windows, Version 22.0. Armonk, NY: IBM Corp). Descriptive statistics were performed to describe the sociodemographic (age, sex, race, etc.) and health characteristics (disability, pain intensity, psychosocial factors, etc.) of the sample. Means and standard deviations were used for continuous data and frequency distributions were analyzed for categorical data, while median values were used to describe duration of symptoms.

Pearson’s r correlation was used to quantify associations between muscle stiffness, pain outcomes, and health history characteristics. Associations were considered statistically significant if 2-tailed p-values were less than 0.05, unless otherwise stated. Correlations were further described using categorization of weak (r=0-.3), moderate (r=.4-.6), and strong (r=.7-.9). [44]

Exploratory factor analysis (EFA) was used to identify patterns (co-variation) of muscle stiffness, pelvic floor function, pain and psychosocial status that might indicate clinical subgroups of CPP. Although a sample size of at least 300 is recommended by Comfrey and Lee, factors with at least four loadings greater than 0.6 are considered reliable regardless of sample size. [45]

Principal component analysis was used as the extraction method while Oblimin with Kaiser Normalization was used as the rotation method. Twenty-five variables were chosen to undergo EFA with a fixed number of three chosen factors for analysis based on the point of inflection in the scree plot, shown in Figure 1. The 20 variables seen in table 3 were chosen from a pool of 70 based on the criteria that they were continuous level variables covering the breadth of impairment systems that were thought to contribute to CPP. Variables were deleted if they did not correlate with any other variable or had a correlation with other variables greater than r =.9 to reduce redundancy of measuring the same phenomena within CPP.

One-hundred and forty-nine women with CPP were enrolled in the study. Descriptive statistics for participants with CPP are summarized in Table 1.

Table 1: Demographic information and clinical characteristics of participants (n=149).

The purpose of this study was to assess the association of extra pelvic muscular stiffness measures with pelvic symptoms and other clinical impairments in a cohort of women with CPP.  These results demonstrate that some aspects of prior health history, psychosocial status, current pain levels, and range of motion are significantly, but weakly, correlated with extra pelvic muscle stiffness measurements. To date, this analysis was the first to explore the relationship between extra pelvic muscle stiffness and the common impairments targeted during physical therapy intervention of CPP. This data reveals that the importance given to extra pelvic muscle stiffness as a pain precipitating impairment in people with CPP may be overstated.

Overall, self-report pain level and extra pelvic muscle stiffness are not strongly correlated in women with CPP. Additionally, clinical importance of the relationship between medical and birth history to extra pelvic muscle stiffness was not strongly supported by this data. The strongest significant correlation of medical history to muscle stiffness was the relationship between a history of abdominal surgery and gluteus medius stiffness (r=.355, p=<.001) which only demonstrated a weak to moderate correlation. One hypothesis for this relationship is increased stiffness of the gluteus medius results from the pelvis seeking increased frontal plane stability when the anterior abdominal wall has been incised, disrupting the anticipatory and reactive function of the transverse abdomens.

The attempt to use a patient’s medical history to guide what extra pelvic tissue or structure to intervene upon by a physical therapist is not supported by this research. The relationship between extra pelvic muscle stiffness, self-reported pain level, and the patient’s medical history may be more meaningful if the identified tissue is reported as the primary area of pain by the patient. The extra pelvic muscles measured in this research were not the areas of primary pain reported by the participants.

There was not a significant correlation between extra pelvic muscle stiffness and the diagnoses of pelvic organ prolapse, interstitial cystitis, endometriosis, recurrent urinary tract infections, or polycystic ovarian syndrome. There are two hypothesized reasons for these findings. First, muscle dysfunction associated with these medical diagnoses is most likely occurring in the pelvic floor muscles. Previous research has noted increased muscle stiffness, tone, and impaired motor function of the pelvic floor muscles in women with provoked vestibulodynia, one type of CPP.⁴⁶ Stiffness of the pelvic floor muscles was not measured in this study due to the limitations of the instrumentation used. Secondly, increased severity of prolapse, increased amount of Hunner’s lesions in interstitial cystitis, and increased number of endometrial lesions are not associated with increased pain.^47,48 These findings add to the evidence that increased path anatomical severity does not correlate to clinical impairments such as pain and muscle stiffness found in CPP.

The current clinical paradigm is that areas of increased muscular stiffness or palpable bands are an important impairment to treat due to their role in pain production through pain referral patterns, altering movement patterns, or restricting range of motion. [46, 49, 50] However, extra pelvic muscle stiffness was not correlated with increased pain with pressure (PPT) of the same muscle. [19] It was also not associated with NPRS in the women with CPP in this study. Without a strong relationship to pain, the clinical meaningfulness of stiffness may lie in its relationship to function.

Increased extra pelvic muscle stiffness may inform the practitioner of neuromuscular and viscoelastic changes in response to pain. These changes could potentially impact movement and function of the pelvic floor and lumbopelvic complex, perpetuating increased extra pelvic muscle stiffness. The previous example of pelvic floor muscle impairments in people with provoked vestibulodynia is an excellent example of muscles changing in response to pain as this diagnosis is classified due to its pain presentation and not by a disease state.

In addition to bivariate correlations, exploratory factor analysis (EFA) was used to identify multivariate clinical presentation patterns that might suggest the existence of clinical subgroups of women with CPP. The EFA resulted in a 3-component solution with at least 6 variables per component with 3 loadings greater than 0.6. We labeled the 3 components: “pelvic floor dysfunction and psychosocial involvement,” “muscle stiffness of the thighs and hips,” and “muscle stiffness of the abdominals and lumbar spine.”

The first component, “pelvic floor dysfunction and psychosocial involvement,” combines higher scores on psychosocial outcome measures with increased pelvic floor dysfunction as measured by the PFIQ and higher levels of pain measured by the NPRS. The combination of pelvic floor dysfunction and psychosocial involvement is common in women with CPP and may explain greater chronicity of symptoms and pain, necessitating a multidisciplinary approach to treatment. [11, 47, 51] Like other chronic pain syndromes, there is a higher incidence of mental health impairments such as depression and anxiety in this population. [10, 11] Uniquely however, people with CPP are more likely to suffer from sexual or other trauma. [52, 53]  A history of trauma uniquely primes their nervous system for sensitization, resulting in increased sensitivity to touch, increased muscle guarding or activation and anticipation of pain in otherwise innocuous experiences. [11] This tissue sensitization may not have been captured in this study because we did not examine the pelvic floor muscles themselves. Delineating this as an independent component, or subgroup, may be useful to appropriately triage patients to specialized PHPTs and multidisciplinary care. The subsequent components reveal symptoms or impairments that are more orthopedic in nature.

The second component “muscle stiffness of the hips and thighs” demonstrated increased stiffness of the piriformis and adductors as the highest loading symptoms. The third component, “muscle stiffness of the low back and abdomen,” demonstrated the highest loading symptoms as muscle association of the lumbar par spinals at both levels and the iliac us. The superficial lumbopelvic nerves that provide sensation to the lower abdomen, upper thigh, inner thigh and genitals all originate at L1-L2 and trace around the abdominal muscles and their fiscal planes as well as through the iliac us in some cases. [54] The iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, genital femoral and obdurate nerve could all be restricted in movement or blood flow with increased stiffness of the muscles within the third component.

The participants enrolled in this study were those who had not yet sought out care, therefore, the latter two components may be more prevalent in the general population than we are clinically aware of now. Due to the presence of less bothersome symptoms, decreased pelvic floor dysfunction, and less sensitization of the central nervous system, these patients may not seek out any care, especially specialized PHPT care. It is recommended that those with pelvic pain seek treatment sooner rather than later to potentially decrease central sensitization and pain chronicity. [55] Early intervention by orthopedic physical therapy (OPT), which is often more accessible, may prevent or decrease progression to centralized pain processing and psychosocial involvement found in CPP.

Continuing to identify clinical components of CPP which are appropriate for all physical therapists to treat may decrease the reliance on specialty care from PHPTs. Although extra pelvic muscle stiffness was not found to be a pain producing impairment to intervene upon, it was helpful in forming distinct sub classifications in the EFA. As stated earlier, muscle stiffness may be a more objective identification of a movement or neuromuscular impairment than the patient’s pain experience; however, the EFA may be a starting point to better understand who may be appropriate for OPT treatment versus specialized PHPT care. Further research looking at the relationship of muscle stiffness and performance of the pelvic floor, changes in gait, and movement impairments of those with CPP is needed to contribute to the utility of clinical sub classifications. This research lays the foundation for clinical sub classifications of CPP as a screening tool that may help appropriately triage women with CPP to appropriate therapeutic interventions.

Limitations

Using the Myoton Pro to only measure peripheral and superficial muscle stiffness in a syndrome that also impacts pelvic floor musculature is a limitation in the ability to fully understand the impact of extra pelvic stiffness on this population and in creating impairment sub classifications. Many of the muscular impairments that are treated by PTs in CPP are within the pelvis itself and were not measured.

Without a strong relationship to pain, the clinical meaningfulness of stiffness lies in its relationship to function. This study fell short in addressing the relationship between muscle stiffness and motor function. Future research quantifying potential movement impairments and their relationship to extra pelvic muscle stiffness in CPP is warranted. This category of research is also necessary to empower physical therapists with strategies to address CPP from an extra pelvic, orthopedic approach that may be more accessible or appropriate for some patients.

This research also has limitations in its ability to be generalized due to sampling bias. Participants were recruited from an active-duty military base which serves civilian and retired individuals, but the activity level, general health, and exposure to trauma may be different than the general population. Additionally, the inclusion criteria were limited to women identified as female at birth and currently identifying as female to decrease the number of variables within the population. However, the researchers understand that every gender identity experiences CPP and being transgender or undergoing gender affirmation surgery may increase the incidence of CPP and necessitates further investigation. [56,57] Also, the average pain level of participants was generally low, presumably due to only recruiting people who were not seeking care. Correlations between pain levels, stiffness and subjective impairment along with clinical sub classifications may differ in those with higher reported pain levels.

This preliminary EFA is not intended to drive treatment decisions. Instead, it can be used to direct future studies of physical therapy sub classifications of CPP. The information provided in this preliminary exploration of the relationship between muscle stiffness and clinical impairments is intended to inform the clinician of the evidence supporting patient presentation patterns rather than anecdotal evidence alone as is currently the practice. As with other treatment-based classifications, these classifications are intended to be used as part of a first line screening tool. Improved efficiency by means of referring to the most appropriate providers could result in improved access to care and possibly decrease unnecessary wait times for specialized PHPT in both the military and civilian population.

xtra pelvic muscle stiffness as measured by the MyotonPro was not strongly correlated to overall self-report pain level. Muscles that are commonly treated by physical therapists in the CPP population had small to moderate correlations to urogynecologic health history. Extra pelvic muscle stiffness should not be a prioritized pain producing impairment when treating CPP unless it is within the area of primary pain. Further research is needed to establish if increased extra pelvic muscle stiffness plays a role in impaired motor function within this population.

The EFA resulted in three components of impairments, 1) pelvic floor dysfunction and greater psychosocial involvement, 2) muscle stiffness of the hips and thighs, 3) muscle stiffness of the abdominal and lumbar spine. These classifications are a preliminary attempt to improve the ability of first line practitioners to triage those with CPP to the appropriate physical therapy practitioner based on their clinical presentation and health history. Patients displaying symptoms and impairments consistent with the first component may be most appropriate to be seen by a trained PHPT and multidisciplinary team, while patients displaying symptoms and impairments consistent with the latter two components may benefit from the care of a more accessible OPT.

I would like to thank the following individuals for their expertise and contributions throughout the data collection of this study, Edita Dragusin, Athena Farias, and Tina Greenlee.

I would also like to acknowledge that this work was funded by the Army Medical Department (AMEDD) Advanced Technology Initiative (AAMTI), through the Telemedicine and Advanced Technology Research Center (TATRC) at the US Army Medical Research and Materiel Command.

Measurement Location for MyotonPro and PPT Participant Positioning

Measurement will be taken with patient lying supine with both hips and knees comfortably bent, supported with a bolster. Measure 6 inches inferior to ASIS

Lumbar paraspinals: Measurements will be taken with the participant lying prone with a pillow under their hips. L1-L2, identify 12th Rectus femoris: rib and follow to the spine and bisect the muscles of the lumbar paraspinals. L4-L5, identify iliac crest and move medial to identify L4-L5 interspinous space, move lateral to bisect muscle bulk.

Rectus abdominus: Measurement will be taken with the patient in supine with knees supported with bolster. Measure 1 inch superior and .5-inch lateral to center of pubic bone. 

Adductors: Measurements will be taken with the patient in sideling with their top leg bent at the knee.  Measurements will be taken of their bottom leg in this position. Measuring adductor longus; 1 inch inferior to pubic bone. Measuring adductor magnus; roll top knee over to pillow. Find the common hamstring insertion into ischial tuberosity, follow pubic ramus medial 2 inch and distal 2 inches.

Hip external rotators with common origin into greater trochanter: Measurements taken in the same positioned as lumbar paraspinals. Identify PSIS and follow sacrum down to coccyx, bisect distance and draw line to greater trochanter.  Identify muscle in that location right off of sacrum.

Iliacus:  Measurements taken in sideling with both knees bent, with measurements being taken of the top leg. Find the ASIS and palpate just medial angeling MyotonPro parallel to the table.  

Tensor Fascia Latae: Measurements taken in sideling with both knees bent, with measurements being taken of the top leg. To take the measurement, bisect the distance between ASIS and greater trochanter. 

Gluteus medius: Measurements taken in sideling with both knees bent, with measurements being taken of the top leg. To measure find the area midway between greater trochanter and the PSIS. 

Quadratus Lumborum: Measurements taken in sideling with both knees bent, with measurements being taken on the superior quadratus lumborum. To find the area, trace immediately inferior to 12th rib and lateral to lumbar erector spinae.

1. Gunter J. Chronic pelvic pain: an integrated approach to diagnosis and treatment. Obstet Gynecol Surv. 2003; 58: 615-623.
2. Speer LM, Mushkbar S, Erbele T. Chronic Pelvic Pain in Women. Am Fam Physician. 2016; 93: 380-387.
3. Gunter J. Vulvodynia: new thoughts on a devastating condition. Obstet Gynecol Surv. 2007; 62: 812-819.
4. Mathias SD, Kuppermann M, Liberman RF, Lipschutz RC, Steege JF. Chronic pelvic pain: prevalence, health-related quality of life, and economic correlates. Obstet Gynecol. 1996; 87: 321-327.
5. Mann J, Shuster J, Moawad N. Attributes and barriers to care of pelvic pain in university women. J Minim Invasive Gynecol. 2013; 20: 811-818.
6. Ball E, Khan KS. Recent advances in understanding and managing chronic pelvic pain in women with special consideration to endometriosis. F1000Res. 2020; 9.
7. Ortiz DD. Chronic pelvic pain in women. Am Fam Physician. 2008; 77: 1535-1542.
8. Dydyk AM, Gupta N. Chronic Pelvic Pain. In: StatPearls. StatPearls Publishing; 2020.
9. Twiddy H, Lane N, Chawla R, et al. The development and delivery of a female chronic pelvic pain management programme: a specialised interdisciplinary approach. Br J Pain. 2015; 9: 233-240.
10. Bonder JH, Chi M, Rispoli L. Myofascial Pelvic Pain and Related Disorders. Phys Med Rehabil Clin N Am. 2017; 28: 501-515.
11. Alappattu MJ, Bishop MD. Psychological Factors in Chronic Pelvic Pain in Women: Relevance and Application of the Fear-Avoidance Model of Pain. Phys Ther. 2011; 91: 1542-1550.
12. Montenegro MLLS, Vasconcelos ECLM, Candido Dos Reis FJ, Nogueira AA, Poli-Neto OB. Physical therapy in the management of women with chronic pelvic pain. Int J Clin Pract. 2008; 62: 263-269.
13. Harris-Hayes M, Spitznagle T, Probst D, Foster SN, Prather H. A Narrative Review of Musculoskeletal Impairments Associated With Nonspecific Chronic Pelvic Pain. PM R. 2019; 11 Suppl 1: S73-S82.
14. Tu FF, As-Sanie S, Steege JF. Musculoskeletal causes of chronic pelvic pain: a systematic review of existing therapies: part II. Obstet Gynecol Surv. 2005; 60: 474-483.
15. Sanses TVD, Chelimsky G, McCabe NP, et al. The Pelvis and Beyond: Musculoskeletal Tender Points in Women with Chronic Pelvic Pain. Clin J Pain. 2016; 32: 659-665.
16. Tu FF, As-Sanie S, Steege JF. Musculoskeletal causes of chronic pelvic pain: a systematic review of diagnosis: part I. Obstet Gynecol Surv. 2005; 60: 379-385.
17. Fuentes-Márquez P, Valenza MC, Cabrera-Martos I, Ríos-Sánchez A, Ocón-Hernández O. Trigger Points, Pressure Pain Hyperalgesia, and Mechanosensitivity of Neural Tissue in Women with Chronic Pelvic Pain. Pain Med. 2019; 20: 5-13.
18. Bradley MH, Rawlins A, Brinker CA. Physical Therapy Treatment of Pelvic Pain. Phys Med Rehabil Clin N Am. 2017; 28: 589-601.
19. Proulx L. Comparison of Peripheral Muscle Stiffness in Women with and without Chronic Pelvic Pain. Presented at the: American Physical Therapy Association Combined Sections Meeting; February 24, 2021; Online.
20. Chuang L-L, Wu C-Y, Lin K-C, Lur S-Y. Quantitative mechanical properties of the relaxed biceps and triceps brachii muscles in patients with subacute stroke: a reliability study of the myoton-3 myometer. Stroke Res Treat. 2012: 617694.
21. Lawrence MV, Saynak M, Fried DV, et al. Assessing the impact of radiation-induced changes in soft tissue density ? thickness on the study of radiation-induced perfusion changes in the lung and heart. Med Phys. 2012; 39: 7644-7649.
22. Romano M, Cacciatore A, Giordano R, La Rosa B. Postpartum period: three distinct but continuous phases. J Prenat Med. 2010; 4: 22-25.
23. Dozois DJA, Dobson KS, Ahnberg JL. A psychometric evaluation of the Beck Depression Inventory–II. Psychol Assess. 1998; 10: 83.
24. Neblett R, Cohen H, Choi Y, et al. The Central Sensitization Inventory (CSI): establishing clinically significant values for identifying central sensitivity syndromes in an outpatient chronic pain sample. J Pain. 2013; 14: 438-445.
25. Mayer TG, Neblett R, Cohen H, et al. The development and psychometric validation of the central sensitization inventory. Pain Pract. 2012; 12: 276-285.
26. Childs JD, Piva SR, Fritz JM. Responsiveness of the numeric pain rating scale in patients with low back pain. Spine. 2005; 30: 1331-1334.
27. Michener LA, Snyder AR, Leggin BG. Responsiveness of the numeric pain rating scale in patients with shoulder pain and the effect of surgical status. J Sport Rehabil. 2011; 20: 115-128.
28. Barber MD, Walters MD, Bump RC. Short forms of two condition-specific quality-of-life questionnaires for women with pelvic floor disorders (PFDI-20 and PFIQ-7). Am J Obstet Gynecol. 2005; 193: 103-113.
29. Ballyns JJ, Shah JP, Hammond J, Gebreab T, Gerber LH, Sikdar S. Objective sonographic measures for characterizing myofascial trigger points associated with cervical pain. J Ultrasound Med. 2011; 30: 1331-1340.
30. Kawchuk GN, Decker C, Dolan R, Fernando N, Carey J. The feasibility of vibration as a tool to assess spinal integrity. J Biomech. 2008; 41: 2319-2323.
31. Peipsi A, Kerpe R, Jäger H, Soeder S, Gordon C, Schleip R. Myoton Pro: A Novel Tool for the Assessment of Mechanical Properties of Fascial Tissues. J Bodyw Mov Ther. 2012; 16: 527.
32. Ditroilo M, Hunter AM, Haslam S, De Vito G. The effectiveness of two novel techniques in establishing the mechanical and contractile responses of biceps femoris. Physiol Meas. 2011; 32: 1315-1326.
33. Technology - Myoton. Myoton. Accessed March 24, 2020.
34. Kelly JP, Koppenhaver SL, Michener LA, Proulx L, Bisagni F, Cleland JA. Characterization of tissue stiffness of the infraspinatus, erector spinae, and gastrocnemius muscle using ultrasound shear wave elastography and superficial mechanical deformation. J Electromyogr Kinesiol. 2018; 38: 73-80.
35. Arturo Leis A, Trapani VC. Atlas of Electromyography. 1 edition. Oxford University Press; 2000.
36. Nair K, Masi AT, Andonian BJ, et al. Stiffness of resting lumbar myofascia in healthy young subjects quantified using a handheld myotonometer and concurrently with surface electromyography monitoring. J Bodyw Mov Ther. 2016; 20: 388-396.
37. Yani MS, Wondolowski JH, Eckel SP, et al. Distributed representation of pelvic floor muscles in human motor cortex. Sci Rep. 2018; 8: 7213.
38. Ptaszkowski K, Paprocka-Borowicz M, S?upska L, et al. Assessment of bioelectrical activity of synergistic muscles during pelvic floor muscles activation in postmenopausal women with and without stress urinary incontinence: a preliminary observational study. Clin Interv Aging. 2015; 10: 1521-1528.
39. Peschers UM, Gingelmaier A, Jundt K, Leib B, Dimpfl T. Evaluation of pelvic floor muscle strength using four different techniques. Int Urogynecol J Pelvic Floor Dysfunct. 2001; 12:27-30.
40. Tuttle LJ, De Lozier ER, Harter SKA, Johnson SSA, Plotts SCN, Swartz SJL. The Role of the Obturator Internus Muscle in Pelvic Floor Function. J womens health phys therapy. 2016; 40: 15-19.
41. Tuttle LJ, Autry T, Kemp C, et al. Hip exercises improve intravaginal squeeze pressure in older women. Physiother Theory Pract. 2019:1-8.
42. Leighton RD. A functional model to describe the action of the adductor muscles at the hip in the transverse plane. Physiother Theory Pract. 2006; 22: 251-262.
43. Pastore EA, Katzman WB. Recognizing myofascial pelvic pain in the female patient with chronic pelvic pain. J Obstet Gynecol Neonatal Nurs. 2012; 41: 680-691.
44. Akoglu H. User’s guide to correlation coefficients. Turk J Emerg Med. 2018; 18: 91-93.
45. Comrey AL, Lee HB. A First Course in Factor Analysis. Psychology Press; 2013.
46. Morin M, Binik YM, Bourbonnais D, Khalifé S, Ouellet S, Bergeron S. Heightened Pelvic Floor Muscle Tone and Altered Contractility in Women With Provoked Vestibulodynia. J Sex Med. 2017; 14: 592-600.
47. Yosef A, Allaire C, Williams C, et al. Multifactorial contributors to the severity of chronic pelvic pain in women. Am J Obstet Gynecol. 2016; 215: 760.e1-e760.e14.
48. Mabrouk M, Raimondo D, Del Forno S, et al. Pelvic floor muscle assessment on three- and four-dimensional transperineal ultrasound in women with ovarian endometriosis with or without retroperitoneal infiltration: a step towards complete functional assessment. Ultrasound Obstet Gynecol. 2018; 52: 265-268.
49. Koppenhaver S, Gaffney E, Oates A, et al. Lumbar muscle stiffness is different in individuals with low back pain than asymptomatic controls and is associated with pain and disability, but not common physical examination findings. Musculoskelet Sci Pract. 2020; 45: 102078.
50. Shah JP, Gilliams EA. Uncovering the biochemical milieu of myofascial trigger points using in vivo microdialysis: an application of muscle pain concepts to myofascial pain syndrome. J Bodyw Mov Ther. 2008; 12: 371-384.
51. Brooks T, Sharp R, Evans S, Baranoff J, Esterman A. Predictors of Psychological Outcomes and the Effectiveness and Experience of Psychological Interventions for Adult Women with Chronic Pelvic Pain: A Scoping Review. J Pain Res. 2020; 13: 1081-1102.
52. Meltzer-Brody S, Leserman J, Zolnoun D, Steege J, Green E, Teich A. Trauma and posttraumatic stress disorder in women with chronic pelvic pain. Obstet Gynecol. 2007; 109: 902-908.
53. Klausner AP, Ibanez D, King AB, et al. The influence of psychiatric comorbidities and sexual trauma on lower urinary tract symptoms in female veterans. J Urol. 2009; 182: 2785-2790.
54. Netter FH. Atlas of Human Anatomy: Including Student Consult Interactive Ancillaries and Guides (Netter Basic Science). 6 edition. Saunders; 2014.
55. Jarrell JF, Vilos GA, Allaire C, et al. Consensus guidelines for the management of chronic pelvic pain. J Obstet Gynaecol Can. 2005; 27: 781-826.
56. O’Sullivan C, Day T, Scurry J. Vestibulovaginal Sclerosis in a Transgender Man on Testosterone. J Low Genit Tract Dis. 2020; 24: 229-231.
57. Moving Toward Gender Inclusive Pelvic Pain Healthcare. Accessed May 20, 2021.