Dataset Information

Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage.

ABSTRACT:

Background

One of the major causes of pelvic organ prolapse is pelvic muscle injury sustained during a vaginal delivery. The most common site of this injury is where the pubovisceral muscle takes origin from the pubic bone. We hypothesized that it is possible for low-cycle material fatigue to occur at the origin of the pubovisceral muscle under the large repetitive loads associated with pushing during the second stage of a difficult labor.

Purpose

The main goal was to test if the origin of the pubovisceral muscle accumulates material damage under sub-maximal cyclic tensile loading and identify any microscopic evidence of such damage.

Methods

Twenty origins of the ishiococcygeous muscle (homologous to the pubovisceral muscle in women) were dissected from female sheep pelvises. Four specimens were stretched to failure to characterize the failure properties of the specimens. Thirteen specimens were then subjected to relaxation and subsequent fatigue tests, while three specimens remained as untested controls. Histology was performed to check for microscopic damage accumulation.

Results

The fatigue stress-time curves showed continuous stress softening, a sign of material damage accumulation. Histology confirmed the presence of accumulated microdamage in the form of kinked muscle fibers and muscle fiber disruption in the areas with higher deformation, namely in the muscle near the musculotendinous junction.

Conclusions

The origin of ovine ishiococcygeous muscle can accumulate damage under sub-maximal repetitive loading. The damage appears in the muscle near the musculotendinous junction and was sufficient to negatively affect the macroscopic mechanical properties of the specimens.

SUBMITTER: Vila Pouca MCP

PROVIDER: S-EPMC9016363 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Publications

Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage.

Vila Pouca M C P MCP Parente M P L MPL Natal Jorge R M RM Ashton-Miller J A JA

Journal of the mechanical behavior of biomedical materials 20200709

<h4>Background</h4>One of the major causes of pelvic organ prolapse is pelvic muscle injury sustained during a vaginal delivery. The most common site of this injury is where the pubovisceral muscle takes origin from the pubic bone. We hypothesized that it is possible for low-cycle material fatigue to occur at the origin of the pubovisceral muscle under the large repetitive loads associated with pushing during the second stage of a difficult labor.<h4>Purpose</h4>The main goal was to test if the ...[more]

PMID: 32957249

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Project description:BackgroundPelvic floor myofascial pain, which is predominantly identified in the muscles of the levator ani and obturator internus, has been observed in women with chronic pelvic pain and other pelvic floor disorder symptoms, and is hypothesized to contribute to their symptoms.ObjectivesTo describe the prevalence of pelvic floor myofascial pain in patients presenting with pelvic floor disorder symptoms and to investigate whether severity of pelvic floor myofascial pain on examination correlates with degree of pelvic floor disorder symptom bother.Study designAll new patients seen at 1 tertiary referral center between 2014 and 2016 were included in this retrospectively assembled cross-sectional study. Pelvic floor myofascial pain was determined by transvaginal palpation of the bilateral obturator internus and levator ani muscles and scored as a discrete number on an 11-point verbal pain rating scale (range, 0-10) at each site. Scores were categorized as none (0), mild (1-3), moderate (4-6), and severe (7-10) for each site. Pelvic floor disorder symptom bother was assessed by the Pelvic Floor Distress Inventory short form scores. The correlation between these 2 measures was calculated using Spearman rank and partial rank correlation coefficients.ResultsA total of 912 new patients were evaluated. After exclusion of 79 with an acute urinary tract infection, 833 patients were included in the final analysis. Pelvic floor myofascial pain (pain rated >0 in any muscle group) was identified in 85.0% of patients: 50.4% rated as severe, 25.0% moderate, and 9.6% mild. In unadjusted analyses and those adjusted for postmenopausal status, severity of pelvic floor myofascial pain was significantly correlated with subjective prolapse symptoms such as pelvic pressure and heaviness but not with objective prolapse symptoms (seeing or feeling a vaginal bulge or having to push up on a bulge to start or complete urination) or leading edge. Severity of myofascial pain at several individual pelvic floor sites was also independently correlated with lower urinary tract symptoms, including pain in the lower abdomen (myofascial pain at all sites) and difficulty emptying the bladder (right obturator internus and left levator ani); and with defecatory dysfunction, including sensation of incomplete rectal emptying (pain at all sites combined and the right obturator internus), anal incontinence to flatus (pain at all sites combined), and pain with defecation (pain at all sites combined, and the right obturator internus and left levator ani).ConclusionPelvic floor myofascial pain was common in patients seeking evaluation for pelvic floor disorder symptoms. Location and severity of pelvic floor myofascial pain was significantly correlated with degree of symptom bother, even after controlling for postmenopausal status. Given the high prevalence of pelvic floor myofascial pain in these patients and correlation between pain severity and degree of symptom bother, a routine assessment for pelvic floor myofascial pain should be considered for all patients presenting for evaluation of pelvic floor symptoms.

Project description:BackgroundVaginal childbirth is a key risk factor for pelvic floor muscle injury and dysfunction, and subsequent pelvic floor disorders. Multiparity further exacerbates these risks. Using the rat model, validated for the studies of the human pelvic floor muscles, we have previously identified that a single simulated birth injury results in pelvic floor muscle atrophy and fibrosis.ObjectiveTo test the hypothesis that multiple birth injuries would further overwhelm the muscle regenerative capacity, leading to functionally relevant pathological alterations long-term.Study designSprague-Dawley rats underwent simulated birth injury and were allowed to recover for 8 weeks before undergoing additional birth injury. Animals were sacrificed at acute (3 and 7 days postinjury), subacute (21, 28, and 35 days postinjury), and long-term (8 and 12 weeks postinjury) time points post second injury (N=3-8/time point), and the pubocaudalis portion of the rat levator ani complex was harvested to assess the impact of repeated birth injuries on muscle mechanical and histomorphological properties. The accompanying transcriptional changes were assessed by a customized NanoString panel. Uninjured animals were used as controls. Data with a parametric distribution were analyzed by a 2-way analysis of variance followed by post hoc pairwise comparisons using Tukey's or Sidak's tests; nonparametrically distributed data were compared with Kruskal-Wallis test followed by pairwise comparisons with Dunn's test. Data, analyzed using GraphPad Prism v8.0, San Diego, CA, are presented as mean ± standard error of the mean or median (range).ResultsFollowing the first simulated birth injury, active muscle force decreased acutely relative to uninjured controls (12.9±0.9 vs 25.98±2.1 g/mm2, P<.01). At 4 weeks, muscle active force production recovered to baseline and remained unchanged at 8 weeks after birth injury (P>.99). Similarly, precipitous decrease in active force was observed immediately after repeated birth injury (18.07±1.2 vs 25.98±2.1 g/mm2, P<.05). In contrast to the functional recovery after a single birth injury, a long-term decrease in muscle contractile function was observed up to 12 weeks after repeated birth injuries (18.3±1.6 vs 25.98±2.1 g/mm2, P<.05). Fiber size was smaller at the long-term time points after second injury compared to the uninjured group (12 weeks vs uninjured control: 1485 (60.7-5000) vs 1989 (65.6-4702) μm2, P<.0001). The proportion of fibers with centralized nuclei, indicating active myofiber regeneration, returned to baseline at 8 weeks post-first birth injury, (P=.95), but remained elevated as far as 12 weeks post-second injury (12 weeks vs uninjured control: 7.1±1.5 vs 0.84±0.13%, P<0.0001). In contrast to the plateauing intramuscular collagen content after 4 weeks post-first injury, fibrotic degeneration increased progressively over 12 weeks after repeated injury (12 weeks vs uninjured control: 6. 7±1.1 vs 2.03±0.2%, P<.001). Prolonged expression of proinflammatory genes accompanied by a greater immune infiltrate was observed after repeated compared to a single birth injury.ConclusionOverall, repeated birth injuries lead to a greater magnitude of pathological alterations compared to a single injury, resulting in more pronounced pelvic floor muscle degeneration and muscle dysfunction in the rat model. The above provides a putative mechanistic link between multiparity and the increased risk of pelvic floor dysfunction in women.

Dataset Information

Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage.

Background

Purpose

Methods

Results

Conclusions

Publications

Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage.

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