In silico prediction of maximum perineal muscle strain during vaginal delivery by design of experiment.

BACKGROUND AND OBJECTIVE: The prevalence of pelvic floor muscle injuries induced by childbirth is higher than 23 % in the general women population. Such injuries can lead to prolapses and other pathologies in future female life. Leveraging computational biomechanics, the study implements an advanced female pelvic floor model for computing the maximum pelvic muscle strain, which serves as an injury risk indicator. The design of experiment method, abbreviated as DoE, is used to compute the maximum strain for boundary values of bony pelvis dimensions, namely the anterior-posterior diameter (abbreviated as APD) and the transverse diameter (abbreviated as TD). This is done in combination with small, medium and large percentiles of fetal head circumference (abbreviated as HC). METHODS: We utilized a previously developed finite element model of a female pelvic floor, as a reference, and enhanced it with new features, including a more detailed tissue geometry and advanced constitutive material models. The APD and TD dimensions were sourced from the set of MRI of 64 nulliparous women. This data was used to estimate the boundary dimensions of the female bony pelvis, combining both small and large values of APD and TD. Together with the 10th and the 95th percentiles for HC, a three-dimensional domain was constructed to assess the maximum pelvic muscle strain. In boundary cases, the maximum pelvic muscle strain was computed across 8 full-factorial design models (each situated at one corner of the domain, thereby combining the minimum and the maximum values of APD, TD and HC). This was done to define a response surface that predicts the maximum pelvic muscle strain within the domain. The accuracy of this response surface prediction was validated using 15 additional intermediate design models. These models were placed at the center of the domain (1 point), the centres of the domain boundary surfaces (6 points), and midway along each domain boundary edge (8 points). RESULTS: The maximum strain results for 8 combinations of APD, TD, and HC were employed to construct a linear response surface as a function of APD, TD, and HC. Tests at an additional 19 domain points served to evaluate the efficiency of the response surface prediction. The response surface demonstrated strong predictability, with an absolute average error of 1.52 %, an absolute median error of 1.52 %, and an absolute maximum error of 11.11 %. HC emerged as the most influencing dimension, accounting for 16 % of influence. CONCLUSIONS: The reference finite element pelvic floor model was scaled to 8 full-factorial female-specific pelvic floor models, which represent the combination of boundary values for APD, TD, and HC. The maximum pelvic floor muscle strain from these 8 models was used to design a response surface. When implementing the DoE approach to construct the response, there was consistent predictability for the maximum perineal muscle strain, as validated by the additional 19 intermediate design models. As a result, the response surface methodology can serve as an initial predictor for potential childbirth-induced pelvic floor muscle injury.

The histological microstructure and in vitro mechanical properties of the human female postmenopausal perineal body.

OBJECTIVE: The perineal body connects muscles from the pelvic floor and is critical for support of the lower part of the vagina and proper function of the anal canal. We determined mechanical parameters and volume fractions of main components of the human female postmenopausal perineal body. METHODS: The specimens were taken from 15 fresh female cadavers (age 74 ±â€Š10, mean ±â€Šstandard deviation). Seventy-five specimens from five regions of the perineal body were processed histologically to assess volume fractions of tissue components using stereological point testing grid. Fifteen specimens taken from the midline region were loaded uniaxially with 6 mm/min velocity until tissue rupture to determine Young's modulus of elasticity, ultimate stresses, and strains. RESULTS: The perineal body was composed of collagen (29%), adipose cells (27%), elastin (7%), smooth muscle (11%), and skeletal muscle (3%). The residual tissue (19%) constituted mostly peripheral nerves, lumina of blood vessels, fibroblasts, and fibrocytes. Young's modulus of elasticity at midline region was 18 kPa (median) at small and 232 kPa at large deformations, respectively. The ultimate stress was 172 kPa and the ultimate strain was 1.4. CONCLUSIONS: We determined the structural and mechanical parameters of the perineal body. The resultant data could be used as input for models simulating pelvic floor prolapse or dysfunction.

Fetal head size and effect of manual perineal protection.

OBJECTIVE: The aim of this study was to evaluate whether a previously identified modification of Viennese method of perineal protection remains most effective for reduction of perineal tension in cases with substantially smaller or larger fetal heads. METHODS: A previously designed finite element model was used to compare perineal tension of different modifications of the Viennese method of perineal protection to "hands-off" technique for three different sizes of the fetal head. Quantity and extent of tension throughout the perineal body during vaginal delivery at the time when the suboccipito-bregmatic circumference passes between the fourchette and the lower margin of the pubis was determined. RESULTS: The order of effectiveness of different modifications of manual perineal protection was similar for all three sizes of fetal head. The reduction of perineal tension was most significant in delivery simulations with larger heads. The final position of fingers 2cm anteriorly from the fourchette (y = +2) consistently remains most effective in reducing the tension. The extent of finger movement along the anterior-posterior (y-axis) contributes to the effectiveness of manual perineal protection. CONCLUSION: Appropriately performed Viennese manual perineal protection seems to reduce the perineal tension regardless of the fetal head size, and thus the method seems to be applicable to reduce risk of perineal trauma for all parturients.

Anal incontinence and fecal urgency following vaginal delivery with episiotomy among primiparous patients.

OBJECTIVE: To investigate anal incontinence following mediolateral or lateral episiotomy during a first vaginal delivery. METHODS: The present prospective follow-up study enrolled primiparous patients who underwent vaginal delivery including mediolateral or lateral episiotomy between April 1, 2010 and March 31, 2012. Participants completed interviews before delivery, and were given anal-incontinence questionnaires to be returned for analysis at 3 months and 6 months postpartum. Anal incontinence was defined as a St Mark's incontinence score above four and individual anal-incontinence components were analyzed separately; results were compared between the two episiotomy techniques. RESULTS: Questionnaires were returned by 300 and 366 patients who underwent mediolateral and lateral episiotomies, respectively; baseline characteristics were similar. Anal incontinence at 3 months and 6 months was recorded among 21 (7.0%) and 9 (3.0%) patients who underwent mediolateral and 27 (7.4%) and 20 (5.5%) who underwent lateral episiotomy, respectively. The study was underpowered to confirm equivalence between the groups; however, no statistically significant differences were observed in the rates of anal incontinence, flatus, solid or liquid incontinence, and de novo incontinence. Fecal urgency (P=0.017) and de novo fecal urgency (P=0.008) were more prevalent among patients who underwent lateral episiotomies at 6 months. CONCLUSION: Anal incontinence was comparable between primiparous patients who underwent mediolateral or lateral episiotomy. The association between lateral episiotomy and fecal urgency merits further scientific interest.

Mediolateral versus lateral episiotomy and their effect on postpartum coital activity and dyspareunia rate 3 and 6 months postpartum.

OBJECTIVES: Comparison of the effects of two episiotomy types on sexual activity, dyspareunia and overall satisfaction after childbirth. STUDY DESIGN: A prospective follow-up study of a randomized comparative trial evaluating peripartum outcome of a vaginal delivery after mediolateral (MLE) or lateral (LE) episiotomy. MAIN OUTCOME MEASURES: The participants completed questionnaires regarding sexual activity, dyspareunia, perineal pain, aesthetic appearance and overall satisfaction 3 (3M) and 6 months (6M) postpartum. RESULTS: A total of 648 women were available for the analyses (306 MLE, 342 LE). The groups showed no difference regarding resumption and regularity of sex, timing of resumption, frequency and intensity of dyspareunia, perineal pain, aesthetic appearance or overall satisfaction 3M or 6M postpartum. 98.0% of women after MLE and 97.7% after LE resumed sexual intercourse within 6M after delivery (p = 0.74). In the same period 15.6% of women after MLE and 16.1% after LE suffered from considerable dyspareunia (p = 0.86). CONCLUSIONS: Quality of sexual life and perception of perineal pain after MLE is equivalent to LE.

Biomechanical comparison of a transiliac internal fixator and two iliosacral screws in transforaminal sacral fractures: a finite element analysis.

PURPOSE: Vertically unstable sacral transforaminal fractures can be stabilized with a transiliac internal fixator (TIFI) or two iliosacral screws (IS). This study was designed to compare stiffness between TIFI and IS. METHODS: Using CT images finite element model of the pelvis was developed. Denis II type fracture was simulated and fixed either with TIFI or two IS. The sacral base was loaded vertically (250-500 N), displacement magnitudes on medial and lateral fracture surface and the maximum bone stress were calculated. The intact pelvis was used as a reference. Stiffness was determined by linear regression of load and displacement, computed stiffness ratio %. The von Mises stress was expressed as % ratio, evaluation of colour mapping was made. RESULTS: The mean stiffness ratio medially in TIFI was 75.22%, in IS 46.54% (p = 0.00005), laterally in TIFI 57.88%, in IS 44.74% ( p = 0.03996). The von Mises stress ratio of TIFI was 139.27%, of IS 565.35% ( p < 0.00001). CONCLUSIONS: Significantly higher stiffness and lower stress were found in TIFI model. TIFI provides a lower risk of over-compression of the fracture line in comparison with IS. TIFI thus exhibits superiority for fixation of trans- foraminal fractures, particularly with comminutive zone.

Clinical evaluation of early postpartum pain and healing outcomes after mediolateral versus lateral episiotomy.

OBJECTIVE: To evaluate short-term perineal pain among primiparous women after mediolateral episiotomy (MLE) and lateral episiotomy (LE). METHODS: The prospective randomized study was conducted in the Czech Republic during 2010-2012. Consecutive primiparous women who gave birth at or after 37 weeks of pregnancy and had indications for an episiotomy were enrolled and randomly assigned to undergo MLE or LE. Patients were unaware of the episiotomy type performed. The primary outcomes were pain at 24 hours, 72 hours, and 10 days post partum, measured by a visual analog scale, verbal rating scale, interference with activities of daily living, and amount of analgesic use. RESULTS: The analysis included 266 women who underwent MLE and 297 women who underwent LE. Complete relief of pain was observed in 6 (2.3%) of 266 women after 24 hours, 21 (8.0%) of 264 after 72 hours, and 77 (29.1%) of 265 after 10 days in the MLE group, and in 11 (3.9%) of 285, 23 (7.7%) of 297, and 78 (26.4%) of 295 in the LE group, respectively (P=0.36). There were no significant differences in overall pain scores from any rating system or in the amount of analgesics used. CONCLUSION: Incidence and extent of pain in the first 10 days after LE correspond to those after adequately performed MLE.

The role of thumb and index finger placement in manual perineal protection.

INTRODUCTION AND HYPOTHESIS: Comparison of the modifications of the Viennese method of manual perineal protection (VMPP) and hands-off delivery techniques by applying basic principles of mechanics with assessments of tensions within perineal structures using a novel biomechanical model of the perineum. Evaluation of the role of the precise placements of the accoucheur's posterior (dominant) thumb and index finger in perineal tissue tension when performing a modified Viennese method of MPP. METHODS: We carried out an experimental study on a biomechanical model of the perineum at NTIS (New Technologies for Information Society, Pilsen, Czech Republic). Hands-off and 38 variations of VMPP were simulated during vaginal delivery with the finite element model imitating a clinical lithotomy position. RESULTS: The main outcome measures were quantity and extent of strain/tension throughout the perineal body during vaginal delivery. Stress distribution between modifications of VMPP showed a wide variation in peak perineal tension from 72 to 102 % compared with 100 % for the "hands-off" technique. Extent of reduction depended on the extent of finger movement across a horizontal, transverse x-axis, and on final finger position on a vertical, antero-posterior y-axis. The most effective modification of VMPP was initial position of fingers 12 cm apart (x = ±6) on the x-axis, 2 cm anteriorly from the posterior fourchette (y = +2) on the y-axis with 1cm movement of both finger and thumb toward the midline on the x-axis (Δx = 1) with no movement on the y-axis (Δy = 0). CONCLUSIONS: In a biomechanical assessment with simulation of vaginal delivery, exact placement of fingertips on the perineal skin, together with their co-ordinated movement, plays an important role in the extent of reduction of perineal tension.

Anal incontinence severity assessment tools used worldwide.

OBJECTIVE: To conduct an international survey of anal incontinence assessment tools and the need to evaluate frequency of occurrence of fecal urgency. METHODS: A questionnaire on the use of anal incontinence assessment tools was distributed between May and December 2012 among clinicians and researchers dealing with anal incontinence, primarily in North America, Europe, and Asia. RESULTS: A total of 143 responses were collected from 56 (39.2%) obstetricians, gynecologists, and urogynecologists; 71 (49.7%) colorectal surgeons, proctologists, and general surgeons; and 16 (11.2%) physiotherapists, theoretical scientists, and gastroenterologists. Fourteen different tools were reported-most commonly Wexner score (n=78; 48.8%) and St Mark's score (n=29; 18.1%). No scoring system was used by 24 (16.8%) respondents. Thirty-four (28.6%) used multiple tools. There was variation in the reasons given for scoring the frequency of fecal urgency as 4 points when using St Mark's score. Of 96 respondents responding to a query about modifying the St Mark's score, 88 (91.7%) agreed that fecal urgency should be scored according to the frequency of occurrence. CONCLUSION: Although the Wexner score neglects fecal urgency, it is the most commonly used scoring system. The study contributes to the standardization of terminology and reproducibility of results in research and clinical management of anal incontinence.

Modeling manual perineal protection during vaginal delivery.

INTRODUCTION AND HYPOTHESIS: We compared hands-on manual perineal protection (MPP) and hands-off delivery techniques using the basic principles of mechanics and assessed the tension of perineal structures using a novel biomechanical model of the perineum. We also measured the effect of the thumb and index finger of the accoucheur's dominant-posterior hand on perineal tissue tension when a modified Viennese method of MPP is performed. METHODS: Hands-off and two variations of hands-on manual perineal protection during vaginal delivery were simulated using a biomechanical model, with the main outcome measure being strain/tension throughout the perineal body during vaginal delivery. RESULTS: Stress distribution with the hands-on model shows that when using MPP, the value of highest stress was decreased by 39 % (model B) and by 30 % (model C) compared with the hands-off model A. On the cross section there is a significant decrease in areas of equal tension throughout the perineal body in both hands-on models. Simulation of the modified Viennese MPP significantly reduces the maximum tension on the inner surface of the perineum measured at intervals of 2 mm from the posterior fourchette. CONCLUSIONS: In a biomechanical assessment with a finite element model of vaginal delivery, appropriate application of the thumb and index finger of the accoucheur's dominant-posterior hand to the surface of the perineum during the second stage of delivery significantly reduces tissue tension throughout the entire thickness of the perineum; thus, this intervention might help reduce obstetric perineal trauma.

Clinical evaluation of peripartum outcomes of mediolateral versus lateral episiotomy.

OBJECTIVE: To evaluate the incidence and extent of vaginal and perineal trauma among primiparous women after mediolateral and lateral episiotomy. METHODS: In a prospective randomized study at University Hospital Pilsen, Czech Republic, 790 consecutive primiparous women were enrolled between April 2010 and April 2012. Mediolateral episiotomy (MLE) followed an angle of at least 60° from the midline. Lateral episiotomy (LE) started 1-2 cm laterally from the midline and was directed toward the ischial tuberosity. A rectal examination was performed before episiotomy repair. RESULTS: MLE was performed for 390 women, and LE for 400. The groups did not differ in maternal or neonatal characteristics. No difference was found in incidence or extent of vaginal and perineal trauma; or in additional perineal (1.8% vs 1.5%, P=0.6) or vaginal (8.5% vs 10.6%, P=0.2) trauma continuing along the episiotomy incision. The incidence of anal sphincter injury did not differ between MLE and LE (1.5% vs 1.3%, P=0.7). MLE was associated with shorter repair times (P<0.05), less suturing material (P<0.05), and shorter distances from the anus (P<0.001). CONCLUSION: Risk of additional vaginal and perineal trauma, and anal sphincter injury after adequately performed mediolateral episiotomy is relatively low and corresponds to that of lateral episiotomy.

Stereophotogrammetry of the perineum during vaginal delivery.

OBJECTIVE: To analyze deformation of the perineum during normal vaginal delivery in order to identify clinical steps that might be beneficial when executing manual perineal protection. METHODS: The present prospective study at Charles University Hospital, Pilsen, Czech Republic, enrolled 10 primiparous women at term undergoing non-instrumental vaginal delivery assisted by the same obstetrician between September 2009 and September 2010. A modified hands-poised technique performed concurrently with stereophotogrammetry was used to analyze and quantify perineal deformation and strain at the final stage of delivery. RESULTS: The highest tissue strain (mean, 177%; 95% confidence interval [CI], 106.3-248.5) was in a transverse direction and occurred at the level of the fourchette (i.e. 1cm was transversely stretched and deformed to 2.77 cm during the final stage of vaginal delivery). This strain was more than 4 times higher than the maximum anteroposterior strain (mean, 43%; 95% CI, 28.6-57.4). CONCLUSION: On the basis of these stereophotogrammetry data, a technique of perineal protection executed by fingers of the posterior (right) hand can be proposed. Further experimental and clinical studies are needed to evaluate whether this technique might assist in reducing obstetric perineal trauma.

Importancia del ángulo de la episiotomía / Significance of the angle of episiotomy

La metodología de los estudios que evalúan el papel de la episiotomía mediolateral carece de la calidad necesaria y no puede extraerse actualmente de ellos conclusión alguna acerca del traumatismo perineal grave y la incontinencia anal. Se identificaron cuatro problemas: la definición y la ejecución práctica de la episiotomía mediolateral, y el diagnóstico y clasificación del traumatismo perineal. La definición y ejecución de la episiotomía mediolateral difieren ampliamente entre las distintas instituciones y los distintos individuos. El problema principal es la precisión de la dirección elegida. Se introdujeron tres términos: ángulo de incisión, de sutura y de cicatrización de episiotomía. Anteriormente, la episiotomía mediolateral se definía por un ángulo de incisión mínimo de 40°. Sin embargo,cuando se incide a 40°, el ángulo mediano luego de la reparación era de 20°, mientras que el ángulo de cicatrización era de 30° en los casos de desgarros de tercer grado frente a 38° en los controles. Al usar un ángulo de incisión de 60°, el ángulo mediano de sutura fue de 45° y el de cicatrización de 48°. Actualmente se propone que la episiotomía mediolateral se defina como “una incisión en el perineo durante la última parte de la segunda etapa del trabajo de parto, que comienza en el perineo medial pero se dirige lateralmente en un ángulo de al menos 60° en dirección de la tuberosidad isquial”. Se requieren más investigaciones para evaluar la seguridad de este ángulo de incisión.