The management of episiotomy technique and its effect on pelvic floor muscles during a malposition childbirth

Vaginal childbirth is the leading cause of pelvic floor muscles injury, which contributes to pelvic floor dysfunction, being enhanced by fetal malposition. Therefore, the aim of the present study is to verify the influence of mediolateral episiotomies in the mechanics of the pelvic floor with the fetus in occiput posterior position when compared to the occiput anterior position. Numerical simulations of vaginal deliveries, with and without episiotomy, are performed based on the Finite Element Method. The biomechanical model includes the pelvic floor muscles, a surface to delimit the anterior region of the birth canal and a fetus. Fetal malposition induces greater extension of the muscle compared to the normal position, leading to increases of stretch. The faster enlargement may be responsible for a prolonged second stage of labor. Regarding the force required to achieve delivery, the difference between the analyzed cases are 35 N, which might justify the increased need of surgical interventions. Furthermore, episiotomy is essential in reducing the damage to values near the ones obtained with normal position, making the fetal position irrelevant. These biomechanical models have become extremely useful tools to provide some understanding of pelvic floor function during delivery helping in the development of preventative strategies.     

盆底电刺激对大鼠盆底肌肌肉、神经发育的形态学影响研究

目的:探讨与研究盆底电刺激对大鼠盆底肌肌肉、神经发育的形态学影响。方法:36只Wistar产后健康雌性大鼠分为对照组、模型组与刺激组,每组12只。模型组与刺激组都建立了压力性尿失禁模型,对照组不给予任何处理。建模后刺激组给予盆底电刺激,每3 d一次,持续治疗12 d;模型组在建模后不给予任何治疗处理。结果:模型组与刺激组建模后6 d、12 d的膀胱最大容量、肌肉拉长收缩力、血清神经肽Y(Neuropeptide Y,NPY)水平低于对照组(P<0.05),刺激组高于模型组(P<0.05)。对照组可见施万细胞,未见神经元细胞,肌束结构完整,肌纤维上可见明暗相间的周期性横纹;模型组神经元及肌纤维出现缺血性改变,肌纤维肿胀,肌膜核内移;刺激组未见靶状纤维改变,肌纤维粉染,肌纤维肌束结构完整,胞浆着色浅。结论:盆底电刺激在压力性尿失禁大鼠的应用能促进血清NPY的释放,提高盆底肌肌肉与膀胱最大容量,促进大鼠盆底神经发育。     

Measuring morphological parameters of the pelvic floor for finite element modelling purposes

The goal of this study was to obtain a complete data set needed for studying the complex biomechanical behaviour of the pelvic floor muscles using a computer model based on the finite element (FE) theory. The model should be able to predict the effect of surgical interventions and give insight into the function of pelvic floor muscles. Because there was a lack of any information concerning morphological parameters of the pelvic floor muscle structures, we performed an experimental measurement to uncover those morphological parameters. Geometric parameters as well as muscle parameters of the pelvic floor muscles were measured on an embalmed female cadaver. A three-dimensional (3D) geometric data set of the pelvic floor including muscle fibre directions was obtained using a palpator device. A 3D surface model based on the experimental data, needed for mathematical modelling of the pelvic floor, was created. For all parts of the diaphragma pelvis, the optimal muscle fibre length was determined by laser diffraction measurements of the sarcomere length. In addition, other muscle parameters such as physiological cross-sectional area and total muscle fibre length were determined. Apart from these measurements we obtained a data set of the pelvic floor structures based on nuclear magnetic resonance imaging (MRI) on the same cadaver specimen. The purpose of this experiment was to discover the relationship between the MRI morphology and geometrical parameters obtained from the previous measurements. The produced data set is not only important for biomechanical modelling of the pelvic floor muscles, but it also describes the geometry of muscle fibres and is useful for functional analysis of the pelvic floor in general. By the use of many reference landmarks all these morphologic data concerning fibre directions and optimal fibre length can be morphed to the geometrical data based on segmentation from MRI scans.These data can be directly used as an input for building a mathematical model based on FE theory.     

Effects of nonlinear muscle elasticity on pelvic floor mechanics during vaginal childbirth

The role of the pelvic floor soft tissues during the second stage of labor, particularly the levator ani muscle, has attracted much interest recently. It has been postulated that the passage of the fetal head through the pelvis may cause excessive stretching of the levator ani muscle, which may lead to pelvic floor dysfunction and pelvic organ prolapse later in life. In order to study the complex biomechanical interactions between the levator ani muscle and the fetal head during the second stage of labor, finite element models have been developed for quantitative analysis of this process. In this study we have simulated vaginal delivery using individual-specific anatomical computer models of the pelvic floor interacting with a fetal head model with minimal restrictions placed upon its motion. Two constitutive relations were considered for the levator ani muscle (of exponential and neo-Hookean forms). For comparison purposes, the exponential relation was chosen to exhibit much greater stiffening at higher strains beyond the range of the experimental data. We demonstrated that increased nonlinearity in the elastic response of the tissues leads to considerably higher (56%) estimated force required for delivery, accompanied by a more homogeneous spatial distribution of maximum principal stretch ratio across the muscle. These results indicate that the form of constitutive relation beyond the presently available experimental data markedly affects the estimated function of the levator ani muscle during vaginal delivery, due to the large strains that occur. Further experimental data at higher strains are necessary in order to more reliably characterize the constitutive behavior required for modeling vaginal childbirth.     

Citrate synthase, sarcoplasmic reticular calcium ATPase, and choline acetyltransferase activities of specific pelvic floor muscles of the rabbit

There is a clear relationship between the pelvic floor muscles and urinary systems, which relates to urgency, frequency, incontinence, pelvic pain, and bowel complaints. The specific mechanisms which relate these two systems are not clear. Improved understanding of the relation between the pelvic floor muscles and bladder function is clinically relevant in establishing effective treatments to such problems as incontinence, secondary to birth. The following tissues were collected from normal adult female rabbits: pubococcygeus (Pc) and ischiocavernosus/bulbospongiosus (Ic/Bs) pelvic floor muscles. Bladder body muscle and mucosa, bladder base muscle and mucosa, and leg skeletal muscle were also collected. The following enzymatic assays were performed on each tissue: citrate synthase (CS), sarcoplasmic–endoplasmic reticular ATPase (SERCA), and choline acetyltransferase (ChAT). CS and SERCA activities were significantly higher in the Pc compared with the Ic/Bs pelvic floor muscles, whereas the ChAT activity of the Ic/Bs was higher than that of the Pc muscle. Based on our results, the Pc muscle is expected to have a significantly greater capacity to contract and a higher metabolic activity than those of the Ic/Bs muscles. We believe that an understanding of the biochemical activities of these three biomarker enzymes in normal pelvic floor muscles is essential in evaluating the effects of specific experimental dysfunctions created in pelvic floor muscle activity.     

The influence of the material properties on the biomechanical behavior of the pelvic floor muscles during vaginal delivery

In this work, a finite element model intends to represent the effects that the passage of a fetal head can induce on the muscles of the pelvic floor, from a mechanical point of view.The finite element method is a valuable tool, that is contributing to the clarification of the mechanisms behind pelvic floor disorders related to vaginal deliveries, although some care is necessary in order to obtain correct results. The present work shows how the variation of the material parameters, used in the constitutive model, can affect the obtained results from a finite element simulation. The constitutive equation adopted in this work for the pelvic floor muscles is a modified form of the incompressible transversely isotropic hyperelastic model proposed earlier by Humphrey and Yin.Results for the pelvic floor strain and stresses obtained during the passage of the fetus head are presented. The results show the importance of the material parameters and the need for a correct constitutive model.     

Tissue Selective Androgen Receptor Modulators (SARMs) Increase Pelvic Floor Muscle Mass in Ovariectomized Mice

Stress urinary incontinence (SUI), a prevalent condition, is represented by an involuntary leakage of urine that results, at least in part, from weakened or damaged pelvic floor muscles and is triggered by physical stress. Current treatment options are limited with no oral therapies available. The pelvic floor is rich in androgen receptor and molecules with anabolic activity including selective androgen receptor modulators (SARMs) may serve as therapeutic options for individuals with SUI. In this study, two SARMs (GTx‐024 and GTx‐027) were evaluated in a post‐menopausal animal model in order to determine their effect on pelvic floor muscles. Female C57BL/6 mice were ovariectomized and their pelvic muscles allowed to regress. The animals were then treated with vehicle or doses of GTx‐024 or GTx‐027. Animal total body weight, lean body mass, and pelvic floor muscle weights were measured along with the expression of genes associated with muscle catabolism. Treatment with the SARMs resulted in a restoration of the pelvic muscles to the sham‐operated weight. Coordinately, the induction of genes associated with muscle catabolism was inhibited. Although a trend was observed towards an increase in total lean body mass in the SARM‐treated groups, no significant differences were detected. Treatment of an ovariectomized mouse model with SARMs resulted in an increase in pelvic floor muscles, which may translate to an improvement of symptoms associated with SUI and serves as the basis for evaluating their clinical use. J. Cell. Biochem. 118: 640–646, 2017. © 2016 The Authors. Journal of Cellular Biochemistry published by Wiley Periodicals, Inc.     

An approach on determining the displacements of the pelvic floor during voluntary contraction using numerical simulation and MRI

The present study was conducted in order to establish a methodology based on the finite element method to simulate the contraction of the pelvic floor (PF) muscles. In the generated finite element model, a downward pressure of 90 cm H₂O was applied, while actively contracting the PF muscles with different degrees of muscular activation (10, 50 and 100%). The finite element methodology of the active contraction behaviour proposed in this study is adequate to simulate PF muscle contraction with different degrees of muscular activation. In this case, in particular, for an activation of 100%, the numerical model was able to displace the pubovisceral muscle in a range of values very similar to the displacement found in the magnetic resonance imaging data. In the analysed case study, it would be possible to conclude that an intensity contraction of 50% would be necessary to produce enough stiffness to avoid possible urine loss.     

An approach on determining the displacements of the pelvic floor during voluntary contraction using numerical simulation and MRI

The present study was conducted in order to establish a methodology based on the finite element method to simulate the contraction of the pelvic floor (PF) muscles. In the generated finite element model, a downward pressure of 90 cm H(2)O was applied, while actively contracting the PF muscles with different degrees of muscular activation (10, 50 and 100%). The finite element methodology of the active contraction behaviour proposed in this study is adequate to simulate PF muscle contraction with different degrees of muscular activation. In this case, in particular, for an activation of 100%, the numerical model was able to displace the pubovisceral muscle in a range of values very similar to the displacement found in the magnetic resonance imaging data. In the analysed case study, it would be possible to conclude that an intensity contraction of 50% would be necessary to produce enough stiffness to avoid possible urine loss.     

Anisotropic effects of the levator ani muscle during childbirth

Pelvic floor dysfunction and pelvic organ prolapse have been associated with damage to the levator ani (LA) muscle, but the exact mechanisms linking them remain unknown. It has been postulated that factors such as vaginal birth and ageing may contribute to long-term, irreversible LA muscle damage. To investigate the biomechanical significance of the LA muscle during childbirth, researchers and clinicians have used finite element models to simulate the second stage of labour. One of the challenges is to represent the anisotropic mechanical response of the LA muscle. In this study, we investigated the effects of anisotropy by varying the relative stiffness between the fibre and the matrix components, whilst maintaining the same overall stress–strain response in the fibre direction. A foetal skull was passed through two pelvic floor models, which incorporated the LA muscle with different anisotropy ratios. Results showed a substantial decrease in the magnitude of the force required for delivery as the fibre anisotropy was increased. The anisotropy ratio markedly affected the mechanical response of the LA muscle during a simulated vaginal delivery. It is apparent that we need to obtain experimental data on muscle mechanics in order to better approximate the LA muscle mechanical properties for quantitative analysis. These models may advance our understanding of the injury mechanisms of pelvic floor during childbirth.     

Dystrophin、MGF及M-Cad在难产大鼠模型盆底肌肉中的表达意义研究

摘要 目的：研究模拟难产大鼠模型盆底肌肉中Dystrophin、MGF及M-Cad的表达,并探讨其表达与压力性尿失禁的相关性。方法：选择未生产过的雌性SD大鼠40只,按照随机数字表法均分为对照组、模型1组、模型2组和模型3组,对照组大鼠正常喂养,模型1组大鼠行阴道扩张手术,模型2组大鼠切除双侧坐骨神经,模型3组大鼠既行阴道扩张术又切除双侧坐骨神经。喂养1月后,称重后处死各组大鼠,并分离盆底肌肉,称重后通过定量PCR法（qPCR）检测Dystrophin、MGF及M-Cad mRNA的表达。结果：与对照组大鼠相比,难产大鼠模型组（模型1组、模型2组和模型3组）体重和盆底肌肉重量无显著变化（P>0.05）,漏尿点压力和最大膀胱容量均显著下降（P<0.05）,盆底肌肉Dystrophin、MGF及M-Cad mRNA表达均显著下降（P<0.05）。Pearson相关性分析：大鼠盆底肌肉Dystrophin、MGF及M-Cad mRNA表达水平与漏尿点压力均呈密切正相关（Dystrophin：r=0.725,P=0.002;MGF：r=0.702,P=0.018;M-Cad：r=0.838,P<0.001）;鼠盆底肌肉Dystrophin、MGF及M-Cad mRNA表达水平与最大膀胱容量也均呈密切正相关（Dystrophin：r=0.733,P=0.001;MGF：r=0.682,P=0.025;M-Cad：r=0.819,P<0.001）。结论：模拟难产大鼠模型盆底肌肉Dystrophin、MGF及M-Cad的表达降低,并且提示其表达降低可能与压力性尿失禁有关。     

盆底超声评价在妊娠妇女盆底结构、功能以及预后上的价值

为探究盆底超声检查评估分析不同的分娩方式对女性晚期妊娠和产后盆底结构、功能及预后效果的影响,本研究选取收治的100例顺利生产的孕妇作为本实验研究对象,根据分娩方式的不同将其分为自然分娩组与剖宫产组,各组50例。在两组孕妇妊娠晚期和产后分别通过盆底超声检测盆底结构和功能(膀胱旋转角,尿道膀胱后角,肛提肌裂孔面积和肛提肌裂孔周长);以及在产后第6~8周和盆底康复治疗后进行压力性尿失禁发生率调查问卷表填写及护垫实验。研究发现,阴道自然分娩比选择性剖宫产对妊娠晚期和产后孕妇盆底结构和功能造成的损伤更为显著;盆底损伤较严重的孕妇压力性尿失禁程度同样较严重;而盆底康复治疗成功的压力性尿失禁患者,盆底超声检测发现孕妇产后盆底结构和功能得到有效改善。本研究结果说明,盆底超声评价在检测不同分娩方式对妊娠晚期和产后孕妇的盆底结构、功能及预后存在一定的预测和预防作用。     

压力性尿失禁动物模型尿道功能和盆底肌力的比较

目的:比较不同压力性尿失禁(stress urinary incontinence,SUI)动物模型在尿流动力学和盆底肌力方面的差异,以寻求最能模拟SUI的动物模型。方法:取64只大鼠随机均分为阴道扩张模型组(vaginal distension,VD)和阴部神经压榨模型组(pudendal nerve crush,PNC)和阴部神经切断模型组(pudendal nerve transection,PNT)以及VD+PNC造模组4组,每组16只,另取4只大鼠作为正常对照组。造模后第2天,所有大鼠行喷嚏试验。造模后第4天、第10天、3周、6周,测定尿流动力学和盆底肌力。正常对照组大鼠在喷嚏试验后进行尿流动力学和盆底肌力测定。结果:喷嚏实验结果显示正常对照组未观察到阳性大鼠(0/4),各模型组喷嚏试验结果阳性率均显著高于正常对照组(P0.05)。动力学检测显示:与正常组(40.3±3.4 cm H_2O)相比,VD组在造模后4d的LPP值显著降低(P0.05),而造模后10d、3周和6周时的LPP值无统计学差异(P0.05);PNC组和PNC+VD组在造模后4d、10d、3周时的LPP值均显著降低(P0.05),而在造模后6周时无统计学差异(P0.05);PNT组在造模后4d、10d、3周和6周时的LPP值均显著降低(P0.05)。最大膀胱容量测定显示:与正常组(2.42±0.12 mL)相比,VD组在造模后10d的MBC值显著降低(P0.05),而造模后4d、3周和6周时无统计学差异(P0.05);PNC组在造模后10d、3周时显著降低(P0.05),而在造模后4d和6周时无统计学差异(P0.05);PNC+VD组和PNT组在造模后10d及3周和6周时均显著降低(P0.05),而在造模后4d时无统计学差异(P0.05)。盆底肌力测定结果显示:与正常组的耻尾肌肌力值(2.71±0.12 g/g)相比,VD组在造模后10d显著降低(P0.05),而造模后4d、3周和6周时无统计学差异(P0.05);PNC组在造模后10d、3周时显著降低(P0.05),而在造模后4d和6周时无统计学差异(P0.05);PNC+VD组和PNT在造模后10d及3周和6周时均显著降低(P0.05),而在造模后4d时无统计学差异(P0.05)。结论:VD、PNC、VD+PNC和PNT造模均能有效模拟出SUI发病中的盆底神经和肌肉损伤。其中,VD造模主要引起盆底肌的直接损伤,但其恢复较快。PNC和PNT造模则能损伤阴部神经并间接地造成盆底肌的失神经性萎缩,但PNT所造成的损伤较难恢复,不能有效地模拟SUI的自然修复过程。而VD+PNC造模则兼具VD和PNC两种造模方法的特点,能从多个层面模拟SUI的发病。因此,在实践中应根据实验研究的层面采用合适的动物模型。     

A shell finite element model of the pelvic floor muscles

The pelvic floor gives support to the organs in the abdominal cavity. Using the dataset made public in (Janda et al. J. Biomech. (2003) 36(6), pp. 749-757), we have reconstructed the geometry of one of the most important parts of the pelvic floor, the levator ani, using NURB surfaces. Once the surface is triangulated, the corresponding mesh is used in a finite element analysis with shell elements.Based on the 3D behavior of the muscle we have constructed a shell that takes into account the direction of the muscle fibers and the incompressibility of the tissue. The constitutive model for the isotropic strain energy and the passive strain energy stored in the fibers is adapted from Humphrey's model for cardiac muscles. To this the active behavior of the skeletal muscle is added.We present preliminary results of a simulation of the levator ani muscle under pressure and with active contraction. This research aims at helping simulate the damages to the pelvic floor that can occur after childbirth.     

Modeling the contraction of the pelvic floor muscles

We performed numerical simulation of voluntary contraction of the pelvic floor muscles to evaluate the resulting displacements of the organs and muscles. Structures were segmented in Magnetic Resonance (MR) images. Different material properties and constitutive models were attributed. The Finite Element Method was applied, and displacements were compared with dynamic MRI findings. Numerical simulation showed muscle magnitude displacement ranging from 0 to 7.9 mm, more evident in the posterior area. Accordingly, the anorectum moved more than the uterus and bladder. Dynamic MRI showed less 0.2 mm and 4.1 mm muscle dislocation in the anterior and cranial directions, respectively. Applications of this model include evaluating muscle impairment, subject-specific mesh implant planning, or effectiveness of rehabilitation.     

Histochemical and stereological analysis of the levator ani (pubocaudal) muscle in nulliparous and multiparous beagles

Fiber-type composition and several stereological parameters of the levator ani (pubocaudal) muscle were evaluated in five nulliparous and five multiparous beagles using myosin ATPase-histochemistry and systematically selected muscle cross-sections. With respect to the narrow canine pelvic cavity, this study was also undertaken to determine whether vaginal birth of at least seven litters causes similar neuromuscular changes in the canine levator ani (pubocaudal) muscle analoguous to those seen in the pelvic floor muscles of women after vaginal delivery. The canine pubocaudal muscle is comprised of approximately equal amounts of slow twitch type I and fast twitch type II (IIA, IIS) fibers. The muscles of both the nulliparous and multiparous beagles did not display any signs indicative of denervation or myopathology. The multiparous dogs exhibited significantly increased mean absolute muscle (1720 mm(3)) and total fiber-type I volumes (850 mm(3)) as well as relevantly increased mean diameter of type I fibers (72.0 microm) when compared with the nulliparous group. The canine levator ani (pubocaudal) muscle is not pathologically affected by vaginal deliveries and seems to adapt to numerous successive pregnancies and births through fiber-type I hypertrophy.     

硬膜外麻醉无痛分娩、剖宫产和自然分娩对盆底组织功能的影响

摘要 目的：比较不同的分娩方法（自然分娩、无痛分娩、剖宫产）对产妇盆底组织功能的影响。方法：选择2019年10月～2020年11月在我院进行分娩的80例产妇,其中,自然分娩组15例,无痛分娩组26例、剖宫产组39例。记录自然分娩组和无痛分娩组第一、第二产程的疼痛程度和第一、第二产程所需时间,巨大儿、新生儿黄疸、低体重儿和新生儿窒息等母婴结局,Apgar评分、产时出血量和胎儿体重;且检查产妇的盆底肌力,记录自然分娩组、无痛分娩组、剖宫产组的尿失禁发生率。结果：无痛分娩组的第一、第二产程的视觉模拟评分法（Visual analog scales,VAS）评分和第一、第二产程所需时间明显低于自然分娩组(P<0.05);自然分娩组和无痛分娩组的巨大儿、新生儿黄疸、低体重儿和新生儿窒息率无明显差异(P>0.05);自然分娩组和无痛分娩组的Apgar评分、产时出血量和胎儿体重无明显差异(P>0.05);无痛分娩组的盆底肌力明显高于自然分娩组(P<0.05),剖宫产组的盆底肌力明显高于无痛分娩组(P<0.05);三组尿失禁的发生率对比差异无统计学意义(P>0.05)。结论：无痛分娩不但能减轻分娩疼痛程度,还能减轻对盆底组织功能的损伤,值得进行推广。     

实时三维盆底超声对产后压力性尿失禁患者疗效评估作用及与尿动力学的相关性分析

摘要 目的：探讨实时三维盆底超声对产后压力性尿失禁（SUI）患者疗效评估作用及与尿动力学的相关性。方法：选择2020年4月至2022年12月石家庄市人民医院收治的139例产后SUI患者,均接受盆底生物反馈电刺激联合盆底肌锻炼治疗。治疗前后分别进行实时三维盆底超声检查和尿动力学检查。比较治疗前后实时三维盆底超声参数、尿动力学指标差异。Pearson法分析实时三维盆底超声参数与尿动力学指标的相关性。结果：实时三维盆底超声图像特征显示：治疗前盆膈裂孔内的结构疏松,回声变弱,盆腔器官结缔组织疏松,间隙增宽,盆膈裂孔面积、尿道旋转角、膀胱尿道后角以及膀胱颈移动度较大;治疗后盆膈裂孔两侧耻骨直肠肌对称,耻骨内脏肌呈带状高回声,盆膈裂孔面积、尿道旋转角、膀胱尿道后角以及膀胱颈移动度较治疗前降低。产后SUI患者治疗后静息状态和Valsalva状态下盆膈裂孔面积、尿道旋转角、膀胱尿道后角、膀胱颈移动度均较治疗前降低（P＜0.05）,腹压漏尿点压、最大逼尿肌压力均较治疗前增加（P＜0.05）。产后SUI患者静息状态和Valsalva状态下盆膈裂孔面积、尿道旋转角、膀胱尿道后角、膀胱颈移动度与最大逼尿肌压力、腹压漏尿点压呈负相关（P＜0.05）,与最大膀胱容量和残余尿量无关（P＞0.05）。结论：产后SUI患者经盆底生物反馈电刺激联合盆底肌锻炼治疗后实时三维盆底超声参数较治疗前降低,与尿动力学改善有关。临床可通过实时三维盆底超声检查,对产后SUI患者进行临床疗效评价,以指导临床治疗。     

Tonic finite element model of the lower limb

It is widely admitted that muscle bracing influences the result of an impact, facilitating fractures by enhancing load transmission and reducing energy dissipation. However, human numerical models used to identify injury mechanisms involved in car crashes hardly take into account this particular mechanical behavior of muscles. In this context, in this work we aim to develop a numerical model, including muscle architecture and bracing capability, focusing on lower limbs. The three-dimensional (3-D) geometry of the musculoskeletal system was extracted from MRI images, where muscular heads were separated into individual entities. Muscle mechanical behavior is based on a phenomenological approach, and depends on a reduced number of input parameters, i.e., the muscle optimal length and its corresponding maximal force. In terms of geometry, muscles are modeled with 3-D viscoelastic solids, guided in the direction of fibers with a set of contractile springs. Validation was first achieved on an isolated bundle and then by comparing emergency braking forces resulting from both numerical simulations and experimental tests on volunteers. Frontal impact simulation showed that the inclusion of muscle bracing in modeling dynamic impact situations can alter bone stresses to potentially injury-inducing levels.     

A biomechanical model on muscle forces in the transfer of spinal load to the pelvis and legs.

Based on musculoskeletal anatomy of the lower back, abdominal wall, pelvis and upper legs, a biomechanical model has been developed on forces in the load transfer through the pelvis. The aim of this model is to obtain a tool for analyzing the relations between forces in muscles, ligaments and joints in the transfer of gravitational and external load from the upper body via the sacroiliac joints to the legs in normal situations and pathology. The study of the relation between muscle coordination patterns and forces in pelvic structures, in particular the sacroiliac joints, is relevant for a better understanding of the aetiology of low back pain and pelvic pain. The model comprises 94 muscle parts, 6 ligaments and 6 joints. It enables the calculation of forces in pelvic structures in various postures. The calculations are based on a linear/non-linear optimization scheme. To gain a better understanding of the function of individual muscles and ligaments, deviant properties of these structures can be preset. The model is validated by comparing calculations with EMG data from the literature. For agonistic muscles, good agreement is found between model calculations and EMG data. Antagonistic muscle activity is underestimated by the model. Imposed activity of modelled antagonistic muscles has a minor effect on the mutual proportions of agonistic muscle activities. Simulation of asymmetric muscle weakness shows higher activity of especially abdominal muscles.