Chanda Arnab, Meyer Isuzu, Richter Holly E, Lockhart Mark E, Moraes Fabia R D, Unnikrishnan Vinu
Department of Aerospace Engineering and Mechanics, University of Alabama, Tuscaloosa, AL 35487 e-mail:
Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, AL 35233 e-mail:
J Biomech Eng. 2017 Oct 1;139(10). doi: 10.1115/1.4037222.
Pelvic organ prolapse (POP), downward descent of the pelvic organs resulting in a protrusion of the vagina, is a highly prevalent condition, responsible for 300,000 surgeries in the U.S. annually. Rectocele, a posterior vaginal wall (PVW) prolapse of the rectum, is the second most common type of POP after cystocele. A rectocele usually manifests itself along with other types of prolapse with multicompartment pelvic floor defects. To date, the specific mechanics of rectocele formation are poorly understood, which does not allow its early stage detection and progression prediction over time. Recently, with the advancement of imaging and computational modeling techniques, a plethora of finite element (FE) models have been developed to study vaginal prolapse from different perspectives and allow a better understanding of dynamic interactions of pelvic organs and their supporting structures. So far, most studies have focused on anterior vaginal prolapse (AVP) (or cystocele) and limited data exist on the role of pelvic muscles and ligaments on the development and progression of rectocele. In this work, a full-scale magnetic resonance imaging (MRI) based three-dimensional (3D) computational model of the female pelvic anatomy, comprising the vaginal canal, uterus, and rectum, was developed to study the effect of varying degrees (or sizes) of rectocele prolapse on the vaginal canal for the first time. Vaginal wall displacements and stresses generated due to the varying rectocele size and average abdominal pressures were estimated. Considering the direction pointing from anterior to posterior side of the pelvic system as the positive Y-direction, it was found that rectocele leads to negative Y-direction displacements, causing the vaginal cross section to shrink significantly at the lower half of the vaginal canal. Besides the negative Y displacements, the rectocele bulging was observed to push the PVW downward toward the vaginal hiatus, exhibiting the well-known "kneeling effect." Also, the stress field on the PVW was found to localize at the upper half of the vaginal canal and shift eventually to the lower half with increase in rectocele size. Additionally, clinical relevance and implications of the results were discussed.
盆腔器官脱垂（POP）是指盆腔器官向下移位导致阴道突出，这是一种非常普遍的病症，在美国每年导致30万例手术。直肠膨出是直肠的阴道后壁（PVW）脱垂，是继膀胱膨出之后第二常见的POP类型。直肠膨出通常与其他类型的脱垂一起出现，伴有多腔室盆底缺陷。迄今为止，直肠膨出形成的具体机制尚不清楚，这使得无法对其进行早期检测和随时间推移的进展预测。最近，随着成像和计算建模技术的进步，已经开发了大量有限元（FE）模型，从不同角度研究阴道脱垂，并有助于更好地理解盆腔器官及其支撑结构的动态相互作用。到目前为止，大多数研究都集中在前阴道脱垂（AVP）（或膀胱膨出），关于盆腔肌肉和韧带在直肠膨出发展和进展中的作用的数据有限。在这项工作中，首次开发了基于全尺寸磁共振成像（MRI）的女性盆腔解剖三维（3D）计算模型，包括阴道管、子宫和直肠，以研究不同程度（或大小）的直肠膨出脱垂对阴道管的影响。估计了由于直肠膨出大小变化和平均腹压产生的阴道壁位移和应力。考虑到从盆腔系统前侧指向后侧的方向为正Y方向，发现直肠膨出导致负Y方向位移，使阴道横截面在阴道管下半部分显著缩小。除了负Y位移外，观察到直肠膨出隆起将PVW向下推向阴道裂孔，呈现出众所周知的“跪姿效应”。此外，还发现PVW上的应力场位于阴道管上半部分，并最终随着直肠膨出大小的增加而转移到下半部分。此外，还讨论了结果的临床相关性和意义。
