Lien Kuo-Cheng, Morgan Daniel M, Delancey John O L, Ashton-Miller James A
Department of Mechanical Engineering, University of Michigan, Ann Arbor 48109-2125, USA.
Am J Obstet Gynecol. 2005 May;192(5):1669-76. doi: 10.1016/j.ajog.2005.01.032.
The purpose of this study was to determine the increase in pudendal nerve branch lengths using a 3D computer model of vaginal delivery.
The main inferior rectal and perineal branches of the pudendal nerve were dissected in 12 hemi-pelves from 6 adult female cadavers. Their 3D courses were digitized in the 4 specimens with the most characteristic nerve branching pattern, and the data were imported into a published 3D computer model of the pelvic floor. Each nerve branch was then represented by a stretchable cord with a fixation point at the ischial spine. The length change in each branch was then quantified as the fetal head descended through the pelvic floor. The maximum nerve strains ([final length minus original length/original length] x 100) were calculated for 5 degrees of perineal descent: reference descent from the literature, 1.25 cm and 2.5 cm caudal and cephalad. The effect of alternative fixation points on resultant nerve strain was also studied.
The inferior rectal branch exhibited the maximum strain, 35%, and this strain varied by 15% from the scenario with the least perineal descent to that with the most perineal descent. The strain in the perineal nerve branch innervating the anal sphincter reached 33%, while the branches innervating the posterior labia and urethral sphincter reached values of 15% and 13%, respectively. The more proximal the nerve fixation point, the greater the nerve strain.
During the second stage: (1) nerves innervating the anal sphincter are stretched beyond the 15% strain threshold known to cause permanent damage in appendicular peripheral nerve, and (2) the degree of perineal descent is shown to influence pudendal nerve strain.
本研究旨在使用阴道分娩的三维计算机模型确定阴部神经分支长度的增加情况。
在6具成年女性尸体的12个半骨盆中解剖阴部神经的主要直肠下分支和会阴分支。在4个具有最典型神经分支模式的标本中对其三维走行进行数字化处理，并将数据导入已发表的盆底三维计算机模型。然后，每个神经分支由一条可拉伸的绳索表示，其固定点位于坐骨棘。然后，随着胎头下降通过盆底，对每个分支的长度变化进行量化。计算了5种会阴下降程度下的最大神经应变（[最终长度减去原始长度/原始长度]×100）：文献中的参考下降、尾侧和头侧1.25 cm及2.5 cm。还研究了替代固定点对所得神经应变的影响。
直肠下分支表现出最大应变，为35%，并且该应变在会阴下降最少的情况到会阴下降最多的情况之间变化了15%。支配肛门括约肌的会阴神经分支应变达到33%，而支配后阴唇和尿道括约肌的分支应变分别达到15%和13%。神经固定点越靠近近端，神经应变越大。
在第二产程中：（1）支配肛门括约肌的神经拉伸超过了已知会导致附属周围神经永久性损伤的15%应变阈值，（2）会阴下降程度显示会影响阴部神经应变。
