Effect of Extralevator Abdominoperineal Excision on Biomechanics of Female Pelvic Floor: A Finite Element Analysis
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摘要:目的
应用有限元分析研究4种个体化ELAPE手术对于女性盆底生物力学的影响。
方法建立6种女性盆底有限元模型:正常模型、ELAPE模型和4种个体化ELAPE模型,测量6种模型在相同载荷作用下的各组织最大应力,并观察应力分布。
结果正常模型和ELAPE模型的非肛提肌组织内最大应力为(1.953±0.060)MPa和(5.111±0.081)MPa。模型1的肛提肌部分保留侧和完整切除侧非肛提肌组织内最大应力分别为(3.101±0.133)MPa和(4.868±0.123)MPa,均低于ELAPE模型(均P<0.01)。模型2的双侧非肛提肌组织内的最大应力均为(5.138±0.091)MPa,与ELAPE模型比较差异无统计学意义(P>0.05)。模型3和模型4的非肛提肌组织内的最大应力为(4.700±0.105)MPa和(3.653±0.156)MPa,均低于ELAPE模型(均P<0.01)。
结论单侧肛提肌切除平面靠近直肠的、双侧耻骨尾骨肌外侧切断肛提肌的、保留直肠前方肛提肌的ELAPE手术对于盆底非肛提肌组织内的应力均有降低作用,其中单侧肛提肌切除平面靠近直肠的ELAPE手术在肛提肌部分保留侧更为明显;单侧肛提肌切除平面靠近盆壁的ELAPE手术对于盆底非肛提肌组织内的应力无明显降低作用。
Abstract:ObjectiveTo explore the effects of four extralevator abdominoperineal excision (ELAPE) procedures on the biomechanics of female pelvic floor through finite element analysis.
MethodsSix finite element models of the female pelvic floor were established, including a normal model, an ELAPE model, and four individual models. The maximum stress in each model was measured under the same pressure, and the stress distribution was observed.
ResultsThe maximum stress of non-levator ani muscle tissues on the partially reserved side and totally removed side of the levator ani muscle were 3.101±0.133 and 4.868±0.123 MPa in individual model 1, respectively, which were lower than the maximum stress in the ELAPE model (5.111±0.081 MPa; both P<0.01). The maximum stress in the non-levator ani muscle tissue were 5.138±0.091 MPa on both sides in individual model 2, which were not significantly different from that in the ELAPE model (P>0.05). The maximum stress of non-levator ani muscle tissues were 4.700±0.105 and 3.653±0.156 MPa in individual models 3 and 4, respectively, which were lower than the maximum stress in the ELAPE model (both P<0.01).
ConclusionThree ELAPE procedures, including ELAPE with unilateral levator ani muscle resection plane close to the rectum, and the bilateral pubococcygeal muscle lateral resection of levator ani muscle and levator ani muscle in front of the rectum preserved could decrease stress in the non-levator ani muscle tissue on both sides. The effect is evident on the levator ani muscle partially reserved side of ELAPE with unilateral levator ani muscle resection plane close to the rectum. ELAPE with unilateral levator ani muscle resection plane close to the pelvic wall has no significant reduction effect on the non-levator ani muscle tissue on either side.
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Key words:
- Rectal neoplasm /
- ELAPE /
- Pelvic floor /
- Biomechanics /
- Finite element analysis
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0 引言
经肛提肌外腹会阴联合切除术(extralevator abdominoperineal excision, ELAPE)相比于腹会阴联合切除术(abdominoperineal resection, APR),增加了肿瘤周围组织的切除范围,切除了全部肛提肌、直肠系膜与肛管,降低术中肠穿孔率(intra-operative perforation, IOP)、环周切缘(circumferential resection margin, CRM)阳性率,最终有助于降低局部复发率[1-11]。但在提高肿瘤根治性的同时,扩大切除范围会增加切口感染、神经损伤和盆底疝等并发症的发生[3-4,11-12]。在提高根治性的基础上,针对不同病例采取个体化ELAPE手术,减少术后并发症,成为新的研究方向[4,13]。有限元分析是一种新型生物力学方法,可逼真地模拟各组织的生物力学状态。本研究通过比较各模型在女性发生盆底疝时的临界腹压下的各组织应力,来探讨4种个体化ELAPE手术对于盆底疝等并发症的预防作用。
1 资料与方法
1.1 研究对象
选择我院于2018年3月—2018年12月身体健康且体型匀称的未育女性志愿者共34例,年龄23~30岁,平均26.03岁,均签署知情同意书。
采用美国通用(GE)电气医疗集团生产的1.5T核磁共振扫描仪对盆底组织进行层厚为0.8 mm的超薄横截面位磁共振扫描,始于膀胱中部,止于阴道外口,获取MRI图像保存为DICOM格式。
1.2 研究方法
1.2.1 个体化ELAPE手术
(1)个体化手术1——单侧肛提肌切除平面靠近直肠的ELAPE手术:若肿瘤局限于一侧直肠壁,则对侧的切除平面靠近直肠,见图1A。(2)个体化手术2——单侧肛提肌切除平面靠近盆壁的ELAPE手术:若肿瘤仅侵犯一侧坐骨直肠窝脂肪或肛提肌,则保留对侧与盆壁附着的部分肛提肌,见图1B。(3)个体化手术3——双侧耻骨尾骨肌外侧切断肛提肌的ELAPE手术:若肿瘤位于肛提肌裂孔下方,可在双侧耻骨尾骨肌外侧切断肛提肌,见图1C。(4)个体化手术4——保留直肠前方肛提肌的ELAPE手术:若肿瘤位于低位直肠后壁,其前部的切除平面尽可能贴近直肠,保留直肠前方的肛提肌。
图 1 单侧肛提肌切除平面靠近直肠(A)、单侧肛提肌切除平面靠近盆壁(B)、双侧耻骨尾骨肌外侧切断肛提肌(C)的ELAPE手术Figure 1 Individual ELAPE with unilateral levator ani muscle resection plane close to the rectum (A), unilateral levator ani muscle resection plane close to the pelvic wall (B), bilateral pubococcygeal muscle lateral resection of levator ani muscle (C)ELAPE: extralevator abdominoperineal excision.1.2.2 有限元模型的建立
将1例女性DICOM格式数据导入MIMICS 10.01软件,逐层选中肛提肌组织,生成肛提肌的三维几何模型。将其导入GeoMagic Studio 12软件,经点阶段和多边形阶段处理后,生成肛提肌的实体模型。再将其导入ANSYS Workbench 14.0软件,在肛提肌下方生成盆底非肛提肌组织的等效模型后,对两者进行网格划分并赋予文献公认的力学参数[14-16],肛提肌的杨氏模量为0.95 MPa,泊松比为0.45,非肛提肌组织的杨氏模量为1.0 MPa,泊松比为0.49,得到正常模型。将各模型之间的接触关系定义为面-面绑定接触,接触行为设置为反对称约束,接触面单元类型为Contact 174,目标面的单元类型为Target l70。随后在正常模型的基础上,完整切除肛提肌组织,得到ELAPE模型;同样在正常模型的基础上,按照以上4种个体化ELAPE手术部分切除肛提肌组织,得到4种个体化ELAPE模型。对5种模型的外侧缘,即对与盆壁等结构的连接处施加约束。再对6种模型施加垂直于上表面的均匀载荷,设定为女性盆底疝时的临界腹压。盆底疝时最大逼尿肌压力为(38±14)cmH2O(1 cmH2O=0.098 kPa),腹压漏尿点压为(94±35)cmH2O,因此载荷大小设定为56 cmH2O[15-17]。随后同理对其余33名女性数据进行处理和计算。观察指标:6种模型非肛提肌组织内的最大应力及前2种个体化ELAPE模型肛提肌部分保留侧的最大应力;正常模型及4种个体化ELAPE模型肛提肌内的最大应力。
1.3 统计学方法
利用SPSS 21.0统计软件进行分析。计量资料数据以$ \overline x $±s表示,多组间比较采用方差分析,多重比较行LSD-t检验。两组间比较采用配对t检验。检验水准为α=0.05。
2 结果
2.1 6种模型的基本数据
本研究建立了6种有限元模型,基本信息见表1。
表 1 6种有限元分析模型的基本信息Table 1 Basic data of six finite element analysis modelsModel Average nodes Average units Normal Model 469676.94±18980.81 331526.71±18920.53 ELAPE Model 10865.14±822.25 10243.14±795.86 Individual
Model 1174514.35±8846.67 121376.44±11354.88 Individual
Model 278569.06±6112.05 56154.35±3644.60 Individual
Model 3279172.29±8645.58 187768.56±5333.99 Individual
Model 4197840.59±5171.61 137655.41±2040.04 2.2 6种模型非肛提肌组织内的应力比较
正常模型和ELAPE模型的高应力区出现的位置一致,均左右对称地出现在双侧与周围结构的连接处,图中由蓝到红为应力逐渐升高,最大应力均出现在左右双侧的最前端,见图2A~B。
模型1的高应力区出现在肛提肌完整切除侧与周围结构的连接处,最大应力出现在该侧的最前端,见图2C。
模型2的高应力区出现在肛提肌完整切除侧与周围结构的连接处及肛提肌部分保留侧下段与周围结构的连接处,最大应力出现在双侧的最前端,见图2D。
模型3的高应力区左右对称地出现在双侧与周围结构的连接处的前部,最大应力亦出现在双侧的最前端,见图2E。
模型4的高应力区左右对称地出现在两侧与周围结构连接处的前部,最大应力亦出现在左右两侧的最前端,见图2F。
模型1的肛提肌部分保留侧最大应力低于完整切除侧,二者最大应力均低于ELAPE模型,但均高于正常模型(均P<0.01)。模型2的最大应力与ELAPE模型比较差异无统计学意义(P>0.05),高于正常模型(P<0.01)。模型3的最大应力低于ELAPE模型,但高于正常模型(均P<0.01)。模型4的最大应力低于ELAPE模型,但高于正常模型(均P<0.01)。通过应力云图对整体应力做定性分析,其趋势与之大致相同,见表2。
表 2 各组模型非肛提肌组织和肛提肌内的最大应力Table 2 Maximum stress of non-levator ani muscle tissue and levator ani muscle in each modelModel Maximum stress(MPa) Non-levator ani
muscle tissueLevator ani muscle Normal model 1.953 ± 0.060 0.791 ± 0.045 ELAPE Model 5.111 ± 0.081 Individual Model 1
Levator ani muscle
partially reserved side1.339 ± 0.032 3.101 ± 0.133 Levator ani muscle
totally removed side4.868 ± 0.123 Individual Model 2 5.138 ± 0.091 1.524 ± 0.024 Individual Model 3 4.700 ± 0.105 0.773 ± 0.033 Individual Model 4 3.653 ± 0.156 1.438 ± 0.041 2.3 正常模型与4种个体化ELAPE模型肛提肌内的应力比较
正常模型的高应力区出现在左右双侧与周围结构的连接处,最大应力出现在左右双侧与前方结构的连接处,见图3A。
模型1的高应力区出现在剩余肛提肌与周围结构的连接处,最大应力出现在该侧的最前端,见图3B。
模型2的高应力区同样出现在剩余肛提肌与周围结构的连接处,而最大应力出现在该侧与后方结构的连接处,见图3C。
模型3的高应力区出现在剩余肛提肌与周围结构的连接处的前部,最大应力并未出现在左右双侧的最前端,而出现在其上部,见图3D。
模型4的高应力区出现在左右两侧与周围结构的连接处的前部,最大应力均出现在左右两侧的最前端,见图3E。
模型1、2和4的剩余肛提肌内的最大应力均高于正常模型(均P<0.01),个体化ELAPE模型3与正常模型差异无统计学意义(P>0.05)。通过应力云图对整体应力做定性分析,其趋势与之大致相同,见表2。
3 讨论
有限元分析方法基于影像学资料重建肛提肌的几何结构,可最大程度保留组织的几何学特征,还原组织的解剖学形态,使结果更加真实。与传统实验生物力学方法通过表面应变来计算内部应力的方式不同,有限元分析方法可直接测量肛提肌等组织的内部应力,有效地减小计算误差,使结果更加精确。此外,有限元分析方法还具有无损伤、可重复、多工况等优势,均使其应用领域越来越广泛。
由于直肠系膜向远端逐渐缩小,按照全直肠系膜切除标准解剖间隙游离直肠,APR标本将形成狭窄的外科腰,术中肠穿孔率和CRM阳性率较前切除术(anterior resection, AR)高,因而局部复发率较AR术高[9]。ELAPE手术通过切除全部肛提肌、直肠系膜和肛管,相比于APR术,降低了术中肠穿孔率和CRM阳性率[3,6-8]。然而肛提肌是人体盆底的重要组成结构,负责增强和提起盆底,承托盆腔器官。ELAPE手术于盆壁起始处切断肛提肌,可导致切口感染、神经损伤,甚至盆底疝等严重并发症。在之前的研究中,ELAPE模型的最大应力显著高于正常模型,提示在完整切除肛提肌后,非肛提肌组织内的应力明显增加,推测术后发生盆底疝的风险增加。
目前有研究认为,针对特定病例,施行个体化ELAPE手术可达到与经典ELAPE手术接近的术中肠穿孔率和CRM阳性率,且并发症发生率更低。在本研究中,模型1的肛提肌部分保留侧非肛提肌组织内的最大应力,低于完整切除侧,二者均低于ELAPE模型,整体应力趋势与之相同,提示该术对于盆底双侧非肛提肌组织内的应力均有降低作用,在肛提肌部分保留侧更为明显。模型3和4的非肛提肌组织内的最大应力,亦低于ELAPE模型,整体应力趋势与之相同,提示这2种术式对于盆底非肛提肌组织内的应力有降低作用。因此推测以上3种术式可降低术后盆底疝的风险。而模型2的非肛提肌组织内的最大应力与ELAPE模型比较差异无统计学意义,整体应力亦无明显差异,提示该术对于盆底双侧非肛提肌组织内的应力无明显降低作用,推测可能无法降低术后盆底疝的风险。
本研究是一项生物力学研究,其结果是对临床观察研究的细化和补充,并探索其物力学机制。本研究模拟了女性盆底的4种个体化ELAPE,其中3种个体化ELAPE术式较经典ELAPE具备生物力学的优势,可在临床上推广。目前还有多种改良的ELAPE术式[5,13],以及盆底疝的预防措施,如肌皮瓣[7,18]或生物网片[19-21]的重建等,其中一些仍然存在争议,后续我们将进一步针对男性盆底和其他改良术式进行生物力学研究。由于肌肉组织的特殊性,我们还将进一步考虑实验测定肛提肌的力学特性,提高计算精度,为临床研究直肠术后生物力学改变提供更多的理论参考。
Competing interests: The authors declare that they have no competing interests.利益冲突声明:所有作者均声明不存在利益冲突。作者贡献:王捷夫:模型制作、整理数据、文章撰写路心然:模型制作王文鹏:研究指导,基金项目负责人 -
图 1 单侧肛提肌切除平面靠近直肠(A)、单侧肛提肌切除平面靠近盆壁(B)、双侧耻骨尾骨肌外侧切断肛提肌(C)的ELAPE手术
Figure 1 Individual ELAPE with unilateral levator ani muscle resection plane close to the rectum (A), unilateral levator ani muscle resection plane close to the pelvic wall (B), bilateral pubococcygeal muscle lateral resection of levator ani muscle (C)
表 1 6种有限元分析模型的基本信息
Table 1 Basic data of six finite element analysis models
Model Average nodes Average units Normal Model 469676.94±18980.81 331526.71±18920.53 ELAPE Model 10865.14±822.25 10243.14±795.86 Individual
Model 1174514.35±8846.67 121376.44±11354.88 Individual
Model 278569.06±6112.05 56154.35±3644.60 Individual
Model 3279172.29±8645.58 187768.56±5333.99 Individual
Model 4197840.59±5171.61 137655.41±2040.04 表 2 各组模型非肛提肌组织和肛提肌内的最大应力
Table 2 Maximum stress of non-levator ani muscle tissue and levator ani muscle in each model
Model Maximum stress(MPa) Non-levator ani
muscle tissueLevator ani muscle Normal model 1.953 ± 0.060 0.791 ± 0.045 ELAPE Model 5.111 ± 0.081 Individual Model 1
Levator ani muscle
partially reserved side1.339 ± 0.032 3.101 ± 0.133 Levator ani muscle
totally removed side4.868 ± 0.123 Individual Model 2 5.138 ± 0.091 1.524 ± 0.024 Individual Model 3 4.700 ± 0.105 0.773 ± 0.033 Individual Model 4 3.653 ± 0.156 1.438 ± 0.041 -
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