A Study On Clinically Oriented Anatomy And Biomechanics Of Pelvic Floor Dysfunction

ObjectivesThe purpose of this study was to further characterize the neurovascular anatomy of the presacral and the sacrospinous ligament(SSL) regions and to determine the safe area for sacrocolpopexy,sacrospinous ligament fixation(SSLF) and iliococcygeus fixation;to measure the pullout strengths of the presacral longitudinal ligament,the iliococcygeus fascia,the fascia on the ischial spine,the SSL as well as the vaginal fornix on the cadavers;and to demonstrate the safety, firmness and convenience of the fascia on the ischial spine as a new fixation site for the vaginal fornix.MethodsDetailed dissections and related measurements of the presacral and SSL regions were performed on 10 Chinese female cadavers(3 unembalmed and 7 embalmed cadavers) after intravascular injection of colored latex.At the same time,the presacral longitudinal ligament,the iliococcygeus fascia,the fascia on the ischial spine,the SSL as well as the vaginal fornix were exposed and the pull-out strength sequentially tested using a digital push-pull force gauge.Fresh cadavers were always dissected within 48 h of death before any storage procedure was started.Results1 The vascular pattern of the presacral space was regular in 9 specimens(9/10). There was one communicating vein connecting the lateral sacral vein(or the internal iliac vein) and the middle sacral vein on the surface of each sacral vertebrae.These communicating vessels are disposed perpendicular to the middle sacral and lateral sacral veins in a stair-like fashion.The corners of a square with a side of 3 cm,centered on the anterior aspect of the body of sacrum, were almost all contained in the avascular areas,with the upper side of this square parallel to a line passing through the sacral promontory,at a 3 cm distance from it.2 The average length of the SSL was measured to be 52.3 mm(SD=±4.2).The width of the SSL at its origin and the point 2.5 cm medial to the ischial spine was 10.0±1.1 mm and 12.0±2.1 mm,respectively.The inferior gluteal vessels left the pelvis by passing behind the lateral half of the SSL in seven hemipelvises(7/20),or by passing in proximity to the superior border of the SSL in 8 hemipelvises(8/20).The majority coursed behind the sacral plexus and the pudendal nerve,with a small segment sometimes left uncovered above the top of the SSL.The coccygeal branch of the inferior gluteal artery was found in 18 hemipelvises(18/20),15.7±5.6 mm medial to the ischial spine at the level of the superior border of the SSL.The pudendal nerve passed posterior to the SSL and exited the pelvis through the lesser sciatic foramen,medial and superior to the pudendal vessels.The pudendal complex was found to be 23.4±3.6 mm and 15.7±1.3 mm medial to the ischial spine at the upper and lower border of the SSL,respectively.Posterior to the iliococcygeus muscle in a 1-2 cm scalloped area from the anterio-inferior to medio-inferior ischial spine lay the internal pudendal vessels,the pudendal nerves,and inferior rectal nerve and vessels.The mean thickness of the iliococcygeus muscle was 2.54 mm(range 1.60-3.80 mm). The levator ani nerve was found in 15 hemipelvises(15/20),at a mean distance of 39.6±8.3 mm from the ischial spine at the level of the superior border of SSL.3 The mean pullout strengths of the presacral longitudinal ligament at the sacral promontory,the first sacral vertebra and the second sacral vertebra were 99.2 Newtons(N)(range 69.4-157.0 N),47.9 N(range 29.0-85.0 N),22.8 N(range 8.5-43.0 N),respectively.It progressively decreased distally along the sacral segments.The pullout strengths of the SSL,the fascia on the ischial spine,the iliococcygeus fascia as well as the vaginal fornix were 102.0±25.7 N(range 74.3-176.0 N),64.4±14.7 N(range 38.0-85.0 N),32.6±8.2 N(range 17.0-42.0 N) and 31.6±5.6 N(range 26.0-46.7 N) respectively.There was a considerable variability for each value.The mean pullout strength at each site was similar between the three fresh cadavers and the seven embalmed cadavers,excluding that of the pre-vertebral ligament at the sacral promontory,which was significantly greater in fresh cadavers(mean=124.0 N) than in embalmed cadavers(86.8 N).4 The fascia on the ischial spine was finn and strong,with the SSL and the coccygeus muscle and the iliococcygeus muscle originating from and the obturator internus fascia,arcus tendineus fascia pelvis and arcus tendineus levator ani attaching to the ischial spine.No major vessels or nerves were noted on the ischial spine.Conlusions1 The vascular pattern of the presacral space is regular in most of the specimens. Among the avascular areas adjacent to each of the four corners of the 3 cm square in the median presacral region at a distance of 3 cm from the sacral promontory.The avascular area at the level of the first presacral foramen is considered the preferred site for sacrocolpopexy;in comparison,both the avascular surface area and the pullout strength of the anterior longitudinal ligament at the level of the third and fourth sacral vertebrae are too small to be a suitable suturing site.2 To preserve the nerves and vessels behind and above the SSL during SSLF, sutures should be placed through the SSL at least 2.5 cm from the ischial spine and within half of the lower margin and within superficial half of the entire thickness.This shall provide sufficient support.3 In iliococcygeus fixation,it is recommended to place the suture within the superficial layer of the muscle and fascia when the iliococcygeus fascia 1 cm inferior to the ischial spine is the site of choice.4 The fascia on the ischial spine,free of major vessels and nerves,is safe and strong and technically simple to be used as a new site for suspension in vaginal prolapse.