An In Vivo Biomechanical Study Of Female Pelvic Floor

Objects:To devise a special in vivo puller measuring instrument for female pelvic floor.To establish a reliable experimental protocol to characterize the in vivo biomechanical properties of female pelvic floor supporting structure. To mesure the in vivo biomechanical properties of several important supporting structure, the anterior longitudinal ligament(ALL) and the tensile free vaginal tape. Accordingly, to provide biomechanical evidence for the efficiency of reconstructive pelvic surgery.Materials and Methods:Ten fresh cadavers were dissected to expose uterosacral Ligament(USL),the ring around cervix, arcus tendineus fascia pelvis(ATFP), fascia on the ischial spine, sacrospinous ligament(SSL) and ALL. After the fascia and ligaments were sewed according to the surgical technique, they were stretched at a steady rate until breakage while allowing constant electronic registration of load and displacement. Then to compare the in vivo biomechanical properties by analyzing the load-displacement curve.Ten fresh cadavers were randomized to (tension free vaginal tape—obturator)TVT-0 or the TVT-Secur group, each group had five bodies. After the surgical procedures was finished, tension tests were performed by the purpose-built puller system to prove the surgical efficiency.Results:1. The ultimate load of USL, the ring around cervix, ATFP, fascia on the ischinal spine and SSL was 37.3±23.5N,49.3±28.4N,46.8±18.7N,42.2±19.8N and 39.4±25.6N, respectively, and there was no significant difference among groups(P>0.05). The coefficient of variation(CV) of ATFP and fascia on the ischial spine were less than the others. That is to say, the individual differences of ultimate load among the first two groups were small.2. The stiffness of USL, the ring around cervix, ATFP, fascia on the ischinal spine and SSL was 1.26±1.22 N/mm,1.45±0.92 N/mm,1.28±0.44 N/mm, 1.47±0.40 N/mm and 1.47±0.62 N/mm, respectively. There was also no significant difference among groups (P>0.05). There was a considerable variability for each value, but the CV of ATFP and fascia on the ischial spine were less than the other three groups.3. The ultimate load of ALL at the sacral promontory, the first sacral vertebra and the second sacral vertebra were 129.55±64.07N,69.46±15.52N and 18.90±7.52N, respectively. It progressively decreased distally along the sacral vertebra, the differences between levels were significant(P<0.01).4. The stiffness of ALL was 4.24±2.14N/mm at the sacral promontory,2.91±1.54N/mmat the first sacral vertebra and 2.14±0.79N/mm at the second sacral vertebra, which was declining(P<0.05). The stiffness of ALL at the sacral promontory was greater than the stiffness of other levels (P<0.01), but there was no significant difference between the lower two levels (P>0.05).5. The mechanical resistance of TVT-0 was 18.71±2.68N, which was stronger than TVT-Secur, but no significant difference could be found(P>0.05).Conclusions:1. We devised a digital in vivo puller measuring instrument for female pelvic floor biomechanical study with high fidelity. The instrument can stretch samples at a continuous and adjustable rate until breakage while allowing constant electronic registration of load and displacement. It can enable orientation in a vertical and horizontal surface plane in order to guide traction.2. We established a reliable experimental protocol to characterize the in vivo biomechanical properties of female pelvic floor supporting structure and ALL. We also optimize the protocol in details to guarantee good test repeatability. For the first time we introduce "stiffness" into the in vivo biomechanics,so as to get comprehensive and accurate biomechanical data.3. This is the first report of the in vivo biomechanical properties of pelvic floor important support structure and ALL in fresh cadavers of Chinese women. We provided biomechanical evidence for the efficiency of reconstructive pelvis surgery.4. This study measured the in vivo biomechanical properties of ring around cervix firstly at home and suggested to sew ring around cervix to provide sufficient strength in reconstructive pelvic surgery.5. As we know, it was the first time that we survey the ultimate load of ATFP in fresh cadavers of Chinese women by simulating the Peking^Union-modified pelvic floor reconstruction surgery. The results showed that the Peking-Union-modified surgery could provide equal strength to the total pelvic floor reconstruction surgery(Prolift).6. The fascia on the ischial spine had similar ultimate load value with SSL and greater stiffness than mesh, which is safe, strong and economical to be used as a new site for suspension in vaginal prolapse.7. There was a considerable variability for the ultimate load value and stiffness index of SSL, which is recognized as a strong ligament.8. The ultimate load and stiffness of ALL both decreased along the sacrum. It was the first time to recommend ALL at the sacral promontory as the best suture point of sacrocolpopexy from these two mechanical parameter.9. It was the first time to compare the in vivo biomechanical properties of TVT-0 and TVT-Secur, furthermore making recommendations for optimizing the experimental protocol of mesh.The mechanical resistance of TVT-Secur-H-type was found to be comparable with that of TVT-0. Therefore, TVT-Secur-H-type could acquire similar clinical effect to TVT-0 in theory.