Midurethral sling procedures are now commonly performed for treatment of female stress urinary incontinence (SUI). The retropubic tension-free vaginal tape (TVT) procedure was first introduced in 1996; several studies have demonstrated high success rates for correction of SUI,1–4 although bowel, bladder, and vascular injury resulting from this technique have been described.5–12 The transobturator approach to midurethral sling placement, first described by Delorme in 2001,13 was developed to potentially prevent these complications by avoiding blind entry into the retropubic space.13–15 The originally described procedure involved passage of a needle by using an outside-in approach, incorporating a vulvar incision near the labial-crural fold, and passage of the needle around the ischiopubic ramus through the obturator membrane, exiting through a dissected submucosal space in the distal anterior vagina. In 2003, de Leval16 first described transobturator passage with an inside-out approach (TVT-Obturator), generally following a similar pathway of needle and mesh placement. By avoiding the retropubic space, purported advantages of transobturator placement included a reduced risk of vascular and bladder injury and not needing to perform cystoscopy at the time of the procedure.17–20 Since the introduction of these procedures, numerous studies have demonstrated high success rates for the treatment of SUI, with efficacy comparable to that achieved with TVT (Cervigni M, Courtieu C, Debodinance P, deRidder D, Fischer A, Herschorn S, et al. Twelve-month follow-up data on 138 patients implanted with the Monarc transobturator sling for treatment of stress urinary incontinence [abstract]. Int Urogynecol J Pelvic Floor Dysfunct 2005;16 suppl:S108.).14,18,20–28
Several anatomic dissection studies have been performed detailing the route of passage of the needle and mesh for both the inside-out and outside-in approaches.15,17,19,29–33 Although both methods of transobturator placement involve penetration of the obturator membrane and passage around the ischiopubic ramus, the actual route of passage differs slightly between the two approaches. Nonetheless, the general conclusion of these anatomic studies is that either approach is “safe” with regard to risk of neurovascular injury. The majority of these dissections involved a single method of placement on cadaver specimens; only two studies, one in the French literature, considered the two methods in the same cadaver specimens, one using a single method on each of the specimens’ sides and the other placing transobturator tapes after extensive dissection of hemipelves.29,32 Our objective was to perform both the inside-out and outside-in approach concomitantly and bilaterally on intact cadaver specimens and compare needle and mesh placement of each approach relative to proximity to neurovascular structures in the obturator region and to the ischiopubic ramus.
MATERIALS AND METHODS
Seven fresh female cadaver specimens were used in this study; these cadavers were used as part of a continuing education course in gynecologic surgery–related pelvic anatomy. The course curriculum included a comprehensive review of anti-incontinence procedures and procedures for correction of pelvic organ prolapse and incorporated dissection of pelvic support structures and anatomic considerations related to performance of these various corrective procedures. Included in the course was placement of both TVT and transobturator midurethral slings, using both approaches, by course participants. Permission was obtained from the Anatomic Material Review Committee of the Uniformed Services University of the Health Sciences to record and report measurements obtained after placement of the transobturator slings, and anatomic dissection was performed as part of the curriculum.
Both the outside-in (Monarc, American Medical Systems [AMS], Minnetonka, MN) and inside-out (TVT-Obturator System, Gynecare, Ethicon Inc, Somerville, NJ) were placed bilaterally in all seven cadaver specimens, resulting in a total of 14 attempts at transobturator needle and mesh placements. In cases in which the tapes were placed by course participants, the procedures were performed under guidance by course faculty, which included subspecialists in urogynecology and pelvic floor reconstructive medicine or generalist obstetrician–gynecologists with focused interest and expertise in urogynecology. In several cadavers, the transobturator tapes were placed by course faculty. In all cases, procedures were performed closely mimicking actual clinical practice before any dissection of the retropubic or obturator areas. There was no “predefined” order in which the transobturator tapes were placed; the order in which the procedures were performed was at the discretion of the course participants and faculty not involved in the investigation.
With the use of stirrups and straps, all cadavers were placed in high lithotomy position, with flexion of the hips to approximately 100–110º. The tapes were placed according to methods described in the literature and manufacturer recommendations. Appropriate helical passers were used according to described procedures for the inside-out and outside-in approaches, including the use of the guide for the inside-out approach. After the transobturator tapes were placed, tension was applied to place the mesh in its appropriate suburethral position. The tapes were cut from the helical passers, leaving a long segment of mesh protruding from the vulvar incision to enhance identification of the tape during subsequent dissection of the obturator area. In each cadaver, only one placement of the inside-out and outside-in methods was used; multiple passes of each method were not performed on any individual cadaver to avoid complicating the dissection and ability to measure mesh placement relative to neurovascular structures.
After all transobturator tapes were placed, while the cadaver specimens were still in high lithotomy position, the groin region was dissected to the level of the obturator membrane and canal. Briefly, this dissection involved a skin incision lateral to the labial-crural fold and dividing the adductor muscle group and the gracilis muscle. This was performed bilaterally on each cadaver. The obturator externus muscle was dissected as necessary to facilitate identification of the obturator canal relative to the location of the transobturator tape. Care was taken in all cases to dissect around the mesh to keep the mesh intact. Once the location of the obturator canal and the position of the tape as it penetrated the obturator membrane was identified, dissection was generally stopped except for fine dissection to allow for accurate measurement.
To achieve the objective of assessing the position of the tape relative to neurovascular structures, we used the passage of the obturator vessels and nerve through the obturator canal as the point of reference to gauge proximity of the tape to major blood vessels and nerves. Therefore, the distance between each of the tapes and the obturator canal was measured bilaterally. For purposes of measurement, the distance between the mesh and the closest aspect of the obturator canal was recorded (Fig. 1).
In addition to proximity of the tape to the obturator canal, we also measured the proximity of the tape to the ischiopubic ramus as it passed around the ramus in penetrating the obturator membrane, based on the concept that the closer the placement of the helical passer is to the ischiopubic ramus, the less the risk of neurovascular injury.15 Because the passage of the helical passer follows different actual trajectories for the inside-out and outside-in methods,17 we sought to determine if there was a difference between the methods regarding proximity of the mesh to the ischiopubic ramus. We therefore measured the closest distance between each tape and the ischiopubic ramus, including recording a measurement of “0” if the tape was in direct contact with the bone.
Overall descriptive statistics are reported, including mean distance ± standard deviation or median and range as appropriate. Comparisons between the outside-in and inside-out approaches with regard to the distance between the tapes and obturator canal and ischiopubic ramus were performed using paired samples t test or Wilcoxon signed-rank test, as appropriate (distribution of measurements was analyzed using the Kolmogorov-Smirnov test). Statistical analysis was performed with SPSS 12.0.2 for Windows (SPSS Inc, Chicago, IL). P<.05 was considered significant.
There were two African-American and five white cadavers; mean age of the cadaveric specimens was 68.7 years (range 51–78 years). Transobturator tapes were placed in all seven cadavers, allowing assessment of all 14 potential data points. Overall, the mean distance between the tape and the obturator canal was 1.83±0.67 cm (range 0.8–3.2 cm). The overall mean distance between the tapes and the ischiopubic ramus was 0.22±0.34 cm (median 0 cm, range 0–1.4 cm).
For the distances between the transobturator tapes and the obturator canal, the differences between paired measurements were determined to be normally distributed, based on the Kolmogorov-Smirnov test (P=.2). Therefore, t tests were used to compare the inside-out and outside-in approaches. Transobturator tapes placed with the outside-in method were farther from the obturator canal than those placed by the inside-out approach (mean±standard deviation [SD] 2.3±0.41 cm compared with 1.3±0.44 cm; P<.001; mean difference 1.0±0.6 cm). Individual analysis of the measurements in each of the 14 pairs of data points demonstrated that the tape placed with the outside-in approach was farther from the obturator canal in all cases. The distance between the tapes and obturator canal were further analyzed according to right or left sides. The tapes placed by the outside-in method remained farther from the obturator canal on each side, although the tapes on the specimen’s right side were closer to the obturator canal compared with the left side measurements (Table 1).
For the distances between the transobturator tapes and the ischiopubic ramus, the distribution of differences between paired measurements was determined to be normal (Kolmogorov-Smirnov test P=.086). Therefore, the paired t test was used to compare the different approaches. Overall, transobturator tapes placed with the outside-in method were closer to the ramus than those placed by the inside-out method (mean±SD 0.04±0.13 cm compared with 0.39±0.44 cm, P=.008; mean difference 0.3±0.4 cm). Analysis of the individual data points in each case demonstrated that the outside-in method was consistently closer to the ischiopubic ramus in all cases in which the tape was not actually in contact with the bone. The distance between the tapes and the ischiopubic ramus according to left or right side is shown in Table 2. Tapes placed using the outside-in method were closer on the right side; there was no difference between the two approaches for tapes placed on the left side.
In this anatomic comparative study, placement of the transobturator tape using the outside-in approach was consistently farther from the major obturator vessels and nerves using the obturator canal as a point of reference and closer to the ischiopubic ramus, compared with those placed by the inside-out approach. These findings are similar to the two other comparative studies of the different approaches. In the study reported by Spinosa et al,29 a single method was used on each side of six cadaver specimens, and measurements were obtained between the transobturator tape and the inferior pudendal vascular pedicle and the posterior branch of the obturator nerve. In five of the six cases, the transobturator tapes were within 1 cm (one case actually cutting the vessel) of the vascular pedicle for those placed with the inside-out approach; all six tapes passed via the outside-in approach were more than 3 cm from the vascular pedicle. In addition, tapes placed via the outside-in approach were consistently farther from the nerve compared with those positioned by the inside-out approach. In another study, 10 pelves were extensively dissected to analyze anatomic relationships; TVT, TVT-Obturator, and Monarc were then placed (after dissection) and measured relative to several structures.32 In this series, the inside-out approach was closer to the obturator canal compared with the outside-in approach (2.7 cm compared with 1.9 cm).
Other anatomic studies of single approaches have detailed routes of the needle passer and tape; several have reported measurements relative to important structures. In an anatomic study of the inside-out approach, the tape was noted to be 2.5 cm from the obturator pedicle.33 Another anatomic study of the inside-out approach in 12 cadavers demonstrated that the closest distance between the tape and obturator nerve was 2.2 cm (mean 2.6 cm), and the greatest proximity of the tape to the nerve was at the level of the obturator canal.17 These authors did not report on the proximity of the tape to major vascular structures. In a detailed anatomic dissection involving passage of the tape with the outside-in method, the authors described potential for injury to the obturator nerve and branches of the obturator vessels with the inside-out approach based on their dissection.19 However, the inside-out method was not actually performed in these specimens to determine if, indeed, these structures were at increased risk. In another study in which the outside-in approach was used in four cadavers, the mean distance between the tape and the obturator canal was 2.3 cm, similar to our findings, with a distance to the most medial vascular branch of 1.1 cm.30 However, the tapes were placed after dissection of the obturator space; it is difficult to ascertain the potential effect of prior obturator dissection on the actual passage of the needle and tape and resultant proximity to major structures. Reisenauer et al31 reported on TVT-Obturator performed in five cadavers; the mean distance to the neurovascular structures in the obturator canal was 2.48 cm, which was greater than the mean distance between the inside-out tapes and the obturator structures measured in our study.
Although other studies incorporated various vascular and neural branches in the measurements reported, we chose to rely on the obturator canal as a point of reference, considering the major neurovascular structures that pass through the canal. We did not further dissect branches of the obturator vessels or nerve due to variations in branching of these structures,17,30 deviation of vascular and nerve branches away from potential injury in high lithotomy position,17,25,30,32 and the fact that vessels supplying the thigh musculature become very small with further branching.19 Due to these variations in anatomy, we considered the obturator canal to be the most consistent location in each cadaver that would allow measurement of the tape relative to neurovascular structures. In addition, other investigators have described that the closest point between the route of the obturator nerve and the midpoint of the ischiopubic ramus was found at the obturator canal, reinforcing the use of the obturator canal as the point of reference for measuring the proximity of the tapes to major neurovascular structures.17,30 Our objective was to assess transobturator tapes relative to neurovascular structures in the obturator region. Therefore, we did not dissect the retropubic space or further dissect the vagina to assess for bladder or urethral injury or injury to other vessels or nerves.
We identified interesting differences between measurements on the specimens’ left compared with right sides. It is tempting to speculate whether the handedness of the surgeon influenced placement of the helical passer. We did not record left- or right-handedness of the surgeons, so we cannot further analyze this potential effect. We also did not record the level of expertise of the surgeon placing the tapes. Bonnet et al,17 in a study of inside-out transobturator tape placement, noted that the tape followed a consistent course independently of surgeon expertise. It would be interesting to determine if differences did exist between surgeons regarding proximity of the tapes to major neurovascular structures or to the ischiopubic ramus.
One concern is whether the placement of a transobturator tape by one approach may have influenced the placement of the tape using the other method and, thus, may have had an effect on the results. As described in Materials and Methods, there was no preset order in which the procedures were performed. Although the order was not “randomized,” the order in which the tapes were placed was arbitrarily decided by the course participants. The fact that consistent differences were identified for each data point despite the tapes being placed in an arbitrary order essentially refutes the possibility that the order in which the procedures were performed impacted the measurements of the tapes relative to the obturator foramen or the ischiopubic ramus.
Although there are anatomic differences between the two approaches for transobturator tape placement relative to proximity to neurovascular structures, clinical consequences thus far do not seem to significantly correlate with theoretical risk based on anatomic dissections. Several large clinical efficacy studies of transobturator midurethral slings for correction of SUI have reported no significant vascular or neural injuries (Delmas V. Re: de Leval J Novel surgical technique for the treatment of female stress urinary incontinence: transobturator vaginal tape inside-out [letter]. Eur Urol 2004;46:134).13,14,16,18,20,21–25,34 This may be due to the deviation of major vascular and nerve branches away from the course of the helical passer with high lithotomy positioning as described. It may also be that vascular injury is self-limited because of muscular anatomy in this region.30 However, case reports of vulvar and retroperitoneal hematomas have recently been published, following both transobturator tape approaches.35–38 As the transobturator approach to correction of SUI becomes more widely incorporated in clinical practice, it will be important to determine if vascular or nerve injury or both become more apparent and if there are differences between the methods of transobturator tape placement.
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