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Anatomic relationships of single-incision midurethral slings

Published:October 08, 2012DOI:https://doi.org/10.1016/j.ajog.2012.10.004

      Objective

      The objective of the study was to evaluate the anatomic relationships of anchor points of single-incision midurethral slings with 2 common placement trajectories.

      Study Design

      In 30 female pelvic halves, a probe was introduced through a suburethral tunnel following 45° and 90° angle trajectories. The corresponding anchor points were tagged. Distances to the obturator canal, accessory obturator vessels, dorsal vein of clitoris, and external iliac vein were recorded.

      Results

      Both suburethral tunnel trajectories and their respective anchor points remained caudad to the obturator internus muscle in 100% of dissections. The closest distance between either anchor point to the obturator canal was 1.6 cm. The closest distance from the 45° and 90° anchor points to the accessory obturator vessels was 1.6 and 1.5 cm, respectively.

      Conclusion

      The anchor points of single-incision midurethral slings are in close proximity to vascular structures that could be injured with inadvertent entry into the retropubic space.

      Key words

      Synthetic midurethral slings have become the gold standard primary surgical treatment for stress urinary incontinence.
      • Ogah J.
      • Cody J.D.
      • Rogerson L.
      Minimally invasive synthetic suburethral sling operations for stress urinary incontinence in women.
      The retropubic midurethral sling, introduced by Ulmsten et al in 1994,
      • Ulmsten U.
      • Johnson J.
      • Petros P.
      Intravaginal slingplasty.
      is considered a minimally invasive procedure that involves passage of needles through small vaginal and suprapubic skin incisions. Complications associated with retropubic midurethral slings include lower urinary tract and bowel injury as well as hemorrhage associated with retropubic vessel injury.
      • Daneshgari F.
      • Kong W.
      • Swartz M.
      Complications of mid urethral slings: important outcomes for future clinical trials.
      • Abouassaly R.
      • Steinberg J.R.
      • Lemieux M.
      • Marois C.
      • Gilchrist L.I.
      • Bourque Jean-Louis
      • et al.
      Complications of tension-free vaginal tape surgery: a multi-institutional review.
      The transobturator approach is an alternative to the retropubic approach that was first described by Delorme in 2001.
      • Delorme E.
      Transobturator urethral suspension: mini-invasive procedure in the treatment of stress urinary incontinence in women (French).
      Compared with retropubic slings, transobturator slings are associated with less visceral injury but have higher rates of neurologic complications.
      • Richter H.E.
      • Albo M.E.
      • Zyczynski H.M.
      • Kenton K.
      • Norton P.A.
      • Sirls L.T.
      • et al.
      Retropubic versus transobturator midurethral slings for stress incontinence.
      • Brubaker L.
      • Norton P.A.
      • Albo M.E.
      • Chai T.C.
      • Deandreo K.J.
      • Lloyd K.L.
      • et al.
      Adverse events over two years after retropubic or transobturator midurethral sling surgery: findings from the Trial of Midurethral Slings (TOMUS) study.
      In an effort to circumvent complications associated with both the retropubic and transobturator approaches, several single-incision sling products (minislings) have been introduced since 2005. Minislings avoid passage of needles or material through the retropubic space or obturator foramen as well as incisions through the suprapubic or groin skin. Although a less invasive approach could point to a safer procedure, recently reported complications associated with minislings include severe hemorrhage, at times necessitating surgical exploration for vessel ligation.
      • Gobrecht U.
      • Kuhn A.
      • Fellman B.
      Injury of the corona mortis during vaginal tape insertion (TVT-Secur™ using the U-Approach).
      • Larsson P.
      • Teleman P.
      • Persson J.
      A serious bleeding complication with injury of the corona mortis with the TVT-Secur procedure.
      • Masata J.
      • Martan A.
      • Svabik K.
      Severe bleeding from internal obturator muscle following tension-free vaginal tape Secur hammock approach procedure.
      • Jain A.
      • Kannan K.
      • Rane A.
      Pelvic haematoma following Miniarc surgery—a case report.
      • Rehder P.
      • Glodny B.
      • Pichler R.
      • Mitterberg M.J.
      Massive retropubic hematoma after minimal invasive mid-urethral sling procedure in a patient with a corona mortis.
      • Jung Y.S.
      • Lee J.H.
      • Shin T.S.
      • Han C.H.
      • Kang S.H.
      • Lee Y.S.
      Arterial injury associated with tension-free vaginal tapes-Secur procedure successfully treated by radiological embolization.
      Minislings are placed through a midline vaginal incision through which a small needle device is used to position the arms of the sling in place. Depending on the specific product, the needle is advanced through an angle trajectory of either 45° or 90° from the midsagittal plane and anchored to structures such as the obturator internus muscle (MiniArc Precise; product insert, 2010, AMS, Minnetonka, MN), obturator membrane (AJUST; product brochure, 2009 Bard, Covington, GA), or connective tissue of the urogenital diaphragm (TVT SECUR in U position; product insert, 2005, Ethicon, Somerville, NJ).
      A recent Food and Drug Administration safety communication regarding serious complications associated with mesh-augmented vaginal procedures has raised a heightened awareness about the risks associated with products involving mesh.
      Food and Drug Administration safety communication: update on serious complications associated with transvaginal placement of surgical mesh for pelvic organ prolapsed, 2011.
      Anatomical studies are helpful in evaluating the safety of innovative products. Previous human cadaver studies have evaluated the relationship of TVT SECUR (Ethicon) to the obturator bundle only.
      • Hubka P.
      • Masata J.
      • Nanka O.
      • Grim M.
      • Martan A.
      • Zvarova J.
      Anatomical relationship and fixation of tension-free vaginal tape Secur.
      • Hubka P.
      • Nanka O.
      • Martan A.
      • Grim M.
      • Zvarova J.
      • Masata J.
      TVT-S in the U position—anatomical study.
      We sought to evaluate the path and anchor point locations of single incision midurethral sling arms relative to the midline vaginal incision following 45° and 90° angle trajectories as well as the average distances from these anchor points to important retropubic vascular structures and obturator canal region.

      Materials and Methods

      The study was deemed exempt from review and oversight by the University of Texas Southwestern Medical Center Institutional Review Board. Twenty-five embalmed and 5 fresh female cadaver halves were obtained from the Willed Body Program at the University of Texas Southwestern Medical Center in Dallas. The pelvises were transected in the midsagittal plane and the retropubic space was exposed, with a total of 16 and 14 left- and right-sided pelvises, respectively. From the inferior border of the mid pubic symphysis, 45° and 90° angles were measured using a bevel protractor (Figure 1). Each angle trajectory was delineated by stapling a segment of string to the outer labia majora. A suburethral tunnel, at the midurethral level, was sharply created and extended towards the inferior pubic ramus.
      Figure thumbnail gr1
      FIGURE 1Perineal view showing 45° and 90° angle trajectories
      Montoya. Minisling anchor points. Am J Obstet Gynecol 2013.
      To simulate the path of the minisling needle, a straight metal probe was introduced through the suburethral tunnel following the 45° and then the 90° trajectories toward the obturator internus muscle until resistance was encountered. The 2 corresponding anchor points, demarcated by the tip of the probe, were palpated from the retropubic side and tagged with metal pins. The anchor points were termed the 45° and 90° anchor points (Figure 2). The anatomic structure through which the pins were passed was noted. The closest distance from the 45° and 90° anchor points to the obturator canal, accessory obturator vessels, external iliac vein, and dorsal vein of the clitoris were measured (Figure 3). Descriptive statistics were calculated using SAS 9.2 (SAS Institute, Cary, NC).
      Figure thumbnail gr2
      FIGURE 2Right pelvic half of unembalmed cadaver showing AP through OI muscle
      Pink pin indicates the 45° AP, with yellow dashed lines showing the distance from midsuperior and midinferior pubic symphysis (PS). Blue pin indicates the 90° AP. Arrowhead indicates the probe through the suburethral tunnel. Yellow pin indicates the ischial spine.
      AP, anchor points; OI, obturator internus.
      Montoya. Minisling anchor points. Am J Obstet Gynecol 2013.
      Figure thumbnail gr3
      FIGURE 3Right retropubic space in right pelvic half of unembalmed cadaver
      The bladder has been mobilized. Arrowhead indicates the obturator canal. Blue pin indicates the ischial spine.
      OI, obturator internus muscle; PS, pubic symphysis.
      Montoya. Minisling anchor points. Am J Obstet Gynecol 2013.

      Results

      A total of 30 cadaver halves were examined (obtained from 3 fresh and 17 embalmed specimens). Limited demographic information was available for review in 15 specimens, with a median age at the time of death 69 years (range, 44–98 years), a median weight 59 kg (range, 43–82 kg), and a median body mass index 22 kg/m2 (range, 16–31 kg/m2). All cadavers were white.

      Anchor point locations

      The suburethral tunnel trajectory remained immediately caudad or external to the obturator internus muscle, between the muscle and the obturator membrane, at both the 45° and 90° angles in 100% of dissections. Table 1 summarizes the 45° and 90° anchor point location relative to the suburethral vaginal incision and to the superior and inferior midpubic symphysis. Figure 2 illustrates the mean distances from the 45° anchor point to the superior and inferior border of the midpubic symphysis.
      TABLE 1Anchor point location relative to 3 identifiable anatomic landmarks
      Anchor pointsDistance from suburethral vaginal incisionDistance from superior midpubic symphysisDistance from inferior midpubic symphysis
      45° angle3.3 ± 0.45.2 ± 0.93.6 ± 0.7
      90° angle3.6 ± 0.56.1 ± 0.94.5 ± 0.8
      Measurements are in centimeters (average ± SD).
      Montoya. Minisling anchor points. Am J Obstet Gynecol 2013.

      Anchor point anatomic relationships

      The closest distance from the inferior border of the mid symphysis to the medial border of the obturator canal was 5.7 ± 0.6 cm on the left and 5.8 ± 0.5 cm on the right. Accessory obturator vessels were identified in 21 of 30 pelvic halves. The dorsal vein of the clitoris was identified in 13 of 30 pelvic halves. Average distances from the anchor points to the obturator canal, accessory obturator vessels, external iliac vein, and dorsal vein of clitoris are summarized on Table 2.
      TABLE 2Anatomic relationships of 45° and 90° angle anchor points
      Anchor pointsObturator canal (n = 30)Accessory obturator vessels (n = 21)Dorsal vein of clitoris (n = 13)External iliac vein (n = 30)
      45° angle2.7 ± 0.5 (1.6–4.2)2.8 ± 0.7 (1.6–4.9)2.5 ± 0.4 (1.9–3.2)5.1 ± 0.8 (3.2–7.0)
      90° angle2.6 ± 0.4 (1.6–3.5)2.8 ± 0.7 (1.5–4.5)3.6 ± 0.6 (2.9–4.4)5.0 ± 0.8 (3.1–6.1)
      Measurements are in centimeters average ± SD (range).
      Montoya. Minisling anchor points. Am J Obstet Gynecol 2013.

      Comment

      The lack of exit points with single-incision midurethral slings has advantages and disadvantages. The less invasive approach with minislings offers a simpler procedure with fewer steps and decreased risk of visceral injury. However, the anchoring of the sling arms with minisling procedures is performed blindly, and procedural guidance is limited to imprecise descriptions regarding anchor location found in product literature. One could argue that the defined trocar and mesh course through the suprapubic or groin skin with the retropubic and transobturator slings may delineate a clearer anatomical trajectory in the surgeon's mind, thus leading to improved control and procedural standardization.
      In all of our dissections, the suburethral tunnel remained just caudad, or external, to the obturator internus muscle, between the muscle and the obturator membrane. Given this finding, it is likely that the minisling arms at both the 45° and 90° angle trajectories are anchored either within the obturator internus muscle or in the obturator membrane. The average distance from the midline vaginal incision to the 45° and 90° anchor points was 3.3 and 3.6 cm, respectively. We believe these distances to be representative of the typical distance traveled during minisling arm placement. In fact, our average distances from the midline vaginal incision at both angle trajectories may be somewhat conservative, considering the length of several minisling products is between 8 and 9 cm. Deviation from the manufacturer's recommended angle trajectories or moving past the recommended distance from the vaginal incision during minisling arm placement may result in inadvertent entry into the retropubic space or perforation and migration caudad to the obturator membrane.
      Injury to the accessory obturator vessels, also known as the crown of death or corona mortis vessels, during minisling placement has recently been reported.
      • Gobrecht U.
      • Kuhn A.
      • Fellman B.
      Injury of the corona mortis during vaginal tape insertion (TVT-Secur™ using the U-Approach).
      • Larsson P.
      • Teleman P.
      • Persson J.
      A serious bleeding complication with injury of the corona mortis with the TVT-Secur procedure.
      • Rehder P.
      • Glodny B.
      • Pichler R.
      • Mitterberg M.J.
      Massive retropubic hematoma after minimal invasive mid-urethral sling procedure in a patient with a corona mortis.
      Indeed, the anchor point locations evaluated in this study were found to be in close proximity to important retropubic vascular structures and the obturator canal region in both 45° and 90° angle trajectories. The accessory obturator vein was one of the closest structures to both the 45° and 90° anchor points, with the shortest distance noted at 1.5 cm. Given its location over the inner surface of the pubic ramus, accessory obturator vessel injury is likely to occur only with inadvertent entry into the retropubic space. Although it is unclear how often unintentional retropubic space entry occurs in clinical practice, Hubka et al
      • Hubka P.
      • Nanka O.
      • Martan A.
      • Grim M.
      • Zvarova J.
      • Masata J.
      TVT-S in the U position—anatomical study.
      reported entry into the lesser pelvis in 36% of cases in their anatomical study of TVT-Secur (Ethicon).
      Although not evaluated in our study, muscular branches that supply the obturator internus muscle may also be injured during sling placement and result in significant hemorrhage, as reported by Hubka et al.
      • Hubka P.
      • Masata J.
      • Nanka O.
      • Grim M.
      • Martan A.
      • Zvarova J.
      Anatomical relationship and fixation of tension-free vaginal tape Secur.
      The average distance observed to the dorsal vein of the clitoris was 2.5 cm from the 45° anchor point. However, given the medial location of this vessel, injury is unlikely because the sling arm is directed away from the midpubic symphysis during placement.
      In general, the management of vessel injury during single-incision midurethral sling placement is dictated by the extent of bleeding and overall patient status. As with traditional midurethral slings, low pressure bleeding is likely to respond to sustained pressure and hemostatic agents, if needed. If these measures are unsuccessful, abdominal entry into the retropubic space may be warranted for identification and ligation of the bleeding vessel.
      Our study has several strengths and limitations. First, we did not use any specific minisling products. We avoided specific product use in attempts to generalize our findings to the multiple kits available in the market without bias toward a specific product. Moreover, our measured distances from the anchor points to the obturator canal are comparable with those previously reported using TVT-Secur (Ethicon).
      • Hubka P.
      • Masata J.
      • Nanka O.
      • Grim M.
      • Martan A.
      • Zvarova J.
      Anatomical relationship and fixation of tension-free vaginal tape Secur.
      • Hubka P.
      • Nanka O.
      • Martan A.
      • Grim M.
      • Zvarova J.
      • Masata J.
      TVT-S in the U position—anatomical study.
      Second, all specimens examined were white and slight variations in anatomy may be found in different racial backgrounds. Third, the effects of embalming on distances recorded are not known; however, limited measurements from unembalmed cadavers were comparable. Fourth, all authors are right handed. It may be possible that surgeon handedness has an impact on anchor point distances on the dominant vs the nondominant side. Based on our results, we do not believe this to be likely because all measurements taken on the right side of the pelvis were compared with those on the left and no statistical difference was noted (data not shown). Hence, measurements from both sides were combined as shown in TABLE 1, TABLE 2. In addition, mapping the anchor point locations using 3 discrete points (midvaginal incision and superior and inferior margins of the midpubic symphysis) was arbitrary; however, we believed this would be useful in providing coordinates that would assist with creating a 3-dimensional reference to assist with the localization of the anchor points.
      Lastly, our study design did not allow us to accurately evaluate the risk of bladder entry because the bladder was mobilized from its natural attachments during exposure of the retropubic space; however, we have now managed several complications in which either the minisling anchor tip or sling mesh was found within the bladder. Therefore, as with other midurethral sling approaches, we support routine cystourethroscopy to assess bladder and urethral integrity following the procedure. Despite these limitations, we have recorded our observations from a relatively large number of cadavers using a consistent measurement system and anatomic landmarks that are clinically identifiable.
      Given that the anatomy in this region is often confusing and product information often lacks detail, we believe that our evaluation of suburethral tunnel and anchor point locations as well as the distance of advancement from the midline vaginal incision, will serve as a useful guide for pelvic surgeons. As we continue to pursue innovative, less invasive procedures for the treatment of stress urinary incontinence, a thorough understanding of anatomy as related to each new product is paramount to ensure patient safety and to appropriately manage complications.

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        TVT-S in the U position—anatomical study.
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