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.
Synthetic midurethral slings have become the gold standard primary surgical treatment for stress urinary incontinence. The retropubic midurethral sling, introduced by Ulmsten et al in 1994, 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. The transobturator approach is an alternative to the retropubic approach that was first described by Delorme in 2001. Compared with retropubic slings, transobturator slings are associated with less visceral injury but have higher rates of neurologic complications.
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.
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. 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.
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.
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).
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/m 2 (range, 16–31 kg/m 2 ). 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.
| Anchor points | Distance from suburethral vaginal incision | Distance from superior midpubic symphysis | Distance from inferior midpubic symphysis |
|---|---|---|---|
| 45° angle | 3.3 ± 0.4 | 5.2 ± 0.9 | 3.6 ± 0.7 |
| 90° angle | 3.6 ± 0.5 | 6.1 ± 0.9 | 4.5 ± 0.8 |
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