Anatomic relation between single-incision slings and the obturator vessels

Abstract

The risk of arterial vascular injury within the retropubic space is a potentially life-threatening complication associated with mid-urethral sling placement for the treatment of female stress urinary incontinence. To determine the relationship between the major blood vessels and a single incision sling, these slings were placed in 12 fresh female cadavers. Following the insertion of each sling, the retropubic space was dissected and sling placement was observed relative to the obturator neurovascular bundle bilaterally. The distance between the most distal aspect of each sling arm, or the point of anchoring, was measured from the most medial aspect of the obturator vessels bilaterally. The mean distance between each sling arm and the medial portion of the obturator vessels was an average of 3.4 cm (range 2.0–6.0 cm) in 24 observations. Placement of the single incision sling may have a lower risk of injuring major vessels within the retropubic space compared to full-length mid-urethral slings.

Stress urinary incontinence (SUI) is a major health problem with a significant health burden affecting 20% to 40% of all women, and surgery remains the most effective treatment option (1). The mid-urethral sling (MUS) is now considered the gold standard of incontinence surgery (2). The long-term efficacy and technical ease in inserting MUSs have resulted in their widespread popularity; however, serious and potentially fatal complications have been reported with these procedures. It is important for any surgeon who treats female SUI to be familiar with the anatomic relationship between their surgical procedure of choice and the vascular anatomy of the retropubic space.

In 2006, the third generation of synthetic slings for SUI emerged with the development of single-incision slings (SIS), or “mini-slings” (3). The TVT-Secur™ (TVT-S; Gynecare, Ethicon, Somerville, NJ) was described first, and subsequently a number of other SISs were reported. This version of sling was described as avoiding the blind passage through the retropubic or obturator spaces via trochars (4). Despite the lack of long-term evidence regarding its efficacy, the SIS offers the least-invasive surgical treatment approach and remains a popular choice among many surgeons who treat SUI (1, 5, 6).

Previous reports have described the vascular anatomy of the retropubic space relative to both retropubic and transobturator approaches of the MUS (7, 8). This article describes observations during cadaveric dissections following the insertion of SISs and reviews the relevant vasculature in proximity of MUS approaches used to treat female SUI.

METHODS

Fellows and faculty from the Walter Reed National Military Medical Center in Bethesda, Maryland, and the Scott & White Hospital in Temple, Texas, participated in training involving female cadavers as part of an educational curriculum in the surgical treatment of SUI. Local approval was granted by the Anatomic Material Review Committees at each institution prior to the use of these cadavers for educational purposes. Slings were donated by Caldera Medical (Agoura Hills, CA; Desara™) and Boston Scientific (Natick, MA; Solyx™).

A total of 12 SISs were placed according to manufacturer guidelines by the first author. Initially, an incision of approximately 1.5 cm was made along the anterior vaginal wall at the level of the mid-urethra in each cadaver. Next, a tunnel was created sharply to the interior portion of the inferior pubic ramus at about a 45-degree angle from the midline to place each sling arm bilaterally. After each sling was placed, the retropubic space was inspected by exposing the space of Retzius via a low transverse abdominal incision.

Each sling was inspected at the most lateral aspect of each point of fixation into the obturator internus fascia. The distance between this anchoring point of the sling arm and the medial aspect of the obturator neurovascular bundle was measured and recorded bilaterally. A total of 24 measurements were performed with a flexible plastic ruler marked in 1 mm increments. Each measurement was taken by one author and confirmed by a second prior to recording to the nearest 0.5 cm. Dissection, measurement, and interpretation of the observations were shared, discussed, and interpreted by all of the authors.

RESULTS

As shown in Table 1, the mean distance in the 24 measurements was 3.4 cm (range 2.0–6.0 cm). Distances for the right side did not differ between the two devices (P = 0.15 using unpaired t test). In addition, distances between sides did not differ in 24 observations (P = 0.54 using unpaired t test).

Table 1.

Distance between single incision sling and obturator vessels in 12 female cadavers

Sling	Insertion	Right (cm)	Left (cm)	Right and left
Boston Scientific (Solyx)	1	3	4
	2	3	3
	3	4.5	5
	4	3	4
	5	6	4
	6	2	3
	Mean ± SD	3.6 ± 1.4	3.8 ± 0.7	3.7 ± 1.1
Caldera Medical (Desara)	7	2.5	3
	8	4	4
	9	4	4
	10	2.5	3.5
	11	3	3
	12	2	2
	Mean ± SD	3.0 ± 0.8	3.3 ± 0.8	3.1 ± 0.8
Both (n = 24)	Mean ± SD	3.3 ± 1.2	3.5 ± 0.8	3.4 ± 1.0

DISCUSSION

Surgical simulation in conjunction with cadaver dissection remains a valuable training tool in pelvic surgery, particularly with the rapidly evolving armamentarium of options to treat SUI. Table 2 compares the distance found in this study to that found in two other reports (8, 9). Muir et al described the distance between the lateral margin of the TVT needle to major vessels in 10 cadavers, highlighting the unique aspects of the blind upward passage of the TVT trochar through the retropubic space and demonstrating that small deviations at the point of trochar insertion could lead to a magnified deviation at the exit point (8). Zahn et al also reported the distance of both the inside-out and the outside-in techniques of the transobturator tape to the obturator canal in 7 cadavers (9). In the current report, the average distance between the most lateral aspect of the SIS tape and the obturator vessels was 3.4 cm in 24 observations. This SIS distance could have a lower risk of injuring obturator vessels compared to the TVT and the outside-in and inside-out TVT-obturator slings. It is important to note that all other major structures in reach of the TVT have been injured by the TVT, to include the superficial epigastric, the inferior epigastric, the external iliac, bowel, bladder, and urethra (10–13). These structures are unlikely to be injured by a SIS procedure.

Table 2.

Mean distance between type of mid-urethral sling and the retropubic vascular structure

Type of mid-urethral sling	Report	Mean distance (cm) to obturator vessels (range)
Retropubic tension-free vaginal tape	Muir et al (n = 20)	3.2 (1.6–4.3)
Transobturator tape	Zahn et al (n = 14)	1.8 ± 0.7 (0.8–3.2)
	Inside-out	1.3 ± 0.4
	Outside-in	2.3 ± 0.4*
Single-incision sling	Current report (n = 24)	3.4 ± 1.0 (2.0–6.0)

^*P < 0.001 for inside-out vs. outside-in using t test; mean difference = 1.0 ± −0.6 cm.

Gynecare removed the TVT-Secur, the first SIS, from the market in June 2012. Although the products used in this report have also since been removed, other newer and refined SISs are still available for the treatment of female SUI. At the present time, quality long-term data regarding the efficacy of currently available SISs and comparative data regarding various delivery and anchoring mechanisms are not available. Despite this, the potential for successfully treating female SUI with a more cost-effective approach continues to make SISs attractive to many surgeons (5). A meta-analysis of trials that compared SISs to standard MUSs showed no significant difference in both subjective and objective cure rates, after excluding trials that included the TVT Secur (14).

As with MUSs, SISs have also been associated with complications, including vaginal mesh exposure, groin pain, persistent urinary incontinence, bladder perforation, urethral obstruction, and significant bleeding complications (7, 15–17). The vessel known as the corona mortis, or “crown of death,” has been reported as a source of significant hemorrhage following the placement of the TVT Secur (10, 11). This anomalous anastomosis between the obturator and epigastric vessels may be at risk when a device closely skims the periosteum of the pubic ramus, a characteristic unique to insertion of the original TVT Secur. Newer devices seem to have evolved to decrease the likelihood of such injuries.

As the need for surgical treatment of SUI continues to grow, so will the demand for more safe and cost-effective treatment options. Although venous bleeding into the retropubic space secondary to blind insertion of the MUSs may be unavoidable, catastrophic arterial hemorrhage should be avoided with proper training and familiarity with the retropubic anatomy. Surgeons should have a clear understanding of the vascular relationships to their MUS sling of choice.