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Cadaveric Nerve and Artery Proximity to Sacrospinous Ligament Fixation Sutures Placed by a Suture-Capturing Device

Katrikh, Aaron Z., MS; Ettarh, Rajuno, MD, PhD; Kahn, Margie A., MD

doi: 10.1097/AOG.0000000000002324
Contents: Original Research
ABOG MOC II

OBJECTIVE: To simulate sacrospinous ligament fixation on cadaveric specimens, describe the surrounding retroperitoneal anatomy, and estimate the risk to nerves and arteries for the purposes of optimizing safe suture placement.

METHODS: Sacrospinous ligament fixation was performed on eight fresh-tissue female cadavers using a Capio ligature capture device. Distances from placed sutures to the following structures were measured: ischial spine; fourth sacral root; pudendal nerve; the nerve to coccygeus muscle; the nerve to levator ani muscle; inferior gluteal artery; and internal pudendal artery. Periligamentous anatomy was examined in an additional 17 embalmed cadaver dissections.

RESULTS: Sacrospinous ligament length was not seen to differ significantly between sides. The fourth sacral spinal nerve was seen most commonly associated with the medial third of the ligament, whereas the pudendal nerve and the nerves to coccygeus and levator ani muscles were associated with the lateral third. The inferior gluteal artery was seen leaving the greater sciatic foramen a median 15.8 mm (range 1.8–48.0, CI 14.9–22.3) above the ligament, whereas the internal pudendal artery exited just above the ischial spine. The two sets of sutures were placed 20.5 mm (range 9.2–34.4, CI 19.7–24.7) and 24.8 mm (range 12.4–46.2, CI 24.0–30.0) medial to the ischial spine, respectively. No structures were directly damaged by placed sutures. The nerves to coccygeus and levator ani were closest and arteries farthest from the placed sutures.

CONCLUSION: The middle segment of the sacrospinous ligament has the lowest incidence of nerves and arteries associated with it. This study confirms that the nerves supplying the pelvic floor muscles are at a higher risk from entrapment than the pudendal nerve.

After sacrospinous fixation in cadavers, the middle segment of the ligament is seen to have the lowest incidence of nerves and arteries associated with it.

Departments of Structural and Cellular Biology, Obstetrics and Gynecology, and Urology, Tulane University School of Medicine, New Orleans, Louisiana; and the Department of Medical Education, California University of Science and Medicine, Colton, California.

Corresponding author: Aaron Z. Katrikh, MS, Department of Structural and Cellular Biology, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112; email: akatrikh@tulane.edu.

Financial Disclosure The authors did not report any potential conflicts of interest.

Presented at the American Urogynecologic Society Pelvic Floor Disorders Week 2016, September 27–October 1, 2016, Denver, Colorado.

The authors thank the generous support of the Department of Structural and Cellular Biology for materials and equipment during this study and Dr. Stephen Jeffery for invaluable mentorship and contribution to the conception of the work.

Each author has indicated that he or she has met the journal's requirements for authorship.

Sacrospinous ligament fixation procedures are a common choice for apical suspension, in which the vaginal vault is anchored to the ligament.1,2 Perioperative complication is typically manifested as enterotomy, cystotomy, hemorrhage, or sacral plexus nerve entrapment causing postoperative pain.3–9 There is a lack of consensus on the recommended number and placement of sutures during sacrospinous ligament fixation, which varies from the lateral third of the sacrospinous ligament close to the ischial spine and as far away medially as 4 cm.3,6,10

Both the inferior gluteal and the internal pudendal arteries arise from the internal iliac artery and exit through the greater sciatic foramen in close proximity to the top of the sacrospinous ligament.11,12 The pudendal nerve originates from contributions of sacral nerves S2, S3, and S4; exits the greater sciatic foramen; and travels through the ischioanal fossa in Alcock's canal to innervate the perineum. The nerve to coccygeus muscle and the nerve to levator ani muscle gain contributions from a combination of S3, S4, or S5. The former pierces the sacrospinous ligament to reach the underlying muscle, whereas the latter will run over the superior surface of the sacrospinous ligament and give off branches to innervate iliococcygeus, pubococcygeus, and the puborectalis muscles.9,13–15

The objective of this study is to simulate standard suture placement on cadaveric specimens in relation to sacrospinous fixation and measure the distances to all nerves and arteries at risk in this procedure for the purposes of optimizing safe suture placement.

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MATERIALS AND METHODS

Eight fresh-tissue and 17 formalin-embalmed cadavers with no history of pelvic reconstructive surgery were used for this study. The cadavers were donated to the Tulane University School of Medicine Willed Body Program. All cadavers used were female, six with a uterus in situ. This study was considered exempt by the Tulane University School of Medicine institutional review board.

A surgeon board-certified in female pelvic medicine and reconstructive surgery in practice for 20 years (M.A.K.) performed transvaginal sacrospinous ligament fixation on eight fresh-tissue cadavers to replicate suture placement during the operation. The cadaver was first placed in the dorsal lithotomy position. A longitudinal incision was made on the posterior vaginal wall to gain access to the rectovaginal space. Using blunt dissection, the pararectal space was opened and a window created to palpate the prominent ischial spine. Using a Capio ligature capture device, a nonabsorbable 2-0 size suture was placed two fingerbreadths medial from the ischial spine. The spine was palpated again, and a second suture was placed just medial to the first suture. This process was replicated on the contralateral sacrospinous ligament. On both sides the ligament was palpated with the left hand while the Capio was fired with the right hand. The combined width of the surgeon's middle and index finger was measured to be 35 mm, right, 32 mm left.

To visualize the sacrospinous ligament, sacral plexus, and nearby arteries, hemisection of the pelvis was performed. Removal of the internal iliac vein and its tributaries was necessary to better visualize the underlying nerves and arteries. The sacrospinous ligament and the following structures were cleaned by fine dissection and identified: ventral rami of sacral spinal nerves forming the roots of the sacral plexus (S1 to S4), lumbosacral trunk, the nerve to coccygeus muscle, the nerve to levator ani muscle, pudendal nerve, inferior gluteal artery, and internal pudendal artery. To accurately examine these structures, the internal iliac vein and its branches were removed.

The lengths of the right and left sacrospinous ligaments were measured from the medial attachment on the sacrum to the lateral attachment on the ischial spine at its widest point. In all 25 pelvises, the location of structures relative to the sacrospinous ligament was noted and measured: (a) ischial spine; (b) S4; (c) pudendal nerve; (d) the nerve to coccygeus muscle; (e) the nerve to levator ani muscle; (f) inferior gluteal artery; and (g) internal pudendal artery. In eight pelvises, measurements were also taken of the distance at which Capio sutures 1 and 2 were placed with the Capio ligature capture device on the sacrospinous ligament relative to the previously mentioned structures (a–g). All measurements were taken twice by the first author (A.Z.K.) using dial calipers and are expressed in millimeters. If these two measurements differed, the values were averaged. Distances between two structures were measured from the closest points between them. Median values of suture placement distances were calculated by aggregating values for the left and right sides for eight pelvises. All median values are expressed with range and the 95% CI in millimeters. Statistical tests of difference were done using nonparametric Wilcoxon rank-sum testing. All data sets collected are normally distributed. Determination for differences of statistical significance was set at the P<.05 level with a 95% CI. All statistical testing was conducted on Microsoft Excel.

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RESULTS

A total of 32 sutures were placed (two in each sacrospinous ligament). The median distance from the ischial spine to Capio suture 1 along the sacrospinous ligament was 20.5 mm (range 9.2–34.4, CI 19.7–24.7), whereas the median distance from the ischial spine to Capio suture 2 was 24.8 mm (range 12.4–46.2, CI 24.0–30.0) (Table 1; Fig. 1). Statistical analysis showed no significant difference between these two sets of distances (P=.98). Additionally, the placement of suture 1 did not significantly differ between the left and right sides (P=.88) nor did the placement of suture 2 (P=.74) The median distances between the sutures and anatomic landmarks are summarized in Table 1. The closest anatomic structures to the sutures were the nerves to coccygeus and levator ani muscles, whereas the arteries were the farthest. The ranges in distance from each suture to landmark are depicted in Figure 2, thus reflecting the nearest that the suture came to damaging each nearby structure. Whereas the inferior gluteal artery was usually the farthest structure from both sutures, in one instance it was as close as 7.2 mm from suture passage. In no cadaver was any gross entrapment of a sacral plexus nerve or injury to an artery by the placed sutures visualized.

Table 1

Table 1

The median length of the sacrospinous ligament was 48.1 mm with no significant difference between the left and right sides (Table 2; Fig. 1; P=.54). The length of the ligament was highly variable, ranging from 30.0 to 65.4 mm (Fig. 2). Traditionally, S4 is described as taking an oblique path over the medial third of the sacrospinous ligament, depicted in Figure 1. This pattern was observed in 96% of hemipelvises (Table 3). The pudendal nerve originates at the point where S3 gains contributions from S2 and S4. This was seen to vary in the dissections: 67% of pudendal nerves began just above the lateral third of the sacrospinous ligament (Table 3). Fifteen percent (7/46) of S3 nerve roots coursed parallel to the superior border of the sacrospinous ligament with no gap present between. The majority, however, 85% (39/46), had a median distance of 7.0 mm (range 2.0–21.0; CI 6.6–9.1) between the nerve and the superior border of the sacrospinous ligament (Fig. 1). The nerves to coccygeus and levator ani were successfully dissected and examined in 12 and 9 specimens, respectively. Both nerves were associated with the lateral third of the sacrospinous ligament in the majority of cases (Table 3; Fig. 1). The vascular anatomy of the inferior gluteal artery and internal pudendal artery is shown in Table 4 and Table 5, respectively. In the majority of specimens, the former exited through the greater sciatic foramen between roots S2 and S3, whereas the latter exited just superior to the ischial spine (Fig. 1).

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

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DISCUSSION

We were successfully able to simulate sacrospinous ligament fixation in eight unembalmed cadavers. We performed a database search with the following parameters: (MEDLINE; 1968–2017; English language; search terms: “sacrospinous,” “fixation,” and “cadaver”). Our study is unique to previous anatomic studies because it is the only one to directly place and visualize suture placement relative to the seven structures observed, closely imitating operative results. In addition to the eight fresh-tissue cadavers, 17 embalmed specimens were dissected, making a total of 50 hemipelvises examined.

Our cohort of cadaveric subjects had no grossly observable signs of prolapse and are therefore not completely representative of the population seen by an operative urogynecologist; however, we believe that the anatomic results of this study are still translatable to the operating room. Cadavers without prolapse may alter the angle at which the sacrospinous ligament was approached as a result of a smaller introitus; however, it should not have an effect on the sacrospinous anatomy examined in this study. Only one surgeon was used for all fixations and therefore surgeon-to-surgeon variability in placement of sutures was not examined. Additionally, the surgeon performing fixation used the nondominant hand to palpate and the dominant hand to place sutures using the ligature capture device, on both sides of the cadaver, although only the side opposite the dominant hand is preferred for unilateral sacrospinous ligament fixation. Even with this limitation, suture placement between the left and right sides was seen to be insignificantly different. Structures of consequence that were not examined during this study were the rectum and the tributaries of the internal iliac vein, both of which have been involved in injury during sacrospinous ligament fixation. Only fixation utilizing the Capio device was assessed excluding other popular techniques including the Michigan four-wall suspension that utilizes a Deschamps ligature carrier or fixation using a Miya hook.16,17

Cases of life-threatening intraoperative hemorrhage during transvaginal sacrospinous ligament fixation have been reported to be as high as 2%.7,8,18 To qualify relative risk to structures, we compared distances of structures to placed sutures. The inferior gluteal artery and internal pudendal artery were generally farthest from suture placement, yet as a result of anatomic variation, they did travel close to the ligament in a few cases. In contrast, nerve injury has been more extensively reported, especially to the pudendal nerve.1–5,10 The suture placement in our study suggests that damage to the innervation to the pelvic floor muscles is likelier than to the pudendal. Additionally, our results, taken together with previous dissections of these nerves, show that their positions may be associated with all three segments of the sacrospinous ligament.9,14,15 Entrapment to those nerves would result in denervation to the pelvic floor muscles and weakening of the pelvic diaphragm, putting a patient at risk for recurrence of prolapse. Suture placement is not recommended in the medial third of the sacrospinous ligament, because the S4 root is most consistently present there. Postoperatively, a patient could present with de novo perineal pain, genital numbness, urinary and fecal incontinence as well as numbness of the associated sacral root dermatome. Placement of sutures in the lateral third or the top of the sacrospinous ligament introduces risk to the pudendal nerve and arteries. Our results suggest that the middle segment has the lowest incidence of nerves and arteries, and therefore placement of sutures here is less likely to entrap a nerve or damage an artery. Given a median length of 48.1 mm, this area is 16.0–32.0 mm medial to the ischial spine. A caveat of suture placement in this location is that the middle of the ligament is closer to the rectum, and therefore extreme care must be taken to ensure the rectum is sufficiently and safely mobilized before placing sutures. In our case, the sutures were placed a median 20.5 and 24.8 mm from the ischial spine and did not directly hit a single at-risk structure. Interestingly, this distance is 18–39% shorter than the measurement of the surgeon's two fingers.

Our results show a high variability in the anatomy of the region, increasing the risk of damaging a nearby structure. This necessitates excellent intraoperative monitoring of hemorrhage as well as for postoperative pain and pelvic organ dysfunction, especially in patients with shorter sacrospinous ligament length. Postoperative pain in the pudendal distribution is an immediate sign of sensory nerve compromise necessitating immediate return to the operating room to relieve the entrapment. However, injury and entrapment to a smaller pelvic floor motor nerve are harder to assess. An area of potential future research is to compare postoperative pelvic floor muscular function with that of baseline preoperative ability to assess whether compromise of the motor innervations to the pelvic floor occurred.

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