Anatomical premises for the variability of the results of transobturator mid-urethral sling

Introduction

Nowadays, the use of a mid-urethral loop for surgical correction of stress urinary incontinence (SUI) in women is the “gold” standard in pelvic floor reconstructive surgery [1]. However, a detailed effectiveness and safety analysis of this approach reveals some problems that require a separate study.

The methods of installing a suburethral loop for SUI treatment have changed over time. The first mid-urethral slings were implanted using a retropubic approach, based on the integral theory of urine retention [2]. In 2001, the urologist and anatomist Emmanuel Delorme proposed an alternative method – transobturator loop installation according to the “outside-in” technique [3]. After 3 years, Jean de Leval modified this technique and the trocar started being carried out “inside-out” [4]. Both the retropubic approach and transobturator sling showed high efficiency at follow-up periods of up to 1 year. However, large comparative studies of objective effectiveness depending on access have just recently begun to appear, and the results are mixed. A recent review of the Cochrane Library compared the retropubic approach and transobturator access basing on an analysis of more than 55 studies. The objective efficiency of the transobturator loop varied in the range of 43–92%, and retropubic loop efficiency was 61–88% [5]. Data from other studies also suggest that the objective effectiveness of retropubic access is more stable than transobturator access, the outcomes of which vary widely [6][7][8][9].

In addition to the wide variability of the objective effectiveness results of the transobturator sling, there are also data proving with a certain probability that the use of this approach is associated with damage to the obturator nerve branches innervating the adductor muscles of the thigh, which leads to pain syndrome [10][11]. According to Rothetal, similar symptoms occur in 20–32% of patients who underwent implantation of a transobturator suburethral sling [12]. In addition to direct damage to the obturator nerve branches, some cases proving that the mesh became a trigger for tension and contraction of tonic adductors, which in turn led to myofascial pain syndrome, have been described [12].

One of the reasons for the ambiguity of clinical results of the transobturator suburethral sling use may be the excessive desire of “mesh” manufacturers to unify and simplify the method of its implantation. This was most clearly demonstrated in the TVT-O system (Ethicon Inc., USA), where the prosthesis instructions indicate “exact” external landmarks that should help the surgeon install the suburethral sling “correctly”. It is important that the main criterion for the “correct” prosthesis position was the point of its exit on the skin [13]. It is important to note that they are based on the methodology proposed by Jean de Leval in 2003 [4]. At the same time, the anatomy of the female pelvis is very variable, and deep structures do not always correspond to external landmarks. There are studies on the influence of pelvic anatomy on surgery outcomes [14][15]. According to Bogusiewicz et al., the bone pelvis has an extremely variable structure, whose linear and angular characteristics can affect the results of surgical treatment of urinary incontinence in women [16]. It was also shown in the work of Gaivoronskiy et al. that the pelvis shape and the obturator foramen had significant anatomical variability, which may affect the position of the transobturator suburethral sling [17]. In addition, a study was based on cadaveric material, which showed the risks of damage to the obturator nerve, depending on the angle of puncture of the obturator complex structures [18].

The purpose of the study was to identify the key anatomical factors that can negatively affect the effectiveness and safety of mid-urethral sling surgery for urinary incontinence in women, followed by the formulation of correct techniques for performing this surgical manual.

Materials and Methods

The study consisted of two parts: anatomical and clinical ones. The first part of the study was conducted at the Department of Normal Anatomy of the Kirov Military Medical Academy, the second part – at the Pirogov High Medical Technologies Clinic of St. Petersburg State University.

As for the anatomical part of the study, 20 preparations of the female pelvis with the lower limb and preserved soft tissues were used. The following parameters were documented for all the samples: age, height, and weight. All the samples belonged to mature white women. In order to determine the most atraumatic and potentially most effective urethral support technique for perforating the obturator complex structures, a transobturator suburethral sling was implanted on each sample employing an “inside-out” technique in two ways. The first method was to apply the technique – “instrument rotation around the lower branch of the pubic bone” with an exit to the skin 1 cm below the palpation-determined lower edge of the tendon m. adductor longus. The second method was based on the recommendations of Ethicon, according to which it is necessary to mentally draw a horizontal line at the level of the external urethra opening (for safe and effective navigation), and then a second line parallel to the first and 2 cm above it. Next, it is necessary to mark the control points of trocar removal on the skin on the 2^nd line (2 cm laterally to the femoral folds) [13]. Following the manufacturer's concept, this version of the sling (“according to external landmarks”) is the least traumatic and the most effective one. It is important that while conducting the trocar through the obturator complex structures, the hip was moved to a position close to the lithotomy one (for maximum approximation to the clinical situation). Therefore, the obtained data were recorded and evaluated. The study was approved by the local independent ethics Committee of the Kirov Military Medical Academy (Protocol No. 199 of the meeting of the Independent Ethics Committee dated August 19, 2018).

The clinical part of the study involved 50 patients with SUI who underwent the installation of a transobturator suburethral sling (Urosling, Lintex LLC) at the University Clinic of St. Petersburg State University during the period from November 2018 to March 2019. All the patients were women between 35 and 78. The diagnosis was made on the basis of complaints, anamnesis, and medical examination with a patient’s full bladder by using a cough test and a Valsalva test. The presence of mixed urinary incontinence, as well as a history of pelvic injuries, were the criteria for the study exclusion. As for a subjective assessment of SUI severity, the short form of the International Consultation on Incontinence Questionnaire – Urinal Incontinence Short Form/ICIQ-SF was used. In order to assess the pain severity in the postoperative period, a visual analogue pain scale was used.

The control assessment of SUI symptoms was carried out on the day after the surgery and 1 year after the surgery using a medical examination in a chair, uroflowmetry with the determination of the residual urine volume, and filling a visual analogue pain scale. Control completion of the ICIQ-SF questionnaire was performed 1 year after surgical treatment. All the surgeons were employees of the University Clinic of St. Petersburg State University and experts in the field of pelvic floor reconstructive surgery. This study was approved by the Ethics Committee of St. Petersburg State University (Protocol No. 02-189 dated August 10, 2019). All the patients signed an informed consent form.

Visualization of the suburethral sling. An original imaging method was used to monitor the position of the tissue implant. An X-ray contrast ureteral catheter with a hydrophilic coating 5 Ch was used as a device that provides the trajectory visibility of the passage of the suburethral sling, which was performed in parallel with the suburethral sling. A day after the surgery, patients underwent a low-dose computed tomography of the pelvis on a Toshiba Aquilion 64 device, after which the ureteral catheter was painlessly removed.

Statistical analysis. Statistical analysis of the results was performed using the STATISTICA 10 (StatSoft Inc., Tucla, USA) program. As for quantitative data, the distribution normality was assessed through the Shapiro-Wilk test. The indicators were described in terms of the average value, the standard error of the average value (in the case of a normal distribution), or in terms of the median and quantiles otherwise. The criterion of statistical significance of the tested hypotheses was considered to be the value of p ˂ 0.05.

Results

Anatomical part of the study.

The first step was to isolate the area of innervation of the obturator nerve through preparation (Fig. 1).

The second step was performed on anatomical preparations of the pelvis with preserved soft tissues by perforating the obturator complex area (internal obturator muscle, obturator membrane and external obturator muscle) by using the “inside-out” technique in two ways described above (Fig. 2).

The third step was to assess the probability of damage to the obturator nerve branches, depending on the point of perforation of the obturator complex (Fig. 3). As a result, the frequency of damage to the obturator nerve branches was 70% in the case of using the technique of “external landmarks” and 30% while using the method of “trocar rotation around the lower branch of the pubic bone”.

It is important that the anterior branch n. obturatorius and its muscular branches (to m. gracilis and m. adductor brevis) were most often damaged.

The clinical part of the study.

In the clinical part, the method presented by the manufacturer Ethicon for the TVT-O system was compared with the implantation method proposed in the anatomical part of this study. After performing visualization of the suburethral sling position, all the patients were divided into two groups. Group 1 included women whose implants were placed according to the proposed anatomical technique (29 patients), and the second group – the technique of “external landmarks” (21 patients) (Fig. 4).

Results of treatment in Group 1 (n = 29). On the next day after surgical treatment, 1 patient (3.4%) complained of discomfort in the perineum. The median value of the visual analogue pain scale indicator in this group was 3 (2; 7), p = 0.0001. The cough test was negative in 27 patients (93.1%).

After 1 year after surgical treatment, no patient complained of pain in the pelvis and perineum. The cough test was negative in 26 patients (89.5%). De novo bladder hyperactivity was observed in 2 patients (6.8%). In 1 patient (3.4%) who reported lifting a heavy load and feeling the sling shift, there was a relapse of urinary incontinence under tension. The median ICIQ-SF score decreased from 9.13 (before surgery) to 2.4 (after surgery) (p = 0.001).

Results of treatment in Group 2 (n = 21). On the next day after surgical treatment, 2 patients (9.5%) complained of pain in the perineum and inner thigh. The median value of the visual analogue pain scale indicator was 4 (2; 6), p = 0.0001. The cough test was negative in 18 patients (85.7%).

One (1) year after the surgical treatment, 2 women (9.5%) complained of discomfort on the inner thigh surface. One patient (4.7%) noted the presence of pain while the leg adduction. The cough test was negative in 18 women (85.7%). In 2 patients (9.5%), the cough test was weakly positive, which, according to them, did not yet bring significant discomfort. The median ICIQ-SF score decreased from 9 (before surgery) to 3.3 (after surgery) (p = 0.001).

Discussion

According to the concept of the hypermobile urethra, proposed by John Delancey in 1994, urinary retention is achieved by urethra supporting, which is provided by the fibromuscular structures of the intra-pelvic fascia, forming a kind of “hammock” [19]. There is a loss of urine at the time of an increase in intra-abdominal pressure with the failure of the fixing urethra apparatus, (while coughing, sneezing, laughing, and physical exertion), which is commonly called urinary incontinence under stress or SUI. Thus, the purpose of suburethral sling installing is to replace the failed fascial “hammock” with a mesh implant that will take over the task of the urethra supporting and provide physiological urine retention. Thus, the sling position in the tissues should play a significant role in surgery effectiveness.

In the anatomical part of the study, the perforation zone of the obturator complex was determined, which is associated with the lowest damage probability to the n. obturatorius branches while sling installing by using the “inside-out” technique. In the second part of the study, differences in the implant position in the tissues were detected by suburethral sling imaging, which could affect the clinical results. In particular, the perineum pain was more often observed in patients from Group 2, where the trocar was installed according to the standard method of external landmarks points. At the same time, the frequency of pain occurrence correlates with the literature data [11][12]. In this light, Moore's works come first; they note that to minimize the damage probability to the obturator nerve branches, the optimal technique is to install the trocar “inside-out” [20][21]. This statement is confirmed in the anatomical studies of Zahn et al., who report that the method of “inside-out” installing the trocar is more atraumatic. It happens since the suburethral sling can be installed with an orientation to the lower branch of the pubic bone and the palpation of the lower edge of the tendon (m. adductor longus) [22]. With this navigation, the damage probability to the n. obturatorius branches or mm. adductor is minimized, but this technique also has its limitations, including extended tissue dissection associated with an increase in the traumatic nature of the intervention [4].

The evaluation of the surgical treatment effectiveness depending on the location of the suburethral sling in the tissues allowed establishing that a higher percentage of objective effectiveness in the first group can theoretically be associated with the U-shaped sling placement. This assumption was previously discussed in Whiteside et al. [23]. The hypothesis is considered that a more acute angle of the “hammock” for the urethra (Fig. 5) with transobturator sling placement creates conditions for the subclinical obstruction development. It provides better urinary retention during long-term observation [21][23][24]. The retropubic loop also works according to the same principle, which can explain the more stable results of its effectiveness in the long-term postoperative period [24].

Fig. 5 shows the variations of the transobturator sling location in the tissues that affect the surgical treatment effectiveness. As the angle of the “hammock” for the urethra increases, the therapeutic space for the reliable fixation of the urethra and ensuring physiological retention of urine decreases. This is especially important in the case of a downward-expanding pelvic shape and an oval-shaped obturator opening [15].

The relapse of urinary incontinence was observed in approximately equal amounts in both groups. Apparently, variations of the sling location in the obturator complex area do not affect the reliability of its fixation in the tissues and do not prevent its displacement in the recommendations violation for limiting physical activity in the first year after surgery. The quality of life estimated 1 year after the surgery through the ICIQ-SF questionnaire was approximately equal, which indicates similar subjective surgery effectiveness.

The results of this study should be taken in light of certain limitations. First, this study did not compare the surgery outcomes performed using the “inside-out” and “outside-in” techniques. This could provide valuable information about the atraumatic nature of the proposed anatomical technique, which is essentially based on the principle of the “outside-in” approach (the trocar rotation around the lower branch of the pubic bone). Second, the patients in the compared groups were not randomized in advance. Third, the implantation of a suburethral sling was performed by experienced pelvic floor surgeons based on an expert centre. Accordingly, the clinical conditions in which the study was conducted cannot be called average/generally available ones. Finally, it is necessary to note that in order to confirm the hypothesis presented in this article, large randomized studies are needed in the future. They will help to compare different methods of implantation of the suburethral sling with the possibility of implant visualization.

Conclusion

Thus, during the anatomical part of this study, it was found out that the trocar installing (using the instrument rotating around the lower branch of the pubic bone) is characterized by a lower probability of damage to the n. obturatorius anterior branch and the muscle branches to m. gracilis and m. adductor brevis. In addition, bone formations are a more reliable guide for implantation than easily displaced external soft tissues. It can be assumed that the U-shaped position of the sling better fixes the urethra in a physiological position, which ensures the retention of urine during an increase in intra-abdominal pressure and a long-term follow-up period.