Risks and benefits of sling procedures

Transcription

1 Keywords intrinsic sphincter deficiency, midurethral tape, urodynamic stress incontinence, sling procedure, voiding dysfunction Risks and benefits of sling procedures Charlotte Chaliha, Stuart Stanton Over the past century over 150 operations have been described for the treatment of urodynamic stress incontinence. The spectrum of operative approaches that are used reflect its variety of causes. Classical sling procedures provide bladder neck support, permitting urethral compression or kinking with increases in intra-abdominal pressure and decreasing voiding dysfunction. There are welldocumented complications associated with sling procedures. Modifications of operative technique and sling materials, in particular the tension-free vaginal tape, have lowered complication rates and operative morbidity. This article discusses potential benefits and risks associated with different surgical options, to aid selection of the most appropriate treatment for any individual. Author details Charlotte Chaliha, MA MD MRCOG, Sub-Specialist Trainee in Urogynaecology, St Mary s Hospital, London W2 1NY UK. c.chaliha@ic.ac.uk (corresponding author). Professor Stuart L Stanton, FRCS FRCOG FRANZCOG (Hon), Emeritus Professor of Pelvic Surgery and Urogynaecology, Flat 10, 43 Wimpole St., London W1G 8AE, UK. sstantonwimpole@yahoo.com Introduction There are two primary causes for development of urodynamic stress incontinence (USI): hypermobility of the urethrovesical junction in women whose sphincter is otherwise intact (anatomical urinary stress incontinence), or damage to the sphincter mechanism (intrinsic sphincter deficiency, ISD). These two forms of incontinence often co-exist. In women with anatomic urinary stress incontinence, increases in intra-abdominal pressure result in descent of the bladder neck and subsequent leakage of urine. In this situation operative procedures are required to elevate the bladder neck to its retropubic position where it will remain during rises in abdominal pressure and so will maintain continence. The Burch colposuspension has traditionally been considered the first-line procedure in this situation as it has a well-documented, high long-term success rate. 1 In women with ISD only (a minority of cases and usually following past continence procedures) incontinence occurs because there is poor coaptation of the urethra. Operations to cure incontinence in this situation aim to improve urethral coaptation and increase outflow resistance. If there is hypermobility in association with ISD, a Burch colposuspension is often used. In cases where ISD exists alone and there is limited mobility of the urethrovesical junction, urethral injectables, sling procedures and the artificial urinary sphincter have been used. Sling procedures have traditionally been reserved for the treatment of recurrent stress incontinence because of technical difficulties with the procedure and the high rate of complications. However, data suggest that slings are effective as a primary procedure in women with congenitally short urethras or evidence of low urethral closure pressures. The American Urological Association analysed the literature on urological procedures for stress incontinence. 2 They concluded that at 48-month follow-up, retropubic suspensions and slings were more efficacious than transvaginal suspensions and anterior repairs. However, retropubic suspensions and sling procedures were associated with higher complication rates, including longer convalescence and postoperative voiding dysfunction. The development of the tension-free vaginal tape (TVT, Gynecare, Ethicon Ltd, Edinburgh, UK) has overcome many of the technical difficulties and morbidity associated with conventional sling procedures and this technique is gaining widespread acceptance as a primary procedure. 3,4 This procedure does have distinct differences from conventional slings: it is inserted without tension, provides mid-urethral and not bladder neck support and requires neither sutures nor catheter. Ulmsten 4 prefers to use the term TVT rather than sling. Because of these differences, it would be clearer to use the generic term sling and subdivide that into bladder neck support and midurethral tapes.the latter term would include TVT and look-alikes, and obturator tapes. Sling materials There have been numerous modifications of the sling technique and materials over time and each 26

2 have their own proponents. The sling procedure was first described by Von Giordano 5 in 1907 using a gracilis muscle flap, brought out through the rectus fascia beneath the urethra and attached to the pubis. Aldridge 6 later described the use of rectus fascia as a sling that is produced by mobilisation of two transverse strips of fascia by detachment of their lateral margins via a Pfannenstiel incision. These two strips of fascia are then sutured below the urethra using a vaginal incision. There have since been a variety of modifications to the technique. Sling placement can be done via an abdominal route, tunnelling the sling under the urethra and bladder neck, a transvaginal route or a combined abdominal vaginal route. A wide variety of materials have been developed for use as slings. Natural slings may be autologous, using rectus fascia or fascia lata, or allogenic from porcine dermis, or from cadaveric fascia (e.g. Stratasis TF Tension Free Urethral Sling, SIS Technology, Cook Biotech Incorporated, West Lafayette, IN; Permacol, Tissue Science Laboratories plc, Aldershot, Hampshire, UK). Synthetic slings include polytetrafluoroethylene (Teflon, Gore-tex ), Silastic bonded to Dacron, polypropylene (Marlex ), and polyethylene terephthalate (Mersilene Ethicon Inc, Somerville, NJ) ribbons or mesh. Natural slings are more readily accessible and rejection rates are lower. However, mobilisation of autologous fascia is often difficult and the tissue may not be of uniform tensile strength and quality. The use of autologous fascia is also associated with a higher rate of wound infection, haematoma formation and wound hernia, mostly related to the harvesting procedure. Synthetic slings were developed in the 1960s to overcome these problems but are associated with higher risks of graft erosion and rejection. Nonabsorbable synthetic materials differ in their composition, porosity and flexibility; these factors affect their individual propensity to causing fibrosis, inflammation and rejection. To minimise the risks of infection and rejection associated with synthetic slings, patch slings have been developed, which decrease the amount of sling material used. bladder neck support and urethral resistance. Urodynamic studies of successful sling procedures show an increase in the pressure transmission ratio and reduction in peak flow rate during voiding, 7,8 as well as an increase in mean urethral closure pressure. 9 The improvement in pressure transmission is seen mainly in the proximal one-half to three-quarters of the urethra and correlates with surgical success. This compressive effect results in an increase in urethral outflow resistance, which is reflected in the decrease in peak flow rate and voiding dysfunction. In order to increase stabilisation of a sling, it can be anchored to the rectus sheath or aponeurosis or Cooper s ligament, or fixed directly to the pubic bone with bone anchors.anchorage to the pubic bone does result in good short-term results but carries an increased long-term risk of osteomyelitis. 10 The tension-free vaginal tape (TVT) is a relatively new technique developed by Ulmsten, 3 which differs from conventional sling procedures as the polypropylene (Prolene,Ethicon Inc,Somerville, NJ, USA) tape is placed under the mid-urethra not the bladder neck (Figure 1). The TVT polypropylene tape is covered by a plastic sheath to allow free passage through the tissue, and is attached at either end to a curved needle. A RISK MANAGEMENT Figure 1. Diagrammatic representation of the tension-free vaginal tape (courtesy of Gynecare UK) Mechanism of action The principle of the procedure is that the sling is placed under the bladder neck, acting as a hammock or platform. This permits urethral compression or kinking with increases in intraabdominal pressure. Lateral fibrosis occurs in response to the sling and so creates further 27

3 suburethral incision is made, approximately 1.5 cm long and 1 cm from the external urethral meatus. Each needle at either end of the tape is passed through a vaginal incision into the ipsilateral paraurethral canal, through the retropubic space, perforating the urogenital diaghragm, then out on to the abdominal wall just internal to the pubic symphysis. Postoperative perineal ultrasound and urethral pressure measurements have shown that the mechanism of action of the TVT is less dependent on bladder neck change when compared with colposuspension, but raises the midurethral pressure on straining so kinking the urethra at this point. 11 There have been various modifications of tape placement, the major one being the development of the transobturator suburethral tape (Mentor Corporation, Santa Barbara, CA). This is a polypropylene, which is passed underneath the midurethra using a transobturator approach. This approach is advocated to reduce the risk of bladder injury and voiding dysfunction. Initial trials, with short-term follow-up only, report good cure rates with no intraoperative complications. 12 However, voiding dysfunction was noted in 18.7% of these women. Indications and benefits Decreased urethral mobility secondary to postoperative scarring may result in poor intrinsic urethral function and a low maximum urethral closure pressure. Customarily use of slings has been reserved for treatment of recurrent incontinence in women with these problems. In these cases retropubic procedures that replace the proximal urethra intra-abdominally may not be so effective because urethral coaptation is required. Slings have been used with caution as a primary procedure.there is concern that extensive vaginal dissection may result in denervation of the urethral sphincter (leading to poor urethral function) as well as the higher complication rate compared with other procedures. 13 In women with already compromised sphincter function and a scarred vagina the effect of further denervation from vaginal dissection is not such an issue. Concerns of denervation damage may not be valid as they relate to dissection performed for anterior colporrhaphy and paravaginal repairs where sutures are placed under the pubocervical fascia. In contrast, dissection and placement of slings occurs at the level of the bladder neck beneath the vaginal wall but not under the pubocervical fascia. Analysis of risk factors associated with failure of standard continence procedures has shown that 75% of women who had failed procedures had evidence of poor intrinsic urethral function, as indicated by urethral closure pressures below 20 cm H 2 O. 14 In a previous retrospective study of 86 women, a low preoperative urethral closure pressure of less than 20 cm H 2 O was associated with failure of the Burch colposuspension compared with women with higher urethral closure pressures. In these women with low urethral closure pressures good results have been achieved after fascial sling procedures. 15 Therefore sling procedures may be the treatment of choice for those with preoperative evidence of poor urethral sphincter function. Women with hypermobility and coexistent ISD will benefit from a sling procedure, even if hypermobility is the only clinical feature, because the sling will correct the ISD that these women have. Slings are also of use in women with stress incontinence and anterior vaginal wall prolapse, and cure rates of 92% for prolapse are reported in these situations. 16 Another group of women who may benefit from this procedure are those with medical conditions that would increase the failure rate of a standard continence procedure. Examples are women with chronic lung disease, e.g. bronchitis and asthma, and those who have weakness of the supportive tissues from chronic steroid use or congenital collagen weakness. Women with impaired cardiovascular or respiratory function or who are in poor physical health are particularly suited to a midurethral tape procedure under local anaesthesia, especially the new TVT procedure that is performed under local anaesthetic. Despite concerns that there would be an increased surgical morbidity of TVT in this age group, encouraging success rates have been reported. Nilsson 17 reported on 85 women aged years who had TVT. At median follow-up time of 56 months the overall cure rate was 85% and this was only slightly lower in those over 70 years.this compares well with procedures such as needle suspensions and urethral injections. These techniques are minimally invasive but have success rates that fall below 50%. Women who are morbidly obese, who have a high failure rate from standard retropubic procedures, and women with decreased vaginal capacity may also be candidates for slings. Women with neuropathic bladders and neurological sphincter weakness are often difficult to treat. A tight sling procedure may be an alternative method of maintaining continence, usually as a last resort procedure. In this situation, after bladder augmentation, a sling can provide over-elevation bladder neck and urethral obstruction. This allows formation of a bladder reservoir so that the woman can be continent 28

4 and empty her bladder with clean, intermittent catheterisation. The indications for sling procedures are as follows: recurrent USI intrinsic sphincter deficiency scarred drainpipe urethra medical conditions chronic lung disease, bronchitis, asthma tissue weakness secondary to chronic steroid use, congenital collagen weakness unfit for general anaesthesia suitable for midurethral tape procedure under local or spinal anaesthesia neuropathic bladder or neurogenic sphincter weakness (in association with bladder augmentation if the woman is able to perform clean, intermittent selfcatheterisation). The wide variety of sling materials and modifications of technique make it difficult to assess the success rates of sling procedures. Most studies consist of small numbers with poor longterm follow-up, and success rates are not validated by objective data. Analysis of success is made more difficult by heterogeneity of the study population, with slings performed as primary and secondary procedures. Objective cure rates of about 86% have been reported with sling procedures in cases of recurrent incontinence and cure rates of 94% are reported in those having slings as a primary procedure. 18 A further advantage the TVT has over conventional sling procedures is that it avoids the need to harvest tissue from the patient and instead uses polypropylene, which is associated with less rejection and erosion than many other synthetic slings.the success rates are at least equivalent and Ulmsten et al. 19 reported that 86% of women were completely cured and 11% improved significantly at three-year follow-up. In a larger, multicentre study from six centres in Sweden of 131 women with USI, 91% were reported as cured at mean follow-up time of one year. 4 Moran et al. 20 reported a two-centre UK study of TVT for incompetent urethral closure mechanism in 40 women. The mean follow-up time was 12.3 months, and 80% of women were subjectively cured and 17.5% were improved significantly. Objective cure of USI was seen in 95% of women.ward and Hilton, 21 in a randomised study comparing TVT with colposuspension as a primary treatment for stress incontinence, reported a similar objective cure rate between the TVT and colposuspension for stress incontinence. This was measured by a pad test and urodynamics at six-month follow-up. Although there were more operative complications with the TVT, there were fewer postoperative complications and a quicker recovery time. In women with mixed incontinence there are similarly high success rates. Rezapour and Ulmsten 22 performed the TVT procedure on 80 women with mixed urinary incontinence and at mean follow-up of four years found that 85% were cured and 4% improved on objective testing. These encouraging results, which seem to persist with time, have led to the adoption of this technique in many units. Complications of sling procedures In assessing the long-term clinical value of a technique both long-term and short-term complications should be assessed, as conventional continence procedures have well-documented complications. Immediate complications include haemorrhage, urinary tract and visceral injuries, and urinary tract infection. Short-term problems include wound infection, osteitis pubis, nerve injuries, and voiding dysfunction. Long-term complications include bladder overactivity, stitch/ sling erosion, dyspareunia and genital prolapse. 23 Common complications associated with slings Infection The rate of urinary tract infection after sling procedures is reported to be around five percent. 24 In a five-year follow-up study of 85 women after TVT, seven (7.8%) had a urinary tract infection within the first two months. 25 The risk of urinary tract infection is also related to the type and duration of catheter use, being more common with use of intraurethral than with suprapubic catheters. 26 Postoperative wound infections are reported to occur in approximately 12% of sling procedures 18 and are more frequent with autologous fascia, which is possibly related to the harvesting procedure. However in their review of the literature, the American Urological Association reported a much lower rate of wound infection with sling procedures: 35/3644 women (0.1%). 2 The wound infection rate was similar among autologous, homologous and synthetic slings. There have been concerns that there is a risk of transmission of HIV and hepatitis with allograft fascia.with screening procedures the risk of HIV transmission with tissue transplants is estimated at 1/ RISK MANAGEMENT 29

5 The use of the TVT polypropylene tape is associated with a low rate of wound infection. In a long-term follow-up study by Nilsson et al. 25 of TVT in 85 women only one woman was noted to have an infection. As the procedure does not result in dead space, this too would reduce the potential for infection. Irrespective of the procedure, preoperative antibiotics have reduced the incidence of wound infections. Haemorrhage and wound haematoma During sling and TVT procedures the retropubic space, containing the perivesical venous plexus, is entered blindly by perforating the endopelvic fascia lateral to the urethra. This can result in bleeding, haematoma formation and bacterial contamination, which can turn a haematoma into a retropubic abscess. However as long as retropubic entry is performed close to the posterior aspect of the pubis the venous plexus is unlikely to be disturbed. Excessive haemorrhage requiring surgical drainage has been reported in 2.1% of pubovaginal sling procedures. 28 Leach et al. 2 reported 6 cases out of 279 (2.1%) requiring transfusion after sling procedures. There have been few reports of retropubic haematoma formation and transfusion after TVT. Nilsson et al. 25 report a rate of 3.3% for the development of retropubic haematoma and 3.3% of cases had intraoperative bleeding exceeding 200 ml. Kuuva and Nilsson 29 assessed by postal questionnaire the complications associated with TVT. In the 1455 TVT procedures performed there were 27 cases of blood loss greater than 200 ml, one case of a vaginal haematoma, 27 cases of retropubic haematoma (18 of which did not require intervention) and one case of injury to the epigastric vessel. Voiding difficulty and urinary retention Sling procedures have a marked effect on outflow resistance. The most common problems are voiding difficulties and urinary retention, particularly if the woman has poor preoperative voiding pressures.this high incidence of voiding dysfunction after sling procedures is a major limiting factor of the procedure. In his systematic review of surgery for stress incontinence, Jarvis 18 found that the mean incidence of postoperative voiding disorders was 12.8% (range 2-37%). The American Urological Association 2 assessed the incidence of temporary and permanent retention after continence procedures.this is often difficult to assess as it is dependent on hospital practice, catheter management and differing lengths of hospital stay. They estimated that the probability of temporary urinary retention lasting longer than four weeks was five percent for retropubic and transvaginal procedures, and eight percent for sling procedures.the risk of permanent retention was thought not to exceed five percent. 2 It is often difficult to determine how much sling tension is required before a sling is fixed or left free (TVT) to avoid the risk of obstruction; this is not easy to measure objectively and relies on operator experience.various methods have been proposed to assess sling tension such as measurement of the Q tip angle, intraoperative urethral pressure profiles and cystoscopy. None of these is entirely reliable. One of the advantages of the TVT is that, unlike sling procedures, the TVT is performed under local anaesthesia.while the woman coughs with a full bladder, tape tension can be adjusted to a level that maintains continence without obstruction. Ideally the tape should exert no tension at rest. In their first series Ulmsten et al. 3 reported no complications of voiding disorder or detrusor overactivity at oneyear follow-up, but a few women had immediate postoperative voiding difficulties. In the Nordic multicentre study, women were followed up approximately five years after TVT; four (4.4%) of these women had immediate voiding difficulties but no long-term voiding difficulties were reported. However, Ward and Hilton 21 reported that in their study of the TVT five women (3%) developed voiding difficulties that lasted longer than six months. All women undergoing sling procedures and the TVT should be warned that there is a risk of prolonged catheterisation and a possible need for intermittent self-catheterisation. If voiding dysfunction persists or complete urinary retention occurs, urethral dilatation may be tried or transvaginal incision of the sling/tape may be attempted. Overactive bladder Overactive bladder is a complication seen after both retropubic and sling procedures. New incidence of overactive bladder after sling procedures is around seven percent. 2 It is seen more commonly after previous continence surgery. The aetiology of newly occurring overactive bladder is unclear and some cases may be those who had pre-existing overactive bladder undiagnosed by preoperative urodynamics. Over-elevation of the bladder neck or excessive sling tension leading to urethral outlet obstruction, and autonomic nerve damage during dissection of the bladder neck have been postulated as potential mechanisms. However, there is no firm evidence to support this. 30

6 In women with postoperative overactive bladder, detrusor hypertrophy may develop as the detrusor contracts against a partially obstructed urethra. High amplitude contractions may predispose a woman to vesico-ureteric reflux and risk of upper tract damage. In view of this, sling procedures should be avoided in those with evidence of preoperative, high-amplitude, uninhibited detrusor contractions. Peschers et al. 30 reported new occurrence of urgency and urge incontinence in 5.1% of women (0 20.6%) after TVT and, in the Nordic multicentre study, 25 new incidence of overactive bladder was 5.9%. 25 Sling erosion Infection, poor healing, impaired vascularity of the vaginal tissue overlying the sling and excessive sling tension all increase the risk of sling erosion. Vaginal erosion may occur as a result of haematoma and infection, leading to separation of the vaginal incision and erosion. This is seen more often with synthetic than with autologous materials. Urethral erosion is more likely to be secondary to excessive sling tension or unrecognised urethral injury at the time of the procedure.the reported rate of sling erosion into the vagina or urethra varies from % The expanded polytetrafluoroethylene (Gore-tex) sling has a particularly high rate of erosion of 23%. 32 With other synthetic slings the reported erosion rates vary from 0 11%. Debodinance et al. 33 reviewed 287 cases where either Gore-tex or Dacron were used for vaginal surgery. They found erosion rates of 30% and 25% respectively, which were related to the surface area of the material used. Materials that are particularly porous are prone to bacterial colonisation. Synthetic slings are more prone to erosion than natural slings because a foreign body reaction to a synthetic sling may develop into a chronic inflammatory response, resulting in erosion through the urethral or bladder surface. This can lead to the development of fistulas and sinus tracts. In the development of the TVT procedure various materials have been used such as Teflon, Gore-tex, polyethylene terephthalate and polypropylene. All these materials were associated with a significant amount of tape rejection, and the polyethylene terephthalate tape particularly was noted to induce a significant inflammatory reaction. However the knotted polypropylene mesh used for TVT has been reported to cause no inflammatory reaction in the paraurethral tissue at two-year follow-up. 34 Ulmsten et al. 4,19 in their three-year follow-up of TVT, reported no erosion or graft-related problems. Diagnosis of erosion is often missed but should be considered in any woman with persistent vaginal or urethral discharge or bleeding, irritative urinary symptoms or recurrent urinary tract infections. Sling erosion may occur over time and has been reported up to four years after the initial operation. 35 Erosion of the polypropylene TVT into the urethra has been reported to occur 12 months postoperatively. 36 Diagnosis is made by pelvic examination and cystoscopy, and the sling/tape should ideally be removed.this can often be difficult, carrying the risks of bleeding and further trauma to the urethral sphincter mechanism. However, despite removal, continence is often maintained by the fibrosis induced by the sling/tape. Visceral and nerve injury The bladder is the most commonly injured organ. A small perforation can occur with insertion of the sling/tape needle if the lateral edge of the bladder has not been identified and dissected adequately. Summitt et al. 37 noted three bladder perforations during 48 Teflon suprapubic sling procedures. In his initial report of the TVT procedure, Ulmsten 3 did not report any bladder perforations. However, Peschers, 30 in a literature review of TVT including 1762 women who had undergone this technique, found a mean bladder injury rate of 5.4%, the highest rate being 23.1%. This complication is recognised at intraoperative cystoscopy, which also assesses patency of the ureteric orifices. Instillation of methylene blue will also enable breaches in the bladder mucosa to be identified. If perforation has occurred, the sling can be removed then repositioned and a catheter inserted, and no further treatment is usually required. If perforation is seen after TVT (Figure 2), the needle should be removed, repositioned more laterally, checked again and a catheter inserted for hours. Attention to technique reduces the risk of perforation. Dissection should always be performed with extreme care when there is a history of prior RISK MANAGEMENT Figure 2. Perforation of the bladder with the TVT needle seen at cystoscopy 31

7 surgery and vaginal scarring. These may distort the anatomy and increase the risk of not only bladder but also urethral and ureteric injury. Obturator nerve injury is rare but there have been two reports of it after TVT. 20,29 This serious complication can be avoided by correct medial insertion of the needle. Conclusions The choice of surgery for women with USI should take into account the clinical and urodynamic findings of the woman, and be tailored to the individual s needs and lifestyle requirements. The modifications of the sling procedure, and the development of the TVT have renewed interest in this procedure as a primary choice. There are no large, randomised trials with long-term follow-up to assess the success rates of the sling procedure for primary surgery. However, the existing data would suggest that the success rate is comparable to retropubic procedures. The long-term complication rate and operative morbidity have been reduced by modifications of technique and sling materials and, in particular, by the development of the TVT. It is essential that the woman is counselled prior to the operation to ensure that the potential risks of bladder injury, voiding dysfunction and, importantly, bladder overactivity are discussed. If there is a high risk of postoperative voiding disorder, she should be prepared for the possibility of long-term or intermittent self-catheterisation. Surgical complications can be minimised by thorough preoperative evaluation and attention to surgical technique. References 1. Alcalay M, Monga A, Stanton SL. Burch colposuspension: a year follow-up. Br J Obstet Gynaecol 1995;102: Leach GE, Dmochowski RR, Appell RA, Blaivas JG, Hadley HR, Luber KM, et al. 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Suprapubic versus transurethral bladder drainage after colposuspension/vaginal repair. Acta Obstet Gynecol Scand 1985;64: Buck BE, Malinin TI, Brown MD. Bone transplantation and human immunodeficiency virus. An estimate of risk of acquired immunodeficiency syndrome (AIDS). Clin Orthop 1989;240: Morgan JE, Farrow GA, Stewart FE.The Marlex sling operation for the treatment of recurrent stress urinary incontinence: a 16-year review. Am J Obstet Gynecol 1985;151: Kuuva N, Nilsson CG. A nationwide analysis of complications associated with the tension-free vaginal tape (TVT) procedure. Acta Obstet Gynecol Scand 2002;81: Peschers UM,Tunn R, Buczkowski M, Peruccchini D.Tension-free vaginal tape for the treatment of stress urinary incontinence. Clin Obstet Gynecol 2000;43: Clemens JQ, DeLancey JO, Faerber GJ,Westney OL, Mcguire EJ. Urinary tract erosions after synthetic pubovaginal slings: diagnosis and management strategy. Urology 2000;56: Bent AE, Ostergard DR, Zwick-Zaffuto M.Tissue reaction to expanded polytetrafluoroethylene suburethral sling for urinary incontinence: clinical and histologic study. Am J Obstet Gynecol 1993;169: Debodinance P, Cosson M, Burlet G.Tolerance of synthetic tissues in touch with vaginal scars: a review to the point of 287 cases. Eur J Obstet Gynecol Reprod Biol 1999;87: Falconer C, Soderberg M, Blomgren B, Ulmsten U. Influence of different sling materials on connective tissue metabolism in stress urinary incontinent women. Int Urogynecol J Pelvic Floor Dysfunct 2001;12 Suppl 2:S Weinberger MW, Ostergard DR. Long-term clinical and urodynamic evaluation of the polytetrafluoroethylene suburethral sling for treatment of genuine stress incontinence. Obstet Gynecol 1995;86: Koelbl H, Stoerer S, Seliger G,Wolters M. Transurethral penetration of a tension-free vaginal tape. BJOG 2001;108: Summitt RL, Bent AE, Ostergard DR, Harris TA. Suburethral sling procedure for genuine stress incontinence and low urethral closure pressure: a continued experience. Int Urogynecol J Pelvic Floor Dysfunct 1992;3: