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Neurourology and Urodynamics Evolution of Midurethral and Other Mesh Slings – A Critical Analysis

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Neurourology and Urodynamics Evolution of Midurethral and Other Mesh Slings – A Critical Analysis
  Neurourology and Urodynamics Evolution of Midurethral and Other Mesh Slings – ACritical Analysis Peter Petros 1,2 * and John Papadimitriou 3 1  Academic Dept of Urology, Case Western University, Cleveland, Ohio 2 UNSW St Vincent’s Clinical School, Sydney, NSW, Australia 3  Department of Pathology and Laboratory Medicine, University of Western Australia, Perth, Western Australia, Australia  We analyzed our srcinal experimental studies on which the midurethral sling was based with reference to FDA meshwarnings. We concluded that 1.  Vascular/organ damage could be avoided by first penetrating the urogenital diaphragm. 2.  A non-stretch tape minimizes obstruction and urethral damage. 3.  A non-obstructive musculoelastic mechanism closes the urethra. 4.  The strength of neocollagen ( > 92.8 lbs/sq inch) indicates that little mesh is required for prolapse repair. 5.  Foreign body (mesh) reaction is different from infection and is related to volume implanted 6.  Urgency is potentially curable by repairing the suspensory ligaments 7.  ‘‘Minislings’’ are promising for incontinence and POP, but more development is required.  Neurourol. Urodynam.   2012 Wiley Periodicals, Inc. Key words:  integral theory; musculoelastic closure; pubourethral ligament; ureterovesical junction; urinary stressincontinence INTRODUCTION Recently, the FDA issued a warning on the use of mesh us-age in pelvic organ prolapse (POP). 1 Though midurethral slingsurgery was largely exonerated, the warning neverthelessstimulated us to review our early experimental studies, asthese have been used as an intellectual cornerstone to justifythe use of mesh in prolapse surgery, wrongly so, as our workwas based on strengthening ligaments, not creating stiff vagi-nal tissue, which needs to be elastic at all times. We foundthat our early works shed considerable light not only on themany issues giving rise to the FDA warnings, for example,tape erosion, infection, obstructed urination, organ, and vas-cular damage, but also on many clinical controversies, surgicalcure of ‘‘mixed’’ incontinence, urgency, pelvic pain, and‘‘obstructed’’ micturition. 1986—Origins of the Midurethral Sling and IntegralTheory In 1986, the dominant theory for USI pathogenesis was the‘‘Pressure Equalization’’ theory. 2 The main operations werethe Kelly repair, Burch colposuspension, fascial bladder necksling, major painful operations, associated with urinaryretention.The midurethral sling 3 and Integral Theory 4 srcinated froman observation of dense fibrous tissue around a Teflon tapeused in the Cato colposuspension. 5 We reasoned that implant-ing a tape for 6 weeks and then removing it, would reinforcethe pubourethral ligament (PUL) sufficiently to cure USI. Twoprototype midurethral sling operations were performed atRPH in 1986. Both patients were discharged next day, cured of USI, with minimal pain and no urinary retention. 1987—Animal studies  were performed in 1987. 6 Our aimwas to use the collagenous foreign body reaction of animplanted Mersilene tape in a positive way, to reinforce thedamaged PUL. A tunneller with a 90 8  curve (Fig. 1) allowedclose application to the pubic bone, minimizing bladderperforations.Thirteen large dogs had a non-stretch Mersilene tapeimplanted as an inverted ‘‘U,’’ both ends free in the vagina forup to 19 weeks. They remained afebrile and well, though10/13 developed a (sterile) suprapubic purulent sinus. Histolo-gy: foreign body inflammatory reaction (FBIR) with multinu-cleated giant cells, rather than infection; Radioactive Galliumstudies indicated minimal inflammation around tapes. A col-lagenous tunnel formed around the Mersilene tape, allowingeasy removal postoperatively. Indian ink injected aroundtapes before removal identified the channel after the dogswere sacrificed. Sinuses closed within 3 days of tape removal.The artificial collagenous ‘‘neoligament’’ was 0.2–2 cm inwidth (Fig. 2).The ‘‘neoligament’’ was invariably attached by thick fibroustissue to pubic bone, vagina, muscle, and skin (Fig. 2). In situtapes were initially surrounded by granulation tissue: Abbreviations: DI, Urodynamic detrusor instability; FDA, Food and DrugAdministration; FBIR, foreign body inflammatory reaction; POP, pelvicorgan prolapse; RPH, Royal Perth Hospital, Perth Western Australia; TVT,tension-free vaginal tape; TOT, transobturator tape; TFS, tissue fixationsystem; UI, urge incontinence; USI, urinary stress incontinence. Conflict of Interest: Peter Petros is the co-inventor of the midurethral sling (‘‘TVT’’1995) the posterior sling ‘‘Infracoccygeal Sacropexy’’ 1997) and the TFS tensionedsling (2005). John Papadimitriou author has no conflict of interest.Peter Petros and John Papadimitriou contributed to the conceptualization andwriting of the manuscript.*Correspondence to: Peter Petros, DSc, PhD, DS, MB, BS, MD, FRCOG, FRANZCOG,CU, Academic Dept of Urology, Case Western University, Cleveland, OH.E-mail: pp@kvinno.comReceived 3 July 2012; Accepted 9 August 2012 Published online in Wiley Online Library(wileyonlinelibrary.com).DOI 10.1002/nau.22308  2012 Wiley Periodicals, Inc.  macrophages, granulocytes, lymphocytes, and multinucleatedgiant cells and a thick outer layer of vascularized collagenousconnective tissue, expected characteristics of an FBIR; initialcollagen III (argyrophilic), maximal at 4 weeks, was subse-quently replaced by collagen I (argyrophobic). Histological ex-amination 6 weeks after tape removal demonstrated acollagenous tunnel forming an artificial ‘‘neoligament’’(Fig. 2), with only little granulation tissue. Macrophages  infil-trated the interstices in all Mersilene tape specimens . A collage-nous ‘‘neoligament’’ formed in the aftermath of theinflammatory reaction is immensely strong: one specimentore out of a tensiometer’s grips at 0.64 megaPascals,(92.8 lbs/sq inch). 7 Lessons Learnt from the Animal Studies 1. Tape implantation even with sinus formation was safe:cutaneous sinuses resulted from FBIR, not infection. FBIR ischaracterized clinically by an afebrile state, histologicallyby giant cells and sometimes, sterile pus, which like a splin-ter, may distend the tissues to cause pain. FBIRs areclinically benign, and quite different to those of infection,which are not.2. Bacterial growth, where present, was of ‘‘mixed’’ nature,with low counts.  Infective inflammation  was uncommon,generally caused by an infected hematoma with pyrexia,and isolation of pathogenic bacteria.3. Three dogs had no sinuses indicating individual immuno-logical variation in tissue reaction.4. Macrophages were found in the interstices of Mersilenetapes, indicating that whatever the cause of the sinuses,it was not absence of macrophages in the spaces.5. The collagenous neoligament is enormously strong, indicat-ing that large meshes are not required to support a 100 guterus, or an even smaller vagina.6. The inflammatory reaction from the tape glued it to any-thing it touched, ‘‘tissue welding.’’ On the positive side : Small strips of tensioned tapes appliedtransversely cure POP, 8–10 reinforcing ligaments and linkingtogether perineal bodies and levator hiatus structures, to pre-vent lateral displacement and POP during straining. On the negative side : Excess FBIR from large meshes maydamage organs and ‘‘glue’’ vagina to rectum to cause dys-pareunia, fistulae, and other complications, as per the FDAwarning. 1988 2nd group of 30 prototype midurethral sling opera-tions  was performed in 1988. 3 An adjustable Mersilene sling(Fig. 3) was inserted immediately behind pubic bone. Post-operatively the sling was lowered sufficiently to allow normalmicturition and was removed after 6 weeks. Obstructed Fig. 1.  Prototype tunneller consisted of a 30 cm length tube, with a verticalhandle and a metal insert with a fairly blunt tip. The insert when reversed,could bring a tape from above down. The tape is shown above with holesfor the adjusting sutures. The right angle was important in defining theposition of the tip. Opening it out beyond 90 8  creates uncertainty whichmay sometimes lead to organ damage. Fig. 2.  Tissue reaction to implanted Mersilene tapes. Specimen after taperemoval from an experimental animal in which a tape had been implantedaround urethra with ends free in the vagina for 12 weeks. Arrows indicatethe artificial pubourethral neoligament formed around the position of theexplanted tape. V, vagina; B, bladder. Fig. 3.  Prototype adjustable midurethral sling The Mersilene tape ‘‘T’’ withholes set 0.5 cm apart was inserted as an inverted ‘‘U’’ through the subure-thral vaginal wall across the rectus abdominis sheath ‘‘A.’’ The two tapeends were passed through a rubber tube (TB) exiting through its inferiorwall, where sutures were placed in parallel holes in the tape. Initial symp-toms of urgency and retention resolved on lowering the tape by sequen-tially cutting the sutures from above down, yet the patient remainedcontinent. This experiment shows conclusively that continence after a mid-urethral sling has nothing to do with physical obstruction by the tape.Rather, it works by restoring the fulcrum point for a musculoelastic closuremechanism (see Figs. 5 and 6). The circle ‘‘V’’ represents vagina. 2  Petros and Papadimitriou  Neurourology and Urodynamics  DOI 10.1002/nau  micturition and urgency improved as the sling was lowered.All 30 patients were continent with a normal stream. Pre-operative X-ray studies  indicated that a tape insertedimmediately behind the pubic symphysis became sited at themidurethra (Fig. 4). Eight patients with a starting position of bladder neck at or below the lower border of pubic symphysiswere cured without elevation, invalidating Enhorning’s ‘‘Pres-sure Transmission Theory.’’ When the tape was grasped witha hemostat, and the patient strained, three directional forcesacting against the midurethra became evident on X-ray(Fig. 4), suggesting the presence of a bidirectional musculoe-lastic closure mechanism acting against the PUL.Lessons Learnt from the ‘‘Lowering’’ of the Tape Experiment1. Excessive tightness may cause obstruction and urgency.2. A tape can cure USI without obstruction or retention.3. Bladder neck elevation is not required for USI cure: a mus-culoelastic mechanism acting against a competent PULeffected urethral closure. 11 The musculoelastic hypothesis , Figures 5 and 6, Video 1,was substantially validated in 1999: 11 a hemostat insertedunilaterally immediately behind the pubic symphysis (‘‘Simu-lated operation’’) restored normal geometry and continence(arrow, Fig. 5). Urodynamically, distal, and proximal urethralpressure rise were observed during this maneouvre. 12 ‘‘Mixed incontinence’’  Of 30 USI patients, 25 also had urgeincontinence (UI) and they reported cure of both symptomspost-operatively. 3 When the tape was removed, 50% reportedrecurrence of both USI and UI. Subsequently, bilateral leaf shaped incisions improved both stress and urge symptoms insome failed cases. These results, subsequently validated byRezapour and Ulmsten, 13 suggested a common etiology forUSI and urgency based on connective tissue laxity. 1990–1993 The 3rd group of prototype operations  wereperformed under local anesthetic/sedation, using a light-weight instrument with a delta wing for more precise orienta-tion of the tip and a Mersilene tape. 14 This method eventuallyled to the intravaginal slingplasty, 15–17 better known as the‘‘TVT’’ (Fig. 7).A hole was made through the urogenital diaphragm imme-diately behind the pubic bone, and the applicator insertedunder direct vision, with the delta wing indicating theposition of the tip. With the patient coughing, the tape wasraised in a staged manner until continence was achieved.There were few instances of post-operative urinary retention, Fig. 4.  X-ray studies taken in the standing lateral position, during rest andon straining, with a dye filled Foley catheter in situ.  Upper X-rays : pre-op atrest.  Middle X-rays : 2 weeks post-op forceps grasping the tape so as to iden-tify it; proximal part of the Foley catheter is pulled backwards and down-wards, and the distal part is pulled forwards, denoting the action of threedirectional muscle forces  which require an adequately tight insertion point  .  Lower X-rays:  8 weeks after tape removed—patient continent. No elevationof the bladder neck. Fig. 5.  Unilateral midurethral anchoring—A ‘‘simulated operation’’ test for PUL competence carried out undervideo ultrasound control. On straining, the bladder neck and proximal urethra demonstrate ‘‘funnelling’’ withurine loss. ‘‘Funnelling’’ is reversed on application of a hemostat at the midurethra (arrow), site of PUL immedi-ately behind symphysis pubis ‘‘S.’’ Anterior ‘‘a’’ and posterior ‘‘b’’ vaginal walls are stretched backwards on strain-ing, and are clearly stretched during midurethral anchoring, indicating the presence of a musculoelastic closuremechanism. Note distal urethral and bladder neck closure. See also Video 1. Evolution of Midurethral and Other Mesh Slings  3  Neurourology and Urodynamics  DOI 10.1002/nau  post-operative pain was minimal and patients were able toreturn to normal duties within days. We found that Mersilenetape had an unacceptably high erosion rate. Though this wasessentially harmless, the discharge was often offensive 1 anddistressing to the patients.Subsequently, the use of a polypropylene tape 15,16 largelysolved the erosion problems encountered with Mersilene.In 1992, this ‘‘tension-free vaginal tape’’ principle was ap-plied for repair of uterine/apical prolapse using the infracoccy-geal sacropexy operation. In such patients, a high rate of curewas observed in patients with symptoms of nocturia, urgency,and some types of pelvic pain. 17 Lessons learnt from the early operations (1990–1995). 1. USI and ‘‘mixed’’ incontinence were surgically curable byplacing small lengths of tape at midurethra.2. A hole in the urogenital diaphragm preceding insertion of the instrument gave greater control of the instrument.3. The staged technique for tightening the tape was accurateand effective.4. Only a permanent tape gave good longer-term results forUSI surgery.5. Polypropylene is the best material for implantation.6. The ‘‘tension-free vaginal tape’’ principle, using shortlengths of tape gave good results for uterine/apical pro-lapse repair using the infracoccygeal sacropexy (posteriorsling). Large sheets of mesh were not required. This opera-tion gave a high cure rate for nocturia, urgency, and sometypes of pelvic pain.7. Heavy densely knit tapes (such as Mersilene, (and later)polypropylene Amid type 3) are more likely to cause exces-sive tissue fluid reaction, surfacing, and erosion. The higherthe density of the implant, the more the erosion. Questions arising on the nature of the unstable bladder(1990–1997)  From the earliest 4 to later urodynamically moni-tored studies 17 the high rates of surgical cure for urge inconti-nence (UI), frequency, and nocturia provoked the question,‘‘what is the mechanism for surgical cure of unstable bladdersymptoms?’’ 1993 A  urodynamically based study indicated that urody-namic ‘‘detrusor instability’’(DI) was consistent with a prema-turely activated micturition reflex, 18 thus providing ananatomical basis for the hypothesis flowing from the Theory,that a lax vaginal membrane may have prematurely activatedthe micturition reflex, and that surgical cure of UI is possibleby tightening the vaginal membrane. 1999 Low compliance  was consistent with a partially acti-vated, but controlled, micturition reflex, while the sinuous Fig. 6.  The mechanics of USI with a lax PUL, the three directional muscleforces (arrows) cannot ‘‘grip’’ on a loose PUL, so that the posterior muscleforces pull open the posterior urethral wall, from ‘‘C’’ closed, to ‘‘O’’ open,lowering the pressure required for urine expulsion. H, sub urethral vaginalhammock; PCM arrow, directional force from pubococcygeus muscle; LP ar-row, directional force from levator plate; LMA arrow, directional force fromconjoint longitudinal muscle of the anus. See also Video 1. Fig. 7.  The midurethral plastic mesh tape reinforces the PUL. 1 Desquamated decomposing vaginal cells attached to the tape created a smell of deadtissue.Inthesrcinalgroupof30patientswherethetapelayinthevaginafor6 weeks, discharge and odour were controlled by vinegar douches. Fig. 8.  Trampoline analogy-function. How the muscle forces control periph-eral neurological function. Like a trampoline, laxity in even one suspensoryligament, PUL (pubourethral), CL (cardinal), ATFP or USL (uterosacral), mayprevent the muscle forces (arrows) from tensioning the vaginal membrane.The stretch receptors ‘‘N’’ cannot be supported, and fire off prematurely.The cortex perceives the afferent impulses as urge symptoms. Surgical res-toration of PUL, USL, and CL explain urgency cure with a midurethralsling, 12,16 cystocele repair, and posterior sling repair. 16,29 See also Videos 2and 3. 4  Petros and Papadimitriou  Neurourology and Urodynamics  DOI 10.1002/nau  urodynamic pattern characteristic of instability was an ex-pression of a struggle between two feedback loops, the mictu-rition and closure reflexes. 19 In a small number of cases, itwas possible to reverse a urodynamic DI pattern by gentle dig-ital pressure below bladder base. 19 See Video 2. Trampoline analogy  The concept of bladder base stretchreceptors ‘‘N,’’ Figure 8 supported by a stretched vaginal mem-brane 4 explains improvement in urge symptoms after midure-thral or posterior sling surgery, and with SimulatedOperations which also work by restoring the insertion point(s)of the pelvic muscles which stretch the vaginal membrane(arrows, Fig. 8). The presence of stretch receptors ‘‘N’’ can beverified in some patients by stretching the bladder base up-wards to activate the micturition reflex (see Video 3). Lessons learnt from examining the nature of urgency andurodynamic detrusor overactivity 1. In a non-neurogenic patient, urgency and urge inconti-nence are most likely clinical manifestations of a prema-turely activated micturition reflex caused by inability of alax vaginal membrane to support the bladder base stretchreceptors; in turn, a consequence of lax suspensory liga-ments inactivating the musculoelastic mechanism whichstretches the vagina.2. Urodynamic detrusor overactivity in the female is consis-tent with a secondary urodynamic manifestation of a pre-maturely activated micturition reflex, as it can, in somecases, be controlled or even reversed. 19 See also Video 2.3. In patients with such anatomic causes, urgency and urgeincontinence are potentially curable surgically by repairinglax ligaments/vagina. 1995–2011 Commercialization  The subsequent course of this new direction in surgery was driven by major interna-tional medical companies. Viewed with the wisdom of hind-sight, commercialization had a bright side and a dark side. The bright side of commercialization  Gynecare initiated anextensive marketing campaign which spread the midurethralsling and the underlying Integral Theory worldwide, creatinga revolution in the treatment of USI. Within a few short yearsthe previous ‘‘gold standard,’’ the Burch Colposuspension wasrelegated to history. Tyco marketed the infracoccygeal sacro-pexy, or posterior IVS sling for apical/uterine prolapse. In addi-tion to prolapse repair, cure of urgency, nocturia, abnormaland emptying was also reported. 17 The dark side of commercialization  Complications beganto appear, those caused by instrument misuse and thosecaused by the tape. The exponential spread of the TVT tech-nique made it impossible to adhere to the srcinal strict teach-ing protocols. It became a free for all ‘‘See one, do one, teachone.’’ Not all errors were due to poor teaching, however. The instrument, the surgeon and surgical methodology  :Bladder perforation was an early problem, but always in thedome of the bladder, not unlike a suprapubic catheter. Injuryto major blood vessels, nerves, small bowel, and large retropu-bic haematomas were a serious problem, with several fatali-ties. Though ascribed to ‘‘faulty technique,’’ the ultimate causeof these problems may have been removal of some core stepsfrom the original operations—perforating the urogenitaldiaphragm prior to insertion of the applicator, preventingexcessive thrust during insertion; a non-elastic tape; controlof bleeding from a subpubic sinus perforation by digitalpressure.The commercial instrument introduced two sharp trochars,eliminating the necessity for a pre-insertion hole, whichmasked bleeding from the venous sinuses below pubic bone,which may collect in the Space of Retzius and proceed unhin-dered cephalad. The heavy screw-on handle removed the oper-ative sensitivity of a light instrument, so the instrument wasoften pushed forcibly at 45 8  before being directed upwards.Prior perforation not only gives greater control, it reveals po-tential bleeding which can be addressed with digital pressure. The Tape Only two polypropylene (PP) tapes were commercially avail-able in early 1990s, both flawed: an elastic Amid type 1‘‘monofilament’’ with wide spaces (Gynecare) which narrowedto thin cord on stretching; a heavier non-stretch Amid type 3,composed of multiple grouped fibers, 20–30  m m in diameter,with narrow 75–200  m m spaces (Tyco). Amid 20 was incorrectin his statements that a macrophage required a 75  m m spaceto be functionally efficient. Macrophages were demonstratedin 5  m m spaces 21 or by developing lamellopodia, traversinginterendothelial gaps 1  m m in width. 22 Nevertheless, Amid’sclassification is important as a reference point for physicalcharacteristics of implanted materials.  Elastic Type 1 tape  stretches when pulled upwards. Initially,the elastic tape was applied directly onto the wall of the ure-thra. Restoration of elasticity in the subsequent 24 h mayhave been responsible for many post-operative incidents of urinary constriction, retention, and even urethral perforationand fistula. Placed under stretch the diamond-shaped tapesstretch like a steel wire, sometimes transecting the urethra tocause fistula. A space left between tape and urethra hashelped this problem, but this method remains imprecise: tootight-retention; too loose- incontinence. The question is ‘‘Howmuch space to leave.’’ Clearly more tape insertion and moreelastic restoration occurs in a 120 kg woman than in a 45 kgwoman.  Non-elastic Type 3 ‘‘multifilament’’ tape : Was the only trulynon-stretch PP tape available in the mid 1990s to mid 2000s.Applied to the wall of urethra, there was no post-operativeretraction, and few retentions. Nevertheless, the higher con-centration of polypropylene per unit volume had the potentialto provoke larger FBIRs around the tapes with greater likeli-hood of slippage, surfacing and erosions 23 or even pain. 24 Though the histology (granulomas), the clinical characteristicsof the reaction and the time frame (24 months duration) wereindicative of a FBIR, many such cases were described as ‘‘infec-tion.’’ 24 We emphasize the importance of understanding thedifference between foreign body induced inflammation (be-nign) and infection (not benign), especially in the context of the FDA warnings on mesh implantation and consequentmedico-legal suits. Though entrapped pus from a foreign bodyreaction may cause pain, 24 it is sterile, and like a splinter,symptoms settle immediately on tape removal; infected puscontains heavy concentrations of pathogenic bacterial species.Infection is potentially serious. Note  Pus is only the liquefactive necrosis of granulocytesand the tissue in which they have invaded – bacteria are notnecessarily involved. 2000–2010—Application of the surgical tape principle toother operations The transobturator ‘‘TOT’’ midurethral sling (Delorme) 25 in2001 was a significant advance, with equivalent results forUSI, with fewer complications, though possibly less effectivein ISD (Intrinsic sphincter defect) patients. The infracoccygealsacropexy (posterior sling) 17 was first performed in 1992 un-der LA/sedation in a woman with emphysema, uterine pro-lapse, and symptoms comprising the ‘‘posterior fornix Evolution of Midurethral and Other Mesh Slings  5  Neurourology and Urodynamics  DOI 10.1002/nau
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