The integral theory of female stress urinary incontinence is not scientifically sound

Dear Editor, Tension-free vaginal tape (TVT) surgery for stress urinary incontinence (SUI) has an overall failure rate of 10-20%. However, the failure rate is much higher for women with hypomobile SUI, and many women who are cured of SUI have de novo or persistent symptoms of urgency and frequency. This suggests that a problem exists. The rationale for TVT surgery is based on the integral theory (IT). Although a correct theory should be able to discriminate between appropriate and inappropriate surgery, IT cannot do this. However, instead of confronting the problems with the theory, failures are blamed on the pathophysiology of SUI, which is alleged to be too multifactorial to be rectified by a single procedure. Therefore, the rationale for IT must be challenged. The abdominal cavity is a closed entity, and the intraabdominal pressure (Pabd) persistently affects all intra-abdominal organs, including the bladder and the proximal two-thirds of the urethra. This is true for both continent and incontinent women, both at rest and during stress. The abdominal cavity is similar to a water bag. All but 10-15% of its content is incompressible water with some gas. As proposed by Enhörning's theory of direct abdominal pressure transmission,1 a change in Pabd affects the whole cavity simultaneously. However, the expression, “pressure transmission,” is inappropriate because no pressure wave travels in any direction. The originators of IT rejected Enhörning's theory. They observed that during straining, many continent women had urethras that hung very low without causing leakage of urine. They also stated that “eight patients with a bladder neck in a starting position at or below the lower border of the pubic symphysis were cured of SUI without elevation of the bladder neck, which invalidates Enhörning's pressure transmission theory.”2 However, this conclusion is incorrect. A very low bladder neck position means that the bladder neck is outside the bony pelvis, but is not outside the abdominal cavity, which is delimited by the endopelvic fascia. Enhörning's pressure transmission theory is incorrect regarding the lower limit of the abdominal cavity but is otherwise correct. Suggesting that Pabd does not fully affect the proximal urethra indicates that the proximal urethra is situated outside the abdominal cavity, and this is incorrect. The significance of pressure transmission during straining was investigated using a virtual operation (VO) technique, that is, the recreation of a competent pubourethral ligament by unilateral midurethral support.3, 4 The authors showed that an equivalent Pabd during straining had different effects on the proximal urethra, depending on the absence or presence of VO-support. Without VO support, there was decreased pressure, funneling, and leakage of urine but with VO support, increased pressure, no funneling, and no leakage of urine were observed. In this experiment, VO neither elevated nor obstructed the urethra, but nevertheless on straining pressure increased in the proximal urethra. The authors concluded that this finding was inconsistent with Enhörning's pressure transmission theory and that the urethral closure must have an alternative explanation. This logic is incorrect. Even without VO, Pabd is fully transmitted to the proximal urethra, although this was not noted because the measurement technique used in the experiment was incapable of discriminating Pabd from the pressures generated by other mechanisms. Pabd appears to not be fully transmitted. A recently published theory of SUI, the urethral hanging theory (UHT),5-7 can help clarify why the VO experiment was misinterpreted and resulted in falsifying Enhörning's theory. In SUI, according to UHT, the proximal urethra is more mobile than the bladder neck. During straining, the urethra is pushed down in relation to the bladder neck until it is stopped and funneled by hanging on the bladder neck. The hanging situation exerts one external shearing force (Fs) and enhances one internal outflow distending force (Fd). These forces counterbalance the transmitted Pabd and at the abdominal leak point pressure (aLPP), the urethra opens and leaks: UCP + aLPP-Fs-Fd = 06; UCP = urethral closure pressure at rest. Eventual prevailing guarding reflexes are disregarded. An acutely high Pabd accomplishes three things. It pushes the urethra down, fully “transmits” its pressure, and generates a shearing force. Realizing that urethral hanging occurs is the key to understanding the pathophysiology of SUI (Figure 1). Without hanging, there is no shearing, no funneling, and no SUI. A closed miniscule meatus internus (m.i.) is a perfect seal,6 precluding the need for any additional closing mechanism. Figure 5A-C, in the referred VO article,4 shows according to UHT, a funneled urethra typically hanging on the bladder (B) and a not funneled urethra with a VO support preventing urethra from hanging (C). The measurement technique used in the VO experiment does not recognize that on straining, the transmitted Pabd is partly masked by the impacts of the “intrinsic” counteracting forces, Fs, and Fd. Consequently, Enhörning's theory has been incorrectly declared false. The rejection of Enhörning's pressure transmission theory required the development of a new theory, IT. However, it was built on false premises. A notable component of IT is the idea that pressure transmission “is most likely an index of a changed intraurethral area”4 where the pubourethral ligaments (PUL) constitute a fulcrum against which the proximal urethra is kinked, stretched, and narrowed by three directional muscle forces. This idea led to the requirement for complicated concepts such as the zone of critical elasticity, musculoelastic effects, the Hagen-Poiseuille and LaPlace law, to explain why TVT surgery cures SUI; however, frequently it does not. IT is partly designed analogously to the ancient Chinese finger trap mechanism. Regarding the truth of IT or UHT, the principle of Occam's razor definitively suggests the latter. The IT concept, whereby PUL act as a fulcrum, led to the decision to recreate the PUL by setting a TVT, starting 0.5 cm from the meatus externus (m.e.). This was later changed to 1 cm. The UHT concept, whereby PUL act as a backstop, led to the decision to create a support, starting 1 cm from the bladder neck. This prevents the proximal urethra from descending downwards. A suburethral backstop is never missing, except in cases of SUI. This always occurs at a higher or lower level. In SUI, the proximal urethra stops by hanging on the bladder before it reaches a backstop. If the proximal urethra and bladder descend to a similar extent, the urethra will not reach a hanging position. Instead, the bladder neck-proximal urethra complex will be stopped due to the backboard effect caused by the stretched anterior vaginal wall or by the posterior vaginal wall (hanging = SUI, backstop = no SUI).5 Urethral movement and funneling can be observed using dynamic ultrasound. “The anterior and posterior walls of the proximal urethra appear to move differently during increases in abdominal pressure. At first, they appear to move together: the urethra begins its descent as a single unit. At some point, however, the anterior urethra becomes arrested in its rotational movement and appears to move more slowly. The posterior portion of the urethra continues to descend along with the vaginal wall. This difference in movement suggests a shearing apart of the two walls, leading to the appearance of funneling, which can be seen as urine leaks out of the urethra.”8 This description of the shearing/funneling occurrence is said to support IT; however, it is also an excellent description of what happens when the proximal urethra is arrested and funneled by hanging from a filled bladder (UHT). IT and UHT, both emphasize PUL as important structures, but are else principally different. Both theories cannot be true. Setting a TVT according to IT has high overall failure rates. No5 clinical study has investigated the outcomes of setting a tape according to UHT. However, a theoretical analysis of the outcomes of surgery according to IT and UHT has been performed.7 According to UHT, urethral mobility can be measured using a fingertip.6, 7 The maximal curative distance is the therapeutic window (t.w.). In cases of hypomobile SUI (small t.w.), the proximal urethra (v.p.) should be elevated above its resting position. In 1977,9 Zacharin proposed “passing two aponeurotic bands … through the paraurethral attachment of the posterior pubourethral ligament on each side. It is our (Zacharin) conviction that urinary continence control in the human female is affected by this upper urethral anatomy and that for a technique to be successful it must exert its influence at this precise point.” This precise point, proposed by Zacharin, corresponds exactly with the vaginal point (v.p.) stipulated by UHT for making a suburethral support (hypermobile SUI) or creating a “lifting” support (hypomobile SUI). To create a lift without the risk of obstruction, the surgeon can use the “TVT technique” to insert one tuned tape in the paraurethral tissue on each side of the v.p.6, 7 Attempting to “cure” hypomobile SUI without lifting the proximal urethra above its resting position results in high failure rates. In 2015,10 Volker Viereck et al. showed the outcomes of different transobturator tape (TOT) positions for different grades of urethral mobility. The cure rates for hypermobile, normomobile, and hypomobile SUI were high, low, and zero, respectively. The outcomes reported in that study are almost identical to the outcomes predicted by the theoretical analysis of TVT/TOT surgery using a virtual biomechanical approach based on UHT.7 Theoretically, the opening of a miniscule m.i. appears impossible because the intravesical pressure is always perpendicular to the bladder wall and generates no shear forces to allow the expansion of the m.i.; the bladder will rupture before it is opened. Therefore, a theory of continence must be able to explain how the bladder opens during normal micturition. IT postulates that the bladder neck opens when the pubococcygeus muscles relax and the levator ani and longitudinal ani muscles contract and pull the vaginal walls down, shearing the posterior urethral wall from the anterior urethral wall. Closure occurs when the pubococcygeus muscles contract, and the two backward/downward directed muscles kink/stretch the proximal urethra against the PUL.11 UHT proposes an alternative mechanism, namely, an intrinsic mechanism entirely confined to the urethra-bladder complex. The longitudinal smooth muscles of the detrusor are in direct continuation with the longitudinal smooth muscles of the urethra and these muscles have parasympathetic innervation. The combined arrangement of these longitudinal muscles creates long “cords” extending from the bladder into the urethra. When the bladder is filled and relaxed, these long cords are curved at the closed bladder neck, but when the detrusor muscles, including these long cords, contract, they shorten, and shift their positions towards “the shortest distance between two points, i.e., a straight line.” This straightening of the many parallel curved cords located around the bladder neck results in the opening of the bladder neck. Simultaneously, with this opening of the bladder neck, the levator plate relaxes and the pelvic floor descends to a lower level. The posterior urethro-vesical angle (PUV) widens. This descending of the levator plate, caused by a change from a high resting tonus to no tonus may falsely give the impression that the vaginal walls are pulled down by active muscle forces (IT). On straining the levator plate and the endopelvic fascia are pushed even further down and it cannot be precluded that urethral hanging occurs normally with strain. Using ultrasonography, magnetic resonance imaging or X-ray, it is difficult to discriminate between a structure being plunged down, pushed down, or pulled down. TVT surgery according to IT has high failure rates because it does not principally prevent urethral hanging. In the case of a long urethra, the tape is too distally set. In the case of hypomobile SUI, the use of a suburethral tape is unwarranted because the proximal urethra (v.p.) is not elevated above its resting position.6, 7 Yours sincerely, Bo S. Bergström Correspondence Dr. Bo S. Bergström, Specialist in obstetrics and gynecology. (Private home adress: Karlavägen 27A 11431 Stockholm Sweden). Email: bosbergstrom@comhem.se