LAUSR

Dear Editor, It has been repeatedly postulated that the tension-free vaginal tape operation (TVT) is based on the integral theory (IT). According to the IT, urinary continence depends on adequate outlet resistance at the midurethra. Forces from three muscles stretch the anterior vaginal wall with the pubourethral ligaments (PUL) as a fulcrum. Awell-supported intrinsic rhabdosphincter compresses the midurethra. During stress, the proximal urethra rotates dorsocaudally against the PUL and is kinked, elongated, and narrowed. Stress urinary incontinence (SUI) emerges when a defective PUL cannot counteract these rotating forces. A lax anterior vaginal wall descends, and the proximal urethra is funneled by external shearing forces when the posterior urethral wall is pulled down in relation to a better-supported anterior urethral wall. Due to the lax vagina, the rhabdosphincter is shortened and weak. At the abdominal leak point pressure (aLPP), the outlet resistance is overwhelmed, and the urethra opens and leaks. The TVT operation, introduced in 1996, claims to reconstruct a defective PUL and restore continence. The IT led to the conclusion of setting the tape 0.5 cm from the meatus externus (m.e.), which was later changed to 1 cm. Although the operation has high rates of success, it also fails 10-20% of the time. The pathophysiology of SUI is considered to be of multifactorial origins, all of which a single procedure cannot correct. Is this true? According to the urethral hanging theory (UHT),5–6 the origin is “one-factorial,” such that a single specific procedure can correct the issue by enforcing a normal spatial relationship, at stress, between the proximal urethra and the bladder neck. These two theories—IT and UHT—both emphasize the PUL as important structures, but are else principally different. In the IT, the PUL designate a midurethral support, and in the UHT, they provide a proximal support—so the UHT, and not the IT, highlights the importance of the strong posterior components of the PUL which are attached to the proximal urethra, “the key site of control of continence” and the only parts of the the PUL with “fusion extensions to the levator ani muscle fascia.” In the IT, the PUL promote the proximal urethra to kink downwards and in the UHT they prevent the proximal urethra to descend downwards. In the IT, the highpressuremidurethral zone is flow-controlling, and in the UHT, a bladder neck sealing mechanism is flow-controlling. These theories also stipulate different tape positions to be curative. The IT stipulates a tension-free suburethral tape that starts 1 cm from the m.e. The UHT stipulates a tension-free suburethral tape that starts 1 cm from the bladder neck, but only in cases with hypermobile SUI. In cases with hypomobile SUI, the proximal urethra should be lifted above its resting position. Because suburethral lifting with a prolene net involves a high risk of obstructing complications, the “TVT technique” can be used to insert one tuned prolene net in the paraurethral tissues on each side of the vaginal point (v.p.) (Fig. 1) to create a lift without the risk of obstruction. The v.p. corresponds to the junction of the upper one-third and distal two-thirds of the urethra where the strong posterior PUL broadly attach to the paraurethral tissues and is also the midpoint of the intra-abdominal urethra. How these different tape positions lead to different curative mechanisms can be theoretically analyzed using a virtual biomechanical approach (Figs. 1-4). The pathophysiology of SUI according to the UHT is illustrated graphically in Fig. 1. At stress, the urethra is forced downward in relation to the bladder neck until it is stopped and funneled by hanging on the bladder neck. The hanging situation exerts oneexternal shearing force (Fs) and enhancesone internal outflow distending force (Fd). The miniscule m.i. that is normally a perfect seal is forced open and the functional urethral length is shortened in proportion to the depth of the funnel. The urethral high-pressure zone canbe engaged. Pascal's principle of fluid mechanics postulates that when the radius (r) of the m.i. widens, the Fd increases abruptly, and at aLPP, the urethra leaks. Fd = (aLPP + Pdet)*pi*r2 (Pdet = detrusor pressure). When funneling prevails at pressures