Figure 26.1 Lateral view of the pelvic ﬂoor drawn from a three-dimensional reconstruction with the urethra, vagina, and fascial tissues transected at the level of the vesical neck. Note how the urethra is compressed against the underlying supportive tissues by the downward force (arrow) generated by a cough or sneeze. (From Delancey J. Structural support of the urethra as it relates to stress urinary incontinence: the hammock hypothesis. Am J Obstet Gynecol 1994;170:1718, with permission.) periods of increased intra-abdominal pressure, resulting in stress incontinence. However, many women remain continent in spite of loss of urethral support (1).
The intrinsic factors contributing to urethral closure include the striated muscle of the urethral wall, vascular congestion of the submucosal venous plexus, the smooth muscle of the urethral wall and associated blood vessels, the epithelial coaptation of the folds of the urethral lining, urethral elasticity, and the tone of the urethra as mediated by α-adrenergic receptors of the sympathetic nervous system.
Effective urethral closure is maintained by the interaction of extrinsic urethral support and intrinsic urethral integrity, each of which is inﬂuenced by several factors (muscle tone and strength, innervation, fascial integrity, urethral elasticity, coaptation of urothelial folds, urethral vascularity). In the clinical setting, damaged urethral support is manifested clinically by urethral hypermobility, which often results in incompetent urethral closure during physical activity and presents as stress urinary incontinence. Intrinsic urethral functioning is more complicated and is not understood nearly as well as incontinence related to loss of urethral support (2).
Clinical appreciation of the importance of extrinsic support and intrinsic urethral function led to the separation of stress incontinence into two broad types: 1.
Incontinence caused by anatomic hypermobility of the urethra 2.
Surgical approaches are based on this arbitrary distinction, with a pubovaginal sling recommended for women with intrinsic sphincter deficiency and a colposuspension (also known as retropubic urethropexy) for those with hypermobility. This rationale was based initially on a small study in which women younger than age 50 years with urethral closure pressure less than 20 cm H2O had a higher failure rate after a Burch colposuspension than did women with a closure pressure greater than 20 cm H2O (3). No difference in outcome was seen in women older than 50 years. This dichotomy was called into question, based on the observation that all women with stress incontinence have some degree of sphincter weakness, regardless of whether they have hypermobility. Minimally invasive synthetic midurethral slings have largely replaced pubovaginal slings and retropubic urethropexy as the most commonly performed surgical procedures for stress urinary incontinence. The use of midurethral slings would seem to lessen the impact of a poorly functioning urethra; however, a similar debate is ongoing about the impact of poor urethral function with both retropubic and transobturator slings. It appears that women with poor urethral function are more likely to experience treatment failure irrespective of the type of procedure performed (4).