Mechanism of postoperative urinary continence.

Stress incontinence used to be attributed mostly to urethral hypermobility, and consequently most surgical techniques focused on the region of the bladder neck and proximal urethra. This article reviews our knowledge about the mechanism of postoperative urinary continence based on anatomic, imaging and urodynamic studies. Reduction of urethral mobility, as measured by cotton swab testing or imaging studies, is not the only reason why continence surgery succeeds. Imaging techniques are of limited value for elucidating the continence mechanism because radiologic landmarks and criteria are not reproducible. Urodynamically, the increased pressure transmission after successful continence surgery is attributed to the retropubic repositioning of the urethra, its compression against the anterior vaginal wall, and improved transmission of intra-abdominal pressure during stress. The role of the 'functional' urethral obstruction remains to be studied. In incontinent patients with hypermobility of the bladder neck and proximal urethra continence can be achieved by surgical correction. However, stress incontinence is possible in the absence of urethral hypermobility, and standard surgical techniques can fail to restore continence in these patients.