Anatomy and physiology of urinary continence.

Each of the three components of the continence mechanism, that is, proximal urethral support, internal sphincter activity, and external sphincter function, contributes to continence. Any one alone may not be able to keep a patient dry. The pressures generated during a cough may easily overcome the internal and external sphincters closing powers, and the normal supportive mechanism works in such a way as to increase closure during increases in abdominal pressure. Normal support, conversely, is not sufficient in and of itself to maintain continence, and must have sufficient resting sphincteric activity to be effective. When one element is abnormal, the other mechanisms may be able to compensate and maintain continence. It is because there are these several interdependent parts of the continence mechanism that no single urodynamic parameter is predictive of stress continence. Each different etiologic type of stress incontinence reflects the malfunction of an anatomic component of the sphincteric mechanism. Therefore, a knowledge of this mechanism's structure is fundamental to an understanding of this common clinical problem. Technologic advances in assessment of the lower urinary tract have made the separation of different types of stress incontinence possible. The further realization that each type requires different treatment has made the distinctions between these clinically important entities.