[Anatomical mechanisms of continence in man]

According to classical concepts, the role of the bladder sphincteric apparatus is to contain without weakness and to expel without effort. Continence without dysuria is the result of: biomechanical properties of the bladder wall which confer: viscoelasticity accounting for its compliance, contractility allowing expulsion of its contents. The action of bladder neck structures and passive urethral mechanisms which, under normal conditions, are practically sufficient to ensure passive continence. Muscle fibre tone collapses the urethra during the continence phase and closes the bladder neck by creating vesicourethral angulation. The arrangement of these muscle fibres in the bladder neck and urethra accounts for the sphincter function over the entire length of these two structures. The external sphincter composed of striated muscle fibres derived from perineal muscles, which are amenable to retraining. The main role of the sphincter under normal conditions is to oppose an unwanted bladder contraction or to rapidly interrupt ongoing micturition and it only has a relatively limited role in passive continence. It is particularly important after prostatic surgery, either for benign prostatic hyperplasia or for cancer, when the striated sphincter remains the only structure able to oppose the pressure forces which tend to expel urine from the bladder.