Functional anatomy of the female lower urinary tract and pelvic floor

Stress continence depends upon three factors: proximal urethral support, vesical neck closure, and urethral contractility. The position of the vesical neck is not static but mobile and under voluntary control. Its support depends upon connections of the urethrovaginal endopelvic fascia to the medial aspect of the levator ani. In addition, these fasciae are attached to the arcus tendineus fasciae pelvis which supports the urethra during levator relaxation, and probably during stress. Levator contraction supports the proximal urethra and also pulls the vesical neck anteriorly against a band of endopelvic fascia which is suspended between the arcus tendinei, compressing it closed. Relaxation of the muscles allows the vesical neck to descend, and facilitates its opening. The connective tissue and smooth muscle of the trigonal ring encircles the vesical neck's lumen, and may contribute to closure of this area. The striated urogenital sphincter muscle can contract to assist in maintaining continence in continent women whose vesical neck is not competent. It has a circular sphincteric portion from 20 to 60% of urethral length. From 60 to 80% it has a considerable bulk of muscle which forms an arch at the perineal membrane that would compress the urethra from above.