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Structural support of the urethra as it relates to stress urinary incontinence: the hammock hypothesis
1Department of Obstetrics and Gynecology, University of Michigan Medical School.
Objective:
This study examines the anatomic factors that could explain the mechanical basis for transmission of abdominal pressure to the urethra.
Study Design:
Dissection of 19 embalmed and 42 fresh cadavers and examination of 13 sets of serial pelvic sections were performed to study the structures involved in urethral support. The effect of simulated increases in abdominal pressure on the pelvic floor and urethra was observed in fresh specimens.
Results:
The urethra lies on a supportive layer that is composed of the endopelvic fascia and the anterior vaginal wall. This layer gains structural stability through its lateral attachment to the arcus tendineus fascia pelvis and levator ani muscle. Pressure from above compresses the urethra against this hammock-like supportive layer, compressing its lumen closed. The stability of the suburethral layer depends on the intact connection of the vaginal wall and endopelvic fascia to the arcus tendineus fasciae pelvis and levator ani muscles.
Conclusion:
Increases in urethral closure pressure during a cough probably arise because the urethra is compressed against a hammock-like supportive layer, rather than the urethra being truly "intraabdominal."