Role of the pelvic floor in bladder neck opening and closure I: muscle forces.

The aim of the study was to identify the striated muscle forces hypothesized to assist bladder neck opening and closure in females. Cadaveric dissection was used to identify the levator plate (LP), the anterior portion of pubococcygeus muscle (PCM), the longitudinal muscle of the anus (LMA), and their relation to the bladder, vagina and rectum. X-ray video recordings were made during coughing, straining, squeezing and micturition in a group of 20 incontinent patients and 4 controls, along with surface EMG, urethral pressure and digital palpation studies. During effort, urethral closure appeared to be activated by a forward muscle force corresponding to PCM, and bladder neck closure by backward muscle forces corresponding to LP and LMA. During micturition the PCM force appeared to relax, allowing LP and LMA to pull open the outflow tract. The data appear to support the hypothesis of specific directional muscle forces stretching the vagina to assist bladder neck opening and closure.