The pelvic diaphragm is a muscular partition between the true pelvis and the perineum. It creates the gutter-shaped pelvic floor. It’s created by the large levator ani and small coccygeus muscles of 2 sides and their covering fasciae. It’s incomplete anteriorly to enable passage for the urethra in the males, and the urethra and vagina in the females.
The pelvic diaphragm gives main support to the pelvic viscera and has a sphincteric actions on the rectum and vagina. It also helps in raising the intra abdominal pressure during defecation, micturition, and parturition.
The pelvic diaphragm presents these openings:
- Hiatus urogenitalis: It’s a triangular gap between the anterior fibres of the 2 levator ani muscles. It carries the urethra in male, and the urethra and vagina in female. The hiatus urogenitalis is closed from below by the urogenital diaphragm.
- Hiatus rectalis: It’s a round opening between the perineal body and the anococcygeal raphe. It gives passage to the anorectal junction.
Development of The Pelvic Diaphragm
In quadrupeds, the muscles of pelvic diaphragm are the muscles of butt. The anterior portion of levator ani is termed pubococcygeus and posterior portion iliococcygeus. The pubococcygeus pulls the tail forwards, and iliococcygeus and ischiococcygeusmove the tail sideways. In human being, together with the assumption of upright position, the pubococcygeus and iliococcygeus jointly create the levator ani and ischiococcygeus lasts as coccygeus muscle.
Injury of pelvic diaphragm: The pelvic diaphragm could be injured (tearing of perineal body) during challenging childbirth. As a consequence it becomes weak and can no longer provide adequate support to the pelvic viscera. This may result in uterine prolapse and rectal prolapse.