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Learning Objectives

  • Location of pelvic diaphragm

  • Muscles forming pelvic diaphragm

  • Openings in the pelvic diaphragm

  • Functions of pelvic diaphragm

  • Disposition of pelvic fascia

Pelvic diaphragm  separates the cavity of true pelvis from Perineum

 

Inferior aperture of true pelvis (pelvic outlet is closed by pelvic diaphragm and urogenital diaphragm.

 

Pelvic diaphragm

  • Limits  the inferior aspect of pelvic cavity.

  • Is Composed of funnel-shaped sling of fascia and muscle.

  • Extends from  symphysis pubis to  coccyx and from one lateral side wall of pelvis  to the other.

 

Urogenital diaphragm

  • is a  muscular membrane that occupies the area between the symphysis pubis and ischial tuberosities and stretches across the triangular anterior portion of the pelvic outlet

  • It is external and inferior to the pelvic diaphragm.

  • It separates pelvis from the perineum (region which includes the genitalia and anus)

 

  • Is formed by right and left levator ani and coccygeus muscles enclosed in superior and inferior layers of pelvic fascia.

 

  • Structures piercing pelvic diaphragm

    •  The anus

    •  The urethra

    •  The vagina (in females)

 

 

 

Pelvic Diaphragm 

Pelvic Diaphragm Openings

 There are two openings/gaps/hiatus in the   pelvic diaphragm to allow the structures to pass from pelvis to perineum

  1. Urogeninital hiatus – An anteriorly situated gap, which allows passage of  urethra (and  vagina in females).

  2. Rectal hiatus – A centrally positioned gap, which allows passage of the anal canal.

Between the urogenital hiatus and the anal canal lies a fibrous node known as the perineal body which joins the pelvic floor to the perineum ( for its clinical relevance in females refer to clinical anatomy)

Pelvic diaphragm

 Levator Ani and Coccygeus Muscles

 

Levator ani and Coccygeus (Ischiococcygeus) with corresponding muscles of the opposite side along with the superior and inferior pelvic fascia   forms the pelvic diaphragm.

 

  • Parts of Levator Ani 

    • Puborcoccygeus

    • Iliococcygeus

  • ​Coccygeous (Ischicoccygeus)

    • is posterior to levator ani.

 

 

 

 

  • They originate from ( green line)

    • Pelvic surface of the body of the pubis

    • Arcus tendinous: Tendinous arch, formed by  thickening of the parietal pelvic fascia over the obturator internus muscle.

    • Ischial spine.

  • The muscle fibers downwards and backwards to unite in the midline with fibers of the opposite side.

 

 

 

Arcus tendinous

Note the origin and placement of levator ani muscle

 Levator Ani and Coccygeus Muscles

 

 

  • They insert onto

    •  Perineal body (Central    perineal tendon)

    •  The wall of the anal canal

    • Anococcygeal ligament

    • Coccyx.​

Subdivisions of Pubococcygeus

 

 Pubococcygens encircles

  In females :  urethra, vagina and  anus

  In males : urethra, prostate and anus.

                                    

  • Anterior fibers:

    • In males : Levator prostatae are the anterior fibres that  run inferior to the prostate (part of this muscle surrounding the urethra is peri-urithralis muscle).

    • In females : Pubovaginalis is attached to the vaginal wall (part of this muscle surrounding the urethra is peri-urithralis muscle).

  • Middle fibers:

    •  Puborectalis, is the part that loops around the anorectal junction

  • Posterior fibers:

    • Pubococcygeus

Pubovaginalis

Puborectalis

You can watch the video to understand the concept of pelvic diaphragm

Pelvic fascia


Pelvic fascia covers both the surface of the pelvic diaphragm forming superior and inferior layers. The inferior layer of the pelvic fascia is called the anal fascia. Which forms the medial wall of ischiorectal fossa . The superior layer is loosely arranged between the peritoneum and the pelvic floor. The loose nature of the fascia favors a rapid spread of pelvic cellulites & supra levator abscess develops.

  

Functions of Pelvic Diaphragm

  • Supports  pelvic viscera - resisting inferior thrust during e.g. coughing, deep expiration etc.

  • Raise the pelvic floor, assisting the anterior abdominal wall muscles in compressing the viscera, e.g. in coughing, deep expiration, vomiting, urinating.

  •  Support of the prostate and the vagina providing sphincteric action of the latter, and urethra.

  • The puborectalis holds the anorectal junction anteriorly, increasing the angle between the rectum, and anal canal. This prevents passage of feces from the rectum, into the anal canal when defecation is not desired, or is inconvenient.

  • Coccygeus muscle  support the coccyx, and pull it anteriorly, after it has been pressed posteriorly during child-birth.

 

 

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