PELVIS OSTEOLOGY AND BORDERS

Primary Bones of Pelvis:

Sacrum

Ala wings jutting laterally and articulating with the ilium, at the sacroiliac joint.

The obturator nerve and lumbosacral trunk enter the pelvis at the sacroiliac joint.

Sacral Promontory Anterosuperior most aspect, connected to LV5 (final lumbar vertebrae) at the lumbosacral joint.

Coccyx Bone at the posterior tip of the sacrum.

Two Coxal Bones = the union of ilium, ischium, and pubic, united in the acetabular (thigh joint) region.

Ilium

ASIS, AIIS, PSIS

Tubercle -- on the lateral aspect of the iliac crest.

Greater and Lesser Sciatic Notches -- on the posterior internal lips of the iliac crest.

Greater Sciatic Notch formed by curvature of the inferior part of the ileum.

Ischium

Ischial Spine

Ischial Tuberosity -- Posterior aspect of ischium, where we sit on our ass.

Ischiopubic Rami

Form the lateral boundaries of the pubic arch, or subpubic angle.

The location of the urogenital diaphragm.

Pubis

Pubic Tubercle -- the anteroinferior aspect of the inguinal ligament (where it attaches). The other point of attachment is the ASIS.

Pubic Crest

Pectin Pubis

Superior and Inferior Pubic Rami

Obturator Foramen formed in between them, where the obturator nerve leaves the pelvis and enters the thigh.

Obturator Groove: The anterior aspect of the obturator foramen, near the pectineal line, where the obturator nerve passes from the

pelvis to the thigh.

Pubic Body

Symphysis Pubis -- anterior most aspect, connecting two pubic bones, under hormonal control by relaxin. It can relax the fibers during childbearing /

pregnancy.

Sacrotuberous Ligament: Tough ligament between sacrum and ischial tuberosity.

Starts on lateral aspect of the posterior surface of the sacrum and extends down to the ischial tuberosity.

Greater Sciatic Foramen is formed from both sacrotuberous and sacrospinous ligaments. The piriformis muscle moves along the anterior surface of

sacrum, through the greater sciatic foramen, and down onto the femur.

Sacrospinous Ligament: Tough ligament between sacrum and ischial spine.

It is anterior to the sacrotuberous ligament.

It extends posterolaterally to connect to the ischial spine.

Lesser Sciatic Foramen: Also formed from both sacral ligaments.

Pathway of Pudendal Canal: It passes out the Greater Sciatic Foramen, over the Ischial Spine, and back into the lesser sciatic foramen, to travel on the

medial aspect of the ischial ramus.

Orientation of the Pelvic Bone: It is tilted forward such that the Anterior Superior Iliac Spine and the Pubic Tubercle are in the same frontal plane.

It is oriented such that the urogenital diaphragm, connected to the ischiopubic rami, is in a horizontal position.

Pelvic Brim: The bony borders of the pelvic diaphragm, separating the false (major) pelvis from the true (minor) pelvis.

Linea Terminalis: Term for the bony line going around the brim.

Promontory of Sacrum -- anterior most part.

Iliopectineale Line = the ridge going over the ileum and pecten pubis, defining the medial aspect of the pelvic brim.

Things that pass over the pelvic brim:

The psoas muscle

The ureters

Gonadal arteries

Superior rectal artery

Pelvic Diaphragm: It is the inferior border of the pelvis, separating the pelvis from the perineum. It supports the pelvic organs.

Genital Hiatus: A hole in the pelvic diaphragm, where there is no muscle, just fascia. It overlies the superior part of the urogenital diaphragm. The following

structures go through it.

Urethra

Vagina (female)

Levator Ani Muscles: Attaches to the tendinous arch (arcus tendineus) of the levator ani. It extends all the way from the pubis back to the ileum, and

sweeps medially back to the coccyx.

Ileococcygeus Muscle: The posterolateral part of the levator ani muscle, associated with the ilium.

Pubococcygeus Muscle: The anteromedial part of the levator ani muscle, associated with the pubis.

Puborectalis Muscle: The most medial part of the pubococcygeus muscle, going around the rectum. Puborectal Sling are the muscle fibers of the

puborectalis that swing around the rectum, holding it in place.

Pubovaginalis / Puboprostatic: There is also a pubovaginalis part in the female, and less prominent puboprostatic part in the male.

Obturator Internus Muscle: The muscle underlying the obturator membrane, which covers the obturator foramen.

Coccygeus Muscles: Laterally attaches to the ischial spine, and medially attaches to the lateral aspect of the sacrum.

Arcus Tendineus: The line of attachment between the obturator internus muscle and levator ani. Okay, not a line, but rather a sweep of fascia.

FUNCTION OF THE PUBORECTAL SLING: It creates an angle between the rectum and anal canal, which allows you to retain fecal matter. The angle is almost

90, and the anal canal points down and posteriorly.

Urogenital Diaphragm: The part of the pelvic diaphragm that extends medially, between the ischiopubic rami.

Through and through, it is located inferior to the pelvic diaphragm.

Anteriorly, it encloses the sphincter urethrae muscle.

Posteriorly, it encloses the deep transverse perianal muscle.

Anteriorly, it encircles the urethra on either side. The anterior recess of the anal fossae becomes smaller and smaller as you move anteriorly.

It encloses the Deep Perineal

Pelvic Roof / Peritoneum: The pelvis roof is defined by the inferior limit of peritoneum, coming down from the abdomen.

Peritoneum covers the anterior aspect of rectum, then reflect off the uterus (in female), forming the Rectouterine Pouch (of Douglas). That is the inferior

most peritoneal recess of the abdomen.

Male analogous structure is rectovesical recess, reflection between the rectum and seminal vesicles, which are directly posterior to the bladder.

The peritoneum then covers the uterus and uterine tubes, before going back up the anterior abdominal wall.

Peritoneum does not cover all of the rectum.

Central Tendon of the Perineum (Male), or Perineal Body (female): The junction of most of the musculature of the pelvic diaphragm. It is the central

support for pelvic diaphragm, which in turn supports the pelvis.

If it is damaged, incontinence results.

It is an attachment point for both the perineum and the pelvis.

Point where fibers from pelvis unite with those of external anal sphincter.

It is the posterior attachment point of the urogenital diaphragm.

Point where external genitalia (corpora) muscles attach.

Point where superficial transverse perineal muscles attach.

Endopelvic Fascia: The name of the visceral fascia in the pelvis.

OBGYN STUFF:

Pelvic Inlet: Line from upper part of pubic symphysis back to the sacral promontory.

Pelvic Outlet: Line from the lower part of pubic symphysis back to tip of coccyx.

True Conjugate Diameter: Measured along the pelvic inlet.

Diagonal Conjugate Diameter: Measured from the bottom of the pubic symphysis back to the sacral promontory.

Obstetrical Conjugate Diameter: The smallest opening, from the widest part of the pubic symphysis, back to the sacral promontory.

Perineum: The area inferior to the pelvic and urogenital diaphragms.

Structures in perineum:

External genitalia.

Anal canal and anal sphincters

Ischiorectal and ischioanal fossa.

Urogenital Triangle: Triangle defining urogenital region of th perineum.

Anterior aspect (apex of triangle): pubic symphysis

Lateral aspects: Ischial tuberosities

Posterior aspect: tip of coccyx bone.

Anal Triangle: Triangle defining the anal region of the perineum.

Apex of anal triangle = the tip of the coccyx bone.

Sides of anal triangle = the sacrotuberous ligaments and the gluteus maximus.

Base of anal triangle = the ischial tuberosities.

Boundaries between the triangles: A line going from one ischial tuberosity to the other one defines the border between the two perineal triangles. The

perineal body is in the middle of that line.

The line also marks the inferior border of the urogenital diaphragm.

Superficial Transverse Perineal Muscle goes between the anal and UG triangles, and converges on the perineal body.