Pelvic Floor Anatomy

Original Editor - Laura Ritchie

Top Contributors -

Laura Ritchie, Venus Pagare, Siobhán Cullen, Scott Buxton and Evan Thomas

Contents

The Pelvic Floor - Overview and Function [1]

The pelvic floor is an area of muscle and connective tissue that spans the area underneath the pelvis, separating the pelvic cavity above from the perineal region below. It provides support to the pelvic viscera including the bladder, intestines and uterus (in females). It also assists with continence through control of the urinary and anal sphincters. It facilitates birth by resisting the descent of the presenting part, causing the fetus to rotate forwards to navigate through the pelvic girdle. Finally, it helps to maintain optimal intra-abdominal pressure.

Osteology, Ligaments and Fascia

Osteology

  • The bony pelvis is composed of sacrum, ilium, ischium, and pubis.
  • It is divided into the false (greater) and true (lesser) pelvis by the pelvic brim.
  • The sacral promontory, the anterior ala of the sacrum, the arcuate line of the ilium, the pectineal line of the pubis and the pubic crest that culminates in the symphsis pubis.
  • The shape of the female bony pelvis can be classified into four broad categories: gynecoid, anthropoid, android, and platypelloid.


Female Pelvic Cavity
Female Pelvic Cavity
Ligaments and Pelvic Fascia[2]

Ligaments of the Pelvis

  • Iliolumbar ligament - from tip of transverse process of L5 to posterior aspect of inner lip of iliac crest; strengthens the lumbo-sacral joint.
  • Lateral lumbosacral ligament
  • Sacrotuberous ligament- from sacrum to tuberosity of the ischium
  • Sacrospinous ligament - from ischial spine to lateral margins of the sacrum

Sacroiliac Ligaments

  • Ventral/Anterior sacroiliac ligament- from antero-lateral aspect of sacrum to auricular surface of the ilium
  • Dorsal/Posterior sacroiliac ligament
    • Upper portion (short posterior sacroiliac ligament) - from 1st and 2nd transverse tubercles of sacrum to tuberosity of ilium
    • Lower portion (long posterior sacroiliac ligament) - from 3rd transverse tubercle of sacrum to posterior superior iliac spine (PSIS)
  • Interosseous sacroiliac ligament- lies deep to posterior SI ligament and runs between the tuberosities of the sacrum and ilium

Sacrococcygeal Ligaments

  • Ventral/Anterio sacrococcygeal ligament -from anterior surface of sacrum to the front of the coccyx; continuation of the anterior longitudinal ligament of the spine
  • Dorsal sacrococcygeal ligament
    • Deep portion - from inside sacral canal at the 5th sacral segment to the dorsal surface of the coccyx; continuation of the psoterior longitudinal ligament of the spine
    • Superficial portion - from free margin of sacral hiatus to dorsal surface of the coccyx; corresponds with the ligamentum flavum of the spine
  • Lateral sacrococcygeal ligament - from inferior lateral angle of the sacrum to the transverse process of the 1st coccygeal vertebra

Pubic Symphysis Ligaments

  • Superior pubic ligament - runs between pubic tubercles
  • Inferior pubic ligament (aka arcuate public ligament) - runs between inferior pubic rami and blends with fibrocartilagnous disc of pubic symphysis
  • Anterior pubic ligament
  • Posterior pubic ligament - membranous structure which blends with periosteum

Endopelvic Fascia - Ligaments

  • Female: Pubovesical ligaments - attach bladder to pubic symphysis
  • Male: Puboprostatic ligaments - attach bladder to pubic symphysis
  • Sacrogenital - these are thickenings of the fascia, not specific ligaments
  • Uterosacral ligaments - attach upper vagina, upper portion of cervix and uterus to the 3rd sacral vertebra
  • Cardinal ligaments (aka Mackenrodt's) - attach upper vagina, cervix and uterus to the side walls of the pelvis
  • Round ligaments - attach uterus to mons pubis
  • Broad ligaments - attach uterus to medial aspect of the ilium
  • Uracus ligament - attaches bladder to umbilicus (formed from the remnants of the umbilican vein)

Penile Suspensory Ligaments

  • Penile Suspensory ligament - attaches to anterior aspect of interpubic disc and divides in two to sling around the penis
  • Fundiform ligament - extends from inferior linea alba and divides to wrap around the penis

Parietal pelvic fascia - lines the internal surface of the muscles of the pelvic floor and walls

Visceral pelvic fascia - invests each pelvic organ

The parietal and visceral fascia are continuous where organs penetrate the pelvic floor. They thicken to form the arcus tendineus, arches of fascia running adjacent to the viscera from the pubis to the sacrum.

Endopelvic fascia* - meshwork of smooth muscle, ligaments, blood vessels and connective tissue lying between the parietal and visceral fascia, sometimes condensing to form fibrous fascial septa which separate and suspend the organs.

  • Anatomists use the name subserous fascia whereas surgeons refer to this layer of retroperitoneal fascia as endopelvic fascia.
  • Hypogastric sheath - separates retropubic space from presacral space; conduit for vessels and nerves
  • Transverse cerical (cardinal) ligaments - part of hypogastric sheath; runs from lateral pelvic wall to uterine cervix and vagina; transmits uterine artery and provides passive support for the uterus
  • Vesicovaginal septum
  • Rectovesical septum
  • Rectovaginal septum

Pelvic Floor Myology [2][1]

Pelvic Floor
Pelvic Floor
Pelvic Floor Muscles
Pelvic Floor Muscles
Sacral and Coccygeal Plexus
Sacral and Coccygeal Plexus

Layer One - Urogenital Triangle

  • Bulbocavernosus (bulbospongiosus in men)
  • Ischiocavernosus
  • Superficial transverse perineal
  • External anal sphincter

Layer Two - Urogenital Diaphragm

The urogenital diaphragm, also called the triangular ligament, is a strong, muscular membrane that occupies the area between the symphysis pubis and ischial tuberosities and stretches across the triangular anterior portion of the pelvic outlet.  The urogenital diaphragm is external and inferior to the pelvic diaphragm.

  • Urethral sphincter (sphincter urethrae)
  • Compressor urethrae
  • Sphincter urethral vaginalis
  • Deep transverse perineal
  • Perineal membrane

Layer Three - Pelvic Diaphragm

The pelvic diaphragm is a wide but thin muscular layer of tissue that forms the inferior border of the abdominopelvic cavity.  Composed of a broad, funnel-shaped sling of fascia and muscle, it extends from the symphysis pubis to the coccyx and from one lateral sidewall to the other.

  • Levator ani (pubococcygeus aka pubovisceral, pubovaginalis, puboanalis, puborectalis, iliococcygeus)
  • Coccygeus
  • Piriformis
  • Obturator internus
  • Arcus tendinous of levator ani
  • Arcus tendinous fasciae pelvis

Perineal Body - a fibromuscular structure located between the vagina/testicles and the anus, attaching to the sides of the ischiopubis rami by the deep transverse perineal muscle. It is know as the central tendon of the pelvis because many pelvic floor structures intersect with the perineum at this structure.

Other muscles related to pelvic dysfunction

  • Psoas
  • Rectus abdominus
  • Transversus abdominus

[3] [4]



Muscle Origin Insertion Action Innervation
Bulbospongiosus

Male: median raphe, ventral surface of bulb of penis

Female: perineal body then divides to wrap around vagina

Male: Corpora spongiosum and cavernosa, fascia of bulb of penis

Female: fascia of corpus cavernosa

Male: Empties urethra, acts as sphincter to compress bulb of penis, assists erection, propels semen down urethra

Female: empties urethra, acts as a sphincter to reduce lumen of vagina and assists erection of clitoris

Deep branch of perineal nerve (branch of pudendal nerve)
Ischiocavernosus Ischial ramus and tuberosity Crus of penis or clitoris Maintains erection of penis or clitoris by compression of outflow veins Deep branch of perineal nerve (branch of pudendal nerve)
Superficial transverse perineal Ischial tuberosity Perineal body Reinforces action of deep transverse perineal muscle to stabilize perineal body Deep branch of perineal nerve (branch of pudendal nerve)
External anal sphincter Perineal body and encircles anal canal
Coccyx Part of voluntary sphincter of anal canal Inferior rectal (anal) nerve
Sphincter urethrae Inferior aspect of pubic ramus and ischial tuberosity Surrounds urethra; in females, some fibres also enclose the vagina Controls flow of urine through urethra; also compresses vagina in females Deep branch of perineal nerve (branch of pudendal nerve)

Compressor urethrae

(only in females)

Ischiopubic ramus
Vaginal wall
Compresses ventral wall of the urethra

Sphincter urethral vaginalis

(only in females)

Vaginal walls
Ventral surface of urethra
Compresses ventral wall of the urethra

Deep transverse perineal Inner aspect of ischiopubic ramus Median raphe (male), perineal body and external anal sphincter Fixes perineal body, supports the function of levator ani and sphincter urethra
Deep branch of perineal nerve (branch of pudendal nerve)
Perineal membrane (fascial thickening, not a muscle) Fasical attachments at pubic symphysis Fascial attachments at ischial spine Suspensory ligament that provides extra support to prevent descent of perineal body

Levator Ani (Pubococcygeus) Dorsal surface of pubis and fascia of obturator internus
Anococcygeal body between tip of coccyx and the anal canal
Voluntary spincter of the anal canal
Nerve to levator ani (branches of S4), inferior rectal nerve (from pudendal nerve - S3, S4), coccygeal plexus
Levator Ani (Puborectalis) Dorsal surface of pubis and  fascia of obturator internus Unites with its partner to make a U-shaped sling around the rectum Controls defecation by pulling anorectal junction forward Nerve to levator ani (branches of S4), branch of pudendal nerve (S2-4)
Levator Ani (Pubovaginalis)


Nerve to levator ani (branches of S4), branch of pudendal nerve (S2-4)
Levator Ani (Iliococcygeus) Posterior aspect of arcus tendineus levator ani and the ischial spine Anococcygeal body and the coccyx Helps to support pelvic viscera and lateral coccyx Nerve to levator ani (branches of S4), inferior rectal nerve (from pudendal nerve - S3, S4), coccygeal plexus

Ischiococcygeus* (Coccygeus)

*some consider this more of a ligament than a muscle

Ischial Spine Lower two sacral and upper two coccygeal spinal segments, blends with sacrospinous ligament on its external surface Supports pelvic viscera, flexion of coccyx, stabilizes sacro-iliac joint Anterior rami of S4 and S5
Piriformis Pelvic surface of sacrum, passes through greater sciatic foramen
Superior border of the greater trochanter of the femur
Hip external rotation, assist with hip abduction if hip is flexed
Anterior rami of S1 & S2
Obturator Internus Internal or pelvic surface of the obturator foramen
Medial surface of the greater trochanter of the femur
Hip external rotation, assists with hip abduction if hip is flexed
Nerve to obturator internus (L5, S1, S2)
Arcus tendinous levator ani (fascial thickening, not a muscle) Fasical attachments at pubic symphysis Fascial attachments at ischial spine Suspensory ligament that provides extra support to prevent descent of perineal body
Arcus tendinous fasciae pelvis (fascial thickening, not a muscle) Fasical attachments at pubic symphysis Fascial attachments at ischial spine Suspensory ligament that provides extra support to prevent descent of perineal body

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References

  1. 1.0 1.1 Wikipedia. Pelvic floor. http://en.wikipedia.org/wiki/Pelvic_floor. (accessed 6 April 2014).
  2. 2.0 2.1 Netter Anatomy. Pelvis and perineum: pelvic floor and contents. http://www.netteranatomy.com/anatomylab/subregions.cfm?subregionID=R53. (accessed 6 April 2014).
  3. Anatomy Zone. Pelvic Floor Part 1 - The Pelvic Diaphragm - 3D Anatomy Tutorial. Available from: http://www.youtube.com/watch?v=P3BBAMWm2Eo [last accessed 11/04/14]
  4. Anatomy Zone. Pelvic Floor Part 2 - Perineal Membrane and Deep Perineal Pouch - 3D Anatomy Tutorial. Available from: http://www.youtube.com/watch?v=q0Ax3rLFc6M[last accessed 11/04/14]