The Pelvis

The pelvic cavity consists of the pelvic inlet, walls, and floor and contains elements of the urinary, gastrointestinal, and reproductive systems.

-  Inlet: S1, alae of sacrum, arcuate line, linea terminalis (pubic crest, pecten pubis, arcuate line), and pubic symphysis

-  Walls: obturator internus, piriformis, sacrospinous and sacrotuberous ligaments, greater and lesser sciatic foramina, sacrum, coccyx, ischium, pubis

-  Floor: levator ani (3 parts: iliococcygeus, pubococcygeus, and puborectalis), coccygeus, perineal membrane, muscles of deep perineal pouch

Apertures of the Pelvis

Aperture / Boundaries / Contents / Significance
Greater Sciatic Foramen / Greater sciatic notch, sacrotuberous and sacrospinous ligaments, and the Ischial spine, it is divided into 2 parts by the piriformis / Above piriformis: superior gluteal nerves and vessels
Below piriformis: inferior gluteal vessels and nerves, sciatic nerve, pudendal nerve, internal pudendal vessels, posterior femoral cutaneous nerves and the nerves to the obturator internus and quadrates femoris muscles / Communication between pelvic cavity and lower limb
Above the pelvic floor
Lesser Sciatic Foramen / Lesser sciatic notch, Ischial spine, sacrospinous and sacrotuberous ligaments / Pudendal nerve and internal pudendal vessels, tendon of obturator internus / Communication between gluteal region and perineum
Below pelvic floor
Obturator Canal / Obturator membrane, obturator muscles, superior pubic ramus / Obturator nerve and vessels / Communication between pelvic cavity and adductor region of thigh
Gap between pubic symphysis and perineal membrane / Dorsal vein of penis and clitoris / Communication between pelvic cavity and perineum
Pelvic Inlet / S1, alae of sacrum, arcuate line, linea terminalis, and pubic symphysis / Separates the true from the false pelvis, communication between the abdomen and the pelvic cavity
Pelvic Outlet / Pubic symphysis, bodies and inferior rami of pubis, rami of ischium, and the Ischial tuberosity, sacrotuberous ligament and coccyx / Terminal parts of the urinary and GI tracts, and the vagina / Area enclosed is the perineum

Male vs. Female Pelvis:

Characteristic / Male / Female
Pelvic Inlet / Heart-shaped, more distinct promontory of sacrum / Circular, broader alae of sacrum
Pubic Arch / 50-60⁰ / 80-85⁰
Ischial Spines / Prominent / Less prominent

Ligaments of the Skeletal Pelvis:

Ligament / Connection / Significance
Sacrospinous / Ischial spine and margins of sacrum and coccyx / Create Sciatic Foramina and stabilize the sacrum by resisting upward tilting
Sacrotuberous / Ischial tuberosity to the PSIS and dorsolateral sacrum and coccyx / Create Sciatic Foramina and stabilize the sacrum by resisting upward tilting
Iliolumbar / Transverse process of L5 to the ilium / Stabilize lumbosacral joints
Lumbosacral / Transverse process of L5 to the sacrum / Stabilize lumbosacral joints
Anterior Sacro-iliac / Runs anteriorly and inferiorly to the sacro-iliac joint / Transmit forces from the lower limbs to the vertebral column
Interosseous Sacro-iliac / Immediately posterosuperior to the sacro-iliac joint and fills the gap between the ilium and sacrum / Largest, strongest sacro-iliac ligament
Transmit forces from the lower limbs to the vertebral column
Posterior Sacro-iliac / Covers the interosseous sacro-iliac ligament / Transmit forces from the lower limbs to the vertebral column
Superior Pubic / Above the pubic symphysis
Inferior Pubic / Below the pubic symphysis

Muscles of the Pelvis:

Muscle / Attachments / Innervation / Action
Obturator Internus / Obturator membrane to greater trochanter / L5, S1: Nerve to obturator internus / Lateral rotation of extended hip, abduction of flexed hip
Piriformis / Anterior sacrum to greater trochanter / L5, S1, S2 / Lateral rotation of extended hip, abduction of flexed hip
Levator Ani / Posterior pubic bone, obturator internus, Ischial spine to perineal membrane, perineal body, around the anal canal, and anococcygeal ligament / Inferior rectal branch of pudendal nerve (S2-S4), and S4 ventral rami / Forms pelvic floor, supports pelvic viscera, maintains angle between rectum and anal canal, reinforces external anal sphincter, acts as vaginal sphincter
Coccygeus / Ischial spine and sacrospinous ligament to coccyx and sacrum / S3 and S4 anterior rami / Forms pelvic floor, supports pelvic viscera, pulls coccyx forward after defecation
External Urethral Sphincter / Inferior ramus of pubis and walls of deep perineal pouch to membranous part of urethra / Perineal Branches of Pudendal Nerve (S2-S4) / Compresses membranous urethra, relaxes during micturition
Deep Transverse Perineal / Ischial ramus to perineal body / Perineal Branches of Pudendal Nerve (S2-S4) / Stabilizes perineal body
Compressor Urethrae / Ischiopubic ramus to its partner anterior to urethra / Perineal Branches of Pudendal Nerve (S2-S4) / Accessory sphincter of the urethra
Sphincter Urethrovaginalis / Perineal body to its partner, surrounding the urethral and vaginal openings / Perineal Branches of Pudendal Nerve (S2-S4) / Accessory sphincter of urethra, may close the vagina
External Anal Sphincter / Anal canal and aperture to perineal body and anococcygeal body / Pudendal Nerve (S2-S4) and branches directly from S4 / Closes anal canal
Ischiocavernosus / Ischial tuberosity and ramus to crus of penis or clitoris / Pudendal Nerve (S2-S4) / Retain blood in penis or clitoris
Bulbospongiosus / Perineal body to perineal membrane, corpus cavernosum, bulb of vestibule, body of clitoris, bulbospongiosus / Pudendal Nerve (S2-S4) / Move blood into glans of penis or clitoris,
in men: remove residual urine from urethra, pulsatile emission of semen
Superficial Transverse Perineal / Ischial tuberosity and ramus to perineal body / Pudendal Nerve (S2-S4) / Stabilize the perineal body

Viscera of the Pelvis:

-  Rectum and Anal Canal: the rectum is continuous with the sigmoid colon at S3 and below at the anal canal as it penetrates the pelvic floor

-  Ureters: enter the pelvic cavity anterior to the bifurcation of the common iliac artery. They are crossed in the pelvis by the ductus deferens or uterine artery

-  Bladder: most anterior pelvic viscera, expands into abdominal cavity when full. Consists of a apex (toward top of pubic symphysis, connected to median umbilical ligament [urachus]), base (faces posteroinferiorly, smooth mucosa, contains trigone), and the inferolateral surfaces (cradled between levator ani and obturator internus muscles). The neck of the bladder is the most inferior and fixed area anchored to the pubic bones by pubovesical or puboprostatic ligaments

-  Urethra: begins at base of bladder and ends with external opening in perineum

o  Women: 4cm long and passes inferiorly through pelvic floor and into perineum, passing through deep perineal pouch and perineal membrane before opening into vestibule between labia minora. Skene’s glands are associated with the lower end of urethra.

o  Men: 20cm long and passes through prostate, deep perineal pouch, perineal membrane, and enters the root of the penis. The male urethra is divided into 4 parts:

- Preprostatic: 1cm, internal urethral sphincter (prevents semen from flowing backward into bladder).

-Prostatic: 3-4cm, contains urethral crest, prostatic sinus, seminal colliculus, and prostatic utricle. Connection between urinary and reproductive tracts occurs here.

-Membranous: narrow, passes through the deep perineal pouch where it is surrounded by the external urethral sphincter (skeletal muscle).

-Spongy: surrounded by erectile corpus spongiosum, forms a bulb at the end of the penis called the navicular fossa. The bulbourethral glands enter into the spongy urethra. Vulnerable to damage during catheterization.

The Perineum: inferior to the floor of the pelvic cavity

-  Contains: Terminal openings of the GI and urinary systems, External openings of reproductive tract, and Roots of the external genitalia

-  Bounded by: the pubic symphysis, coccyx, ischiopubic rami (Anterolateral), and sacrotuberous ligaments (posteriorly), levator ani (roof)

-  Pudendal nerve (S2-S4) and Pudendal artery are main nerve and artery of the region

-  2 Triangles: divided by imaginary line between the two Ischial tuberosities

o  Urogenital: anterior triangle, in the horizontal plane, contains openings of the urinary systems and reproductive systems (in the Urogenital hiatus), the perineal membrane anchored to the perineal body, the superficial perineal pouch (contains erectile fibers), and this triangle functions to anchor the external genitalia (via the perineal membrane and deep perineal pouch)

o  Anal : posterior triangle, faces posteriorly, contains the anus and the external anal sphincter (3 skeletal muscle parts: deep, superficial, and subcutaneous)

-  Ischio-anal Fossae: Inverted wedge shaped gutters between the levator ani muscles, deep perineal pouch, and the adjacent pelvic walls (ischium, obturator internus, and sacrotuberous ligament).

o  The anterior recesses project into the Urogenital triangle superior to the deep perineal pouch

o  Allow movement of the pelvic diaphragm and expansion of the anal canal during defecation

o  Normally filled with fat

Layers of Pelvic Floor: Deep to Superficial

Structure / Contents
1 / Levator ani and coccygeus muscles / Skeletal muscle
2 / Superior fascia / Ischio-anal fossae and recesses (fat)
3 / Deep Perineal Pouch / External urethral sphincter, sphincter urethrovaginalis, compressor urethrae, deep transverse perineal muscles, bulbourethral glands
4 / Perineal Membrane / Fibrous membrane
5 / Superficial Perineal Pouch / Erectile structures that form the penis or clitoris, bulbs of vestibule, glans clitoris, corpus spongiosum (proximal part is bulb of penis)
skeletal muscles: ischiocavernosus, bulbospongiosus, superficial transverse perineal
6 / Inferior (superficial) fascia / A membranous deep layer, Colles’ fascia , which is attached to the perineal membrane and ischiopubic rami (it does not extend into the anal triangle or into the thigh). It defines the external limits of superficial perineal pouch and enters the scrotum/labia and extends around the body if the penis/clitoris
*Because this layer is continuous with the abdomen, infectious materials that accumulate in the superficial perineal pouch can track out of the perineum and enter the lower abdominal wall*

Male Reproductive System:

Structure / Location / Function / Key Features
Testis / Inside scrotum, attached to abdominal wall by spermatic cords / Produce sperm cells in seminiferous tubules / Tunica vaginalis, tunica albuginea, rete testis, mediastinum testis
Epididymis / Posterolateral side of testes / Stores sperm as they mature before ejaculation / Head (efferent ductules), (true epididymis) body and tail
Ductus Deferens / Scrotum, inguinal canal, bends medially around inferior epigastric a., crosses external iliac v. and a. , pelvic cavity, crosses ureter, inferomedially along bladder, anterior to rectum, and enters duct of seminal vesicle / Transports sperm from the tail of the epididymis to the ejaculatory duct / Very long
Ejaculatory Duct / Through prostate gland / Carries secretions of ductus deferens and seminal vesicles into urethra / Penetrates prostate to enter urethra
Urethra / From neck of bladder to the external urethral opening in tip of penis / Conducts urine from bladder to outside of body / 4 parts: preprostatic, prostatic, membranous, and spongy
Penis / Outside of body in pubic region, attached to the pubic arch and anchored to the perineal membrane / Conducts urine and semen / Copulatory organ Erectile tissue, composed of 2 corpora cavernosa and a corpus spongiosus. As a bulb, roots (crura), body , and glans
Prostate Gland / Inferior to bladder, posterior to pubic symphysis, and anterior to rectum / Contributes secretions to semen / Surrounds urethra
Seminal Vesicles / Between bladder and rectum / Contributes significant secretions to semen / Accessory gland
Bulbourethral Glands / Within deep perineal pouch, lateral to membranous urethra / Contribute to lubrication of the urethra and pre-ejaculatory emissions / Ducts open into spongy urethra at the root of the penis

Female Reproductive System:

Structure / Location / Function / Key Features
Ovaries / Adjacent to lateral pelvic wall just inferior to pelvic inlet / Produce egg cells / Suspended by mesovarium, connected to body wall by suspensory ligament and to uterus by ligament of ovary
Uterine Tubes / Project laterally from body of uterus, passing superiorly over ovaries / Conduct egg cells into body of uterus / Enclosed by mesosalpinx, Have fimbriae, infundibulum, and ampulla (usual site of fertilization)
Uterus / Midline, between bladder and rectum / Holds developing fetus during pregnancy / Consists of a fundus, body, and cervix (canal forms external and internal os, and it forms fornix at junction with vaginal wall)
Vagina / Extends from cervix, through pelvic floor, and perineum to the outside of the body (introitus). Between bladder and rectum. / Accepts semen deposited during intercourse, serves as birth canal during childbirth / Copulatory organ in women
Clitoris / Beneath pubic symphysis and the underside of the ischiopubic rami and anchored to the perineal membrane / Great sensitivity / Composed of the glans and the corpora cavernosa: has a root and a body
Greater Vestibular Glands / Located posterior to the bulbs of the vestibule on either side of the vaginal opening / Produce lubricating secretions during arousal / Also called Bartholin’s Glands, found in superficial perineal pouch
Para-urethral Glands / Located on either side of the urethra, its ducts open into the vestibule at the lateral margins of the urethral opening / Produce lubricating secretions / Also called Skene’s Glands

Erectile Tissues:

-  Erection is a vascular event mediated by the parasympathetic fibers of the pelvic splanchnic nerves (anterior rami of S2-S4)

-  The pelvic splanchnics branch from the hypogastric plexus and pass through the deep perineal pouch and perineal membrane to innervate the erectile structures in the superficial perineal pouch

-  Stimulation of these nerves causes branches of the internal pudendal arteries to relax, allowing blood to fill the penis or clitoris, causing erection

-  Branches of the Pudendal nerve (S2-S4) carry sensory nerves from the penis/clitoris

Fascia, Peritoneum and Ligaments: continuation of extraperitoneal connective tissue of the abdomen

Fascia / Location/Function
Rectovaginal / Separates the posterior surface of the vagina from the rectum
Pubocervical Ligament / Stabilize the uterus in the pelvic cavity
Transverse Cervical Ligament / (Cardinal Ligament) Stabilize the uterus in the pelvic cavity
Uterosacral Ligament / Stabilize the uterus in the pelvic cavity
Vesico-uterine Pouch / Between the bladder and the uterus
Pouch of Douglas (recto-uterine) / Between uterus and rectum
Recto-uterine Folds / Raised ridge of peritoneum on each side near the base of the recto-uterine pouch. Covers the Uterosacral ligaments.
Broad Ligament / Runs from lateral pelvic walls to the uterus and covers the ovaries, uterine tubes, round ligaments and ligaments of ovaries (remnants of gubernaculum)
Prostatic / Contains and surrounds the prostatic plexus of veins
Rectovesical Pouch / Occurs between the bladder and the rectum
Rectovesical Septum / Separates the posterior surface of the prostate and the base of the bladder from the rectum
Suspensory Ligament of Penis / Supports base of body of penis, attached superiorly to pubic symphysis
Fundiform Ligament of Penis / Supports body of penis, attached to the linea alba of the anterior abdominal wall and splits into 2 bands that unite under the penis

Important Nerves in the Pelvis: