204_T2L1_PelvicRegion_LR_Updated12424 (1).pdf

Anatomy of the Pelvic Region Mr Luke Reid ([email protected]) Deputy Head of Anatomy Learning outcomes By the end of this lecture, the successful student should be able to: 1. Describe the structures/landmarks of the lesser and greater pelvis 2. Describe the bones of the pelvis and its principal fo...

Anatomy of the Pelvic Region Mr Luke Reid ([email protected]) Deputy Head of Anatomy Learning outcomes By the end of this lecture, the successful student should be able to: 1. Describe the structures/landmarks of the lesser and greater pelvis 2. Describe the bones of the pelvis and its principal foramina 3. Describe the muscles that form the wall of the pelvis and the pelvic floor 4. Describe the vessels of the pelvis 5. Describe the somatic and autonomic innervation of the pelvis Recommended reading: - Gray’s Anatomy for Students - Moore’s Clinically Oriented Anatomy The Human Pelvis 2x Hip bones (aka os coxa, innominate) Functions: Bear and transfer weight between lower limbs and trunk, upper limbs and head. Contain and protect pelvic viscera Support abdominopelvic viscera Provide attachment of external genitalia Provide attachment for muscles of pelvic floor and lower limbs Sacrum Coccyx Osteology of the pelvis Sacral promontory Innominate (hip) bone - Formed by ilium, ischium, pubis Ala of sacrum ASIS Ilium ASIS Ischial spine AIIS AIIS Ischial tuberosity Obturator foramen Anatomical position Pubic crest Greater sciatic notch Ischial spine Lesser sciatic notch Pubic tubercle Ischium Ischial tuberosity Pubis Ischiopubic ramus Joints and ligaments of the Pelvis Pubic symphysis Relaxin produced by ovaries and placenta loosens pelvic ligaments during pregnancy in preparation for labour Primary joints of the pelvis: Sacroiliac joints (posteriorly) Fibrous and synovial joint elements Pubic symphysis (anteriorly) Secondary cartilaginous joint with fibrocartilaginous disc Anterior sacroiliac ligaments ANTERIOR VIEW OF PUBIS Posterior sacroiliac ligaments Sacroiliac joint Synovial portion Fibrous portion ANTERIOR VIEW POSTERIOR VIEW MEDIAL VIEW LATERAL VIEW OF SACRUM Pelvic ligaments and foramina Greater sciatic foramen - Allow passage of structures from the lesser pelvis to gluteal and perineum - Structures include: Pudendal nerve, internal pudendal vessels, superior and inferior gluteal neurovasculature, sciatic nerve Lesser sciatic foramen - - Allow passage of structures to the perineum after passing through greater sciatic foramen Sacrospinous ligament - From sacrum to ischial spine Structures include: Pudendal nerve, internal pudendal vessels, nerve to obturator internus Sacrotuberous ligament - From sacrum to ischial tuberosity MEDIAL VIEW Pelvic apertures Pelvic inlet (brim) Sacral promontory Pelvic outlet Ala of sacrum Pubic symphysis Ischiopubic ramus Arcuate line Pectin pubis Pubic symphysis Ischial tuberosity Pubic crest * Terminal line = arcuate line, pectin pubis, pubic crest Sacrotuberous ligament Coccyx Sexual dimorphism of the Pelvis Bony Pelvis Male Female General Thick, Heavy Thin, Light Greater Pelvis Deep Shallow Lesser Pelvis Narrow, Deep Wide, Shallow Pelvic Inlet Heart Shaped Oval Pelvic Outlet Small Large Pubic Arch Narrow Wide Obturator Foramen Round Oval FEMALE Pubic arch 80° - 85° MALE Pubic arch 50° - 60° What are the pelvic and perineal regions? Greater pelvis Abdominopelvic cavity is divided into: Abdominal cavity Pelvic cavity - Pelvis region above the pelvic inlet - Contains abdominal viscera Lesser pelvis Perineum is located between: Pelvic floor Skin between the thighs - Pelvis region below the pelvic inlet - Aka pelvic cavity - contains reproductive, urinary, GI viscera, and deep portion of perineum Pelvic cavity FEMALE LOWER URINARY TRACT REPRODUCTIVE TRACT MALE GASTROINTESTINAL TRACT LOWER URINARY AND REPRODUCTIVE TRACT GASTROINTESTINAL TRACT N.B. – The visceral contents of the pelvic cavities are covered in separate lectures. Pelvic cavity Sacral plexus and branches of internal iliac artery The pelvic cavity a space bounded by bony, muscular and ligamentous structures Boundaries: Antero-inferior wall - bodies and rami of public bones Lateral wall - right and left hip bones, obturator internus muscle, obturator fascia Posterior wall - sacrum, piriformis muscle and sacral plexus Pelvic floor - pelvic diaphragm = coccygeus and levator ani muscles. Piriformis Obturator internus Pubic body and superior ramus Coccygeus Levator ani Pelvic Floor - The pelvic floor consists of the coccygeus and levator ani muscles - These structures protect and support pelvic viscera and contribute to maintenance of intraabdominal pressure. Piriformis Tendinous arch of levator ani - A thickening of the obturator fascia Obturator internus Levator ani: - Iliococcygeus - Pubococcygeus - Puborectalis Innervated by nerve to levator ani (S3,S4), with some contribution from the pudendal nerve. Levator ani Attaches: Pubic bones, ischial spines and tendinous arch of levator ani Perineal body, coccyx and walls of organs in midline Tonically contracted most of time Must relax to allow urination and defecation Forms the urogenital hiatus Allow urogenital viscera to pass from pelvis cavity to perineum Puborectalis N.B. - You are not be expected to know: Puboprostaticus Puboperinealis Puboanalis Pubovaginalis UG Hiatus Peritoneal Reflections in the Pelvis - Fluids (blood, ascitic, pus) can collect in these spaces. Rectovesical pouch Vesicouterine pouch MALE MID-SAGITTAL SECTION Recto-uterine pouch (of Douglas) FEMALE MID-SAGITTAL SECTION Broad ligament Pararectal fossa ANTERIOR VIEW FEMALE PELVIS *These peritoneal reflections will be expanded in separate lectures Perineum Diamond-shaped surface extending from the mons pubis (in females) to the medial surface of the thighs and posteriorly to the gluteal folds A transverse line joining the two ischial tuberosities splits the perineum into two triangles: Urogenital and anal triangles The mid-point of this line defines the perineal body The perineal body sees the convergence of several sphincter and perineal pouch muscles. UG triangle * MALE Anal triangle *Ischial tuberosity * Perineal body FEMALE Urogenital triangle The urogenital triangle is divided into two potential spaces/pouches (superficial and deep) by a strong perineal membrane. FEMALE Deep perineal pouch contains: - Portion of the urethra - External urethral sphincter and other muscles - Anterior portions of ischioanal fat pads MALE - Neurovasculature of penis or clitoris Superficial perineal pouch contains: - Erectile bodies and associated muscles - Portion of the urethra - Neurovasculature from pudendal nerve and internal pudendal vessels Superficial pouches of UG triangle Anal triangle Allows passage of the rectum and anal canal Contains pudendal nerve and internal pudendal vessels A large fat filled cavity that is continuous on both sides and extends anteriorly. This can allow infections and abscesses to freely move in this space Obturator internus Levator ani CORONAL SECTION AT THE ANAL CANAL Pudendal nerve and Internal pudendal vessels (in pudendal canal) Vasculature of the pelvis Pelvic viscera receive blood supply from branches of the internal iliac arteries Gonads (testes/ovaries) receive blood from the gonadal artery (branch of aorta) Note the relationship of the vessels to the bony pelvis Pelvic fractures can cause extensive internal bleeding Common iliac artery Internal iliac artery External iliac artery MEDIAL VIEW Branches of the Internal Iliac Artery Branches of the internal iliac artery are highly variable and the veins in more variable. Pelvic vessels are highly anastomotic. It better to understand which arteries supply which region rather than the branching order. INTERNAL ILIAC ARTERY ANTERIOR DIVISON Umbilical artery Superior vesical arteries Obturator artery Middle rectal Inferior vesical artery (male only) Uterine artery (female only) Vaginal artery (female only) Inferior gluteal artery Internal pudendal artery POSTERIOR DIVISON Iliolumbar artery Lateral sacral artery Superior Gluteal artery Anterior division of the Internal Iliac Artery Posterior division (cut) - Some of these arteries will be discussion in detail in future lectures Umbilical artery - Proximal portion (patent) Inferior vesicle or uterine artery Distal portion (obliterated) - supplies inferior bladder, prostate, seminal vesicles, cervix, vagina Superior vesicle arteries - supplies superior bladder Internal pudendal artery Obturator artery - passes through obturator canal to medial thigh - supplies perineal structures - Wraps around sacrospinous ligament Innervation of the pelvis and perineum Pelvic innervation provides fundamental understanding of function and sensation – highly clinically relevant. Somatic nerves Motor and general sensation to perineum and pelvic walls – from sacral plexus Autonomic (sympathetic and parasympathetic) Supply viscera Controls micturition, erection, ejaculation, uterus and uterine tube contraction, blood flow, bowel contraction/inhibition. Visceral afferent Sensation of pelvic organ will follow autonomic fibres Somatic innervation of the perineum Mostly supplied by branches of pudendal nerve (S2-4), but other contributions to scrotum and labia Course: Pudendal nerve exit pelvic cavity through greater sciatic foramen Passes lateral to sacrospinous ligament Enters lesser sciatic foramen and into the pudendal (Alcock’s) canal. Runs anteriorly in the pudendal canal towards the pubic symphysis Supplies: Muscles of anal and urogenital triangle Sensation of external genitalia and skin of perineum Autonomic Innervation of the Pelvis SUPERIOR HYPOGASTRIC PLEXUS Same as other side INFERIOR HYPOGASTRIC PLEXUS Pass through intermesenteric plexus to superior hypogastric plexus Some fibres from the pelvic splanchnic nerves pass superiorly in retroperineum and through hypogastric nerve to supply hindgut organs. Sacral splanchnic nerve branch from sacral sympathetic chain to supply lower limbs S2 S3 S4 Post-ganglionic sympathetic fibres arise from lower thoracic and upper lumbar spinal cord regions HYPOGASTRIC NERVE Retroperitoneal parasympathetic fibres PELVIC SUB-PLEXUSES - Lateral to rectum - Inferior bladder (with differences in males and females) Anterior rami to sacral plexus/pudendal nerve (somatic) Autonomic innervation of the pelvis Superior mesenteric plexus Hypogastric nerve Inferior mesenteric plexus Pelvic splanchnic nerves Visceral afferent fibres of the pelvis Convey pain and stretch sensations from pelvic viscera As a general rule (Pelvic Pain Line): Above pelvic pain line - VA’s follow sympathetics Visceral afferent fibres from portions of pelvic viscera in contact with peritoneum – follow sympathetic fibres to ~T12-L2 spinal cord levels Visceral afferent fibres from pelvic viscera not in contact with peritoneum – follow parasympathetic fibres to S2-4 spinal cord regions. This has clinical consequences for pain / referred pain. Below pelvic pain line - VA’s follow parasympathetics Learning outcomes By the end of this lecture, the successful student should be able to: 1. Describe the structures/landmarks of the lesser and greater pelvis 2. Describe the bones of the pelvis and its principal foramina 3. Describe the muscles that form the wall of the pelvis and the pelvic floor 4. Describe the vessels of the pelvis 5. Describe the somatic and autonomic innervation of the pelvis Recommended reading: - Gray’s Anatomy for Students, - Moore’s Clinically Oriented Anatomy,