Pelvic Region 2022SC(2).pptx

Anatomy of the Pelvic Region Prof. C. Smith Head of Anatomy Learning outcomes By the end of this lecture, the successful student should be able to: Gain an understanding of the structures/landmarks that define the lesser and greater pelvis spaces, the bones that compose the pelvis and its principa...

Anatomy of the Pelvic Region Prof. C. Smith Head of Anatomy Learning outcomes By the end of this lecture, the successful student should be able to: Gain an understanding of the structures/landmarks that define the lesser and greater pelvis spaces, the bones that compose the pelvis and its principal foramina, the muscles that line the wall of the pelvis and compose the pelvic floor and the main vessels plus nerves intrinsic to the pelvis. Specifically explain the: • The boundaries of the lesser and greater pelvis. • The bones that compose the pelvis. • The muscles and form the pelvic wall and floor. • The vasculature and innervation (somatic and autonomic) of the pelvic walls and floor. The bony pelvis The bones that together make the pelvis (os coxa) are: Two innominate (hip) bone that form from 3 bones: ilium, ischium and pubis Sacrum, formed by the fusion of the 5 sacral vertebrae Coccyx, formed by the fusion of the 4 coccygeal vertebrae 3 Features of the hip bones The articulated pelvis The primary joints of the pelvis are the sacro-iliac joints (posteriorly) and the pubic symphysis (anteriorly). Weight is transferred from the axial skeleton to the ilia via ligaments to the femurs during standing and the ischial tuberosities during sitting. The pubic symphysis is a fibrocartilaginous disc The sacroiliac joint is a secondary cartilaginous joint. The pelvic brim/ Inlet The bony edge defining the pelvic inlet is known as the pelvic brim and is formed by the: Promontory and ala (wing) of sacrum (Yellow line) Right + Left linea terminalis: Arcuate line (red line)- inner surface of the ilium Pectineal line (blue and purple line)- superior ramus and body of pubis The pelvic outlet The bony edge defining the pelvic outlet is known as the inferior pelvic aperture and is formed by the: Pubic arch- anteriorly Ischial tuberosities- laterally Sacrotuberous ligamentposterolaterally Coccyx- posteriorly Ligaments of the pelvis Posteriorly ligaments support the pelvis and transform notches into foramen. •Sacroiliac: between the sacrum and the ilium, has an anterior and posterior components • Sacrococcygeal: between the sacrum to the coccyx • Sacrospinous: between the ischial spine and the sacrum/coccyx • Sacrotuberous: posterior to the sacrospinous; between the lateral aspect of sacrum + coccyx onto medial margin of ischial tuberosity, Ligaments of the pelvis Sex Differences in 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 Oral Pelvic Outlet Small Large Pubic Arch Narrow Wide Obturator Foramen Round Oval Acetabulum Large Small Greater and Lesser Pelvis The Greater Pelvis (false) is the part of the pelvis that is superior to the pelvic brim/inlet and contains the abdominal viscera. The Lesser Pelvis (true) is between the pelvic inlet and outlet and contains reproductive, urinary and gastrointestinal organs. The Pelvic Cavity The pelvic cavity is the space bounded by the bony, ligamentous, muscular pelvic walls and floor. The cavity has: 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. The contents of the pelvic cavity are covered in separate lectures Lateral Pelvic Walls The lateral pelvic walls are formed by the right and left hip bones and provide attachment for the obturator internus muscle that is covered by obturator fascia. The obturator foramen is closed by the obturator membrane expect to allow passage of the obturator nerve, artery and vein. Obturator internus rotates the thigh laterally. Posterior Pelvic Walls The posterior pelvic walls are formed by the sacrum and coccyx and provide attachment for the piriformis muscle. Piriformis rotates the thigh laterally, abducts the thigh. Further information on piriformis is provided in module 204 the thigh. The Pelvic Floor The pelvis floor if formed by the pelvic diaphragm which consists of the coccygeus (ischiococcygeus) and levator ani muscles. Its function to to support the pelvic viscera Levator Ani is formed of: Puborectalis Pubococcygeus Iliococcygeus Innervation is from nerve to levator ani S4 The perineum • The perineum refers to the space located at the pelvic outlet and inferior to the pelvic diaphragm (i.e. muscles of the pelvic floor). • It can be said to describe the narrow region between the thighs • 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. rther details of the male perineum to be covered in the next lecture ther details of the female perineum to be covered in the next lecture Blood Supply and Drainage Arteries Main artery is the Internal iliac artery. -Anterior division of internal iliac, providing several branches (Superior, vesical, inferior vesical, uterine, vaginal, obturator, internal pudendal, middle rectal, inferior gluteal) -Posterior division of internal iliac, (Iliolumbar, lateral sacral, superior gluteal) -Gonadal, from abdominal aorta, supplying the gonads Veins -Internal iliac, to common iliac veins -Gonadal, to IVC or L renal vein Anterior and Posterior divisions of the internal iliac artery Anterior division • Umbilical artery (obliterated) • Obturator artery • Superior vesical • Inferior Vesical/ vaginal artery • Uterine artery • Middle rectal • Internal pudendal • Inferior gluteal Posterior division • Iliolumbar artery • Lateral sacral artery • Superior gluteal artery Other arteries: Ovarian (from Aorta) Median Sacral (from abdominal aorta) Superior rectal (from inferior mesenteric) Nerves in the pelvis The pelvis is innervated by the sacral and coccygeal spinal nerves and the pelvic part of the autonomic system. Somatic plexuses (L4-Co), subdivided into: • Lumbosacral (L4-S4 <=Note: joined by lumbar L4/5) • Coccygeal (S4-Co) Function as motor or sensory e.g. sciatic nerve, sup/inf gluteal, pudendal nerve Sacral Plexus The sacral plexus is located on the posterolateral wall of the lesser pelvis. Its main nerves are: Sciatic nerve- supplies leg and foot Pudendal nerve- supplies the perineum and external genitalia Superior gluteal nerve- supplies gluteal region Inferior gluteal nerve- supplies gluteal region Note: Details of how the sacral plexus innervates the leg is covered in 2 Pudendal nerve (Perineal) The pudendal nerve traverses through the greater and lesser foramen to enter the pudendal canal. It gives rise to the inferior rectal, perineal branches, posterior scrotal/labia branches and dorsal nerve to the penis/clitoris. It supplies sensory to the genitalia, muscular branches to the perineal muscles, external urethral sphincter and external anal sphincter Visceral nerves •Parasympathetic flow: Pelvic splanchnic nerves (S2-4) •Sympathetic flow: Sacral sympathetic trunk Superior and Inferior hypogastric plexuses Summary The boundaries of the lesser and greater pelvis. • The bones that compose the pelvis. • The muscles and form the pelvic wall and floor. • The vasculature and innervation (somatic and autonomic) of the pelvic walls and floor. 

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