Pelvic Cavity Anatomy PDF

INTRODUCTION TO THE PELVIS DPM PROGRAM Learning Objectives: 1.Describe the differences between the greater and lesser pelvis. 2.Describe the pelvic inlet. 3.Describe the pelvic outlet. 4.Describe the differences between male and female pelvis structures. 5.Describe the muscles of the pelvic wall....

INTRODUCTION TO THE PELVIS DPM PROGRAM Learning Objectives: 1.Describe the differences between the greater and lesser pelvis. 2.Describe the pelvic inlet. 3.Describe the pelvic outlet. 4.Describe the differences between male and female pelvis structures. 5.Describe the muscles of the pelvic wall. 6.Describe the apertures in the pelvic wall. 7.Describe the obturator canal and the structures that pass through this canal. 8.Describe the greater sciatic foramen and structures that pass through the greater sciatic foramen. 9.Describe the lesser sciatic foramen and the structures that pass through this foramen. 10.Describe the pelvic floor muscles. 11.Describe the levator ani muscles. 12.Describe the coccygeus muscles. 13.Describe the perineal membrane. 14.Describe the deep perineal pouch. 15.Describe the perineal body. 16.Explain the functional and clinical significance of the perineal body. 1 SMU - Internal Data Describe the differences between the greater and lesser pelvis. The pelvis and perineum are interrelated regions associated with the pelvic bones and terminal parts of the vertebral column. The pelvis is divided into two regions: 1) Greater pelvis (false pelvis): • Superior region related to upper parts of the pelvic bones and lower lumbar vertebrae • Generally considered part of the abdominal cavity 2) Lesser pelvis (true pelvis): • Related to the inferior parts of the pelvic bones, sacrum, and coccyx, and has an inlet and an outlet. • Bowl-shaped pelvic cavity enclosed by the true pelvis consists of: • pelvic inlet, walls, and floor • This cavity is continuous superiorly with the abdominal cavity and contains elements of the urinary, gastrointestinal, and reproductive systems. 2 SMU - Internal Data Describe the pelvic inlet. Pelvic inlet • Somewhat heart-shaped and completely ringed by bone • Structures pass between the pelvic cavity and abdomen through the pelvic inlet Boundaries: • Posteriorly • Body of vertebra SI, projects into the inlet as the sacral promontory • Alae (wings) contribute to the margin of the pelvic inlet • Laterally • a prominent rim on the pelvic bone continues the boundary of the inlet forward to the pubic symphysis, where the two pelvic bones are joined in the midline 3 SMU - Internal Data Describe the pelvic outlet. Pelvic outlet • diamond shaped, with the anterior part of the diamond defined predominantly by bone and the posterior part mainly by ligaments Boundaries: • Anterior • Pubic symphysis • Laterally/posteriorly • Pubic arch which includes: • Inferior border of the body of the pubis • Inferior ramus of pubis • Ramus of ischium • Ischial tuberosity • Posterior/medially • Sacrotuberous ligament on both sides to the coccyx Terminal parts of the urinary and gastrointestinal tracts and the vagina pass through the pelvic outlet. The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum. 4 SMU - Internal Data Describe the differences between male and female pelvis structures. The pelvises of women and men differ in a number of ways, many of which have to do with the passing of a baby through a woman’s pelvic cavity during childbirth. 1. The pelvic inlet in women is circular (Figure A) compared with the heart-shaped pelvic inlet (Figure B) in men. The more circular shape is partly caused by the less distinct promontory and broader alae in women. Female pelvis 2. The angle formed by the two arms of the pubic arch is larger in women (80°–85°) than it is in men (50°–60°). 3. The ischial spines generally do not project as far medially into the pelvic cavity in women as they do in men. Male pelvis SMU - Internal Data 5 Do you remember sacrotuberous and sacrospinous ligaments? These ligaments stabilize the sacrum on the pelvic bones by resisting the upward tilting of the inferior aspect of the sacrum. They also convert the greater and lesser sciatic notches of the pelvic bone into foramina. ▪ Greater sciatic foramen: -lies superior to the sacrospinous ligament and the ischial spine ▪ Lesser sciatic foramen: -lies inferior to the ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments 6 SMU - Internal Data Describe the muscles of the pelvic wall. Two muscles, the obturator internus and the piriformis, contribute to the lateral walls of the pelvic cavity. These muscles originate in the pelvic cavity but attach peripherally to the femur. Obturator internus • flat, fan-shaped muscle that originates from the deep surface of the obturator membrane and from associated regions of the pelvic bone that surround the obturator foramen. • forms a large part of the anterolateral wall of the pelvic cavity Piriformis • triangular and originates in the bridges of bone between the four anterior sacral foramina • passes laterally through the greater sciatic foramen, crosses the posterosuperior aspect of the hip joint, and inserts on the greater trochanter of the femur above the insertion of the obturator internus muscle. 7 SMU - Internal Data Describe the apertures in the pelvic wall. Vessels and nerves coursing between the pelvic cavity and the gluteal region pass through apertures in the pelvic wall. Apertures in the pelvic wall Each lateral pelvic wall has three major apertures through which structures pass between the pelvic cavity and other regions: 1) the obturator canal 2) the greater sciatic foramen 3) the lesser sciatic foramen Greater sciatic foramen Obturator canal Lesser sciatic foramen 8 SMU - Internal Data Describe the obturator canal and the structures that pass through this canal. Obturator canal • At the top of the obturator foramen is the obturator canal. It is bordered by: • Obturator membrane • Obturator internus muscle • Superior pubic ramus Contents: • Obturator nerve • Obturator artery and vein These vessels travel through the canal to innervate the muscles of the medial thigh (adductors). Obturator nerve Obturator artery Obturator canal Obturator internus muscle 9 SMU - Internal Data Describe the greater sciatic foramen and structures that pass through the greater sciatic foramen. Greater sciatic foramen is a major route of communication between the pelvic cavity and the gluteal region of the lower limb. Piriformis muscle It is formed by the greater sciatic notch in the pelvic bone, the sacrotuberous and the sacrospinous ligaments, and the spine of the ischium. Contents: • Piriformis muscle passes through the greater sciatic foramen, dividing it into two parts. 1) Superior to piriformis muscle contents: • Superior gluteal nerves and vessels 2) Inferior to piriformis muscle contents: • inferior gluteal nerves and vessels • sciatic nerve • pudendal nerve • internal pudendal vessels • posterior femoral cutaneous nerves • nerves to the obturator internus • quadratus femoris muscles Piriformis muscle 10 SMU - Internal Data Structures that pass through the greater sciatic foramen. Superior gluteal vein, artery, nerve Superior to piriformis muscle Piriformis muscle Inferior to piriformis muscle Inferior gluteal nerves and vessels Sciatic nerve Pudendal nerve Internal pudendal vessels Posterior femoral cutaneous nerves Nerves to the obturator internus Quadratus femoris muscles 11 SMU - Internal Data Describe the lesser sciatic foramen and the structures that pass through this foramen. Lesser sciatic foramen is formed by the lesser sciatic notch of the pelvic bone, the ischial spine, the sacrospinous ligament, and the sacrotuberous ligament. Contents passing to gluteal region: • Tendon of the obturator internus muscle Contents passing between pelvic cavity and perineum (space between the thighs): • Pudendal nerve • Internal pudendal vessels • Nerve to obturator internus Route explained: first passing out of the pelvic cavity through the greater sciatic foramen and then looping around the ischial spine and sacrospinous ligament to pass through the lesser sciatic foramen to enter the perineum. Lesser sciatic foramen Because the lesser sciatic foramen is positioned below the attachment of the pelvic floor, it acts as a route of communication between the perineum and the gluteal region. 12 SMU - Internal Data Pudendal nerve Tendon of obturator internus muscle Nerve to obturator internus 13 SMU - Internal Data 14 SMU - Internal Data Describe the pelvic floor muscles Pelvic floor • formed by the pelvic diaphragm and, in the anterior midline, the perineal membrane and the muscles in the deep perineal pouch • pelvic floor separates the pelvic cavity, above, from the perineum, below. Pelvic diaphragm • is the muscular part of the pelvic floor • shaped like a bowl or funnel and attached superiorly to the pelvic walls, it consists of the: • levator ani muscle • coccygeus muscle 15 SMU - Internal Data Describe the levator ani muscles Levator ani • 2 levator ani muscles originate from each side of the pelvic wall they join together in the midline • The attachment to the pelvic wall follows the circular contour of the wall and includes: ▪ posterior aspect of the body of the pubic bone ▪ linear thickening called the tendinous arch, in the fascia covering the obturator internus muscle ▪ spine of the ischium Midline: • • Muscles blend together posterior to the vagina in women In all individuals, they go around the anal aperture Posterior to anal aperture: • Muscles come together as a ligament or raphe called anococcygeal ligament • This attaches to the coccyx Anteriorly: • Muscles are separated by a U-shaped defect or gap termed the urogenital hiatus • Margins of this hiatus merge with the walls of the associated viscera and with muscles in the deep perineal pouch below • The hiatus allows the urethra (in both men and women), and the vagina (in women), to pass through the pelvic diaphragm SMU - Internal Data 16 Levator ani Muscles are divided into at least three collections of muscle fibers: 1. Pubococcygeus 2. Puborectalis 3. Iliococcygeus 17 SMU - Internal Data Pubococcygeus • originates from the body of the pubis and courses posteriorly to attach along the midline as far back as the coccyx • This part of the muscle is further subdivided on the basis of association with structures in the midline into the: • puboprostaticus (levator prostatae) muscle • pubovaginalis muscle • puboanalis muscle 18 SMU - Internal Data Puborectalis • portion of the levator ani muscles, originates, in association with the pubococcygeus muscle • from the pubis and passes inferiorly on each side to form a sling around the terminal part of the gastrointestinal tract • this muscular sling maintains an angle or flexure, called the perineal flexure, at the anorectal junction • This angle functions as part of the mechanism that keeps the end of the gastrointestinal system closed. 19 SMU - Internal Data Iliococcygeus • Part of the muscle originates from the fascia that covers the obturator internus muscle • It joins the same muscle on the other side in the midline to form a ligament or raphe that extends from the anal aperture to the coccyx 20 SMU - Internal Data Describe the coccygeus muscles. Coccygeus • The two coccygeus muscles, one on each side, are triangular and overlie the sacrospinous ligaments • together they complete the posterior part of the pelvic diaphragm • They are attached, by their apices, to the tips of the ischial spines and, by their bases, to the lateral margins of the coccyx and adjacent margins of the sacrum. Innervation: • Branches from anterior rami of S3 and S4 Coccygeus muscle The coccygeus participates in supporting the posterior aspect of the pelvic floor. 21 SMU - Internal Data Describe the perineal membrane. Perineal membrane • A thick fascial, triangular structure attached to the bony framework of the pubic arch • Oriented in the horizontal plane and has a free posterior margin • Anteriorly, there is a small gap between the membrane and the inferior pubic ligament (a ligament associated with the pubic symphysis) 22 SMU - Internal Data Describe the deep perineal pouch. Deep perineal pouch (space) • Provides attachment for roots of external genitalia and muscles associated with them • Parts of the perineal membrane and structures in the deep perineal pouch are enclosed by the urogenital hiatus above: • Therefore, contribute to the pelvic floor and support elements of the urogenital system in the pelvic cavity, even though the perineal membrane and deep perineal pouch are usually considered parts of the perineum • Urethra penetrates vertically through a circular hiatus in the perineal membrane as it passes from the pelvic cavity above to the perineum below • Within a sheet of skeletal muscle functions as a sphincter, mainly for urethra, and as a stabilizer of the posterior edge of the perineal membrane SMU - Internal Data 23 Describe the perineal body. Perineal body • is an ill-defined but important connective tissue structure into which muscles of the pelvic floor and the perineum attach • positioned in the midline along the posterior border of the perineal membrane, to which it attaches • the posterior end of the urogenital hiatus and the levator ani muscles is also connected to it Deep transverse perineal muscles that attach to perineal body: • External anal sphincter • Superficial transverse perineal muscles • Bulbospongiosus • Muscles of the perineum 24 SMU - Internal Data Explain the functional and clinical significance of the perineal body. Episiotomy • During childbirth, the perineal body may be stretched and torn • Traditionally it was felt that if a perineal tear is likely, the obstetrician may proceed with an episiotomy: • This is a procedure in which an incision is made in the perineal body to allow the head of the fetus to pass through the vagina. There are two types of episiotomies: • a median episiotomy • cuts through the perineal body, while a • mediolateral episiotomy • is an incision 45° from the midline The maternal benefits of this procedure have been thought to be less traumatic to the perineum and to result in decreased pelvic floor dysfunction after childbirth. 25 SMU - Internal Data