Pelvis Flashcards
Which 3 bones make up the pelvic girdle and what is its function
Right and left hip bones and the sacrum
Supports body weight by transferring it to the lower limbs.
Describe the different types of joints found in the pelvis
Joints: synovial sacro-iliac joints exist between the sacrum and hip bones; secondary cartilaginous joint exists at the pubic symphysis
Synovial joint here strange- as there is no movement
Where are the joints in the pelvis found
The sacrum articulates superiorly with the vertebral body of LV at the lumbosacral joint
The pelvic bones articulate posteriorly with sacrum at the sacro-iliac joints and with each other anteriorly at the pubic symphysis
Summarise the pelvic bones
comprised of the ilium (superior), pubis (anterior) and ischium (posterior), forming the acetabular fossa where the head of the femur articulates
What are the two regions of the pelvis
Superior region- upper part of the pelvic bones and lower lumbar vertebrae is the false pelvis (greater pelvis) and is generally considered part of the abdomen
The true pelvis (lesser pelvis) is related to the inferior parts of the pelvic bones, sacrum and coccyx, and has an inlet and an outlet
Describe the components of the pelvic bone at birth
The bones are connected by cartilage in the area of the acetabulum; later between 16-18 they fuse into a single bone
Describe the true pelvis
Cylindrical and has an inlet, a wall and an outlet
The inlet is open, whereas the pelvic floor closes the outlet and separates the pelvic cavity above, from the perineum below
Describe the function of the pelvic inlet
Circular opening between the abdomen and the pelvic cavity through which structures (nerves, blood vessels) traverse between the abdomen and the pelvis
Describe the formation of the pelvic inlet
it is completely surrounded by bones and joints
The promontory of the sacrum protrudes into an inlet, forming its posterior margin in the midline
On either side of the promontory- the margin is formed by the alae of the sacrum
The margin crosses the sacro-iliac joint and then continues along the linea terminalis ( consisting of the arcuate line, pectin pubis/pectineal line and the pubic crest)
Pubic crest is the anterior margin
What is the arcuate line
A ridge separating the upper and lower parts of the ilium.
Describe the pelvic outlet
Diamond shaped, with the anterior part defined by bone and the posterior part by ligaments
Midline anteriorly- pubic symphysis
Extending laterally and posteriorly, the boundary on each side is the inferior border of the body of the pubis, the inferior ramus of the pubis, the ramus of the ischium, and the ischial tuberosity
Together, these elements on both sides form the pubic arch
From the ischial tuberosities, the boundary continues posteriorly and medially along the sacrotuberous ligament on both sides of the coccyx
Describe the function of the pelvic outlet
Terminal parts of the urinary and G.I tracts and vagina pass through the pelvic outlet
The area enclosed by the boundaries of the pelvic outlet and below the pelvic floor is the perineum.
Summarise the pelvic cavity
The Iliac fossae form a shallow basin containing lower abdominal viscera
The axis of the pelvic cavity is antero- inferiorly inclined
Pelvic cavity is conical or cylindrical (birth canal)
Cavity is mainly lined by muscles and nerves
Describe the features of the pelvic cavity
Lined by peritoneum continues with the peritoneum of the abdominal cavity that drapes over the superior aspects of the pelvic viscera, but in most regions does not reach the pelvic floor
What is found in the pelvic cavity
The pelvic viscera are located in the midline of the pelvic cavity
Bladder is anterior and the rectum is posterior
In women, the uterus lies between the bladder and rectum
Other structures, such as vessels and nerves, lie deep in the peritoneum in association with the pelvic walls and on either side of the pelvic viscera.
Describe the axis of the pelvic cavity
angled at 45deg to that of the abdomen (antero-inferior)
Describe the orientation of the pelvic cavity
ASIS and pubic symphysis lie in the same vertical plane- consequently the pelvic inlet is angled at 50-60 degrees
anterior relative to the horizontal plane and the pelvic cavity projects posteriorly from the abdominal cavity
Meanwhile, the urogenital part of the pelvic outlet (the pubic arch) is orientated in a nearly horizontal plane, whereas the posterior part of the outlet is positioned more vertically
The urogenital triangle of the perineum therefore faces inferiorly, while the anal triangle faces more posteriorly
How can the pelvis be split into the abdominal and posterior part
Pelvic bone above the linea terminalis -represents the lateral wall of the false pelvis- which is part of the abdominal cavity
Pelvic bone below this line- represents the lateral wall of the true pelvis- which contains the pelvic cavity
Describe the structure of the pubis
Consists of a body and two arms (rami)
Body- joints with body of other pubic bone at the pubic symphysis. Has a rounded pubic crest on its superior surface- that ends laterally as the pubic tubercule
Superior pubic ramus- projects posterolaterally and joins with ilum and ischium at its base, which is positioned toward the acetabulum
Superior margin of this triangular surface is the pectineal line, anteriorly this line is continuous with the pubic crest- and it is marked on its inferior surface by the obturator groove
Inferior ramus- projects laterally and inferiorly to join with the ramus of the ischium
Describe the ischium
Large body projects superiorly to join with the ilium and the superior ramus of the pubis
a ramus projects anteriorly to join with the inferior ramus of the pubis
posterior margin of bone is marked by a prominent ischial spine that separates the lesser sciatic notch, below, from the grater sciatic notch above
Most prominent feature is the ischial tuberosity- on the psoteroinferior aspect of the bone- important for attachment of lower limb muscles when sitting.
What does the pelvic wall consist of
Sacrum, coccyx, pelvic bones inferior to the linea terminalis, two ligaments and two muscles
Describe the sacrospinous ligament
Smaller, triangular- apex attached to the ischial spine and its base attached to the related margins of the sacrum and coccyx
Describe the sacrotuberous ligament
Triangular and superficial to the sacrotuberous ligament
Base- broad attachment from the posterior superior iliac spine and extends along the dorsal, lateral margin of the sacrum, and onto the dorsolateral surface of the coccyx
Laterally, the apex of the ligament is attached to the medial margin of the ischial tuberosity
Describe the functions of these ligaments
Stabilise the sacrum on the pelvic bones by resisting the upward tilting of the inferior aspect of sacrum- they also convert the greater and lesser sciatic notches of the pelvic bone into foramina
Greater- superior to sacrospinous ligament and ischial spine
lesser- inferior to ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments.
Summarise the muscles of the pelvic wall
Two- obturator internus and the piriformis
contribute to the lateral walls of the pelvic cavity
originate in the pelvic cavity but attach peripherally to the femur
Describe the obturator internus muscle
Origin: anterolateral wall of the true pelvis (deep surface of the obturator membrane and surrounding bone)
Insertion: medial surface of the greater trochanter
Innervation: L5/S1
Function: lateral rotation of the extended hip joint and abduction of flexed hips
Flat and fan shaped muscle- muscle fibres converge to form a tendon that leaves the pelvic cavity through the lesser sciatic foramen
Describe the piriformis muscle
Origin: Anterior surface of the sacrum between anterior sacral foramina
Insertion: medial side of the superior border of the greater trochanter
Innervation: Branches from S1/2
Function: lateral rotation of the extended hip joint and abduction of flexed hips
Passes laterally through the greater sciatic foramen- separating it into two regions- one above the muscle and one below
vessels and nerves course between the pelvic cavity and the gluteal region pass between these two regions
Explain sexual differences in pelvic skeletal anatomy
Pelvic inlet of a woman is circular and heart-shaped in men
Angle formed by the arms of the pubic arch is larger in women (80-85deg) than men (50-60deg)
Ischial spines do no project as medially into pelvic cavity in women as do in men
Summarise the pelvic diaphragm and perineum
A bowl-like sheet of muscle called levator ani forms the pelvic diaphragm.
Slung from the pelvis and sacrum
Supports the main pelvic viscera (bladder, uterus, rectum)
Below the diaphragm is the perineum, containing voluntary sphincters and external genitalia
Describe the pelvic floor
Formed by the pelvic diaphragm in the anterior midline, the perineal membrane and the muscles in the deep perineal pouch
The pelvic diaphragm is formed by the levator ani and the coccygeous muscles from both sides
The pelvic floor separates the pelvic cavity above, from the perineum below
What is meant by the pelvic diaphragm
The muscular part of the pelvic floor
Bowl shaped and attached superiorly to the pelvic walls
Consists of the levator ani and coccygeous muscles
Its circular line of attachment to the cylindrical pelvic wall passes, on each side between the greater sciatic foramen and lesser foramen, therefore:
greater- situates above pelvic floor and is a route of communication between the pelvic cavity and gluteal region of the lower limb
lesser- situated below pelvic floor- providing a route of communication between the gluteal region of the lower limb and the perineum
Describe the levator ani muscle
Originate from each side of the pelvic wall, course medially and inferiorly and join together in the midline
Has two bony attachments: anteriorly to the body of the pubis, and posterolaterally to the ischial spine
In between the bony attachments- it arises from a thickening in the fascia that overlies the obturator internus muscle- the tendinous arch of the levator ani.
At the midline, the muscles converge posterior to the vagina and around the anal aperture in both sexes
Posterior to the anal aperture- the muscles converge as a ligament or raphe called the anococcygeal ligament and attaches to the coccyx
Anteriorly, the muscles are separated by a U-shaped defect or gap called the urogenital hiatus.
What is the purpose of the urogenital hiatus
The margins associate with the walls of the associated viscera and the muscles in the deep perineal pouch below
The hiatus allows the urethra and the vagina to pass through the pelvic diaphragm
Describe the 3 regions of the levator ani
Pubococcygeous- originates from body of pubis- courses posteriorly to attach along the midline as far back as the coccyx
Puborectalis- originates in association with the pubococcygeous muscle, from the pubis and passes inferiorly on each side to form a sling around the G.I tract- maintaining the perineal flexure at the anorectal junction- which helps to keep that end of the G.I system closed
Iliococcygeous- originates from the fascia that covers the obturator internus- 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.
Summarise the levator ani
Origin: line around the pelvic wall beginning on posterior aspect of the pubic bone and extending across obturator internus as a tendinous arch to the ischial spine
Insertion: anteriorly to the superior surface of the perineal membrane, posteriorly to the meet its partner around the anal canal
Innervation: anterior ramus of S4 and inferior rectal branch of the pudendal nerve (S2-S4)
Function: contributes to formation of pelvic floor to support viscera and reinforces external anal sphincter
Openings: urethral, anal (surrounded by anal sphincter), vaginal
What else can the pubococcygeous muscle be divided into
levator prostate- most anterior of the medial fibres of the pubococcygeous muscle- attach the pubis to the perineal body, below the male prostate
similar fibres in females form the pubovaginalis muscle- which acts as a vaginal sphincter and assists in maintaining urinary continence
puboanalis- thickened group of medial fibres unite with their fellows of the opposite side, attaching at the perineal body, anocooygeal body and the anal sphincters in between.
Describe the coccygeous muscle
One on each side- triangular and overlie the sacrospinous ligaments- together- complete the posterior part of the pelvic diaphragm
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
Summarise the coccygeus muscle
Origin: ischial spine and pelvic surface of the sacrospinous ligament
Insertion: lateral margin of the coccyx and related border of the sacrum
Innervation: anterior rami of S3/4
Function: forms pelvic floor and pulls coccyx forward after defecation
Describe the urinary bladder
most anterior element of the pelvic viscera; triangular pyramid with the apex pointing anteriorly lined by the urothelium (3-layered membrane with slow cell turnover and large, impermeable luminal cells)
Summarise the urinary bladder
The bladder is tetrahedral shaped.
It has a structure at each corner of the tetrahedron
Describe the apex of the bladder
Directed toward the top of the pubic symphysis; the median umbilical ligament (a remanant of the embryological urachus that contributes to the formation of the bladder) continues from it superiorly up the anterior abdominal wall to the umbilicus
Describe the base of the bladder
Shaped like an inverted triangle and faces posteroinferiorly
The two ureters enter the bladder at each of the upper corners of the base, and the urethra drains inferiorly from the lower corner of the base
Inside, the mucosal lining is smooth and firmly attached to the underlying smooth muscle coat of wall- unlike elsewhere in the bladder where the mucosa is folded and loosely attached
This area is the trigone
Describe the inferolateral surfaces
Cradled between the levator ani muscles and the adjacent obturator internus muscles above the attachment of the pelvic diaphragm
Superior surface is domed when the bladder is empty- but balloons superiorly as the bladder fills
Describe the neck of the bladder
Neck of the bladder: anchored in position by tough fibromuscular bands, connecting neck/pelvic part of the urethra to the posteroinferior aspect of each pubdic bone
Women: pubovesical ligaments - supported by peritoneum and associated muscles
Men: puboprostatic ligaments - blend with fibrous capsule of the prostate which surrounds the neck of the bladder
Most inferior aspect of bladder- surrounds the origin of the urethra at the point where the two inferolateral surfaces and the base intersect
Outline the features of the urinary bladder
Tetrahedral when empty
Ureters enter at supero-posterior angles
Urethra leaves through inferior angle
Superior surface covered in peritoneum
Expands between transversalis fascia and lining peritoneum
Smooth muscle sphincter (vesicae) at neck
Skeletal muscle sphincter (urethrae) in perineum
Describe the urinary sphincters
Urinary sphincters: two are present - s. urethrae and s. Vesicae - needed to maintain urinary continence
Sphincter vesicae: internal smooth muscle sphincter at the neck of the bladder that opens reflexively in response to bladder wall tension - relaxed by PSNS and contracts due to SNS
Sphincter urethrae: external striated muscle sphincter in the perineum, whose tone is maintained by somatic nerves in the pudendal nerve (S2-4), opened by voluntary nervous inhibition
Describe the features of the human rectum
human rectum has a double-S bend, probably functioning as an anti-gravity device keeping load off the sphincter
Continuous above with the sigmoid colon at S3
Continuous below with the anal canal as this structure penetrates the pelvic floor and passes through the perineum to end as the anus
Most posterior element of the pelvic viscera, is immediately anterior to and follows the concave contour of sacrum
Describe the shape of the rectum
Anorectal junction is pulled forward (perineal flexure) by the action of the puborectalis part of the levator ani muscle- so the canal moves posteriorly as it passes inferiorly through the pelvic floor
The rectum has 3 lateral curvatures- upper and lower to the right and the middle to the left- the lower part is expanded to form the rectal ampulla
The rectum lacks distinct taenia coli, omental appendices and sacculations (haustra)
Describe the anal canal
Begins at the terminal end of the rectal ampulla- where it narrows in the pelvic floor- terminates as the anus after passing through the perineum
As it passes through the pelvic floor- the anal canal is surrounded along its entire length by the internal and external sphincters- which are normally kept closed
Describe rectal innervation
The rectum is supplied by the autonomic NS and is mainly sensitive to filling. The anal canal is supplied by somatic nerves and is extremely sensitive to injury.
Describe faecal continence
The skeletal muscle sphincter ani surrounding the anal canal is much less important to faecal continence than the puborectalis part of Levator ani, which puts a sharp angle into the recto-anal junction. Can be injured in a badly-performed episiotomy.
Summarise the rectum and anal canal
Rectum descends within concavity of sacrum
Shows three lateral curvatures
Right-angle bend back at recto-anal junction
Smooth muscle (internal) and skeletal muscle (external) sphincters
Main functional sphincter is pubo-rectalis sling of levator ani
Nerves: rectum - visceral; anal canal - somatic
Summarise the arterial supply of the pelvic organs
The Internal Iliac Artery supplies all the pelvic organs (except the ovaries), the pelvic walls and much of the buttock (gluteal) region
Describe the blood supply to the rectum
Terminal branch of the IMA (superior rectal) supplies the rectum and the upper part of the anal canal
The lower part of the anal canal is supplied by branches of the internal pudendal artery- the inferior rectal artery
There are corresponding veins- upper part of canal drains into portal system
Lower part drains into systemic veins- anal canal is an important site for porto-systemic anastomoses
Middle rectal vessels supply the muscle layer of the middle part of the rectum- don’t pass deep to interfere with the porto-systemic anastomoses. Middle rectal vessels come from interior iliac vein
