3.3 Anatomy of the pelvis Flashcards
what is the pelvic inlet formed by?
- arcuate line
- pecten pubis (pectineal line)
- ala of sacrum and promontory
what is the pelvic outlet formed by?
- pubic symphysis
- ischiopubic rami
- sacrotuberous ligament
- sacrum and coccyx
which parts of the pelvis are in the same vertical plane in anatomical position>
In anatomical position (erect posture), the right and left anterior superior iliac spines (ASIS) and the anterior aspect of pubic symphysis lie in the same vertical plane. The pubis and the ischium are aligned more towards the anterior and inferior region while the ilium and sacrum is aligned more posteriorly and superiorly.
what does the true (obstretrical) conugate refers to?
minimum antero-posterior (AP) diameter of lesser pelvis extending from middle of sacral promontory to postero-superior margin of pubic symphysis (around 11cm). It is the first bony landmark the foetus will pass through.
how is the diagonal conjugated measured?
palpating the sacral promontory with the tip of middle finger to the level of inferior margin of pubic symphysis
what is the anterior inferior pelvic wall formed by?
- Formed by bodies and rami of pubic bones and the public symphysis.
- Behind the pubis lies the urinary bladder.
- Between the pubis and the urinary bladder lies a space called the retropubic space. The weight of a full bladder will be borne by the anterior inferior pelvic wall.
what is the lateral pelvic walls formed by?
- Formed by right and left innominate (hip) bones
- The obturator membrane covers the obturator foramen, which lies below the superior ramus of the pubis, lateral to the inferior pubis and ischial pubic rami and above the ischial tuberosity.
- The obturator internus muscle covers most of the lateral wall of pelvic cavity
- The thickened portion of obturator fascia forms as tendinous arch (represented in red dotted line), provides attachment to pelvic diaphragm
What is the posterior pelvic walls formed by?
- Sacrum and coccyx
- Sacroiliac ligament (at the SI joint)
- Sacrotuberous and sacrospinous ligaments (connects sacrum to the ischium)
- Piriformis muscle: Piriformis originates from pelvic surface of sacrum, passes through greater sciatic foramen and inserts at superior border of greater trochanter of femur
- Anteromedial to pyriformis lies the sacral plexus
- Nerve supply: nerve to piriformis (S1,S2)
what is the pelvic floor formed by?
- Formed by funnel shaped pelvic diaphragm (fibromuscular structure)
- Consists of coccygeus and levator ani muscles (consist of pubococcygeus and iliococcygeus) and the fascia covering the superior and inferior aspects of the muscles
Where does the levator ani attach to and its nerve supply ?
- Anteriorly to public bones
- Posteriorly to ischial spines
- Laterally to tendinous arch of obturator fascia
Nerve supply: Nerve to levator ani (S3,S4)
what kind of joint is the sacroiliac joint and what are its movements?
- atypical synovial
- Minimal movement (slight anterior and posterior tilting of hip bones)
what kind of joint is the pubic symphysis and what are its movements?
- secondary cartilaginous
- None (for shock absorption and allows delivery of baby)
what kind of joint is the sacrococcygeal joint and what are its movements?
- secondary cartilaginous
- Flexion and extension of coccyx (passive movements during defecation and labour → further increases AP diameter of the pelvic outlet)
when we sit down, which part of the hip bone do we sit on?
part of the hip bones which one sits on (transmits weight to the ground in the upright sitting position
what is the promontory?
Anterior projecting edge of the body of S1 (important obstetrical landmark →
what is the ala and what does it serve as an attachment for?
Large lateral projections (wings) on each side of the base of sacrum (articulation with the hip bones → sacroiliac joints):
• Attachment for: psoas major, iliacus muscle
what is the sacraal foramina?
4 pairs of openings for the exit of the posterior and anterior (larger) rami of the pelvic spinal nerves
what is the sacral canal?
Continuation of vertebral canal in the sacrum (contains cauda equina)
What is the sacral hiatus?
Inverted U-shaped structure resulting from the absence of the laminae and spinous processes of S5 and (sometimes) S4
obturator internus
- origin
- insertion
- innervation
- function
- obturator membrane
- lesser sciatic foramina –> greater trochanter of femur
- Nerve to obturator internus (L5 – S2)
- Abduction of lower limbs, Lateral rotation of hip
Piriformis
- origin
- insertion
- innervation
- function
- Pelvic surfaces of S2 – S4; superior margin of greater sciatic notch and sacrotuberous ligament
- greater sciatic foramina –> greater trochanter of femur
- Nerve to piriformis (S1 – S2)
- Abduction of lower limbs, Lateral rotation of hip
coccygenus
- origin
- insertion
- innervation
- function
- ischial spine
- inferior end of sacrum & coccyx
- S4- S5
- Support pelvic viscera & flexion of coccyx
levator ani
- origin
- insertion
- innervation
- function
- Body of pubis, tendinous arch of obturator fascia, ischial spine
- Perineal body, coccyx, anococcygeal ligament, walls of prostate/vagina, rectum, anal canal
- Nerve to levator ani (S3 – S4), Inferior rectal nerve, Coccygeal plexus
- Support pelvic viscera &
resist increases in IAP (prevents vaginal and uterine prolapse)
where do the fibers of the pubovaginalis run?
Fibres running along the sides of the vaginal opening (sphincter)
where do the fibers of the puborectalis run?
Fibres running along the sides of the rectum → maintains continence:
• Faecal: most important part in the anal sphincter complex
• Urinary: pre-rectal fibres loop around urethra and vagina
where do the fibers of the pubococcygenus run?
Fibres run from the ischiopubic ramus to the anococcygeal raphe
where do the fibers of the ileococcygenous run?
Fibres run from the ischium to the anococcygeal raphe (often thin and poorly developed → more aponeurotic than muscular)
ovarian artery
- origin
- course
- supply
- Abdominal aorta
- Descends in suspensory ligament of ovary
- Pelvic ureter, ovary, ampullary end of uterine tube
median sacral artery
- origin
- course
- supply
- Abdominal aorta
- Descends in midline over L4 to coccyx
- Inferior lumbar vertebrae, sacrum, coccyx
superior rectal artery
- origin
- course
- supply
- IMA
- Crosses left common iliac vessels
- superior part of rectum
obturator artery
- origin
- course
- supply
- anterior division of internal iliac arteries
- Runs anteroinferiorly on obturator fascia of lateral pelvic wall → obturator canal
- Pelvic muscles, ilium, lower limb
uterine artery
- origin
- course
- supply
- anterior division of internal iliac arteries
- Runs in base of broad ligament → crosses ureter superiorly to lateral uterine cervix
- Uterus, ligaments of uterus, medial parts of uterine tube and ovary, superior vagina
vaginal artery
- origin
- course
- supply
- anterior division of internal iliac arteries
- Divides into vaginal and inferior vesical branches
- Vaginal branch: lower vagina, vestibular bulb, rectum
- Inferior vesical branch: fundus of urinary bladder
internal pudendal artery
- origin
- course
- supply
- anterior division of internal iliac arteries
- Exits pelvis via greater sciatic foramen → enters perineum via lesser sciatic foramen → pudendal canal → UG triangle
- Main artery of the perineum: muscles and skin of anal and urogenital triangles, erectile bodies
middle rectal artery
- origin
- course
- supply
- anterior division of internal iliac arteries
- Descends in pelvis to inferior rectum
- Inferior part of rectum, vagina
inferior gluteal artery
- origin
- course
- supply
- anterior division of internal iliac arteries
- Exits pelvis via greater sciatic foramen
- Pelvic diaphragm, piriformis, quadratus femoris, lower limbs
The pelvis is mainly drained by the pelvic venous plexuses, which are formed by the interjoining veins surrounding the pelvic viscera (e.g. vesical, rectal, vaginal, uterine):
• Various plexuses unite and drain into the internal __________________ (mainly) and _______ and _________ (minor)
o Internal iliac veins form superior to the greater sciatic foramen and lie posteroinferior to the internal iliac arteries (roughly along arterial branches)
• Drain into the common iliac veins then the IVC (at the level of __________)
iliac veins ;
the inferior mesenteric vein and internal vertebral venous plexus ;
L4/L5