Pelvis and Perineum Flashcards
Describe the pelvis
Basin-shaped, caudal end of body cavity Continuous with abdomen above, surrounded by bony pelvis, limited below by pelvic floor/diaphragm
Describe the perineum
Area inferior (superficial) to pelvic floor, bounded by pelvic outlet, limited inferiorly by the skin.
What separates the pelvic cavity from the perineum?
Pelvic floor (muscular sheet)
Pelvis labels (superior view) –> NEED TO KNOW
Pelvis labels (medial surface) –> NEED TO KNOW
What is the sacroiliac joint (x2)?
Connects the sacrum to the ilium bones of the pelvis
What 3 parts is the hip bone comprised of? Together, what do these 3 parts form?
- Ileum 2. Pubis 3. Ischium A cup-shaped socket known as the acetabulum
What articulates with the acetabulum?
Head of the femur
Describe the ilium
The widest and largest of the three parts of the hip bone, and is located superiorly.
Which part of the acetabulum does the ilium body form?
Forms the superior part of the acetabulum (acetabular roof)
Describe the ilium
The widest and largest of the three parts of the hip bone, and is located superiorly.
What are the 2 surfaces of the wing of the ilium?
- Inner surface 2. External surface
Immediately above the acetabulum, what does the ilium expand to form?
The wing (or ala)
Describe the external surface of the wing of the ilium
(Gluteal surface) – has a convex shape and provides attachments to the gluteal muscles.
What does the superior margin of the wing form?
Thickens to form the iliac crest
Where does the iliac crest extend from and to?
It extends from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS).
What indentation is found on the posterior aspect of the ilium?
Greater sciatic notch.
How is the ASIS an important anatomical landmark?
- Mid-inguinal point 2. Mid-point of the inguinal ligament
Describe the mid-inguinal point
Halfway between the ASIS and the centre of the pubic symphysis The femoral artery can be palpated here
Describe the mid-point of the inguinal ligament
Halfway between the ASIS and the pubic tubercle.
Describe the pubis
The most anterior portion of the hip bone
What are the 3 parts of the pubis?
- Pubic body 2. Superior pubic ramus 3. Inferior pubic ramus
What does the pubic body articulate with?
With the opposite pubic body at the pubic symphysis
What is the superior aspect of the pubic body marked by?
A rounded thickening (the pubic crest), which extends laterally as the pubic tubercle.
Together, what does the superior and inferior rami enclose?
Part of the obturator foramen
What passes through the obturator foramen?
The obturator nerve, artery and vein pass through to reach the lower limb.
Describe the ischium
Forms the posteroinferior part of the hip bone. Much like the pubis, it is composed of a body, an inferior ramus and superior ramus.
What does the inferior ischial ramus combine with? What does this form?
The inferior ischial ramus combines with the inferior pubic ramus forming the ischiopubic ramus, which encloses part of the obturator foramen. NEED DIAGRAM
Together, what does the superior and inferior rami enclose?
Part of the obturator foramen
What is the ischial spine?
Near the junction of the superior ramus and body is a posteromedial projection of bone; the ischial spine
What 2 important ligaments attach to the ischium?
- Sacrospinous ligament 2. Sacrotuberous ligament
Where does the sacrospinous ligament run from and to?
Runs from the ischial spine to the sacrum Thus creating the greater sciatic foramen (superiorly) through which lower limb neurovasculature (including the sciatic nerve) transcends.
Where does the sacrotuberous ligament run from and to?
Runs from the sacrum down to the ischial tuberosity. Forming the lesser sciatic foramen (inferiorly)
Describe the sacrococcygeal symphysis
Between the sacrum and the coccyx.
What can the pelvic region be divided into?
- Greater pelvis (false pelvis) 2. Lesser pelvis (true pelvis) Diagram
Where is the false pelvis located? What is its function?
Superiorly Provides support of the lower abdominal viscera (such as a ileum and sigmoid colon). It has little obstetric relevance.
Where is the true pelvis? What is its function?
Inferiorly. Within the lesser pelvis reside the pelvic cavity and pelvic viscera.
What is the junction between the true and false pelvis known as?
Pelvic inlet
What are the outer bony edges of the pelvic inlet called?
Pelvic brim (mickey mouse head shaped)
What is found posterior to the pelvic inlet?
Sacral promontory (the superior portion of the sacrum) and sacral wings (ala).
What is found lateral to the pelvic inlet?
Arcuate line on the inner surface of the ilium, and the pectineal line on the superior pubic ramus.
What is found anterior to the pelvic inlet?
Pubic symphysis
What covers the obturator foramen?
Obturator membrane and muscle (obturator internus)
What are the functions of the bony pelvis?
- Surface for muscle attachment: muscles of trunk and lower limb 2. Transfers weight of trunk to lower limbs (standing) or to ischial tuberosity (sitting) 3. Protect pelvic organs and developing embryo/foetus
Where is the pelvic outlet?
Located at the end of the lesser (true) pelvis and at the beginning of the pelvic wall
What is the pelvic outlet bounded by?
The pelvic floor muscles
Where does the obturator internus attach to?
Attaches to the head of the femur
How does the obturator internus leave the pelvis?
Through the lesser sciatic foramen
What defect is found in the obturator muscle and membrane?
Goes on to form obturator canal (acts as passage)
Where does levator ani attach to? How does it leave the pelvis?
From sacrum, leaving out through greater sciatic foramen and attaching to femur
What overlies the obturator muscle?
Thick layer of fascia (extra thick bit called tendinous arch)
What is function of tendinous arch?
Gives attachment to levator ani
What viscera reside within the pelvic cavity (true pelvis)?
Bladder, rectum, pelvic genital organs, terminal part of urethra
What is the pelvic floor? What does it separate?
It attaches to the walls of the lesser pelvis, separating the pelvic cavity from the perineum inferiorly
What are the 3 main components of the pelvic floor?
- Levator ani muscles (largest component) 2. Coccygeus muscle 3. Fascia coverings of the muscles
What is the levator ani composed of?
3 paired muscles: 1. Pubococcygeus 2. Puborectalis 3. Iliococcygeus
What is the puborectalis muscle?
A U-shaped sling that extends from the pubic bones around the anal canal
What is the main function of the puborectalis muscle?
To maintain faecal continence – during defecation this muscle relaxes.
How does the puborectalis muscle create the anorectal angle?
Caused by puborectalis looping around rectum like a sling Its tonic contraction bends the canal anteriorly, creating the anorectal angle (90 degrees) at the anorectal junction (where the rectum meets the anus).
Some fibres of the puborectalis muscle (pre-rectal fibers) form another U-shaped sling that flank the urethra in the male and the urethra and vagina in the female. Why is this important?
These fibres are very important in preserving urinary continence, especially during abrupt increase of the intra-abdominal pressure i.e. during sneezing.
What is the pubococcygeus muscle? Where does it arise/attach?
Arises from the body of the pubic bone and the anterior aspect of the tendinous arch. The fibres travel around the margin of the urogenital hiatus and run posteromedially, attaching at the coccyx and anococcygeal ligament.
What is the iliococcygeus muscle?
Thin muscle fibres that originate from the ischial spine (ilium) and posterior aspect of the tendinous arch. They attach posteriorly to the coccyx and the anococcygeal ligament.
What is the action of the iliococcygeus muscle?
The actual “levator” of the three: its action elevates the pelvic floor and the anorectal canal.
What is the coccygeus?
The smaller, and most posterior pelvic floor component
Where does the coccygeus start/end?
It originates from the ischial spines and travels to the lateral aspect of the sacrum and coccyx, along the sacrospinous ligament.
What forms the pelvic floor?
Levator ani and coccygeus
Levator ani and coccygeus fibres from left and right converge in the middle of the pelvic floor to form what?
- Perineal body 2. Anococcygeal body
What are the gaps in the pelvic floor?
- Urogenital hiatus 2. Rectal hiatus
What is the urogenital hiatus?
An anteriorly situated gap, which allows passage of the urethra (and the vagina in females).
What is the rectal hiatus?
A centrally positioned gap, which allows passage of the anal canal
What is found between the urogenital hiatus and the anal canal?
The perineal body (fibrous) which joins the pelvic floor to the perineum
What is the perineal body essential for?
Essential for integrity of pelvic floor, particularly in females. Rupture during pregnancy can predispose women to prolapse
What are the roles of the pelvic floor muscles?
- Support of abdominopelvic viscera (bladder, intestines, uterus etc.) through their tonic contraction. 2. Resistance to increases in intra-pelvic/abdominal pressure during activities such as coughing or lifting heavy objects. 3. Urinary and faecal continence.The muscle fibres have a sphincter action on the rectum and urethra. They relax to allow urination and defecation.
What type of pelvis do women tend to have?
A gynaecoid pelvis, as opposed to the male android pelvis.
How is a gynaecoid pelvis adapted to childbirth?
- A wider and broader structure yet it is lighter in weight - An oval-shaped inlet compared with the heart-shaped android pelvis. - Less prominent ischial spines, allowing for a greater bispinous diameter - A greater angled sub-pubic arch, more than 80-90 degrees. - A sacrum which is shorter, more curved and with a less pronounced sacral promontory.
