Describe the formation of the greater sciatic foramen and the lesser sciatic foramen
The greater sciatic notch and the lesser sciatic notch become the greater and lesser sciatic foramen above and below the ischial spine.
They are divided by the membranes - sacrospinous ligament (horizontal) and the sacrotuberous ligament (running vertically from sacrum to ischial tuberosity)
Describe the formation of the obturator canal. Is it the same size as the obturator foramen of the hip bone?
Large obturator foramen (large in bone) becomes a much smaller obturator canal because it is closed by the obturator membrane.
What are the three major muscles associate with the pelvic walls/floor?
1. Obturator Internus
3. Pelvic Floor Muscles (mainly levator ani)
Describe the origin of the obturator internus muscle
The obturator internus muscle lies on the lateral wall of the pelvis arising from three major parts:
- The obturator membrane
- The margins of the obturator foramen
- Part of the posterosuperior aspect of boney part of the wall.
Describe the path of the obturator internus muscle through the pelvis.
Fibres of obturator internus converge on and through the lesser sciatic foramen and make a sharp turn into the gluteal region and onto the greater trochanter.
What is the origin of the piriformis muscle?
It arises from the middle 3 pieces of sacrum (closing interior aspect of the sacrum)
Describe the path of the piriformis muscle
From its attachment to the sacrum, it passes through the greater sciatic foramen closing the posterior area of the pelvis. And exits by the greater sciatic notch on route to the greater trochanter.
The pelvic floor comprises of three muscles. What is common to them all?
Desribe this commonality
All three components share one continuous origin, suspended from the lateral walls of the pelvis.
They also come together in the midline in a central raphe.
The pelvic floor is often referred to as the pelvic diaphragm. Why is this so?
Because of its circumferential origin and central insertion. It is a large dome muscle that is separating the pelvis from perineium.
Where are the hiatuses of the pelvic floor (diaphragm) located?
Centrally and anteriorly.
They allow passage of viscera from pelvis to perineum.
Outline the continuous attachment of the pelvic floor muscles
It is a continuous linear attachment running from...
- The midline of the internal aspect of the body of the pubis
- Running laterally through a fascia (thickening) halfway down the obturator internus muscle
- Then continuing on the ishium (bone) to the ishial spine.
What is meant by the fascial origin of the pelvic floor muscles off the obturator internus muscles?
What is the significance of this to the muscle?
There is a thickening of the fascia surrounding obturator internus that gives origin to fibres of pelvic floor.
This means that half obturator internus lies in pelvis and half lies in the perineium.
How does the raphe close the rest of the pelvis?
The raphe extends posteriorly from tip of coccyx forwards to the anorectal junction
Called the ANOCOCCYGEAL RAPHE.
Describe the function of the pelvic floor muscles
The pelvic floor is like hammock.
Contraction causes it to lift to increase intraabdominal pressure for evacuation processes. If at the same time diaphragm comes up (as abdomen contracts).
The hammock is also vital for rotation of baby’s head in birthing process.
What are the three parts to the pelvic floor?
Which parts form the functional levator ani?
- Pubococcygeus muscle
- Iliococcygeus muscle
- Ischicoccygeus muscle
Only the Pubococcygeus and Iliococcygeus muscles are able to lift (ishicoccygeus is effectively funtionless)
Describe the pubococcygeus muscle, what is unique about it?
The most anterior fibres (from pubic bone and first part of obturator internus).
It is argueably the most important (the outflow tracts are anterior) because it forms slings around the terminal portions of the tracts.
The pubococcygeus muscle itself is further subdivided into THREE parts.
What are these parts? Describe each
Pubovaginalis (supports vagina and indirectly the urethra as it sits just in on top of it). In the male the urethra is embedded in the prostate so it slings around the prostate gland called the puboprostaticus
Puborectalis slings around ano-rectal junction and blends with anorectal junction.
- Last portion of it that comes behind anorectal junction an blends with the raphe
Describe the ileococcygeus muscle
Comes from the middle part of the pelvic floor coming from most of the obturator internus fascia.
It underlaps pubococcygeus and meets/interdigitates in the raphe in the middle.
What is the important function of the puborectalis muscle?
Puborectalis is vital to fecal continance.
The sling structure creates an angulation (80 degree) such that contration pulls the rectum forward on the anal canal.
When it relaxes, the anorectal junction straightens out for defectaion to occur.
Describe the ishicoccygeus muscle.
What structure of the pelvis is very closly related to it?
A posterior and rudimentary part of pelvic floor containing only a few muscle fibres running from ishcial spine to the coccyx. The two sides join at the centre raphe.
It doesn’t have much of a function in humans. It does not move or lift.
It runs on the internal aspect of the sacrospinous ligament.
Label the following diagram...
What is the pelvic fascia?
A dense fascia that is overlying structures that don’t move. It comprises of two major parts:
Pelvic wall fascia is dense and strong membrane continuation of fascia that line anterior and posterior abdominal wall.
- Note the fascia of pelvic floor is loose (overlying levator ani).
- Visceral fascia varies on the movement of what it overlies. Bladder, rectum and uterus have loose fascia c.f. prostate glands and cervix.
What is unique about the fascia in the pelvis?
There is loose aerolear connective tissue filling the space of the pelvis between lateral wall fascia and visceral fascia (infection spread is a problem).
It condenses around the nerves and vessels (on the side walls of the pelvis and supply the midline viscera). They leave side walls and head towards middle of the pelvis aided by the loose fascia which condense around structures and form ligaments.
Describe the sacral plexus in relation to structures of the pelvis
Sacral plexus exits on the posterior pelvic wall. It lies on piriforms and attached firmly to it by a parietal fascia of pelvic wall.
The internal ileac artery supplies the pelvis. Describe the divisions of it
Internal ileac artery dividing into anterior and posterior divisions at the pelvic rim
- Posterior (and some anterior) divisions go to supply the lower limb (are parietal branches)
- Anterior gives rise to the visceral branches and come from the side wall of pelvis. It is these branches that get the connective tissue wrapping of aerolar fascia that condenses around them and forms ligaments
How does the peritoneum of the abdomen end?
Does descend to the pelvic floor diaphragm (analogus to what it does in the diaphram in the thorax) such that viscera are intraperitoneal like some abdominal viscera are?
The pelvis is another visceral cavity.
The peritoneum descends from the abdomen and the walls are the fascia cts w/ the walls of the anterior and posterior abdominal wall.
It does not go all the way down to the pelvic floor instead the peritoneal lining drapes over the top of the viscera and invests them in part with a serous coat.
Pelvic viscera are EXTRAPERITONEAL structures.
Describe the termination of the peritoneum
- The peritoneum comes down the anterior abdominal wall and on top of syphysis pubis.
- Then it reflects onto the top of the bladder running backwards
- It dips down to cover part of the posterior surface of the bladder but then dips up to line the rectum
- It then ascends onto posterior abdominal wall
This creates the rectovescical pouch between the posterior bladder and the anterior rectum in the (to do with bladder). It is the lowest part of the peritoneum.
What is the significance of the rectovesical pouch?
Any free fluid in the abdomen will fall into this pouch
What happens to the peritoneum when the bladder fills with urine?
When the bladder expands it pushes the peritoneal cavity up. Pushing up of the bladder it pushes the peritoneal cavity up with it.
Clinically relevant: Needle through anterior abdominal wall muscles goes directly into the bladder and drain the urine and nowhere near peritoneal cavity or contents.
Child with UTI: safely penetrate anterior abdominal and aspirate the bladder.
Describe the inferior reaches of the pelvic cavity in the female
It is lining the anterior abdominal wall then hits the top of the pubic bone. It then drapes over the top of the bladder and dips slightly onto the posterior wall of the bladder before ascending on the top of the uterus. It then covers the whole posterior wall of the uterus and then covers only part of the posterior wall of the vagina before it reflects back up on the anterior rectum up the posterior abdominal wall
What two pelvic structures that the peritoneum overly that are not completely covered/draped by peritoneum?
What does this form?
Doesn’t cover the whole extent of the anterior part of the uterus
Doesn't cover the whole vagina (only small part of the posterior wall)
This creates pouches where the peritoneum reflects back off
The inferior reaches of the peritoneal cavity create 2 dependent folds/pouches in the females. What are these?
- 1 between bladder and uterus anteriorly
= Vesico-uterine pouch (not as deep)
- 1 between uterus and rectum posteriorly.
= Recto-uterine pouch (Pouch of Douglas)
What are the clinical implications of these 2 inferior pouches in the peritoneum in the female?
- This is the lowermost part of the cavity; in upright position fluid will collect in this pouch. Eg. inflammed appendix or ovarian cyst rupturing sending fluid into the cavity and this collects in the pouch of douglas. It directly relates to the posterior wall of the vagina so a per vaginal examinatino (2 fingers inside the vagina) the tip of the fingers abut the posterior wall of the vagina and can palpate fluid in the pouch of douglas. Can aspirate the fluid to examine it via the posterior wall of the vagina.
- Angle of the uterus bent forward over the top of the vagina on top of the bladder - abortion. Through the posterior superior vaginal wall rupture causing introduction sepsis in peritoneal cavity.
Does the peritoneum only cover the central structures of the pelvic cavity? (ie. is it related to the lateral wall somehow)?
The peritoneum drops over the whole of the pelvic viscera and extending out the lateral walls of the pelvis.
The whole of the bladder, uterus and uterine tubes and lining pelvic wall that the rectum relates to. Beyond the viscera to the side wall is called the broad ligament.