Pelvis - content, vessels and nerves

Question 1

Describe the sacrum

Answer 1

• The sacrum is made up of 5 fused sacral vertebrae
• There are extra masses of bone of the side of the vertebrae that look like butterfly wings and these are called ala
• There are 4 paired anterior sacral foramen and 4 paire posterior sacral foramen and these are used for the passage of ant and post nerve roots to exit/enter
• At the base of the sacrum the coccyx is attached

Question 2

Why is the sacral hiatus used for putting in nerve blocks?

Answer 2

It is where the spinal cord splits into the cauda equina (individual nerve fibres) and so it easy to a nerve block here as there is less risk of damaging the spinal nerves

Question 3

What is the true vs false pelvis?

Answer 3

The pelvic inlet marks the division between the true and false pelvis. The true pelvis is everything below this line whereas the false pelvis is everything above the line. The false pelvis contains structures from the abdominal cavity.

Question 4

What are the landmarks in the pelvis that help mark out the pelvic inlet and pelvis outlet?

Answer 4

Inlet:
Sacrolumbar joint posteriorly, ala (wings) of the sacrum, the arcuate line (over the iliac fossa), the pectineal line , and then the pubic crest - pubic symphysis.

Outlet:
Pubic symphysis - ischiopubic ramus - ischial tuberosity - sacrotuberous ligament - coccyx

Question 5

What is the shape of the pelvic outlet and what two shapes make up this outlet?

Answer 5

The entirety of the pelvic outlet is a diamond in shape and this is made up of the urogenital triangle and the anal triangle. The urogenital triangle is inferior and faces anterior and the anal triangle is more superior and faces posteriorly.

Question 6

What are the bony prominences forming the “points of the pelvic outlet” shape?

Answer 6

anterior - pubic symphysis
laterally - ischial tuberositys
posteriorly - coccyx

Question 7

What is the perineal body?

Answer 7

A spot of thick fibrous connnective tissue between the urogenital and anal triangles that is a site of many muscle attachments. eg Levator ani, bulbospongiousus, perineal muscles and external anal sphincter

Question 8

What branches does the pudendal nerve give off? What nerve roots supply the pudendal nerve?

Answer 8

Inferior rectal
Scrotal
Dorsal nerve of the penis

S2, 3, 4 keeps the penis off the floor

Question 9

Aside from the pudendal nerve what other nerves are important in this area? (somatic nerve supply)

Answer 9

Superior gluteal - supplies motot to glut med and min
Inferior gluteal - supplies motor to glut max
Sciatic - supplies motor and sensory to post thigh and all of the leg

nerve to levator ani/ coccxygeus - motor supply to levator ani and coxxygeus

Question 10

What is the ANS supply to the pelvic area (para and sympathetic nervous supply)

Answer 10

Superior hypogastric and inferior hypogastric.

Sympathetic supply is from L1/2 nerve fibres which descend via the Superior hypogastric plexus and also directly from sacral splanchnic nerves.

Parasympathetic is from S2-S4 nerve fibres and these ascend via the hypogastric plexus to the superior hypogastric plexus in the abdomen.

Question 11

What is a saddle fracture?

Answer 11

A break in the pelvis that includes the pubic bones - you can imagine these to have happened from having a really hard jarring downward motion onto a horse saddle or something.

These fractures can split right through ischial bone, can split the sacro-iliac joint etc.

Question 12

What is the difference in shape of the pelvic outlet in males and females?

Answer 12

In females it is a big, oval pelvic outlet to allow for the passage of the baby during birth.
In males it is a heart shape as the pubic bones are closer together. Also, looking from a superior perspective you can see the ischial spines poking intowards the pelvic outlet. If this were to occur in women it would restrict the baby from being able to pass out of the canal.

Question 13

What is referred to as the “pelvic tilt”?

Answer 13

The pelvis is not sitting flat (the diamond shaped pelvic outlet is not a flat diamond, it is 2D). The pelvis is tilted anteriorly 60 degrees so that the ASIS is in line with the pubic symphysis. Physios will often palpate to check this for alignment.

Question 14

What are the main sacral ligaments in the pelvis and what foramen do they form?

Answer 14

Sacrotuberous extends from the sacrum to the ischial tuberosity and the sacrospinous extends from the sacrum to the ischial spine. These help divide the sciatic foramen into the greater and lesser sciatic foramen.

Question 15

What happens to some of the pelvis joints during pregnancy in preparation for childbirth?

Answer 15

The anterior sacroiliac and the pubic symphysis both widen in order to increase the size of the pelvic outlet for the baby to come through. This is why a lot of women get back pain during end stages of pregnancy as this canal is widening.

Question 16

What are the two main muscles of butt that contribute to the pelvic wall? Describe their origin, insertion, actione etc

Answer 16

Piriformis - originates from the sacral vertebrae and exits the sacrum through the greater sciatic foramen to then insert onto the greater trochanter of the femur. It acts as an external/lateral rotator of the hip.

Obturator internus - originates in the obturator foramen (fills most of this space) on the obturator membrane and the surrounding ischio-pubic ramus and then passes out to attach to the greater trochanter of the hip. (alongside the pririformis)

Question 17

What is the relationship between most of the pelvic vessels and the piriformis muscle?

Answer 17

Most of the pelvic vessels exit via the greater sciatic foramen but most will be below the piriformis muscle. The only to exit above piriformis muscle in the greater sciatic foramen is the superior gluteal nerve.

Question 18

What exits out of the obturator canal?

Answer 18

The obturator canal is the space left open in the obturator foramen by a small deficiency in the obturator membrane. This allows for passage of the obturator vessels (artery, vein and nerves).

Question 19

What is piriformis syndrome?

Answer 19

A condition where there is tingling/numbness/pain to areas of the lower limb due to compression of the sciatic nerve as it passes out underneath the piriformis muscle.

Question 20

What vessels travel out of the greater sciatic foramen (above and below piriformis), the lesser sciatic formane and the obturator canal?

Answer 20

GSF (above piriformis) =
Superior gluteal nerve and artery

GSF (below piriformis) = 
Inferior gluteal nerve and artery
Sciatic nerve 
Posterior cutaneous nerve of the thigh 
Internal pudendal artery and pudendal nerve 
Nerve to obturator internus 
Nevre to quadratus femoris 

LSF =
re-entry of the internal pudendal artery and pudendal nerve into the pelvis
Re-entry of the nerve to obturator internus

Obturator canal =
exit of the obturator nerve and obturator vessels

Question 21

Where should an intramuscular injection be given in the buttocks?

Answer 21

The upper lateral quadrant - in order to avoid the sciatic nerve. Damage to this nerve could result in loss of motor control/sensation to the leg.

Question 22

The aorta branches into the common iliacs at the level of L4. This then branches into the external iliac and internal iliac artery. Which of these two supplies the pelvic cavity?

Answer 22

The external iliac goes on to form the femoral artery as it passes under the inguinal ligament. The internal iliac branches into anterior and posterior and supplies the pelvic cavity.

Question 23

What is the sacral plexus?

Answer 23

The sacral plexus is a network of nerve fibres that supplies the skin and muscles of the pelvis and lower limb. It is located on the surface of the posterior pelvic wall, anterior to the piriformis muscle.

The plexus is formed by the anterior rami (divisions) of the sacral spinal nerves S1, S2, S3 and S4. It also receives contributions from the lumbar spinal nerves L4 and L5.

These nerves then descend down the posterior pelvic wall. They have two main destinations:

Leave the pelvis via the greater sciatic foramen – these nerves enter the gluteal region of the lower limb, innervating the structures there.
Remain in the pelvis – these nerves innervate the pelvic muscles, organs and perineum.

Question 24

What are the main branches of the sacral plexus?

Answer 24

Superior gluteal
Inferior gluteal
Posterior cutaneous nerve of the thigh 
Sciatic 
Pudendal

(other smaller branches include nerve to obturator internus and nerve to quadratus femoris)

Question 25

What are the main branches of the anterior division of the internal iliac artery?

Answer 25

Superior vesical
Inferior vesical

Vaginal/prostatic

Obturator

Middle rectal

Inferior rection

Termiantes as Internal pudendal and inferior gluteal

Note: the arrangement of branches from the anterior divison of the internal iliac are highly variable so dont know order just know names

Question 26

What branches of the anterior division of the internal iliac artery supply the prostate, seminal vesicles and the vas deferens?

Answer 26

Middle rectal and inferior vesical (the testes are supplied by the testicular artery from L2 spinal level).

Question 27

What branch of the anterior division of the internal iliac artery supply the vagina?

Answer 27

The uterine artery gives off the vaginal artery. (the ovaries are supplied by the ovarian artery from L2 spinal level).

Question 28

What is the main branch of the posterior division of the internal iliac?

Answer 28

Superior gluteal

Question 29

Describe the venous drainage of the pelvic cavity?

Answer 29

The bladder, prostate, rectum, uterus and vagina all have very rich venous plexuses draining them which drain into the internal iliac veins.

The rest of the perineum will drain into the internal pudendal veins.
The exception to this is the deep dorsal artery of the penis/clitoris which drains into the vesical/prostatic plexuses and then thus into the internal iliac veins.

Question 30

What main branches come off the pudendal nerve?

Answer 30

Inferior rectal
Dorsal nerve to clit/penis
Perineal
scrotal/labial

Question 31

What is the perineum?

Answer 31

The perineum is an anatomical region located in the pelvis. It is the most inferior part of the pelvic outlet, located between the thighs. It is separated from the pelvic cavity superiorly by the pelvic floor.

Question 32

What two muscles make up the pelvic floor?

Answer 32

Levator ani and coccygeus

Question 33

What 4 muscles act to seperate the pelvic viscera (organs of the pelvis) in the pelvic cavity from the perineum (region which contains the genitalia and anus)?

Answer 33

Laterally and posteriorly = Obturator internus and piriformis

Inferiorly = Levator and coccygeus (pelvic floor)

Question 34

What is another name for the pelvic floor and what shape does it have?

Answer 34

The pelvic diaphragm - it has a funnel like shape.

Question 35

What makes up the Levator ani muscle?

Answer 35

Levator ani is a broad like muscle comprised of 3 paired muscles:

Iiococcygeus
Pubococcygeus
Puborectalis

Question 36

What is the importance of the puborectalis muscle of Levator ani?

Answer 36

It forms a sling around the anal canal which pulls it anteriorly and creates an angulation of the anal canal. This is important in maintaining faecal contenence as it means the path of the faeces isnt directly straight out of the perineum.
If you lose the function of the pudendal nerve (S2, S3, S4) or the nerve to levator ani (S4) then this muscle will relax and therefore less control over defaecation.

Question 37

Describe the anal sphincters

Answer 37

There is an internal anal sphincter which is involuntary smooth muscle and an external anal sphincter which is voluntary skeletal muscle.

The external one is most important as this allows us to control our poop. It is innervated by the inferior rectal branch of the pudendal nerve.

Question 38

What is the ischioanal fossas?

Answer 38

The ischianal fossas are wedge shaped spaces located to either side of the anal canal. The inferior border is skin and the superior is the pelvic floor. The contents of the ischioanal fossas include fat for support of the anal canal, the pudendal nerve and internal pudendal vessels laterally (just medial to the ischial tuberosity) and the inferior rectal vessels and nerves which cross these fossa to reach the rectum.

Question 39

Where does the rectum become the anal canal?

Answer 39

Where the rectum pierces the pelvic floor/ the pelvic diaphragm.

Question 40

What is the significance of the anastomoses between the superior rectal vein and the inferior rectal vein?

Answer 40

This is a common site for varices veins as a result of portal hypertension.

Question 41

Why are hemorrhoids that occur externally (external to the anal canal) more painful?

Answer 41

There is where somatic innervation comes in (not just autonomic innervation).

Question 42

What is the contents of the anal triangle?

Answer 42

Anal aperture (opening of the anal canal at the skin surface), the two ischioanal fossas and the external anal sphincter

Question 43

What is the contents of the urogenital triangle?

Answer 43

The genitalia and the urethra. In contrast to the anal triangle the urogenital triangle also has a deep layer of fascia called the perineal membrane. Above and below this there are deep and superficial perineal pouches and deep and superficial perineal fascia.

The deep perineal pouch contains the compressor urethra muscle, the external urethra sphincter and the deep transverse perineal muscles.

The superficial perineal pouch contains the erectile tissues that form the penis and clitoris, and three muscles – the ischiocavernosus, bulbospongiosus and superficial transverse perineal muscles. The greater vestibular glands (Bartholin’s glands) are also located in the superficial perineal pouch.

Question 44

What are the 3 main/important branches of the internal pudendal artery?

Answer 44

The inferior rectal -
The perineal - supplies perineal muscles
The dorsal artery of the penis/clitoris

Question 45

What is the nervous supply to the structures involved in sex?

Answer 45

Para - inferior hypogastric plexus
Sympa - superior hypogastric plexus
motor/sensory - pudendal nerve

Question 46

What is an episiotomy?

Answer 46

A surgical cut in the perineum of the female to relieve stress on the area during the second stage of labour and prevent any serious tearing.

Question 47

An episiotomy can be performed as “midline” cut or a “mediolateral” cut, which is more common and why?

Answer 47

Medio-lateral. This is because there is less risk of the cut extending down into the anal canal.