Pelvis: Bones & Muscles

Question 1

What delineates the greater and lesser sciatic notches?

What forms the foramina?

Answer 1

Ischial spine

Sacrospinous ligament

Question 2

What are the features of the sacrum?

Answer 2

5 fused vertebra
Lateral masses
Top of lateral masses = ala
Top of fused vertebral body region = promontary

Question 3

What are the 3 joints associated with the sacrum?

Answer 3

Sacro-iliac joint
Sacro-coccygeal joint
Lumbosacral joint

Question 4

What ligaments are associated with the sacral joints & prevent displacement of the sacrum?

Answer 4

Sacrospinous ligament - ischial spine to sacrum
Sacroiliac x 3 (anterior, posterior & interosseous) - iliac to sacrum
Sacrotuberous ligament - sacrum and ischial tuberosity
Iliolumbar - iliac fossa to transverse process of L5

Question 5

What movements of the sacrum occur?

How does it affect the pelvic inlet & outlet?

Answer 5

Nutation & counter-nutation
Nutation - top of sacrum forwards and bottom backwards - CLOSES inlet, opens outlet
Counter-nutation - OPENS inlet, closes outlet

Question 6

What is the pubic symphysis?

What reinforces it?

Answer 6

Secondary carilagenous joint between pubic bones in the midline

Reinforced by criss-crossing fibres of rectus abdominus, oblique abdominal muscles + adductor longus
Inferior arcuate ligament & superior pubic ligament prevent separation

Question 7

What bony and ligamentous structures form the obtrurator foramen & canal?

Answer 7

Obtrurator foramen formed from joining of rami of the pubic and ischial bones
Obtrurator membrane covers the foramen, leaving a space called the obtrurator canal

Question 8

What muscles make up the lateral & posterior walls of the pelvis and the pelvic floor?

Answer 8

Lateral = obtrurator internus
Posterior = piriformis
Pelvic floor = levator ani (pubococcygeus + iliococcygeus_ & ischiooccygeous

Question 9

What is the origin & insertion of obtrurator internus?

Answer 9

Arises from obtrurator membrane converges as it moves backwards towards the lesser sciatic foramen where it exits the pelvis and collects the germelli muscles

Enters the gluteal region and inserts on the the greater trochanter of the femur

Question 10

What is the origin & insertion of piriformis?

Answer 10

Arises along the middle & lateral components of the sacrum, running along the posterior aspect of the pelvis and exiting through the greater sciatic foramen

Enters the gluteal region and inserts onto the greater trochanter of the femur

Question 11

What are collective the origins & insertions of levator ani?

Function?

Answer 11

Levator ani = pubococcygeus + iliococcygeus

Collectively it arises halfway along obtrurator internus, running along the lateral pelvic wall until the ischial spine

Sweeps down to form sling structures and insert into the midlife anococcygeal raphe

Close the pelvis off to the perineum below
Contract to lift the pelvic floor

Question 12

Arrangement of pubococcygeus (part of LA)

Answer 12

3 components
Most anterior fibres form a sling around the vagina (pubovaginalis) or the prostate (puboprostaticus)
More lateral fibres form a sling around the ano-rectal junction
Most lateral fibres insert in the midline anococcygeal rap he

Question 13

Arrangement of iliococcygeus (part of LA)

Answer 13

Arises form fascia of obtrurator internus, passes beneath pubococcygeus and inserts into the midline anoccygeal raphe

Question 14

What is the origin & insertion of ischiococcygeus?

What is its function?

Answer 14

Extends from the ischial spine to the coccyx

Non-functional in humans

Question 15

What is functionally important about puborectalis?

Answer 15

Part of pubococcygeous (part of LA)

Needs to relax in order for defecation to occur

Question 16

Describe the features of endopelvic fascia

Answer 16

Loose and dense - loose covers things that need to move or expand (i.e. LA, bladder) and dense covers fixed structures (i.e. piriformis)

Fill spaces in the pelvis - good environment for spread of sepsis

Condensations occur around neurovascular structures from the lateral pelvic walls
Condensations also form ligaments that support midline viscera