5. Bones and Joints of Pelvis

Question 1

What is the line that divides the false and true pelvis?

Answer 1

The Illiopectineal line

Goes from the top pubic symphisis to the 1st lumbosacral disc

Question 2

What is the difference between female and male pelvis?

Answer 2

Female pelvis is shallower from the above down, savrum is broad, so length and wideth is the same

Sub-Pubic angle is broader in females

Male pelvis is much narrower (length > width)

Sub-pubic angle is narrow

Question 3

What comes out of the anterior sacral foramina?

Answer 3

Ventral rami

Sacral plexus lie on the sacrum before forming sciatic nerves etc.

Question 4

What enters the Anterior sacral formamina?

Answer 4

These foramina are also roots for veins draining pelvic viscera. Pelvic viscera are drained by plexuses of veins. (Prostate, uters, etc) Normal drainage are normally IVC, but should there be blockage, anterior sacral veins can pass into vertebral canal into the back.

A common method of spread of cancers into the spinal canal.

Question 5

What are the types of pelvis? What are their distribution?

Answer 5

50% women have Gyanecoid Pelvis.

Need to be broad as possible for baby to pass through the birth canal. Pelvic inlet is broad from side to side and from front to back.

In contrast the male pelvic inlet is heart shaped. Narrow form front to back and side to side.

When we get to true pelvis the shape is maintained. So the true pelvis is broad in female. Extends to the outlet

Approximately 30% of female pelvis are android pelvis. Has narrow inlet, narrow true pelvis and narrow outlet.

Question 6

How is the fetal head orientated in the pelvis?

Answer 6

Fetal head comes into pelvic inlet and rotate 90* towards the pelvic outlet.

Question 7

What is the effect os the line of gravity on the pelvis?

Answer 7

Line of gravity passes infront of the saccrum

So it tilts in the reverse direction to the lumbar spine.

The result of that tilting is when you have the hip bone in normal orientation the ASIS is in line with the pubic symphysis.

The top of pubic symphysis is same horizontal plane as the tip of the coccyx.

Tilt is accentuated in females due to increase lumbar lodrosis.

Question 8

Describe the pelvic outlet

Answer 8

Outlet transmit tubular viscera into the exterior. Via a triangle.

Divided into two triangles.

Urogenital Triangle

• Urethra and vagina (female)

Prostatic urethra –> Membranous urethra –> Penile Urethra (male)

Anal Triangle

• Opening of anus

Question 9

What is the boundary of the triangle of pelvic outlet?

Answer 9

Ligament from ischeal tuberosity into the sacrum

Question 10

What is the narrow pelvic plane?

Answer 10

Plane of least dimensions - Passes through the ischial spine, S4 and the base of pubic bone - negotiated by the widest part of foetus (the head) during childbirth

Question 11

What is the pelvic plane line?

Answer 11

Pelvic pain line and narrow pelvic plane pretty much correspond. Site from which pain is referred back to the CNS.

Whatever viscera is located above the pelvic pain line will refer to the LOWER THORAXIC UPPER LUMBAR SPINAL CORD via Sympathetic nerves (visceral)

Below the pelvic

Transmitted to Parasympathetic into S2,3 and 4 (referred to skin especially perineum)

Question 12

What are the apertures of the pelvis?

Answer 12

Pelvic Inlet - From Abdomen

Anterior sacral foraminae - to back

Obturator canal - to lower limb

Greater sciatic foramen - to lower limb

Lesser sciatic foramen - to perineum & gluteal region

Question 13

How can the pelvis be used for forensics?

Answer 13

Body of the pubic is narrow from front to back in male and angulation is acute

Question 14

What are the bony arches of the pelvis?

Answer 14

Acetabulum to sacrum –> Primary arch

Underneath 2 pubis bone –> smaller arch

Question 15

How is the force distributed on the pelvics?

Answer 15

Question 16

Describe the Sacroiliac joint

Answer 16

Part synovial (anterior) Part Fibrous (posterior)

Illiac & Sacral auricular surfaces

Held together by powerful ligaments

• Interosseous sacroiliac
• Illiolumar
• Sacrotuberous
• Sacrospinous

All resist tendency of sacrum to rotate (nutation)

Question 17

Which of the ligaments of the sacroiliac joint is the most powerful?

Answer 17

Interosseous sacroiliac

Question 18

What is the reverse keystone effect?

Answer 18

When we get up sacrum sinks between two iliac bone. If we didn’t have ligamentous fibers would open the space upwards but because we have ligamentous fibers the movement down actually tighten and result in increased stability at the joint.

Stability at sacroiliac joint is due to tightening of ligaments located posteriorly

Net effect is reverse keystone effect.

Question 19

What is the axis of rotation at the sacrum during trunk flexion/extension?

Answer 19

Sacral base moves forwards & backwards axis of rotation S2

Question 20

Most movement in the SIJ occurs when?

Answer 20

Rising from recumbent position to standin - May amount to 2-8 degrees through the ROM

Question 21

When is ROM increased at the SIJ?

Answer 21

Mid to late stages of pregnancy (under influence of relaxin) when supporting ligaments relax

Question 22

Why do women sometimes experience backpain after pregnancy? and where is the pain refered?

Answer 22

Ligaments may re-tighten but with slight discrepancy and cause pain .

Joint get nerve supply from dorsal rami of L5-S3

Pain may be referred to buttock region and perhaps radiating to lateral thigh.

Question 23

What muscles transfer loads between trunk & lower limb muscles?

Answer 23

Lat dorsi & gluteus maximus.

Tension increases compression at the SIJ. Exercise involving contralateral limb movements may enhance this

Question 24

Describe the pubic symphisis

Answer 24

2nd Cartilaginous joint (hyaline cartialge on bones external to symphisis)

Has ligaments

• Superior
• Arcuate (resist vertical forces)
• Anterior

Reinforces by criss-crossing fibres from rectus abdominis & transversus (+adductor longus & internal oblique)

Acts as tie beam. preventing seperation laterally.

Question 25

What are the types of pelvic fractures?

Answer 25