PELVIS OSTEOLOGY + ARTHROLOGY

Question 1

Greater pelvis

Answer 1

Greater pelvis the superior parts bonded by the expanded bladelike portions of each ilium superior to the acute and iliopectineal lines

Function
encloses organs of the inferior abdominal canal

Question 2

Lesser Pelvis

Answer 2

located inferiorly. Within the lesser pelvis reside the pelvic cavity and pelvic viscera.

Boundaries of true pelvis:
•superior pelvic aperture (above) SPA
• Inferior pelvic aperture (below) IPA

SPA- Pelvic brim includes base of sacrum iliopectineal line superior margin of the pubic symphysis

IPA – bonded by sacrum and coccyx posteriorly ischial tuberosity laterally and symphysis pubis anteriorly

Question 3

Functions of pelvis

Answer 3

Supports and protects the contained viscera

Provides bony surfaces from muscle and ligament attachment

Transfers weight to the ischial tuberosities in sitting

Transferred weight to the lower limbs in standing

Question 4

Weight transference

Answer 4

1)Posteriorly arch
Made up of sacrum and 2 strong pillars of bone running from sacroiliac joint to acetabular fossa

2)Anterior arch
•Made up of pubic bone and and superior rami
Connect space of lateral pillars of the posteriorly arch
•Acts typing to prevent separation of posteriorly arch and strapped to resist medial force of femoral head

Question 5

How is the pelvis stable during weight transmission

Answer 5

The weight of the trunk falls on to the sacrum at the top of the posterior arch.
As the position of the pelvis is angled 30° in normal standing due to the superior surface of the sacrum

The force is taken in two ways:

1) The first component of force drives the sacrum downwards and backwards between the iliac bones. This force is resisted by the wedge shape of the sacrum, the sacroiliac + iliolumbar ligaments, and by the ligaments of the symphysis pubis (superior + inferior pubic ligaments).

The SIJ is a ‘self-locking’ joint, so the more tightly it is held, the more weight it is able to bear.

2) The second component of force tends to push the upper end of the sacrum downwards and forwards towards the pelvic cavity.

This is resisted by the interlocking nature of the middle segment of the SIJ.

A rotatory movement results (the anterior segment rotating downwards while the posterior segment rotates upwards).

The posterior and interosseous sacroiliac ligaments resist the anterior rotation, while the sacrotuberous and sacrospinous ligaments resist the posterior rotation.

Question 6

Articulations of the pelvis

Answer 6

1) Lumbosacral joint- L5 and sacrum where mobile meets immobile
2) Sacroiliac joint- ilium and sacrum
3) Sarcococcygeal joint- coccyx and sacrum
4) Symphysis pubis- pubic bones

Each innominate bone articulates with the sacrum posteriorly at the sacroiliac joint and with each other anteriorly at the symphysis pubis

Articulation with the lower limb is at the acetabulum and with the trunk via sacrum which articulautes with L5 superiorly at the Lumbosacral joint and coccyx inferiorly

Question 7

Lumbosacral joint

Answer 7

1)Secondary cartilaginous
between L5 VB and sacrum

2)Synovial plane
L5 V arch and sacrum (articular surface sacrum)

Very thick, thicker anteriorly, thinner posteriorally.

 Anterior longitudinal ligament;
 Posterior longitudinal ligament;
 Ligamentum flavum;
 Interspinous ligament;
 Supraspinous ligament;
 ILIOLUMBAR LIGAMENT
 LATERAL LUMBOSACRAL LIGAMENT

Question 8

Iliolumbar ligament

Answer 8

S: Strong ligament

O: T.P of the 5th lumbar vertebrae (sometimes additional band from 4th Lv)

I: anterior lip of the iliac crest

D: inferiorly and laterally

A: prevents unwanted lateral movement of L5 L4
Prevents anterior movement L5 on S1

Question 9

Lateral lumbosacral ligament

Answer 9

Partially continuous with the lower part of the iliolumbar ligament

O: T.P of 5th lumbar vertebrae

I: ala of sacrum

D: obliquely and inferiorly

A: later movement of L5

Question 10

Sacroiliac joint classification

Answer 10

1) Synovial, modified plane anteriorly

2) Fibrous posteriorly

Question 11

Sacroiliac joint- articular surface

Answer 11

Auricular surface of the sacrum is covered by hyaline cartilage, its central part being concave with raised crests peripherally.

The corresponding auricular surface on the ilium is covered by fibrocartilage and its surface is raised centrally by a crest surrounded by two furrows.

Both surfaces are L-shaped, being broader above and narrower below.

They both show marked reciprocal irregularities which enable the bones to fit into each other thus restricting movement and contributing to the strength and stability of the joint

Question 12

Sacroiliac joint - JC

Answer 12

Completely surrounds the joint.

Question 13

Sacroiliac joint - synovial membrane

Answer 13

Lines the non-articular parts of the joint.

Question 14

Sacroiliac joints - factoids

Answer 14

Does not move much

Glides and rotates but only 2 mm downward and 5° rotation

It is restricted in movement- compensated with being very stable due to articular contours and surface regularity and argument

Common source of back pain

Question 15

Sacroiliac joint – ligaments

Answer 15

Ligaments of the SIJ

Anterior sarcoiliac ligament
Posterior sarcoiliac ligament
Interosseous sacroiliac ligament

Accessory ligament (no attatchments in SIJs)

Sarcotuberous ligament
Sacrospinous ligament

Question 16

Anterior sacroiliac ligament

Answer 16

lies on pelvic surface of the joint

S:Broad consist of numerous thin bands

O: Ala and pelvic surface of sacrum

I: adjoining margin of the articular surface of ilium

D: obliquely

A: prevents posterior movement

Stronger in females

Question 17

Posterior sarcoiliac ligament

Answer 17

Thicker and stronger than anterior
Lie in upper part of cleft

1)Horizontal fibers of the short posterior sacroiliac ligament
1st+2nd transverse tubercles of sacrum to PSIS resist forward movement of the sacrum

2)Long posterior sacroiliac ligament = most superficial passing almost vertically
PSIS-3rd and 4th transverse tubercles of sacrum resist downward movement of Sacrum

Question 18

Interosseous sacroiliac ligament

Answer 18

Posterior

S: Deep short thick v strong

Fills the cleft behind and above the articular surfaces

Horizontally running fibres

Keeps sacrum and ilium tightly secured

Question 19

Sarcotuberous ligament

Answer 19

S:Flat 🔺 very strong

O: lower transverse tubercles and inferior margins of sacrum and upper coccyx

I: ischial tuberosity

D: downwards and laterally

A: forward tilt of sacrum

Question 20

Sacrospinous

Answer 20

S:🔺deeper

O: lower sacral and upper coccygeal segments

I: ischial spine

D: laterally

A: forward tilt of sacrum

Question 21

Sacrococcygeal joint

Answer 21

Secondary cartilaginous.
Disc of fibrocartilage

Between apex of sacrum and base of the coccyx

Longitudinal fibres completely surround and reinforce the joint.
Anterior posterior lateral sarcocygeal ligs

The sacrococcygeal joints frequently become either totally or partially obliterated with age.

Question 22

Symphysis pubis- classification

Answer 22

Secondary cartilaginous.

No movement except in pregnancy

Question 23

Symphysis pubis- Articulating surfaces

Answer 23

Articular surfaces formed by oval facets on the medial surfaces of the bodies of the pubic bones = corresponding irregularities which help the bones fit together snugly.

Each surface is covered by a thin layer of hyaline cartilage.

Articular surfaces are connected by a thick fibrocartilaginous interpubic disc.

Question 24

Symphysis pubis- ligaments

Answer 24

Superior pubic ligament

Inferior (arcuate) ligament

Question 25

Superior pubic ligament

Answer 25

Horizontal Fibers attaching to both pubic crest and tubercles

Strengthens the superior pubis superolatterally

Question 26

Inferior (arcuate) ligament

Answer 26

fibre is between both inferior pubic Rami

Strengthens the superior pubis inferolatterally

Question 27

Junction between greater and lesser pelvis

Answer 27

The junction between the greater and lesser pelvis is known as the pelvic inlet. The outer bony edges of the pelvic inlet are called the pelvic brim.

Question 28

Sacrotuberous and sacrospinous break sciatic formen

Answer 28

Greater and lesser formen