PELVIS OSTEOLOGY + ARTHROLOGY Flashcards
Greater pelvis
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
Lesser Pelvis
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
Functions of pelvis
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
Weight transference
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
How is the pelvis stable during weight transmission
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.
Articulations of the pelvis
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
Lumbosacral joint
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
Iliolumbar ligament
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
Lateral lumbosacral ligament
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
Sacroiliac joint classification
1) Synovial, modified plane anteriorly
2) Fibrous posteriorly
Sacroiliac joint- articular surface
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
Sacroiliac joint - JC
Completely surrounds the joint.
Sacroiliac joint - synovial membrane
Lines the non-articular parts of the joint.
Sacroiliac joints - factoids
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
Sacroiliac joint – ligaments
Ligaments of the SIJ
Anterior sarcoiliac ligament
Posterior sarcoiliac ligament
Interosseous sacroiliac ligament
Accessory ligament (no attatchments in SIJs)
Sarcotuberous ligament
Sacrospinous ligament
Anterior sacroiliac ligament
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
Posterior sarcoiliac ligament
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
Interosseous sacroiliac ligament
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
Sarcotuberous ligament
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
Sacrospinous
S:🔺deeper
O: lower sacral and upper coccygeal segments
I: ischial spine
D: laterally
A: forward tilt of sacrum
Sacrococcygeal joint
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.
Symphysis pubis- classification
Secondary cartilaginous.
No movement except in pregnancy
Symphysis pubis- Articulating surfaces
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.
Symphysis pubis- ligaments
Superior pubic ligament
Inferior (arcuate) ligament
Superior pubic ligament
Horizontal Fibers attaching to both pubic crest and tubercles
Strengthens the superior pubis superolatterally
Inferior (arcuate) ligament
fibre is between both inferior pubic Rami
Strengthens the superior pubis inferolatterally
Junction between greater and lesser pelvis
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.
Sacrotuberous and sacrospinous break sciatic formen
Greater and lesser formen
