Pelvis and SIJ Flashcards
At what vertebral level is PSIS?
S2
What part of the ilium articulates with the sacrum?
Auricular Surface
Which way do the facets at the sacral base face?
Posteriorly
How many vertebrae make up the coccyx?
4
Gender differences in pelvis shape
Female: Wider and shorter
What part of pelvis tends to fracture?
Pubic rami
Pelvic Chain
Connection of axial and peripheral skeleton
- (B) sacroiliac joints
- Pubic symphysis
- Connected pliable ring
SI Joint
S1-3 articulating with right and left ilia
Joint is C/ auricular/ boomerang shaped
Surfaces covered with hyaline cartilage
Articular surfaces of SIJ
(Hyaline cartilage)
Childhood: Diarthrodial joint (smooth joint surfaces, more movement)
Adulthood: Synarthrodial joint
- Joint surfaces more rough
- Aging –> Fibrotic capsule (males lose more motion than females)
- Irregular joint surfaces correspond to each other (fit together –> stability)
- 80 y/o, 10% fused
Primary SIJ stabilizers (ligaments)
Iliolumbar ligaments
Anterior sacroiliac ligament
Short and long posterior sacroiliac ligaments
Interosseous ligament (internal to joint)
Secondary SIJ stabilizers (ligaments)
Sacrospinous ligament
Sacrotuberous ligament
Iliolumbar ligaments
- Ventral, dorsal, and sacral bands
- TPs of L4,5 to iliac crests/ sacral ala
- Strong bonds between L5 and ilium
- Stabilize lumbosacral joint
- Reinforce anterior side of SIJ
Anterior Sacroiliac Ligaments
Thickening of anterior and inferior regions of capsule
- Reinforce anterior side of SIJ
Posterior Sacroiliac Ligaments
- Short posterior
- Long posterior
- Reinforce posterior SIJ
- Fibers blend with sacrotuberous ligament
Interosseous ligament
- Deep to short posterior SI ligaments
- Fills “gap” between posterior and superior margins of SIJ
- Strongly and rigidly binds sacrum with ilium
- Similar in nature to the interosseous ligament in tibfib joint
Sacrotuberous ligament
- PSIS, ILA, and lateral sacrum/ coccyx to ischial tuberosities
- Blends with fibers of biceps femoris
- Assists indirectly with SIJ stability (doesn’t actually cross SIJ)
Sacrospinous Ligament
- Ischial spine to lateral border of sacrum
- Controls lateral/ torsional strain and rotational strain
- Pelvic floor muscles have attachments to ligament
SIJ Innervation
- Sensory nerves
- Debate re: which exact nerves (L5-S3, dorsal or ventral rami?)