Sacroiliac Joint Flashcards
Sacrum
5 fused vertebrae S1-S5
Wedged shaped
Base: S1
Apex: S5
Articulating surfaces: Ala
2 auricular (ear-shaped) surfaces (S1-3)
Multiplanar and corresponds to iliac surfaces
Covered with hyaline cartilage (thicker on sacral surfaces)
Base: S1
supports two zygapophyseal facets that face posteriorly for articulation with the inferior facets of the fifth lumbar vertebra
Apex: S5
the fifth sacral vertebra, articulates with the coccyx
Innominate bone
refers to one side of the pelvis formed by the consolidation of the ilium, ischium, and pubis
Innominates
2 ilium: innominates
Each has an auricular articulating surface that corresponds to the sacral articulating surface
Covered with hyaline cartilage (thinners and denser collagen)
Multiplanar (correspond to sacral surfaces)
Anterior Structure
Synovial joint
Posterior structure
Syndesmosis
Role of the SIJ
Relieve the stress on the pelvic ring imparted by movement of the trunk and lower limbs, muscle contractions, the weight of the body, and ground reaction forces
Sacroiliac ligament
joints’ stability
strongest ligaments in the body
Anterior SI ligament
capsular ligaments
Long posterior SI ligament
medial fibers are connected to the deep lamina of the posterior layer of the thoracolumbar fascia and the aponeurosis of the erector spinae
Sacrospinous ligament
connect the ischial spines to the lateral borders of the sacrum and coccyx
inferior border of the greater sciatic notch
Sacrotuberous ligament
connect the ischial tuberosities to the posterior spines at the ilia and the lateral sacrum and coccyx
inferior border of the lesser sciatic notch
Interosseous sacroiliac ligaments
create the more posteriorly located syndesmoses (fibrous union) between the tuberosities of the sacrum and ilia
Symphysis Pubis
Cartilaginous joint
Located between the two ends of the pubic bones
Supported by:
superior pubic ligament
inferior pubic ligament
posterior pubic ligament
Superior pubic ligament
thick and dense fibrous band that attaches to the pubic crests and tubercles and helps support the superior aspect of the joint
Inferior pubic ligament
arches from the inferior rami on one side of the joint to the inferior portion of the rami on the other side and thus reinforces the inferior aspect of the joint
Posterior pubic ligament
fibrous membrane that is continuous with the periosteum of the pubic bones
Axis of motion: Sacrum
Subclinical amount of motion available
-Rotation and translation
Primary axis to emphasize: Coronal
Sagittal Plane
Nutation: movement of the sacrum whereby the sacral base rotates or tips anteriorly on the relatively fixed innominates
Counternutation: the sacral base rotates or tips posteriorly on the relatively fixed innominates
Nutation
Sacral base tips/rotates anteriorly (fwd + down)
Sacral “flexion”
Close-packed position
Counternutation
Sacral base tips/rotates posteriorly (back +up)
Sacral “extension”
Open-packed position
Lumbosacral Flexion
- Segmental flexion of lumbar vertebrae
- Sacrum initiates with counternutation while the innominates rotate anteriorly to lock in place
-Sacrum then shifts to nutation to move w/pelvis as a unit - Hip flexion
Lumbosacral Extension
- Segmental extension of lumbar vertebrae
- Sacrum initiates with nutation while the innominates rotate posteriorly to lock in place
-Sacrum then shifts to counternutation to move w/pelvis as a unit - Hip extension
Dynamic Stability: Force Closure
Muscle action/support to stabilize SIJ
Form Closure
Describes the stability of the joint from the design of the pelvic anatomy itself
