DSA 3: Introduction to Sacrum Flashcards
The sacrus is formed by the union of how many modified vertebrae?
5 modified vertebrae
What does the sacrum articulate with?
- Superiorly: 5th lumbar vertebra
- Inferiorly: coccyx
- Laterally: Os Coxae (inominates) through C shaped SI articulations
What are the four sacral joints?
- Right SI Joint
- Left SI Joint
- L5-S1 Intervertebral disc
- Sacrococcygeal Joint
What is the appearance of the SI joint ligaments in males and females after puberty?
- Male: SIJ ligaments are well-developed and strong
- Female: SIJ ligaments are less developed, allowing mobility during childbirth
What is the appearance of the SI joint in a patient in his or her 20s?
- Crescent-shaped ridge develops along the iliac surface which articulates with a depression in the sacrum
- Add stability and limits mobility
What is the appearance of the SI joint in a patient’s 30s?
Crescent-shaped ridge becomes more pronounced, decreases ROM more
Males: degenerative changes may begin to appear on iliac side
What is the appearance of the SI joint in the 4th and 5th decades of life?
- Males: Degenerative changes appear on sacral side
- Fibrous ankylosis may further limit joint motion
What is the SI joint classified as?
Diarthroidal joint - contanis synovial fluid and matching articular surfaces
What does the posterior sacroiliac ligament connect?
- Origin: Third and fourth sacral segments
- Insertion: PSIS and posterior end of internal lip of iliac crest
Thicker than Anterior Sacroiliac Joint
What does the anterior sacroiliac ligament connect?
- Origin: Third sacral segment
- Insertion: Lateral side of pre-auricular sulcus
What ligament is the major bond between the ilium and the sacrum?
Interosseous Sacroiliac Ligament
What is the attachment of the long dorsal SI ligament?
PSIS to the lateral aspect of 3rd and 4th sacral segments
When does the long dorsal SI joint become stretched?
When the sacrum is rotated posteriorly relative to the ilium (counternutation):
- Early stages of pregnancy
- Aging & Degeneration
- Backward torsions or unilateral/bilateral sacral extensions
Where is the sacrospinous ligament found?
- Origin: Ischial spine
- Insertion: Lateral margins of sacrum
Origin of coccygeus muscles
Where is the sacrotuberous ligament found?
- Origin: Lower sacral tubules
- Insertion: Ischial tuberosity
Connects with fascia of pelvis
What is the role of sacrospinous and sacrotuberous ligaments?
Stabilize to limit posterior-superior rotation of the sacral apex around a transverse axis
Where is the piriformis muscle found?
- Origin: Antertior surface fo sacrum and sacrotuberous ligament
- Insertion: Superior border fo greater trochanter of femur
What is the function of the piriformis?
- Externally rotate thigh when hip is extended
- Abduct thight when hip is flexed
- Holds femoral head in acetabulum
What nerve plexuses and ganglion can be found in the sacrum area?
- Lumbar Plexus (L1-4)
- Sacral Plexus (L5-S4)
- Coccygeal Plexus (S5-Coccygeal nerve)
What is the purpose of the self-locking mechanism of the sacrum?
Resistance against shear
What are the two aspects of the sacral self-locking mechanism?
Form closure
Force closure
What is form closure of the sacrum due to?
How the joint fits together, specific properties of the articular surfaces of the SI joint
What is force closure of the sacrum due to?
Compression produced by body weight, muscles, and ligaments holding it together
What are the dorsal muscles that may affect SI joint stability?
- Latissimus dorsi
- Thoracolumbar fascia
- Gluteus maximus
- Iliotibial Band