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
What are the ventral muscles that may affect SI joint stability?
Abdominal obliques
Transverse abdominals
Linea alba (not a muscle but listed on the slide)
Where does the Superior Transverse Axis of the sacrum pass through?
When would the sacrum move around this axis?
Posterior aspect of S2
Respiratory cycle
Where does the Middle Transverse Axis of the sacrum pass through?
When would the sacrum move around this axis?
Anterior aspect of S2
Nutation and counternutation in the standing position
Where does the Inferior Transverse axis of the sacrum travel through? When would the sacrum move around it?
S3
Axis of movement of ilia on the sacrum
As the lumbar spine extends, what is the sacrum doing?
Flexes
As the sacrum extends, what is the lumbar spine doing?
Flexion
What is the motion of the sacrum in counternutation?
Sacral extension
- Base moves posteriorly
- Apex moves anteriorly
What is the motion of the sacrum in nutation?
Sacral flexion
(Sacrum needs a drink, tilts foward as the “bowl” of the pelvis tips back)
Rotation through the lumbar spine causes what movement of the sacrum?
Rotation towards ipsilateral side
Sidebending to contralateral side
Downward force of the lumbar spine onto the sacrum causes what motion of the sacrum?
Nutation (sacral flexion)
Traction applied from above the lumbosacral junction causes what motion of the sacrum?
Counternutation (sacral extension)
Sidebending applied through the lumbar spine causes what motion of the sacrum?
Sidebending to the ipsilateral side
What is the relationship of the movements of ilium and sacrum?
Ilium moves in the same direction but in lesser degree
An occipital condylar compression can cause what to occur in the sacrum?
Lowered sacral base on the ipsilateral side
What is occurring in this x-ray?
Lumbarization of S1
- May be unilateral or bilateral
What is occurring in this x-ray?
Sacralization of L5
Note: atypically large TPs of L5
Bat wing deformity
May be unilateral or bilateral
Sacrum dysfunction will commonly manifest as what symptom?
Chronic low back pain
What are the two criteria for a compensated lumbar spine?
- Lumbar spine is rotated toward the deep sulcus (PTP and deep sulcus on the same side)
- Lumbar spine should be sidebent toward the axis in the case of a torsion
What is the position of the compensated L5 for a flexed sacrum?
Neutral (Type 1 spinal mechanics)
What is the position of the compensated L5 for an extended sacrum?
Flexed or extended (Type 2 Spinal mechanics)
