Intro to Sacrum DSA Flashcards
What is the coccyx?
lowest part of the spinal column, four vertebra (some fused, some not)
How is the sacrum formed?
union of 5 modified vertebrae
When does the bony vertebral arch fuse with its adjacent costal part?
between years 2 and 5
When do the epiphyseal plates fuse?
after puberty, beginning with lowest segments and working up
Where does the dura attach?
level of the second sacral segment
What does the sacrum articulate with?
5th lumbar vertebra superiorly
coccyx inferiorly
two os coxae through SI articulation
What difference occurs after puberty in males vs females with the SI joint?
males SI joint ligaments are well developed and strong, while women’s SI joint ligaments are less developed for child birth
What occurs to the SI joint during the second decade of life?
cresent shaped ridge develops along iliac surface that interdigiates with a depression on the sacral side, adding stability and limits mobility
What occurs to the SI joint during the 3rd decade of life?
cresent shaped ridge becomes more pronounced, decreasing ROM
What occurs to the SI joint during the 4th and 5th decades of life?
males: degenerative changes begin on sacral side
fibrous ankylosis may further limit joint motion
Why is the SI joint described as L or C shaped?
contoured with a shorter upper arm and longer lower arm with the junction occurring at S2
Which way does the apex point?
anteriorly
What kind of joint is the SI?
diarthrodial; contains synovial fluid and matching articular surfaces
How is the SI joint different than any other joint in the body?
one side is hyaline cartilage and the other is fibrocartilage
How is the sacral surface described?
smooth, hyaline cartilage, decreases in width inferiorly, wedged between the two ilia
How is the iliac surface described?
anteriorly smooth, posteriorly fibrous giving rise to interosseous ligaments, fibrocartilage
Describe the posterior sacroiliac ligament
inferior fibers from the 3rd and 4th sacral segments
ascends to the PSIS and posterior end of the internal lip of the iliac crest
thicker than anterior SI ligaments
Describe the anterior sacroiliac ligament
connects the third sacral segment to the lateral side of the pre-auricular sulcus
iliolumbar ligaments blends
Describe the interosseous sacroiliac ligament
major bond between the bones
covered posteriorly by the posterior sacroiliac ligament
Long dorsal SI ligament
connects PSIS to lateral aspect of the 3rd and 4th sacral segments
What is the long dorsal SI ligament in close anatomic relationship with?
- erector spinae muscle group
- posterior layer of the thoracolumbar fascia
- sacrotuberous ligament
What happens to the long dorsal SI ligament when it is rotated in a posterior manner relative to the ilium?
- becomes stretched
- occurs during early stages of pregnancy, aging and degenerative changes, backward torsions or sacral extensions
Anatomy of the sacrospinous ligament
- from ischial spine to lateral margins of the sacrum where it blends with the sacrotuberous ligament
- forms part of the origin from which coccygeus muscle arises
Anatomy of sacrotuberous ligament
- runs from lower sacral tubercles to ischial tuberosity
- gluteus maximus attachment
- tendon of the biceps femoris attachment
- connects with fascia of the pelvis
