Lecture 2: Sacrum Flashcards
When do the bony vertebral arch of the sacrum fuse w/ its adjacent costal parts; when do they unit w/ their respective centrum?
Between the years of 2 and 5; uniting w/ their respective centrum by the age of 8
Epiphyseal plates of the sacrum separate what; when and how do they fuse?
- Separate adjacent sacral segments
- Fuse sequentially after puberty, beginning w/ the lowest segments and working up
What does the sacrum articulate superiorly and inferiorly?
- L5 superiorly
- Coccyx inferiorly
How are the SI joint ligaments different between males and females after puberty?
Males: SIJ lig. are well-developed and strong
Females: SIJ lig. are less developed, allowing the mobility required during childbirth
What occurs to the sacrum during the second decade of life?
Crescent-shaped ridge develops along the iliac surface, adds stability and limits mobility
What may occur in the sacrum of males during the third decade of life?
Degenerative changes may begin to occur on the iliac side
What may occur to the sacrum during the 4th and 5th decades of life; especially in males?
- Degenerative changes begin on the sacral side
- Fibrous ankylosis may further limit joint motion
Describe the lengths of the upper and lower arm of the SI joint?
- Described as L- or C-shaped
- Contoured w/ a shorter UPPER arm and a longer LOWER arm, w/ junction occuring at S2
What type of joint is the SI joint and why is it different from any other joint in the body?
- Diarthrodial joint
- One side is hyaline cartilage and the other is fibrocartilage
The iliac surface of the sacrum is composed of what posteriorly and gives rise to which lig.?
- Fibrocartilage
- Interosseous lig.
Which of the Sacroiliac ligaments is thicker?
Posterior Sacroiliac Ligament
Which ligament becomes stretched when the sacrum is rotated in a posterior manner relatice to the ilium (counternutation), as commonly seen in which conditions?
- Long Dorsal SI ligament
- Early stages of pregnancy
- Aging and degenerative changes
- Backward torsions or unilateral/bilateral sacral extensions
What important roles do the sacrospinous and sacrotuberous ligaments play in regards to the sacrum?
- Stabilize to limit posterior-superior rotation of the sacral apex around a transverse axis
Which muscle assists in holding the femoral head into the acetabulum; where does it insert?
- Piriformis
- Inserts upon the superior border of the greater trochanter
Evidence indicates that what may lead to sciatica?
Piriformis hypertonicity leading to a chemical rxn that irritates peroneal nerve fibers of the sciatic nerve causing referred pain down the posterior thigh
What are the posterior pelvic landmarks?
- PSIS
- PIIS
- ILA
What is form closure vs. force closure; what are these mechanisms critical for?
Form closure: specific properties of the articular sufaces of the SIJ; requiring the proper size, shape, and attitude of articulating surfaces. How the joint fits together!
Force closure: the compression produced by body weight, muscle action, and ligament force. Due to gravity, muscles, fascia, and ligaments
*Critical for resistance against shear
Which muscles/fascia may affect the SI joint stability, posteriorly?
Latissimus dorsi, thoracolumbar fascia, gluteus maximus, and the ITB
Which muscles may affect the SI joint ventrally; which have been found to be the most significant?
- Abdominal obliques, linea alba, and transverse abdominals
- In both standing and sitting, the acitvity of the oblique muscles, especially, the internal obliques, was found to be significant
What has shown to help patients w/ low back pain and SI syndrome?
Therapeutic exercise and osteopathic tx for the core lumbar and pelvic musculature.
Motion about the oblique axes of the sacrum result from motions occuring about which axes?
- Vertical
- Anterior-posterior (AP)
- Transverse
Which axis does the sacrum move about during the respiratory cycle; which sacral level?
ST Axis at S2
Which axis is the functional transverse axis of nutation (flexion) and counternutation (extensions) in the standing position; which sacral level?
MT (postural) axis; at level of S2
Lumbar flexion = sacral ______; which way does the sacrum move?
- Lumbar flexion = sacral extension
- Base moves posteriorly; apex anteriorly
