Classification of the SI Joint
- Diarthrodial joint (synovial)
- Upper 1/3 is amphiarthrosis (ligamentous bridge)
Much of this kind of pain comes from SI problems:
Low back pain
What percentage of chronic low back pain is caused by SI problems?
Major mechanical functions of pelvis:
- Attaches spine to legs.
- Transfers weight to legs.
- Shock absorption.
- Gyroscopic action during gait.
- Females - birth.
- 2 SI joints
- Pubic symphysis
SI classified as this joint:
Diarthrodial or Synovial
Pubic symphysis classified as this kind of joint:
Fibrocartilaginous or Amphiarthrosis
Iliac surface has this cartilage:
Sacral surface has this kind of cartilages:
What do intrinsic SI ligaments do?
bind sacrum to ilium
Muscles related to pelvic biomechanics:
Multifidus, erector spinae, hamstrings, gluteus maximus, piriformis, psoas, quadratus lumborum
What innervates the SI joint?
No one knows
What is the difference from male pelvis to female SI joint?
Female SI joint has less of an “S” = more mobility. Male SI joint has a more defined “S” shape and decreased mobility.
SI joint development at birth:
Joints undeveloped, smooth, flat, glides in any direction. Stability provided by ligaments. Begins to develop during walking.
SI joint development during teenage years:
Roughening of surfaces, development of grooves and ridges. Male more pronounced than female.
SI joint development during 20s and 30s:
Articulate changes are well established. Joint surfaces become more irregular. Iliac tuberosity gets bigger. Joint surface erosions begin.
SI joint development during 40s and 50s:
Each individual SI joint is unique to varying degrees (more in males)
SI joint in the 20s and beyond, this possible issue on iliac surface:
In 40s and 50s, possibililty of developing these issues in your SI joint:
Joint adhesions, osteophytes, fusion
60s and beyond, SI joints have a high prevalence of:
Bony ankylosis (fusion)
What is bony ankylosis?
Bony ankylosis is gender dependent (percentages)
Male 27.7% and Female 2.3%
Bony ankylosis is age dependent in men (percentages)
- 20-39 years 5.8%
- 60-79 years 31.1%
- Over 80 years 46.7%
Fusion occurs mainly in this part of the SI Joint
Major STATIC function of the pelvis:
Bear trunk weight
What is the posterior arch of the pelvis?
2 pillars of bone running through SI and acetabular fossa
Which arch is the major weight bearer of the pelvis?
Name the 2 gravitational forces acting on the posterior arch:
- Down and posterior, weight resisted by wedge-shaped sacrum
- Down and anterior, weight resisted by “S” shaped joint, posterior ligaments, interosseous ligaments, sacrotuberous ligaments
What is the anterior arch of the pelvis?
Pubic rami connects posterior arches and acts as a compression strut
Self-locking mechanism of the SI joint is called:
What is form closure?
- Wedge shape of sacrum
- Interlocking groove (sacrum) and ridge (ilium)
- S-shaped joint surfaces
What is force closure?
Tension in muscles, ligaments and thoracolumbar fascia aids in stabilizing the SI joints
Force closure in the pelvis:
Creates lateral to medial pressure from ilia to the sacrum which compresses the SI joints
Research finds the average ROM for total flexion and extension in the SI is:
Describe Sacral Nutation and Counternutation in terms of sacral base movements and lumbosacral extension/flexion
Nutation: Sacral base moves anterior and inferior (lumbosacral extension)
Counternutation: Sacral base moves posterior and superior (lumbosacral flexion)
When the lumbosacral region extends, the sacrum:
When the lumbosacral region flexes, the sacrum
During pregnancy there is _________ pelvic joint mobility
Increased (2.5 times)
During delivery, the sacrum
Counternutates and nutates
When you inhale, your sacrum
When you exhale, sacrum
In flexion, PSIS moves ____ and ___ and in extension, PSIS moves ____ and ___
Flexion: posterior and inferior
Extension: anterior and superior
SI joint motion is named according to __________ movement relative to the _________, NO MATTER what bone moves.
Is this flexion or extension of the SI joint: ilium flexes relative to the sacrum
Is this flexion or extension of the SI joint: the sacrum nutates relative to the ilium
Is this flexion or extension of the SI joint: ilium extends relative to the sacrum
Is this flexion or extension of the SI joint: the sacrum counternutates relative to the ilium
If PSIS go away from midline:
If PSIS go toward midline: