SI joint and Axial Skeleton Muscle and Joint Interactions Flashcards
What is the sacroiliac joint?
Junction between auricular surfaces of the sacrum and ilium, tight fitting for stability
What is the keystone of the pelvic ring?
The sacrum
Where is the sacrum located anatomically?
Wedged between the two ilia and secured bilaterally by the sacroiliac joints
What do the sacroiliac joints do?
transfer the weight of the upper body to the LE, shock absorber with heel pcontact
What percentage of LBP is from the SIJ as a origin?
~25%
What happens if leg length is not equal by 1 cm?
5X increased compression at the SIJ on the longer side
What does the anterior sacroiliac ligament do?
Thickening of the capsule
What does the iliolumbar ligament do?
Stabilizer of lumbosacral joint and SIJ
What does the Interosseous ligament do?
Fills the gap, strong like a syndesmosis at tib/fib
What does the sacrotuberous ligament do?
Blends with biceps femoris - broad attachment
Where does the sacrospinous ligament run?
Sacrum to ischial spine
What is the primary passive stabilizer for the SI joint?
Pelvic girdle ligaments
What SIJ innervation can cause pain?
Not clear the level, L5-S3 spinal nerve roots usually and less often L4-S2
Where can pain locations from the SIJ innervation be?
Ipsilateral lower lumbar region, medial buttock, PSIS, and along short and long SIJ ligs
What is the role of the thoracolumbar fascia?
An important role in mechanical stability of the low back and SIj
Where is the thoracolumbar fascia most extensive?
In the lower back, surrounds various muscle groups
Where is the sacral sulcus?
PSIS and up a tad superiorly and will feel a dip in, this is how we monitor the base of the sacrum
What is the sacral sit test?
Patient sits with your thumbs on their PSIS while they flex, both should move in a symmetrical position
What is the Sphinx test?
Patient is prone, comes up to elbows, you monitor sacral sulcus and ILAs to assess sacrum
What does ILA stand for?
Inferior lateral angles
How can we describe the sacral joint surface?
ear-shaped or L-shaped; vertical short arm and more horizontal long arm
What kind of cartilage is sacral articular cartilage?
White and smooth hyaline - from 1-3 mm
What prevents downward gliding of the sacrum?
Irregular ridges and depressions on the sacral joint surface that are matched by reciprocal shapes on the ilium, which interlock in contours
Why are the contours of the sacral joint surface variable?
Depending on age
The articular surface of the sacrum is twisted from _______ downwards
From above downwards like a propeller
The ilia side of the SIJ is also cartilage. What kind?
Fibrocartilage 1-2mm thickness
What kind of joint is the SIJ?
Synovial joint
What are the two layers of the joint capsule of the SIJ?
External fibrous layer and inner synovial layer
Can we palpate the SIJ depth?
NO
What is different about the SIJ in early life?
Surfaces generally flat
What is different about the SIJ during puberty?
Surfaces develop ridges/grooves and enhance stability
What are the osteo/arthrokinematics of the iliac crests on the sacrum?
Iliac crests move on the sacrum = innominate motion/iliosacral
What are the osteo/arthrokinematics of the sacrum on the iliac crests?
Sacrum moves on innominates = sacroiliac motion
How much posterior rotation of the SIJ when NWB?
10-12 degrees innominate posterior rotation couples with 6mm anterior translation
How much anterior rotation of the SIJ with NWB?
2 degrees innominate anterior rotation coupled with 8mm anterior translation
How much innominate rotation of the SIJ when WB?
2.5 degrees innominate rotation and 0.5-1.6mm translation
When does motion at the SIJ occur?
During movements of the trunk and extremities
What are the 3 planes of motion at the SIJ?
FLX/EXT, Lateral flexion, rotation
How many degrees for rotation at SIJ? Translation?
2-4 degrees for rotation and 1-2mm translation
What is the closed packed position of the SIJ?
Full nutation (flexion), standing when loaded, gravity/ligs/muscles
When is the SIJ unloaded?
When supine, sacrum tends to return to counternutation or less stable
What does nutation mean?
Nodding
When does bilateral movement of the sacrum occur?
With forward/backwards bending of the trunk
When does unilateral motion of the sacrum occur?
With flexion/extension of the LEs
What is sacral nutation relative to the innominates?
The forward motion of the sacral promontory into the pelvis on the coronal axis; anteriorly and inferiorly
- glides inferiorly down the short arm and posteriorly along the long arm
What is sacral nutation resisted by?
Wedge shape of sacrum, ridges/depressions in joint surface, interosseous and sacrotuberous ligaments
What is sacral counternutation relative to the innominates?
Sacral base moves posteriorly and superiorly; glides anteriorly along long arm and superiorly up short arm
What is sacral counternutation resisted by?
Long dorsal ligament
Why is sacral counternutation considered less stable?
Because ST and Interosseous ligaments are lax
What does the sacrum do with forward bend?
Sacrum counternutates
What does the sacrum do with lumbar extension?
Sacrum nutates
During gait, what does the sacrum do?
One side nutates with side bend and induces rotation, which becomes a coupled motion called sacral torsion
What is the superior axis used for?
Breathing - inhale base forward and coccys/ILA posterior; L/S flexes; reverses with exhale
What is the middle axis used for?
Nutation (flexion) and counternutation (extension); postural
What is the inferior transverse axis used for?
Ilia on sacral movements
What is the vertical axis used for?
Unilateral rotation
What are torsions?
Motions or can be a dysfunction /sacrum in a ‘stuck’ position
What are the two types of torsions?
physiological motions
non physiological motions
What are physiological motion?
anterior motion fixation/ nutation
What are non-physiological motions?
Posterior motion fixation/counter-nutation
What are the two types of physiological motions?
1.) L on L (look left and nutates)
2.) R on R (look right and nutates)
What are the two types of non-physiologcial motions?
3.) L on R ( comes backwards, looks left because rotates on right axis)
4.) R on L (sacrum tips back to look right, moves on left axis)
Which types of torsion is painful?
Non-physiological
What kind of torsion does not occur in the normal gait cycle?
Posterior nutational movement
In the normal walking cycle, what torsion DOES happen?
The sacrum appears to move with left torsion on the left oblique axis, return to neutral, rotate in right torsion on the right oblique axis and then return to normal
