Lecture 4: SI Joint Flashcards
SI joint is the junction between what
auricular surfaces of the sacrum and illium
tight fitting for stability
what is the key stone of the pelvic ring
sacrum
wedged between the two ilia and secured by the SI joints bilaterally
functions of the SI joint
transfer weight of the upper body to LE
shock absorber with heel contact
how much back pain is associated with SI joint
25% of LBP has SI origin
possibly mechanisms of SI joint pain
falling
stepping in hole
childbirth
repetitive unilateral torsion
postural abnormalities
what happens if the LL (lower limb?) is not equal by 1cm
5 x increase in compression at SI joint
describe the anterior sacroiliac ligament
thickening of the capsule
describe the iliolumbar ligament
stabilizer of the lumbosacral joint and SI joint
describe the interosseous ligament
fills the gap
strong like syndemosis at the tib/fib
describe the sacrotuberous ligament
blends with the biceps femoris
broad attachment
describe the sacrospinous ligament
sacrum to ischial spine
name all the ligaments of the pelvic girdle
anterior SI
iliolumbar
interosseuos
short and long posterior SI
sacrotuberous
sacrospinous
describe the SI joint innervations and referred pain locations of the SI joint
exact spinal level source is uncelar
L5-S3 spinal nerve roots
less often L4-S2
where all can pain be referred from the SI joint
ipsilateral lower lumbar region
medial buttock
PSIS
along short and long SI joint ligaments
describe the role of the thoracolumbar fascia in relation to low back/SI
important for mechanical stability
most extensive in low back
attaches to the PSIS
describe the sacral joint surface shape and articular cartilage
ear shaped or L shaped
vertical short and more horizontal arm
sacral articular cartilage = white/smooth hyaline form 1-3 mm
describe the topography of the sacral joint surface
irregular ridges/depressions matched by reciprocal shapes on ilium; interlocking contours prevent downward glide of sacrum
contours = highly variable (age dependent)
articular surface = twisted from superior to inferior like a propeller
describe the cartilage on the ilia side of the SI joint
mainly fibrocartilage
1-2 mm thickness
SI joint is a synovial joint; describe the joint capsule
2 layers
external fibrous layer that has abundant fibroblasts and collagen fibers
internal synovial layer
how does the SI joint change throughout the life span
early life = surfaces are generally flat
puberty = surfaces develop ridges/grooves that enhance stability
what is innominate motion
iliac crest moves on the sacrum
what is sacroiliac motion
sacrum moves on innominates
what are the different methods of investigation of the biomechanics of the SI joint
manipulation during surgery/cadaver lab
radiographic (sagittal plane; harder to recognize landmarks)
imaging after insertion of tantalum balls into innominates and sacrum
inclinometers
computerized analysis
describe innominate non weight bearing movement at the sacrum during posterior and anterior rotation
10-12 degrees posterior rotation cpupled with 6 mm anterior translation
2 degrees innominate anterior RT coupled with 8 mm anterior translation
describe innominate weight bearing motion at the sacrum
2.5 degree innominate RT and 0.5-1.6 mm translation
desribe the motion occuring at the SI joint via the sacrum
motion occurs during movement of trunk and extremities
3D RT and translation
3 planes of motion (FLX/EXT, lat FLX, and RT)
1-4 degrees RT and 1-2 mm translation
what is the closed packed position of the SI Joint
full nutation
standing when loaded
gravity/lig/muscles
when is the SI joint unloaded
supine
sacrum tends to return to counternutation or less stable position
what are the 2 main types of movement WITHIN the innominate bones
anterior/fwd motion or nutation (flexion of sacrum)
posterior/bwd motion or counternutation (ext of sacrum)
what does nutation mean
nodding
when does bilateral motion of the sacrum occur
with forward/backward bending of the trunk
when does unilateral motion of the sacrum occur
with flexion and ext of the LEs
describe the anatomical definition of nutation
relative to innominates
forward motion of the sacral promontory into the pelvis around the coronal axis (medial lateral) anteriorly and inferiorly
glides inferiorly down short arm and posteriorly along long arm
the motion of nutation is resisted by what
wedge shape of sacrum
ridges/depressions
interosseous and sacrotuberous ligaments
also aided by the muscles that insert into said ligaments
describe the anatomical movement of sacral counternutation
relative to innominates
sacral base moves posteriorly and superiorly
glides anteriorly along the long arm and superiorly along the short arm
counternutation is resisted by what
long dorsal ligament
why is counternutation less stable
sacrotuberous and interosseuos ligaments are lax
what sacral movement occurs with forward bend and extension of the spine
FB = sacrum counternutates
EXT = sacrum nutates
describe sacral torsion
coupled motion of rotation and lateral flexion
one side nutates with SB and this induces RT
occurs during walking/gait cycle; not the same as movements with FB and EXT
what is the axis of movement of the ilium on the sacrum
inferior transverse ligament
what is the axis of movement of unilateral RT of the sacrum
vertical axis
what is the axis for nutation and counternutation of the sacrum
middle axis
how does the sacrum move with breathing
inhale = base of sacrum goes forward and coccyx/ILA go posterior; L/S flexes
exhale is reverse
axis of RT for the sacrum during breathing
superior axis
what are physiological motions
anterior motion fization/Nutation
L on L or R on R
what are non physiological motions
posterior motion fixation/counter nutation
L on R or R on L
how does the sacrum move in the normal walking cycle
sacrum moves with L torsion on the L oblique axis, return to neutral, and then rotate in R torsion on the R oblique axis, then return to neutral again
posterior nutational movement doesnt appear past neutral in the normal walking cycle
