Lecture 4: SI Joint Flashcards by Braden Talbert

SI joint is the junction between what

auricular surfaces of the sacrum and illium

tight fitting for stability

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what is the key stone of the pelvic ring

sacrum

wedged between the two ilia and secured by the SI joints bilaterally

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functions of the SI joint

transfer weight of the upper body to LE

shock absorber with heel contact

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how much back pain is associated with SI joint

25% of LBP has SI origin

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possibly mechanisms of SI joint pain

falling
stepping in hole
childbirth
repetitive unilateral torsion
postural abnormalities

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what happens if the LL (lower limb?) is not equal by 1cm

5 x increase in compression at SI joint

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describe the anterior sacroiliac ligament

thickening of the capsule

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describe the iliolumbar ligament

stabilizer of the lumbosacral joint and SI joint

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describe the interosseous ligament

fills the gap

strong like syndemosis at the tib/fib

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describe the sacrotuberous ligament

blends with the biceps femoris

broad attachment

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describe the sacrospinous ligament

sacrum to ischial spine

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name all the ligaments of the pelvic girdle

anterior SI
iliolumbar
interosseuos
short and long posterior SI
sacrotuberous
sacrospinous

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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

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where all can pain be referred from the SI joint

ipsilateral lower lumbar region
medial buttock
PSIS
along short and long SI joint ligaments

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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

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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

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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

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describe the cartilage on the ilia side of the SI joint

mainly fibrocartilage

1-2 mm thickness

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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