Introduction to the Sacrum Flashcards
At what level of the sacrum is the inferior lateral angle?
at S4 & S5
Name some sacral anterior anatomic landmars
Sacral base
Sacral Promontory
Sacral Apex
What is the coccyx?
the lowest part of the spinal column
consists of 4 vertebra
What separates adjacent sacral segments?
epiphyseal plates that fuse after puberty
Bony articulations of the sacrum
articulates w/ 5th lumbar vertebra superiorly
articulates w/ coccyx inferiorly
Sacral Joints
Right SI joint
Left SI joint
L5-S1 intervertebral disc
Sacrococcygeal joint
Considerations for SI joint after puberty
in males, SIJ ligaments are well-developed & strong
in females, SIJ ligaments are less developed
Considerations for SI joint in 2nd decade of life
ridge develops along iliac surface that interdigitates w/ depression on sacral side to add stability & limits mobility
Considerations for SI joint in 3rd decade of life
crescent shape ridge is more pronounced & decreases ROM
some degenerative changes occur on iliac side in males
Considerations for SI joint in 4th & 5th decades of life
in males, degenerative changes begin on sacral side
SI joint characteristics
L or C shaped with shorter upper arm & longer lower arm
Which direction does the apex point?
points anteriorly
What type of joint is the SI joint?
diarthrodial joint b/c contains synovial fluid & matching articular surfaces
1 side is hyaline cartilage & other side is fibrocartilage
Sacral surface of SI joint
smooth, hyaline cartilage, decreases in width inferiorly & wedged between 2 ilia
Iliac surface of SI joint
smooth anteriorly, is fibrous on posterior side (gives rise to interosseous ligaments), fibrocartilage
Posterior Sacroiliac Ligament
from 3rd & 4th sacral segments & ascents to PSIS & posterior end of iliac crest
thicker
Anterior Sacroiliac Ligament
connects 3rd sacral segment to lateral side of pre-auricular surface
blends w/ iliolumbar ligaments
Interosseous Sacroiliac Ligament
major bond between the bones, filling irregular space
covered posteriorly by posterior sacroiliac ligament
Long Dorsal SI ligament
connects PSIS to lateral aspect of 3rd & 4th sacral segments
close relationship w/ erector spinae muscles, posterior layer of thoracolumbar fascia & sacrotuberous ligament
Sacrospinous Ligament
from ischial spine to lateral margins of sacrum
forms part of origin from which coccygeus ms arise
Sacrotuberous ligament
runs from lower sacral tubercles to ischial tuberosity
where gluteus maximus attaches & tendon of biceps femoris attaches
What is the role of the sacrospinous & sacrotuberous ligaments?
stabilize to limit posterior-superior rotation of sacral apex around transverse axis
Piriformis m
from ant surface of 2-4 lateral masses of sacrum & sacrotuberous ligament to superior border of greater trochanter of femur
externally rotates thigh when hip joint is extended & abducts thigh when hip joint is flexed
What can cause sciatica?
piriformis hypertonicity due to chemical reaction that irritates peroneal fibers of the sciatic nerve
causes referred pain down posterior thigh
Nervous system of the sacrum
Lumbar Plexus (L1-L4) Sacral Plexus (L5-S4) Coccygeal plexus (S5-coccygeal nerve)
What ganglion are found in sacrum?
inferior mesenteric ganglion
superior hypogastric ganglion
ganglion impar
What are some posterior landmarks used to identify sacral SD?
PSIS
AIIS
inferior lateral angle
L5 spinous process
Self-locking mechanism of the sacrum
critical for resistance against shear due to form closure and force closure
Force closure
compression produced by body weight, muscle action, and ligament force
What is sacral dysfunction related to?
common cause of low back pain & produces many possible viscerosomatic & somatovisceral reflexes
What are important to the stability of the SI joint?
postural muscles
What are important anterior muscles to the SI joint?
activity of oblique abdominal muscles in both standing & sitting (especially internal obliques)
Describe physiological sacral motion
2 oblique axes of sacral motion
named according to side of body toward which the superior end of oblique axis is located
ST axis
transverse axis about which sacrum moves during respiratory cycle
passes from side to side through articular processes posterior to point of attachment of dura @ S2
MT axis
functional transverse axis of nutation & counternutation in standing position, passing thru anterior aspect of S2
IT axis
functional transverse axis @ level of S3 through inferior auricular surface & represents axis for movement of ilia on sacrum
Describe the reciprocal relationship of lumbar spine & sacral base
lumbar flexion with sacral extension
lumbar extension w/ sacral flexion
Sacral extension counternutation
base tips posterior & apex moves anteriorly
Sacral flexion nutation
base tips anteriorly & apex moves posteriorly
Principles of sacral motion
all of the movements of the sacrum on ilium are gliding movements
How does rotation in lumbar spine affect sacral motion?
causes sacrum to rotate towards the same side & sidebends toward contralateral side
How does sidebending in lumbar spine affect sacral motion?
causes sacrum to sidebend towards same side
What way does the ilium move?
ilium always moves in same direction as sacrum
Lumbarization
transitional segment in which 1st sacral segment becomes like an additional lumbar vertebra articulating w/ 2nd sacral segment
Sacrilization
incomplete separation & differentiation of L5 so takes on characteristics of sacral vertebra
also caused by TP of L5 being atypically large
What does form closure of sacrum require?
proper size, shape & attitude of articulating surfaces
