what is a synchondrosis
union of two bones formed by hyaline cartilage or fibrocartilage; allows for slight movement
cranial base is formed in what kind of bone
cartilaginous bone
describe cranial flexion
SBS rises superiorly
occiput expands inferiorly and widens
greater wings of sphenoid move inferiorly and widens
head feels wider side-to-side and narrower superior-to-inferior
axes of cranial flexion
rotate in opposite directions about two parallel transverse axes
describe cranial extension
SBS rises inferiorly
occiput expands superiorly and gets thinner
greater wings of sphenoid move superiorly and get narrower
head feels narrower side-to-side and longer superior-to-inferior
axes of cranial extension
rotate in opposite directions about two parallel transverse axes
connection b/t SBS and sacrum
SBS flexion, sacral (CRI) extension (counternutation; sacral base tilts posterior )
SBS extension, sacral (CRI) flexion (nutation; sacral base tilts anterior)
physiologic strain patterns
flexion/extension, torsions, sidebending rotations
non-physiologic (pathologic) strain patterns
vertical strains, lateral strains, SBS compression
describe non-physiologic strain patterns
usually due to trauma or fever/infection, abnormal motion
can you have more than one strain pattern at a time?
yes
describe SBS torsion
greater wings of sphenoid move superiorly
axes of SBS torsion
rotate in opposite directions about one AP axis (basion <–> opisthion)
axes of SBS sidebending rotation
rotate in same direction about AP axis
rotate in opposite directions about two parallel vertical axes
cause of SBS vertical strain
shearing force at the SBS (i.e., helmet to helmet hit to the top of the head)
describe SBS vertical strain
superior vertical strain: sphenoid base is superior in relation to basi-occiput
inferior vertical strain: sphenoid base is inferior in relation to basi-occiput
axes of SBS vertical strain
rotate in same direction about two parallel transverse axes
cause of SBS lateral strain
shearing force applied just anterior or posterior to the SBS (i.e., bat nailing you on the side of the head)
describe SBS lateral strain
right lateral strain: sphenoid base is sheared right in relation to basi-occiput
left lateral strain: sphenoid base is sheared left in relation to basi-occiput
axes of SBS lateral strain
rotate in same direction about two parallel vertical axes
causes of SBS compression
severe blow, fever, or metabolic problem
describe SBS compression
little or no motion at the SBS
