Biomechanics, Mvmts, Diagnostic Imaging of Lumbar Spine Flashcards
what motion occurs when every point on the bone moves in the same direction
translation
translation is caused by what force?
shear
what is the difference b/w stress and strain
stress = the applied or elongated force
strain = the extent to which the CNT is elongated
when do micro tears occur in collagen?
after > 4% of elongation
what is the resistance to deformation and the slope of the stress-strain curve
stiffness
if a constant force is applied to a collagenous structure for a more prolonged period, further mvmt is detectable
creep
why does creep occur
due to a gradual realignment of collagen fibers and proteoglycans
how do we apply the creep phenomenon
stretch
restoration of initial length of CNT occurs at a less rate and to a lesser extent than the deformation
hysteresis
what does hysteresis indicate?
that energy was lost during deformation
after several frequent repetitions of a stress, the structure becomes weaker
fatigue failure
in fatigue failure, material may fail under ______
normal stress
when is fatigue failure seen most often
overuse syndrome
during slow loading of the axial spine with compression, what happens to the:
- VB
- NP
- AF
- end plate
VB - approximates
NP - increase in pressure
AF - bulges radially
end plate - bows towards vertebrae
during slow axial compression of L spine, where is there a greater amt of bulging?
greater anteriorly vs posterolaterally
describe the creep phenomenon in relation to slow axial compression of the L spine
rapid creep of 1.5 mm in the first 2-10 min
then slower rate 1mm/hr - plateau is at 90 min
what is the weakest component of the disc
end plate
what is the intradiscal pressure of the lumbar spine in standing
100%
when do you have the least amt of intradiscal pressure
supine with knees up posture
what is the intradiscal pressure of the lumbar spine in sidelying
75% of standing (or decreases by 25% from standing)
what is the intradiscal pressure of the lumbar spine in supine
25 % of what standing pressure is
what is the intradiscal pressure of the lumbar spine in slight lean forward
increases by 50-100% (150% -200% of what it is in standing)
what is the intradiscal pressure of the lumbar spine in sitting
increases by 50%
what positions aggravate the disc or increase the intradiscal pressure?
what factors relieve it?
aggravating - sitting, leaning forward, lifting objects, jumping, twisting
relieving - SL, supine, supine with knees up
with a normal disc, the facets take how much pressure?
abt 8%
with a diseased disc, how much load does the facet take?
40-70%
during axial distraction, what happens to the:
- disc
- capsules of facets
disc = less stiff
capsule = strong when subject to traction
____ % of lengthening of the L spine during traction occurs due to ______ of lumbar Lordosis.
the remaining ______ % occur due to _____ of the VB
40% - flattening
60% - separating
how much creep occurs immediately during axial distraction of L spine
1-2mm
how does traction affect young vs old
lengthening is greater in young than old
describe what is happening to the curve of the lumbar spine during flexion
straightening in the upper L spine
- does not occur at L5-S1
describe the kinematics of flexion if the L spine
anterior sagittal rotation (rocking forward of VB) and anterior sagittal translation
what happens to the facets in flexion
slide superior and anterior
describe the pressure on the facets, anterior and posterior disc during flexion
facet and post disc = decrease in compression
anterior disc = compression increase
what structure resists sagittal rotation (rocking of VB) in flexion
tension of capsule
what structures resist segmental flexion (4, list in order of greatest to least)
- joint capsule (39%
- IV disc (29%)
- supraspinous lig and interspin lig
- lig flavum
what are the top 2 structures that resist segmental flexion
- joint capsule
- IV disc
what 4 things resist anterior sagittal translation of top VB on bottom VB during flexion at end range
- direct impact on facet joint (C and J curves)
- superior/anterior orientation of lateral fibers of annulus
- iliolumbar and supraspinous lig
- MF and ES
about how much segmental flexion occurs at each segment?
L1-2
L2-3
L3-4
L4-5
L5-S1
L1-2 = 8 deg
L2-3 = 10
L3-4 = 12
L4-5 = 13
L5-S1 = 9
what effect does bending alone have on the disc?
what about when you have bending + compression
alone = little effect
+ compression = causes failure in disc or pars interarticularis
describe the kinematics of extension of VB in L spine
posterior sagittal rotation (rock backward) + posterior sagittal translation
what happens to the facets during extension
approximation of inferior facet on superior facet
- slide inferior and posterior
what happens to the WB status of the facet during extension
it becomes WB, whole IV joint becomes compressed
what end feel should you feel with extension
bony from SP on SP
what happens to the interspinous ligament during extension
buckles
what 4 things restrict segmental extension of L spine
- SP on SP
- inferior articular process on the laminae below
- ability of disc to allow compression
- ability of ant structures to allow elongation
about how much segmental extension occurs at each segment?
L1-2
L2-3
L3-4
L4-5
L5-S1
L1-2 = 5
L2-3 = 3
L3-4 = 1
L4-5 = 2
L5-S1 = 5
most of the segmental extension occurs at what segments?
L1-2 and L5-S1
describe what happens to the disc, I/L and C/L facets during axial rotation
disc = torsion
I/L facet = gapping
C/L = compression/approximation
maximal segmental rotation is limited to ______ because collagen can only be elongated to ______
3 degrees
4%
how much rotation does it take to increase tension in interspinous and supraspinous ligaments
< 1 degree
what has the greatest resistance to rotation
65% - facet joint, ligaments, capsule
35% - from disc
rotation + flexion increases the chances of injury to what structure?
Why?
annulus fibrosus b/c minimal contact of facet joints
describe what happens to the facets during lateral flexion/side bending
I/L glides inferior
C/L glides superiorly
if the segments in the thoracic or lumbar spine are in neutral, ROTATION is in the _____ direction of SIDE BENDING
which law is this?
Law 1 - rotation and SB in OPPOSITE directions
if segments in the cervical, thoracic or lumbar spine are in full flexion or extension with the z-joints engaged (locked), ROTATION and SB occur _______
what law is this
Law 2 - occur to the same side
if motion is introduced into a segment in any plane _______
what law is this?
motion in the other is reduced
law 3
what is the standard view for radiographic views of the L spine
AP view
what are the 4 basic projections of the L spine for radiograph
AP
lateral
R and L oblique
Lateral L5-S1
