The “Dehydrated” Lumbar The “Dehydrated” Lumbar Intervertebral Disk on MR, Intervertebral Disk on MR,
its anatomy, biochemistry and its anatomy, biochemistry and biomechanicsbiomechanics
Victor Haughton MDVictor Haughton MD
University of WisconsinUniversity of Wisconsin
"dehydrated", "desiccated" or "dehydrated", "desiccated" or "dark" disks. "dark" disks.
The defining feature is The defining feature is diminished signal intensity in diminished signal intensity in the nucleus pulposus on T2 the nucleus pulposus on T2 weighted images. weighted images. Meets criteria for a stage III Meets criteria for a stage III degenerated disk in the degenerated disk in the Pfirrmann or the Thompson Pfirrmann or the Thompson scalesscalesStage III is distinguished Stage III is distinguished from stage I and II disks by from stage I and II disks by decreased T2 signal decreased T2 signal
Background:Background:
The terms “dehydrated” or “dessicated The terms “dehydrated” or “dessicated disk” have not been adequately defined.disk” have not been adequately defined.
Used in radiologic reports, the terms Used in radiologic reports, the terms suggest a process different from suggest a process different from degeneration and perhaps less significant degeneration and perhaps less significant clinically. clinically.
Methods:Methods:
Scientific reports were reviewedScientific reports were reviewed
Anatomical, biochemical, and Anatomical, biochemical, and biomechanical properties of dark disks biomechanical properties of dark disks summarized summarized
Conclusions:Conclusions:
The dehydrated or dessicated disk, The dehydrated or dessicated disk, because of its morphological, biochemical because of its morphological, biochemical and biomechanical features warrants the and biomechanical features warrants the designation of early disk degeneration. designation of early disk degeneration.
Dark disks: HIZ on MRDark disks: HIZ on MR
• High intensity High intensity zone in annulus zone in annulus fibrosusfibrosus
• Minority of Dark Minority of Dark DisksDisks
Dark Disk: Discography Dark Disk: Discography (100% sensitivity)(100% sensitivity)
Concordant pain at L4-5 on discography, No pain at L3-4 or L5-S1. Disposition: L4-5 interbody fusion; pain free following surgery
Dark Disk: Anatomic correlation.Dark Disk: Anatomic correlation.Radial tear in all casesRadial tear in all cases
Radial tear in anatomic sections of Radial tear in anatomic sections of cadaver diskscadaver disks
Radial tear: axial MR and Radial tear: axial MR and anatomic sectionsanatomic sections
Anatomic section demonstrating Anatomic section demonstrating granulation tissue in the radial teargranulation tissue in the radial tear
Staging of intervertebral disk Staging of intervertebral disk degeneration (MR)degeneration (MR)
Pfirrmann
Differential diagnosis: annular tearsDifferential diagnosis: annular tears
Transverse tear Concentric tear
Biochemistry of dark diskBiochemistry of dark disk
Diminished glycosaminoglycans Diminished glycosaminoglycans
Increased collagen contentIncreased collagen content
Change in GlucosulfonatesChange in Glucosulfonates
Increase in aggregated proteinsIncrease in aggregated proteins
Water content, GAG content Water content, GAG content diminished in dark diskdiminished in dark disk
T2 relaxation times correlated to proteoglycan content in intervertebral disk
y = 11.307x + 19.092
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6 7 8
proteoglycan content (%)T
2 r
ela
xti
on
tim
e (
ms
)
BiomechanicsBiomechanics
““Dark Disk” responds abnormally to forces Dark Disk” responds abnormally to forces and torquesand torques
Diminished resistance to rotagtory torqueDiminished resistance to rotagtory torque
Behaves as a biomechanically failed diskBehaves as a biomechanically failed disk
Biomechanical TestingBiomechanical Testing
Increase torque Increase torque incrementally incrementally Measure rotation of Measure rotation of vertebrae for each torque vertebrae for each torque incrementincrementCalculate stiffnessCalculate stiffnessSmall changes for aging Small changes for aging disksdisksSignificantly larger Significantly larger changes in dark diskschanges in dark disks
Rotations of motions of segments for flexion and extension torques
-6
-4
-2
0
2
4
6
-10 -5 0 5 10
torque (Nm)
flexi
on o
r ex
tens
ion
(deg
rees
)
normal disks
transverse tears
radial tears
collapsed disks
Poly. (normal disks)
Poly. (radial tears)
Poly. (collapsed disks)
Rotations of dark disks and Rotations of dark disks and control disks measured in vivocontrol disks measured in vivo
Rotations at levels with normal disks or radial tears
0
5
10
15
0.4 1.6 2.8 4.0 >4
axial rotation (degrees)
nu
mb
er o
f sp
ecim
ens
NormaldisksRadialtears
Dark disk: Degenerating diskDark disk: Degenerating disk
Type III in Pfirrmann grading on morphologyType III in Pfirrmann grading on morphology
Radial tear of the annulus fibrosusRadial tear of the annulus fibrosus
Abnormal biochemically: water and GAG content Abnormal biochemically: water and GAG content diminisheddiminished
Abnormal biomechanically : mechanical failure of Abnormal biomechanically : mechanical failure of intervertebral diskintervertebral disk
Early disk degenerationEarly disk degeneration
Early disk degenerationEarly disk degeneration
Radial tear: Sagittal sectionRadial tear: Sagittal section
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