1. The Dehydrated Lumbar Intervertebral Disk on MR, its anatomy, biochemistry and biomechanics Victor Haughton MD University of Wisconsin

2. "dehydrated", "desiccated" or "dark" disks. The defining feature is diminished signal intensity in the nucleus pulposus on T2 weighted images. Meets criteria for a stage III degenerated disk in the Pfirrmann or the Thompson scales Stage III is distinguished from stage I and II disks by decreased T2 signal

3. Background: The terms dehydrated or dessicated disk have not been adequately defined. Used in radiologic reports, the terms suggest a process different from degeneration and perhaps less significant clinically.

4. Methods: Scientific reports were reviewed Anatomical, biochemical, and biomechanical properties of dark disks summarized Anatomical, biochemical, and biomechanical properties of dark disks summarized

5. Conclusions: The dehydrated or dessicated disk, because of its morphological, biochemical and biomechanical features warrants the designation of early disk degeneration.

6. Dark disks: HIZ on MR High intensity zone in annulus fibrosus High intensity zone in annulus fibrosus Minority of Dark Disks Minority of Dark Disks

7. Dark Disk: Discography (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

8. Dark Disk: Anatomic correlation. Radial tear in all cases

9. Radial tear in anatomic sections of cadaver disks

10. Radial tear: axial MR and anatomic sections

11. Anatomic section demonstrating granulation tissue in the radial tear

12. Staging of intervertebral disk degeneration (MR) Pfirrmann

13. Differential diagnosis: annular tears Transverse tearConcentric tear

14. Biochemistry of dark disk Diminished glycosaminoglycans Increased collagen content Change in Glucosulfonates Increase in aggregated proteins

15. Water content, GAG content diminished in dark disk

16. Biomechanics Dark Disk responds abnormally to forces and torques Diminished resistance to rotagtory torque Behaves as a biomechanically failed disk

17. Biomechanical Testing Increase torque incrementally Measure rotation of vertebrae for each torque increment Calculate stiffness Small changes for aging disks Significantly larger changes in dark disks

19. Rotations of dark disks and control disks measured in vivo

20. Dark disk: Degenerating disk Type III in Pfirrmann grading on morphology Radial tear of the annulus fibrosus Abnormal biochemically: water and GAG content diminished Abnormal biomechanically : mechanical failure of intervertebral disk Early disk degeneration

21. Radial tear: Sagittal section