Abstract
PurposeBoth posture and loading rate are key factors in the herniation process and can determine the mechanism of disc failure. The aim of this study was to test the hypothesis that disruption visible with HR-MRI post-testing corresponds with microstructural features and further elucidate the mechanism by which this disruption weakens the disc. This will enable us to gain new insights into the herniation process.MethodsThirty ovine lumbar spinal segments were subjected to combinations of four loading conditions (0–12° flexion, 0–9° lateral bending, 0–4° axial rotation, 0–1500 N axial compression) for 1000 loading cycles at 2 Hz in a dynamic disc loading simulator. The discs were scanned in an ultra-high field MRI (11.7 T) then examined using brightfield microscopy to examine their microstructure.ResultsFour discs herniated and seven discs suffered nucleus displacement. These discs contained pre-existing defects in the central posterior annulus. Generally, following testing discs contained more posterior annulus disruption, Microstructural investigation revealed there was clear correspondence between HR-MRI and microstructural observations, and that the mid-outer annular-endplate junction had failed in all discs examined in this study.ConclusionsWhile all discs suffered outer annulus damage, only the discs containing pre-existing defects herniated. These pre-existing defects weakened the inner and mid annulus, allowing herniation to occur once the mid and outer annular wall was compromised. We propose this can occur during the degenerative cascade.
Highlights
It seems logical that certain discs are more likely to herniate than others because they contain defects which weaken their annular wall
It has been suggested that this may be the reason that herniation is common in middle-aged patients whose discs have a weakened annulus but a highly hydrated nucleus [1] and it is well known that artificial defects can act as initiation sites for herniation or degeneration [2,3,4,5,6]
Loading rate must be sufficiently rapid to overcome viscoelastic effects and can determine whether the disc fails in the mid-annulus or the endplate junction [9,10,11]
Summary
It seems logical that certain discs are more likely to herniate than others because they contain defects which weaken their annular wall. It has been suggested that this may be the reason that herniation is common in middle-aged patients whose discs have a weakened annulus but a highly hydrated nucleus [1] and it is well known that artificial defects can act as initiation sites for herniation or degeneration [2,3,4,5,6]. Both posture and loading rate are known to be key factors in the herniation process [1, 7, 8]. Longer-term loading simulating occupational loading is known to cause disc wall failure [16,17,18,19] via disruption and limited nucleus displacement in the inner and mid annulus which was recently observed at the microstructural level in the ovine disc [20, 21]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
