Quantitative MRI to Characterize the Nucleus Pulposus Morphological and Biomechanical Variation According to Sagittal Bending Load and Radial Fissure, an ex vivo Ovine Specimen Proof-of-Concept Study

Background and context: Low back pain is a dramatic burden worldwide. Discography studies have shown that 39% of chronic low back pain patients suffer from discogenic pain due to a radial fissure of intervertebral disc. This can have major implications in clinical therapeutic choices. The use of discography is restricted because of its invasiveness and interest in it remains low as it represents a static condition of the disc morphology. Magnetic Resonance Imaging (MRI) appears to be less invasive but does not describe the biomechanical dynamic behavior of the fissure.Purpose: We aimed to seek a quantitative MRI protocol combined with ex vivo sagittal loading to analyze the morphological and biomechanical changes of the intervertebral disc structure and stress distribution.Study design: Proof of concept.Methods: We designed a proof-of-concept ovine study including 3 different 3.0 T-MRI sequences (T2-weighted, T1 and T2 mapping). We analyzed 3 different mechanical states (neutral, flexion and extension) on a fresh ovine spine specimen to characterize an intervertebral disc before and after puncturing the anterior part of the annulus fibrosus. We used a mark tracking method to calculate the bending angles and the axial displacements of the discal structures. In parallel, we created a finite element model to calculate the variation of the axial stress and the maximal intensity shear stress, extrapolated from our experimental boundary conditions.Results: Thanks to an original combination of specific nuclear relaxation time quantifications (T1, T2) of the discal tissue, we characterized the nucleus movement/deformation into the fissure according to the synchronous mechanical load. This revealed a link between disc abnormality and spine segment range of motion capability. Our finite element model highlighted significant variations within the stress distribution between intact and damaged disc.Conclusion: Quantitative MRI appears to provide a new opportunity to characterize intra-discal structural morphology, lesions and stress changes under the influence of mechanical load. This preliminary work could have substantial implications for non-invasive disc exploration and could help to validate novel therapies for disc treatment.

‘Progressive-Onset’ versus Injury-Associated Discogenic Low Back Pain: Features of Disc Internal Derangement in Patients Studied with Provocation Lumbar Discography

Chronic low back pain (LBP) can be ‘progressive onset’ or injury-related. This study compares the patient-reported cause of chronic LBP to features of disc internal derangement at painful concordant discs evaluated by provocation lumbar discography. Concordant LBP was identified in 114 patients with chronic LBP studied by provocation discography. LBP cause, discogram pain response and discogram/post-discogram CT features of internal derangement were retrospectively reviewed. ‘Progressive-onset’ LBP was reported in 32 (28%) patients, injury-related LBP in 75 (66%) with LBP equated to non-specific causes in seven. Injury-related LBP was more commonly identified in men (52 of 63 [83%]) with women reporting near-equal frequency of ‘progressive-onset’ (23 of 44 [52%]) and injury-related (21 of 44 [48%]) LBP (p=0.002). In 172 concordant painful discs, near-equal frequency of severely degenerative (Dallas grade-3: 82 of 172 [47.3%]) and full-thickness radial fissure discs (Dallas grade-3: 90 of 172 [52.7%]) were identified. Women with ‘progressive-onset’ LBP demonstrated more frequent severely degenerative discs (24 of 37 [65%]); women with injury-related LBP demonstrated more frequent radial-defect discs (21 of 31 [68%]; p=0.01). In men with injury-related LBP, severe degeneration-only (44 of 89 [49%]) and radial defect discs (45 of 89 [51%] were seen with equal frequency. In men with ‘progressive-onset’ LBP, radial defects are more common (11 of 15 [73%]). ‘Progressive-onset’ and injury-related chronic LBP subgroups are definable. Gender-related differences in incidence and internal derangement features at concordant discs are identified at discogram/post-discogram CT. These differences may have implications related to LBP origin/treatment-response.