107. Internal deformations in human intervertebral discs under axial compression: a 9.4T MRI study

Abstract

BACKGROUND CONTEXT Back pain will be experienced by 70-85% of all people at some point in their lives, and is linked with intervertebral disc (IVD) degeneration. However, few studies have attempted to quantify changes in the internal deformations within IVDs as they degenerate without disrupting the disc continuity. Recent advances in MRI technology provide the opportunity to observe 3D deformations within intact IVDs in unprecedented detail. PURPOSE The aim of this study was to quantify human IVD deformations under axial compression. STUDY DESIGN/SETTING 9.4T MRI images were obtained of human cadaveric motion segments under pure axial loading. PATIENT SAMPLE Four human vertebral body–IVD–vertebral body specimens (L4-L5) were used for this study. Two were classed as degenerate (age = 55.5 ± 3.5 years (average ± SD), Pfirrmann rank = 3.5 ± 0.4) and two were classified as nondegenerate (age = 24.0 ± 2.8 years, Pfirrmann rank = 2.0 ± 0.3). OUTCOME MEASURES Digital volume correlation (DVC) was used to calculate the 3D strains within the IVDs. METHODS Specimens were aligned with the transverse plane of the disc parallel to the base of the mounting pots of a custom-made compression rig, and fixed in place using polymethylmethacrylate (PMMA). MR Images were acquired before, and after 2 mm of compression using a T2-weighted RARE sequence (coronal plane, resolution = (90 × 90) µm2, slice thickness = 800 µm, 17 min scan time). RESULTS High lateral strains were seen in the AF regions of the nondegenerate discs, while high lateral strains were seen in both the AF and the NP of the degenerate discs, particularly close to the end plates. The axial strain in both the NP and AF of the degenerate specimens was significantly higher (two tailed, unpaired t-test, p CONCLUSIONS This is the first study to use high field MRI to obtain images with in plane resolution as high as (90 × 90) µm2 to investigate internal deformations within degenerate and nondegenerate human discs. The 3D strain maps are useful for designers of partial or total disc replacement technologies who aim to restore the mechanical behavior of degenerate discs back to their nondegenerate state. Future investigations into 3D strains under different modes of loading will inform physical activities to mitigate high IVD strains, and the optimization of rigid instrumentation for fusion surgery by ensuring that modes of loading associated with the highest IVD strains are minimized. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.