Human internal disc strains in axial compression measured noninvasively using magnetic resonance imaging

STUDY DESIGN. Internal deformations and strains were measured within intact human motion segments. OBJECTIVE. Quantify 2-dimensional internal deformation and strain in compression of human intervertebral discs using MRI. SUMMARY OF BACKGROUND DATA. Experiments using radiographic or optical imaging have provided important data for internal disc deformations. However, these studies are limited by physical markers and/or disruption of the disc structural integrity. METHODS. MR images were acquired before and during application of a 1000 N axial compression. Two-dimensional internal displacements, average strains, and the location and direction of peak strains were calculated using texture correlation, a pattern matching algorithm. RESULTS. The average height loss was 0.4 mm, which corresponded to 4.4% compressive strain. The inner AF radial displacement was outward, even with degeneration; the average outward displacement of the inner AF (0.16 mm) was less than the outer AF (0.36 mm). High shear peak strains (2%-26%) occurred near the endplate and at the inner AF. Shear was higher in the anterior AF compared to the posterior. CONCLUSION. This technique allows quantification of displacement and strain within the intact disc. The radial displacements of inner AF suggest NP translation under compression. Peak tensile radial strains occurred as vertical bands throughout the anulus, which may contribute to radial tears and herniations. The tensile axial and shear strains at the interface between the AF and endplate could be related to the occurrence of rim lesions. Peak strains at the endplate are likely due to the AF curvature and the oblique fibers angle at fiber insertion sites. In the future, this technique may be used to measure disc strain under a variety of loading conditions, such as bending or torsion, and could also be used to study the mechanical effects of disc degeneration and potential clinical interventions.