An MRI investigation of intervertebral disc deformation in response to torsion

Background The nucleus pulposus deforms towards an area of least compression in response to offset loading, however, there is a lack of data reporting the deformation patterns of nuclear material in rotated positions of the lumbar spine. Our purpose was to assess a novel methodology using MRI to track nuclear deformation in response to flexion and extension positions, and the combined positions of flexion with left rotation and extension with left rotation, at L1–2 and L4–5. Methods Three asymptomatic female subjects, mean age 27 years, underwent T2 weighted MRI sequences in flexed, extended, and left rotated positions combined with flexion and extension. A pixel profile technique was employed to determine direction and magnitude of nuclear deformation. Results In 5 of 6 discs examined, deformation of the nucleus occurred anteriorly in extension and posteriorly in flexion. Left rotation resulted in migration of nuclear material to the right in 9 of 12 discs. Of the three discs that demonstrated a right nuclear migration, two occurred at L4–5 and one at L1–2. Interpretation This methodology demonstrated that nucleus pulposus deformation can be measured reliably in various positions achieved within the confines of the MRI. The consistent migration of nuclear material following sagittal plane movement and the less consistent response to rotation positions suggest other asymmetrical loading on the intervertebral disc may accompany rotation.