In Vivo Morphological Features of Human Lumbar Discs

Abstract

Recent biomechanics studies have revealed distinct kinematic behavior of different lumbar segments. The mechanisms behind these segment-specific biomechanical features are unknown. This study investigated the in vivo geometric characteristics of human lumbar intervertebral discs.Magnetic resonance images of the lumbar spine of 41 young Chinese individuals were acquired. Disc geometry in the sagittal plane was measured for each subject, including the dimensions of the discs, nucleus pulposus (NP), and annulus fibrosus (AF). Segmental lordosis was also measured using the Cobb method.In general, the disc length increased from upper to lower lumbar levels, except that the L4/5 and L5/S1 discs had similar lengths. The L4/5 NP had a height of 8.6 ± 1.3 mm, which was significantly higher than all other levels (P < 0.05). The L5/S1 NP had a length of 21.6 ± 3.1 mm, which was significantly longer than all other levels (P < 0.05). At L4/5, the NP occupied 64.0% of the disc length, which was significantly less than the NP of the L5/S1 segment (72.4%) (P < 0.05). The anterior AF occupied 20.5% of the L4/5 disc length, which was significantly greater than that of the posterior AF (15.6%) (P < 0.05). At the L5/S1 segment, the anterior and posterior AFs were similar in length (14.1% and 13.6% of the disc, respectively). The height to length (H/L) ratio of the L4/5 NP was 0.45 ± 0.06, which was significantly greater than all other segments (P < 0.05). There was no correlation between the NP H/L ratio and lordosis.Although the lengths of the lower lumbar discs were similar, the geometry of the AF and NP showed segment-dependent properties. These data may provide insight into the understanding of segment-specific biomechanics in the lower lumbar spine. The data could also provide baseline knowledge for the development of segment-specific surgical treatments of lumbar diseases.

Revisiting Radiographic L5-S1 Parallelism Using MRI T1 Mapping

“…A recent study on a cohort similar to ours but of Asian origin has shown that the L5-S1 disc has the greatest segmental lordosis of all the lumbar discs [22]. This finding is in agreement with the usual radiographic morphology of the L5-S1 disc, which appears higher anteriorly than posteriorly rather than parallel in a lateral view of the spine [2324].…”

Design Requirements for Annulus Fibrosus Repair: Review of Forces, Displacements, and Material Properties of the Intervertebral Disk and a Summary of Candidate Hydrogels for Repair

“…Disk height and depth, measured from X-ray and magnetic resonance images, varies from 4 to 6 mm posteriorly and 30 to 34 mm between different levels of the spine (minimum values correspond to L1/2 and L5/S1, respectively) ( Table 2) [50,51]. Dimensions of the IVD are useful for informing the required volume for an AF repair biomaterial, for example, a 5 mm square [29] and [33][34][35][36] were multiplied by 0.0981 to convert from kg/cm 2 to MPa.…”

The segment-dependent changes in lumbar intervertebral space height during flexion-extension motion

“…Recently, Zhong et al 1 measured the in vivo morphology of lumbar intervertebral discs and found that the anterior annulus fibrosus was longer than the posterior annulus fibrosus at all lumbar segments except at L5/S1, where both were similar in length. Edmondston et al 8 evaluated the influence of sagittal plane position on lumbar intervertebral disc height and nucleus displacement as seen on MRI in a small asymptomatic population.…”