Oral Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

INTRODUCTION: Intradiscal pressure (IDP) represents a fundamental parameter for the estimation of loads and muscle forces acting on the spine and is a major biomechanical indicator for various spinal pathologies, such as deformities and degenerative diseases. However, potential factors influencing the IDP are indeterminate. The aim of this study was to evaluate primary effects of intervertebral disc degeneration, age, sex, and segmental level on lumbar IDP using a large in vitro data collective.

METHODS: 107 human functional spinal units (32x L2-L3, 16x L3-L4, 59x L4-L5) from 68 donors (50±12 years, 19-74 years, 42% female) were evaluated from an in-house database. All specimens were loaded displacement-controlled (1°/s) with pure moments of 7.5 Nm in flexion/extension, lateral bending, and axial rotation using a well-established spine tester [1]. IDP was measured by means of flexible pressure sensors (FMSPEZ50, MIPM GmbH). Disc degeneration was assessed from radiographs using a validated classification system for the lumbar spine [2]. Statistical differences between IDP values were evaluated using the Kruskal-Wallis test with Dunn-Bonferroni post-hoc correction for degeneration grade, age, and level, as well as the two-sided Mann-Whitney-U test for sex in SPSS 27. The significance level was set to 0.05.

RESULTS: The IDP was significantly reduced for degeneration grades 1 (mild degeneration) and 2 (moderate degeneration) compared to grade 0 (no degeneration) in all motion directions (p<0.05). The IDP significantly correlated with age (p<0.05), especially in extension (Pearson’s r=-0.687), and was significantly reduced for an age >40 years in all motion directions (p<0.05). Sex did not significantly affect the IDP in any motion direction (p>0.05). The IDP at L4-L5 level was significantly reduced compared to the IDP at L2-L3 level in all motion directions (p<0.05). IDP-moment curves generally exhibited V-shaped characteristics for young, non-degenerated discs in flexion/extension and lateral bending, while being rather flat for older, more degenerated discs as well as bilateral axial rotation movements (Fig. 1). In general, the IDP was significantly lower in axial rotation compared to flexion/extension and lateral bending (p<0.05). In the overall collective (n=107), no mutual effects of intervertebral disc degeneration, age, sex, and level were detected (p>0.05), except significantly lower age for degeneration grade 0 compared to both grades 1 and 2 (p<0.05).

DISCUSSION: Increasing intervertebral disc degeneration and age as well as lower segmental level substantially reduce the IDP of the lumbar spine. These factors therefore can be seen as key drivers for spinal pathologies involving the intervertebral disc by altering the load sharing situation within the spinal motion segment, particularly in the endplates and the anulus fibrosus. Sex, however, does not appear to have an effect on the IDP. Effects of severely degenerated intervertebral discs (grade 3) could not be investigated in this study, since they usually do not have a nucleus pulposus anymore. However, it can be assumed that these discs do not maintain any load sharing capacity, further increasing the risk for spinal pathologies. In general, more degenerated discs exhibit low or even negative intradiscal pressure, questioning measurements in moderate or severely degenerated discs.