The intradiscal pressure of the lumbar spine is affected by intervertebral disc degeneration, age, level, and motion direction: evaluation of an in vitro database comprising 107 specimens

BACKGROUND CONTEXT: Intradiscal pressure (IDP) is a fundamental parameter for the estimation of loads and muscle forces acting on the spine and a major biomechanical indicator for various spinal pathologies. PURPOSE: To investigate primary effects of intervertebral disc degeneration, age, sex, segmental level, and motion direction on lumbar IDP using a large in vitro data collective. STUDY DESIGN: Evaluation of an internal database comprising 107 human functional spinal units of L2-L3, L3-L4, and L4-L5 from 68 donors (19-74 years, mean 50±12 years, 42% female). METHODS: All specimens had been loaded with pure moments of 7.5 Nm in flexion/extension, lateral bending, and axial rotation and IDP had been measured using flexible pressure sensors. Disc degeneration was assessed from radiographs using a validated classification system. RESULTS: IDP was significantly (p<.05) reduced for degeneration grades 1 (mild degeneration) and 2 (moderate degeneration) compared to grade 0 (no degeneration) in all motion directions and for the intrinsic pressure (INTP) without any loading (moment of 0 Nm). IDP significantly (p<.05) negatively (-0.69≤r≤-0.45) correlated with age and was significantly (p<.05) reduced for an age >40 years in all motion directions and for the INTP. Sex did not significantly (p<.05) affect the IDP. The IDP at L4-L5 level was significantly (p<.05) reduced compared to the IDP at L2-L3 level in all motion directions and for the INTP and significantly (p<.05) lower in axial rotation and for the INTP compared to flexion/extension and lateral bending. CONCLUSIONS: This study revealed that more degenerated discs and discs from elderly donors exhibit low or even negative intradiscal pressure, overall questioning in vitro and in vivo IDP measurements which disregard the degenerative condition of the intervertebral discs and the age of the donors and participants. CLINICAL SIGNIFICANCE: Increasing disc degeneration and age as well as more distal lumbar level are associated with decreased IDP of the lumbar spine, possibly less maintaining the load sharing capacity and thus representing risk factors for spinal pathologies.