A finite element biomechanical investigation of lumbar spine segments through novel intervertebral disc design

Abstract

Advancements in laser additive manufacturing have significantly contributed to the design and optimization of complex, biomimetic, and patient-specific spinal implants, particularly intervertebral disc (IVD) replacements. The proposed study investigates the biomechanical performance of a novel titanium alloy artificial IVD, engineered with an auxetic cellular core to restore spinal stiffness while enhancing biocompatibility and mechanical compliance. A validated finite element (FE) model of the lumbar spine was established from DICOM datasets, incorporating anatomically accurate geometries and material properties for cortical and cancellous bone, annulus fibrosus (AF), nucleus pulposus (NP), and major spinal ligaments. Simulations were conducted to compare the mechanical responses of stress, strain, and deformation for the intact spine (ISM), the spine implanted with a SB Charité™ (SBC), and a proposed novel implant (XCEL). Loading conditions along with human physiological motion activities such as flexion, extension, lateral bending, and twisting were considered. For one of the key results obtained by the application of a 1000 N compressive load and 10 Nm moment during the twisting motion, the maximum von-Mises stress observed was 116 MPa, 191.82 MPa, and 127.45 MPa in ISM, SBC, and XCEL, respectively. The proposed implant demonstrated improved stress distribution and mechanical resilience. Moreover, the auxetic core, characterized by a re-entrant geometry and the endplate curvatures closely mimicked those of natural lumbar vertebral endplates. Range of motion (ROM) analysis under flexion revealed the values of 17.3°, 11.9° and 11° for ISM, SBC and XCEL respectively. These findings confirm the suitability of the titanium alloy-based implant to restore near physiological ROM and spinal mechanics. The predicted parameters revealed that XCEL geometry implant can be engineered to the required ROM, effectively restoring natural biomechanics when replacing a natural IVD, highlighting its future clinical potential. Advanced models can be applied to customized, patient-oriented design, micro-structure mimicking manufacturing, pre-surgery planning, clinical follow-up, testing, and overall implant success.