Abstract: BACKGROUND: Endplate defects are one of the important causative factors of lumbar degeneration, and their morphological characteristics may significantly affect the local mechanical environment of the spine. However, the effects of their different morphologic defects on the biomechanical properties of the lumbar spine have not been fully elucidated.
OBJECTIVE: To investigate the effects of focal marginal defects, focal central defects, and angular defects on the stress distribution of lumbar endplates, intervertebral discs, and small joints, and to reveal their underlying biomechanical mechanisms.
METHODS: Lumbar CT images were obtained from a healthy 36-year-old male volunteer, and a complete endplate model of the L4-L5 segment was reconstructed. Three typical endplate defect models (focal marginal defect, focal central defect, and angular defect) were constructed based on the classification of vertebral endplate defects in clinical imaging studies. By applying dynamic loads and corresponding moments to simulate physiological spinal muscle loads and typical motion loads, such as stance, forward flexion, backward extension, lateral bending, and rotation, the biomechanical stress distribution characteristics and peak changes in the vertebral cartilage endplates, intervertebral disc annulus fibrosus, nucleus pulposus, and facet joints during physiological spinal motion were evaluated under different defect types. The mechanisms by which different defect types affect lumbar spine biomechanical stability were explored.
RESULTS AND CONCLUSION: (1) Different defect types significantly altered the stress conduction pathways in the endplates and adjacent structures. Edge defects primarily affected the stress distribution on the lateral side of the annulus fibrosus, while central defects significantly altered load bearing capacity during extension. (2) Significant stress gradient concentrations were observed at the defect edges, indicating potential microinjury risk. (3) Angular endplate defects produced significant stress concentrations under dynamic loading, potentially contributing to segmental instability and accelerated degeneration. (4) These results provide a biomechanical basis for elucidating the involvement of endplate defects in intervertebral disc degeneration and facet joint injury, providing valuable guidance for early clinical identification of high-risk defect types and the development of targeted preventive strategies.

Key words: endplate defects, finite element analysis, lumbar spine biomechanics, stress distribution, disc degeneration