Finite element model reveals the involvement of cartilage endplate in quasi-static biomechanics of intervertebral disc degeneration

Background and Objective: The biomechanical functionality of intervertebral discs is intrinsically linked to their compositional and structural attributes. However, the specific influence of cartilage endplate (CEP) degeneration on these discs' biomechanical behavior remains inadequately understood. Methods This study developed and quantitatively validated four biphasic swelling-based finite element models. We then applied four quasi-static tests and simulated daily loading scenarios to examine the effects of CEP degradation. Results In free-swelling conditions, short-term responses were prevalent, with CEP performance changes not significantly impacting response proportionality. Creep test results showed over 50% of strain attributed to long-term responses. Stress-relaxation testing indicated that all responses intensified with disc degeneration, yet CEP degeneration's impact was minimal. Daily load analyses revealed that disc degeneration significantly reduces nucleus pulposus pressure and disc height, whereas CEP degeneration marginally increases nucleus pressure and slightly decreases disc height. Conclusions Glycosaminoglycan content and CEP permeability are critical to the fluid-dependent viscoelastic response of intervertebral discs. Our findings suggest CEP's contributory role in disc degeneration under daily loading conditions.