Soft tissue injuries induce lumbar instability and intervertebral disc degeneration: A mechanobiological study based on a rabbit model

BACKGROUND: Lumbar instability, often associated with intervertebral disc degeneration, is a key contributor to chronic low back pain. However, the mechanobiological interplay between soft tissue injury and the onset of spinal instability remains poorly elucidated.This study aimed to develop and characterize a rabbit model of lumbar instability based on endogenous (ligamentous) and exogenous (muscular) soft tissue injuries, and to investigate the biomechanical and biological progression of intervertebral disc degeneration over time. METHODS: Fifty-four New Zealand white rabbits were randomly assigned to three groups: endogenous ligament injury, exogenous muscle injury, and control. Multiple evaluation methods-including X-ray imaging, finite element analysis, creep and fatigue testing, histological staining, TUNEL apoptosis detection, and Western blotting for Aggrecan, Collagen II, and Caspase-3-were conducted at 0, 4, 8, 16, and 24 weeks post-modeling. FINDINGS: Both injury models led to progressive lumbar instability and intervertebral disc degeneration, evidenced by decreased disc elasticity, increased displacement under load, and structural deterioration in imaging and histology. FEA revealed altered stress distribution and increased mechanical burden over time. Aggrecan and Collagen II expression significantly declined, while Caspase-3 levels and TUNEL-positive apoptotic cells increased, especially in the exogenous group. INTERPRETATION: Muscle and ligament injuries are sufficient to induce lumbar instability and promote progressive disc degeneration through biomechanical failure and apoptosis. These findings underscore the importance of early mechanical and biological interventions targeting soft tissue integrity to prevent intervertebral disc degeneration and lumbar instability.