Lumbar Modic Changes Concentrate Stress at the Endplate–Vertebral Interface

Background Modic changes occur where the lumbar disc transfers load to the vertebral body. Regional stress and segmental motion together describe their mechanical effects. We examined how material inputs for each Modic type changed local stress, with and without disc degeneration. Methods Paired computed tomography measurements from 24 patients with Modic changes provided stiffness multipliers for each type: seven type I, ten type II, and seven type III cases. Eight L4–L5 finite element models included normal anatomy, isolated disc degeneration, isolated Modic types I–III, and each type combined with disc degeneration. The models shared one base geometry, with a predefined reduction in disc height in degenerated models. Geometry and loading were matched to assess material effects. We applied 500 N compression and a 10 N·m moment in six directions and descriptively compared endplate and vertebral margin stress, disc stress, and range of motion. Results Models containing Modic changes showed focal stress concentration near the mapped region. Isolated Modic changes reduced range of motion by 0.5%–7.7%. Type III had the highest mean margin stress in every tested condition, and maximum stress rankings varied. Maximum L4 margin stress in isolated type III ranged from 13.97 to 36.28 MPa. Geometric mean stiffness multipliers were 2.05, 2.09, and 5.02 for types I, II, and III, respectively. With coexisting disc degeneration, margin stress redistribution depended on vertebral level and loading direction. Conclusions In the tested L4–L5 geometry, Modic-related material heterogeneity concentrated stress at the endplate and adjacent vertebral margin. Segmental motion changed relatively little. Local stress assessment complements segmental motion when studying Modic biomechanics.