Study of Double-level Degeneration of Lower Lumbar Spines by Finite Element Model

Background Degeneration of intervertebral disks in the lower lumbar spine is associated with significant structural alterations. Finite element model has been widely used in the study of spinal mechanical behaviors. Our study used this technique to characterize the motional influence to the double-level (L4-5 and L5-S) degeneration. Methods and Results Three grades of disk degeneration were modeled with the changes in geometry and material properties. In the extension and flexion of range of motion (ROM), single segment degeneration in L4-5 or L5-S resulted in a decreased angle in itself and increased angle in the other segment. Double-level degeneration resulted in a decreased rotation in both segments. Bending resulted in a decreased ROM in all 3 grades of degeneration in the double-level degeneration. In torsion loading, mild and moderate single degeneration in L4-5 and L5-S increased the rotation angle. In double-level degeneration, mild and moderate L4-5 degeneration increased the L4-5 rotation angle by 14%−19%. In contrast, severe L4-5 decreased L4-5 rotation angle. Concurrently, mild and moderate L5-S degeneration increased the rotation angle, respectively, by 15% and 6%, and severe degeneration decreased the rotation angle by 29%. Conclusions Different loading motions in double-level degeneration had differing effects on the ROM. These changes are important to understand the biomechanics of the progression of disk degeneration in the lower lumbar spine. Our results provide insights for the clinical intervention of double-level intervertebral disks.