Comparison of Lumbar Disc Degeneration, Fusion and Disc Arthroplasty on Biomechanics of Adjacent Segment

Back pain is an unavoidable discomfort that is very common in the United States. It happens naturally while aging and people who do laborious work may experience pain earlier. In severe cases, surgical treatments are needed by fusing the segment or introducing disc arthroplasty. Once, degeneration takes place, the adjacent segment starts to degenerate whether the degeneration at the original level was addressed or not; this phenomenon is known as adjacent segment degeneration disease. To study the biomechanics of adjacent segments in various cases, a three-dimensional finite element model of the lumbar spine was created from CAT scan based-data using a 3D finite element program. The study included analysis of motions, facet forces, and von Mises stresses at the segments adjacent to the degenerated discs or fused segment or disc arthroplasty. First, the effect of a single level degeneration at L5S1 in the lumbar spine was studied. Then, a comparison of the changes in the motions of segments adjacent to a single fusion and a single arthroplasty was studied. Finally, the effects of a disc arthroplasty on the degenerated disc of an adjacent segment were also studied. In conclusion, a single-level degenerated disc leads to an increase in motions, facet forces and von Mises stresses at the adjacent segments and also the skipped segments. However, disc arthroplasty decreased rotation, facet forces and von Mises stresses at the adjacent segment. Therefore, disc arthroplasty produced better results on the adjacent segment. In addition, in the case with a disc arthroplasty with adjacent disc degeneration, a decrease in motions, facet forces and von Mises stresses under flexion and extension at the degenerated adjacent segment were observed. On the contrary, an increase in the motions and stresses were observed under lateral bending and torsion.