Introduction:

Interbody fusion is a very common surgical treatment for degenerative disc diseases. It is necessary to explain the effect of pedicle based hybrid stabilization systems (PBHS) on the lumbar spine, as there is no consensus in the literature about their performance.

Hypothesis:

Topping off a fusion with a PBHS may provide some protection against adjacent segment failure.

Material and methods:

The biomechanical effect PBHS on fused and adjacent to fusion levels were investigated, including range of motion, bending stiffness, Von Mises stress A 3D Finite Element model of the L2-S1 spine was used and modified to simulate pre and postoperative changes during combined loading. Five models instrumented with different systems [Titanium and PEEK fusion; Dynesys hybrid system; NFlex hybrid stabilization and PEEK topping off fusion] were compared to those of healthy model.

Results:

After hybrid instrumentation, the L4-L5 level did not lose its motion completely, NFlex hybrid stabilization system maintained 82% of flexion at the adjacent to fusion level, reduced bending stiffness by 40% in axial rotation. Dynesys hybrid system represented more restricted motion than NFlex. PEEK topping off fusion system was the most rigid one among all three systems. It increased bending stiffness at the adjacent level and increased the axial motion by 25%. High risk of rod breakage was computed for PEEK topping off system as 48.8 MPa in lateral bending.

Conclusion:

Hybrid stabilization can delay adjacent segment failure and compensate lumbar spine mobility. However, it is clear that PBHS need to be further tested before being considered for clinical use.

Level of evidence:

III; Well-designed computational non experimental study.