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Biomechanical Effects of the Geometry of Ball-and-Socket Artificial Disc on Lumbar Spine: A Finite Element Study

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Abstract

Study Design.

A three-dimensional finite element model of intact lumbar spine was constructed and four surgical finite element models implanted with ball-and-socket artificial discs with four different radii of curvature were compared.

Objective.

To investigate biomechanical effects of the curvature of ball-and-socket artificial disc using finite element analysis.

Summary of Background Data.

Total disc replacement (TDR) has been accepted as an alternative treatment because of its advantages over spinal fusion methods in degenerative disc disease. However, the influence of the curvature of artificial ball-and-socket discs has not been fully understood.

Methods.

Four surgical finite element models with different radii of curvature of ball-and-socket artificial discs were constructed.

Results.

The range of motion (ROM) increased with decreasing radius of curvature in extension, flexion, and lateral bending, whereas it increased with increasing radius of curvature in axial torsion. The facet contact force was minimum with the largest radius of curvature in extension, flexion, and lateral bending, whereas it was maximum with the largest radius in axial torsion. It was also affected by the disc placement, more with posterior placement than anterior placement. The stress in L4 cancellous bone increased when the radius of curvature was too large or small.

Conclusion.

The geometry of ball-and-socket artificial disc significantly affects the ROM, facet contact force, and stress in the cancellous bone at the surgical level. The implication is that in performing TDR, the ball-and-socket design may not be ideal, as ROM and facet contact force are sensitive to the disc design, which may be exaggerated by the individual difference of anatomical geometry.

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