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Dynamic Stiffness Matrix Testing of Porcine Specimens with Intact Discs and After Total Disc Replacement with the DePuy In Motion Device
The dynamic stiffness matrix testing of porcine lumbar specimens was completed, both with and without an axial preload. Intact specimens were tested, and the testing repeated after a total disc replacement procedure with a DePuy In Motion artificial disc.

The testing demonstrated the disc replacement device compared favourably with the intact porcine disc both in shear and axial stiffness. However, the low-friction, double ball and socket design of the In Motion device lacks stiffness in the three rotational axes, and it is unstable in lateral bending. Rotations are the primary movements in the spine, and it is crucial if the natural biomechanics are to be restored, that a disc replacement device should replicate the stiffnesses of these axes.

The testing protocol used provides a means to complete standardised performance tests of new spinal devices and lays the foundations for future comparison studies. Additionally, the spine simulator and testing protocol would provide valuable data during the design stage of new total disc replacements, aiding the development of the next generation of artificial discs.

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