Validated finite element analysis of the maverick total disc prosthesis.

STUDY DESIGN

Combining in vitro tests and finite element analysis to provide a more complete picture of the role that a disc prosthesis implant would play in the biomechanics of the spine.

OBJECTIVE

Analysis of the disc function after total disc prosthesis insertion with and without antero-posterior or lateral offset and in combination with adjacent fusion.

SUMMARY OF BACKGROUND DATA

To avoid the risk of degenerative cascade the total disc replacement may be considered as an alternative. Few finite element analysis combined with cadaver testing under loading conditions have been published today.

MATERIALS AND METHODS

In vitro tests were performed using 6 fresh human cadaver specimens to quantify the load-displacement behaviors before and after insertion of a total disc replacement (Maverick, Memphis) implant. A finite element (FE) spine model was validated with the data from the in vitro tests. This model is built on the basis of ANSYS software. The effect of the prosthesis positioning on the motion behavior at L4-L5 and on the inner loads over facets was evaluated in 4 configurations.

RESULTS

The study showed that the motion behavior at the levels adjacent to the Maverick prosthesis remained the same as the intact spine, unlike a single level fusion at L5-S1. In the biomechanical study settings, Maverick prosthesis, once properly positioned, does not modify the motion behavior of the spine as compared with its intact state. The less-than-ideal positioning of the prosthesis, especially with anterior offset, affect significantly the range of motion of the spine segment and cause increase of inner load in the facets. Those results indicated a good reliability of the finite element model in representing both intact and instrumented spine segments.

DISCUSSION

The in vitro test results demonstrated that Maverick disc prosthesis provides near physiologic function of a natural disc restores stability of the spine and preserves the segmental motion without undue stress on adjacent segments.To our knowledge, this study suggested for the first time the importance of the prosthesis positioning into the spine model.