Author: Bharath K. Parepalli

Publisher:

Published: 2009

Total Pages: 204

ISBN-13:

Fusion has been the gold standard treatment for treating the disc degeneration. Fusion surgeries restrict the motion at the implanted level there by imposing additional load at the adjacent levels. Many clinical studies have showed that adjacent segment degeneration was observed in patients over time. In order to overcome problems with fusion devices, dynamic stabilization systems are being used to treat disc degeneration related problems. These implants restore intersegmental motion across the implanted level with minimal effects on the adjacent levels. In vitro cadaveric testing was conducted on seven harvested sheep spines using established protocols. Axient was implanted in the spines 3 months prior to sacrificing. Main aim of this testing is to see if the performance is altered by the presence of surrounding muscle tissue. The specimens were prepared and tested under load control protocol. All six loading modes were tested by applying a pure moment of 10Nm (in steps of 2.5Nm) and angular displacement was calculated for the following cases: 1) Intact spine + Axient with surrounding muscle tissue, 2) Intact spine + Axient with muscle tissue removed, 3) Intact spine (with implant removed). Relative motion of L4 vertebra with respect to L5 was calculated. Statistical analysis was performed (on the implanted level data) to see if there is a statistical significance between cases 1 and 2. Biomechanical testing was also performed on 4 human cadavers to observe the trend with Axient compared to FE results. A validated 3-D non linear finite element model of the L3-S1 lumbar spine was used to evaluate biomechanics of various dynamic stabilization systems in comparison with traditional rigid rod system. The model was modified at L4-L5 level to simulate three different dynamic stabilization systems (DSFM-1, DSFM-2 and Axient, Innovative Spinal Technologies Inc., Mansfield, MA). Grade I was simulated at L4-L5 level. Follower preload of 400N and a 10Nm bending moment was applied to simulate physiological flexion, extension, lateral bending and axial rotation. Range of motion (ROM), intra discal pressure (IDP) and facet loads were calculated for all the models. Implant with better performance was then compared with fusion system in both grade I and grade II degenerated spines. In vitro results showed that there is no significant difference in the performance of the Axient with and without surrounding muscle tissue in terms of range of motion. Coming to FE results, Axient performed better over the other two implants (DSFM-1 and DSFM-2). Axient device was able to restore the motion at the implanted level compared to fusion device. Higher motions were observed at the adjacent level (L5-S1) with fusion device compared to intact and injured models. Both devices were able to stabilize the diseased spine and unload the treated disc.