AbstractsBiology & Animal Science

Dynamic stabilization devices such as the Stabilimax (Applied Spine Technologies Inc.) are being considered as a viable alternative to fusion for patients suffering from low back pain. As opposed to fusion, the Stabilimax provides controlled range of motion in patients undergoing decompression procedures for central or lateral lumbar spinal stenosis at one or two adjacent levels. This pedicle screw based system features an internal dual spring mechanism which combined with a ball and socket joint provides stability by allowing controlled motion to the treated level(s) of the lumbar region. In the recent times, efforts are being made to have the motion preserving devices stabilize the segments, like the rigid instrumentation, if needed. The Stabilimax could be made to achieve this goal by limiting the range of motion of the treated segment with different spring travel lengths (interpedicular travel). More recently, hybrid stabilization has been proposed with an intention to treat patients with segmental lumbar degenerative pathologies. If needed, Stabilimax could also be modified to achieve this goal by using it in conjunction with rigid rod instrumentation. The aim of this study was to evaluate the biomechanics of the decompressed segment (s) implanted with single, multilevel, and hybrid Stabilimax devices with three different spring travel distances. The hypotheses here are 1) the overall stabilization of the decompressed segment implanted with Stabilimax devices does not change with variations in interpedicular travel. 2) A dynamic system in conjunction to a fusion system reduces the risk of adjacent level degeneration as seen in lumbar arthrodesis. A validated 3-D nonlinear finite element model of the intact L3-S1 lumbar spine was used to evaluate the biomechanics of the following devices:a) L4-L5 Single level Stabilimaxb) L3-L4-L5 Multilevel Stabilimaxc) L4-L5-S1 Multilevel Stabilimaxd) L4-L5 Stabilimax + L5-S1 Fusion The intact model was modified to simulate the decompression at the corresponding level(s) followed by the implantation of the devices. The load control and hybrid protocols were used to evaluate these devices. Various biomechanically relevant parameters like Range of motion, Intradiscal pressure, Facet loads, Implant stresses, Instantaneous axis of rotation (COR), Maximum spring forces and displacements were calculated. Results show that different Stabilimax devices are capable of stabilizing the decompressed segment (s) in flexion, extension and lateral bending but not in axial rotation. The overall stabilization of the decompressed segment (s) with Stabilimaxdevices did not alter with variations in interpedicular device travel in most of the cases. The hybrid stabilization system also produced favorable results ascertaining with our hypothesis that a dynamic system in conjunction to a rigid rod system reduces the risk of adjacent level degeneration as seen in lumbar arthrodesis.