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Caution: Investigational device, limited by Federal (or United States) law to investigational use. The FSU device is currently not available in the United States. Information is presented on the website for general education. Flexuspine's FSU (Functional Spinal Unit) Total Spinal Segment Replacement is designed to provide an alternative to fusion by reestablishing mobility to an affected segment of the lumbar spine. It is a comprehensive device comprised of an interbody disc component (Core) and posterior dynamic resistance component (Dampener) that was designed as a system to replace the natural kinematics of the motion segment.
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FSU CORE – Size – Fit – Subsidence Resistance
FSU CORE - Size – Fit – Subsidence Resistance It is well known that artificial disc replacement devices should have as large a coverage area as possible to resist subsidence into the vertebral endplates.1 Although the posterior implantation approach offers advantages over the anterior approach, such as direct access to the nerve roots for effective decompression, anatomic constraints limit the size of the device that can be implanted. The FSU Core component, however, has been designed to take advantage of the benefits of the posterior approach while still accommodating the implantation of a larger device. This is possible because the Core Component is part of a Total Spinal Arthroplasty device system that replaces not only the disc, but the complete three-joint complex (disc and facets). By removing the facets, a wider surgical window is available for the larger FSU Core disc component to be inserted.
Benchmark Fit Comparison
The fit of the Flexuspine Core Component on the vertebral endplate is comparable in coverage to a typical anterior TDR and greater than common fusion cage footprints.
Weighted Area Comparison Another advantage of the FSU Core Component is that the footprint is placed on the posterior lateral portion of the endplate, which is stronger than the central portion of the endplate, where the majority of interbody implants are placed1. A detailed evaluation incorporating both the crossâsectonal area of the FSU and typical interbody implants, along with the strength of the underlying bone1 on which they are implanted, has been performed3. The area and strength of the underlying bone on which the implants are placed were used to calculate a weighted coverage area to provide an indication of subsidence resistance.
The study found that the weighted coverage area of the Flexuspine Core implant was greater than a similarly sized Anterior TDR due to
*We are proud to mention that the information above was part of a more extensive poster exhibit that was voted “Highest Scored” poster at the 2008 SAS (Spine Arthroplasty Society) meeting.
FSU Wear Testing and Particulate Animal Study The motion of any joint, human or man-made, will experience the effects of wear, which can produce microscopic particles. All arthroplasty devices exhibit wear, and, in the vast majority of cases, the body can manage the resultant particles. But depending on their size and amount, the body's cellular response to these foreign elements can sometimes lead to the destruction of surrounding bone leading to possible device loosening.4 Wear testing of the Flexuspine FSU was performed to characterize the volumetric wear potential of the FSU system. Testing in animals was also performed to evaluate the physiological response to wear debris comparable to that produced by the FSU system in vitro. The FSU Core CoCr metal-on-metal articulation demonstrated wear comparable to metal-on-metal total disc replacements.5 The FSU silicone dampeners also showed minimal wear and sufficient durability under clincally relevant motions.
Bushelow M, Walker J, Coppes J, Hinter M, Nechtow W, Kaddick C, "Comparison of Wear Rates: Metal/UHMWPE and Metal-on-Metal Total Disc Arthroplasty," Spine J, 2007, 7(5S): 97S-98S.
FSU – Managing the Forces / Sharing the Load The spinal segment’s three joint complex (disc and facets) is designed to work as a unit to achieve stability and motion. The FSUCore and Dampeners)
are designed to function seamlessly by sharing the anticipated load of
the spine while continuing to encourage physiological motion. The
interbody Core is considered to be the foundational support of the FSU.
It features a shear face designed to provide stability to the spine
segment, which is intended to help off-load the pedicle screws. This
design feature is intended to deter pedicle screw loosening. In turn,
the Dampeners (attached via pedicle screws) are designed to work with the Core providing resistance to flexion-extension, lateral bending, and axial rotation. The Core . . . managing the forces of the three joint complex The core is designed to allow motion while providing the stability necessary to protect the pedicle screws from excessive loading. This is particularly important for Total Spine Arthroplasty devices as the removal of the facets requires the device to play a greater role in shear. Due to the Core’s shear-resistant design, it has been shown in pre-clinical in vitro testing to be able to carry shear loads far surpassing anticipated in vivo loads.6
The Dampener . . . managing the forces of the three joint complex Pedicle screw loosening can be a clinical concern when replacing the total three joint complex with a motion preservation device. A finite element model analysis was conducted to evaluate the stresses at the pedicle screw-bone interface. Finite Element Model of a ligamentous L4/L5 motion segment.9
1Grant
JP, Oxland TR, Dvorak MF, “Mapping the structural properties of the
lumbosacral vertebral endplates,” Spine, 2001, 26(8):889-96. |
