Patent Application
20060229608
The inventive concepts relate generally to spinal implants. More particularly, the invention concerns apparatus and associated methods for spinal implants with dynamic stabilization systems that can provide flexible or rigid support, as desired.
Modern spine surgery often involves the use of spinal implants to correct or treat various spine disorders or to support the spine. Spinal implants may help, for example, to stabilize the spine, correct deformities of the spine, facilitate fusion, or treat spinal fractures. Typical spinal implants either provide flexible or rigid (i.e., in a fusion procedure) support for the affected regions of the spine. Furthermore, they either limit movement in the affected regions in virtually all directions (for example, in a fused region), or they fail to limit undesired movement of the spine while allowing the desired movement. A need exists for a spinal implant that provides flexible or rigid support, as desired, while allowing desired movement of the affected levels of the spine and limiting the undesired movement of those levels.
The inventive concepts relate to apparatus and methods for spinal implants with dynamic stabilization systems. In one exemplary embodiment, an implant includes a rod with a multi-curve flexible portion. Each end of the flexible portion couples or connects to a respective rigid portion of the rod. A pair of fasteners fasten the rod to vertebrae (e.g., at a desired level of the spine).
In another exemplary embodiment, a system for supporting vertebral bodies in a spine includes an implant rod, and a pair of fasteners. The implant rod includes a serpentine spring portion with two ends. Each of the ends of the spring portion couples or connects to a respective pair of rigid portions of the rod. Fasteners couple the implant rod to a pair of spinal vertebrae.
In yet another exemplary embodiment, a method of producing a spinal implant includes forming an implant rod from a block of material (such as titanium Beta C). The block of material is formed so as to generate a multi-curve flexible portion with two ends. The ends of the flexible portion of rod are formed so as to couple, respectively, to a pair of rigid portions of the rod.
The appended drawings illustrate only exemplary embodiments of the invention and therefore should not be considered or construed as limiting its scope. Persons of ordinary skill in the art who have the benefit of the description of the invention appreciate that the disclosed inventive concepts lend themselves to other equally effective embodiments. In the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks.
The disclosed novel concepts relate to spinal implants with dynamic stabilization systems. In a dynamic stabilization procedure, the surgeon typically attaches an implant construct to either side of the affected vertebral level. The implant serves the function of stabilizing the spine. The inventive implants allow a controlled range of motion in some directions (or allow some types of motion), while inhibiting or limiting motion in other directions (or inhibit or limit other types of motion). The implants allow the patient to maintain flexibility and a functioning spine. The implant can also protect the loading at a level in the early stages of degeneration and allow healing of the soft tissues and bony structures at that level.
The implants can also allow flexibility in one or more levels, while supporting fusion in one or more other levels. Fusion surgery (for example, in the case of degenerative vertebral disease), allows fusion of adjacent vertebrae. Although the fusion reduces the pain, it also limits or reduces functionality of the spine, and may affect the stresses at levels superior and/or inferior to the fused level(s). By using the appropriate combination of rigid and flexible implant rods, the surgeon can provide flexibility in one or more levels and provide fusion in one or more other levels, as desired. The implant allows selective control of the loads and ranges of motion at the levels adjacent to a fusion and may help to prevent adjacent disc disease.
The novel spinal implants provide many advantages over conventional implants, as described below in detail. The spinal implants tend to allow desired movements of the affected parts of the spine, while tending to limit undesired movement of those regions. For example, the implants allow controlled flexion or extension, which may benefit the spine and promote nutritional exchange in the disc. At the same time, the implants limit or tend to disallow torsion or shear, movements considered harmful to the affected parts of the spine, which may include the nucleus pulposus or annulus fibrosis.
The disclosed implants allow rigid or flexible support for the spine, as desired (rather than providing either rigid or flexible support exclusively). The disclosed implants also offer relative ease of manufacturing. One may manufacture implants with low-profile springs or flexible regions, with no articulating pieces (no joints) that would generate wear debris.
The implants provide a flexible mechanism for providing support for one or more levels of the spine, as desired. The surgeon may vary the type of support from one level to another. For example, for one level, the surgeon may use the implant to provide flexible support, while for another level, the implant may provide rigid support. As another example, the surgeon may use alternating flexible and rigid segments of the implant to provide the desired support for the spine.
The implants can also combine rigid and flexible rods in a modular fashion to support both fusion and non-fusion applications. The ability to custom-fit the implants to the patient's needs provides the surgeon and the patient with an improved option over conventional implants. The disclosed implants also allow preloading of the implant to create distraction or lordosis of the instrumented level(s) of the spine (i.e., help to produce a desired profile of the affected regions of the spine).
Spring portion 103 couples to rigid portions 109 via optional transition portions 106. Transition portions 106 serve to reduce the stress concentrations between the spring portion 103 and the rigid end portions 109. Note, however, that one may omit transition portions 106, depending on a variety of factors, such as the type of materials used, the desired strength and profile of the implant, etc., as desired. In the embodiment shown, spring portion 103 has a curvilinear, non-helical shape.
Note that spring portion 103 has two curved portions (one portion with the shape of a “U” coupled to a portion shaped like an upside-down “U”). As described below in detail, however, one may use a variety of other shapes and configurations, as desired.
Spring portion 103 of rod 200 includes five curved portions. As persons of ordinary skill in the art who have the benefit of the description of the invention understand, one may use a wide variety and configurations of spring portion 103, such as the number and shape of the curved regions, as desired. The number of curves and configuration of spring portion 103 depends on a number of factors, such as the patient's physical size, the materials used, the degree of flexibility desired, etc., as persons of ordinary skill in the art who have the benefit of the description of the invention understand.
Implant rod 300A couples to vertebral bodies 305 and 310 through a desired type of fastener, such as pedicle screws 320A and 320B. More specifically, end portions 109 of implant rod 300A couple to pedicle screws 320A and 320B, respectively. Pedicle screws 320A and 320B hold end portions 109 in place so that the overall height of the implant matches the desired spacing for a particular patient. Pedicle screws 320A and 320B also fasten implant rod 300A to pedicles 325 (see
As noted above, the disclosed implants can support both fusion and non-fusion situations, in a wide variety of configurations.
In
Referring to
Ordinary, one may construct multi-level implant rods from one piece of material. In other words, one may process a single piece of material to produce a multi-level implant rod. Alternatively, one may construct multi-level implants by joining implant rods with a mating or coupling mechanism, as desired.
One may use a variety of configurations, shapes, and materials for the implants, including the implant rods.
Rod 900 includes spring or flexible portion 103, optional transition portions 905, and end or rigid portions 910. Spring portion 103 couples to rigid portions 910 via transition portions 905. Transition portions 905 provide a relatively rigid mechanism for coupling spring portion 103 to the rigid end portions 910, as desired.
In the embodiment shown, spring portion 103 has a curvilinear, non-helical shape. Note, however, that spring portion 103 may have other shapes and configurations, as desired, and as persons of ordinary skill in the art who have the benefit of the description of the invention understand. For example, spring portion 103 may have any of the shapes shown in
Rigid portions 910, rather than extending radially outward (see, for example,
Implant rod 900 couples to vertebral bodies 305 and 310 through pedicle screws 320A and 320B. More specifically, end portions 910 of implant rod 900 couple to pedicle screws 320A and 320B, respectively. Pedicle screws 320A and 320B hold end portions 910 in place so that the overall height of the implant matches the desired spacing and loading for a particular patient. Pedicle screws 320A and 320B also fasten implant rod 900 to pedicles 325 of vertebral bodies 305 and 310.
The surgeon can adjust the distance between the vertebral bodies 305 and 310 by preloading implant rod 900, as described above. Once the adjustment has been made, the surgeon can use pedicle screws 320A and 320B to secure rod 900, as described above.
To assist in orientation and securing rods according to various embodiments of the invention, one may use a variety of orientation aids/mechanisms or location features.
Note that one may use a wide variety and configuration of orientation mechanisms, as desired. For example,
As another example,
Note that, rather than using flat regions as described above, one may use other mechanisms, as desired, and as persons of ordinary skill in the art who have the benefit of the description of the invention understand. For example, one may use dimples, grooves, or other indicators of orientation. Furthermore, one may use various numbers of such indicators, as desired.
As noted, one may manufacture the disclosed implants (including the implant rods) from a variety of materials. For example, one may use stainless steel, titanium, other metals, or polymers, as desired. In one embodiment, one may use titanium Beta C, a titanium alloy having the composition Ti-3Al-8V-6Cr-4Mo-4Zr (or similar compositions, as desired). Titanium Beta C may be solution treated at 815° C., and aged at 565° C., or may be treated to other conditions to achieve the desired material characteristics.
Titanium Beta C provides relatively high resistance to fatigue. One may manufacture the implant rods and the pedicle screws from titanium Beta C to take advantage of that property. Using titanium Beta C helps to provide relatively robust, fatigue-resistant implants with improved longevity and performance characteristics, given the ability to vary the mechanical properties of this titanium alloy by varying the heat treat parameters
As noted above, the disclosed implants offer relative ease of manufacturing as an advantage. To manufacture the implants, one may use a lathe and wire EDM to fabricate the implant by shaping and forming a piece or block of material. Advantageously, one may manufacture each implant from a monolithic piece of material, thus reducing joints and associated manufacturing expenses. As an alternative, one may fabricate the implants by using mill processes, as desired.
Various modifications and alternative embodiments of the invention in addition to those described here will be apparent to persons of ordinary skill in the art who have the benefit of the description of the invention. Accordingly, the manner of carrying out the invention as shown and described are to be construed as illustrative only. Persons skilled in the art may make various changes in the shape, size, number, and/or arrangement of parts without departing from the scope of the invention described in this document. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described here, or use certain features of the invention independently of the use of other features, without departing from the scope of the invention.
