WO2009064419A1

WO2009064419A1 - Dynamic spinal stabilization device

Info

Publication number: WO2009064419A1
Application number: PCT/US2008/012718
Authority: WO
Inventors: Dong Myung Jeon; Patrick Dennis Moore; Sang K. Lee
Original assignee: Dong Myung Jeon; Patrick Dennis Moore; Lee Sang K
Priority date: 2007-11-12
Filing date: 2008-11-12
Publication date: 2009-05-22

Abstract

Interspinous vertebral implants and methods for interspinous process decompression and dynamic stabilization of spine. In one illustrative example, interspinous vertebral implants are attached to poly-axial bone screws affixed to either side of one inferior vertebral body at the standard pedicle location for spinal fusion procedures. Nitinol rod and interspinous process hook components are attached to the installed poly-axial bone screws and are positioned between adjacent superior and inferior spinous processes to provide dynamic decompression and stabilization to adjacent vertebral bodies. A transverse link component which provides a means to prevent and stabilize the stresses or forces that may interact on the installed Poly- Axial Bone Screws resulting from the dynamic nature of the Nitinol rod and interspinous process hook components is also installed.

Description

TITLE OF THE INVENTION

DYNAMIC SPINAL STABILIZATION DEVICE

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/987,275, filed 12 November 2007, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention concerns spinal instrumentation systems. More particularly, the invention pertains to a system for use in interspinous process decompression and dynamic stabilization of the spine.

BACKGROUND

Dynamic stabilization of damaged or diseased spinal segments has long been desired. However, until recently, the technology has yet been underdeveloped.

Numerous techniques and devices have been developed with varying degrees of success. Such dynamic stabilization devices have included flexible rod systems, Interspinous Process Decompression devices, and artificial disks, among others.

These different systems have been successful in some aspects, but failures in others.

Additionally, no such device is all inclusive for all applications.

Some of the failures can be attributed to the devices' material of manufacture. By nature, dynamic stabilization requires movement in the device. These devices utilize relatively static materials for construction, and therefore lack inherent dynamic material qualities.

There is a need for a dynamic spinal stabilization device which utilizes a dynamic material and overcomes the shortcomings of these prior devices for certain applications. SUMMARY

Various interspinous vertebral implants and methods for using the same for interspinous process decompression and dynamic stabilization of spine are disclosed. In one illustrative example, interspinous vertebral implants are attached to poly-axial bone screws affixed to either side of one inferior vertebral body at the standard pedicle location for spinal fusion procedures. Nitinol rod and interspinous process hook components are attached to the installed poly-axial bone screws and are positioned between adjacent superior and inferior spinous processes to provide dynamic decompression and stabilization to adjacent vertebral bodies. A transverse link component which provides a means to prevent and stabilize the stresses or forces that may interact on the installed Poly- Axial Bone Screws resulting from the dynamic nature of the Nitinol rod and interspinous process hook components is also installed. Without being bound by any theory, it is believed that the utilization of this pedicle screw based interspinous process decompression and dynamic stabilization apparatus provides interspinous process distraction and stabilization forces to restore at least some spinal segment moment, alleviating some compression on the intervertebral disk and stabilizing adjacent spinal segments.

DESCRIPTION OF THE DRAWINGS It will be appreciated by those of ordinary skill in the art that the elements depicted in the various drawings are not to scale, but are for illustrative purposes only. The nature of the present invention, as well as other embodiments of the present invention may be more clearly understood by reference to the following detailed description of the invention, to the appended claims, and to the several drawings attached hereto.

FIG. 1 is a diagram of the shape memory of Nitinol components. FIG. 2 is a diagram of a loading/unloading curve for Nitinol. FIG. 3 shows a model of a multi-level spine segment with the preferred embodiment installed in a one level construct. FIG. 4 shows an example of a Poly- Axial Screw that may be used with the preferred embodiment.

FIG. 5 shows a left and right Inter Spinous Rod/Hook Component of the preferred embodiment in regards to a one level construct.

FIG. 6 shows a Transverse Link Component of the preferred embodiment in regards to a one level construct. DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Nitinol-based products have been on the market since the late 1960's. These early products were dependent on Nitinol's thermal shape memory behavior. Today the emphasis has shifted to using Nitinol's superelastic behavior for products related to medical device industries. The first Nitinol applications were based on the thermal shape memory effect. In the medical device industry, Nitinol is becoming more popular for reusable medical instruments. Surgeons can shape an instrument on-site to fit a patient's geometry, then after heat sterilization the device returns to its original shape for the next procedure.

Superelastic Nitinol medical devices can be deployed using the shape memory effect as well. Chilling the device in the delivery system keeps the device in the soft martensite phase in a lower force state. After deployment, the device warms to its new surroundings, recovers its "programmed" shape and becomes superelastic, as illustrated in diagram shown in FIG. 1.

Nitinol possesses increased elasticity in comparison to stainless steel, which allows it to be bent more significantly than stainless steel without taking a set. Nitinol wires and tubes will thus pass through tortuous paths in the body and remain straight and torqueable. Medical guidewires, shafts for baskets and snares, catheter tubes and instruments all benefit from Nitinol's kink resistance and flexibility. Additionally, Nitinol's elasticity or "springback" is some 10 times greater than stainless steel. Superelastic Nitinol has an unloading curve that stays flat over large strains, thus, i.e. Nitinol devices can be designed that apply a constant stress over a wide range of shapes. FIG. 2 depicts a diagram of a loading/unloading curve for Nitinol. Nitinol has been approved for use in a number of clinical applications including orthopedic bone anchors, vena cava filters, cardiovascular endoprostheses, and orthopedic archwires. Additional orthopedic applications include osteosynthesis staples and scoliosis correction rods. Nitinol' s biocompatibility results mainly from its tight intermetallic bounded structure, its chemically stable and homogeneous TiO₂ surface layer, and its corrosion resistance similar to other Titanium alloys. The material specification for Nitinol conforms to ASTM standard ASTM F 2063-00, which is incorporated herein by reference in its entirety. The material specification is set forth in Table 1 below.

TABLE l

FIG. 3 shows a model of a multi-level spine segment with the one illustrative embodiment installed as a one level construct. Two Poly- Axial Bone Screws 100 are affixed to an inferior vertebral body, one on either side at the standard pedicle location for spinal fusion procedures. FIG. 4 depicts a cut-away side view of one illustrative embodiment of a suitable Poly- Axial Bone Screw 100 and the components thereof. It will be appreciated that Poly- Axial Bone Screw 100 is a multi-component connection system. It will be further appreciated that other- suitable bone screws may be used. Example of some suitable bone screw systems are disclosed in pending U.S. Patent Application Serial Number 11/648,983, entitled MULTI- AXIAL DOUBLE LOCKING BONE SCREW ASSEMBLY, the contents of which are incorporated by reference herein. Returning to FIG. 3, two rod and interspinous process hook components 200 (depicted in detail in FIG. 5) are positioned between adjacent superior and inferior spinous processes, with the hook component 204 placed around the posterior side of the adjacent superior spinous process and the proximal end of the rod 202 connected to the bone screw 100 anchoring member, thus positioned to provide dynamic decompression and stabilization to adjacent vertebral bodies. Rod 202 acts as a resiliently compressible member and may include a resilient structure, such as bend 206.

In the illustrated embodiment, at least process hook component 204 may be formed of Nitinol, although it will be appreciated that another biocompatible dynamic material, or combination of materials, i.e. polymer and Stainless Steel or Polymer and Titanium, may be used. It is presently preferred that each entire rod and interspinous process hook component 200 be constructed of a dynamic material, such as Nitinol, to allow the rod and interspinous process hook components, once installed, to be flexible without yielding under the stresses of the application.

A transverse link component 300 (depicted in detail in FIG. 6) is installed between the anchoring members of the two bone screws 100. Distal attachment portions 302 of the transverse link component 300 thus reside in the anchoring member of each bone screw 100. It will be appreciated that the angle of the attachment portions 302 and the distal end of rod 202 are designed to allow attachment to the bone screws 100 while maintaining appropriate positioning of the spinous hooks 204. Transverse link component 300 may also include a recessed portion 304 to allow for accommodation over the anterior surface of the inferior spinous process. Transverse link 300 provides a means to prevent and stabilize the stresses or forces that may interact on the installed bone screws 100 resulting from the dynamic nature of the rod and interspinous process hook components 200.

Without being bound by any theory, it is believed that the utilization of this pedicle screw based interspinous process decompression and dynamic stabilization apparatus provides interspinous process distraction and stabilization forces to restore at least some spinal segment moment, alleviating some compression on the intervertebral disk and stabilizing adjacent spinal segments. It will be appreciated that although depicted as a single level attachment, systems in accordance with the present invention may be used for multi-level attachment as well as in combination with traditional pedicle screw or hook fusion systems. In such embodiments, as with the one level Pedicle Screw based, Interspinous Process Decompression and Dynamic Stabilization system described above a plurality of Titanium Poly- Axial Bone Screws; one each affixed to either side of one inferior vertebral body at the standard pedicle location for such spinal fusion procedures; and two each Nitinol rod and interspinous process hook components that provide resiliently compressible members are positioned between adjacent superior and inferior spinous processes and attached to the installed anchoring member of the Poly- Axial Bone Screws to provide dynamic decompression and stabilization to the adjacent vertebral bodies for each vertebral body where such support is desired. Additionally, at each such vertebral body, a transverse link component is installed to provide a means to prevent and stabilize the stresses or forces that may interact on the installed Poly- Axial Bone Screws from the dynamic nature of the Nitinol rod and interspinous process hook components. Thus, such a multi-level construct, repeats the one basic construct per spinal level and/or can be realized to be used in conjunction traditional pedicle screw based fusion systems and/or hook systems and/or any other fusion fixation system.

For placement in a patient, the unique properties of Nitinol may be utilized to facilitate installation of the device in a less invasive manner than other prior art systems. Ligament tissue surrounds the Spinous Process. A rod and interspinous process hook component 200 may be chilled in saline to convert the Austenite structure of the Nitinol to a Martensite structure, thus becoming very malleable. The surgeon then has the ability to deform the "forks" of the interspinous component, allowing easy installation through the interspinous ligament without total removal of the ligament. Once installed, the surgeon may flood the rod and interspinous process hook component 200 with heated saline, converting the Martensite structure of the Nitinol to an Austenite structure, and reverting to the rod and interspinous process hook component 200 to its original shape. While the present invention has been shown and described in terms of preferred embodiments thereof, it will be understood that this invention is not limited to any particular embodiment and that changes and modifications may be made without departing from the true spirit and scope of the invention as defined and desired to be protected.

Claims

CLAIMS What is claimed is:

1. An interspinous process decompression and dynamic stabilization system comprising: at least a first bone anchor affixed to an inferior vertebral body at a first standard pedicle location for spinal fusion procedures; at least a first rod and interspinous process hook component that provides a resiliently compressible member adapted for position between adjacent superior and inferior spinous processes, the at least a first rod and interspinous process hook component attached to the at least one bone anchor and positioned to provide dynamic decompression and stabilization to adjacent vertebral bodies.

2. The system of claim 1, wherein the at least a first bone anchor comprises a poly-axial bone screw.

3. The system of claim 1, further comprising a second bone anchor affixed to the inferior vertebral body at a second standard pedicle location for spinal fusion procedures; and a second rod and interspinous process hook component that provides a resiliently compressible member adapted for position between adjacent superior and inferior spinous processes, the second rod and interspinous process hook component attached to the second bone anchor and positioned to provide dynamic decompression and stabilization to adjacent vertebral bodies.

4. The system of claim 2, wherein the second bone anchor comprises a poly-axial bone screw.

5. The system of claim 3, further comprising a transverse link component which provides a means to prevent and stabilize the stresses or forces that may interact on the at least a first bone anchor and the second bone anchor resulting from the dynamic nature of the at least a first rod and interspinous process hook component and the second rod and interspinous process hook component.

6. The system of claim 5, wherein the transverse link component comprises a two attachment portions at either end of an elongated member and a central portion extending between the at least a first bone anchor and second bone anchor.

7. The system of claim 6, wherein the at least a first rod and interspinous process hook component and the transverse link component are each attached to the at least a first bone anchor by insertion of an attachment portion of the transverse link component and a distal portion of the at least a first rod and interspinous process hook component into a common attachment channel on the bone anchor.

8. The system of claim 6, wherein the central portion of the transverse link component comprises a recessed portion to allow for accommodation over the anterior surface of the inferior spinous process.

9. The system of claim 8, wherein recessed portion of the central portion of the transverse link component is formed by two symmetrical bends in a rod forming the central portion.

10. The system of claim 5, wherein the transverse link component is constructed of Nitinol.

11. The system of claim 1, wherein the at least a first rod and interspinous process hook component is constructed of a combination of static and dynamic materials.

12. The system of claim 1, wherein the at least a first rod and interspinous process hook components is constructed of Nitinol.

13. The system of claim 1, wherein the at least a first rod and interspinous process hook component that provides a resiliently compressible member includes a resilient structure comprising a bend portion therein.