Spine stabilization system with dynamic screw
A spine stabilization system having a dynamic screw comprises at least one bone anchor assembly comprising a receiver member and a bone engaging member. In one embodiment, the bone engaging member is a screw shank extending from the receiver member. A rod is connected to the receiver member. In one embodiment, the rod comprises a ball-shaped member that engages a bearing surface provided within a cavity of the receiver member. In this embodiment, the rod is pivotably connected to the receiver member. In one such embodiment, a central axis defined by the rod pivots about a pivot point located on the central axis when the rod pivots relative to the receiver member. Accordingly, the pivot point for the rod may be provided within the cavity of the receiver member. The rod may be a fixed length or adjustable to accommodate different segmental units and patients of different sizes.
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This application relates to the field of spinal stabilization devices. In particular, this application relates to a posterior stabilization unit configured for use with a segmental unit of the spine.
BACKGROUNDSpinal surgeries are commonly used in the medical profession to treat spinal conditions that result when functional segmental units of the spine are moved out of proper position or otherwise damaged. Examples of procedures used to treat spinal conditions include disc replacement, laminectomy, and spinal fusion.
Following certain spinal procedures, such as spinal fusion, it is typically desirable to stabilize the spine by preventing movement between the vertebrae while the spine heals. This act of stabilizing the spine by holding bones in place during healing has greatly improved the success rate of spinal fusions and other procedures.
With spinal stabilization procedures, a combination of metal screws and rods creates a solid “brace” that holds the vertebrae in place. These devices are intended to stop movement from occurring between the vertebrae. These metal devices give more stability to the fusion site and allow the patient to be out of bed much sooner.
During the spinal stabilization procedure, pedicle screws are placed through the pedicles on the posterior portion of two or more vertebrae of the spinal column. The screws grab into the bone of the vertebral bodies, giving them a good solid hold on the vertebrae. Once the screws are placed on the vertebrae, they are attached to metal rods that connect all the screws together. When everything is bolted together and tightened, the assembly creates a stiff metal frame that holds the vertebrae still so that healing can occur.
Posterior dynamic stabilization (PDS) generally refers to such a stabilization procedure where dynamic rods are positioned between the pedicle screws. These dynamic rods can generally bend, extend, compress, or otherwise deform in order to allow some limited movement between the pedicle screws. By allowing this limited movement between the pedicle screws and the associated vertebrae, less strain is placed on adjoining, non-stabilized functional segmental units during patient movements. In addition, the dynamic rod generally decreases the stresses on the screw shank, minimizing the possibility of screw backout or related screw failures. However, even with dynamic rods, stresses are experienced by the screw shank which could potentially result in screw backout or related failures under the appropriate circumstances. Accordingly, it would be desirable to provide a PDS system capable of further protecting the screw-bone interface and reducing the chances of screw backout. For example, it would be advantageous to provide a PDS system with a flexible stabilization element that offers different kinematics and loading requirements from those stabilization elements found in the prior art. Such a stabilization element would offer additional options to the surgeon when traditional PDS stabilization elements appear problematic.
SUMMARYVarious embodiments of a dynamic screw for a spine stabilization system are disclosed herein. A dynamic screw for a spine stabilization system comprises at least one bone anchor assembly comprising a bone engaging member and a receiver member. The bone engaging member may comprise a bone screw including a screw head retained within the receiver member and a screw shank extending from the receiver member. The screw head may be pivotably retained within the receiver member. An elongated connecting member is pivotably connected to the bone engaging member. The elongated connecting member may be provided as a rod spanning between two or more bone anchor assemblies. The elongated connecting member is pivotably connected to the receiver member of the bone anchor assembly.
In one embodiment, the pivotable connection between the elongated connection member and the receiver member is provided by a ball-shaped pivot member on the rod which engages a bearing surface provided within a cavity of the receiver member. Accordingly, the pivot point for the rod may be provided within the cavity in the receiver member. In one such embodiment, the rod may define an axis wherein the axis pivots about a pivot point on the axis when the rod pivots relative to the receiver member. In other embodiments, the pivot point of the rod is offset from the axis defined by the rod.
The rod may be a fixed length or adjustable to accommodate different segmental units and patients of different sizes. In the adjustable embodiment, the rod comprises a shaft with a flexible central portion and at least one adjustable end. The adjustable end may be provided by various means. For example, the adjustable end may include a post configured to slide within the shaft of the rod. In one embodiment, the adjustable end is configured to threadedly engage the shaft. In another embodiment, the adjustable end is comprised of a shape memory alloy.
When assembled, the spine stabilization system generally comprises at least two bone anchors with a rod extending between the two bone anchors. As mentioned above, each bone anchor includes a bone screw and a receiver member configured to retain the bone screw. The rod extends between the two receiver members. In one embodiment where the rod is fixed relative to the receiver members, the rod is adapted to bend when the receiver members move relative to one another. In another embodiment, the rod is pivotably connected to both the receiver members, and the rod is adapted to extend or compress when the receiver members move relative to one another.
In an alternative embodiment, one or more bone anchors of the spine stabilization system include an insert in the form of a retention member that acts to lock a bearing for the bone screw within the receiver member. To this end, the receiver member includes a screw head cavity and a rod cavity with an insert positioned between the screw head cavity and the rod cavity. The screw head cavity is configured to receive a bearing that engages the head of the bone screw with the screw shank extending from the receiver member. In one embodiment, the bone screw bearing is a split bearing. The insert is positioned between the rod cavity and the bearing member and is configured to secure the split bearing within the receiver member. The insert may be provided to fit within a groove formed in an interior sidewall of the receiver member. In this embodiment, the insert comprises a retaining ring that secures the split bearing within the screw cavity. In another embodiment, the insert is comprised of a compressible material positioned between the bearing member and the rod cavity. When the rod is positioned in the rod cavity, the insert is compressed against the bearing member, thus locking the bearing member within the screw cavity.
In yet another embodiment, the bone anchor assembly is configured with a low profile, wherein the rod is locked within the receiver member without the use of a fixation screw. In this embodiment, the bone anchor assembly includes a head and a screw shank extending from the head. The screw shank is pivotable with respect to the head. Furthermore, a rod cavity is formed within the head. The end of the rod includes features that lock the rod within the rod cavity when the rod is inserted into the rod cavity, thus connecting the rod to the head. For example, in one embodiment, the end of the rod comprises a plurality of fingers that may be flared to lock the rod within the rod cavity. The rod may also include a plurality of teeth that grasp or mesh with the rod cavity to further secure the rod within the cavity.
The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.
With reference to
The bone anchor 24 is comprised of titanium, stainless steel, or other appropriate biocompatible material. As explained in further detail herein, each bone anchor 24 comprises a bone engaging member 34, such as a bone screw (as shown in
In addition to the bone engaging member 34, each bone anchor 24 also comprises a receiver member 40. The receiver member 40 is configured to receive a bone engaging member 34 and/or an elongated connecting member 26. If the bone engaging member 34 is a bone screw, the bone screw 34 includes a screw head 36 and a screw shank 38. The screw head 36 is retained within the receiver member 40 and the screw shank 38 extends from the receiver member 40. The screw shank 38 is configured to screw into the bone and secure the bone screw 34 to the pedicle or other portion of bone. The receiver member 40 may be rigidly or pivotably connected to the screw 34.
The receiver member 40 is also configured to receive an elongated connecting member, such as the rod 26. The rod 26 includes two rigid ends 30, 32 with an elastic/resilient central portion 28 disposed between the rod ends. The elastic central portion 28 allows for some limited flexibility in the rod, while still allowing the rod to spring back to its original shape. Therefore, when opposing forces are applied to the ends 30, 32 of the rod 26, the central portion flexes, allowing the rod to bend and/or elongate. When the opposing forces are removed, the rod returns to its original shape. With this configuration, the PDS system generally stabilizes two adjacent vertebrae, while still allowing for some limited movement between the vertebrae 20, 21. However, one of skill in the art will recognize that other types of rods are possible, including rigid rods or other flexible rods comprised of elastomeric material, metal, or superelastic material, or other types of PDS rods as are known in the art.
With reference now to
In the embodiment of
The fixation screw cavity 50 is designed and dimensioned to receive a fixation screw 70 (also referred to herein as a setscrew). Accordingly, the cylindrical sidewalls 42 of the receiver member are threaded at the superior end 44. These threads are configured to engage the threads on the fixation screw 70. The fixation screw includes a slot 72 in the top that is adapted to receive the tip of a screwdriver, thus allowing the fixation screw 70 to be driven into the fixation screw cavity 50.
The rod passage 52 is provided directly below the fixation screw cavity 50. The rod passage is designed and dimensioned to receive one of the dynamic rods 26 of the PDS system 22. In particular, the rod passage 52 is designed to receive one of the rod ends 30. In the embodiment of
The bone screw cavity 48 is designed and dimensioned to retain the screw head 36 of the bone screw 34, with the shank 38 of the bone screw extending from the receiver member 40. An opening 56 is formed in the inferior end 46 of the receiver member 40. In this disclosed embodiment, the diameter of the opening 56 is smaller than the diameter of the screw head 36, but it is large enough to allow the screw shank 38 to pass through the opening 56. Accordingly, the cylindrical wall 42 is slightly thicker at the inferior end 46 of the receiver member 40.
A bearing member 54 is positioned within the bone screw cavity 48 along with the screw head 36. The bearing member 54 includes an inner bearing surface that generally conforms to the spherical shape of the screw head 36. The screw head 36 is configured to rotate and pivot within the bearing member 54. The outer bearing surface is designed and dimensioned to engage the interior portion of the cylindrical sidewalls 42 of the receiver member.
In one embodiment, the bearing member 54 is a split bearing that includes a left side member 54a and a right side member 54b. The split bearing, 54a, 54b provides for easier assembly by allowing the bearing surface to be assembled around the spherical screw head 36. In addition, the split bearing members 54a, 54b facilitate the use of different bearing materials. Appropriate bearing materials will be recognized by those of skill in the art. In the embodiment of
An insert 60 is provided in the receiver member. The insert 60 acts as a retention member to secure the bearing member 54 in place within the bone screw cavity 48 of the receiver member 40. In the embodiment of
As shown in
Rod Fixed to Receiver Member Providing with Pivot Point Offset from Rod Axis
From
An alternative embodiment of a bone anchor 24 where the center axis of the rod is offset from the pivot point of the rod within the anchor assembly is shown in
The rod holder 88 is pivotably mounted on the pivot pin 94. The rod holder 88 is similar to the receiver member 40 described in
In the embodiment of
Another alternative embodiment of a bone anchor 24 where the center axis of the rod is offset from the pivot point of the rod is shown in
Rod Pivotably Connected to Receiver Member with Pivot Point on Rod Axis
With reference now to
Two different bearings are retained within the receiver member 40. In particular, a first bearing 110 provides a bearing surface for the screw head. The first bearing acts to stabilize the screw head 36 within the receiver member 40 while providing a surface upon which the screw head may pivot relative to the receiver member 40. In one embodiment, the first bearing may be comprised of a metallic insert that acts to lock the bone screw 34 in place when a fixation screw is tightened, as discussed in further detail below.
In addition to the first bearing 110, a second bearing 112 is also provided within the receiver member 40 shown in
In the embodiment disclosed in
The components of the anchor assembly 24 may all be loaded into the receiver member 40 through a top hole. First, the bone screw 34 is inserted into the receiver member 40 with the screw head 36 seated in the screw head cavity and the shank 38 extending through the hole in the bottom of the receiver member 40. Second, the first bearing 110 is placed over the screw head. Next, the inferior bearing member 118 of the second bearing 112 is placed on top of the first bearing 110. The rod 26 is then placed in the receiver member with the spherical ball 114 engaging the bearing surface of the inferior bearing member 118, and the cylindrical portion of the rod passing through the rod passage formed in the sidewalls of the receiver member. The superior bearing member 116 is then placed over the spherical ball 114. This provides a superior bearing surface for the spherical ball. Finally, the fixation screw 70 is threaded into the top of the receiver member until it compresses against the second bearing member. Alternatively, the bearing components, screw, and rod may be pre-assembled and inserted into the receiver member as a unit.
In the embodiment of
In the embodiment of
One alternative embodiment to that of
Another example of an alternative embodiment for the bone anchor of
Yet another embodiment of a bone anchor 24 where the pivot point of the rod is located along the central axis of the rod is shown in
In an alternative embodiment, the ball shaped members 114 of the rod may be adjustably connected to the rod. With this arrangement, a single rod may be used to accommodate various size differences between patients and/or segmental units. Examples of rods 26 where the ball shaped member 114 is adjustable relative to the dynamic portion 28 are shown in
In
In
In the embodiment of
In the embodiment of
Low Profile Design
In the exemplary embodiment of
In one embodiment, a cap is provided over the superior end 44 of the bone anchor. This may be desirable if the rod will be passed through tissue. The cap could either be permanent or temporary. As best seen in
Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. For example, although the invention has been disclosed for use with reference to a single segmental spine unit, it could also be adapted for use with multi-level constructions. As another example, the dynamic rods disclosed herein include a helical flexible portion, but different dynamic rods may be used in other embodiments. As yet another example, the connection of the rod to the bone anchor may vary from those embodiments disclosed herein. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.
Claims
1. A spine stabilization system configured for connection between vertebrae, the spine stabilization system comprising:
- a) at least one bone anchor assembly comprising a bone engaging member; and
- b) an elongated connecting member pivotably connected to the bone engaging member of the at least one bone anchor assembly, wherein the elongated connecting member defines an axis that extends along the elongated connecting member and the axis pivots about a pivot point on the axis when the elongated connecting member pivots relative to the bone engaging member.
2. The spine stabilization system of claim 1 wherein the elongated connecting member is adjustable in length.
3. The spine stabilization system of claim 1 wherein the at least one bone anchor assembly further comprises a receiver member engaging both the elongated connecting member and the bone engaging member.
4. The spine stabilization system of claim 3 wherein the elongated connecting member is pivotably connected to the receiver member.
5. The spine stabilization system of claim 3 wherein the elongated connecting member is fixedly connected to the receiver member.
6. The spine stabilization system of claim 3 wherein the receiver member is pivotably connected to the bone engaging member.
7. The spine stabilization system of claim 3 wherein the receiver member is fixedly connected to the bone engaging member.
8. The spine stabilization system of claim 1 wherein the bone engaging member comprises a shank.
9. The spine stabilization system of claim 8 wherein the bone engaging member further comprises a head.
10. The spine stabilization system of claim 9 wherein the head is a screw head and the shank is a threaded screw shank.
11. A spine stabilization system configured for connection between vertebrae, the spine stabilization system comprising:
- a) at least one bone engaging member;
- b) at least one receiver member pivotably connected to a portion of the bone engaging member; and
- c) an elongated connecting member pivotably connected to the at least one receiver member.
12. The spine stabilization system of claim 11 wherein the elongated connecting member defines an axis and the axis pivots about a pivot point when the elongated connecting member pivots relative to the receiver member.
13. The spine stabilization system of claim 12 wherein the pivot point is located within the receiver member.
14. The spine stabilization system of claim 12 wherein the axis is a central axis and the pivot point is located along the central axis.
15. The spine stabilization system of claim 11 wherein the elongated connecting member includes a shaft having an elastic central portion.
16. The spine stabilization system of claim 14 wherein the elongated connecting member is an adjustable length rod.
17. The spine stabilization system of claim 16 wherein the rod includes a shaft having at least one adjustable end.
18. The spine stabilization system of claim 17 wherein the at least one adjustable end includes a post configured to slide within the shaft in order to provide a telescoping rod.
19. The spine stabilization system of claim 17 wherein the at least one adjustable end is configured to threadedly engage the shaft.
20. The spine stabilization system of claim 19 wherein a ball is provided on the at least one adjustable end, and rotation of the ball effectively lengthens or shortens the rod.
21. The spine stabilization system of claim 17 wherein the shaft or the at least one adjustable end is comprised of a shape memory alloy.
22. The spine stabilization system of claim 12 wherein the at least one receiver member comprises a cavity configured to receive the elongated connecting member.
23. The spine stabilization system of claim 22 further comprising a bearing positioned within the cavity and configured to engage the elongated connecting member.
24. The spine stabilization system of claim 22 wherein the pivot point is located within the cavity.
25. The spine stabilization system of claim 11 wherein the at least one bone engaging member comprises a first bone engaging member and a second bone engaging member, wherein the at least one receiver member comprises a first receiver member and a second receiver member, wherein the elongated connecting member extends between the first receiver member and the second receiver member, and wherein the elongated connecting member is pivotably connected to both the first receiver member and the second receiver member.
26. The spine stabilization system of claim 25 wherein the elongated connecting member is configured for extension or compression, and wherein movement of the first bone engaging member relative to the second bone engaging member causes compression or extension of the elongated connecting member.
27. The spine stabilization system of claim 11 wherein the at least one bone engaging member comprises a bone screw including a screw head and a screw shank, wherein the screw head is pivotably connected to the receiver member.
28. A spine stabilization system comprising:
- a) at least one bone engaging member;
- b) an elongated connecting member pivotably connected to the at least one bone engaging member;
- c) a pivot member fixed to the elongated connecting member; and
- d) a receiver member connected to the at least one bone engaging member, the receiver member configured to engage the pivot member such that the pivot member is pivotable within the receiver member.
29. The spine stabilization system of claim 28 wherein the pivot member is integral with the elongated connecting member.
30. The spine stabilization system of claim 28 wherein the pivot member is clamped onto the elongated connecting member.
31. The spine stabilization system of claim 28 wherein the pivot member is a ball-shaped member.
32. The spine stabilization system of claim 28 wherein the receiver member is fixed to the at least one bone engaging member.
33. The spine stabilization system of claim 28 wherein the receiver member is pivotably connected to the at least one bone engaging member.
34. The spine stabilization system of claim 28 wherein the bone engaging member comprises a shank extending from the receiver member.
Type: Application
Filed: Dec 28, 2006
Publication Date: Jul 3, 2008
Applicant: DePuy Spine, Inc. (Raynham, MA)
Inventors: Benjamin Arnold (San Diego, CA), Charles M. Bartish (Providence, RI), Seungkyu Daniel Kwak (Grafton, MA), William L. Dunbar (Bethlehem, CT), John Riley Hawkins (Cumberland, RI), Amie Borgstrom (Stanford, CA), Erasmo A. Lopez (Seattle, WA), Anwar M. Upal (Fall River, MA)
Application Number: 11/646,877
International Classification: A61B 17/58 (20060101); A61B 17/56 (20060101);