Patent Application
20090030465
The present invention generally relates to devices, systems, and methods for the fixation of the spine. In particular, the present invention relates to a rod system applied to the spine that provides dynamic support to spinal vertebrae.
Damage to the spine as a result of advancing age, disease, and injury, has been treated in many instances by fixation or stabilization of vertebrae. Conventional methods of spinal fixation utilize a rigid spinal fixation device to support an injured spinal vertebra relative to an adjacent vertebra and prevent movement of the injured vertebra relative to an adjacent vertebra. These conventional spinal fixation devices include anchor members for fixing to a series of vertebrae of the spine and at least one rigid link element designed to interconnect the anchor members. Typically, the anchor member is a screw and the rigid link element is a rod. The screw is configured to be inserted into the pedicle of a vertebra to a predetermined depth and angle. One end of the rigid link element is connected to an anchor inserted in the pedicle of the upper vertebra and the other end of the rod is connected to an anchor inserted in the pedicle of an adjacent lower vertebra. The rod ends are connected to the anchors via coupling constructs such that the adjacent vertebrae are supported and held apart in a relatively fixed position by the rods. Typically two rods and two pairs of anchors are installed each in the manner described above such that two rods are employed to fix two adjacent vertebrae, with one rod positioned on each side of adjacent vertebrae. Once the system has been assembled and fixed to a series of two or more vertebrae, it constitutes a rigid device preventing the vertebrae from moving relative to one another. This rigidity enables the devices to support all or part of the stresses instead of the stresses being born by the series of damaged vertebra.
While these conventional procedures and devices have been proven capable of providing reliable fixation of the spine, the resulting constructs typically provide a very high degree of rigidity to the operative levels of the spine resulting in decreased mobility of the patient. Unfortunately, this high degree of rigidity imparted to the spine by such devices can sometimes be excessive. Because the patient's fixed vertebrae are not allowed to move, the vertebrae located adjacent to, above or below, the series that has undergone such fixation tend to move more in order to compensate for the decreased mobility. As a result, a concentration of additional mechanical stresses is placed on these adjacent vertebral levels and a sharp discontinuity in the distribution of stresses along the spine can then arise between, for example, the last vertebra of the series and the first free vertebra. This increase in stress can accelerate degeneration of the vertebrae at these adjacent levels.
Sometimes, fixation accompanies a fusion procedure in which bone growth is encouraged to bridge the intervertebral body disc space to thereby fuse adjacent vertebrae together. Fusion involves removal of a damaged intervertebral disc and introduction of an interbody spacer along with bone graft material into the intervertebral disc space. In cases where fixation accompanies fusion, excessively rigid spinal fixation is not helpful to the promotion of the fusion process due to load shielding away from the fixed series. Without the stresses and strains, bone does not have loads to adapt to and as bone loads decrease, the bone becomes weaker. Thus, fixation devices that permit load sharing and assist the bone fusion process are desired in cases where fusion accompanies fixation.
Various improvements to fixation devices such as a link element having a dynamic central portion have been devised. These types of dynamic rods support part of the stresses and help relieve the vertebrae that are overtaxed by fixation. Some dynamic rods are designed to permit axial load transmission substantially along the vertical axis of the spine to prevent load shielding and promote the fusion process. Dynamic rods may also permit a bending moment to be partially transferred by the rod to the fixed series that would otherwise be completely born by vertebrae adjacent to the fixed series. Compression or extension springs can be coiled around the rod for the purpose of providing de-rotation forces as well as relative translational sliding movement along the vertical axis of the spine. Overall, the dynamic rod in the fixation system plays an important role in recreating the biomechanical organization of the functional unit made up of two fixed vertebrae together with the intervertebral disc.
In conclusion, conventional spinal fixation devices have not provided a comprehensive solution to the problems associated with curing spinal diseases in part due to the difficulty of creating a system that mimics a healthy functioning spinal unit. Hence, there is a need for an improved dynamic spinal fixation device that provides a desired level of flexibility to the fixed series of the spinal column, while also providing long-term durability and consistent stabilization of the spinal column.
According to one aspect of the invention, a dynamic rod is provided. The dynamic rod includes a first rod portion having a first engaging portion at a first end. The dynamic rod includes a second rod portion having a second engaging portion at a first end. The first and second rod portions connected to each other at the first and second engaging portions and at least one bias element is provided. The at least one bias element is configured to provide a bias force in response to deflection or translation of the second rod portion relative to the first rod portion. Also, at least one side spring is provided and disposed adjacent to the second rod portion to provide a bias force in response to deflection of the second rod portion relative to the first rod portion.
According to another aspect of the invention, a method for dynamically stabilizing a patient's spine is provided. The method includes the step of connecting a first vertebral body and an adjacent second vertebral body with at least one dynamic link element. The at least one dynamic link element comprised of two portions joined together is implanting. And the method includes the step of stabilizing the first vertebral body with respect to the second vertebral body with said at least one dynamic link element having a netural position that is extendable when the patient's spine is flexed forward and does not contract in length from the neutral position when patient's spine is extended backward.
According to another aspect of the invention, a dynamic rod is provided. The dynamic rod includes a first rod portion and a second rod portion connected to the first rod portion such that at least part of the second rod portion is nested inside at least part of the first rod portion. The second rod portion and first rod portion define a neutral longitudinal axis and the second rod portion is deflectable from the neutral longitudinal axis relative to the first rod portion. The dynamic rod further includes at least one bias element formed in the at least part of the first rod portion nesting the second rod portion. The bias element includes a free end and a fixed end and is configured to bias a deflection from the longitudinal axis of the second rod portion relative to the first rod portion wherein the bias is in the direction to return the rod toward the neutral longitudinal axis.
Other advantages will be apparent from the description that follows, including the drawings and claims.
The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity.
a illustrates a cross-sectional view of a first rod portion of the dynamic rod of
b illustrates an end view of a first rod portion of the dynamic rod of
a illustrates a perspective view of a retainer of the dynamic rod of
b illustrates a cross-sectional view of the retainer of
a illustrates a side view of a dynamic rod in a contracted state according to the present invention.
b illustrates a side view of a dynamic rod in an extended state according to the present invention.
c illustrates a side view of a dynamic rod in an extended and deflected state according to the present invention.
d illustrates a side view of a dynamic rod in a contracted and deflected state according to the present invention.
a illustrates a cross-sectional view of the dynamic rod of
b illustrates a cross-sectional view of the dynamic rod of
a illustrates a cross-sectional view of another variation of a dynamic rod according to the present invention.
b illustrates a cross-sectional view of another variation of a dynamic rod according to the present invention.
Before the subject devices, systems and methods are described, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a spinal segment” may include a plurality of such spinal segments and reference to “the screw” includes reference to one or more screws and equivalents thereof known to those skilled in the art, and so forth.
All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.
The present invention is described in the accompanying figures and text as understood by a person having ordinary skill in the field of spinal implants.
Referring now to
A typical anchor system comprises, but is not limited to, a spinal bone screw that is designed to have one end that inserts threadably into a vertebra and a seat at the opposite end thereof. Typically, the seat is designed to receive the link element in a channel in the seat. The link element is typically a rod or rod-like member. The seat typically has two upstanding arms that are on opposite sides of the channel that receives the rod member. The rod is laid in the open channel which is then closed with a closure member to both capture the rod in the channel and lock it in the seat to prevent relative movement between the seat and the rod.
With particular reference to
Referring now to
Turning back to
Turning now to
Still referencing
Referring back to
Turning now to
Referring back to
Movement of the second rod portion 14 relative to the first rod portion 12 along the longitudinal axis such that the rod 10 is moving from a normal or neutral position into extension is biased by the bias element 16. In response to such extension, the bias element 16 exerts a force to return the second rod portion 14 into a normal position. When fully extended from the first rod portion 12, the second rod portion 14 defines a distance “d” between the end of the collar 43 and the abutment 31. This distance “d” defines in part the extent of movement along the longitudinal axis of the second rod portion 14 relative to the first rod portion 12. In one variation, the distance “d” is approximately one or two millimeters. Distance “d” may be customized according to surgeon preference such as upon implantation or be selected to be a suitable distance.
After the dynamic rod 10 is assembled, it is ready to be implanted within a patient and be connected to anchors planted in pedicles of adjacent vertebral bodies preferably in a manner such that the first rod portion 12 of the dynamic rod 10 illustrated in
In an alternative variation, the dynamic rod 10 is implanted into the patient such that the first rod portion 12 is oriented caudad and the second rod portion 14 is oriented cephalad. In this variation, the second rod portion 14 includes an anchor connecting portion 44 that is partially spherical in shape and includes oppositely disposed outwardly extending pins 54 for engaging slots formed in the upper anchor to allow the dynamic rod 10 to pivot about pins 54 when connected to the anchor. Of course, any connection means is permitted and not limited to a pin-slot engagement. The anchor connecting portion 44 may also include oppositely disposed flat areas 56 as described above. The second rod portion 14 of the dynamic rod 10 is oriented cephalad and connected to the upper anchor and the first rod portion 12 is placed caudad and connected to the lower anchor. Because the second rod portion 14 includes an anchor connecting portion 44 configured such that connection with the anchor does not result in excessive rod extending cephalad beyond the anchor, this orientation and configuration of the dynamic rod is advantageous particularly because it avoids impingement of adjacent anatomy in flexion or in extension of the patient.
Therefore, it is noted that the preferred implantation method and preferred orientation of the dynamic rod 10 is such that there is minimal or substantially no “overhanging” rod extending cephalad beyond the upper anchor. Such orientation is achieved by the orientation of the rod during implantation as well as by the configuration of the anchor connecting portion 22, 44 of either one or both of the first rod portion 12 and second rod portion 14 such that the anchor connecting portion 22, 44 is configured such that there is substantially no overhang beyond the anchor.
The implanted dynamic rod and anchor system fixes the adjacent vertebral bodies together in a dynamic fashion providing immediate postoperative stability and support of the spine. Referring now to
Hence,
In one variation, the bias element 16 is a compression spring that becomes shorter when axially loaded and acts as an extension mechanism such that when disposed in the assembled dynamic rod 10 and axially loaded, the bias element 16 exerts a biasing force pushing the first rod portion 12 and the second rod portion 14 apart. In one variation, the bias element 16 is configured such that it exerts a biasing force pushing the first rod portion 12 and second rod portion 14 apart by the maximum degree permitted by the dynamic rod configuration such that when longitudinally loaded the second rod portion 14 will move inwardly towards the first rod portion 12.
The adjacent vertebrae are slightly distracted and the rod is implanted in a patient's spine to relieve pressure on the nerves and offload pressure on the facet and disc. The dynamic rods may be used alone or as an adjunct to fusion. When the rod is implanted in a patient's spine and the patient bends forward, the rod is capable of extending thereby preserving the natural motion of the spine while at the same time offloading pressure and relieving pain. When the patient bends backward, the rod serves as an extension blocker, thereby maintaining the vertebral distraction to relieve pain and assist in reducing impact to allow better load distribution through the level and help prevent adjacent level disease.
In another variation, the bias element 16 is a coil configured to not exhibit spring-like characteristics when loaded along the longitudinal axis. Instead, the coil serves a stabilizer for loads having a lateral force component, in which case the lateral biasing is provided by the bias element.
Another dynamic rod 10 according to the present invention is shown in
Still referencing
Other dynamic rods 10 according to the present invention is shown in
Still referencing
The dynamic rods 10 of
The disclosed devices or any of their components can be made of any biologically adaptable or compatible materials including PEEK, PEK, PAEK, PEKEKK or other polyetherketones. Materials considered acceptable for biological implantation are well known and include, but are not limited to, stainless steel, titanium, tantalum, combination metallic alloys, various plastics, polymers, resins, ceramics, biologically absorbable materials and the like. Any components may be also coated.
The preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims.
This application claims the benefit of and is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 60/994,899 entitled “Dynamic rod” filed on Sep. 21, 2007 which is incorporated herein by reference in its entirety. This application also claims priority to and is a continuation-in-part of co-pending U.S. patent application Ser. No. 12/154,540 entitled “Dynamic rod” filed on May 23, 2008 which is a non-provisional of U.S. Provisional Patent Application Ser. No. 60/931,811 entitled “Dynamic rod” filed on May 25, 2007, all of which are hereby incorporated by reference in their entireties. This application also claims priority to and is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/427,738 entitled “Systems and methods for stabilization of the bone structures” filed on Jun. 29, 2006 which is a continuation-in-part of U.S. patent application Ser. No. 11/436,407 entitled “Systems and methods for stabilization of the bone structures” filed on May 17, 2006 which is a continuation-in-part of U.S. patent application Ser. No. 11/033,452 entitled “Systems and methods for stabilization of the bone structures” filed on Jan. 10, 2005 which is a continuation-in-part of U.S. patent application Ser. No. 11/006,495 entitled “Systems and methods for stabilization of the bone structures” filed on Dec. 6, 2004 which is a continuation-in-part of U.S. patent application Ser. No. 10/970,366 entitled “Systems and methods for stabilization of the bone structures” filed on Oct. 20, 2004. All of the above-referenced applications are each incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60994899 | Sep 2007 | US | |
| 60931811 | May 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12154540 | May 2008 | US |
| Child | 12233212 | US | |
| Parent | 11427738 | Jun 2006 | US |
| Child | 12154540 | US | |
| Parent | 11436407 | May 2006 | US |
| Child | 11427738 | US | |
| Parent | 11033452 | Jan 2005 | US |
| Child | 11436407 | US | |
| Parent | 11006495 | Dec 2004 | US |
| Child | 11033452 | US | |
| Parent | 10970366 | Oct 2004 | US |
| Child | 11006495 | US |
