Pedicle screw-based dynamic posterior stabilization systems and methods

The present invention provides a pedicle screw-based dynamic posterior stabilization system that is used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts. The system includes a plurality of pedicle screws, each of the plurality of pedicle screws including a head portion, and the head portion of each of the plurality of pedicle screws forming a first half of a joint that allows relative pivoting movement about the head portion of each of the plurality of pedicle screws and up-and-down movement with respect to the head portion of each of the plurality of pedicle screws. The system also includes a stabilization body coupled to the plurality of pedicle screws, the stabilization body including a plurality of end portions, and the end portions of the stabilization body forming a plurality of second halves of the joints formed by the head portion of each of the plurality of pedicle screws.

FIELD OF THE INVENTION

The present invention relates generally to the medical device and surgical fields. More specifically, the present invention relates to improved pedicle screw-based dynamic posterior stabilization systems and methods that are used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts—formerly also using fusion cages, various pedicle screws, and/or rigid rods. The pedicle screw-based dynamic posterior stabilization systems and methods of the present invention are used in the treatment of degenerative spondylolisthesis, degenerative disc disease, lumbar spinal stenosis, and the like.

BACKGROUND OF THE INVENTION

The spine is a complex columnar structure that is comprised of vertebral bone and connective tissues. The vertebrae, intervertebral discs, and ligaments are intricately arranged such that the interaction between these structures provides strength and support for the distribution of body forces and flexibility for body motion, as well as protection for the spinal cord. In a diseased or injured spine, this intricate arrangement is disrupted. In many cases, such disruptions can be treated by conservative, non-surgical methods, such as medication, exercise, physical therapy, etc. In some cases, however, more radical, surgical methods are required to treat the pain and other symptoms caused by nerve element compression and unstable intervertebral joints. Such more radical, surgical methods involve the dissection of soft tissue and often the removal of load-bearing structures, such as vertebral bone and intervertebral discs. This can lead to spinal instability, and it is often necessary to fuse the associated segments (also referred to as levels) in order to restore spinal stability. Internal fixation with instrumentation typically accompanies spinal fusion to provide temporary spinal stabilization and alignment, as well as an environment in which fusion can take place over time.

A variety of internal fixation systems have been developed to provide temporary spinal stabilization and alignment. These internal fixation systems can be defined as anterior or posterior assemblies, depending on how and where they are implanted with respect to the spine. Anterior assemblies, such as total intervertebral disc replacement assemblies and the like, are coupled to the anterior (front) portion of the spine, while posterior assemblies are coupled to the posterior (rear) portion of the spine, using various pedicle screws and rigid rods, for example. These posterior assemblies typically include adjacent pairs of screws that are inserted through the pedicles and into the vertebral bodies at predetermined angles and depths. Pairs of parallel, longitudinally-aligned rigid rods are then disposed through and/or attached to the adjacent pairs of pedicle screws, essentially creating an immobilizing frame or support structure. Disadvantageously, although providing temporary spinal stabilization and alignment, these internal fixation systems often require an open posterior insertion procedure with a typical incision and muscle retraction, destroy significant portions of the pedicles (facets), result in an undesirably limited range of motion (ROM), are difficult to revise and/or extract, and can lead to adjacent-level degenerative disc disease.

One conventional system for the stabilization of the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to conventional spinal fusion (incorporating autogenous bone grafts only)—formerly also using fusion cages, various pedicle screws, and/or rigid rods—is the Dynesys® Dynamic Stabilization System (Zimmer Spine, Minneapolis, Minn. USA). This system uses a plurality of titanium alloy pedicle screws (disposed lateral to the facets of adjacent vertebrae, on either side of the facets) through which a pair of parallel, flexible polyethylene terepthalate (PET) cords are threaded, the cords secured to the plurality of pedicle screws subsequent to proper sizing. A pair of flexible polycarbonate urethane (PCU) spacers are disposed about the cords. The push-pull interaction between the cords and the spacers stabilizes the intervertebral segment. In addition, the tension of the cords decreases post-operatively, due to body temperature warming, repetitive deformation, etc., resulting in a controlled increase in ROM. Advantageously, the system allows for an open posterior insertion procedure with a typical incision and muscle retraction or a minimally-invasive insertion procedure, preserves significant portions of the pedicles (facets), and results in an improved ROM (at rest, in flexion, and in extension). Disadvantageoulsy, the system is difficult to revise if the pedicle screws become loose.

Thus, what are still needed in the art are improved pedicle screw-based dynamic posterior stabilization systems and methods that are used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts—formerly also using fusion cages, various pedicle screws, and/or rigid rods. Advantageously, the pedicle screw-based dynamic posterior stabilization systems and methods of the present invention have a more physiologic dynamic interface that allows for more “normal” spine motion, as well as a decreased incidence of pedicle screw loosening.

BRIEF SUMMARY OF THE INVENTION

In various exemplary embodiments, the present invention provides improved pedicle screw-based dynamic posterior stabilization systems and methods that are used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts—formerly also using fusion cages, various pedicle screws, and/or rigid rods. The pedicle screw-based dynamic posterior stabilization systems and methods of the present invention are used in the treatment of degenerative spondylolisthesis, degenerative disc disease, lumbar spinal stenosis, and the like. Advantageously, the pedicle screw-based dynamic posterior stabilization systems and methods of the present invention have a more physiologic dynamic interface that allows for more “normal” spine motion, as well as a decreased incidence of pedicle screw loosening.

In one exemplary embodiment of the present invention, a pedicle screw-based dynamic posterior stabilization system that is used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts includes a plurality of pedicle screws, each of the plurality of pedicle screws including a head portion, and the head portion of each of the plurality of pedicle screws forming a first half of a joint that allows relative pivoting movement about the head portion of each of the plurality of pedicle screws and up-and-down movement with respect to the head portion of each of the plurality of pedicle screws. The system also includes a stabilization body coupled to the plurality of pedicle screws, the stabilization body including a plurality of end portions, and the end portions of the stabilization body forming a plurality of second halves of the joints formed by the head portion of each of the plurality of pedicle screws. Preferably, the head portion of each of the plurality of pedicle screws defines at least one hollow channel. Preferably, the stabilization body also defines at least one hollow channel. The system further includes a band that is threaded through the at least one hollow channel defined by the head portion of each of the plurality of pedicle screws and the at least one hollow channel defined by the stabilization body, the band selectively coupling the stabilization body to the plurality of pedicle screws. Preferably, the joints formed by the head portion of each of the plurality of pedicle screws comprise “double-saddle” joints.

In another exemplary embodiment of the present invention, a pedicle screw-based dynamic posterior stabilization method that is used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts includes inserting a plurality of pedicle screws in the facets of a plurality of adjacent vertebrae of a spine, each of the plurality of pedicle screws including a head portion, and the head portion of each of the plurality of pedicle screws forming a first half of a joint that allows relative pivoting movement about the head portion of each of the plurality of pedicle screws and up-and-down movement with respect to the head portion of each of the plurality of pedicle screws. The method also includes disposing a stabilization body between and coupling the stabilization body to the plurality of pedicle screws, the stabilization body including a plurality of end portions, and the end portions of the stabilization body forming a plurality of second halves of the joints formed by the head portion of each of the plurality of pedicle screws. Preferably, the head portion of each of the plurality of pedicle screws defines at least one hollow channel. Preferably, the stabilization body also defines at least one hollow channel. The method further includes threading a band through the at least one hollow channel defined by the head portion of each of the plurality of pedicle screws and the at least one hollow channel defined by the stabilization body, the band selectively coupling the stabilization body to the plurality of pedicle screws. Preferably, the joints formed by the head portion of each of the plurality of pedicle screws comprise “double-saddle” joints.

In a further exemplary embodiment of the present invention, a pedicle screw-based dynamic posterior stabilization system that is used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts includes a plurality of pedicle screws, each of the plurality of pedicle screws including a head portion, and the head portion of each of the plurality of pedicle screws forming a first half of a joint that allows relative pivoting movement about the head portion of each of the plurality of pedicle screws and up-and-down movement with respect to the head portion of each of the plurality of pedicle screws. The system also includes a stabilization body coupled to the plurality of pedicle screws, the stabilization body including a plurality of end portions, and the end portions of the stabilization body forming a plurality of second halves of the joints formed by the head portion of each of the plurality of pedicle screws. Preferably, the stabilization body defines at least one hollow channel. The system further includes a band that is threaded about the head portion of each of the plurality of pedicle screws and through the at least one hollow channel defined by the stabilization body, the band selectively coupling the stabilization body to the plurality of pedicle screws. Preferably, the joints formed by the head portion of each of the plurality of pedicle screws comprise “double-saddle” joints.

In a still further exemplary embodiment of the present invention, a pedicle screw-based dynamic posterior stabilization method that is used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts includes inserting a plurality of pedicle screws in the facets of a plurality of adjacent vertebrae of a spine, each of the plurality of pedicle screws including a head portion, and the head portion of each of the plurality of pedicle screws forming a first half of a joint that allows relative pivoting movement about the head portion of each of the plurality of pedicle screws and up-and-down movement with respect to the head portion of each of the plurality of pedicle screws. The method also includes disposing a stabilization body between and coupling the stabilization body to the plurality of pedicle screws, the stabilization body including a plurality of end portions, and the end portions of the stabilization body forming a plurality of second halves of the joints formed by the head portion of each of the plurality of pedicle screws. Preferably, the stabilization body defines at least one hollow channel. The method further includes threading a band about the head portion of each of the plurality of pedicle screws and through the at least one hollow channel defined by the stabilization body, the band selectively coupling the stabilization body to the plurality of pedicle screws. Preferably, the joints formed by the head portion of each of the plurality of pedicle screws comprise “double-saddle” joints.

DETAILED DESCRIPTION OF THE INVENTION

In various exemplary embodiments, the present invention provides improved pedicle screw-based dynamic posterior stabilization systems and methods that are used to stabilize the segments of the cervical, thoracic, lumbar, and sacral spine as an adjunct to, or in place of, conventional spinal fusion using bone grafts—formerly also using fusion cages, various pedicle screws, and/or rigid rods. The pedicle screw-based dynamic posterior stabilization systems and methods of the present invention are used in the treatment of degenerative spondylolisthesis, degenerative disc disease, lumbar spinal stenosis, and the like. Advantageously, the pedicle screw-based dynamic posterior stabilization systems and methods of the present invention have a more physiologic dynamic interface that allows for more “normal” spine motion, as well as a decreased incidence of pedicle screw loosening.

FIGS. 1 and 2are side and top planar views, respectively, illustrating one exemplary (multi-segment) embodiment of the pedicle screw-based dynamic posterior stabilization system of the present invention, the pedicle screw end portions being partially exploded from the stabilization bodies for clarity inFIG. 1. The pedicle screw-based dynamic posterior stabilization system10includes a plurality of pedicle screws12that are configured to be laterally inserted in either side of the facets of a plurality of adjacent vertebrae associated with a plurality of segments of the spine. It will be readily apparent to those of ordinary skill in the art that one or more segments can be stabilized using the pedicle screw-based dynamic posterior stabilization system10, and that it is scalable in terms of the number of pedicle screws12or levels. Each of the pedicle screws12includes a head portion14that is configured to selectively receive a pedicle screw insertion device (i.e. a pedicle screw driver), and that forms one half of one “double-saddle” joint16, in the case of the pedicle screw end portions18, and one half of two “double-saddle” joints16, in the case of the pedicle screw center portion20. Each of the pedicle screws12is made of a substantially-rigid, medically-implantable metallic or non-metallic material, such as a titanium alloy or the like, well known to those of ordinary skill in the art. In general, each of the pedicle screws12has a head diameter or width of between about 10 mm and about 16 mm, a shaft diameter or width of between about 4.5 mm and about 7.5 mm, and an overall length of between about 30 mm and about 50 mm, although it will be readily apparent to those of ordinary skill in the art that other suitable dimensions can be used.

The pedicle screw-based dynamic posterior stabilization system10also includes a plurality of stabilization bodies22that are configured to be selectively disposed between the head portions14of the plurality of pedicle screws12, the end portions of each of the stabilization bodies22forming the other half of one of the “double-saddle” joints16described above. Advantageously, these “double-saddle” joints allow the stabilization bodies22to pivot about the head portions14of the pedicle screws12, as well as up and down with respect to the head portions14of the pedicle screws, providing the implanted pedicle screw-based dynamic posterior stabilization system10with improved ROM (at rest, in flexion, and in extension). Again, it will be readily apparent to those of ordinary skill in the art that one or more segments can be stabilized using the pedicle screw-based dynamic posterior stabilization system10, and that it is scalable in terms of the number of stabilization bodies22or levels. Each of the stabilization bodies22is made of a substantially-rigid, medically-implantable metallic or non-metallic material, such as a PCU or the like, well known to those of ordinary skill in the art. In general, each of the stabilization bodies has diameter or width of between about 10 mm and about 16 mm and an overall length of between about 10 mm and about 50 mm, although it will be readily apparent to those of ordinary skill in the art that other suitable dimensions can be used.

FIG. 3is a plurality of side and top cross-sectional views of two exemplary embodiments of the head portions of the plurality of pedicle screws and the stabilization bodies ofFIGS. 1 and 2, highlighting various band channel configurations. Specifically, in the case of the pedicle screw end portions18, the head portion14of each of the pedicle screws12includes a band channel24that is formed partially through the head portion14. In one example, this band channel24comprises a substantially U-shaped hollow channel through which a band26(FIGS. 1 and 2), wire, or the like is selectively threaded, passing into and out of the head portion14of the pedicle screw12on the same side and securing a given pedicle screw12to a given stabilization body22(FIGS. 1 and 2), as described in greater detail herein below. In another example, the band channel24comprises a substantially cylindrical or rectangular hollow channel through which the band26, wire, or the like is selectively threaded, again passing into and out of the head portion14of the pedicle screw12on the same side and securing a given pedicle screw12to a given stabilization body22, as described in greater detail herein below. In the case of the pedicle screw center portion20, the head portion14of the pedicle screw12includes a band channel28that is formed completely through the head portion14. In one example, this band channel28comprises two substantially cylindrical or rectangular hollow channels through which the band26, wire, or the like is selectively threaded, passing into and out of the head portion14of the pedicle screw12on opposite sides and securing a given pedicle screw12to a plurality of given stabilization bodies22, as described in greater detail herein below. In another example, the band channel28comprises a substantially cylindrical or rectangular hollow channel through which the band26, wire, or the like is selectively threaded, again passing into and out of the head portion14of the pedicle screw12on opposite sides and securing a given pedicle screw12to a plurality of given stabilization bodies22, as described in greater detail herein below. In the case of the stabilization bodies22, each of the stabilization bodies22includes a band channel30that is formed completely through the stabilization body22. In one example, this band channel30comprises two substantially cylindrical or rectangular hollow channels through which the band26, wire, or the like is selectively threaded, passing into and out of the stabilization body22on opposite sides and securing a given pedicle screw12to a given stabilization body or bodies22, as described in greater detail herein below. In another example, the band channel30comprises a substantially cylindrical or rectangular hollow channel through which the band26, wire, or the like is selectively threaded, again passing into and out of the stabilization body22on opposite sides and securing a given pedicle screw12to a given stabilization body or bodies22, as described in greater detail herein below.

Referring again toFIGS. 1 and 2, as well as toFIG. 3, the band26, wire, or the like is selectively threaded through the head portions14of two or more pedicle screws12and one or more stabilization bodies22such that the two or more pedicle screws12are movably secured to the one or more stabilization bodies22. In order to accomplish this purpose, at least one of the one or more stabilization bodies22are formed with a plurality of ports32in communication with the band channels24,28,30, one port forming an inlet port for the band26, wire, or the like and another port forming an exit port for the band26, wire, or the like. Once the band26, wire, or the like has been threaded into the inlet port26, through the band channel30of the stabilization body22, through the band channel24of the head portion14of one pedicle screw12, back through the band channel30of the stabilization body, through the band channel24of the head portion14of another pedicle screw12, back through the band channel30of the stabilization body22, and out of the outlet port26, and once the band tension (and thus the frictional forces present in the “double-saddle” joints16) has been adjusted as desired, a plurality of retention screws34or the like are inserted into a plurality of retention holes36disposed adjacent to the band26, wire, or the like, thereby holding the band26, wire, or the like secure in the band channels24,28,30.

It should be noted that the “double-saddle” joints16of the present invention can be held together or formed via any other suitable mechanical means, provided that an adequate ROM with respect to the head portion14of the pedicle screws12and stabilization bodies22is maintained.

FIG. 4is a top planar view illustrating another exemplary (single-segment) embodiment of the pedicle screw-based dynamic posterior stabilization system of the present invention. The pedicle screw-based dynamic posterior stabilization system40includes a plurality of pedicle screws12that are configured to be laterally inserted in either side of the facets of a plurality of adjacent vertebrae associated with one segment of the spine. It will be readily apparent to those of ordinary skill in the art that one or more segments can be stabilized using the pedicle screw-based dynamic posterior stabilization system40, and that it is scalable in terms of the number of pedicle screws12or levels. Referring toFIGS. 4 and 5, each of the pedicle screws12includes a head portion14that is configured to selectively receive a pedicle screw insertion device (i.e. a pedicle screw driver), and that forms one half of one “double-saddle” joint16. Each of the pedicle screws12is made of a substantially-rigid, medically-implantable metallic or non-metallic material, such as a titanium alloy or the like, well known to those of ordinary skill in the art. In general, each of the pedicle screws12has a head diameter or width of between about 10 mm and about 16 mm, a shaft diameter or width of between about 4.5 mm and about 7.5 mm, and an overall length of between about 30 mm and about 50 mm, although it will be readily apparent to those of ordinary skill in the art that other suitable dimensions can be used.

The pedicle screw-based dynamic posterior stabilization system40also includes a stabilization body22that is configured to be selectively disposed between the head portions14of the plurality of pedicle screws12, the end portions of the stabilization body22forming the other half of the “double-saddle” joints16described above. Advantageously, these “double-saddle” joints allow the stabilization body22to pivot about the head portions14of the pedicle screws12, as well as up and down with respect to the head portions14of the pedicle screws, providing the implanted pedicle screw-based dynamic posterior stabilization system40with improved ROM (at rest, in flexion, and in extension). Again, it will be readily apparent to those of ordinary skill in the art that one or more segments can be stabilized using the pedicle screw-based dynamic posterior stabilization system40, and that it is scalable in terms of the number of stabilization bodies22or levels. The stabilization body22is made of a substantially-rigid, medically-implantable metallic or non-metallic material, such as a PCU or the like, well known to those of ordinary skill in the art. In general, each of the stabilization bodies has diameter or width of between about 10 mm and about 16 mm and an overall length of between about 10 mm and about 50 mm, although it will be readily apparent to those of ordinary skill in the art that other suitable dimensions can be used.

The band26, wire, or the like is selectively threaded through/around the head portions14of the plurality of pedicle screws12and the stabilization body22such that the plurality of pedicle screws12are movably secured to the stabilization body22. In order to accomplish this purpose, the stabilization body22is formed with a plurality of ports32in communication with the band channels of the stabilization body22and the plurality of pedicle screws, one port forming an inlet port for the band26, wire, or the like and another port forming an exit port for the band26, wire, or the like. Once the band26, wire, or the like has been threaded into the inlet port26, through the band channel of the stabilization body22, through the band channel of the head portion14of one pedicle screw12, back through the band channel of the stabilization body, through the band channel of the head portion14of another pedicle screw12, back through the band channel of the stabilization body22, and out of the outlet port26, and once the band tension (and thus the frictional forces present in the “double-saddle” joints16) has been adjusted as desired, a plurality of retention screws34or the like are inserted into a plurality of retention holes36disposed adjacent to the band26, wire, or the like, thereby holding the band26, wire, or the like secure in the band channels.

Again, it should be noted that the “double-saddle” joints16of the present invention can be held together or formed via any other suitable mechanical means, provided that an adequate ROM with respect to the head portion14of the pedicle screws12and stabilization bodies22is maintained.