Patent Application
20070299442
The present disclosure relates generally to the field of orthopedic surgery, and more particularly to systems and methods for stabilizing a spinal joint. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to embodiments or examples 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. Any alteration and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates.
Referring to
A facet joint 42 is formed, in part, by the adjacent articular processes 29, 38. Likewise, another facet joint 44 is formed, in part, by the adjacent articular processes 31, 40. Facet joints also may be referred to as zygapophyseal joints. A healthy facet joint includes a facet capsule extending between the adjacent articular processes. The facet capsule comprises cartilage and synovial fluid to permit the articulating surfaces of the articular processes to remain lubricated and glide over one another. The type of motion permitted by the facet joints is dependent on the region of the vertebral column. For example, in a healthy lumbar region, the facet joints limit rotational motion but permit greater freedom for flexion, extension, and lateral bending motions. By contrast, in a healthy cervical region of the vertebral column, the facet joints permit rotational motion as well as flexion, extension, and lateral bending motions. As the facet joint deteriorates, the facet capsule may become compressed and worn, losing its ability to provide a smooth, lubricated interface between the articular surfaces of the articular processes. This may cause pain and limit motion at the affected joint. Facet joint deterioration may also cause inflammation and enlargement of the facet joint which may, in turn, contribute to spinal stenosis. Removal of an afflicted articular process may result in abnormal motions and loading on the remaining components of the joint. The embodiments described below may be used to stabilize a deteriorated facet joint while still allowing some level of natural motion.
Injury, disease, and deterioration of the intervertebral disc 12 may also cause pain and limit motion. In a healthy intervertebral joint, the intervertebral disc permits rotation, lateral bending, flexion, and extension motions. As the intervertebral joint deteriorates, the intervertebral disc may become compressed, displaced, or herniated, resulting in excess pressure in other areas of the spine, particularly the posterior bony elements of the afflicted vertebrae. This deterioration may lead to spinal stenosis. The embodiments described below may restore more natural spacing to the posterior bony elements of the vertebrae, decompress an intervertebral disc, and/or may relieve spinal stenosis. Referring still to
Connected at each end to the vertebral fasteners 54, 56, the flexible connector 52 may provide compressive support and load distribution, providing relief to the intervertebral disc 12. In addition, the flexible connector 52 may dampen the forces on the intervertebral disc 12 and facet joint 44 during motion such as flexion. Because the flexible connector 52 is securely connected to the vertebral fasteners 54, 56, the flexible connector 52 also provides relief in tension. Accordingly, during bending or in extension, the flexible connector 52 may assist in providing a flexible dampening force to limit the chance of overcompression or overextension when muscles are weak. On top of this, the flexible connector 52 also allows torsional movement of the vertebra 14 relative to the vertebra 16.
The flexible connector 52 may be formed of an elastic, multi-directionally flexible material such as silicone, polyurethane, or hydrogel, which, in some embodiments, may be un-reinforced. In alternative embodiments, a flexible connector similar to connector 52 is reinforced to provide a desired stiffness. For example, in one exemplary embodiment, reinforcement fibers are uniformly disposed within the flexible connector. The fibers could be glass, carbon, or other material, preferably being biologically compatible. Further, desired fiber alignment may provide desired strengthening. For example, in one embodiment, fibers are aligned to strengthen and limit movement in the tension and/or compressive directions, while allowing near-un-reinforced levels of torsional movement. Other desired arrangements also may be provided by selectively aligning the reinforcing fibers. In some examples, the reinforcement is not uniform throughout the flexible connector. In one example, different regions of the flexible connector are reinforced while other regions are not, or alternatively, different regions of the flexible are reinforced by different amounts. In some examples, the regions of the flexible connector including aperatures 66 (described below) may be reinforced, while the central region of the flexible connector is not. In another exemplary embodiment, a flexible connector is reinforced through a vulcanization process. As would be apparent to one of ordinary skill in the art, others reinforcement methods also may be used, including a number of fiber lay-ups that maybe utilized to achieve various effects.
The reinforcement members 60 are optional components that may be used to strengthen the apertures 66. In the embodiment shown, the reinforcement members 60 are grommets that fit within the apertures 66 and distribute loads from the vertebral fasteners 54, 56 to the flexible connector 52. In the exemplary embodiment shown, the grommets have a flange 68 at one side and a body 70 having a length substantially similar to the thickness of the flexible connector 52. Accordingly, when the grommet is placed within the aperture 66, the flange 68 may lie flat against the flexible connector 52, while the body 70 may extend substantially entirely through the aperture 66. Accordingly, the entire aperture 66 is reinforced with the reinforcing member 60.
It should be noted that the reinforcing member 60 may differ from that shown, so long as it provides an element of support or load distribution to the flexible member 52. For example, when the reinforcement member 60 is the disclosed grommet, a flange 68 may be disposed on each side of the flexible connector 52. In another embodiment, the grommet may extend only partially through the flexible connector 52. In one exemplary embodiment, the flexible connector 52 is formed to include a recess about the apertures 66 to receive the flange so that, when inserted into the aperture 66, the flange 68 of the reinforcement member 60 lies recessed into, flush with, or below the surface of the flexible connector 52. In other exemplary embodiments, the reinforcement member may be a tubular liner or, alternatively, a rivet. In other alternative embodiments, the reinforcement member is reinforcing thread, rope, or wire that may be sewn into the flexible connector about the apertures. The reinforcement members may be any member configured to reduce point loads or strengthen the apertures of the flexible connector.
As shown in
In one embodiment, each screw 74 may include external threads 76 configured to embed in and secure the screw 74 to the bone. In some embodiments, the screws 74 may include perimeter threads 79 usable to attach to additional components of the vertebral fasteners 54, 56. For example, the perimeter threads 79 may be configured to engage the threads formed on the set screw 78. It should be noted that the screws 74 may be compatible with attachment devices that do not use a set screw, but use other means and systems for attaching the flexible connector 52 in place. In the exemplary embodiment shown in
In
The set screw 78 may be configured to operate to secure the flexible connector 52 on the screw 74. In one embodiment, the set screw 78 may be configured to engage the perimeter of the screw 74. In this example, the set screw 78 includes an axially extending hex head 82 with a wide rim 84. In use, the rim 84 engages the flexible connector 52 and secures it in place. A physician may tighten the set screw 78 using a tightening tool (not shown) configured to engage the hex head 82. In the embodiment shown, the set screw 78 is a snap-off set screw. Accordingly, when a proper amount of torque is reached, the hex head 82 may snap off the set-screw 78, thereby notifying the physician that the set screw 78 is sufficiently tight. Although the device 50 is described using a snap-off set screw 78, other attachments methods could be used. For example, in some embodiments, the set screw 78 does not include a snap-off hex head, but may be tightened to a desired torque using a torque wrench. In other embodiments, instead of a set screw, the flexible connector 52 is held in place by a nut attachable to the screws 74. In one example, the nut is a lock-nut. In other embodiments, a lock-washer or clamping connector is used. Still other devices also could be used to secure the flexible connector 52 to the screw 74, as would be apparent to one skilled in the art. In other embodiments, the vertebral fasteners 54, 56 may include cables, crimps, loops, press fits, tethers, and adhesives, among others.
Implanting the vertebral stabilizing system 50 may be accomplished using, for example, a posterior, posterior-lateral, or lateral approach. First, a small incision may be created in the patient's skin for access to the pedicle region. The pedicle region of the vertebrae 14, 16 may be visualized directly or may be visualized with radiographic assistance. Using a drill, a suitably sized hole may be formed into the pedicle of one of the vertebrae 14, 16 in the area between the transverse process 22 and the superior articular process 30. The screw 74 may be driven partially into the hole, while leaving a portion extending outwardly for connection to the flexible connector 52. The drilling process may be repeated for the other of the vertebrae 14, 16 at a proper distance from the first hole, and a second screw 74 may be driven into the hole.
The flexible connector 52 may then be placed over the two screws 74 so that the two screws protrude through the apertures 66 at the ends 62, 64 of the flexible connector 52. In some embodiments, if it is desired to apply the flexible connector 52 either in tension or in compression, and thereby apply loading to the vertebrae, the flexible connector 52 may be either compressed or stretched while being placed over the two screws 74. Once the flexible connector 52 is in place, set screws 78 may be threaded onto the screws 74. The set screws 78 are threaded onto the screw 74 until they engage the flexible 52 connector with a desired torque. While threading, the rim 84 engages and presses against the flexible connector 52.
The flexible connector 52 may be placed directly adjacent the vertebrae 14, 16, or alternatively, may be spaced from the vertebrae 14, 16. In some embodiments, placement of the flexible connector 52 directly adjacent the vertebrae 14, 16 may impart specific characteristics to the flexible connector 52. In some examples, the flexible connector 52 may be spaced from the vertebrae 14, 16. Accordingly even when the vertebral column is in flexion, causing the spine to bend forward, the first and second vertebral fasteners 54, 56 maintain a line of sight position, so that the flexible connector 52 extends only along a single axis, without bending. In other examples, after placement, the flexible connector 52 may contact portions of the vertebrae 14, 16 during the flexion process. For example, during flexion, the vertebrae 14, 16 may move so that the first and second vertebral fasteners 54, 56 do not have a line of sight position. Accordingly, the flexible connector 52 may be forced to bend around a protruding portion of the vertebrae. This may impart additional characteristics to the flexible connector 52. For example, because the flexible connector 52 would effectively contact the spinal column at three locations (its two ends 62, 64 and somewhere between the two ends), its resistance to extension might be increased.
In the exemplary embodiments described, the flexible connector 52 is the only component extending from one vertebral fastener 54, 56 to the other. This may be referred to as a single flexible connector. This single flexible connector may be contrasted with conventional systems that employ more than one connector extending between attachment points, such as systems with one component connected at the attachment points and another component extending between attachment points. Because it employs a single flexible connector 52, the vertebral stabilizing system 50 disclosed herein may be easier and quicker to install, may be less complex, and may be more reliable than prior devices.
It should be noted however, that a spinal column may employ the flexible connector 50 to extend across a first vertebral space, with a second flexible connector extending across a second vertebral space. Accordingly, more than one vertebral stabilizing system 50 may be used in a spinal column. In some instances where more than one stabilizing system is use, the first and second vertebral spaces may be adjacent. In alternative embodiments, a vertebral stabilizing system 50 may have a single flexible connector with a length allowing it to extend across more than one intervertebral space, with or without connecting to an intermediate vertebra.
In certain anatomies, the vertebral stabilizing system 50 may be used alone to provide decompression or compression to a single targeted facet joint or to relieve pressure on a particular side of the intervertebral disc, such as a herniation area. However, in some instances, a second vertebral stabilizing system may be installed on the opposite lateral side of the vertebrae 14, 16, across from the vertebral stabilizing system 50. Use of first and second vertebral stabilizing systems may provide more balanced support and equalized stabilization. The second vertebral stabilizing system may be substantially similar to system 50 and therefore will not be described in detail.
The vertebral stabilizing system 50, as installed, may flexibly restrict over-compression of the vertebrae 14, 16, thereby relieving pressure on the intervertebral disc 12 and the facet joint 44. In addition, the vertebral stabilizing system 50 may flexibly restrict axial over-extension of the intervertebral disc 12 and the facet joint 44. By controlling both compression and extension, the vertebral stabilizing system 50 may reduce wear and further degeneration. The flexible connector 52 may also dampen the forces on the intervertebral disc 12 and facet joint 44 during motion such as flexion and extension. Because the flexible connector 52 may be positioned relatively close to the natural axis of flexion, the vertebral stabilizing system 50 may be less likely to induce kyphosis as compared to systems that rely upon inter-spinous process devices to provide compressive and tensile support. Additionally, the system 50 may be installed minimally invasively with less dissection than the inter-spinous process devices of the prior art. Furthermore, an inter-pedicular system can be used on each lateral side of the vertebrae 14, 16, and may provide greater and more balanced stabilization than single inter-spinous process devices.
It should be noted that in some embodiments, the flexible connector 52 may be configured so that orientation in one direction provides one set of stabilizing properties to the vertebrae, while orienting the flexible connector 52 in the other direction would provide a second set of stabilizing properties. In such an embodiment, the body 58 of the flexible member may be asymmetrically shaped.
Although disclosed as being used at the posterior areas of the spine, the flexible connector may also be used in the anterior region of the spine to support the anterior column. In such a use, the flexible connector may be oriented adjacent to and connect to the anterior column, and may span a vertebral disc space.
Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. Accordingly, all such modifications and alternative are intended to be included within the scope of the invention as defined in the following claims. Those skilled in the art should also realize that such modifications and equivalent constructions or methods do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. It is understood that all spatial references, such as “horizontal,” “vertical,”“top,” “upper,” “lower,” “bottom,” “left,” “right,” “cephalad,” “caudal,” “upper,” and “lower,” are for illustrative purposes only and can be varied within the scope of the disclosure. In the claims, means-plus-function clauses are intended to cover the elements described herein as performing the recited function and not only structural equivalents, but also equivalent elements.
