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CROSS-REFERENCE TO RELATED APPLICATION
Claim of Priority: Pursuant to the provisions of 35 U.S.C. § 1 19(e), this application claims the benefit of the filing date of provisional patent application Ser. No. 60/574,282, filed May 25, 2004, for “OCCIPITOCERVICAL PLATE,” the contents of which are incorporated by reference herein.
The present invention relates generally to apparatus and methods for spinal fixation. More specifically, the present invention relates to apparatus and methods for providing internal support and spinal fixation for patients suffering from occipital-cervical instability.
Spinal fixation is a well known and frequently used medical procedure. Pedicle, lateral, and oblique mounting devices may be used to secure corrective spinal instrumentation to a portion of the spine that has been selected to be fused by arthrodesis. Fixation of the skull to the cervical spine may be used to treat trauma to the neck, degenerative diseases such as rheumatoid arthritis, and congenital instability. Many current implantable devices designed to immobilize the skull with respect to the upper cervical spine are assemblies of several components which are not designed specifically for fusing the cervical spine to the skull, but instead are assembled from multiple components designed for other applications. Such assembly may prolong and complicate the implantation procedure.
A typical spinal fixation system includes corrective spinal instrumentation that is attached to selected vertebrae of the spine by screws, hooks, and clamps. Various types of screws, hooks, and clamps have been used for attaching such corrective spinal instrumentation to selected portions of a patient’s spine. Examples of pedicle screws and other types of attachments are illustrated in U.S. Pat. Nos. 4,763,644; 4,805,602; 4,887,596; 4,950,269; and 5,129,388. Each ofthese patents is incorporated by reference as if fully set forth herein. Examples of such multipart spinal fixation systems include U.S. Pat. Nos. 5,360,429 and 5,542,946, the disclosure of each of which is incorporated by reference.
With respect to occipital-to-cervical spinal fixation systems, contoured loop and wire constructs, rod constructs, rod and plate constructs and pre-contoured “U-loop”-type constructs have been used. An example of such a device is the OMI “U loop” device manufactured by Ohio Medical Instruments. However, such devices have a number of limitations, including the lack of appropriately sized loops for children under five years of age; the extensive modification and bending of the loops required during surgery, which can lead to failure of the device even before installation; cumbersome methods of coupling the devices to the anchor screws; and the lack of an option for installing a posterior cervical screw, which can be an urgent need for patients with missing lamina or inadequate laminar bone quality.
With these multi-piece systems, a number of problems may occur. For example, pressure necrosis may occur at the points of hook or wire fixation, leading to failure. Supplementation of such systems with halo vests often then fails to prevent micro-motion leading to non-union of the arthrodesis. Addi
tionally, the time for surgery may be extended by the need to build and install a multi-piece assembly from separate components.
A few occipital-cervical spinal fixation systems, such as that disclosed in U.S. Pat. No. 6,146,382, the disclosure of which is incorporated by reference herein, attempt to simplify the implantation of the system by reducing the number of parts.A single plate attaches to an attachment site on the skull, and arms extend down from the plate to the cervical vertebrae. The anns are coplanar with the plate and bend at the tips where a separate connection member is attached. The separate attachment member is then attached at the top surface of the C2 vertebra. A cable is then attached by a hook system to the plate to a vertebra posterior to the arms, in order to retain a bone graft material in place. The ’382 device thus still includes a number of parts that are assembled in situ, retaining the issues described with multi-piece systems.
Approximately 500 surgical cases of pediatric occipitocervical fusions are perfonned in North America each year on children suffering from occipital-cervical instability. Current occipital-cervical fixation devices, such as the ’382 device, are designed for adults and are therefore typically too large for use in children. Additionally, as the relationship of a cl1ild’s head to the body differs from that of an adult due to allometric growth, devices designed for adults may not sustain the correct relationship of the head and neck for children. Surgical concerns are magnified when treating children, due to their smaller physical size, the abnonnal anatomy that may be caused by craniovertebral anomalies, and their growth potential.
Previously, graft/wire constructs were reported to be associated with a nonunion rate as high as 30% for C1-C2 fusion; however, this incidence improves considerably with the use of a halo orthosis. Transarticular screw placement creates immediate atlantoaxial joint stability and, in contrast to previous posterior wiring/ graft constructs, does not require postsurgical brace therapy. However, such procedures require surgical precision because serious potential risks are associated with improper screw placement. Thus, many spine surgeons are reluctant to perform such a procedure.
Accordingly, an occipital-cervical spinal fixation system that operated as a single plate, not requiring the use of additional component plates, hooks or rods would be an improvement in the art. Such a system that is configured for use in children or small adults would be an additional improvement in the art.
One aspect of the present invention relates to occipitalcervical spinal fixation systems. In some embodiments the system includes a plate configured for attachment to the occipital bone, with two arms that extend out from either side of the plate, with the distal end of the arms turning downwards parallel to one another. A bend is placed in the arms, such that the arms extend down from the occipital bone upon installation, behind the spinous process of the C1 and C2 vertebrae. A second bend is placed in the anns, allowing attachment to the C2 vertebrae. Some embodiments are configured in appropriate dimensions for installation in a child for pediatric applications.
Other aspects of the present invention include methods of spinal fixation of the C1 and C2 vertebrae to the occiput. A one-piece spinal fixation system is attached to the C2 vertebra with transarticular screws that extend through the C2 vertebra into the C1 vertebra. The system extends from the occipital bone, behind the spinous process of the C1 and C2 vertebrae.
The transarticular screws may be headless screws requiring only a single emplacement. The system is attached to the occipital bone by one or more attachment screws extending through a top plate. A bone graft material may be held inplace between the cervical vertebrae and the skull by installing a cable to the installed system to retain the bone graft material in place.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention and the best mode can be more readily ascertained from the following detailed description when read in conjunction with the accompanying drawings in w11ich:
FIG. 1 is a side perspective view of an occipital-cervical fixation system, in accordance with the present invention.
FIG. 2 is a back view of the embodiment of FIG. 1.
FIG. 3 is a side view ofthe embodiment of FIGS. 1 and 2.
FIG. 4A is an exploded perspective view of bone screw and a retaining nut, useful with the system of FIGS. 1 to 3.
FIG. 4B is a perspective view of the retaining nut of FIG. 4A.
FIG. 4C is a top view of the bone screw of FIG. 4A.
FIG. 5 is a back view of emplacement of the bone screw of FIG. 4A in a patient, in accordance with the present invention.
FIGS. 6 and 7 are back views of the embodiment of FIGS. 1 to 3, shown in situ in a patient.
FIG. 8 is a side view of the embodiment of FIGS. 1 to 3, shown in situ in a patient.
FIG. 9 is aback view of the embodiment of FIGS. 1 to 3, shown in situ in a patient, in conjunction with a bone graft material.
FIG. 10 is a back view of a second embodiment of an occipital-cervical fixation system, in accordance with the present invention.
FIGS. 11A and 11B are back views of alternate embodiments of lower attachment holes for embodiments of occipital-cervical fixation systems in accordance with the present invention.
FIGS. 1, 2 and 3 depict an illustrative embodiment of an occipital-cervical spinal fixation system 10. An attachment plate 12 may be configured for attachment to the occipital bone. Attachment plate 12 may include an enlarged area 13, with one or more attachment holes 16, through which attachment screws 160 (FIG. 6) may be placed to attach the plate to the occipital bone. Each of attachment holes 16 may include beveled edges, allowing an attachment screw placed therein to lie flush with the plate surface (by being countersunk therein). As depicted, the plate 12 may be planar in conformation. The plate 12 may be contoured as desired to fit the surface of the occiput prior to installation.
At opposite sides of plate 12, two arms 14A and 14B extend out from the plate 12 in opposite directions. Each arm 14 then extends downwards becoming generally parallel to one another and generally sharing a common plane throughout their length. It will be appreciated that while the arms 14 may be generally parallels, some variation for individual patients may be required, based on the patients anatomy. Viewed from the front or back (as in FIG. 2), the relationship of the plate 12 and arms 14A and 14B may generally resemble a horseshoe.
Each arm 14A or 14B contains a bend 20A or 20B in the length thereof, at a distance from the plate. The bends 20A
and 20B are generally parallel to one another in the respective arms 14A and 14B, such that the arms 14A and 14B remain generally parallel. Again, it will be appreciated that while the bends 20A and 20B may be generally parallel to each other and arms 14A and 14B may be generally parallel to each other, some variation for individual patients may be required, based on the patient’s anatomy. The angleA of bends 20A and 20B is selected to ensure that, upon installation, the arms 14A and 14B extend down from the occipital bone, behind the spinous process of the C1 and C2 vertebrae (as best depicted in FIG. 8). In one embodiment, an angle of about 1 15 to about 135 degrees, as depicted in FIG. 3 as about 127 degrees, may be used. It will be appreciated that other angles may be used based upon the anatomy of the individual patient.
A second bend 30A and 30B may be placed in each arm, 14A and 14B, respectively, at a point distal to the first bend 20A or 20B. The second bend 30A or 30B positions a distal end of each respective arm such that it may be attached to the lower surface of the spinous process of the C2 vertebrae (as best depicted in FIG. 8). In one embodiment, the angle B of the second bend 30A or 30B may be from about 140 to about 160 degrees, as depicted in FIG. 2 as about 151 degrees, although it will be appreciated that other angles may be used, based upon the anatomy of the patient. Attachment may be accomplished by insertion of a fastener, such as bone screw 20 (FIG. 6) through a fastener hole 18A or 18B located near the distal end of the arm 14. Fastener hole 18A or 18B may include beveled edges, allowing a screw placed therein to lie flush with the plate surface (by being countersunk therein). Long screws 40 that extend through both the C1 and C2 vertebrae may be used, where desirable for the procedure.
A headless bone screw 20, together with a retaining nut 22, depicted in FIGS. 4A, 4B and 4C, may be used to attach system 10 to the lower surface of the spinous process of the C2 vertebrae. Headless bone screw 20 includes an elongated shaft S, extending from a distal tip T, which may be configured for penetrating bone, to a retaining end R. Bone threads 24 are disposed around the shaft S, extending from near the distal tip T back along the shaft S allowing for secure rotational placement of the bone screw 20 into bone, such as the C1 and C2 vertebrae. It will be appreciated that the depicted bone threads 24 are illustrative only and any spacing and size of t11read suflicient to retain the bone screw 20 in place may be used. Retention threads 26 are located on the shaft S near retaining end R, and are configured to rotatably connect with threads 28 disposed on the intemal channel 23 of the retaining nut 22. Retention threads 26 are typically smaller in size and more closely spaced than bone threads 24. However, it will be appreciated that the depicted retention threads 26 are illustrative only and any spacing and size of thread suflicient to retain a fastener to the bone screw 20 may be used. A non-threaded area of shaft S, which may be the thickness of the threads 24 or 26, may be disposed between the two sets of threads.
Retaining end R includes structures allowing headless bone screw 20 to be rotatably inserted into bone. As depicted in FIG. 4C, a socket 30 may be formed in retaining end R, into which a tool can be inserted to rotate the headless bone screw 20 by interaction with the sides thereof. It will be appreciated that, although depicted in FIG. 4C as hexagonal, socket 30 may have any desired shape that allows a tool to be inserted therein, examples include square, triangular, irregular, and radially pattemed sockets for customized tools. It will also be appreciated that non-socket tool interconnection structures may be used, such as one or more slots for a screwdriver tip disposed on the retaining end R or within a shallow recess disposed thereon.