Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-03-01
2001-09-25
Mancene, Gene (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06293949
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of instrumentation and systems for treatment of the spine, and more particularly to a device for flexibly stabilizing the cervical spine.
BACKGROUND OF THE INVENTION
As with any bony structure, the spine is subject to various pathologies that compromise its load bearing and support capabilities. Such pathologies of the spine include, for example, degenerative diseases, the effects of tumors and, of course, fractures and dislocations attributable to physical trauma. In the treatment of diseases, malformations or injuries affecting spinal motion segments (which include two adjacent vertebrae and the disc tissue or disc space therebetween), and especially those affecting disc tissue, it has long been known to remove some or all of a degenerated, ruptured or otherwise failing disc. In cases in which intervertebral disc tissue is removed or is otherwise absent from a spinal motion segment, corrective measures are indicated to insure the proper spacing of adjacent vertebrae formerly separated by the removed disc tissue.
Commonly, the adjacent vertebrae are fused together using a graft structure formed of transplanted bone tissue, an artificial fusion element, or other suitable compositions. Elongated rigid plates have been helpful in the stabilization and fixation of the spine when used alone or in conjunction with a grafting procedure, especially in the thoracic and lumbar regions of the spine. These plating systems also have the potential advantage of increasing union rates, decreasing graft collapse, minimizing subsequent kyphotic deformity, and decreasing the need for bulky or rigid postoperative immobilization. Additionally, rigid internal fixation systems may improve the overall quality of life of the patient and may provide the opportunity for earlier rehabilitation.
The plating techniques described above have also found some level of acceptance by surgeons specializing in the treatment of the cervical spine. The cervical spine can be approached either anteriorly or posteriorly, depending upon the spinal disorder or pathology to be treated. Many well-known surgical exposure and fusion techniques of the cervical spine are described in the publication entitled
Spinal Instrumentation
, edited by Drs. Howard An and Jerome Cotler. The primary focus of cervical plating systems has been to restore stability and increase the stiffness of an unstable spinal motion segment. During the development of cervical plating systems, various needs have been recognized. For example, the system should provide strong mechanical fixation that can control movement of the vertebral segments. The system should also be able to maintain stress levels below the endurance limits of the plate material, while at the same time exceeding the strength of the anatomic structures or vertebrae to which the plating system is engaged. Additionally, the system should preferably be capable of accommodating for the natural movement of the vertebrae relative to one another, including torsional movement during rotation of the spine and translational movement during flexion or extension of the spine.
There is increased concern in the spinal medical community that anterior or posterior plating systems may place excessive loads on the vertebrae or graft structure in response to small degrees of spinal motion. See, e.g., K. T. Foley, D. J. DiAngelo, Y. R. Rampersaud, K. A. Vossel and T. H. Jansen,
The In Vitro Effects of Instrumentation on Multi
-
level Cervical Strut
-
Graft Mechanics,
26th Proceeding of the Cervical Spine Research Society, 1998. If the plating system is used in conjunction with grafting, these loads may promote pistoning, which can ultimately lead to degradation or failure of the graft construct. Additionally, even small degrees of spinal motion can cause significant forces to be placed on the spinal plate and the bone anchor devices which attach the plate to the vertebrae, whether they be bone screws, hooks, etc. These forces may lead to failure of the plate or loosening of the points of attachment between the bone anchors and the vertebrae, thus resulting in the potential loss of support by the plate.
Thus, there is a general need in the industry to provide a device for flexibly stabilizing the spine, and in particular the cervical region of the spine. The present invention meets this need and provides other benefits and advantages in a novel and unobvious manner.
SUMMARY OF THE INVENTION
The present invention relates generally to a system for flexibly stabilizing the spine, and more particularly the cervical region of the spine. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms of the invention that are characteristic of the preferred embodiments disclosed herein are described briefly as follows.
In one form of the present invention, a device is provided for stabilizing at least a portion of the spinal column. The device includes a longitudinal member sized to span a distance between at least two vertebral bodies and being at least partially formed of a shape-memory material exhibiting pseudoelastic characteristics when implanted within the body. The device also includes bone anchors for securing the longitudinal member to each of the vertebral bodies. The longitudinal member is reformed from an initial configuration to a different configuration in response to the imposition of stress caused by relative displacement between the vertebral bodies and recovers toward the initial configuration when the stress is removed.
In another form of the present invention, a device is provided for stabilizing at least a portion of the spine. The device includes a compliant element at least partially formed of a pseudoelastic shape-memory material displaying reversible stress-induced martensitic behavior at about human body temperature. The compliant element has a length sized to span a distance between at least two spinal motion segments and is secured to each of the spinal motion segments by at least two anchoring elements. The length of the compliant element is variable between an initial length and a different length through the imposition of stress caused by relative displacement between the spinal motion segments, with the different length occurring through the transformation of at least a portion of the pseudoelastic shape-memory material into reversible stress-induced martensite, and with the compliant element recovering or reforming toward the initial length when the stress is removed.
In yet another form of the present invention, a spinal stabilization system is provided, comprising an elongate member for placement adjacent the cervical region of the spine and being at least partially formed of a pseudoelastic shape-memory material displaying reversible stress-induced martensitic behavior at about human body temperature. The system is further comprised of at least two bone engaging members, each adapted to engage a respective one of at least two cervical vertebrae to secure the elongate member thereto. The elongate member is deformed during relative displacement between the cervical vertebrae, thus transforming a portion of the shape-memory material into a stress-induced martensitic state. The elongate member exerts a substantially constant restorative force on the cervical vertebrae when the shape-memory material is in the stress-induced martensitic state to thereby flexibly stabilize the cervical region of the spine.
In still another form of the present invention, a connector apparatus is provided for connecting a first member to a second member. The apparatus is comprised of a central portion having a longitudinal axis and being at least partially formed of a shape-memory material exhibiting pseudoelastic characteristics at about body temperature. The central portion includes a number of alternating ridges and grooves disposed along the longitudinal axis. The apparatus also includes at least two connection portions, each configured to enga
Justis Jeff R.
Sherman Michael C.
Mancene Gene
Robert Eduardo C.
SDGI Holdings Inc.
Woodard Emhardt Naughton Moriarty & McNett
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