Patent Application
20110257685
n/a
The present invention relates to systems and methods of use thereof for orthopedic stabilization, and particularly, spinal stabilization.
Spinal fusion is considered the “gold standard” for surgically treating patients whose condition has become so severe and debilitated that conservative, non-surgical measures fail to provide relief. Using bone grafts along with implants such as metal plates, rods and screws, spinal fusion adjoins two adjacent vertebrae, thus stabilizing the segment and easing the patient's pain, numbness, weakness and/or lack of mobility. Recently, advances in spine surgery technology—including a greater focus on the principles of spinal load sharing—have led to significant advancements in the materials selected for spinal fusion implants or prostheses. In particular, the development of semi-rigid alternatives to replace the traditional metal rods used in the past has been undertaken in an effort to replicate the motion and loading characteristics of a healthy spinal segment. Such alternatives typically provide less rigidity than metal rods, with material characteristics more closely approximating that of natural bone. Approximating the natural biomechanics of a healthy spine segment or “motion preservation” aims to provide some degree of controlled motion that can, in part, prevent deterioration of adjacent discs experiencing increased forces and loading following a fusion procedure. A significant limitation, however, for non-metallic implants includes increased vulnerability to accelerated fatigue and resulting increased failure rates compared to metallic components.
In addition to motion preservation efforts, long-term success of a fusion procedure greatly benefits from bone ingrowth around the implanted prostheses. Achieving such bone growth is often difficult, as the implanted prostheses shield surrounding tissue from naturally occurring stresses and motion. Such stress shielding can result in tissue degradation, and reduce the overall health and condition of a treated spinal segment. Various approaches have been employed to stimulate bone growth, but they are not without their limitations. For example, stimulating bone growth may include using extra bone from a patient's pelvis (autograft), using bone and tissue from a donor (allograft), or using a manufactured bone substitute. However, such techniques maybe limited or undesirable due to the overall health of a patient (e.g., subjecting a patient to an additional procedure to procure bone tissue from another site on the patient); sterilization concerns of donor tissue; and/or availability of synthetic bone substitutes.
The promotion of bone growth has also been attempted from a hardware standpoint, but such micro-motion mechanisms typically require the implantation of additional components on an implanted pedicle screw or rod, which increases the overall complexity and cost of a surgical procedure. Accordingly, such hardware-based approaches have grown out of favor with hospitals and surgeons in recent times.
In view of the above limitations, it is desirable to provide a spinal stabilization system facilitating motion preservation of a spinal segment, providing a high degree of resistance to fatigue and cyclic loading associated with spinal segment forces, and promoting bone growth without adding to the complexity of an implantation procedure.
The present invention advantageously provides a spinal stabilization system and methods of use and manufacturing thereof that facilitate motion preservation of a spinal segment, provide a high degree of resistance to fatigue and cyclic loading associated with spinal segment forces, and promote bone growth without adding to the complexity of an implantation procedure.
In particular, a spinal implant is provided, including an elongate polymer body; a wire embedded in the body, the wire straining the polymer body; and a mounting element coupled to the elongate polymer body to facilitate engagement of the body to a spinal segment. The wire may be metallic; may be constructed from at least one of Nitinol, cobalt, stainless steel, or titanium; may have a substantially circular cross-section; may have a substantially rectangular cross-section; and/or may compress at least a portion of the polymer body. The polymer body may be constructed from polyetheretherketone (PEEK) and may have an arcuate shape. The mounting element may define an aperture therethrough for engaging an orthopedic anchor.
An orthopedic anchor is provided, including a threaded shaft; a head coupled to the threaded shaft, the head defining a cavity therein; a prosthesis coupling element at least partially disposed in the cavity and movable with respect to the head; and at least one asymmetrical ring circumscribing a portion of the prosthesis coupling element. The anchor may further comprise a cap securing the prosthesis coupling element to the head; and/or a plurality of asymmetrical rings circumscribing a portion of the prosthesis coupling element, where at least one of the asymmetrical rings may define a first surface having an asymmetrical curvature and/or at least one of the asymmetrical rings may define a varying thickness. The prosthesis coupling element may define an elongated threaded portion extending from the head; and/or may be movable between approximately 0.001 inches and 0.010 inches from a centerline longitudinal axis defined by the head.
A method of manufacturing a spinal implant is provided, including applying a force to a wire; coupling a polymer to the wire through at least one of extrusion or injection molding processes; awaiting a time duration for the polymer to at least partially cure; and removing the force from the wire. The applied force may be between approximately 30% and 80% of an ultimate tensile strength of the wire.
Another method of manufacturing a spinal implant is provided, including inserting a wire into a substantially cured polymer body; applying a force to the wire; introducing a substantially uncured polymer onto the substantially cured polymer body; awaiting a time duration for the substantially uncured polymer to at least partially cure; and removing the force from the wire. Introducing the substantially uncured polymer onto the substantially cured polymer body may include overmolding the substantially uncured polymer onto the substantially cured polymer body.
A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:
The present disclosure advantageously provides a spinal stabilization system and methods of use and manufacturing thereof that facilitate motion preservation of a spinal segment, provide a high degree of resistance to fatigue and cyclic loading associated with spinal segment forces, and promote bone growth without adding to the complexity of an implantation procedure. Referring now to the drawing figures in which like reference designations refer to like elements, an embodiment of a spinal stabilization system constructed in accordance with principles of the present invention is shown in
The one or more orthopedic anchors 14 may generally define or include a shaft 16 at least partially insertable or implantable into a targeted tissue region. The shaft 16 may include a threaded portion and a narrow or sharpened tip 18 to ease insertion. At an end of the shaft 16 opposite the tip 18, the anchor 14 may include a head 20 defining a cavity 22 therein. The cavity 22 may be dimensioned to receive a portion of an implant or prosthesis and/or intermediary structures facilitating engagement between the anchor 14 and an implanted prosthesis. For example, the anchor 14 may include a prosthesis coupling element 24 that is at least partly positionable within the cavity 22.
Referring now to
The anchor 14 may provide a degree of motion between the anchor 14 and an attached prosthesis, and may further conduct or otherwise deliver stimulating motion into the surrounding tissue to promote tissue in growth. For example, the prosthesis coupling element 24 may be movable within or about the head 20 of the anchor 14, where such motion reverberates or is otherwise translated into micro stresses into the surrounding tissue to promote growth. Continuing to refer to
Referring again to
The elongated body 36 may further include one or more wires 40 coupled to the polymer layer 38 to strain or otherwise exert a force on the polymer layer 38. For example, the one or more wire(s) 40 may exert a compressive force on at least a portion of the polymer section 38, thereby providing increased resistance to cyclical tensile stresses and bending associated with flexion/extension movement of the spine. The wire 40 may include a strand, filament, or tendon-like length of a material traversing substantially the entire length of the elongate body 36. The wire 40 may be constructed at least in part, from Nitinol, cobalt, stainless steel, titanium, carbon fiber, or the like. The wire 40 may have a substantially circular or substantially rectangular cross-section depending upon a particular application or desired biomechanical result. Further, the cross-sectional dimensions and/or percentage of the overall width of the elongate body 36 may vary by application and the desired amount of strain or pre-stress on the prosthesis. For example, the diameter of the elongate body 36 may range from approximately 4.0 mm and approximately 9.0 mm, while an example of a diameter of a wire 40 may range between approximately 0.05 mm to approximately 0.3 mm.
The prosthesis 12 may further include one or more mounting elements 42 coupled to the elongate body 36 to facilitate or aid in coupling the prosthesis 12 to one or more orthopedic anchors, such as one or more pedicle screws. For example, a mounting element 42 may be coupled to either end of the elongate body 36, and provide a plurality of mounting or coupling positions through an elongated opening or hoop. The mounting element(s) 42 may be embedded or fused to the polymer layer 38 and/or also coupled to the wire 40 of the elongate body 36. Though illustrated at both ends of the elongate body 36, it is contemplated that the mounting elements 42 may be positioned at other locations, such as a mid-length mounting point or lateral location adjacent to the elongate body 36. The mounting element(s) 42 may be constructed from a crush-resistant material, such as titanium, stainless steel or the like to reduce the likelihood of compromised structural integrity resulting from over-tightening or over-zealous securement of the prosthesis to an orthopedic anchor 14 or pedicle screw.
The pre-stressed configuration between the wire 40 and polymer layer or portion 38 of the elongate body 36 may be achieved by manufacturing techniques manipulating the wire 40 while one or more remaining portions of the elongate body 36 are formed or cured. For example, referring now to
Alternatively, as shown in
In an exemplary use of the spinal stabilization system 10, one or more of the orthopedic anchors 14 may be inserted into a spinal segment, such as in two adjacent vertebral discs or pedicles of a spinal joint. The prosthesis 12 may then be coupled to the one or more anchors 14. For example, the threaded portion 26 of the prosthesis coupling element 24 may be passed through the opening of the mounting element 42 of the prosthesis. Once the desired relative positions of the prosthesis coupling element 24 and mounting element 42 have been attained, a locking element such as a set screw or the like (not shown) may be fastened to the threaded segment 26 of the prosthesis coupling element 24 to lock the prosthesis 12 into place.
The spinal stabilization system provides increased tension resistance and thus increased prosthesis lifespan by implementing its pre-stressed configuration with the wire(s) and the one or more polymer layers. This decreased susceptibility to cyclic fatigue and failure avoids having to choose between a stabilization system that provides extended durations of use (e.g., such as with traditional exclusively metallic-based implants) and a system that provides increasingly desired biomechanical characteristics and motion preservation (e.g., such as with traditional exclusively polymer-based implants). Moreover, because of the articulation provided between the prosthesis coupling element and the head, growth-promoting stresses and movement are translated into the surrounding tissue to promote the overall health and longevity of the treated tissue area and the implanted system.
It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.
This application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 61/234,600, filed Apr. 15, 2010, entitled “Spinal Fixation and Pedicle Screws,” the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61324600 | Apr 2010 | US |
