Patent Application
20110106162
Various devices and methods for stabilizing bone structures have been used for many years. For example, one type of stabilization technique uses one or more elongated rods extending between components of a bony structure and secured to the bony structure to stabilize the components relative to one another. The components of the bony structure are exposed and one or more bone engaging fasteners are placed into each component. The elongated rod is then secured to the bone engaging fasteners in order to stabilize the components of the bony structure.
In some instances, different elongated rods each having desired mechanical and/or material properties are provided, but are not readily engageable to a variety of bone engaging fasteners due to their respective outer dimensions or their external configurations.
Elongated connecting elements include bodies having composite cross-sections defined by a center core that is surrounded by an outer portion. The center core includes a first material and the outer portion includes a second material that is distinct from the first material. In one particular form, a connecting element includes a maximum dimension across an outer cross-sectional shape of the outer portion that is less than a minimum dimension across an oblong or round outer cross-sectional shape of a polyetheretherketone (PEEK) connecting element, and the connecting element exhibits mechanical and/or material properties that are at least equivalent to the mechanical and/or material properties of the polyetheretherketone (PEEK) connecting element.
According to one aspect, a connecting element for a spinal stabilization system includes an elongate body extending along a longitudinal axis between opposite first and second ends. The elongate body includes a composite cross-section with a center core that includes a non-circular cross-sectional shape and is comprised of a first material defined by a reinforcing material randomly dispersed throughout a polymer. An outer portion that includes a circular, outer cross-sectional shape is positioned around the center core and is comprised of a second material.
According to another aspect, a method includes producing an elongate connecting element for a spinal stabilization system. The connecting element includes an elongate body extending along a longitudinal axis and including a composite cross-section. The connecting element further exhibits mechanical properties that are at least equivalent to mechanical properties of a polyetheretherketone (PEEK) connecting element having an oblong or round outer cross-sectional shape. The method further includes providing a center core comprised of a first material and including a first cross-sectional shape, and positioning an outer portion around the center core. The outer portion includes a second material and has a maximum dimension across an outer cross-sectional shape that is less than a minimum dimension across the oblong outer cross-sectional shape of the polyetheretherketone (PEEK) connecting element.
According to another aspect, a method for spinal stabilization includes engaging an anchor to a first vertebral body. The anchor includes a receiver positioned adjacent the first vertebral body. The method also includes positioning a connecting element in the receiver of the anchor. The connecting element is produced by providing a center core comprised of a first material and including a first cross-sectional shape, and positioning an outer portion comprised of a second material around the center core. The connecting element includes an elongate body extending along a longitudinal axis and including a composite cross-section. The connecting element further exhibits mechanical properties that are at least equivalent to mechanical properties of a polyetheretherketone (PEEK) connecting element having an oblong or round outer cross-sectional shape, and the outer portion includes a maximum dimension across an outer cross-sectional shape that is less than a minimum dimension across the outer cross-sectional shape of the polyetheretherketone (PEEK) connecting element.
Related features, aspects, embodiments, objects and advantages of the present invention will be apparent from the following description.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments 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 such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated herein are contemplated as would normally occur to one skilled in the art to which the invention relates.
A connecting element for connection with anchors engaged to one or more vertebral bodies is provided with a composite cross-section that extends along all or a substantial portion of a length of a body of the connecting element. In one embodiment, the composite cross-section is constant in dimension and material properties along the entire length of the connecting element. Other embodiments contemplate cross-sections that vary in dimension and/or material properties along all or a portion of the entire length of the connecting element.
Each of anchors 22 includes a receiver for receiving connecting element 23 therein, and a bone engaging portion for engaging vertebrae V. The bone engaging portion can be a threaded screw-like member that extends into and engages the bony structure of vertebrae V. Other embodiments contemplate that one or more of anchors 22 can include a bone engaging portion in the form of a hook, staple, bolt, clamp, cable, or other suitable bone engaging device. In one form, the receiver can include a pair of arms defining a passage therebetween for receiving the connecting element 23 therebetween. The arms can be top-loading and internally and/or externally threaded to engage a set screw or other member to couple connecting element 23 with anchors 22. Other embodiments contemplate receivers that are side-loading, bottom loading, end-loading, clamping members, or any other suitable arrangement for securing connecting element 23 along the spinal column. The receiver can pivot or rotate relative to the bone engaging portion, or can be fixed relative to the bone engaging portion. In one embodiment, anchor 22 is a bone screw with a U-shaped head pivotally mounted or fixed to the proximal end of a bone screw.
As further shown in
In one embodiment, the composite connecting element 23 is provided with core 30 made from a material having a higher modulus of elasticity and outer portion 40 made from a material having a lower modulus of elasticity than the material of core 30. In the form illustrated in
Further examples of materials that may be used for all or part of core 30 include non-resorbable materials, cobalt-chrome alloys, titanium alloys, superelastic metallic alloys (for example, NITINOL®, GUM METAL®), stainless steel alloys, and/or reinforced members of the polyaryletherketone family, such as continuous carbon fiber reinforced PEEK, short carbon fiber reinforced PEEK, or shape-memory PEEK for example. Further examples of suitable materials for outer portion 40 include non-resorbable materials and/or members of the polyaryletherketone family. More particular examples of suitable materials for outer portion 40 include short carbon fiber reinforced PEEK, continuous carbon fiber reinforced PEEK, shape-memory PEEK, superelastic metal alloys, polyetherketoneketone (PEKK), polyethylene, polyphenylene, polysulfone, polyetherimide, polyimide, and/or ultra-high molecular weight polyethylene (UHMWPE).
In the embodiment of
Another embodiment composite connecting element includes a circular, oval, elliptical, oblong, racetrack, or rectangular core made from Ti-6Al-4V and a circular outer layer around the core made from PEEK. Another example composite connecting element includes a circular, oval, elliptical, oblong, racetrack or rectangular core made from Ti-6Al-4V and a circular outer layer around the core made from polyurethane. Another embodiment composite connecting element includes a circular, oval, elliptical, oblong, racetrack, or rectangular core made from Co—Cr and a circular outer layer around the core made from PEEK. Another example composite connecting element includes a circular, oval, elliptical, oblong, racetrack or rectangular core made from Nitinoland a circular outer layer around the core made from silicone. Another embodiment composite connecting element includes a circular, oval, elliptical, oblong, racetrack, or rectangular core made from stainless steel and a circular outer layer around the core made from epoxy. Another embodiment composite connecting element includes a circular, oval, elliptical, oblong, racetrack, or rectangular core made from carbon-fiber or glass-fiber reinforced PEEK and a circular outer layer around the core made from PEEK. Still, other variations in the composition and shape of core 30 and outer portion 40 are contemplated.
As illustrated in
Referring now to
As suggested above, it is contemplated that the composite connecting elements disclosed herein could be provided with outer portions that include non-circular cross-sectional shapes. More particularly, in one or more forms, it is contemplated that the outer portion could have a cross-sectional shape that corresponds to the cross-sectional shape of the core, including for example any of the shapes illustrated in
In one aspect, the connecting elements described herein include composite cross-sections that allow a surgeon to use a connecting element having a maximum external dimension that that is smaller than the minimum external dimension of an oblong or round shape connecting element formed only of polyetheretherketone (PEEK). In another aspect, the connecting elements disclosed herein allow the surgeon intra-operative freedom to select or adjust the flexion-extension stiffness of the connecting element by selecting the bending axis that is aligned in the direction of bending of the spinal motion segment. In one form, the connecting elements include an outer round or circular profile having a configuration suitable for engagement with a variety of different bone anchors. In one or more forms, the composite connecting elements include a non-circular core that is centrally located in the outer portion, although offset locations of the core relative to the outer portion are contemplated. When utilized, the non-circular cross-section of the core allows the stiffness of the rod in a particular plane of patient motion to be selected or adjusted during implantation or manufacture by changing the orientation of the core relative to the selected plane. In one specific example, the plane of motion of the patient is flexion and extension motion in the sagittal plane of a spinal motion segment including two or more vertebrae.
In one embodiment, the core of the connecting elements is made from a higher modulus material and the outer portion is made from a lower modulus material. The connecting element may be linear and straight along its entire length, or may be curved along all or part of its length. The connecting element may be pre-shaped, or shaped in the operating room or in situ. The connecting elements can be manufactured with various manufacturing processes, including over-molding the outer portion on the core, injection molding, extrusion, compression molding, or casting, for example. The core may also include surface treatments, such as shot-peening, grit-blasting, texturing, plasma treatment, anodizing or adhesive, for example, to facilitate and maintain engagement between the outer portion and the core. The composite structures discussed herein also have application with other types of implants, such as screws, plates, or cages, and may be used in other portions of the body. The connecting elements described herein may also be used in surgical procedures involving animals, or in demonstrations for training, education, marketing, sales and/or advertising purposes. In addition, the connecting elements may be also used on or in connection with a non-living subject such as a cadaver, training aid or model, or in connection with testing of surgical systems, surgical procedures, orthopedic devices and/or apparatus.
In certain embodiments, the area of the cross-section and/or the shape of the cross-section of the core of the composite connecting element is constant along the entire length of the connecting element. In other embodiments, the area of the cross-section and/or the shape of the cross-section of the core of the composite connecting element varies along the length of the connecting element. The outer portion surrounding the core may be solid, continuous, non-continuous, braided, knitted, or woven, for example. In addition, the outer portion may be of a composite material or contain any suitable additive.
Although various embodiments have been described as having particular features and/or combinations of components, other embodiments are possible having a combination of any features and/or components from any of embodiments as discussed above. As used in this specification, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the terms “proximal” and “distal” refer to the direction closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical implant and/or instruments into the patient. For example, the portion of a medical instrument first inserted inside the patient's body would be the distal portion, while the opposite portion of the medical device (e.g., the portion of the medical device closest to the operator) would be the proximal portion.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that all changes and modifications that come within the spirit of the invention are desired to be protected.
