Patent Application
20080154378
Severe back pain and nerve damage may be caused by injured, degraded, or diseased spinal joints and, particularly, spinal discs. Similarly, hip and knee pain can be caused by injured, degraded, or diseased hip and knee joints. For example, disc deterioration and other spinal deterioration may cause spinal stenosis, a narrowing of the spinal canal and/or the intervertebral foramen, that causes pinching of the spinal cord and associated nerves. Severe hip joint degradation, for example, can often require implantation of a hip implant in what is commonly referred to as a hip replacement surgery.
Current methods of treating damaged spinal discs include vertebral fusion, nucleus replacements, or motion preservation prostheses. A spinal prostheses joint, such as that described U.S. Pat. No. 6,740,118, the disclosure of which is incorporated herein by reference, for example, is placed between two vertebral bodies to maintain or restore motion similar to the normal motion provided by natural intervertebral joints. Artificial disc implants, such as described in U.S. Pat. No. 6,402,785, the disclosure of which is incorporated herein by reference, have also been used as a disc replacement therapy. Other spinal therapies include fixation systems whereby bone screws, for example, are inserted into vertebral bodies and a connecting rod is secured between the screws to provide spinal stability, such as that described in U.S. Pat. No. 6,454,773, the disclosure of which is incorporated herein by reference.
Generally, surfaces of these implant and other bone-related implant devices are roughened and coated with a bone-growth promoting material, such as Infuse®, which is commercially available from Medtronic, Inc. of Minneapolis, Minn., hydroxyapatite, or other similar bone-growth promoting material. INFUSE is a registered trademark of Medronic Sofamor Danek, Inc, Minneapolis, Minn. Chemical etching, plasma spraying, and porous coating are typically used to roughen the bone engaging surfaces of the implants. With conventional roughening techniques, the roughened surface is randomly patterned. As a result, there is little control in defining the surface pattern or bone engaging interface. Therefore, there is a need for bone implants with engineered surfaces to provide controlled bone growth interfaces.
In one aspect, this disclosure is directed to an implant having a body and a bone engaging interface. The bone engaging interface is formed on a portion of the body and is shaped to favor movement of the implant in a first direction and to resist movement in a second direction opposite the first direction.
In another aspect, this disclosure is directed to an intervertebral prosthetic joint that has a first articular component and a second articular component. A first bone engaging surface is defined on a portion of the first articular component and a second bone engaging surface is defined on a portion of the second articular component. Each bone engaging surface provides a migration promoting interface along a first direction and provides an anti-migratory interface along a second direction opposite the first direction.
According to another aspect, this disclosure is directed to an artificial implant having an implant body that includes a bone engaging interface. Cavities are formed by laser machining a portion of the bone engaging surface of the implant body. Bone growth material is then deposited in the cavities.
In yet another aspect, this disclosure is directed to a surgical method for positioning an intervertebral implant. The method includes preparing a disc space for reception of an intervertebral implant. An intervertebral implant is inserted along a first direction into the disc space. The intervertebral implant is then withdrawn from the disc space generally along a second direction opposite the first direction. The implant is withdrawn from the disc space until the implant engages a vertebral body defining the disc space.
This disclosure is also directed to a method of manufacturing an implant. The manufacturing process includes the formation of an implant body. The implant body is laser machined to define a plurality of protrusions and cavities. Bone growth promoting material is deposited into the cavities.
In another aspect, this disclosure is directed to a bone screw. The bone screw has a shaft and a plurality of threads formed thereon. A bone ingrowth cavity is formed in the shaft in a space between a pair of threads.
These and other aspects, forms, objects, features, and benefits of the present invention will become apparent from the following detailed drawings and descriptions.
The present disclosure relates generally to the field of orthopedic surgery, and more particularly to systems and methods for replacing or 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. While the present disclosure will be described with respect to spinal or vertebral implants, it is understood that the present disclosure is also applicable with other implant types, such as hip or knee implants.
Referring to
The articular components 12, 14 are permitted to pivot relative to one another about a number of axes, including lateral or side-to-side pivotal movement about longitudinal axis L and anterior-posterior pivotal movement about a transverse axis T. In a preferred embodiment of the invention, the articular components 12, 14 are permitted to pivot relative to one another about any axes that lies in a plane that intersects longitudinal axis L and transverse axis T. Additionally, the articular components 12, 14 are preferably permitted to rotate relative to one another about a rotational axis R. Although the articulating joint 10 has been illustrated and described as providing a specific combination of articulating motion, it should be understood that other combinations of articulating movement are also possible and are contemplated as falling within the scope of the present invention. It should also be understood that other types of articulating movement are also contemplated, such as, for example, relative translational or linear motion.
Although the articular components 12, 14 of prosthetic joint 10 may be formed from a wide variety of materials, in one embodiment of the invention, the articular components 12, 14 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F799 or F-75). However, in alternative embodiments of the invention, the articular components 12, 14 may be formed of other bio-compatible metallic materials such as titanium or stainless steel, a bio-compatible polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art. The surfaces of the articular components 12, 14 that are positioned in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the surface of the articular components 12, 14 that are positioned in direct contact with vertebral bone include bone growth promoting interfaces, which will be described in greater detail below.
Articular component 12 includes a support plate 16 having an articular surface 18 and an opposite bearing or bone engaging surface 20. Support plate 16 is sized and shaped to substantially correspond to the size and shape of an end plate of an adjacent vertebra (not shown). The articular component 12 also includes a tool engaging groove 22 defined between the articular surface 18 and the bone engaging surface 20, and is designed to receive a tool or other instrument to aid in the placement of the joint between vertebral members.
Articular component 12 includes a concave recess (not shown) formed in the convex articular surface 18 of support plate 16. Preferably, the concave recess has a semi-spherical shape sized to receive a correspondingly shaped projection 24 of articular component 14. Projection 24 extends from substantially planar articular surface 26 of support plate 28 of articular component 14. Opposite of articular surface 26 is bearing or bone engaging surface 30. Similar to articular component 12, a groove 32 designed to receive a corresponding portion of a surgical tool or instrument is formed between the articular surface 26 and bone engaging surface 30 in support plate 28. Extending from the respective bone engaging surfaces 20, 30 of articular components 12, 14 are flange members or keels 32, 34. The keels are sized to fit within an opening formed in adjacent vertebral endplates (not shown). The keels preferably extend perpendicularly from the bone engaging surfaces and are centrally disposed so as to divide the respective bone engaging surfaces in half. Each keel preferably includes a pair of openings 36, 38 to facilitate bone-through growth to promote fixation to adjacent vertebra. While only two openings are shown, it is contemplated that the keels may be constructed to have any number of openings. Additionally, while only a single respective keel is shown extending from the bone engaging surfaces, it is contemplated that the joint may be constructed to have any number of keels, and those keels can be of different shapes and/or sizes.
Articular component 14 also includes a tool engaging groove 40 similar to that of articular component 12. Groove 40 is designed to receive a tool or other instrument to aid in the placement of the joint between vertebral bodies.
As referenced above, the bone engaging surfaces of the articular components provide a bone engaging interface that can be deposited with bone growth promoting or cellular material. In a preferred example, the bone engaging surfaces are machined, using a laser, for instance, to provide a controlled interface that, for example, can include cavities, recesses, grooves, and the like for housing seeds of bone growth promoting material. In another example, the bone engaging interfaces can be formed to favor movement of the joint in one direction but resist movement of the joint in an opposite direction. Laser machining the bone engaging surfaces of the joint provides a textured surface that, unlike chemical etching or plasma spraying, for example, is not necessarily random and thus can be used to develop a pre-defined bone engaging interface. In one example, a pulsing Nd:YV04 laser is used to machine the bone engaging surfaces of the joint. However, it is recognized that other lasers may be used. It also recognized that the bone engaging surfaces may be machined using Electrical Discharge Machining (EDM) or other machining techniques.
In the illustrated example, the protrusions are formed by machining the body 48. As shown, in this example, the protrusions are identically shaped, sized, and spaced. However, it is contemplated that the protrusions may be machined to be non-uniformly shaped, sized, and/or spaced. Moreover, while only a portion of the bone engaging interface of keel 32 is shown, it is recognized that other portions of the bone engaging interface may be differently constructed from that shown in
Also, while only the bone engaging interface of a keel has been shown and described, it is understood that other bone engaging surfaces of the joint may be machined to form a bone engaging interface similar to that described herein.
Referring now to
As illustrated, the height of the protrusions 62 increases from left-to-right along the profile of the bone engaging interface 60. In one preferred example, the direction of descending protrusion height, as indicated by arrow A, coincides with the direction of implantation. That is, the bone engaging interface 60 is constructed such that end 64 represents the leading edge of the interface and end 66 represents the trailing edge of the interface. This configuration of the bone engaging interface 60 allows the implant to bite in or otherwise engage the adjacent vertebral member when being implanted. Additionally, when preparing the vertebral member for the keel, for example, a slight taper can be cut into the vertebral member that matches the taper provided by the bone engaging interface 60.
Bone engaging interface 60, as referenced above, is designed to scratch or otherwise bite into the vertebral member when implanted in the vertebral member. Specifically, the trailing walls 68 of protrusions 62 are angled to engage the vertebral member when the implant is inserted into the vertebral member. As a result, cellular material can be scraped from the vertebral member and into the cavities 66 during implantation. This cellular material can then help promote bone growth into the cavities 66. Further, the height and angle of the trailing walls 68 can be controlled during fabrication to provide a desired degree of bio-scraping. In other words, the amount of cellular material scraped from the vertebral member and deposited in cavities 66 can be controlled by precise formation of the bone engaging interface. The leading walls 70 of the bone engaging interface 60 bite into the vertebral member along a direction opposite the direction of implantation. In this regard, when loaded, the bone engaging interface is locked relatively in place.
In the example illustrated in
In the example illustrated in
The bone engaging interfaces have been described above as being formed on a bone engaging surface of a keel or other member of an articulating prosthetic joint. The bone engaging interfaces have been described as having protrusions that, in one example, are angled to assist with implantation but also provide a bio-locking. In this regard, it is contemplated that the draft of the protrusions can be machined to provide a desired release-ability. That is, with more draft, it would be more difficult to release or remove the implant after bone ingrowth. On the other hand, with less draft, it would be easier for a surgeon to remove the implant after bone ingrowth and, such removal could be done without significant bone loss. Also, it is noted that in the example of
Heretofore, the present disclosure has been described with respect to joint replacements. The present disclosure, however, is not so limited. The present disclosure can be implemented with other implantable devices, such as a bone screw. A representative bone screw is shown in
Bone screw 88 includes a shaft 90 connected to a curvate head 92. Curvate head 92 has a centrally disposed notch 94 configured to receive the driving end of driving instrument. Bone screw 88 includes a series of threads 96 formed circumferentially around shaft 90. The screw is configured to sit within a rod-receiver coupler (not shown) designed to hold a stabilization rod. The shaft 90 of bone screw 88 includes, in the illustrate example, three engineered bone engaging interfaces 98. These areas of the shaft 90 are, in the illustrated example, disposed between adjacent threads 96 to define bone growth promoting areas along the bone screw. In the illustrated example, the bone engaging interfaces do not extend circumferentially around the shaft 90; however, it is contemplated that an engineering surface may be formed circumferentially around shaft 90.
The present disclosure has been described with respect to a representative intervertebral prosthetic joint and a representative bone screw; however, the present disclosure is applicable with other implants not specifically described herein. For example, the present disclosure is also applicable with bone plates, cages, and artificial discs. The present disclosure is also applicable with knee, hip, and other anatomical implants in addition to the vertebral implants described herein.
As described herein, the bone engaging interfaces are preferably formed using laser machining. With laser machining the size, shape, orientation, position, depth, and pattern of the bone engaging interfaces can be controlled. In a preferred example, the cavities defined in the bone engaging interfaces have a depth of approximately 100 microns; however, the present disclosure is not so limited. Also, while laser machining has been identified as one technique for engineering the surfaces of an implant, it is recognized that other techniques, such as EDM, could be used for engineering the surfaces of an implant.
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. Further, the embodiments of the present disclosure may be adapted to work singly or in combination over multiple spinal levels and vertebral motion segments. Also, though the embodiments have been described with respect to the spine and, more particularly, to vertebral motion segments, the present disclosure has similar application to other motion segments and parts of the body. 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.
