BONE PLATE STABILIZATION SYSTEM AND METHOD FOR ITS USE
An example device for implantation into a patient at a location between two bone bodies.
This application claims the benefit of priority from and incorporates herein by reference in their entirety all of the several applications identified herein. Specifically, this application claims the benefit of, as a continuation-in-part application of, U.S. patent application Ser. No. 11/735,723 filed Apr. 16, 2007, which in turn claims benefit of, as a non-provisional application of, U.S. Provisional Patent Application No. 60/745,294 filed Apr. 21, 2006, and which also in turn claims benefit of, as a continuation-in-part application of, U.S. patent application Ser. No. 11/620,255 filed Jan. 5, 2007, now U.S. Pat. No. 8,100,976, and, as a continuation-in-part application of, U.S. patent application Ser. No. 11/248,651 filed Oct. 12, 2005, now U.S. Pat. No. 7,985,255, both of which just-identified applications (Ser. Nos. 11/620,255 and 11/248,651) claim benefit of and are continuations-in-part applications of U.S. patent application Ser. No. 10/419,652 filed Apr. 21, 2003, now U.S. Pat. No. 6,984,234, the contents of all of which are incorporated herein by reference in their entirety.
FIELD OF THE INVENTIONThe present invention relates generally to implant devices for the fixation and support of bone bodies. In particular, the present invention relates to an implant device that provides and controls limited movement between bone bodies during fusion, having subsidence control.
BACKGROUND OF THE INVENTIONThe spinal column of vertebrates provides support to bear weight and protection to the delicate spinal cord and spinal nerves. The spinal column comprises a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior which covers the neural structures. Between each vertebral body is an intervertebral disk, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior the laminar arch covers the neural structures of the spinal cord and nerves for protection. At the junction of the arch and anterior vertebral body are articulations to allow movement of the spine.
Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disk or the articulating joints, traumatic disruption of the disk, bone or ligaments supporting the spine, tumor or infection. In addition congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) anterior of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurologic damage if the conditions are not treated appropriately.
One technique of treating these disorders is known as surgical arthrodesis of the spine. This can be accomplished by removing the intervertebral disk and replacing it with bone and immobilizing the spine to allow the eventual fusion or growth of the bone across the disk space to connect the adjoining vertebral bodies together. The stabilization of the vertebra to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal, much like placing a cast on a fractured bone. Such techniques have been effectively used to treat the above described conditions and in most cases are effective at reducing the patient's pain and preventing neurologic loss of function. However, there are disadvantages to the present stabilization devices.
The spinal fixation device needs to allow partial sharing of the weight of the vertebral bodies across the bone graft site. Bone will not heal if it is stress shielded from all weight bearing. The fixation device needs to allow for this weight sharing along with the micromotion that happens during weight sharing until the fusion is complete, often for a period of three to six months or longer, without breakage. The device must be strong enough to resist collapsing forces or abnormal angulation during the healing of the bone. Loss of alignment during the healing phase can cause a poor outcome for the patient. The device must be secure in its attachment to the spine to prevent migration of the implant or backout of the screws from the bone which could result in damage to the structures surrounding the spine, resulting in severe and potentially life threatening complications. The device must be safely and consistently implanted without damage to the patient.
Several types of anterior spinal fixation devises are in use currently. One technique involves placement of screws all the way through the vertebral body, called bicortical purchase. The screws are placed through a titanium plate but are not attached to the plate. This device is difficult to place, and over penetration of the screws can result in damage to the spinal cord. The screws can back out of the plate into the surrounding tissues as they do not fix to the plate. Several newer generation devices have used a unicortical purchase of the bone, and in some fashion locking the screw to the plate to provide stability and secure the screw from backout. Problems have resulted from over ridged fixation and stress shielding, resulting in nonunion of the bony fusion, chronic micromotion during healing resulting in stress fracture of the fixation device at either the screw or the plate, insecure locking of the screw to the plate resulting in screw backout, or inadequate fixation strength and resultant collapse of the graft and angulation of the spine.
These devices are often designed to support and bridge across a group of vertebrae, for example a group of three. Because these devices are typically bridged across the bone, for example in the cervical region, they occasionally aggravate the esophagus, making it difficult for one to swallow food. In addition, the screws are installed into the bone normal, i.e., 90° to the plate's surface. Local angularity in the vertebral column often causes high shearing stresses to be applied to the screws. These stresses may fatigue the screws or cause deformation of the screw holes.
Thus, there is a need for a device and method of supporting adjacent vertebrae that avoids these problems and risks to the patient.
Bone mechanical properties greatly influence the stiffness of vertebra-implant-vertebra constructs. Bone properties are a function of many factors including bone mineral density, age, and sex. For comparative purposes, it will be assumed that bone properties are constant in the following discussions. Preparation of the bone to receive the implant can influence strength and stiffness. Again, for comparative purposes, it will be assumed that bone preparation is not a variable except when specifically discussed.
Interbody devices are typically classified as threaded cylinders or screws (e.g., BAK C), boxes (usually tapered rectangular boxes with ridges like the Brantigan cage), or vertical cylinders (e.g., Harms cage). Threaded cylinders usually have small pores and graft material is located inside the hollow interior of the cylinder. Device stiffness might be an issue for such designs. Boxes and vertical cylinders are generally open structures and in these devices a combination of device stiffness and subsidence are responsible for loading the graft.
The stiffness of a material and the stiffness of the structure (device) are often confused. Material stiffness is quantified by Modulus of Elasticity, the slope of the stress-strain curve. Steel has a high modulus, and gold has a low modulus. Structural or device stiffness is a function of dimensions of the part and the material from which the part is made. For example, steel is a very stiff material. However, when formed into the shape of a structure like a paperclip it is easily bent. Stiffness of an assembly or construct can be influenced by connections. While a paperclip and even a piece of paper are strong in tension, when assembled with a piece of paper a paperclip can be easily pulled off because they are only held together by friction.
The same analogy holds for inter-vertebral implants. For instance, consider a simplified construct consisting of a bone block, an interbody device, and a bone block, stacked on top of each other and loaded in compression. If the device is made from a low modulus material but has a large footprint on the bone, and conforms very well to the bone, the assembly can be very stiff in compression. The slope of the load-deflection curve would be steep. A device made from a high modulus material that has a small footprint on the bone and sharp edges might simply punch into the bone under compressive load. The slope of the load-deflection curve would be low, making the construct appear very compliant despite the fact that the device is rigid.
The terms flexibility and stiffness are used in connection with both the range of motion of the spine and the mechanical performance of implant constructs, and the distinction is not always clearly defined.
The spinal column of vertebrates provides support to bear weight and protection to the delicate spinal cord and spinal nerves. The spinal column includes a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior, which covers the neural structures. Between each vertebral body is an intervertebral disc, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior the laminar arch covers the neural structures of the spinal cord and nerves for protection. At the junction of the arch and posterior vertebral body are articulations to allow movement of the spine.
Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disc or the articulating joints, traumatic disruption of the disc, bone or ligaments supporting the spine, tumor or infection. In addition congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) anterior of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurological damage if the conditions are not treated appropriately.
One technique of treating these disorders is known as surgical arthrodesis of the spine. This can be accomplished by removing the intervertebral disc and replacing it with bone and immobilizing the spine to allow the eventual fusion or growth of the bone material across the disc space to connect the adjoining vertebral bodies together. The stabilization of the vertebra to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal, much like placing a cast on a fractured bone. Such techniques have been effectively used to treat the above-described conditions and in most cases are effective at reducing the patient's pain and preventing neurological loss of function. However, there are disadvantages to the present stabilization devices.
Several types of anterior spinal fixation devices are in use currently. One technique involves placement of screws all the way through the vertebral body, called bicortical purchase. The screws are placed through a titanium plate but are not attached to the plate. This device is difficult to place, and over penetration of the screws can result in damage to the spinal cord. The screws can back out of the plate into the surrounding tissues, as they do not fix to the plate. Several newer generation devices have used a unicortical purchase of the bone, and in some fashion locking the screw to the plate to provide stability and secure the screw from back out. Problems have resulted from over rigid fixation and stress shielding, resulting in nonunion of the bony fusion, chronic micromotion during healing resulting in stress fracture of the fixation device at either the screw or the plate, insecure locking of the screw to the plate resulting in screw back out, or inadequate fixation strength and resultant collapse of the graft and angulation of the spine.
These devices are often designed to support and bridge across a group of vertebrae, for example a group of three. Because these devices are typically bridged across the bone, for example in the cervical region, they occasionally aggravate the esophagus, making it difficult for one to swallow food. In addition, the screws are installed into the bone normal, i.e., 90° to the plate's surface. Local angularity in the vertebral column often causes high shearing stresses to be applied to the screws. These stresses may fatigue the screws or cause deformation of the screw holes.
BRIEF SUMMARY OF THE INVENTIONThe following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
In accordance with an aspect of the present invention, at least one implant device is provided.
The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings.
The present invention relates to a device, such as an implant device that provides and controls limited movement between bone bodies during fusion. The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to similar elements throughout. It is to be appreciated that the various drawings are not necessarily drawn to scale from one figure to another nor inside a given figure, and in particular that the size of the components are arbitrarily drawn for facilitating the understanding of the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention can be practiced without these specific details. Additionally, other embodiments of the invention are possible and the invention is capable of being practiced and carried out in ways other than as described. The terminology and phraseology used in describing the invention is employed for the purpose of promoting an understanding of the invention and should not be taken as limiting.
While some embodiments of the present invention are described for supporting adjacent cervical vertebrae in the anterior region of the vertebrae, persons skilled in the art would recognize that the bone plate of the present invention may be utilized to support adjoining thoracic and lumbar vertebrae in the lateral or posterior regions of the vertebrae. Further, the device and method of the invention is not limited to vertebral bodies, but can also be used to join two other pieces of bone in other parts of the body.
Some aspects provide a bone stabilization plate system for stabilizing two adjacent bones (including bone fragments), such as adjacent vertebral bodies, while they heal, as well as to methods for its use. A useful bone stabilization plate system 10 constructed in accordance with the present invention is shown in
The base plate 20 may be made of any suitable material, and can be made from titanium or a titanium alloy. The thickness of the base plate 20 is not critical, and can range from about 1 mm to about 2 mm, and more specifically is about 1.6 mm. The thickness of the base plate 20 will depend on the particular application.
The secondary member 22 has a front surface 30 that is generally continuous with the top surface 28 of the primary member 21 and a back surface 31 that is generally continuous with the bottom surface 26 of the primary member. The primary member 21 and secondary member 22 are arranged relative to each other so that their top surfaces form an angle α that is greater than 90° and less than 180°, specifically from 110° to about 160°. As will become apparent, the angle at which the primary and secondary members are joined is provided so that bone screws can be introduced through the base plate at desired angles, as discussed further below. Accordingly, the base plate 20 can be designed in any other manner that permits the bone screws to be introduced therethrough at the desired angles.
The primary member 21 includes at least one, and possibly two (as shown in the depicted embodiment) first bone screw holes 42 extending therethrough for receiving a corresponding number of first bone screws 24. The bone screw holes 42 in the primary member 21 are angled relative to the bottom surface 26 of the base plate and primary member so that a first bone screw extending through first a bone screw hole extends through the base plate at an angle relative to the bottom surface, for example, through the corner joining the bottom surface 26 to the side wall 32, as best shown in
The secondary member 22 includes a bone screw hole in the form of an elongated bone screw slot 48 for receiving a second bone screw 25. The second bone screw 25 is introduced into the bone screw slot 48 and into the second vertebral body 16. The bone screw slot 48 is designed so that the second bone screw 25 can slide within the slot relative to the base plate 20 generally toward the first member 21. Thus, in use, as the two vertebral bodies 14 and 16 to which the base plate 20 is fixed collapse or settle and move toward each other, the second bone screw 25 contained within the bone screw slot 48 will slide within the slot and move with the second vertebral body 16 into which it extends in a direction toward the primary member 21 and the first vertebral body 14.
The bone screws 24 and 25 can be made of any suitable material, and can be made of the same material as the base plate 20, such as titanium or a titanium alloy. The bone screws 24 and 25 can all have the same shape, such as that shown in
The system 10 is designed so that the bone screws 24 and 25 are introduced into the vertebral bodies 14 and 15 at an angle other than 90° relative to the bone surface. In one case, the first bone screws 24 are introduced into the first vertebral body 14 so that the axis of each bone screw is at an angle relative to the bone surface ranging from about 20° to about 60°, more specifically from about 40° to about 50°. The second bone screw 25 can be introduced into the second vertebral body 16 so that the axis of the bone screw is at an angle relative to the bone surface ranging from about 20° to about 70°, more specifically from about 45° to about 65°.
The bone stabilization plate system includes a bone screw retaining means, which is any means for securedly covering at least a part of each of the bone screws 24 and 25 so that the bone screws cannot back out from the bone once screwed in through the base plate 20. In the depicted embodiment, the bone screw retaining means comprises a retaining plate 50 and a retaining plate fixing means.
As best shown in
The retaining plate 50 includes at its first end 51 two generally-rounded notches 55 on the sides of its bottom surface 54. When the retaining plate 50 is fixed in place over the base plate 20, the two generally-rounded notches 55 each cover a portion of a corresponding one of the first bone screws 24. The generally-rounded nature of the notches 55 permits the first bone screws 24 to toggle within the first bone screw holes 42.
The retaining plate includes at its second end 52 a U-shaped notch 56, which, in the depicted embodiment, is centered at the edge of the second end. The U-shaped notch 56 includes a generally U-shaped sidewall between the top and bottom surfaces of the retaining plate that is curved outwardly from the top surface 53 to the bottom surface 54 so that the opening formed by the notch is larger at the bottom surface of the retaining plate and smaller at the top surface of the retaining plate. When the retaining plate 50 is fixed in place over the base plate 20, the top of the second bone screw 25 sits within the U-shaped notch 56 with the top of the second bone screw covered by the top surface 53 of the retaining plate. With this design, the second bone screw 25 is permitted to slide and toggle within the bone screw slot 48 even when the retaining plate 50 is fixed over the second bone screw.
The retaining plate 50 also includes a set screw aperture 57 between its first and second ends. The set screw aperture 57 in the retaining plate 50 is aligned with a set screw aperture (not shown) in the base plate 20, both of which can receive a set screw (not shown) for fixing the retaining plate in place over the base plate. The set screw can be made of any suitable material well known in the art, and can be titanium or a titanium alloy. In one embodiment, the set screw is an hexagonal set screw that can be turned with an hexagonal driver. Other types of set screws can also be used, as well as any other suitable mechanism for fixing the retaining plate to the base plate. The precise mechanism by which the retaining plate is fixed to the base plate is not critical to the invention.
Any other suitable bone screw retaining means can be used in connection with the invention. For example, the bone screw retaining means can comprise multiple retaining plates that cover different bone screws. Alternatively, the bone screw retaining means can comprise one or more screws with heads that overlap at least a portion of one or more bone screws to thereby prevent the bone screws from backing out. The precise mechanism by which the bone screws are covered is not critical to the invention.
In the depicted embodiment, the base plate 20 further includes a pair of lateral tabs 60 integrally formed with the primary member 21 and extending outwardly from opposite ends of the bottom surface 26 of the primary member to form, together with the primary member, a unitary substantially U-shaped structure. In use, the lateral tabs 60 extend around the bone graft 12 to prevent lateral shift of the graft and control subsidence of adjacent vertebrae as they set during healing. The lateral tabs 60 may be made of any suitable material, and can be made of the same material as the base plate 20. Each tab 60 includes a generally-pointed nub 66 that extends outwardly from its corresponding tab. The function of the nubs 66 is described further below.
In use, the base plate 20 is placed directly on the bone graft 12 such that the bottom surface 26 contacts the bone graft and the side wall 32 engages a side 70 of the first vertebral body 14, as shown in
The secondary member 22 is secured to the second vertebral body 16 by the second bone screw 25 being received through the bone screw slot 48. The second bone screw 25 received by the bone screw slot 48 penetrates the second vertebral body 16 through the lip osteophite 74. It is possible to anchor the base plate 20 to the vertebral body 16 through the lip osteophite because the lip osteophite is structurally the strongest part of the bone. The angle of the secondary member 22 relative to the primary member 21 and the angle through which the bone screw slot 48 extends through the second member determine the angle at which the second bone screw 25 will be inserted in the second vertebral body 16.
To provide an enhanced fit, a few millimeters of bone can be trimmed or otherwise removed from the lip osteophite 74 of the second vertebral body 16 at an angle corresponding to the angle of the secondary member 22. The trimmed surface provides a substantially flat surface for anchoring the second bone screw 25 into the lip osteophite 74 of the second vertebral body 16.
The angles of the bone screws 24 and 25 relative to the bone surfaces of the vertebral bodies 14 and 16 are particularly important. As note above, the lip osteophite is the strongest part of the bone, and thus angling the bone screws through the lip osteophite increases the ability of the base plate 20 to stay anchored to the vertebral bodies. Moreover, by being angled, each bone screw 24 or 25 is positioned along the angle of rotation of the corresponding vertebral body as well as the angle of settling of the vertebral body. This places each screw in a protected position against motion of the spinal column. As a result, significant sheer forces are not exerted on the screws as the vertebral bodies rotate and settle.
As is generally known in the art, a drilling tool may be used to drill holes in the bone to “tap” or prep the bone for receiving the bone screws 24 and 25. If desired before drilling, a tack tool, a tool having an elongated stem and a removable sharp tack at its distal end, may be used to create a starter hole in the bone to facilitate drilling. After drilling, a tapping tool may be used to tap the drilled holes. Following tapping, the bone screws 24 and 25 are screwed into the drilled and tapped holes through the bone screw holes 42 and the bone screw slot 48 of the base plate 20.
Once the bone screws 24 and 25 are inserted into the bone screw holes 42 and the bone screw slot 48, the retaining plate 50 is placed over the base plate and fixed in place to prevent the screws from “backing out” of the screw holes. The second bone screw 25 that extends through the bone screw slot 48 is nonetheless permitted to slide along the length of the slot, even when the retaining plate 50 is secured in place. Thus, second the bone screw 25 and the bone screw slot 48 cooperate to control any lateral or rotary movement of one vertebral body relative to an adjacent vertebral body during “settling” of the bone. Further, the angled orientation of the second member 22 provides the base plate 20 with resilient properties, for example, enabling the base plate “flex” when one vertebrae is rotated relative to an adjacent vertebrae.
As noted above, all of the bone screws 24 and 25 are possibly permitted to toggle, or pivot, even after the retaining plate 50 is fixed over the base plate 50. The ability of the screws to toggle permits the system 10 to migrate and self-center after it has been implanted.
If the base plate 20 includes lateral tabs 60 with nubs 66, the nubs will also share in the weight-bearing during settling of the vertebral bodies. Specifically, as the vertebral bodies move toward each other during settling, the pointed nubs 66 will contact and slowly enter the second vertebral body 16 to a limited extent. This contact can help in controlling the rate of settling.
In the alternative, relatively smaller (shorter and/or smaller in diameter) bone screws may be used. Because the bone screws penetrate the lip osteophite, which is structurally the strongest portion of the bone, shorter bone screws may be used to anchor the base plate to the bone. Moreover, because the screws are positioned along the angle of rotation of the corresponding vertebral body as well as the angle of settling of the vertebral body, as discussed above, significant sheer forces are not exerted on the screws as the vertebral bodies rotate and settle, thereby minimizing the diameter of screw needed.
The present invention provides an additional benefit of providing a vertebral support device having a “low profile.” Namely, the base plate of the present invention is specially designed to have an outer periphery that coincides with or generally matches the outer diameter of the cortex. The top surface of the base sits at, and possibly below, the top surface of the vertebral bodies. As such, the bone plate system of the present invention does not have any parts that would significantly interfere with or irritate the trachea, esophagus, and/or other sensory nerves of the user.
Another advantage of the present bone plate system is that it is stackable. Frequently after a bone graft is inserted and a bone plate joined to the surrounding vertebral bodies, for example, C4 and C5, an adjacent disk, for example, between C5 and C6, subsequently deteriorates. With traditional bone plates, it would be necessary to remove the plate from C5 before attaching a second bone plate to C5 and C6 because each plate covers a significant surface of the vertebral body. To remove a bone plate, it is necessary cut through scar tissue, which can have a negative impact on the patient. In contrast, the bone plate systems of the present invention cover an insignificant portion of the top surfaces of the vertebral bodies to which it is attached, instead being located primarily between the vertebral bodies. As a result, multiple bone plate systems can be introduced over adjacent bone grafts (i.e., between a common vertebral body) so that two bone plate systems are attached to a common vertebral body without the bone plate systems contacting one another. Thus, subsequent procedures where new bone grafts are to be inserted do not require the removal of a pre-existing bone plate prior to introduction of a new bone plate. The depicted systems where the bone screws are provided in a generally triangular arrangement further enhances the stacking ability of the bone plate systems of the invention.
It is presently considered to provide a kit having base plates of different sizes, bone screws of differing lengths and retaining plates complementary to the base plates. The kit may further comprise a tack tool, a drilling tool, tapping tool and/or one or more screw driving tools.
Referring to
The interbody device 110 also includes a restraining means for restricting movement of one or more bone fasteners 150 coupled to the base member 120. The restraining means can be any means for securely covering at least a part of each of the bone fasteners 150 so that the bone fasteners 150 cannot back out from the bone bodies once screwed in through the base member 120 of the device 110. In the depicted embodiment, the bone screw restraining means comprises a restraining plate 160 and a restraining plate fixing means 170.
Turning now to
Subsidence is further controlled by the presence of the interface members 130 that extend from a portion of the base member 120. The interface members 130, as depicted in the present embodiment, can include a plurality of teeth extending from bottom surfaces of the primary member 200, the first leg 220, and the second leg 230. Accordingly, when coupled with the bone bodies, the interface members 130 extend from the base member 120 in a direction that is aligned with an elongate direction of the spine. The interface members 130 thus, are configured to provide a progressive penetration into the bone body over a period of time in a direction aligned with the elongate direction of the spine. It is to be appreciated, however, that any suitable configuration of interface members can be provided at any suitable location on the base member that interfaces with a surface of the bone body.
The interface members can include teeth, knife-edges, spikes, posts, pegs, and the like, including any combination thereof. The configuration of the interface members includes interlocking external features that impact a subsidence profile, which is a relationship between an applied load and an amount of settling the interbody device 110 experiences when secured to the bone bodies. Or in other words, the subsidence profile is a relationship between a depth of subsidence of the interface members and a force required to achieve the depth of subsidence. When first implanted, the interface members 130 will rest on top of the bone surface. When load is applied to the interbody device 110, the interface members 130 will penetrate, or subside, into the bone in a controlled manner. The interface members can readily dig into the bone initially and then slow down as more of the tooth cross section embeds. Different interface member configurations provide different controlled subsidence profiles. The density of the bone body also impacts the subsidence profile. For example, in a lower density bone body representation, such as 15 pcf foam, the interface members can penetrate the bone body by about 1 mm using between about 50-100 N of force and by about 2 mm using between about 150-250 N of force. In a medium density bone body, such as 20 pcf, the interface members can penetrate the bone body by about 1 mm using between about 100-200 N of force and by about 2 mm using between about 400-900 N of force. In a higher density bone body, such as 40 pcf, the interface members can penetrate the bone body by about 1 mm using between about 100-500 N of force and by about 2 mm using between about 1000-2250 N of force. The amount of force needed for displacement and the rate of penetration of the interface members into the bone body depends, in part, upon the configuration of the interface members. It should be noted that all of the pcf densities refer to polyurethane foam (which is referenced to ASTM standards) that is used as a bone analog for test purposes. The tests were also conducted using a straight test “blade” that was 40 mm long, not an actual implant.
The height (H) of the interface members 130 determines a depth of penetration into the bone body (see
In addition to the height (H) of the interface members 130, the shape of the interface members 130 also affects subsidence of the interbody device 110. The shape of the interface members 130 controls a shape of the subsidence profile; and therefore, affects the load shared with the graft material. For instance, if the interface members 130 were limited to a few sharply pointed spikes, subsidence would occur substantially immediately and the interbody device 110 would rapidly seat in the bone to the fullest extent under low force. In this instance, any graft material would be immediately and highly loaded. Such immediate subsidence is not desirable because the joint space could narrow and cause nerve root or spinal cord compression. Also, the graft would be overloaded, inhibiting fusion. However, some subsidence is needed to load the graft and ensure fusion. Accordingly, by configuring the interface members 130 to have a broadly shaped portion, the interbody device 110 has increased resistance to subsidence as the interface members 130 penetrate into the bone body; and the graft material is gradually loaded as the device subsides. For instance, turning to
Once the interface members 130 have fully penetrated the bone, the surface area of the base member 120 is of an area large enough to resist further subsidence of the interbody device 110. To increase subsidence resistance, at an interface between the a plurality of teeth 130 and the bottom surfaces of the primary member 200 and the first and second legs 220, 230, a shelf-like area 235 is created. The shelf-like area 235 provides an extended surface area to contact the bone material, thereby increasing subsidence resistance once the interface members 130 have fully subsided. As mentioned, the screw will typically be at the end of the slot.
Turning back to the primary and secondary members 200, 210 of the base member 120, the secondary member 210 has a front surface that is generally continuous with a front surface of the primary member 200, as illustrated in
The primary member 200 includes at least one, and possibly two (as shown in the depicted embodiment) first bone screw holes 240 extending therethrough, each configured to receive a corresponding bone screw. The first bone screw holes 240 in the primary member 210 are configured such that bone screws extend through the holes 240 at an angle, as illustrated in
The secondary member 210 includes a second bone screw hole 280 in the form of an elongated slot for receiving a bone screw. The bone screw is introduced into the second bone screw hole 280 and into a second bone body. The second bone screw hole 280 is configured such that a bone screw can slide and rotate within the slot relative to the base member 120 and generally toward the primary member 200. Thus, in use, as two adjacent bone bodies, to which the base member 120 is fixed, collapse or settle and move toward each other, the bone screw contained within the second bone screw hole 280 will slide within the slot and move with the bone body into which it extends in a direction toward the primary member 200 and the other bone body.
At least one and possibly two projections 283 extend upwardly from the top surface 250 of the base member 120. The projections 283 contact a surface of the bone bodies to provide a stop when inserting the base member 120 between the bone bodies. The base member 120 also includes holes 287 provided through each of the first and second legs 220, 230. The holes 287 facilitate visualization of the fusion mass on x-rays and bone growth therethrough when the interbody device 110 is positioned between two bone bodies.
The base member 120 may be made of any suitable material, and can be made from titanium or a titanium alloy. The thickness of the base member 120 is not critical, and possibly ranges from about 1 mm to about 2 mm, and more specifically is about 1.6 mm. The height of the base member 120 will depend on the needs of the particular patient.
Turning now to
The bone fasteners 150 can be undersized to permit the bone fastener to slide in a bone screw hole. For instance, the bone fastener may be positioned in a bone body such that the retaining portion, such as the head, does not rest on the seat of the hole and the portion of the bone fastener extending into a bone body is not fully embedded. In this case, it is desirable that the portion of the bone fastener extending into a bone body is substantially small. Reducing the non-embedded portion of the bone screw tends to ensure that the retaining portion of the bone fastener does not protrude outward from the hole in a manner that renders it difficult to position a retaining means over the bone fastener. To permit the bone fastener 150 to slide in the hole, the diameter of the portion extending into a bone body is substantially less than the diameter of the hole. The bone fastener 150 can be positioned at one edge of the hole so that the bone fastener may slide within the diameter of the hole until it becomes in contact with the opposite edge of the hole. The hole in this case functions as an elongated slot as described with regard to
The bone fasteners are secured to the base member 120 via restraining means. As stated above, the restraining means can include a restraining plate 160, an example of which is illustrated in
Turning to
The restraining plate 160 also includes an aperture 370 formed therethrough. The aperture 370 in the restraining plate 160 is aligned with a hole 270 in the primary member 210 of the base member 120, both of which can receive a restraining member fastener 170 for fixing the restraining plate 160 in place over the base member 120. The restraining member fastener 170 can be made of any suitable material well known in the art, possibly titanium or a titanium alloy. The restraining member fastener 170 can be a screw, such as a hexagonal screw that can be turned with a hexagonal driver. Other types of fasteners can also be used, as well as any other suitable mechanism for fixing the restraining plate 160 to the base member 120. In one embodiment, the mechanism does not permanently fix the restraining plate 160 to the base member 120 so that device 110 can be removed if desired. The precise mechanism by which the restraining plate 160 is fixed to the base member 120 is not critical to the invention.
In one embodiment the restraining plate 160 functions to prevent the bone screws 150 from backing out of the bone bodies once the bone screws 150 are screwed in. That is, the notches 350 and the U-shaped notch 360 cover the bone screws 150 extending through the base member 120 such that the top surface of the restraining plate 160 does not come into contact with the bone screws 150. When the restraining plate 160 is fixed in place over the bone screws 150, the top surface of the restraining plate 160 does not interfere or contact the bone screws 150 as they toggle or slide in the bone screw hole 140 or slot 280. The top surface of the restraining plate 160 contacts or restricts the movement of the bone screws when the bone screws 150 back out or loosen from the bone bodies. Thus, during normal use of the implanted device 110, the restraining plate 160 does not tend to impede the movement of the bone screws 150.
In another embodiment, which is not shown, the restraining plate 160 can have a top surface and/or notches that contact or interface with the head of at least one bone screw 150. The interface between the top surface or notch of the restraining plate 160 and a corresponding bone screw 150 prevents the bone screw 150 from backing out of the bone body and tends to exert force on the bone screw 150 so as to control the movement of the screw 150 in the hole 240 or slot 280 of the base member 120. Depending on the surface dimensions of the restraining plate 160 and the shape of the bone screw 150 head, the interface between the plate 160 and a bone screw 150 can control the amount of toggle or slide of a bone screw 150. For example, the restraining plate 160 can include a notch configured to match the rounded head of a corresponding bone screw 150, wherein the notch also has a stop plate or restraining surface. When the bone screw 150 toggles in the slot of the base member 120, the head rotates along the interface with the corresponding notch in the restraining plate 160 until the head of the bone screw 150 reaches the stop plate. In this regard, the top surface or notch of the restraining plate 160 can be designed so the interface with a bone screw 150 can be used to control the amount of movement or resistance a bone screw 150 is subject to in order to create resistance to movement thereof.
In yet another embodiment, which is not shown, the surface portions of the restraining plate 160 that interface with the bone screws 150 can be substantially angled such that the interface portions of the restraining plate 160 are flush with the top surface of the bone screw 150 heads. That is, the surface portions of the restraining plate 160 that interface with the top surface of the bone screw 150 heads rest flat against the heads and restrain the bone screws from toggling or rotating in the hole or slot the bone screws 150 extend through. In the case which the bone screw 150 extends through a slot in the interbody device 110, the restraining plate 160 can also include a stop plate that extends from the surface of the restraining plate 160 into the slot. When the bone screw 150 is at one end of the slot, the stop plate extending downward into the slot can prevent the bone screw 150 from sliding along the entire elongation length of the slot. The stop plate can be positioned at any point along the elongation length of the slot so that the distance the bone screw 150 slides in the slot can be controlled. Subsidence resistance can also be controlled in part by the positioning of the stop plate in the slot. For example, if the stop plate is positioned near the opposite end of the slot from the end where the bone screw 150 is located, the bone screw 150 can slide along substantially the entire elongation length of the slot and thus subsidence resistance may be decreased. On the other hand, if the stop plate is positioned near the location of the bone screw 150 in the slot, the distance the bone screw 150 can slide along the elongation length of the slot is decreased and subsidence resistance may be increased.
Additionally, it is to be appreciated that any other suitable bone screw restraining means can be used in connection with the present invention. For example, the bone screw restraining means can comprise multiple restraining plates that cover different bone screws. Alternatively, the bone screw restraining means can comprise one or more screws with heads that overlap at least a portion of one or more bone screws to thereby prevent the bone screws from backing out.
To provide an enhanced fit, a few millimeters of bone can be trimmed or otherwise removed from a lip osteophyte of the second vertebral body 390 at an angle corresponding to the angle of the secondary member 210 of the base member 120. The trimmed surface provides a substantially flat surface 400 for anchoring the bone screw 150 into the lip osteophyte of the second vertebral body 390. The surface also accommodates sliding of the tab as the teeth subside into the second vertebral body 390.
The angles of the bone screws 150 relative to the bone surfaces of the vertebral bodies 380, 390 are important. The lip osteophyte is the strongest part of the bone, and thus angling the bone screws 150 through the lip osteophyte increases the ability of the base member 120 to stay anchored to the vertebral bodies 380, 390. Moreover, by being angled, each bone screw 150 is positioned along an angle of rotation of a corresponding vertebral body 380, 390 as well as an angle of settling of the vertebral body 380, 390. This places each screw 150 in a protected position against motion of the spinal column. As a result, significant shear forces are not exerted on the screws 150 as the vertebral bodies 380, 390 rotate and settle.
A first guide tool 410 as illustrated in
A second guide tool 440 is illustrated in
In another embodiment, the bone screw 150 configured to pass through the apertures in the base member 120 can have pointed ends which comprise a cutting flute on the tip. The cutting flute at the tip of the bone screw 150 allows the screw to be self-drilling or self-tapping. Thus, the use of a bone screw 150 having a self-drilling or self-tapping tip makes the use of a drill or center punch optional.
Turning back to
As shown in
Another advantage of the interbody device 110 is that it is stackable. Frequently after a bone graft is inserted and a bone plate joined to the surrounding vertebral bodies, for example, C4 and C5, an adjacent disk, for example, between C5 and C6, subsequently deteriorates. With traditional bone plates, it would be necessary to remove the plate from C4-C5 before attaching a second bone plate to C5 and C6 because each plate covers a significant surface of the vertebral body. To remove a bone plate, it is necessary dissect scar tissue, which can have a negative impact on the patient. In contrast, the interbody device 110 of the present invention covers an insignificant portion of the top surfaces of the vertebral bodies to which it is attached, instead being located primarily between the vertebral bodies. As a result, multiple interbody devices can be introduced over adjacent bone grafts (i.e., between a common vertebral body) so that two interbody devices are attached to a common vertebral body without the bone plate systems contacting one another. Thus, subsequent procedures where new bone grafts are to be inserted do not require the removal of a pre-existing device prior to introduction of a new device. The depicted systems where the bone screws are provided in a generally triangular arrangement further enhance the stacking ability of the interbody devices of the invention.
It is to be appreciated that a kit having base plates of different sizes, bone screws of differing lengths and restraining plates complementary to the base plates can be provided. For instance, because of the different physical dimensions of the patients on whom the invention is used, it is considered that bone plate systems of correlative dimensions be available. The present invention is capable of being provided in various sizes for that purpose.
As noted above, all of the bone screws 150 may be permitted to toggle, or pivot, even after the restraining plate 160 is fixed over the base member 120. The ability of the screws 150 to toggle permits the interbody device 110 to migrate and self-center after it has been implanted.
The base member 120 is configured such that when first installed on the cervical vertebrae, the interface members 130 contact a surface of at least one of the bone bodies. For instance, in the present example, the base member 120 is positioned between the vertebrae 380 and 390 such that the top surface 250 of the base member 120 contacts an end surface of one vertebral body 380 and the interface members 130 contact an end surface of the other vertebral body 390. As discussed above, the interface members 130 are configured such that substantially immediate penetration does not occur. Rather, the interbody device 110 gradually subsides as the vertebrae and bone graft fuse to share in the weight bearing during settling of the vertebral bodies. Specifically, as the vertebral bodies move toward each other during settling, the interface members 130 will contact and enter the second vertebral body 390 with increased resistance to subsidence. This contact controls the rate of settling.
The interbody device 110 provides such an interface design by controlling the height, size, shape, and spacing of the teeth that interdigitate with the endplate of the vertebral body. In addition screw fixation is provided. The length of screw travel in the slot 280 is possibly matched to the height of the interface members 130. Accordingly, subsidence is arrested once the bone screw 150 reaches the intended limit as provided by the slot 280. Screw fixation also addresses expulsion of the interbody device, a concern common to all interbody devices. The interbody device 110 accommodates a large graft surface area further increasing the probability that fusion will occur.
The interbody device 110 as described above can have a variety of alternative configurations. Various configurations can include, but are not limited to, those shown in
The interbody device 110 of
The primary member 200 of the interbody device 110 has a plurality of interface members 130 extending from the bottom surface. The interface members 130 can comprise, for example, teeth, knife-edges, spikes, posts, pegs, or combinations thereof. The interface members 130 provide a controlled subsidence interface between the interbody device 110 and a corresponding bone body. Although not shown in
As illustrated in
The elongated slots 242, 280 of the primary and secondary members 200, 210 in
Although
The elongation length of the at least one slot 242 in the primary member 200 can be substantially the same as, less than or greater than the elongation length of the at least one slot 280 in the secondary member 210 depending on the desired controlled subsidence profile. Varying the elongation length of at least one slot 242, 280 can mitigate the effects that poor bone quality or an irregular surface of a bone body can have on the controlled subsidence profile. In the case that the elongation length of any one slot 242, 280 is matched to or about the same as the height of the interface members 130, 132, further subsidence resistance can occur after the bone screw slides relative to the interbody device 110 the intended limit as provided by the elongation length of the slot 242, 280. As at least one interface member 130, 132 becomes fully penetrated into a bone body, at least one bone screw becomes positioned at the end of the slot 242, 280 the screw extends through. As the bone screw rests at the end of the slot 242, 280, further subsidence resistance can occur as the bone screw toggles at the end of the slot 242, 280. The toggling of the bone screw at the end of the slot 242, 280 permits the interface members 130, 132, of which some members 130, 132 may not be fully embedded in a bone body, to further penetrate into the bone body. In theory, without being bound thereto, one reason for the continued penetration of a fully-embedded interface member 130 into a bone body is poor bone quality. In another aspect, the surface of a bone body can be irregular such that a substantially flat or flush surface is not available on which the shelf-like bottom or top surface of the primary member 200 can rest. The irregular surface of a bone body can result in some of the interface members 130 not becoming fully embedded in a bone body. Depending on the degree of irregularity of a bone body surface, some of the interface members 130, 132 may also not be in contact with a bone body when the bone screw 150 slides relative to the interbody device 110 to the end the slot 242, 280. Therefore, as discussed above, toggling of the bone screw at the end of the slot 242, 280 can force the interface members 130, 132 that are not fully embedded in a bone body to penetrate further and become fully embedded.
In the case that the elongation length of any one slot 242, 280 is less than the height of the interface members 130, 132, the bone screw tends to not reach or slide to the end of the slot 242, 280 prior to any single interface member 130, 132 becoming fully embedded into a bone body. Thus, the subsidence resistance is increased when the elongation length of any one slot 242, 280 is less than the height of at least one single interface members 130, 132. In use, as the interface members 130, 132 begin to penetrate into a bone body, but before any single member becomes fully embedded, a bone screw may slide along the elongation length of the slot 242, 280 and reach the end of the slot 242, 280. Being positioned at the end of the slot 242, 280, the bone screw is forced to toggle so the interface members can further penetrate into a bone body and thus subsidence resistance is increased. In this instance, toggling of the bone screw at the end of the slot 242, 280 can assist the interface members 130, 132 that are not fully embedded in a bone body to penetrate further and become fully embedded.
In the case that the elongation length of any one slot 242, 280 is greater than the height of the interface members 130, 132, the bone screw tends to not reach or slide to the end of the slot 242, 280 prior to any single interface member 130, 132 becoming fully embedded into a bone body. Increasing the length a bone screw can travel or slide in a slot 242, 280 can decrease subsidence resistance. For example, an irregular bone body surface can cause at least one interface member 130, 132 to become fully embedded in a bone body before a bone screw slides relative to the interbody device 110 to the end of the slot 242, 280. The bone screw in this instance can continue to slide along the elongation length of the slot 242, 280 as the remaining interface members 130, 132 continue to further penetrate into a bone body surface. The additional distance or length the bone screw 150 can travel before reaching the end of the slot 242, 280 generally makes it unnecessary for the bone screw 150 to toggle in slot 242, 280 to ensure that the interface members 130, 132 become fully embedded in a bone body. The subsidence resistance profile in this case would be substantially lower because, in part, the bone screw generally does not need to toggle in the slot 242, 280 in order to ensure the interface members 130, 132 become fully embedded. Further, the bone screw 150 in this case will not generally rest at the end of the slot 242, 280, which can increase the subsidence resistance.
In another aspect, the elongation length of any one slot 242, 280 of the interbody device 110 of
As can be seen above with regard to the interbody device 110 of
Turing to
Each elongated slot 242, 280 of
In one aspect, the height of the interface members 130, 132 may be about half of the overall desired controlled subsidence distance. For example, if it is desirable to have a total of 2 mm of penetration into the corresponding bone bodies, the top interface members 132 and bottom interface members 130 may each respectively have a height of about 1 mm. In another aspect, the interface members 130, 132 may each respectively have about 1 to 99 percent of the overall desired subsidence control. In yet another aspect, interface members 132 can be located on only the top surface of the first leg 220, second leg 230 or primary member 200 (see
In another aspect, the single screw hole 282 in the secondary member 210 of the interbody device 110 of
Although not shown in
In another embodiment, the various configurations of the interbody device 110, including but not limited to those shown in
While shown embodiments of the present invention are described for supporting adjacent cervical vertebrae in the anterior region of the vertebrae, persons skilled in the art would recognize that the bone plate of the present invention may be utilized to support adjoining thoracic and lumbar vertebrae in the lateral or posterior regions of the vertebrae. Further, the device and method of the invention is not limited to vertebral bodies, but can also be used to join two other pieces of bone in other parts of the body.
Referring initially to
As shown in
The base member 520 is configured such that when first inserted between two adjacent bone bodies, the interface members 530 contact a surface of at least one of the bone bodies. The interface members 530 are configured such that substantially immediate penetration into a bone body occurs. The implant device 510 gradually subsides as the bone bodies and bone graft fuse to share in the weight bearing during settling of the bone or vertebral bodies. Specifically, as the bone bodies move toward each other during settling, the interface members 530 will penetrate the bone bodies with increased resistance to subsidence.
Controlled subsidence relates to resistance to subsidence and total amount of subsidence. To promote controlled subsidence, the interface members 530 may extend from a surface of the base member in a direction that is aligned with an elongate direction of two adjacent bone bodies, such as two vertebrae in a spine. The interface members are thus configured to provide progressive penetration into a bone body over a period of time. The subsidence profile, which is a relationship between an applied load and an amount of settling the implant device 510 experiences when secured to the bone bodies, is dependent on the configuration or shape of the interface members 530. For example, the interface members 530 can readily penetrate into a bone body initially and then slow down as more of the interface member cross section embeds. The height (H) of the interface members 530 relative to the depth of penetration into a corresponding bone body. Generally, when the implant device 510 has subsided to a point where the interface members are fully embedded in the bone, the applied load will be distributed across the entire surface of the implant device 510 and subsidence resistance will increase. The controlled subsidence relationship between the interface members 530 and the at least one corresponding bone body that the members 530 extend into is described herein.
The base member 520 of the implant device 510 includes a primary member 600 and a secondary member 610, which extends from and is angled relative to the primary member 600. The primary member 600 forms an enclosed loop or peripherally-surrounded chamber 692 that is configured to receive and hold fusion material, such as a bone graft. As shown, the chamber 692 is peripherally-surrounded, but not fully enclosed, such that bone bodies residing above and below the chambers 692 can be in contact with fusion material located in the chamber 692. It is to be appreciated, and for the description purposes of the present invention herein, the peripherally-surrounded chamber 692 can be positioned at any angle in order to accommodate the orientation of bone bodies to be fused together. In any case, the chamber 692 can mitigate lateral shift of the fusion material and control subsidence of adjacent bone bodies as they set during fusion. Subsidence is further controlled by the presence of the interface members 530 that extend from a surface of the base member 520. In the present embodiment, the primary and secondary members 600, 610 are contiguous and unitary. The secondary member 610 has a front surface that is generally continuous with a front surface of the primary member 600, and a back surface that is generally continuous with a back surface of the primary member 600. The primary member 600 and secondary member 610 are arranged relative to each other so that their front surfaces form an angle. Of course, the angle is not of great importance and typically depends upon a compromise between low profile and the amount of bone that would need to be removed. Suffice to say that the angle can be any angle (e.g., greater than 90° and less than 180°). However, a typical angle would be in the range, from about 140° to about 170°. The angle at which the primary and secondary members 600, 610 are joined is provided so that bone screws can be introduced through the base member 520 at desired angles. Alternatively, the base member 520 can be designed in any other manner that permits the bone screws to be introduced there through at the desired angles.
The primary member 600 can form the peripherally-surrounded chamber 692 to be of any shape or size to accommodate adjacent bone bodies of various shapes, sizes and positions. The peripherally-surrounded chamber 692 of the present invention is designed to have an outer periphery that coincides with or generally matches the outer diameter of the cortex or adjacent vertebrae. The top surfaces of the implant device 510 sit at, and possibly below, the top surface of the vertebral bodies. As such, the implant device 510 of the present invention does not have any parts that would significantly interfere with or irritate the adjacent anatomic structures of the patient. As shown, the peripherally-surrounded chamber 692 has a rounded-edge rectangular shape that would adequately accommodate two adjacent vertebrae of a spinal column. The primary member 600 generally forms the vertically-open and peripherally-surrounded area 692, when viewed in the implanted position in a spinal column, that can receive and hold fusion material between two or more bone bodies. In use, the primary member 600 laterally extends around an amount of fusion material, such as a bone graft, in order to mitigate lateral shift of the graft and control subsidence of adjacent vertebrae as the vertebrae set during fusion. The fusion material can be packed into the peripherally-surrounded chamber 692 formed by the primary member 600. The chamber 692 of the implant device 510 creates a one-piece fusion material housing that substantially reduces the need for other devices that may be necessary to fuse multiple bone bodies together. The peripherally-surrounded chamber 692 adequately houses fusion material that would generally be supported by a cage design implant. In this case, a plate would generally also be needed to keep the bone bodies and the cage in the desired location. The implant device 510 described herein significantly reduces the cost associated with multiple-device fusion methods such as those associated with the above cage and plate combination devices.
Another advantage of the implant device 510 is that it is stackable. The implant device 510 of the present invention covers an insignificant portion of the top surfaces of the vertebral bodies to which it is attached. As a result, multiple implant devices can be introduced over adjacent bone grafts (i.e., between a common vertebral body) so that two implant devices 510 are attached to a common vertebral body without devices 510 contacting one another. Thus, subsequent procedures where new bone grafts are to be inserted do not require the removal of a pre-existing device prior to introduction of a new device. The depicted systems where the bone screws are provided in a generally triangular arrangement further enhance the stacking ability of the implant devices 510 of the invention. It is to be appreciated that the implant device 510 can be of different scales or sizes, have differing bone screw lengths and restraining plates that are complementary to different physical dimensions of the patients on whom the invention is used and the spinal location or level at which the device is implanted. The present invention is capable of being provided in various sizes for that purpose.
The peripherally-surrounded chamber area 692 provides a retaining region or open area into which fusion material can be packed or loaded. It is possible to load fusion material, such as particulate graft material including bone chips and/or bone paste, into the chamber 692 prior to the insertion of the implant device 510 between adjacent bone bodies such as vertebrae. Bone chips and/or bone paste and possibly in combination with growth factors can be used in place of a block of bone graft material. Often it is the case that bone chips and bone paste are more easily retained in a peripherally-surrounded chamber 692 as opposed to an implant device 510 which has an open posterior end. Thus, a combination of bone chips and bone paste is better retained in a center region of an implant device 510 such as that provided in the Figures shown herein.
In accordance with another aspect of the present invention, any portion or the entire implant device 510 can be constructed from radiotransparent or radiolucent materials. Specifically, in order to facilitate radiographic evaluation of the fusion material and the corresponding bone bodies, the base member 520, primary member 600, secondary member 610, any other portion or component of the implant device 510 or combinations thereof can be constructed from radiotransparent or radiolucent materials. For example, the entire implant device 510 can be constructed from radiolucent material. Radiolucent materials permit x-rays to pass through components of the implant device 510 so that developed x-ray pictures provide more visibility of the fusion material and bone bodies without significant interference, such as imaging artifacts, caused by the device 510. Radiolucent materials enable clear visualization through imaging techniques such as x-ray and computer tomography (CT), whereas traditional metallic or alloy implant materials that are radiopaque can generate imaging artifacts and scatter that prevent a comprehensive inspection of the surrounding tissue, bone and fusion material. Thus, radiolucent materials allow for clearer imaging of bone bodies and fusion materials.
Radiolucent materials can include, but are not limited to, polymers, carbon composites, fiber-reinforced polymers, plastics, combinations thereof and the like. One example of a radiolucent material that can be used with the aspects of the present invention described herein is PEEK-OPTIMA® polymer supplied by Invibio Inc., Greenville, S.C. The PEEK-OPTIMA® polymer is a polyaromatic semicrystalline thermoplastic known generically as polyetheretherketone. The PEEK-OPTIMA® polymer is a biocompatible and inert material. Known alternatives to PEEK-OPTIMA® include, but are not limited to, biocompatible polymers such as ENDOLIGN® polymer composite supplied by Invibio Inc., Greenville, S.C. The ENDOLIGN® polymer is a biocompatible carbon fiber-reinforced thermoplastic material. Radiolucent materials, including those described above, can optionally be doped or combined with radiopaque materials in different concentrations in order to vary the level of x-ray contrast and/or visual characteristics. The portions of the implant device 510 constructed from radiolucent material can be prepared by any conventional technique known in the art such as machining, injection molding or compression molding.
In another embodiment, the implant device 510 can include a combination of components constructed from both radiolucent materials and radiopaque materials. Radiopaque materials are traditionally used to construct devices for use in the medical device industry. Radiopaque materials include, but are not limited to, metal, aluminum, stainless steel, titanium, titanium alloys, cobalt chrome alloys, combinations thereof and the like. Radiopaque materials tend to obstruct x-rays and thus restrict x-ray visibility to the regions in which the materials are located. However, radiopaque materials generally have structural characteristics that are advantageous with regard to medical devices. That is, some radiolucent materials lack the strength and/or rigidity of radiopaque materials and certain design modifications may be made to provide adequate structural integrity of the implant device 510. Radiopaque materials generally have increased rigidity as compared to radiolucent materials and thus radiopaque materials may tend to maintain bone body alignment despite the rigorous pressures and forces generated by a patient implanted with the implant device 510. Thus, it may be desirable to construct portions of the implant device 510 from radiopaque materials such as metal and other portions of the implant device 510 from radiolucent materials so that a desired level of strength and/or rigidity is obtained and also x-ray visibility is enhanced. For example, as shown in
The base member 520 of the implant device 510 can include a plurality of apertures, each of which is configured to receive a corresponding bone fastener or screw 550 there through. The bone fastener 550 can include a bone screw, a plurality of which is used for securing the implant device 510 to adjacent bone bodies. The bone fasteners 550 can be made of any suitable material, such as titanium or a titanium alloy, a radiolucent material, a radiopaque material, or combinations thereof. The plurality of bone fasteners 550 can all have the same shape, such as that shown in
In another embodiment, the bone screws 550 configured to pass through the apertures in the base member 520 can have pointed ends which include a cutting flute on the tip. The cutting flute at the tip of the bone screw 550 allows the screw to be self-drilling or self-tapping. Thus, the use of a bone screw 550 having a self-drilling or self-tapping tip makes the use of a drill or center punch optional.
For an enhanced fit of the implant device 510, a portion of bone can be trimmed or otherwise removed from a lip osteophyte of a bone body at an angle corresponding to bone screw holes 640, 680. The angles of the bone screws 550 relative to the bone surfaces of the bone bodies can affect the anchoring of bone screws 550. For example, the lip osteophyte is the strongest part of a vertebra, and thus angling the bone screws 550 through the lip osteophyte increases the ability of the base member 520 to stay anchored to the vertebral bodies. By being angled, each bone screw 550 is positioned along an angle of rotation of a corresponding bone body as well as an angle of settling of the bone body. This configuration places each screw 550 in a protected position against motion of the spinal column. As a result, significant shear forces are not exerted on the screws 550 as the vertebral bodies rotate and/or settle.
The primary member 600 includes at least one, and possibly two as shown, first bone screw holes 640 extending there through, each being configured to receive a corresponding bone fastener or screw 550. The first bone screw holes 640 in the primary member 600 are located on the front face of the primary member 600 and face outward from the patient when the implant device 510 is inserted. The bone screw holes 640 are configured such that the bone screws 550 extend through the holes 640 at an angle. As a result, each bone screw extending through the first bone screw holes 640 can enter the bone body at an angle. Each of the first bone screw holes 640 is sufficiently large to allow a portion of a respective bone screw 550 to pass there through but not large enough to allow a retaining portion of the bone screw through, such as the head 690 of the bone screw. Further, each of the first bone screw holes 640 has a seat 665 on which the retaining portion of a respective bone screw rests. Each seat 665 has a generally concave spherical shape and the surface of the retaining portion of the bone screw 550 in contact with the seat 665 has a complementary convex spherical configuration. Consequently, the bone screws 550 are free to pivot on the seats 665. The primary member 600 also includes a threaded hole 670 for receiving a restraining means configured to mitigate the backing out of at least one bone fastener from a bone body.
The secondary member 610 includes a second bone screw hole 680 in the form of an elongated slot for receiving a bone screw. The bone screw is introduced into the second bone screw hole 680 and into a second bone body. The second bone screw hole 680 is configured such that a bone screw can slide and rotate within the slot relative to the base member 520 and generally toward the primary member 600. Thus, in use, as two adjacent bone bodies, to which the base member 520 is fixed, collapse or settle and move toward each other, the bone screw contained within the second bone screw hole 680 will slide within the slot and move with the bone body into which it extends in a direction toward the primary member 600 and the other bone body. It is worth noting that since the slot is at an angle to the surface features, it is actually longer in the plane of the secondary member than the surface features are tall. In other words, the slot provides screw movement in the vertical direction equivalent to the height of the surface features.
At least one and possibly two projections 683 extend upwardly from the top surface 650 of the base member 520. The projections 683 contact a surface of the bone bodies to provide a stop when inserting the base member 520 between the bone bodies. The projection 683 provides a base or shelf that contacts a bone body in order to stop the implant device 510 against a corresponding bone body upon insertion into a patient. Although not shown in
As shown in
Additionally, it is to be appreciated that any other suitable bone screw restraining means can be used in connection with the present invention. For example, the bone screw restraining means can include multiple restraining plates that cover different bone screws. Alternatively, the bone screw restraining means can include one or more screws with heads that overlap at least a portion of one or more bone screws to thereby prevent the bone screws from backing out.
In another embodiment, the peripherally-surrounded chamber 692 formed by the primary member 600 can be divided into multiple interior compartments by interior members. Interior members can be composed or radiolucent or radiopaque materials. In order to increase radiographic evaluation of adjacent bone bodies and fusion material contained in each compartment of the peripherally-surrounded chamber 692, the interior members are possibly composed of radiolucent material. The peripherally-surrounded chamber 692 has a substantially flat inner face surface formed by the primary member 600. As illustrated, the interface members 530 can extend from the bottom surface of the peripherally-surrounded chamber 692 in order to provide controlled subsidence with an adjacent bone body. Although not shown, the interface members can alternatively extend from the top surface of the peripherally-surrounded chamber 692 or from both the top and bottom surfaces of the chamber 692.
As shown in
It is possible to load fusion material such as bone paste or bone chips into the peripherally-surrounded chamber 692 prior to insertion of the implant device 510 between adjacent bone bodies (e.g., vertebrae). However, it may be easier to insert a chamber member having an open anterior face between adjacent bone bodies. In this case, the chamber member can then be packed with fusion material from the anterior face and then sealed off with a plate, such as the base member 520. Along this line, in order to ease the packing of the peripherally-surrounded chamber 692 and the overall insertion of the implant device 510 into a patient, it may be desirable to detach the chamber member 696 which forms a portion of the peripherally-surrounded chamber 692 from the primary member 600. In accordance with another aspect of the present invention,
The chamber member 696 can be constructed from radiolucent material or radiopaque material. Because the chamber member 696 can potentially limit radiographic evaluation of the fusion material and adjacent bone bodies, it may be desirable to construct the chamber member 696 from radiolucent material. As shown, the chamber member 696 has a U-shape. However, the chamber member 696 can have any shape or be configured to match the shape of an adjacent bone body. When the chamber member 696 is connected with the first and second legs 620, 630 of the primary member 600, the peripherally-surrounded chamber 692, as shown, is generally rectangular. Although not shown, the peripherally-surrounded chamber 692 can be circular or any other desirable shape depending on the configuration of the chamber member 696 and first and second legs 620, 630. The chamber member 696 further has a top surface and a bottom surface that corresponds and aligns with the top 650 and bottom 651 surfaces of the primary member 600.
As shown in
It is to be appreciated that the peripherally-surrounded chamber 692 can be divided into more than one interior compartment if desired, such as that shown in
The chamber member 696 can be attached to the primary member 600 in a number of alternative methods. For example, in another embodiment,
In order to address the disadvantage that some radiolucent materials lack the strength of radiopaque materials, design modifications may be required to provide adequate structural integrity to the implant device 510. As illustrated in
It is to be appreciated that the implant device may include various other features. Some of these features may include features set forth within the patent applications identified herein and incorporated herein by reference. Some examples of the feature are shown in
Turning to
Other examples concerning relative dimensioning are contemplated. Such other examples include relative sliding travel of the screw within the slot 680 to end before the interface members 530 reach a fully-embedded state and relative sliding travel of the screw within the slot 680 to still be permitted after the interface members 530 reach a fully-embedded state. Such examples can generally be characterized by considering H to be greater than D and by considering H to be less than D, respectively. Also, placement and sliding travel are possible variables. For example, the respective bone fastener can be placed to reach an end of the elongated slot and then toggle in the slot to permit the interface members to further penetrate into the bone body.
Also, the above-mentioned modifications can be combined within various arrangements. For example,
Also, another aspect that can affect the subsidence profile, the interface members 530, 532 can be of any height or combination of heights. Thus, if a plurality of interface members 530, 532 extend from a surface of the base member, each interface member can be of equal heights or substantially taller or shorter than other interface members.
Still further, it is contemplated that no relative sliding movement occurs between one, some or all of the plurality of fasteners and the base member during the controlled subsidence. This could be accomplished via use of only holes and no slots. In the alternative, a bone screw could be held against movement along a slot. For such a scenario, pivoting may occur and one of more of the bone screws.
While shown embodiments of the present invention are described for supporting adjacent cervical vertebrae in the anterior region of the vertebrae, persons skilled in the art would recognize that the bone plate of the present invention may be utilized to support adjoining cervical, thoracic and lumbar in the region of the vertebral body. Further, the device and method of the invention is not limited to vertebral bodies, but can also be used to join two other pieces of bone in other parts of the body.
While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claim(s).
Claims
1. An implant device for two adjacent vertebrae, the device including:
- at least one portion configured for subsidence engagement with at least one of the vertebrae; and
- at least portions that are configured for contacted relative movement during the subsidence engagement with at least one of the vertebrae.
Type: Application
Filed: Mar 4, 2016
Publication Date: Jan 26, 2017
Inventors: Robert S. Bray, JR. (Studio City, CA), James M. Moran (North Royalton, OH), Mark T. Whiteaker (Rocky River, OH)
Application Number: 15/061,007
