WO2018222801A1 - Load sharing plating system and surgical procedure - Google Patents

Abstract

A load sharing plate assembly for connecting vertebral bodies, including a plate having at least one insert pocket for retaining at least one insert and at least one slider pocket for retaining at least one slider, wherein the insert pocket is interconnected to the slider pocket, and wherein the slider is engageable with the insert, and a bone screw received within the at least one insert for engaging bone, wherein the at least one slider toggles from an unlocked position to a locked position compressing the at least one insert against the bone screw, and wherein the bone screw is load sharing with the plate and angulation of the bone screw can change at increased loads. A load sharing plate assembly, including a plate having an insert including a locking mechanism for receiving and securing a bone screw in the insert, the bone screw being load sharing and acting as a dynamic screw and fixed screw. Methods of using a load sharing plate assembly for connecting vertebral bodies.

Description

LOAD SHARING PLATING SYSTEM AND SURGICAL PROCEDURE

BACKGROUND OF THE INVENTION

1. TECHNICAL FIELD

[0001] The present invention relates to the field of spinal implants. More specifically, the present invention relates to a bone plate and locking mechanism where the locking mechanism can secure a bone screw to a plate while allowing the bone screw to load share with the plate.

2. BACKGROUND ART

[0002] Spinal fixation has become a common approach in treating spinal disorders, fractures, and for fusion of vertebrate. A common device used for spinal fixation is a bone fixation plate assembly. Typical bone fixation plate assemblies have a relatively flat, rectangular plate with a plurality of apertures therethrough. Fasteners, such as bone screws, are utilized to secure the bone fixation plate assembly. The screws are firmly tightened to secure the bone fixation plate to the bone or bones to be fixed. There are numerous examples of bone fixation plates existing in the art. These are illustrated in US Pat. No. 5,364,399 to Lowery, et al., US Pat. No. 5,601,553 to Trebing, et al., US Pat. No. 6,017,345 to Richelsoph, US Pat. No. 6,152,927 to Farris, et al., US Pat. No. 6,235,034 to Bray, US Pat. No. 6,139,550 to Michelson, and US Pat. No. 6,258,089 to Campbell, et al. The above referenced patents are cited as examples illustrating the general state of the art with regard to bone fixation plate technology. Generally, these types of devices can be utilized for the fixation of any bone or bones, but are more particularly suited for the fixation of the vertebrae of the spine with regard to the cervical, lumbar and/or thoracic regions.

[0003] The basis of interior fixation or plating is to approach the spine from the anterior or anterior lateral side and use the screws to solidly mount the bone fixation plate to the affected vertebrate. This approach is commonly used in cases of trauma, tumors, and degenerative conditions. Often, in addition to the application of a bone fixation plate, vertebral interbody devices and graft material can be combined in an attempt to permanently fuse together adjacent vertebrae. The graft material can consist of bone grafts obtained from other bones in the patient's body or from cadaver bones.

[0004] A common problem associated with the use of such bone fixation plates is a tendency of the bone screws to "back out" or pull away from the bone onto which they were fixed. This problem occurs primarily due to the normal motion of the body and the spine. Since the spine is a very dynamic entity and is constantly moving, this problem is especially prevalent in areas of high stress such as the spine wherein the gravity and musculature are working to move the vertebrae against the fixation of the fixation plate. Once a screw becomes loose and pulls away from the bone, the head of the screw can rise above the surface of the bone fixation plate causing local trauma and the screw itself can even work its way completely out of the bone. This creates a number of potentially serious problems given the number and proximity of blood vessels and other critical structures near the locations of in situ spinal fixation plate assemblies.

[0005] A number of various designs of fixation plates have been brought forth in attempts to prevent screws from pulling away from the bone and/or to prevent the screws from backing out or pulling away from the surface of the bone fixation plate. For example, the Lowery, et al. patent cited above discloses an anterior cervical plating system incorporating a locking screw that engages the heads of the bone screws used to secure the cervical plate to the vertebrae. The locking screw is positioned above the bone screws and is driven against the heads of the bone screws to rigidly fix the bone screws to the plate. For this locking mechanism to work however, the distance between the heads of the bone screws must be kept to a minimum, thereby limiting the potential applications of the bone fixation plate. Additionally, while the Lowery, et al. patent discloses that the bone screws to be angled, if the screws are not angled exactly the same amount, which is very difficult to achieve, the locking screw cannot adequately contact both bone screw heads.

[0006] Another example of a mechanism for preventing bone fixation screws from backing out or becoming dislodged from the bone is set forth in the Trebing, et al. patent disclosed above. The Trebing, et al. patent discloses a bone fixation plate that is threaded and used in combination with a bone screw having both bone engaging threads and a threaded portion near the head of the bone screw which is complimentary to the threaded hole in the bone fixation plate. The screw is rigidly fixed to the bone fixation plate. It is possible, however, to lock the bone screw to the bone fixation plate while leaving a gap between the bone fixation plate and the bone. This problem can cause inferior fixation of the bone or even total failure of the fixation.

[0007] Various other mechanisms used to prevent bone screws from pulling out of bones include cams, which engage and lock the screws and the use of expanding head screws, which expand outwardly when adequate force is applied thereto to engage the holes in the bone fixation plate. All of these particular designs have drawbacks including potential for breakage or requiring particular precision and alignment in their application in order to correctly work.

[0008] Another apparatus for preventing bone screw back-out from a bone fixation plate is shown in US Pat. No. 5,578,034, issued Nov. 26, 1996, to Estes. The Estes patent discloses a bone fixation plate having a number of bores therethrough, a corresponding number of screws each having an enlarged head portion, and an elongated shaft portion including bone engaging threads thereabout and a non-threaded portion between the head and the threaded portions, and a corresponding number of screw anti-backout members each having a bore therethrough. The screw anti-backout members are inserts positioned within the bores of the fixation plate and are initially sized to slidingly receive an elongated screw shaft therethrough. During application of the fixation plate, the bone screws are advanced through the bone fixation plate bores and the screw anti-backout members are positioned within the plate bores to screw the bone fixation plate to the underlying bone. Thereafter, the apparatus is sufficiently heated to shrink the bores of the screw anti-backout members, thereby trapping the non-threaded portion of the screw shafts located between the fixation plate and the threaded portions. The anti-backout members are immobilized within the bore of the fixation plate. The anti-backout members and fixation plate remain in fixed relationship to each other after fixation to the underlying bone.

[0009] Other types of anti-backout inserts or collars have been used with bone fixation plates for a variety of reasons, such as those shown in US Pat. No. 4,388,921, issued Jun. 21, 1983, to Sutter, et al. and US Pat. No. 5,607,428, issued Mar. 4, 1997, to Lin. Sutter, et al. discloses a bone fixation plate in which sleeves are placed in openings provided in a bone fixation plate. A screw is placed through the sleeve and into the underlying bone. By tightening the screw, the sleeve is clamped in place with relation to the bone fixation plate thus assuring that the fixation plate will stay rigidly connected with the screws.

[00010] The Lin patent discloses a bone fixation plate having a direction adjusting ring disposed in at least one hole in the fixation plate. Upon insertion and tightening of the threaded bone screw, arresting edges of the direction adjusting ring are urged into engagement within the hole to securely fix and retain the direction adjusting ring therein.

[00011] Other examples of recent systems utilize small setscrews or locking screws, sometimes in combination with bulky covers or cams, to achieve a mechanism for locking and retaining the screw to the plate. One such example is illustrated in US Pat. No. 6,152,927 to Farris, et al. The Farris, et al. patent discloses a set screw that is longer so that it can remain in the plate and in the bone even if it is backed out a certain distance. The screw can be backed out further so that the bone screws have clearance to enter the holes in the plate (Figure 19 in Farris, et al.). The end result is the screw penetrates through the plate and creates an unnecessary load against the vertebrate, which opposes the bone screws and tends to try and lift the plate off the bone.

[00012] US Pat. No. 6,258,089 to Campbell, et al. discloses another type of mechanism that prevents the screw from backing out. The Campbell, et al. patent discloses the use of a tab that is integral to the plate and machined into the plate. The tab must be bent to cover the screw to prevent it from backing out. If a surgeon needs to revise or to fix the screw position, the tab needs to be bent back prior to accessing the screw. As a result, stress is created in the metal and possibly require the replacement of the plate.

[00013] Another example is found in US Pat. No. 6,139,550 to Michelson. The Michelson patent discloses an apparatus for locking three set screws at once utilizing a cam mechanism. In order to guarantee the cam lobes stop exactly where they must be to engage the three screws, the threads in the plate and the threads on the cam must be carefully controlled and timed so that the threads begin exactly the same.

[00014] Finally, another example of a bone plate and screw guide mechanism is disclosed in US Pat. No. 6,235,034 to Bray. The Bray patent discloses a bone plate including a base plate, wherein a retaining plate is also provided therein. The retaining plate is fixedly attachable to the base plate and the retaining plate covers at least a portion of each of the bone screws. The retaining plate is secured to the base plate with set screws that are inserted into set screw apertures. This invention therefore requires a separate screw to retain the bone screws within the base plate and bones. [00015] I n the prior art designs discussed, two types of screws are generally provided. The variable angle or "dynamic" screw is placed at various angles relative to the plate but is only retained within the plate. This allows the screw to free float and rotate. The fixed screw is generally locked to the plate at one angle relative to the plate. Fixed screws hold plate position relative to the vertebral body. However, dynamic screws can also move if there is bone resorption.

[00016] I n examining the above locking mechanisms and screw types, the primary goal of the prior art is to provide a retaining mechanism. However, in use, other than retention, they do not contribute to better surgical outcomes. Accordingly, there is a need for a bone fixation plate assembly that allows fixation of a bone fixation plate to a bone with a novel and new screw fixation approach, which allows a single screw to load share with the plate and effectively work as both a fixed screw and a dynamic screw that responds to actual in-vivo surgical placement and loads exerted during healing and fusion while retaining the bone screw to the plate.

[00017] I n addition, there is a need for dynamic load sharing of the plate assembly with the adjacent vertebral bodies. More specifically, there is a need for a bone fixation plate assembly that provides for active load sharing or a mechanism that pulls the vertebral bodies towards each other to exert a controlled force against the interbody and/or graft material inserted into the disc space.

SUMMARY OF THE INVENTION

[00018] The present invention provides for a load sharing plate assembly for connecting vertebral bodies, including a plate having at least one insert pocket for retaining at least one insert and at least one slider pocket for retaining at least one slider, wherein the insert pocket is interconnected to the slider pocket, and wherein the slider is engageable with the insert, and a bone screw received within the at least one insert for engaging bone, wherein the at least one slider toggles from an unlocked position to a locked position compressing the at least one insert against the bone screw, and wherein the bone screw is load sharing with the plate and angulation of the bone screw can change at increased loads.

[00019] The present invention further provides for a load sharing plate assembly, including a plate having an insert including a locking mechanism for receiving and securing a bone screw in the insert, the bone screw being load sharing and acting as a dynamic screw and fixed screw.

[00020] The present invention also provides for a method of using a load sharing plate assembly for connecting vertebral bodies, by inserting at least one bone screw through at least one insert in a plate and into bone until a head of the bone screw is seated in the insert, locking the bone screw in the insert, and securing and holding the plate against the vertebral bodies, thereby connecting the vertebral bodies.

[00021] The present invention also provides for a method of using a load sharing plate assembly for connecting vertebral bodies, by inserting at least one bone screw through a plate into bone and locking the bone screw in the plate, providing load sharing of the bone screw with the plate and allowing angulation of the bone screw to change at increased loads, and securing and holding the plate against the vertebral bodies, thereby connecting the vertebral bodies.

DESCRIPTION OF THE DRAWINGS

[00022] Other advantages of the present invention are readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[00023] FIGURE 1 is an iso view of a plate assembly with screws;

[00024] FIGURE 2 is an iso view of a bone plate;

[00025] FIGURE 3 is a close-up view of a bone plate pocket;

[00026] FIGURE 4 is a side iso view of the bone plate pocket;

[00027] FIGURE 5 is a section view of a plate;

[00028] FIGURE 6 is a side view of an insert;

[00029] FIGURE 7 top iso view of an insert;

[00030] FIGURE 8 is a top iso view of a slider;

[00031] FIGURE 9 is a back iso view of a slider;

[00032] FIGURE 10 is a top iso view of a plate assembly;

[00033] FIGURE 11 is a bottom iso view of a plate assembly;

[00034] FIGURE 12 is a side view of a bone screw;

[00035] FIGURE 13 is a side view of a plate assembly with bone screws;

[00036] FIGURE 14 is a section view of the plate, insert, and bone screw assembly; [00037] FIGURE 15 is a top view of the plate, insert, bone screw, and slider assembly unlocked;

[00038] FIGURE 16 is a top view of the plate, insert, bone screw, and slider assembly in locked position; and

[00039] FIGURE 17 is top iso view of a multilevel anterior cervical plate assembly with bone screws.

DETAILED DESCRIPTION OF THE INVENTION

[00040] The present invention generally provides for a load sharing plate assembly implant system that adjusts to the anatomy of the spine and connects two or more vertebral bodies securely, including a bone plate and locking mechanism where the locking mechanism can secure a bone screw to a plate while allowing the bone screw to load share with the plate. The locking mechanism can selectively exert controlled force against the bone screw head to allow the load sharing plate assembly to resist various levels of rotational loads while retaining the bone screw in the plate. The plate can also be constructed in several forms, including a dynamic plate construct that allows the plate to exert a controlled force on interbody graft to improve on fusion rates. The load sharing plate assembly of the present invention allows for simpler and more accurate connection of multiple spinal implants while providing enhanced load sharing and a reduction of inventory of bone screws.

[00041] Alternate embodiments may be devised without departing from the spirit or the scope of the invention. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention.

[00042] Before the present invention is disclosed and described, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms "a" or "an", as used herein, are defined as one or more than one. The term "plurality," as used herein, is defined as two or more than two. The term "another," as used herein, is defined as at least a second or more. The term "coupled," as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.

[00043] Relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises ... a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[00044] Herein various embodiments of the present invention are described. In many of the different embodiments, features are similar. Therefore, to avoid redundancy, repetitive description of these similar features may not be made in some circumstances. It shall be understood, however, that description of a first-appearing feature applies to the later described similar feature and each respective description, therefore, is to be incorporated therein without such repetition.

[00045] Referring now to the figures in detail, there is shown a first embodiment of a new load sharing plate assembly implant, illustrated generally at 100 in Figures 1 through 10, that, by its construction, permits the implant 100 to attach to and retain bone screws while exerting force against the bone screw heads to hold the bone screws at a desired angle for low loads, but allows the bone screw angulation to change at a desired increased load such that the bone screw shares anatomical loading with the plate and allows the screw to move in the plate to behave dynamically to maintain compression on bone graft and reduce the risk of screw fracture.

[00046] A plate 1 includes an upper surface la, lower surface lb, a first end lc, and a second end Id. Also shown is an opening lh in the middle of the plate. The opening lh is optional and can be of different shapes and sizes and will likely vary with the length and size of the plate. Machined into plate 1 are pockets lk and lp for accepting at least one insert 2 and slider 3. A bone screw 4 is designed to fit within the insert 2 and go through the plate 1 to engage bone. The bone screw 4 includes a top surface 4a, tip 4b, and a driving feature 4d for turning the bone screw 4 into the bone. The combined components create a cervical plate assembly 100. In general, two bone screws 4 are inserted per vertebral body, thus a single level plate 1 for fusing two vertebrae has four screws 4, four inserts 2, and four sliders 3. However, a plate 1 having only one screw 4 per level is also possible. This type of plate 1 for a single level fusion has two inserts 2, two sliders 3, and two screws 4. Obviously, to add levels or to fuse additional vertebral bodies together, additional inserts 2, sliders 3, and screws 4 can be added in as needed. Figure 1 shows a representative example of a single level plate assembly 100.

[00047] Figure 2 shows the plate component 1 of embodiment 100 having openings le extending through the plate 1 and pockets lk for retaining insert 2. Under top surface la, a pocket or recess lk is cut. This creates an upper lip In and lower surface Is. The lower surface Is is generally flat but a not a uniform shape, as will be clearer in additional Figures. A through hole or bore le extends through the plate, preferably leaving a small section If generally cylindrical in shape. A chamfer or blend radius lg removes the sharp edge from the intersection of opening le and the lower surface of the recess Is. A pocket lp for the slider 3 is also machined into the plate 1, extending through the top surface la but preferably not through bottom surface lb. The outside of the plate 1 can be shaped to form a reduced section lab, leaving a wider portion lj around the pockets lk and lp. This allows the plate 1 to be minimized in size where possible to do so.

[00048] Figures 3 and 4 are close up views of pockets lk and lp in plate 1. As mentioned above, the recess or groove lk is not uniform and consists of a partially cylindrical section lac, which also has a flat section lq. In addition, a second pocket lu may extend from the flat section lq, preferably with a blend radius It. Recess pocket lk extends through to the slider opening lp, and is thus interconnected with slider opening pocket lp, leaving two ledges, ly and lw. The opening lp for the slider 3 is essentially a groove where the bottom surface lps extends lower than recess lk lower surface Is, creating an edge lx. It is preferred to have the slider opening lp widen into a larger opening Is and have an edge and/or radius laa at the junction between the two. When the slider 3 is in the pocket lp, it can slide into this wider opening Is to aid in retaining the slider 3 in the desired position, as feature laa helps prevent the slider 3 from moving backwards. It is also beneficial to have the ledges ly and lz extend inwards and at least slightly over pocket lp. This creates a retention feature to help hold the slider 3 from coming out of the plate 1 when the slider 3 is in the unlocked position. [00049] Figure 5 is a cross section taken through the center of the through hole or bore le to clarify the recess or undercut in the plate 1 to hold the insert 3. At the top of the cylindrical portion If is a chamfer or radius lr. This allows the insert 3 to have a blend radius and still permit the insert 3 to sit fully in the pocket lp. Also clear in this figure is that the top la and bottom lb of the plate 1 are curved in this embodiment. The bottom lb is curved to match the anatomy to all the plate 1 to sit as flush as possible to the vertebral body surface.

[00050] Figure 6 shows an embodiment of insert 2. Insert 2 has a top surface 2a and a bottom surface 2b. The outside 2c of insert 2 is partially cylindrical. A top cylindrical section 2d is smaller in diameter than the outside partially cylindrical section 2c. This creates a lip and an upper flat surface 2e. The same is true of the bottom 2b, where a cylindrical portion 2f is smaller in diameter than outer partially cylindrical section 2c. This creates a lip and flat surface 2g. As can be further seen, an arm 2h extends from outside 2c as does a smaller arm 2j. Inside the insert 2 is a spherical or semi-spherical seat 2h. The diameter or cylinder 2j at the top of spherical seat 2j can be a sharp edge or be a section of a cylindrical wall, as shown in this embodiment. A chamfer 2k aids the bone screw head 4c in spreading open the insert 2 and entering the insert spherical seat 2h. Of course, to allow this spreading motion to occur, the insert 2 must be flexible. Therefore, a slot 2m extends through one side of the insert 2. The split 2m runs through the middle of two extensions or arms 2n and 2p extending from insert 2. The first arm 2n is preferably longer than the second arm 2p. A recess 2q in the surface of arm 2n allows for additional clearance with slider 3. This provides some benefits, but is not required. A chamfer 2r runs around a portion of the generally cylindrical section 2c to assist in insertion of insert 2 into the plate. In addition, to adjust flexibility of the insert 2, the outside cylindrical portion 2c can be increased to make it stiffer, decreased to make it more flexible, or small grooves cut to increase flexibility. As shown, this embodiment has small grooves 2s around 2c. At the top of cylindrical section 2d, a blend radius 2t helps prevent any sharp edges from contacting soft tissue. In addition, a blend radius 2w reduces stress risers at the junction between cylindrical section 2m and surface 2e.

[00051] Figure 7 shows a different view of the insert described above. The arms 2n and 2p can be easily seen. The smaller arm 2p extends from a flat section 2u of insert 2. This flat section 2u is created by cutting away some of cylindrical portion 2c. A blend radius 2v from the flat section 2u to the side of the arm 2p reduces stress risers and creates a hook for engagement with a portion of the plate 1. This arm 2p and hook 2v of this embodiment are preferable, but having the flat 2u alone will allow function. A portion of arm 2p is chamfered or cut away and is shown as 2w. On the longer arm 2n, a recess 2q can be added to allow for more room for the slider 3 to fit within the plate 1.

[00052] Figures 8 and 9 show slider 3. The slider 3 is basically a rectangular shaped component that can be slid or toggled from one unlocked position to a locked position where it compresses the insert 2 against the bone screw head 4c. More specifically in this embodiment, slider 3 has a top surface 3a, bottom surface 3b, a front curved surface 3cm and a back face 3d. The sides 3e are cut in at a distance from top 3a, leaving a flat face 3f and a ledge 3g. This is the same for both sides 3e. The ledge 3g allows for the plate pocket lp to have lips ly and lz on either side of the plate 1 that helps to contain the slider 3, as discussed previously. The side walls 3e have blend radii 3h that blend into back wall 3d. The side walls 3e also have a recess 3j cut into the sides 3e and front blend radii 3k. The blend radius 3k on the side that engages the arm 2n of the insert 2 helps to allow for easier sliding of slider 3. Back radii 3m extend from back wall 3j to the side face 3e. Slider 3 also has an opening 3n for engagement with an instrument. While the slider 3 can be moved without an opening and pushed from the back face 3d, it is easier to have a place for an instrument to engage. Opening 3n consists of a generally rectangular opening with corner radii 3q, extending downward but not through slider 3, leaving a face 3p at the bottom of the opening. Of course, the opening 3n could be a through hole or geometry other than rectangular. However, it is preferred to have a rectangular opening 3n that does not extend completely through the slider 3 to maximize the slider 3 strength and the strength of the instrument that engages the slider 3 to move it from one position to another.

[00053] Figure 10 shows a single level plate assembly 100 designed to hold and help fuse two vertebrae together. Inserts 2 are compressed into the plate 1 such that the external surface 2c of insert 2 snaps into recess lk in plate 1. This retains the insert 2, as the insert 2 is elastic and springs back to its original shape. There is clearance between the insert 2 external features and the plate pocket lk features. This allows sufficient room for the insert 2 to flex outward to allow a screw head 4c to be inserted. The sliders 3 are then inserted. The slider lip 3g is slid under the plate lips ly and lz, which requires some initial compression of insert 2. Once the slider 3 is in position, it is retained by the lips ly and lz and the compression of the insert 2 is relieved. As can be seen in this embodiment, the insert 2 has a recess 2q that provides for clearance for nose 3c of slider 3. Thus, the slider 3 is now able to engage the long arm 2n of insert 2. The other end of the insert 2p will engage plate features It and/or lu when the insert 2 is compressed. With the above descriptions and the figures, it can be seen that by moving the slider 3 from the unlocked position to locked, or from the insert 2 being uncompressed to being compressed, the slider 3 engages long arm 2n and presses against the long arm 2n as it is slid. The other end of insert 2 is constrained in that it cannot freely rotate and effectively hits a stop. Thus, the long arm 2n functions as a lever, and by providing load to the lever, the insert 2 will be deflected inward. The amount of deflection can be altered as needed by increasing or decreasing the length of the arm 2n or the amount of interference between the slider 3 and the arm 2n when the slider 3 is moved to engage the arm 2n. In addition, in the preferred embodiment, the arm 2n at least partially engages within the recess 3j in the side 3e of slider 3 and presses against a portion of recess 3j. This aids in retaining the slider 3 in the plate 1.

[00054] Figure 11 shows a view from the bottom of plate 1. As can be seen, the inserts 2 do not extend below the bottom lb of plate 1, and in this embodiment, the screw head seat 2h is entirely within insert 2. It is possible to have a small lip (not shown) on the bottom lb of the plate 1 to prevent the screw head 4c from being pulled through and the insert 2 to have a partial seat 2h.

[00055] Figure 12 shows an example of a bone screw 4 for interfacing with insert 2. Bone screw 4 has a top surface 4a, tip 4b, a spherical or partially spherical head 4c, a driving feature 4d for engagement with a screw driver, a threaded portion 4e having a major diameter 4f and a minor diameter 4g. Bone screw 4 also has a neck portion 4h between the head 4c and the start of the threads 4e. In this example, a flute 4j is provided to allow for the bone screw 4 to be able to aid in self tapping, or cutting and forming threads as it is inserted into bone. While the screw head 4c can be smooth and still be retained by the insert 2, it is preferable that it be textured. There are a number of ways to texture the head 4c, which included machining grooves, a helical thread around the spherical surface, grit blasting, and other techniques. In the preferred embodiment, the textured surface allows for higher levels of friction and more of a mechanical lock with insert 2. The drive feature 4d is shown here as a hex, however, it can be a square drive, torx, hex, pentalobe, or any other feature that will engage with a screw driver.

[00056] Figure 13 shows the bone screw 4 inserted into the plate 1 and inserts 2. In this example, there are four bone screws 4 as this is a single level plate 1. The plate 1 is held against the bone, the holes into the bone are started with an awl or a drill, and the screws 4 inserted through the plate 1 and inserts 2 until they are fully seated in the inserts 2 and the plate 1 is held against the vertebral body. Alternatively, the screws 4 are inserted through plate 1 and inserts 2 until the screws contact a small lip in the bottom lb of plate 1.

[00057] Figure 14 shows a section view of a screw 4 seated in an insert 2 that is seated in a plate 1. In this embodiment, the plate 1 is curved transverse to the center long axis and also curved along the long axis to match the cervical anatomy. To fit the inserts 2 and allow for optimum screw angle, the pockets lk and lp in the plate 1 are at an angle. The insert 2 snaps into the plate 1 as described earlier, and then the screw 4 is inserted and threaded into the bone until the head 4c of the screw 4 sits within the insert 2. It is preferable that the insert seat 2h extend above the centerline of the screw head 4c to aid in screw head 4c retention in the insert 2. There is a balance that permits the screw head 4c to enter the insert 2 yet when the insert 2 is locked prevents the screw head 4c from being able to back out.

[00058] The present invention allows for the bone screws 4 to be locked in the plate 1 without the need for additional set screws or bulky retaining mechanisms as in the prior art. Most generally, by toggling the slider 3 to compress insert 2 against the bone screw head 4c, the bone screw 4 is locked in the plate 1. In Figures 15 and 16, the plate assembly is shown progressing from an unlocked position in Figure 15 to fully locked in Figure 16. The slider 3 is moved from left to right, and in doing so, it pushes against the arm 2n of insert 2. As the insert 2 cannot rotate due to the engagement of the insert arm 2b against the plate 1, the insert 2 wraps around the screw head 4c and exerts compressive force against the screw head 4c. This locking is novel and provides advantages. The amount of force exerted against the screw head 4c can be controlled by the length of arm 2n and the amount of interference between the arm 2n and slider 3. The more interference the greater the force against the screw head 4c. Of course, the more interference, the more force it takes to move the slider 3 from the unlocked to locked position. The amount of force against the screw head 4c can be used to correlate the amount of force it takes to move the screw 4. Thus, by controlling the force against the screw head 4c, the desired force to move the screw 4 can be built into the construct.

[00059] The benefit of this locking mechanism is that the force against the screw head 4c is two-fold. First, when in the locked position, the screw 4 is prevented from backing out of the plate 1 under normal anatomical conditions. Secondly, the screw 4 can perform in a novel way, behaving as a fixed screw or dynamic screw under desired loading conditions as described below.

[00060] I n most anterior cervical plating systems, fixed screws and dynamic screws are provided as system options. Fixed screws allow little to no angulation when inserted into the plate and locked. Dynamic screws allow for angulation relative to the plate when inserted and can be locked to the plate to prevent them from backing out. However, they are never actually angularly locked to the plate and therefore can freely rotate in the plate even after locking. Dynamic screws allow the screws to rotate in the plate if there is bone resorption, but do not hold the vertebral body steady relative to the plate. The surgeon can pick which screw he prefers, but either screw is a compromise. It would be better to have a screw that can be placed at any angle and behaves like a fixed screw to hold vertebral alignment unless there is bone resorption, when the screw behaves like a dynamic screw to better load the bone graft and reduce the risk of screw breakage.

[00061] By having the novel locking mechanism described herein, this new type of screw approach can be described as a true load sharing screw, rather than dynamic or fixed. Under desired loads, the screw 4 and plate 1 maintain the surgeon's desired position. Under loads that exceed set limits, the screw 4 can be set so that it moves with the load to a new set point. The limits can be preset by the interference of the arm 2n and the slider 3, as previously discussed. In addition, it is possible to have more than one position of the slider 3, such that the limits can be altered by the surgeon in vivo. The bone screw 4 can remain locked to a set load, move once a threshold of the set load is reached, and can then reset and lock once the load is reduced below the threshold.

[00062] The present invention is applicable to many different plate constructions and designs as well as uses within the body, and is not limited to the present embodiments using a cervical plate. In addition, there are plates that use one bone screw per vertebral body. The mechanism described herein can easily be used with this type of design.

[00063] In addition, plate 1 is shown as substantially rectangular in shape. Of course, the plate 1 does not need to be rectangular, but can also be other shapes. Plate 1, as well as the other components of the implant can be made of various materials, such as, but not limited to, metals, such as titanium, or stainless steels, polymers, or a combination of both. In addition, the other components can be out of other suitably compatible materials.

[00064] As shown in Figure 17, multiple inserts 2 can be provided in a single plate assembly 100. This example is a three level anterior cervical plate. Note that the middle inserts 2 and sliders 3 are effectively mirror imaged, showing that the orientation of the slider 3 and insert 2 can be altered as needed to fit within the plate 1 as long as the general design and slider 3 engagement of the insert arm 2n is maintained.

[00065] As the assembly 100 is self-contained and small, it is possible to supply the plate/insert construct assembly 100 complete and sterile packed, and provide a range of sterile sizes ready for surgery. Bone screws 4 can also be supplied sterile packed, individually or in pairs. As can be imagined, this implant system 100 also requires a minimal number of instruments, simplifying the surgical implant procedure and allowing the instruments to be supplied sterile.

[00066] The present invention also provides for a method of using a load sharing plate assembly 100 for connecting vertebral bodies, by inserting at least one bone screw 4 through at least one insert 2 in a plate 1 and into bone until a head 4c of the bone screw 4 is seated in the insert 2, locking the bone screw 4 in the insert 2, and securing and holding the plate 1 against the vertebral bodies, thereby connecting the vertebral bodies. The steps of this method have been generally described above. The method can include further including before the inserting step, the steps of holding the plate 1 against the bones to be connected, and making a hole in the bone to receive the bone screw 4. The plate 1 can include at least one insert pocket lk for retaining at least one insert 2 and at least one slider pocket lp for retaining at least one slider 3. The locking step can include preventing a head 4c of the bone screw 4 from backing out of the insert 2, and toggling a slider 3 within the plate from an unlocked position to a locked position and compressing the insert 2 against the bone screw 4. The toggling step can include the slider 3 engaging an arm 2n of the insert 2, the insert 2 wrapping around the head 4c of the bone screw 4, and the insert 2 exerting compressive force against the head 4c. The method can further include the step of controlling an amount of force exerted against the head 4c by adjusting a length of an arm 2n of the insert 2 that interacts with a slider 3 within the plate 1. The method can further include the step of altering a load limit of the bone screw 4 by adjusting the slider 3. The bone screw 4 can be a load sharing screw and behave as a fixed screw to hold vertebral alignment and a dynamic screw when there is bone resorption. The inserting step can be further defined as inserting the at least one bone screw 4 at an angle. Under a set load, the bone screw 4 and plate 1 can maintain a position, and under a load that exceeds the set load, the bone screw 4 can move to a new set point. The bone screw 4 can then reset and lock once the load is reduced below the set load (threshold). Multiple vertebral bodies can be connected with plates 1 that include multiple inserts 2 and sliders 3. Each of these steps have been described above.

[00067] The present invention also generally provides for a method of using a load sharing plate assembly for connecting vertebral bodies, by inserting at least one bone screw through a plate into bone and locking the bone screw in the plate, providing load sharing of the bone screw with the plate and allowing angulation of the bone screw to change at increased loads, and securing and holding the plate against the vertebral bodies, thereby connecting the vertebral bodies.

[00068] The foregoing description and accompanying drawings illustrate the principles, exemplary embodiments, and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art and the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims.

[00069] Throughout this application, various publications, including United States patents, are referenced by author and year and patents by number. Full citations for the publications are listed below. The disclosures of these publications and patents in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.

[00070] The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation.

[00071] Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention can be practiced otherwise than as specifically described.

Claims

CLAIMS What is claimed is:

1. A load sharing plate assembly for connecting vertebral bodies, comprising:

a plate including at least one insert pocket for retaining at least one insert and at least one slider pocket for retaining at least one slider, wherein said insert pocket is interconnected to said slider pocket, and wherein said slider is engageable with said insert; and

a bone screw received within said at least one insert for engaging bone, wherein said at least one slider toggles from an unlocked position to a locked position compressing said at least one insert against said bone screw, and wherein said bone screw is load sharing with said plate and angulation of said bone screw can change at increased loads.

2. The load sharing plate assembly of claim 1, wherein said slider pocket does not extend through a bottom surface of said plate

3. The load sharing plate assembly of claim 1, wherein said slider pocket is wider at one end for retaining said slider in position.

4. The load sharing plate assembly of claim 1, wherein said slider pocket includes ledges that extend inwards for retaining said slider in said plate when in an unlocked position.

5. The load sharing plate assembly of claim 1, wherein said plate is curved, and wherein a bottom of said plate is curved to match a vertebral body surface.

6. The load sharing plate assembly of claim 1, wherein said insert includes a seat for receiving said bone screw.

7. The load sharing plate assembly of claim 1, wherein said insert is flexible.

8. The load sharing plate assembly of claim 7, wherein said insert includes a slot extending through one side.

9. The load sharing plate assembly of claim 7, wherein an outside cylindrical portion on said insert includes grooves cut to increase flexibility.

10. The load sharing plate assembly of claim 1, wherein said insert includes a first arm longer than a second arm.

11. The load sharing plate assembly of claim 10, wherein said second arm extends from a flat section of said insert.

12. The load sharing plate assembly of claim 10, wherein said first arm includes a recess for providing room for said slider to fit within said plate.

13. The load sharing plate assembly of claim 10, wherein said first arm functions as a lever and deflects said insert inwards.

14. The load sharing plate assembly of claim 10, wherein said first arm engages within a groove in a side of said slider and presses against a portion of a wall for retaining said slider in place.

15. The load sharing plate assembly of claim 10, wherein said insert wraps around a head of said bone screw and exerts compressive force against said head.

16. The load sharing plate assembly of claim 1, wherein said slider includes a top surface, a bottom surface, a front curved surface, and a back face.

17. The load sharing plate assembly of claim 16, wherein said slider includes sides cut in at a distance from said top surface having a flat face and ledge.

18. The load sharing plate assembly of claim 1, wherein said slider includes an opening for engagement with an instrument.

19. The load sharing plate assembly of claim 18, wherein said opening is rectangular and does not extend completely through said slider.

20. The load sharing plate assembly of claim 1, wherein an external surface of said insert snaps into said insert pocket in said plate.

21. The load sharing plate assembly of claim 1, further including a clearance between an external surface of said insert and said insert pocket allowing said insert to flex outward when said bone screw is inserted.

22. The load sharing plate assembly of claim 1, wherein said bone screw includes a head that is textured for providing a mechanical lock with said insert.

23. The load sharing plate assembly of claim 1, wherein said insert pockets are angled.

24. The load sharing plate assembly of claim 1, wherein an insert seat extends above a screw head when said bone screw is inserted in bone.

25. The load sharing plate assembly of claim 1, wherein said bone screw behaves as a fixed screw to hold vertebral alignment and a dynamic screw when there is bone resorption.

26. The load sharing plate assembly of claim 1, wherein a load limit is preset with said slider.

27. A load sharing plate assembly, comprising a plate having an insert including a locking mechanism for receiving and securing a bone screw in said insert, said bone screw being load sharing and acting as a dynamic screw and fixed screw.

28. The load sharing plate assembly of claim 27, wherein said bone screw remains locked to a set load, moves once a threshold of said set load is reached, and resets and locks once the load is reduced below the threshold.

29. A method of using a load sharing plate assembly for connecting vertebral bodies, including the steps of:

inserting at least one bone screw through at least one insert in a plate and into bone until a head of the bone screw is seated in the insert;

locking the bone screw in the insert;

securing and holding the plate against the vertebral bodies, thereby connecting the vertebral bodies.

30. The method of claim 29, further including before said inserting step, the steps of holding the plate against the bones to be connected, and making a hole in the bone to receive the bone screw.

31. The method of claim 29, wherein the plate includes at least one insert pocket for retaining at least one insert and at least one slider pocket for retaining at least one slider.

32. The method of claim 29, wherein said locking step is further defined as preventing a head of the bone screw from backing out of the insert.

33. The method of claim 29, wherein said locking step is further defined as toggling a slider within the plate from an unlocked position to a locked position and compressing the insert against the bone screw.

34. The method of claim 33, wherein said toggling step is further defined as the slider engaging an arm of the insert, the insert wrapping around the head of the bone screw, and the insert exerting compressive force against the head.

35. The method of claim 33, further including the step of controlling an amount of force exerted against the head by adjusting a length of an arm of the insert that interacts with a slider within the plate.

36. The method of claim 33, further including the step of altering a load limit of the bone screw by adjusting the slider.

37. The method of claim 29, wherein said bone screw is a load sharing screw and behaves as a fixed screw to hold vertebral alignment and a dynamic screw when there is bone resorption.

38. The method of claim 29, wherein said inserting step is further defined as inserting the at least one bone screw at an angle.

39. The method of claim 29, wherein under a set load, the bone screw and plate maintain a position at a first angle, and under a load that exceeds the set load, the bone screw moves to a new set point at a second angle.

40. The method of claim 39, wherein the bone screw resets and locks once the load is reduced below the set load.

41. The method of claim 29, wherein said connecting vertebral bodies step is further defined as connecting multiple vertebral bodies.

42. A method of using a load sharing plate assembly for connecting vertebral bodies, including the steps of:

inserting at least one bone screw through a plate into bone and locking the bone screw in the plate;

providing load sharing of the bone screw with the plate and allowing angulation of the bone screw to change at increased loads; and

securing and holding the plate against the vertebral bodies, thereby connecting the vertebral bodies.