Abstract:
A method is disclosed for preparing a space in bone of a human body to receive an insert at least in part therein. The method is performed with a device having a mid-longitudinal axis and a rotatable abrading element having an abrading surface. The method includes the steps of: activating the device to cause the abrading surface to move; contacting the abrading surface of the abrading element against the bone to remove bone therefrom to form a surface on the bone to create the space; rotating the abrading element about an axis different from the mid-longitudinal axis of the device; removing the abrading surface from the space; and positioning an insert into the space created in the bone.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is a continuation of Application No. 10/360,242, filed Feb. 6, 2003; which is a continuation of Application No. 09/663,311, filed Sep. 15, 2000, now U.S. Pat. No. 6,517,544; which is a continuation of and claims priority to International Application No. PCT/US99/12890, filed Jun. 9, 1999; all of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a device for insertion into a disc space between adjacent vertebral bodies in the human spine, and a method of working on those portions of the vertebral bodies adjacent that disc space to remove bone material and thereby access vascular bone. The device and associated method forms a surface on each of the vertebral body surfaces that are adjacent the intervertebral disc space, either sequentially, or in an alternative embodiment, simultaneously. The formed surface(s) have a shape and a contour corresponding to an interbody spinal insert to be implanted in the disc space.  
       BACKGROUND OF THE INVENTION  
       [0003]     Inserts for placement between adjacent vertebrae in the spine come in a variety of shapes and sizes and are made of a variety of materials. Such inserts may or may not be designed to promote fusion of the adjacent vertebral bodies. Inserts not intended to participate in or to promote fusion of the adjacent vertebrae, for example an artificial spinal disc, are intended to maintain the spacing between the adjacent vertebrae and to permit relative motion between those vertebrae. Such inserts may or may not include some type of surface treatment or structure designed to cause the vertebrae to attach and grow onto the surface of the insert to thereby stabilize the insert. Another type of insert comprises bone grafts. Such bone grafts are typically intended to participate in and to promote fusion of the adjacent vertebrae. Another type of insert for use in human spinal surgery comprises implants made of selected inert materials, such as titanium, that have a structure designed to promote fusion of the adjacent vertebrae by allowing bone to grow through the insert to thereby fuse the adjacent vertebrae. This last type of insert is intended to remain indefinitely within the patient&#39;s spine.  
         [0004]     The first known example of this last type of insert (for use in humans) is described in U.S. Pat. No. 5,015,247, which, in its preferred embodiment, discloses a hollow, threaded, cylindrical, perforated fusion implant device made of a material other than and stronger than bone and which is intended to cause fusion of adjacent vertebral bodies. A fusion promoting material, such as cancellous bone for example, is packed within the hollow portion of the implant and participates in the fusion. As used herein, the term fusion defines the growth of bone tissue from one vertebral body across a disc space to an adjacent vertebral body to thereby substantially eliminate relative motion between those vertebrae.  
         [0005]     Human vertebral bodies are comprised of a dense, hard outer shell and a relatively less dense inner mass. The hard outer shell is very densely compacted cancellous bone, resembling cortical bone at all but high magnification, and is generally referred to as the cortex. The inner mass is softer cancellous bone. The outer shell of cortex bone that is adjacent the disc and the bone immediately adjacent, and deep to it (both are subchondral, that is, beneath the cartilage layer that separates the bone from the disc), are defined for the specific purposes of this specification to comprise the “end plate region” or “end plate” to avoid any confusion that might otherwise arise from any inconsistency in the use of any of these terms. While it is understood that these terms may have other meanings more ordinary or special, and that those of ordinary skill in the art might otherwise differ as to the correct meanings of these terms, it is exactly for the purpose of removing any ambiguity that these terms are being so precisely defined specifically for this specification.  
         [0006]     For the purposes of this application only, and to avoid any possible confusion, the term “apophysical rim” is defined to be the bony rim of the densely compacted cancellous bone disposed peripherally about each of the opposed bony vertebral end plate regions of a human vertebral body. The rim is at least in part the all-bony remnant of what was the cartilaginous apophysical growth area prior to the conversion of that cartilage to bone at skeletal maturation.  
         [0007]     The spinal disc that resides between adjacent vertebral bodies maintains the spacing between those vertebral bodies and, in a healthy spine, allows for relative motion between the vertebrae. At the time of surgery, for example in the instance where fusion is intended to occur between adjacent vertebral bodies of a patient&#39;s spine, the surgeon typically prepares an opening at the site of the intended fusion by removing some or all of the disc material that exists between the adjacent vertebral bodies to be fused. Because the outermost layers of bone of the vertebral end plate are relatively inert to new bone growth, the surgeon must work on the end plate to remove at least the outermost cell layers of bone to gain access to the blood-rich, vascular bone tissue within the vertebral body. In this manner, the vertebrae are prepared in a way that encourages new bone to grow onto or through an insert that is placed between the vertebrae.  
         [0008]     Present methods of forming this space between adjacent vertebrae generally include the use of one or more of the following: hand held biting and grasping instruments known as rongeurs; drills and drill guides; rotating burrs driven by a motor; and osteotomes and chisels. Sometimes the vertebral end plate must be sacrificed as occurs when a drill is used to drill across the disc space and deeper into the vertebrae than the thickness of the end plate. Such a surgical procedure necessarily results in the loss of the hardest and strongest bone tissue of the vertebrae—the end plate—and thereby robs the vertebrae of that portion of its structure best suited to absorbing and supporting the loads placed on the spine by everyday activity. Nevertheless, the surgeon must use one of the above instruments to work upon the adjacent end plates of the adjacent vertebrae to access the vascular, cancellous bone that is capable of participating in the fusion and causing active bone growth, and also to attempt to obtain an appropriately shaped surface in the vertebral bodies to receive the insert. Because the end plates of the adjacent vertebrae are not flat, but rather have a compound curved shape, and because the inserts, whether made of donor bone or a suitable implant material, tend to have a geometric rather than a biologic shape, it is necessary to conform the vertebrae to the shape of the insert to be received therebetween.  
         [0009]     It is important in forming the space between the adjacent bone structures to provide a surface contour that closely matches the contour of the inserts so as to provide an adequate support surface across which the load transfer between the adjacent bone structures can be evenly applied. In instances where the surgeon has not been able to form the appropriately shaped space for receiving the inserts, those inserts may slip or be forcefully ejected from the space between the adjacent vertebrae, or lacking broad contact between the insert and the vertebrae, a failure to obtain fusion may occur.  
         [0010]     Furthermore, no known prior art device for preparing the vertebral end plates to receive an insert includes a working element that corresponds in shape, size, or contour to the shape of the insert to be implanted. That is, the known devices must be moved from side to side and in and out within the intervertebral space by an amount that exceeds the dimensions of the working element of the device, e.g., the rotating burr of a motor driven routing instrument or the working end of known osteotomes and chisels.  
       OBJECTS OF THE PRESENT INVENTION  
       [0011]     It is an object of the present invention to provide a device and method for quickly, safely, effectively, and accurately working upon a vertebral body end plate adjacent a disc space so as to, while preserving that end plate at least in part, remove bone to produce a receiving surface corresponding in size, shape, and contour to an insert to be implanted between the adjacent vertebrae.  
         [0012]     It is a further object of the present invention, in at least certain embodiments, to provide a device capable of simultaneously working upon both of the vertebral body end plates adjacent a disc space to produce opposed receiving surfaces in the adjacent end plates corresponding in size, shape and contour to an insert to be implanted, and in so doing to define the shape to the insert space.  
         [0013]     It is a further object of the present invention to provide a vertebral interspace preparation device that, in a preferred embodiment, is capable of working with linear insertion, i.e., insertion along a single axis, and without the need to substantially move the device from side to side within the disc space along a second axis. In such a preferred embodiment, the device has at its working end an abrading element having a width generally corresponding to the width of the insert to be implanted.  
         [0014]     It is a further object of the present invention to have a safety mechanism built into the device that limits the depth of insertion of the device into the spine.  
         [0015]     It is a further object of the present invention to provide a vertebral interspace preparation device that has interchangeable ends so as to be capable of producing a variety of differently sized and contoured surfaces and shapes within the intervertebral space.  
         [0016]     It is a further object of the present invention to have abrading surfaces extending to the leading end of the device such that the device may remove bone along its leading end as it is advanced within the disc space.  
         [0017]     These and other objectives of the present invention will occur to those of ordinary skill in the art based on the description of the preferred embodiments of the present invention described below. However, not all embodiments of the inventive features of the present invention need achieve all the objectives identified above, and the invention in its broadest aspects is not limited to the preferred embodiments described herein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a partial top view of a first preferred embodiment of a device embodying the present invention, which device includes an abrading element having a single abrading surface;  
         [0019]      FIG. 1A  is a full top view of the device of  FIG. 1  illustrating the handle of the device;  
         [0020]      FIG. 2  is a side view of the device shown in  FIG. 1 ;  
         [0021]      FIG. 3  is an end view of the device shown in  FIGS. 1 and 2 ;  
         [0022]      FIG. 4  is a second top view of the device shown in  FIG. 1  and also illustrates the preferred range and type of motion of the abrading element;  
         [0023]      FIG. 4A  is a partial view of the device of  FIGS. 1-4  showing a preferred mechanism for connecting the handle to the device shaft;  
         [0024]      FIG. 5  is a detailed view of a portion of the device shaft illustrating notches used to hold a stop member in a selected position;  
         [0025]      FIG. 6  is a detailed view of a spring-biased lever mechanism that may be used to adjust the position of a stop member;  
         [0026]      FIG. 7  is a detailed view of a coupling mechanism that may be used to movably couple the drive mechanism to the abrading element;  
         [0027]      FIG. 8  is a detailed view of the mounting member disposed at the distal end of the device shaft;  
         [0028]      FIG. 9  is a further detailed view of the coupling mechanism and mounting member illustrated in  FIGS. 7 and 8 ;  
         [0029]      FIG. 10  is a detailed view illustrating a preferred way of movably connecting the coupling mechanism to the abrading element;  
         [0030]      FIG. 11  is top view of a first vertebral body having a surface prepared in one of the end plates by a device incorporating the present invention;  
         [0031]      FIG. 12  is a top view of a second vertebral body, different than that shown in  FIG. 11 , having a surface prepared in one of the end plates by a device incorporating the present invention;  
         [0032]      FIG. 13  is a cutaway side view of the vertebral body shown in  FIG. 12 ;  
         [0033]      FIG. 14  is a cutaway side view of adjacent vertebral bodies having their respective adjacent end plates prepared by a device incorporating the present invention to form a space configured to receive an insert;  
         [0034]      FIG. 15  is an exaggerated perspective view of the vertebral body illustrated in  FIG. 12  showing the formation of the receiving surface in the vertebral end plate;  
         [0035]      FIG. 15A  is a top view of a section of a human spine illustrating the portion of the disc that is typically removed to accommodate the implantation of an intervertebral insert;  
         [0036]      FIG. 16  is a top view of a second preferred embodiment of a device embodying the present invention, which device includes an abrading element having two abrading surfaces;  
         [0037]      FIG. 16A  is a top view of the device of  FIG. 16  illustrating irrigation and suction tubes that may be incorporated into the device;  
         [0038]      FIG. 17  is a side view of the device shown in  FIG. 16 ;  
         [0039]      FIG. 17A  is a side view of the device shown in  FIG. 16A ;  
         [0040]      FIG. 17B  is a detailed view of one possible drive mechanism that may be used with the second embodiment of the present invention;  
         [0041]      FIG. 18  is an alternative embodiment of an abrading element having two abrading surfaces, which abrading surfaces are inclined relative to one another to form a space between the adjacent vertebral bodies that approximates the lordotic curvature of a human spine at the location that will receive the interbody insert;  
         [0042]      FIG. 19  is a cutaway side view of adjacent vertebral bodies showing a lordotically configured space created between the vertebrae by the abrading element shown in  FIG. 18 ;  
         [0043]      FIG. 20  shows an alternative embodiment of a mechanism for driving an abrading element;  
         [0044]      FIG. 21  illustrates an alternative path of motion possible for an abrading element according to the present invention;  
         [0045]      FIG. 22  illustrates a further alternative path of motion possible for the abrading element;  
         [0046]      FIG. 23  illustrates an alternative configuration of the abrading element suitable for creating concave insert receiving surfaces on the adjacent vertebral end plates;  
         [0047]      FIG. 24A  is a side view of a vertebral body illustrating end plates or end plate regions;  
         [0048]      FIG. 24B  is a cutaway top view of a vertebral body illustrating the apophysical rim and cancellous bone;  
         [0049]      FIG. 25A  is a perspective view of an alternative to the second preferred embodiment of a device embodying the present invention, which device includes an abrading element having two abrading surfaces;  
         [0050]      FIG. 25B  is a top view of the device shown in  FIG. 25A ;  
         [0051]      FIG. 26  is a detailed side view of one possible drive mechanism that may be used with the alternative to the second preferred embodiment of the present invention;  
         [0052]      FIG. 27  is an alternative embodiment of an abrading element having upper and lower disc-shaped members angled relative to each other to form a space between the adjacent vertebral bodies that approximates the lordotic curvature of a human spine at the location that will receive the interbody insert;  
         [0053]      FIG. 28  is a top view of the device of  FIG. 25A  illustrating irrigation and suction tubes that may be incorporated into the device;  
         [0054]      FIG. 29  is a perspective view of the device of  FIG. 25A  and a guide for providing protected access to the space between adjacent vertebral bodies;  
         [0055]      FIG. 30  is a side view of a disc penetrating extension inserted between adjacent vertebral bodies;  
         [0056]      FIG. 31A  is a rear perspective view of the guide of  FIG. 25A ;  
         [0057]      FIG. 31B  is a perspective view of the guide of  FIG. 25A  illustrating tapered disc penetrating extensions;  
         [0058]      FIG. 31C  is a perspective view of the guide of  FIG. 25A  illustrating disc penetrating extensions with parallel upper and lower surfaces;  
         [0059]      FIG. 31D  is a perspective view of the guide of  FIG. 25A  illustrating substantially lordotic disc penetrating extensions;  
         [0060]      FIG. 32A  is a rear perspective view of the guide of  FIG. 25A  illustrating female tracks;  
         [0061]      FIG. 32B  is a rear perspective view of the guide of  FIG. 25A  illustrating the absence of tracks;  
         [0062]      FIG. 33  is a rear perspective view of the guide of  FIG. 25A  including a slotted extension;  
         [0063]      FIG. 34A  is a partial perspective view of the guide of  FIG. 25A  illustrating a distance between the front and rear portions;  
         [0064]      FIG. 34B  is a partial side view of the guide of  FIG. 34A ;  
         [0065]      FIG. 35A  is a cross-sectional view of the body of the guide of  FIG. 25A ;  
         [0066]      FIG. 35B  shows an alternative circular cross-section of the body of the guide of  FIG. 25A ; and  
         [0067]      FIG. 35C  shows an alternative oval or rounded cross-section of the body of the guide of  FIG. 25A . 
     
    
     SUMMARY OF THE INVENTION  
       [0068]     The device, in its preferred embodiment, generally comprises an abrading element movably and replaceably mounted on the distal end of a shaft, and a depth limiting mechanism to control the depth of insertion of the abrading element into the intervertebral space (i.e., the disc space). The device also includes a handle that may be detachable from the shaft. As used herein, the term “handle” refers to a portion of the device that a surgeon may grip or otherwise manipulate to guide the working end of the device. That “handle” may, in fact, have multiple purposes. For example, the handle may be a portion of the shaft on which the abrading element is mounted at one end. Alternatively, the handle may be part of a segment that connects the device to a power source, for example, part of a conduit that supplies pressurized gas if the power source is turbine driven. In any event, the term “handle” is used herein in its broadest context to refer to that portion of the device that the surgeon chooses to grasp.  
         [0069]     Additionally the shaft may be detachable from the abrading element. The device also includes a drive mechanism for transmitting power to activate, i.e., move, the abrading element, and the drive mechanism is connected to an energy source, e.g., a rechargeable battery, that may be housed within the handle of the device. By way of example only, the drive mechanism may comprise an electric motor or an electromagnetic oscillating mechanism. Or, again by way of example only, the drive mechanism and handle in which it is disposed may comprise the head unit of a gas powered turbine of the type commonly used in other surgical instruments.  
         [0070]     In the preferred embodiment, the abrading element is generally as wide as the insert to be implanted between the adjacent vertebral bodies adjacent the disc space. The receiving bed, i.e., the prepared surface of the vertebrae, when formed by the device, will correspond in shape, size, and contour to the corresponding surfaces of the insert to be implanted. By way of example only, the surface produced may be flat or concave, or of some other desired shape and size so as to correspond to the upper or lower vertebrae contacting surfaces of the insert that will be implanted between the vertebrae. The device may also include a leading end that is capable of cutting through bone and/or disc material to form a pocket having a contour corresponding to the forward aspect and leading end of the insert to be implanted.  
         [0071]     In a first preferred embodiment, the abrading element includes a single abrading surface that works on one vertebral surface at a time within the disc space.  
         [0072]     In a second preferred embodiment, the abrading element includes a pair of opposed, outwardly facing abrading surfaces which lie in planes that may be either parallel to each other or, alternatively, convergent to each other. This embodiment of the present invention offers the further benefits of saving time by simultaneously preparing both of the vertebral end plates adjacent a disc space. The second embodiment not only includes the ability to simultaneously create two opposed surfaces, but also to shape the three-dimensional space that will be created between the adjacent vertebrae, which shape can be made to conform to the desired lordosis of that portion of the spine that will receive the insert.  
         [0073]     However, the abrading element of the present invention is not limited to being a unitary, one piece construction, regardless of the number of abrading surfaces the abrading element may have. The abrading element may comprise multiple pieces that, by way of example and not limitation, are mountable on the end of the device to, in combination, define the overall shape of the abrading element and its abrading surface or surfaces. Thus, the term “abrading element” is used herein to refer to both a unitary, one piece construction or a multi-piece construction.  
         [0074]     Thus, the present invention provides a device and method for preparing a disc space between adjacent vertebral bodies to receive an insert, and prepares that disc space by removing a portion of the end plate of the vertebrae adjacent that disc space to form predetermined surfaces in the end plates. The prepared surfaces are sized and contoured to have broad intimate contact with the insert to be implanted between the adjacent vertebrae, which broad contact provides for increased insert stability. This broad area of intimate contact between the vertebrae and the insert promotes bone ingrowth from the vertebrae into the insert, and also provides a broad area over which to support the incumbent loads so as to minimize the risk of vertebral collapse or subsidence of the insert into the vertebra.  
         [0075]     The abrading element is mounted on the mounting member and may be removable and interchangeable. In such an embodiment, the mounting member may be, but does not have to be, attachable to a shaft that is attachable to the handle. The abrading element and the mounting member may be separable from each other. Alternatively, the abrading element and the mounting member may, together, be removable from the handle. Various configurations of the abrading element and its abrading surface or surfaces can be used to form various contours in the adjacent vertebral bone structures.  
         [0076]     In the instance where the abrading element has one abrading surface, the opposite surface of the abrading element, or the opposite surface of the mounting member, may be specifically designed to be non-abrading to the opposed adjacent vertebral end plate. Such a non-abrading surface may be designed to provide a mechanical advantage (such as achieved with a fulcrum) to allow the surgeon to increase the pressure of the abrading surface against the end plate being worked on, and, further, may be curved so as to be centering within the disc space by contact with a vertebral surface.  
         [0077]     While the preferred embodiment of the present invention is discussed and disclosed herein with respect to creating a space between adjacent vertebrae in the spine, the present invention is not limited to a device for creating a space between adjacent vertebrae, but can also be used in other portions of the body where it is desirable to place an insert between adjacent bone structures. Furthermore, and as alluded to above, an embodiment of the present invention may have upper and lower abrading surfaces that are in angular relationship to each other so as to, for example, match the natural lordotic curvature of the human spine at the location of the vertebrae to be operated upon. Similarly, certain of the abrading surfaces of the abrading element may be configured with a convex, or even compound, geometry so as to form surfaces in the adjacent bone structures having a desired contour. Additionally, sequentially larger ones of the abrading element, or mounting member, may be used to form the desired space in a step-wise fashion, or the abrading element may be sized to substantially match the final desired width of the surface to be formed in the vertebral end plate. Furthermore and also as noted above, the abrading element may be configured with a sharpened leading edge to allow the abrading element to “forward cut” as it is inserted between the adjacent vertebrae. In this manner, progressive insertion * of the abrading element between the vertebrae can be facilitated.  
         [0078]     While the present invention has been generally described above, and the preferred embodiments of that invention will be described in detail below, neither that general description nor the detailed description limits the scope of the present invention. That scope is defined solely by the claims appearing at the end of this patent specification.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0079]     With reference to  FIGS. 1 and 1 A, a first embodiment of the present invention comprises a disc space preparation device generally referred to by numeral  10 . Device  10  includes a shaft  12  and a handle  13 . Handle  13  may be formed with any number of known shapes designed to make the surgeon&#39;s grip on the handle more secure or comfortable. Similarly, handle  13  may include a soft rubber covering or may be formed, at least partially, of a material designed to promote a secure grip of the surgeon&#39;s hand on the handle. Those of ordinary skill in the art will recognize the many types of surface configurations or materials of which the handle can be made to achieve these goals.  
         [0080]     With continued reference to  FIGS. 1 and 1 A, disposed within handle  13  is a drive mechanism diagrammatically depicted by box  14 . Although in the embodiment of the device shown in  FIGS. 1 and 1 A the drive mechanism  14  is disposed within handle  13 , it need not be disposed in the handle. The drive mechanism may be disposed completely or partially outside of the handle, for example, where the drive mechanism is a gas powered turbine element such as is used in some known surgical instruments. Drive mechanism  14  is operably connected to the proximal end of shaft  12  and is capable of moving an abrading element  18  disposed at a distal end  15  of shaft  12 . Abrading element  18  has an abrading surface  19 . Drive mechanism  14  moves abrading element  18  at a sufficiently high rate to quickly and efficiently cause abrading surface  19  to form the desired space and the desired surface contours in the adjacent vertebral bone structures. As illustrated in  FIG. 2 , the abrading element  18  is mounted on a mounting member  16  disposed at the distal end  15  of shaft  12 . In this embodiment, the mounting member is fixed to shaft  12  and only the abrading element moves. However, many alternative mechanisms for mounting the abrading element on the device are possible within the scope of the present invention, including a mechanism wherein mounting member  16  is movably attached to shaft  12  and the drive mechanism moves both the mounting member and the abrading element attached thereto. Also, mounting member  16  may be designed with a surface  17  on the side of the mounting member  16  opposite abrading element  18 . Surface  17  is designed, in the embodiment shown, to bear against the end plate that is opposite the end plate being worked on by abrading element  18 . In this manner, surface  17  provides a bearing surface that the surgeon may use to gain a mechanical advantage (such as with a lever) to contact abrading surface  19  of abrading element  18  against the end plate being worked on. Additionally, surface  17  may be curved as shown in  FIG. 2 , or otherwise shaped, to contact one end plate and, thereby, center or otherwise position abrading element  18  in the disc space.  
         [0081]     As presently contemplated, the motion of the abrading element may be vibratory, reciprocatory, oscillatory, or rotary. In the first preferred embodiment of device  10 , the motion of the abrading element is rotary in a clockwise then counterclockwise direction through a preferred range of motion of between 20□ to 45□, as illustrated in  FIG. 4 . Whatever type and range of motion is selected for the abrading element, it will likely, although not necessarily, be in a direction that is generally parallel to the plane of the surface to be formed in the vertebral end plate. However, since the shape of that surface contour is not necessarily flat, neither is the direction of the motion of the abrading element necessarily parallel to all points on that desired surface contour.  
         [0082]     By way of example and not limitation, the drive mechanism may comprise a magnetic driver of the type described in U.S. Pat. No. 5,263,218. Alternatively, the drive mechanism may take the form of a mechanical drive utilizing a cam mechanism such as described in U.S. Pat. No. 5,383,242. Additionally, drive mechanisms used in known surgical power milling apparatus may also be used. U.S. patent application Ser. No. 08/688,758 titled Milling Instrumentation and Method for Preparing a Space Between Adjacent Vertebral Bodies is hereby incorporated by reference. As presently contemplated, the drive mechanism should be capable of moving the abrading element and its abrading surface or surfaces at a speed sufficient to abrade the hard cortical bone of the vertebral end plate. The working range and speed of motion of the drive mechanism will be readily selected by those of skill in the art.  
         [0083]     In one embodiment of the present invention utilizing reciprocating motion, the stroke or amount of reciprocating movement is relatively small and can be selected as desired to achieve the purpose of abrading the adjacent bone structures. That stroke may be selected based on the relative strength of the bone structures to be abraded, the relative strength of the material forming the abrading element, and the type of surface roughening formed on one or more surfaces of the abrading element. This relatively small reciprocating movement of the abrading element results in a tightly controlled excursion area between the adjacent vertebrae being prepared to receive an insert. In contrast, a motorized burr must be moved free hand and in a side-to-side motion within the disc space by the surgeon to form a space to receive an insert. Thus, use of such a motorized burr does not provide a way of forming a precise surface shape in the vertebral end plate. Additionally, because the motorized burr rotates in a single direction, it may catch on a piece of the vertebra and cause the burr to jerk forcefully out of the intervertebral space. Such an occurrence will not happen with the device  10  because of the controlled excursion of the device.  
         [0084]     In the first embodiment of the present invention described herein, drive mechanism  14  is powered by a rechargeable battery illustrated as box  66  in  FIG. 1A . Battery  66  is also preferably located within handle  13  of device  10 . However, the present invention is not limited to use with a rechargeable and/or replaceable battery  66 , but may also be configured to run on any standard electrical source, such as 110 volt, 60 cycle power sources, with or without the accompanying use of a transformer to reduce that voltage as may be necessary and desirable. Alternatively, the drive mechanism may comprise a gas turbine mechanism as is common for many types of powered surgical instruments. The particular power source that powers drive mechanism  14  does not form a part of the present invention except to the extent it is adapted to achieve the appropriate and desirable amount of movement of the abrading element.  
         [0085]     Referring now to  FIG. 2 , which shows a portion of device  10  in side view, mounting member  16  extends from the distal end  15  of shaft  12 . As described below with reference to  FIGS. 7-10 , the mounting member may be configured to house a portion of a coupling mechanism that, in turn, couples drive mechanism  14  to an abrading element  18  to move the abrading element in at least one degree of freedom while the mounting member remains stationary relative to the handle. The term “degree of freedom” is used herein in its ordinary sense to refer to motion in a standard three-dimensional environment. That three dimensional environment may be defined by X, Y, and Z axes. In such a three-dimensional environment, 6 degrees of freedom exist: translational motion along each of the X, Y, and Z axes, and rotational motion about each of the X, Y, and Z axes. Thus, drive mechanism  14  is operable to move abrading element  18  in a reciprocating, oscillating, or vibrating motion transversely along one or more of the X, Y, and Z axes. Alternatively, or in conjunction, drive mechanism  14  may be configured to move abrading element  18  around one or more of the X, Y, or Z axes. Of course, for purposes of achieving the objectives of the present invention, it may not be necessary that the drive mechanism reciprocate or oscillate mounting member  16  in anything more than a single degree of freedom.  
         [0086]     Referring now to  FIGS. 7-10 , in a present preferred embodiment, abrading element  18  includes a projection  20  (as best seen in  FIG. 10 ) that is to be received in a corresponding aperture  21  formed in mounting member  16  (as best seen in  FIG. 8 ). Mounting member  16  may be fixedly disposed on distal end  15  of shaft  12 . Alternatively, mounting member  16  may be removably attached to distal end  15  of shaft  12 . In the present embodiment, a coupling mechanism is used to couple abrading element  18  to mounting member  16  and to the drive mechanism.  FIG. 10  illustrates that coupling mechanism with mounting member  16  removed to show in clearer detail the coupling mechanism.  
         [0087]     With reference to  FIGS. 7 and 9 , the coupling mechanism in the first preferred embodiment of the present invention comprises a generally tubular member  100  received within a hollow, longitudinal aperture of shaft  12 . Tubular member  100  includes a proximal end  102  and a distal end  104 . A T-shaped connector  108  is configured at the end of a drive rod  112 . Drive rod  112  is adapted to be received within a corresponding aperture  110  in tubular member  100 . A pivot rod  114  extends from the distal end  104  of tubular member  100  and is adapted to fit in a corresponding hole  115  formed in mounting member  16  at the end of shaft  12 .  
         [0088]     With reference to  FIG. 8 , mounting member  16  includes a central aperture  21  and an oblong slot  23  formed through a wall of mounting member  16 . Slot  23  is configured to allow connector  108  to pass through when the connector is turned (as illustrated by the arrows in  FIG. 7 ) so that the branches forming the “T” extend laterally. Mounting member  16  also includes a post  25  that projects into aperture  21 . Post  25  is sized to mate with an aperture  27  formed in projection  20  of abrading element  18  as shown in  FIG. 10 . Projection  20  is also formed with a slot  29  designed to receive connector  108  as described below.  
         [0089]     With reference to  FIG. 9 , tubular member  100  fits within shaft  12  with connector  108  extending from distal end  13  of the handle. Projection  20  of abrading element  18  is inserted into aperture  21  of mounting member  16  such that post  25  fits into aperture  27  of projection  20 . Connector  108  is initially rotated such that its “T” branch fits through slot  23  of mounting member  16  and then is rotated 90□ as shown by the arrows in  FIG. 7 . With the “T” branches of connector  108  extending parallel to post  25 , projection  20  of abrading element  18  fits into aperture  21  of mounting member  16  such that connector  108  fits into slot  29 , and post  25  fits into aperture  27 .  
         [0090]      FIG. 10  shows the same structure as  FIG. 9  but with mounting member  16  removed for purposes of better illustrating the mating of connector  108  with slot  29 . As shown in  FIG. 10 , pivot rod  114  fits into a mating aperture  115  formed at the distal end of shaft  12 , and projection  20  includes a second slot  120  formed laterally from slot  29 . Slot  120  is configured to allow connector  108  to toggle back and forth as tubular member  100  is reciprocatingly pivoted about pivot rod  114  by the device&#39;s drive mechanism. This “toggling” action of member  100  about pivot rod  114  moves T-shaped connector  108  and abrading element  18  in the direction indicated by the double headed arrow in  FIG. 10 .  
         [0091]     Of course, many variations exist for mechanisms to couple the drive mechanism  14  to abrading element  18 . The coupling mechanism described above is provided by way of example and not limitation.  
         [0092]     In the embodiment described, mounting element  16  may interchangeably receive various ones of abrading element  18 . Thus, abrading element  18  may be quickly and easily attached to and detached from mounting member  16  during surgery. While in the preferred embodiment the abrading surface of the abrading element is selected to have a width that is substantially the same as the width of the surface to be formed in the vertebral end plate (to eliminate any need to move the abrading element side to side in the disc space as noted earlier), a surgeon might also elect to use an abrading element that is smaller in width than the ultimate desired width of the surface to be formed. Thereafter, the surgeon may use successively larger abrading elements  18  until she arrives at the desired dimensions of the space formed between the adjacent bone structures. This approach also eliminates any need to significantly move the abrading element in a side to side path within the disc space.  
         [0093]     Referring back to  FIGS. 1 and 1 A, device  10  includes at least one stop member  28  adjustably disposed on mounting element  16  to limit the travel of the abrading element into the adjacent bone structures. Stop member  28  includes an abutment  30  that will eventually contact the vertebrae to limit travel of the abrading element  18  as the abrading element forms the space between the adjacent vertebrae. Stop member  28  is not limited to a single abutment. Two or even more abutments may be formed around the circumference of stop member  28  and the leading edges of such multiple abutments may be configured to terminate at different positions relative to shaft  12 . Other mechanisms for limiting the depth of insertion of the device into the disc space are possible, and this example is provided by way of illustration.  
         [0094]     In the embodiment of stop member  28  shown in  FIGS. 1, 2 , and  3 , a slot  29  is formed in stop member  28  and an extension  31  projects from shaft  12  through slot  29 . Slot  29  is dimensioned to correspond to the desired maximum amount of adjustment of the stop member relative to the handle. As shown in  FIG. 2 , and in  FIGS. 5 and 6 , stop member  28  is held at a desired position on shaft  12  by spring-biased lever  32 . Lever  32  includes an actuator end  33  with grooves, notches, knurls, or other surface preparation that is pushed toward shaft  12  against the bias of spring member  34  to lift engaging end  35  of lever  32  away from shaft  12 . Engaging end  35  is configured to mate with notches  36  formed in shaft  12  as shown in  FIG. 5 . Notches  36  in shaft  12  are not visible in  FIG. 2  since they are covered by stop member  28 . Step member  28  is also formed with an opening sized to allow engaging end  35  of lever  32  to fit in notches  36 . Numerous other structures for holding stop member  28  at a desired position on shaft  12  are possible, and spring biased lever  32  is provided in this embodiment of the present invention by way of example and not limitation. For instance, shaft  12  may include threads on a portion of its outer surface to receive a threaded adjusting collar that will lock stop member  28  in a desired position.  
         [0095]     With reference to  FIGS. 21 and 22 , examples of the types of motion through which abrading element  18  may be moved are illustrated. In  FIG. 21 , the motion is vibratory in a plane generally parallel to the abrading surface of the abrading element. In  FIG. 22 , the motion is linear and reciprocating as indicated by the double headed arrow of that figure. Alternatively, the motion may comprise slight rotation about a pivot point near distal end  15  of shaft  12  such that the oscillation is arcuate about an axis extending into and out of the sheet of paper on which  FIGS. 21 and 22  are illustrated. Other motions such as full and complete rotation as described below with reference to the second preferred embodiment are also useful.  
         [0096]     Any of these types of motion will be adequate to cause the abrading surface or surfaces of abrading element  18  to abrade adjacent bone structures to thereby form the appropriately sized and dimensioned space between those bone structures for receiving an insert. In this regard, at least one or more of the surfaces of abrading element  18  is roughened such that it can abrade the adjacent bone structures.  
         [0097]      FIGS. 11, 12 ,  13 ,  14 , and  15  illustrate various views of vertebral bodies that have been worked on by a device incorporating the present invention. The cross-hatching in these figures represents the softer, blood-rich cancellous bone of the vertebrae beneath the harder, outer cortical bone shell.  FIG. 11  shows a top view of a first vertebral body  70  with a surface  72  formed by a circular abrading element  18  as shown in  FIG. 1 . The width of surface  72  formed on first vertebral body  70  closely matches the width of an abrading element  18  that was advanced into the disc space along a single front to back axis. A second vertebral body  77  has a greater depth than vertebral body  70 . The second vertebral body  77  shown in  FIG. 12  has a surface  75  formed by extending abrading element  18  deeper into the distal interspace along front-to-back axis  74 .  FIG. 13  illustrates a cutaway side view of the vertebral body shown in top view in  FIG. 12 .  FIG. 14  shows a cutaway side view of adjacent vertebral bodies  70  and  76  that have had surfaces  72  and  78  formed in their respective adjacent end plates. Note that, as shown in exaggerated view in  FIG. 15 , the vertebral end plate surface is prepared to a uniform shape, which while preserving the deeper portions of the end plate, also forms a socket depressed from the hard cortical uprisings of bone such as the uncovertebral joints  80 . Recognize that the depth of this remaining end plate is exaggerated in  FIG. 15  to illustrate this result of using the present invention. This remaining portion of the more cortical rim  80  assists in retaining the insert in the desired position between the adjacent vertebrae by acting as an abutment preventing lateral or posteriad movement of the insert. The prepared faces of these abutment portions of the vertebral end plate also increase the surface area of contact between the insert and the vertebral body.  
         [0098]      FIG. 15A  illustrates, in top view, the ideal portion of a disc that is removed to accommodate implantation of the insert. In  FIG. 15A , the annulus fibrosus is illustrated with rings  200  extending around the periphery of the intervertebral disc space. Inside the annulus fibrosus is the nucleus pulposus  202  illustrated in cross-hatching. The general area and volume of the nucleus pulposus to be removed with the device of the present invention is illustrated with additional cross-hatchings  204 . The preferred dimensions of the space created by the device is generally not as wide as the entire nucleus pulposus.  
         [0099]     Referring now to  FIGS. 16 and 17 , a second embodiment of the present invention is shown wherein abrading element  18  includes two abrading surfaces: an upper abrading surface  90  and a lower abrading surface  92 .  FIG. 16  is a top view of such a device and  FIG. 17  is a side view. In this embodiment, abrading element  18  includes two disc-shaped members,  81  and  83 , that are mounted on the distal end of the device by a recessed screw  147  and screw shaft  148  as described below. Abrading surface  90  is formed on one side of disc-shaped member  81 , and abrading surface  92  is formed on one side of disc-shaped member  83 . Thus, the abrading element  18  illustrated in  FIGS. 16 and 17  provides an example of an instance where the abrading element comprises multiple pieces that fit together to form the abrading element. As previously described, the present invention contemplates unitary, one piece constructions for the abrading element as well as multi-piece constructions. In the embodiment of the present invention shown in  FIGS. 16 and 17 , the upper and lower disc-shaped members  81  and  83  and their associated abrading surfaces may be rotated in opposite directions so as to counteract and balance any torque applied to the shaft and handle of the device as the abrading element digs into and abrades the vertebral end plates. This counter-rotation of the members  81  and  83  also prevents the device from being pulled to one side as the vertebral end plates are being worked on. This counter-rotating motion of the two members  81  and  83  is illustrated by the arrows in  FIG. 17  and may be achieved, as illustrated in  FIG. 17B , by using a spinning drive rod  160  that extends through shaft  12  and is configured with a gear  162  at its distal end that engages with mating gear teeth  93  and  94  formed on respective inner sides of disc-shaped members  81  and  83  as shown in  FIGS. 17A and 17B . Disc-shaped members  81  and  83  may be attached to the end of shaft  12  by a recessed screw  147  that is received in a mating, threaded screw shaft  148  as shown in  FIG. 17B . Thus, in this second embodiment, the mounting member comprises threaded screw shaft  148  and recessed screw  147  disposed at the distal end of a tapered extension  149  that protrudes from shaft  12 .  
         [0100]      FIGS. 16A and 17A  show a further enhancement to the device shown in  FIGS. 16 and 17  wherein the shaft  12  also includes an irrigation tube  150  and a suction tube  152  that may be formed within, or outside of, shaft  12 . These irrigation and suction tubes may be connected to appropriate sources of irrigation fluid and a source of vacuum, respectively, to efficiently irrigate and clear the surgical site during use of the device.  
         [0101]     Alternatively, and as shown in  FIG. 20 , upper and lower disc-shaped members  94  and  96  may be formed with inwardly sloping, ramped surfaces  97  and  98  that engage a cone-shaped driver  99  disposed on the distal end of a rotating drive rod  160  to turn the upper and lower abrading surfaces in opposite directions as the drive rod spins about its axis. Alternatively, the lower surfaces of the abrading element  18  and the cone-shaped driver can be radially splined to engage one another. Such a dual surface abrading element can simultaneously work on both adjacent end plates of adjacent vertebrae. Abrading member  18  having such dual abrading surfaces can even be constructed such that the distance between the abrading surface is adjustable to accommodate variations in the height of the disc space. By way of example and not limitation, paired, wedge-shaped blocks may be disposed between the abrading surfaces and an adjusting screw can be provided to extend through threaded apertures in each wedge-shaped block. As the adjusting screw is turned, the wedge-shaped blocks move relative to one another to change the distance between the abrading surfaces.  
         [0102]     In a still further embodiment of the present invention as illustrated in  FIG. 18 , the abrading element  18  may have upper and lower abrading surfaces  140  and  142  that are angled or tilted relative to each other. The degree of angle or tilt may be selected to match the natural lordotic curvature of the spine at the location of the vertebrae to be worked on. The distance between the upper and lower abrading surfaces  140  and  142  in this embodiment may also be adjustable to accommodate differing disc heights between the vertebrae. Such angled abrading surfaces may also be driven in counter rotation by drive rod  160  as shown by the arrows in  FIG. 18 . As illustrated in  FIG. 19 , the slope of the surfaces  144  and  146  formed in the adjacent vertebrae by the abrading element shown in  FIG. 18  matches the lordotic curvature of the spine at that location.  
         [0103]     Numerous other configurations of abrading element  18  are possible within the scope of the present invention. For example and with reference to  FIG. 23 , abrading elements  218  may be convex to form concave receiving surfaces  220  in the vertebral end plates. The geometry and configuration of the shapes of the abrading elements can be matched to the desired shape and configuration of the space which the surgeon intends to create between adjacent bone structures and to the desired contour of the surfaces created in the bone structures.  
         [0104]     Additionally, the abrading surface of abrading element  18  may be configured as roughenings, knurls, ridges, small pyramid shaped projections, or any other surface configuration that is capable of abrading the bone structures.  
         [0105]     Where only one surface of the abrading element is configured to abrade an end plate of the vertebral body, an opposite surface (or the opposite surface of mounting member  16  as illustrated by element  17  in  FIG. 2 ) may be configured to be supported by the adjacent end plate without causing any significant abrasion of that adjacent end plate. In such an instance, the non-abrading surface of the abrading element, or surface  17  of mounting member  16 , may be configured to allow the surgeon to achieve a mechanical advantage that increases the bearing pressure of the abrading surface against the end plate being worked on, and also to locate and center the device. In this manner, one adjacent end plate provides mechanical support to the device while the device works on the adjacent end plate. After an appropriate surface is formed on one end plate, the device can be turned 180□ to use the abrading surface on the other end plate.  
         [0106]      FIGS. 24A and 24B  show two views of human vertebral bodies.  FIG. 24A  shows a side view of a vertebral body V with end plates or end plate regions EP 1  and EP 2 .  FIG. 24B  is a top cutaway view of vertebral body V with apophysical rim AR and cancellous bone CB.  
         [0107]      FIGS. 25A and 25B  show an alternative to the second embodiment of the present invention, wherein abrading element  250  includes two abrading surfaces, upper abrading surface  252  and lower abrading surface  254 , and abrading surfaces  252  and  254  are configured with a sharpened leading edge.  FIG. 25A  is a perspective view of such a device and  FIG. 25B  is a top view. In this embodiment, abrading element  250  includes two disc-shaped members,  256  and  258 , that are removably mounted on the distal end of the device by a recessed screw  147  and screw shaft  148  as described above. Abrading surface  252  is formed on the edge of disc member  256 , and abrading surface  254  is formed on the edge of disc member  258 . The mounting facilitates removing disc-shaped members  256  and  258  to replace them with other disc-shaped members of similar or alternative abrading surface design. Brace  255  prevents rotation of shaft  12  during use of the device.  
         [0108]     Alternatively, abrading surfaces  252  and  254  may be manufactured separately from disc-shaped members  256  and  258 . In such a design, abrading ring  251  includes abrading surface  252  and abrading ring  253  includes abrading surface  254 . Abrading ring  251  is mounted on disc-shaped member  256 , and abrading ring  253  is mounted on disc-shaped member  258 . Such a mounting may be accomplished by threadably connecting an abrading ring to its associated disc-shaped member. The threads of such a threadable connection preferably oppose the direction of rotation of the disc-shaped member when the device is in use. Other equivalent mountings to the threadable connection may be employed.  
         [0109]      FIG. 26  shows the counter-rotation of disc-shaped members  256  and  258  and their associated abrading surfaces. This counter-rotating motion may be achieved by using a spinning drive rod  160  that extends through shaft  12  and is configured with a gear  162  at its distal end that engages with mating gear teeth  93  and  94  formed on respective inner sides of disc-shaped members  256  and  258 .  
         [0110]     Alternatively, and as shown in  FIG. 27 , abrading element  250  may have upper and lower disc-shaped members  256  and  258  that are angled or tilted relative to each other. The degree of angle or tilt may be selected to match the lordotic curvature of the spine at the location of the vertebrae to be worked on. The distance between the upper and lower disc-shaped members may also be adjustable to accommodate different disc heights between the vertebrae. Such angled disc-shaped members may also be driven in counter-rotation by drive rod  160  and cone-shaped driver  270 .  
         [0111]      FIG. 28  shows a further enhancement to the device shown in  FIGS. 25A and 25B  wherein the shaft  12  also includes an irrigation tube  280  and a suction tube  282  that may be formed within, or outside of, shaft  12 . These irrigation and suction tubes may be connected to appropriate sources of irrigation fluid and a source of vacuum, respectively, to efficiently irrigate and clear the surgical site during the use of the device.  
         [0112]      FIG. 29  shows device  10  and guide  290 . Guide  290  includes a front portion  292 , a rear portion  294 , a body  295 , an opening  296 , a first disc penetrating extension  298 , and a second disc penetrating extension  299 . Placing front portion  292  of guide  290  against adjacent vertebral bodies inserts first disc penetrating extension  298  and second disc penetrating extension  299  into the disc space between the adjacent vertebral bodies. Guide  290  provides protected access to the disc space and the adjacent vertebral bodies for abrading element  250  via opening  296 . Opening  296  may be taller than the height of abrading element  250 . Such a taller opening  296  allows the sequential use of abrading elements  250  of increasing height or the insertion of an insert taller than the height of abrading element  250 . The insert is preferably sized and shaped to match the space formed in the spine by the abrading element. Front portion  292  may include one or more holes  291  for securing front portion  292  of guide  290  to at least one of the adjacent vertebral bodies using a pin, screw, or equivalent fastening device. Guide  290  may also include one or more tracks  293  to direct abrading element  250  while accessing the disc space and adjacent vertebral bodies via opening  296 . Such tracks  293  may include any surface designed to direct abrading element  250 . As shown in  FIG. 29 , first disc penetrating extension  298  and second disc penetrating extension  299  have an anatomic shape as discussed below. Other shapes may desired as also discussed below.  
         [0113]      FIG. 30  shows a side view of vertebral bodies V 1  and V 2  and second disc penetrating extension  299  in the disc space between the vertebral bodies. As shown, the anatomic shape of disc penetrating extension  299  substantially matches the contours of the adjacent vertebral bodies.  
         [0114]      FIG. 31A  shows a rear perspective view of guide  290  with anatomic shaped disc penetrating extensions  298  and  299 .  
         [0115]      FIGS. 31B, 31C , and  31 D show alternative shapes for the disc penetrating extensions of guide  290 . In  FIG. 31B , disc penetrating extensions  310  and  312  are tapered in the direction away from front portion  292 . In  FIG. 31C , upper surface  311  and lower surface  313  of disc penetrating extension  314  are substantially parallel. Similarly, upper surface  315  and lower surface  317  of disc penetrating extension  316  are substantially parallel. In  FIG. 31D , disc penetrating extensions  318  and  319  are substantially lordotic, or tapered in the direction toward, front portion  292 .  
         [0116]     Alternatively, and as shown in  FIGS. 31A, 32A , and  32 B, guide  290  may have male tracks, female tracks, or no tracks.  FIG. 31A  shows male tracks  293 .  FIG. 32A  shows female tracks  293 .  FIG. 32B  shows no tracks. It must be emphasized again that such tracks  293  may include any surface designed to direct abrading element  250 .  
         [0117]      FIG. 33  shows guide  290  having front portion  292  including slotted extension  330 . Front portion  292  may be secured to one of the adjacent vertebral bodies via slotted extension  330  using a pin, screw, or equivalent fastening device. Slotted extension  330  provides the capability to unsecure front portion  292  from one adjacent vertebral body, and then resecure front portion  292  to that same adjacent vertebral body after changing the amount of distraction between the adjacent vertebral bodies.  
         [0118]     Alternatively,  FIGS. 34A and 34B  show two views of an elongated version of guide  290 . Elongated guide  290  is preferably used for posterior lumbar interbody fusion. Body  295  includes a height, a width, and a distance between front portion  292  and rear portion  294 . The height of body  295  is preferably 8-20 mm. The width of body  295  is preferably 10-20 mm. The distance between front portion  292  and rear portion  294  of body  295  is preferably 150-350 mm. Disc penetrating extensions  298  and  299  may have any of the shapes disclosed above. Preferably, the disc penetrating extensions have a height of 5-20 mm and a length of 15-32 mm. For posterior lumbar interbody fusion, abrading element  250  is preferably 5-20 mm in height and 10-20 mm in width.  
         [0119]      FIGS. 35A, 35B , and  35 C show alternative cross-sectional shapes for body  295 .  FIG. 35A  shows a rectangular cross-section.  FIG. 35B  shows a circular cross-section.  FIG. 35C  shows an oval or rounded cross-section.  
         [0120]     Since any device incorporating the subject matter of the present invention is designed to be used within a surgical theater, it is desirable that the device be susceptible of sterilization by any one of many known expedients. In this regard, handle  12  of device  10  may be waterproof such that the device can be sterilized.  
         [0121]     Although various embodiments of the present invention have been disclosed for purposes of illustration, it will be understood by those of ordinary skill in the art that changes, modifications, and substitutions may be incorporated in these embodiments without departing from the spirit or scope of the present invention as defined by the claims, which follow.