Abstract:
A method and apparatus for customizing an intervertebral implant includes the initial step of obtaining a 3D anatomy of a series of vertebrae including an abnormal vertebra in a computer. The 3D anatomy of the series is then repositioned in the computer to eliminate the deformity caused by the abnormal vertebra. It is next determined whether a superior or inferior surface of the abnormal vertebra is an abnormal surface which causes the deformity, whereby an approximate gap between the abnormal surface and a desired normal surface is determined. Using that gap determination, a custom implant is constructed to engage the abnormal surface and fill the determined gap. Thus, when the implant is implanted between the abnormal surface and an adjacent surface of an adjacent vertebrae, the deformity is substantially compensated for. The implant may have articulation between the endplates to allow relative movement therebetween.

Description:
FIELD OF THE INVENTION 
     The invention relates to intervertebral implants, and an particular it relates to a customized intervertebral implant and a method of providing same. 
     BACKGROUND OF THE INVENTION 
     Patients with a broken vertebra and/or degenerative disc disease often have a deformed spine caused by trauma or the like due to a collapsed vertebra. The deformed spine results in a scoliotic or kyphotic spine. The usual treatment for such a condition where the adjacent vertebrae are collapsed is a fusion of the vertebrae concerned. With fusion, after accompanying repositioning of the spine during surgery, the deformed spine is returned to its desired anatomical shape. However, after fusion the adjacent levels of the spine experience increased movement as the adjacent levels must compensate for the immobility of the fused vertebrae. This results in higher strains for the adjacent levels and discs, leading to more disc disease problems and back pain. 
     While various artificial vertebrae have been proposed in the prior art to serve as a replacement for a damaged vertebra, and thus to help avoid the problems associated with fusion, this requires removal of the damaged vertebra. An example of such a replacement vertebra is shown in US Published Application 2005/0060034 to Berry et al. 
     Another major improvement in the treatment of the spine are intervertebral implants of the type which provide articulation such as universal movement between upper and lower endplates thereof, and hence between adjacent vertebrae. Examples of such intervertebral implants are those disclosed in US Published Applications 2005/0085917 (Marnay et al.) and 2004/0117022 (Marnay et al.); and examples of exemplary tools and methods for insertion of such intervertebral implants are those disclosed in International Published Application No. WO01/19295 (Beyersdorf et al.) and in US Published Applications 2004/0215198 (Marnay et al.), 2005/0021042 (Marnay et al), and 2004/0117022 (Marnay et al.). The disclosures of these published applications are hereby incorporated by reference. However, such intervertebral implants are not currently adaptable for use with broken or damaged vertebrae. 
     Besides trauma or the like which results in a deformity, natural miss-shaping of vertebrae may also result in a deformity or undesired curvature of the spine. Typical of such conditions are scoliosis or kyphosis. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a method for customizing an intervertebral implant is provided, wherein the intervertebral implant is implanted in an intervertebral space within a series of vertebrae because the series of vertebrae have a deformity. The deformity may result from trauma which results in a resultant damaged vertebra, or by malformation during growth. For convenience, hereafter such a damaged or malformed vertebra will be referred to as “abnormal”. 
     Also for convenience, the series of vertebra is considered to include an abnormal vertebra which is the cause of the deformity, a vertebra superior to the abnormal vertebra, and a vertebra inferior to the abnormal vertebrae. The customized intervertebral implant then replaces the disc between the abnormal surface of the abnormal vertebra and the surface adjacent to the abnormal surface of the adjacent vertebra, so that the abnormal vertebra is retained (not removed). 
     A particular advantage of the present invention is to provide a customized intervertebral implant wherein the implant is of the type described above having opposed endplates which are articulated so as to provide movement such as universal movement therebetween and hence between the adjacent vertebrae. 
     The method comprises the initial step of obtaining a 3D anatomy of the series of vertebrae in a computer. Next, a repositioning of the 3D anatomy of each vertebra of the series is made in the computer to eliminate as far as possible the deformity of the series. It is then determined whether a superior or inferior surface of the abnormal vertebra is an abnormal surface which causes the deformity of the series. In addition, an approximate gap between the abnormal surface of the abnormal vertebra and a desired normal or desired surface of the abnormal vertebra is also determined. Using that determination of the gap, a custom implant is constructed which will engage the abnormal surface and fill the determined gap. In this manner, when the implant is implanted between the abnormal surface of the abnormal vertebrae and an adjacent surface of an adjacent vertebrae of the series, the deformity is substantially or desirably compensated for. 
     In a preferred embodiment of the present invention, the constructing step includes constructing an adjacent surface of the implant with a height which will engage the abnormal surface and fill the determined gap. When the surface of the implant is so customized, preferably the abnormal surface is smoothed in the computer so that the custom surface of the implant is matched to the smoothed surface. Conveniently, the constructing step further includes the step of transferring data from the computer to a CAD/CAM milling machine which makes the custom surface. 
     In a preferred arrangement, wherein the implant is of the type having opposed endplates with articulation for relative movement therebetween and an inlay received in one of the endplates, the constructing step includes the constructing of the inlay with a varying height which will cause a surface of the endplate adjacent the abnormal surface to fill the determined gap. In this embodiment, the constructing step includes the step of smoothing of the abnormal surface in the computer so that the varied height of the inlay is matched to the gap of the smoothed surface. Further, the constructing step includes the step of transferring data from the computer to a CAD/CAM milling machine which makes the varying height inlay. 
     The present invention also includes a method for providing a custom designed intervertebral implant for insertion into an irregularly shaped intervertebral space, where the space is bounded on one side by an abnormal vertebra. This method comprises the steps of determining a shape of the irregular intervertebral space, custom designing an implant to match opposing vertebral surfaces of the intervertebral space, and then inserting the custom designed implant into the intervertebral space such that the custom designed implant essentially fills the intervertebral space. 
     Preferably, the custom designed implant is of the type wherein the endplates have articulation for relative movement therebetween. In addition, where the custom designed implant has keels, the invention further includes the step of forming a trial implant to assist in forming grooves for the keels in the adjacent vertebra. 
     The present invention further includes a method of providing a customized implant of the type having opposed endplates with articulation for relative movement therebetween. This method comprises the steps of determining the shape of an intervertebral space between adjacent vertebrae, shaping at least one component of the implant to fit the space shape, and inserting the custom designed implant into the space. 
     Also in accordance with the present invention, an intervertebral implant of the type having opposed endplates adapted to engage adjacent vertebral surfaces is provided. The implant has at least one component which is custom made to have a shape such that the implant matches a specific intervertebral space into which the implant is to be inserted. 
     In one embodiment, the component which is custom made is an exterior surface of one of the endplates, so that this surface is customized to fit an irregular shaped intervertebral space. In another embodiment, the component which is custom made is an inlay which is attached to an interior surface of one of the endplates, so that the inlay is customized to fit the implant into an irregular shaped intervertebral space. 
     It will be appreciated that the method for customizing an intervertebral implant is capable of compensating for the deformity in more than one plane. 
     It is an object of the present invention to treat an abnormal vertebra having a deformity without requiring removal of the abnormal but otherwise usable vertebra and without resorting to fusion of the abnormal vertebra. Instead, an intervertebral implant is customized to fit against the abnormal surface of the abnormal vertebra in a manner which compensates for the deformity caused by the abnormal vertebra. 
     It is also an object of the present invention to provide a custom designed universal implant for treatment of an abnormal vertebra. 
     It is also an object of the present invention to retain relatively full spinal mobility despite the damage or malformation of a vertebra. 
     Other features and objects of the present invention are stated in or apparent from detailed descriptions of presently preferred embodiments of the invention found hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIGS. 1   a ,  1   b  and  1   c  are, respectively, a left side, a front, and a front, top and left side perspective view of a series of vertebrae including a middle abnormal vertebra which results in a deformity of the series. 
         FIGS. 2   a ,  2   b  and  2   c  are, respectively, a left side, a front, and a front, top and left side perspective view of the series of vertebrae including a abnormal vertebra of  FIG. 1 , but which have been repositioned to correct for the deformity. 
         FIGS. 3   a ,  3   b , and  3   c  are, respectively, a right side, a front, and a left side view of the series of vertebrae including the abnormal vertebra of  FIG. 1 , but which now have a customized intervertebral implant in accordance with the present invention in the series which customized implant compensates for the deformity. 
         FIGS. 4   a  and  4   b  are, respectively, a front, top and left side and a front, top and right side perspective view of the customized implant depicted in  FIG. 3 . 
         FIG. 5  is a front sectional view of an alternative customized implant in accordance with the present invention. 
         FIGS. 6   a - d  depict a trial implant in a) a front, top and left side perspective view, b) a front view, c) a left side view and d) a front, top and left side perspective view and with a vertebra surface cutting tool therein. 
         FIG. 7  is a schematic representation of the apparatus used in making the customized implant. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As noted above, the present invention is useful with either a damaged vertebra or, where appropriate or where a disc replacement is otherwise being made, with malformed vertebra. Where the present invention is used with malformed vertebrae, it will be appreciated that there will be a targeted vertebra whose abnormality is being compensated for or two adjacent targeted vertebra whose common disc is being replaced. While the targeted vertebra (or adjacent vertebrae) may contribute only to a part of the overall deformed curvature as in scoliosis, correction of that vertebra (or vertebrae) may be desired to reduce the overall curvature and achieve a meaningful improvement in the undesired curvature. In such a case, the targeted vertebra or both targeted vertebrae on either side of the disc being replaced may be overcompensated for in order to help correct the undesired curvature of the adjacent vertebra. For convenience, this overcompensation will still be referred to as “natural” even though it is beyond what would be the compensation to the “natural” surface location of a damaged vertebra which would not have adjacent vertebrae contributing to the curvature. 
     With reference now to the drawings in which like numerals represent like elements throughout the views, there is depicted in  FIGS. 1   a ,  1   b  and  1   c  different views of a series  10  of vertebrae  12 ,  14  and  16 . In series  10 , vertebra  14  has been damaged and hence is abnormal due to trauma or the like. Thus, hereafter the vertebra in series  10  will be referred to as abnormal vertebra  14 , superior (to vertebra  14 ) vertebra  12  and inferior (to vertebra  14 ) vertebra  16 . The damage and resultant malformation of abnormal vertebra  14  causes series  10  to be compressed and deformed, as shown by the curves of axes  18   a ,  18   b  and  18   c  in the  FIGS. 1   a - c . It is this deformity which the present invention is designed to compensate for while retaining abnormal vertebra  14  in place. 
     In accordance with the present invention, in order to compensate for the curvature of series  10 , a 3D anatomy of series  10  is obtained. This is simply and conveniently done with a CT scanning device  60  or the like (see  FIG. 6 ), with slices smaller than 1 mm preferred, and optimally between 0.2-1 mm. A high resolution for the slices is required since the deformity of abnormal vertebra  14  must be determined from the CT scan slices. It will be appreciated that the 3D anatomy of all three vertebra of series  10  is required since the proper positioning of abnormal vertebra  14  must also be determined using the obtained 3D anatomy. It will be appreciated that other scanning devices besides a CT scanning device can be used so long as they produce a three dimensional anatomy or the like of the series  10 . 
     With the 3D anatomy of series  10  obtained and loaded into a computer  62 , the 3D anatomy are depicted in a suitable screen  64  or the like as by the appearances of  FIG. 1 . Next, the user (surgeon) is able using standard software typical in the art to reposition each vertebra of series  10  so that vertebrae  12 ,  14  and  16  are returned to their natural or desired (including for scoliosis, overcompensated for) positions and/or orientations, that is with axes  18   a ′,  18   b ′ and  18   c ′ now straight lines. With such a repositioned 3D anatomy, the user is able to determine (see) what surface of abnormal vertebra  14  has been abnormal and is causing the deformity (or for scoliosis, how far the two surfaces adjacent to the disc to be replaced should be moved). In this example, it is inferior surface  20  of abnormal vertebra  14  which has been damaged, as best shown in  FIG. 2   b.    
     Again using standard software typical in the art, the user is then able to determine where a desired surface  20 ′ of abnormal vertebra  14  would be if vertebra  14  were not damaged. The software then also determines an approximate gap between abnormal surface  20  and a desired surface  20 ′. With this gap determined, an intervertebral implant  30  is constructed. The construction advantageously takes places by downloading or transferring of data from computer  62  with suitable software to a CAD/CAM milling machine  66  or the like. It will be appreciated that the abnormal surface  20  is preferably smoothed somewhat in the computer before the gap is determined. This smoothing is performed because an exact match of abnormal surface with every (small) peak and valley of the abnormal is not needed; and to some extent, the smoothing will be dependent on the milling machine which is used and the degree of matching attainable with the milling process. 
     Implant  30  is shown in position in series  10  in  FIGS. 3   a - c . In accordance with the present invention, implant  30  is preferably of the type which allows relative movement between opposed endplates  32  and  34 , and hence relative movement of the adjacent vertebrae, as shown in the above identified published applications. As such, the present invention not only provides a customized treatment for abnormal vertebrae, but does so in a manner which allows relative movement between the abnormal vertebra and the adjacent vertebra on the opposite side of the intervertebral space in which implant  30  is inserted. Instruments for insertion of the implant are also shown in the above referenced published applications. It will be appreciated that implant  30  has replaced the disc (not shown, and typically damaged as well) between abnormal vertebra  14  and inferior vertebra  16 . Implant  30  is constructed so that the desired (straight) axes  18 ′ shown in  FIG. 2  are maintained after implantation of implant  30 . 
     Prior to insertion of the implant  30 , it is necessary to utilize a trial implant  70  to guarantee creation of keel grooves in the two vertebrae adjacent implant  30 . Trial implants suitable for this purpose are shown in the above identified published application No. 2004/0215198.  FIGS. 6   a - c  show this type of trial implant  70 , but after being formed to the custom shape using the features of the present invention, in order to fit into the intervertebral space. To properly cut the grooves in the adjacent vertebrae in which the keels of the implant  30  are then secured, a tool  72  is used which is constructed as shown in published application No. 2004/021519. Tool  72  has a suitably angled base end which fits into and is oriented by angled reception slot  74 . 
     In this embodiment of the present invention, implant  30 , which is of the type which allows relative universal movement between the endplates, is customized as shown in  FIG. 4 . In particular, it will be appreciated that implant  30  (see the above referenced published applications for further details of implant  30  as well as similar implant  50 ′ in  FIG. 5 ) is constructed of a superior endplate  32  and an inferior endplate  34 . Superior endplate  32  has an upper vertebral surface engaging surface  36  which is designed to engage abnormal surface  20  and be secured thereto via keel  38 . Likewise, inferior endplate  34  has a lower vertebral surface engaging surface  40  which is designed to engage normal surface  22  of inferior vertebra  16  and be secured thereto via keel  42 . Provided between endplates  32  and  34  is a suitable articulation, such as a universal joint  44 . In this preferred embodiment, universal joint  44  is formed by: a) an inlay  46  having a convex upper surface  48 , where inlay  46  is securely received in inferior endplate  34 ; and b) a mating concave lower surface  50  (not seen, but shown in published application 2005/0085917) formed in superior endplate  34 . 
     If there were no deformity resulting from vertebra  14 , so that only the disc between vertebra  14  and  16  were being replaced with implant  30 , superior endplate  32  would have a constant thickness or height like that of inferior endplate  34 . However, as there has been damage to vertebra  14  so that there is a gap between the location of abnormal surface  20  of vertebra  14  and the desired surface  20 ′ of vertebra  14 , it will be seen in  FIG. 4  that upper surface  36  of superior endplate  32  has been built up appropriately to fill this gap. Thus, as shown in  FIG. 3 , with implant  30  in place between vertebrae  14  and  16 , no gap exists between abnormal surface  20  and upper surface  36 . 
     It will be appreciated that the build up of upper surface  36  has occurred over most of upper surface  36  thereof, starting from the right (as viewed) and building up to the left as well as back to front. Thus, built up upper surface  36  is not necessarily planar, or even angled in any one plane; rather it may be undulating, or as shown in  FIG. 4 , built up left to right as well as back to front with some curvature therealong. As a result, the deformity of abnormal vertebra  14  is compensated for in more than one plane in this depicted embodiment. 
     Depicted in  FIG. 5  is a second embodiment of an implant  30 ′ which has been customized in accordance with the present invention. Implant  30 ′ is broadly similar to implant  30  described above, and thus the same identifying numbers but with a prime (′) thereafter will be used for the same or similar elements. It will be appreciated that implant  30 ′ is designed for use with an abnormal vertebra having an abnormal superior surface, which in the first embodiment would have occasioned a customized lower vertebral surface engaging surface  40 . However, in this embodiment, neither lower vertebral surface engaging surface  40 ′ nor upper vertebral surface engaging surface  36 ′ have been customized. Rather, inlay  46 ′ has been customized so that one side, the left side as viewed, is higher (has a greater thickness) than the right side. This higher left side causes, upon implantation, lower vertebral surface engaging surface  40 ′ to be angled as shown to compensate for the damage to the adjacent vertebral superior surface when the universal joint  44 ′ is at the neutral or centered position (which is shown in  FIG. 5 ). 
     As inlay  46 ′ is the element which provides the compensation, implant  30 ′ is usable primarily where the abnormal surface of the vertebra is relatively planar. However, where appropriate, the use of a customized inlay may afford some advantages, such as easier and quicker fabrication since inlay  46 ′ is formed of polyethylene. 
     It will also be appreciated that where a disc between two vertebrae which are malformed as by scoliosis is to be replaced, the adjacent vertebral surfaces will be undamaged and thus implant  30  or  30 ′ is usable. As noted above, implant  30 ′ can be designed to overcompensate for the curvature so that the remaining malformed vertebra are advantageously oriented relative to the implant. In such a case, both endplates of implant  30  could have customized (built up) surfaces, or both the inlay of implant  30 ′ and the other endplate surface  36 ′ could be customized (built up). It will further be appreciated that besides building up inlay  46 , or in addition thereto, the opposite facing surface of endplate  32  could be built up in the same manner as inlay  46 . 
     It is anticipated that the methods described above can be accomplished relatively quickly and easily. Thus, such a method could even be performed while surgery is underway to repair a trauma. Once the 3D anatomy scan is made, the CAD/CAM machine would be immediately directed to make the needed customized implant part from a stock of parts ready to be milled. 
     While the present invention has been described with respect to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that variations and modifications can be effected within the scope and spirit of the invention.