Abstract:
An apparatus for implanting an intervertebral implant in a void between a pair of vertebral endplates comprises a power source, a drive mechanism coupled to the power source, and an implant adapter driven by the drive mechanism. The intervertebral implant is removably coupled to the implant adapter to create a seat in at least one of the vertebral endplates as the intervertebral implant is moved relative to the at least one vertebral endplate.

Description:
BACKGROUND  
       [0001]     In the treatment of diseases, injuries or malformations affecting spinal movement and disc tissue, it has long been common practice to remove a portion or all of a degenerated, ruptured, or otherwise failing disc. Following the loss or removal of disc tissue, intervertebral devices have been implanted between the remaining vertebrae to promote fusion or to restore motion to the treated area of the spine. To properly seat the implant, conventional methods of implantation often require the use of complex measurement and instrumentation systems for preparing the bone to match the implant. A mismatch between the implant and the prepared bone can cause an improper seating of the implant. Therefore, a method and apparatus are needed which simplify the instrumentation required for implantation and improve the fit between the implant and the adjacent vertebrae.  
       SUMMARY  
       [0002]     This disclosure relates to a new apparatus and method for implanting an intervertebral implant in a void between a pair of vertebral endplates. One embodiment comprises a power source, a drive mechanism coupled to the power source, and an implant adapter driven by the drive mechanism. The intervertebral implant is removably coupled to the implant adapter to create a seat in at least one of the vertebral endplates as the intervertebral implant is moved relative to the at least one vertebral endplate.  
         [0003]     Another embodiment comprises positioning the vertebral implant between the vertebral endplates and coupling an implantation tool to the vertebral implant. The implantation tool is actuated to generate alternating motion relative to the vertebral endplates. The alternating motion has a speed and creates a displacement of the vertebral implant. The vertebral implant is seated into a profile formed in at least one of the vertebral endplates, and the implantation tool is decoupled from the vertebral implant. The vertebral implant remains implanted in the at least one vertebral endplate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a side view of vertebral column having a destroyed disc.  
         [0005]      FIG. 2  is a exploded schematic view of an apparatus for installing an intervertebral device.  
         [0006]      FIGS. 3   a - 3   f  are exemplary implant adapters configured for a variety of intervertebral implants.  
         [0007]      FIGS. 4-10  are perspective views of a vertebral implant between a pair of vertebral bodies according to embodiments of the current disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0008]     The present disclosure relates generally to the field of orthopedic surgery, and more particularly to the instrumentation and techniques for inserting intervertebral devices. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to embodiments or examples illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alteration and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0009]     Referring first to  FIG. 1 , the numeral  10  refers to vertebral column with a damaged intervertebral disc  12  extending between vertebrae  14  and  16 . In a typical surgical discectomy, the disc  12  is removed, creating a void between the two intact vertebrae  14  and  16 . This procedure may be performed using an anterior, anterolateral, lateral, or other approach known to one skilled in the art. An implant according to an embodiment of the present invention may then be provided to fill the void between the two intact vertebrae  14  and  16 . The embodiments of this disclosure may be generally directed toward articulating intervertebral prostheses which restore at least some range of motion at the site of the removed disc  12 . It is understood, however, that in alternate embodiments, the methods and apparatus of this disclosure may be used to implant non-articulating devices which may promote fusion of the vertebrae  14  and  16 . Furthermore, although the embodiments to be described are premised upon the removal of a single disc, it is understood that the methods and apparatus of the invention may be applied to the insertion of a vertebral body replacement device between two vertebrae following a corpectomy, in which at least one vertebral body has been removed.  
         [0010]     Referring now to  FIG. 2 , an implantation tool  20  for inserting an implant  22  between two vertebrae  14 ,  16  (of  FIG. 1 ) may include a handpiece  24 , a coupling mechanism  26 , and an implant adapter  28 .  
         [0011]     In the embodiment of  FIG. 2 , the handpiece  24  may include a handpiece body  30  for housing a power device  32 , such as an electric motor, coupled to an electrical power connector  36  for driving a drive shaft  38 . Although this embodiment describes an electrically powered apparatus, it is understood that alternative power devices may be selected including pneumatic, battery, or gas powered devices. These alternative power devices may be supported by additional or alternative components.  
         [0012]     The coupling mechanism  26  may be provided to convert and control, if needed, the motion from the power device  32  into a vibratory, reciprocating, oscillatory, or other type of direction alternating movement. The coupling mechanism  26  may include a body  40  for housing a drive mechanism  42  for transferring output motion to the implant adapter  28 . The drive mechanism  42  may be connected to a conversion mechanism  44 , such as one or more cams, for creating reciprocating motion. The coupling mechanism  26  may further include a reduction mechanism  46 , such as a gearbox connected to the conversion mechanism  44  and/or the drive mechanism  42 , for selectively altering the speed and/or force transmitted by the drive mechanism  42 . The coupling mechanism  26  may also include a drive mechanism  48  for transmitting motion from the handpiece  24 . The coupling mechanism  26  may include additional or alternative mechanisms as may be necessary to convert and control the motion from the power device  32  into a desired output motion. U.S. Pat. No. 6,610,066, which is incorporated by reference herein, discloses a reciprocating surgical tool having components for converting rotary motion of a powered handpiece into reciprocating motion.  
         [0013]     The implant adapter  28  may include a housing  50  and a drive adapter  52  for removably connecting the implant adapter  28  to the coupling mechanism  26 . The implant adapter  28  may further include an implant engagement mechanism  54  for engaging the implant  22 . The implant engagement mechanism  54  may be configured to engage a particular implant  22  or may be adjustable to permit engagement with a variety of implants.  FIGS. 3   a - 3   f  illustrate exemplary embodiments of the implant adapter  28  configured to mate with a variety of implant devices  22 . The engagement mechanisms  54  can be hooks ( FIG. 3   a ,  3   d ), pins ( FIG. 3   b ), clamps ( FIG. 3   c ), gripping arms ( FIG. 3   e ), or a threaded projection ( FIG. 3   f ). This list is not exhaustive, and other mechanisms may be used for attaching an implant  22  to the implant adapter  28 .  
         [0014]     The components of the implantation tool  20  may be made of durable, medically acceptable materials, such as stainless steel, hard coated anodized aluminum, or titanium, for example, capable of being sterilized to medical standards, such as by steam or flash autoclaving, gas sterilization, and/or soaking in a disinfectant solution. Accordingly, the implantation tool  20  may be designed for repeated use. The shape, size, and configuration of the components  24 - 54  are merely exemplary and any of a variety of alternative configurations may be desirable.  
         [0015]     The implant  22  may be a prosthesis such as is disclosed in U.S. Pat. No. 6,540,785; U.S. patent application Ser. No. 10/303,569; or U.S. patent application Ser. No. 10/042,589 which are incorporated herein by reference. However, as previously stated, other articulating and non-articulating implant  22  designs, including fusion promoting devices, may be installed using the implantation tool  20 . The implant  22  may have a surfaces  60  and  62  having a rough coating  64 , features  66  and/or other surface textures for abrading the endplates of the adjacent vertebrae in preparation for seating the implant. For example, a coating  64  of biocompatible and osteoconductive material such as nonspherical sintered beads or hydroxyapatite may cover all or a portion of the surfaces  60  and  62 . Other suitable coatings  64  or treatments may include a porous bead coating, a porous mesh coating, osteogenic peptide coating, growth factor coating, rh-BMP coating, and/or grit blasting. Suitable features  66  may include spikes (as shown in  FIG. 2 ), serrations, ridges, fins, pyramidal projections, and/or other surface textures.  
         [0016]     The implantation tool  20  may be assembled by attaching the handpiece  24  to the coupling mechanism  26 , specifically, the drive shaft  38  may engage the drive mechanism  48 . The implant adapter  28  may be attached to the coupling mechanism  26 , specifically, the drive mechanism  42  may engage the drive adapter  52 . The electrical power connector  36  may be connected to a power source (not shown) such as an electrical outlet. The implant  22  may be attached to the engagement mechanism  54 .  
         [0017]     The components  24 ,  26 ,  28  of the implantation tool  20  may be modular, permitting an implantation tool  20  to be assembled and tailored for a particular application. For example, to achieve a desired type of motion or a desired displacement in the implant adapter  28 , a coupling mechanism  26  may be selected having a conversion mechanism  40  designed to generate the desired motion. Likewise, to adapt to a particular implant  22 , an implant adapter  28  may be selected having an engagement mechanism  54  suitable for engaging the implant  22 . In some embodiments, the design of the handpiece  24 , the coupling mechanism  26 , and/or the implant adapter  28  may combine or eliminate components. For example, drive shaft  38  may directly engage the conversion mechanism  44  or the reduction mechanism  46  without requiring a drive mechanism  48 .  
         [0018]     In preparation for installing the implant  22 , a decompression procedure may be performed by removing the diseased or damaged disc  12 . The space vacated by the disc  12  may be distracted to receive the implant  22 . The implant  22  may be placed into the space between the vertebrae  14  and  16 . Power may be supplied to the power device  32  by the power connector  36  to rotably drive the drive shaft  38 . The drive shaft  38 , in turn, may drive the drive mechanism  48  of the coupling mechanism  26 . The rotary output of the handpiece  24  may pass through the reduction mechanism  46  of the coupling mechanism  26  to reduce the speed, increase force, or change direction of the rotary motion. The rotary motion may be converted to a selected vibratory, reciprocating, oscillatory, pulsating or other alternating movement by the conversion mechanism  44  of the coupling mechanism  26 . The selected alternating movement may be transmitted by the conversion mechanism  44 , through the coupled drive mechanism  42  and drive adapter  52 , to vibrate the implant adapter  28 .  
         [0019]     The vibration of the implant adapter  28  may, in turn, cause the implant  22  to vibrate or otherwise generate an alternating movement relative to the adjacent bone of the vertebral endplates. The vibration may cause the rough or featured surfaces  60 ,  62  of the implant  22  to abrade the adjacent bone, creating an impression of the contour and features of the surfaces  60  and  62  in the vertebral endplates. Thus, the implant  22  may be the master pattern for its own implantation seat, allowing the general geometry of the host bone to be duplicated and the normal anatomy generally matched, and thereby potentially creating a better fit between the implant  22  and the vertebrae  14 ,  16 . After the implant  22  is seated in the adjacent bone of the vertebral endplates, the implant  22  may be decoupled from the implant adapter  28  by releasing the engagement mechanism  54  from the implant  22 . After the decoupling, the implant  22  may be securely installed between the vertebral bodies  14 ,  16 .  
         [0020]     This technique may also reduce the need for complex fixtures, milling instrumentation, and measurement devices such as trials. Correspondingly, the surgical access area may be smaller than is required with more complex rigging. The surgical preparation needed may also be reduced.  
         [0021]     Given that most vertebral endplates are typically not flat, but instead have a convex superior endplate and a concave inferior endplate, the self seating action described above may permit an implantation that is uniquely suited to the particular patient&#39;s spine, thus promoting long term stability. To further promote the long term stability of the implant  22 , the abrading action may releases bone particles which may be redeposited in the area of the implant  22  to stimulate bone ingrowth.  
         [0022]     As shown in  FIGS. 4-8 , a relative alternating movement  70 , provided by the implant adapter  28  (not shown) for seating the implant  22 , may be a vibration which moves the implant  22  generally back and forth along a longitudinal axis  72  which extends through the vertebral bodies  14 ,  16 .  
         [0023]     Referring to  FIG. 4 , in addition to or alternative to the movement  70 , a relative movement  74  may reciprocally rotate the implant  22  about the longitudinal axis  72 .  
         [0024]     Referring to  FIG. 5 , a relative movement  76  may also or alternatively vibrate the implant  22  along an axis  78  which extends from the anterior side of the implant through the disc space to the posterior side of the implant. A relative motion  80  may also or alternatively vibrate the implant  22  along an axis  82  which extends transversely through the disc space. The transverse motion  80 , in this embodiment, may be particularly suited to an implant  22  having a projection  66 , such as the fin of  FIG. 5 , which extends in the anterior-posterior direction  78 . Vibrating the implant  22  in a direction opposite of the anterior direction of implantation may help to prevent the implant from ejecting after implantation.  
         [0025]     Referring now to  FIG. 6 , in an embodiments where the implant  22  is configured to contact a side portion of the adjacent vertebrae  14 ,  16 , the relative motions  70 ,  76  may also abrade a side portion of the adjacent vertebrae  14 ,  16  as the implant is seated.  
         [0026]     Referring now to  FIG. 7 , in an embodiment where the implant  22  includes a plurality of elongated spikes, the relative motion  70  in the direction of the longitudinal axis  72  may be appropriate to drive the spikes into the adjacent vertebrae  14 ,  16 .  
         [0027]     Referring now to  FIG. 8 , the relative movement  76  may also or alternatively vibrate the implant  22  along the anterior-posterior axis  78 . The relative motion  80  may also or alternatively vibrate the implant  22  along the transverse axis  82 . The transverse motion  80 , in this embodiment, may also be particularly suited to an implant  22  having a transverse projection  66 , such as the fin of  FIG. 8 . Vibrating the implant  22  in a direction opposite of the anterior direction of implantation may help to prevent the implant from ejecting after implantation.  
         [0028]     Referring now to  FIG. 9 , in an embodiment where the implant  22  is generally cylindrical and implanted along the axis  78 , a relative motion  84  may reciprocally rotate the implant  22  about the axis  78 .  
         [0029]     In one embodiment, as shown in  FIG. 10 , a force  90  may be applied to draw the vertebrae  14 ,  16  together while the vibration motion  70  is delivered in the longitudinal direction  72 . The force  90  may push the endplates together (as shown) or may, alternatively, pull the endplates together. The combination of force  90  and vibration motion  70  may enhance the seat of the implant  22 .  
         [0030]     It is understood that the relative movements  70 ,  74 ,  76 ,  80 ,  84  are merely exemplary and other relative motions, such as arc shaped motions, multi-directional, or random motions, may be selected based upon the spinal location, implant configuration, surgical approach or surgical application. The speed, force, and other characteristics of the movement of the implant  22  may be adjusted, for example, by varying the speed of the power device  34  or components of the reduction mechanism  46 .  
         [0031]     Other characteristics of the movement of the implant  22  such as the displacement distance, may be controlled by, for example, the conversion mechanism  44 . In one embodiment, for example, a cam may be designed to provide a stroke of 2-3 millimeters in the implant  22 . The displacement of implant  22  may also be managed by controlling the magnitude of the vibration, oscillation, or other alternating movement. The displacement of the implant caused by the alternating movement  70 ,  74 ,  76 ,  80 ,  84  may be, for example 2 to 3 millimeters, however larger or smaller displacements may be appropriate for certain applications.  
         [0032]     The speed/frequency of the movements  70 - 74 ,  76 ,  80 ,  84 , the compressive force  90  and the displacement of the implant  22  may be varied as the implant  22  is embedded in the vertebral endplates. For example, greater speed, force, and displacement may be required to embed an elongated projection of the implant  22 , however as that projection becomes embedded and the profile of the implant  22  becomes less pronounced, the speed, force, and displacement may be reduced to seat the remainder of the implant  22 . In some embodiments, software and circuitry (not shown) may be provided to the implantation tool  20  to control the movement implant  22  according to the profile of the implant  22 , the hardness of the bone, the material of the coating  64 , or other characteristics of the surgical application or components. In some embodiments, a dampener (not shown) may be included in the implantation tool  20  for dampening the vibration of the implant  22 . The speed/frequency of the movements  70 ,  74 ,  76 ,  80 ,  84  may also be selected to confine motion to the area of the implantation without creating micro motion of the whole spine.  
         [0033]     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.