Abstract:
An apparatus and method for creating a space of defined length, height, width and shape with a vibrating cutting apparatus in preparation for receiving an interbody spinal implant or graft of known size and configuration is disclosed.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
       [0001]     This application claims priority to and the benefit of, pursuant to 35 U.S.C. §119(e), U.S. provisional patent application Ser. No. 60/777,261, filed Feb. 28, 2006, entitled “Apparatus and method of creating an intervertebral cavity with a vibrating cutter” by John K Song and Jeffrey David Gordon and is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to a vibratory or orbital device for creating a cavity between or within bones of the human body.  
       BACKGROUND OF THE INVENTION  
       [0003]     Surgery of the bones of the human body has been greatly facilitated with the advent of powered tools, most notably surgical drills. Most commonly, traditional rotating surgical drills are similar to their non-surgical counterparts and incorporate a motor rotating a drive shaft about its long axis and a cutting tool attached to the drive shaft. Occasionally the drive shaft is powered by pneumatics or other power source. The cutting tool rotates around the long axis of its shaft in a continuous motion and when applied to bone will remove material.  
         [0004]     More recently, ultrasonic surgical drills have been introduced. These typically incorporate piezoelectric crystals to actuate a drive shaft in a linear manner along its long axis. Ultrasound may comprise a defined frequency range but for the purposes of the present invention we define vibrational and orbital motions to include ultrasonic, subsonic and suprasonic ranges. Ultrasonic drills abrade bone surfaces in a controlled manner with none of the problems of traditional rotating surgical drills such as “skipping” (whereby the cutting tool grabs the bone surface and “skips” away) or wrapping up soft tissue.  
         [0005]     In addition, ultrasound surgical drills may employ cutting tools which are asymmetric about any axis, especially about the long axis of the drive shaft and thus more advantageous geometries may be used for specific surgical procedures.  
         [0006]     For the purposes of the present invention, drills which rotate continuously in one direction along the long axis of the drive shaft are referred to as “rotating” and drills which move the cutting tool in a substantially linear or rotational back-and-forth manner along any axis ( FIG. 14 ) are referred to as “vibratory” or “ultrasonic”. Alternatively, drills or similar tools which cause the cutting tool to move in a non-linear, continuous, planar path ( FIG. 14 , XY, XZ, YZ planes) are referred to as “orbital”. An example of orbital motion is an orbital sander for finishing wood surfaces.  
         [0007]     For the purposes of the present invention, “bones” refers to any two or more anatomically distinct bones or two or more pieces of the same bone. It is not intended by specific mention of any particular bone within this work to limit the scope of the present invention.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is a vibrating cutter for surgically creating a cavity between, or partially within, two bones. Specifically, the invention creates the cavity by means of a vibratory actuator such as an ultrasound actuator. By eliminating standard rotating cutting means such as mills or drills, the invention offers improved safety and is capable of creating a geometrically complex cavity with a relatively simple cutting tool. The preferred embodiment of the invention has utility in creating a precise cavity in the intervertebral space between two vertebrae of the spine.  
         [0009]     It is an object of the present invention to provide an instrument for surgically creating a cavity between, or partially within, two bones.  
         [0010]     It is another object of the present invention to provide an instrument for facilitating implantation of an interbody device, such as a fusion device, a total disc arthroplasty, a bone graft, or a nucleus replacement, or for facilitating implantation of a facet replacement.  
         [0011]     It is another object of the present invention to provide an instrument incorporating a sizer/introducer which (1) acts to distract the bones, (2) acts to aid in selection of the cutter and implant or bone graft size, and (3) acts as a guide for safe, precise placement and orientation of the cutting tool.  
         [0012]     These and other objects of the present invention will become apparent from a review of the accompanying drawings and the detailed description of the preferred embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of the vibrating cutter and vibrational actuator assembly of the present invention.  
         [0014]      FIG. 2   a  is a perspective view of the vibrating cutter illustrating insertion into a disc space.  
         [0015]      FIG. 2   b  is a perspective view of the vibrating cutter showing the cutter inserted into a disc space.  
         [0016]      FIG. 2   a  is a perspective view of the vibrating cutter illustrating withdrawal from a disc space and the cut created in the vertebral endplates.  
         [0017]      FIG. 3  is a perspective view of the vibrating cutter of the present invention.  
         [0018]      FIG. 4  is a perspective detailed view of the vibrating cutter of the present invention.  
         [0019]      FIG. 5  is an alternate embodiment of the vibrating cutter.  
         [0020]      FIG. 6  is an alternate embodiment of the vibrating cutter with circular shape and pyramidal cutting teeth  
         [0021]      FIG. 7  is an alternate embodiment of the vibrating cutter with a protrusion incorporated on the top and bottom surfaces.  
         [0022]      FIG. 8  is an alternate embodiment of the vibrating cutter with a cylindrical shape.  
         [0023]      FIG. 9  is an alternate embodiment of the vibrating cutter with an angular shape and conical cutting teeth.  
         [0024]      FIG. 10  is an alternate embodiment of the vibrating cutter with a partial conical shape and holes through the cutter.  
         [0025]      FIG. 11  is an alternate embodiment of the vibrating cutter with a keel incorporated on the top and bottom surfaces and teeth on a portion of the side surfaces  
         [0026]      FIG. 12  is an alternate embodiment of the vibrating cutter with a hollow cutting body, holes through the cutting surfaces and cutting teeth on the front surfaces.  
         [0027]      FIG. 13  is the reverse view of the embodiment shown in  FIG. 13 .  
         [0028]      FIG. 14  is a perspective view of the vibrating cutter showing some of the possible axes of translations and rotations of vibration.  
         [0029]      FIG. 15  is a perspective view of an alternate embodiment of the vibrating cutter with a spacer and an enclosed, rotatable cutter for cutting a protrusion in the vertebral endplates.  
         [0030]      FIG. 16  is a perspective view of an alternate embodiment of the vibrating cutter with a spacer and an enclosed, partially rotatable cutter for cutting a protrusion in the vertebral endplates.  
         [0031]      FIG. 17  is a sectioed front view of the alternate embodiment of the vibrating cutter shown in  FIG. 16 .  
         [0032]      FIG. 18   a  is a perspective view of the sizer/introducer.  
         [0033]      FIG. 18   b  is a perspective view of the sizer/introducer and vibrational actuator-vibrating cutter assembly illustrating the guiding action of the sizer/introducer.  
         [0034]      FIG. 18   c  is a perspective view of the sizer/introducer and vibrational actuator-vibrating cutter assembly. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Referring to  FIG. 1 , a vibrational actuator  100  and vibrating cutter  110  assembly is shown. Vibrational actuator  100  is of the type demonstrated in the prior art, such as the “Ultrasonic Nailing and Drilling Apparatus” described by Hur (U.S. Pat. No. 6,204,592). The vibrational actuator  100  is capable of producing vibratory motion in at least one degree of freedom (DOF) as described in  FIG. 14  below. The frequency of the vibratory motion is preferably in the ultrasonic range but alternatively can be sub-ultrasonic or super-ultrasonic. The actuator is preferably powered by a source of electricity such as an AC or DC power source or battery, but can alternatively be gas powered such as a pneumatic actuator. The actuator is preferably driven by a piezo-ceramic material such as PZT, or a magnetostrictive material such as Terfonol-D. The preferred embodiment is a vibrational actuator  100  that is connected to an electrical energy source (not pictured) by an electric cord  16 . An actuation tip  14  protruding from a body  5  or an end cap  12  of the vibrational actuator  100  is constructed to engage a driving end  20  of the vibrating cutter. The preferred connection means is mechanical threads, but alternatively a mechanical quick-release mechanism, a chuck, a collet, a pin, a fastener, multiple fasteners, a clamp or other mechanical connection means can be encorporated. In the preferred embodiment, internal threads on the driving end  20  of the vibrating cutter  110  are engaged with external threads on the actuation tip  19  by using a wrench (not pictured) engaged in flats  18  on driving end  20  of the vibrating cutter  110 . Counter rotation during assembly is provided by means internal to the vibrational actuator  100  but can alternatively be provided by a feature incorporated into the construction of actuation tip  14 . An elongated shaft  24  transmits the vibratory motion to a cutting tip of the vibrating cutter. Reduction in diameter, where necessary to facilitate insertion into the body cavity of the patient, may be strengthed by inclusion of a fillet  22 , however a chamfer may be utilized. Strengthening means may not be necessary. A depth stop  26  is preferably incorporated into shaft  14  to control the depth of penetration of the vibrating cutter into the intervertebral space. Alternatively, depth can be controlled by other means including radiography.  
         [0036]      FIGS. 2   a ,  2   b  and  2   c  demonstrate the procedure of preparing an intervertebral space for an implant(s).  FIG. 2   a  shows a superior vertebral body  1 , an inferior vertebral body  2 , a disc space  5  and vibrating cutter  110 . Shaft  24  is aligned such that cutting teeth  30  will cut the appropriate contour into endplate(s)  3  of the disc space  5 .  FIG. 2   b  shows the vibrating cutter  110  advanced into disc space  5 .  FIG. 2   c  shows the cut made in superior vertebral body  1  and inferior vertebral body  2  and vibrating cutter  110  withdrawn from disc space  5 . The resulting cut forms a cavity  70  in superior vertebral body  1 , and inferior vertebral body  2  which has side walls  75  and a front edge  80  which can be of various shapes as will be demonstrated in the following figures.  
         [0037]      FIGS. 3 and 4  show a preferred embodiment of vibrating cutter  110  with driving end  20  as described above, shaft  24 , and depth stop  26  to engage into an adjustable or non-adjustable stop incorporated into a guide mechanism (not pictured). In this embodiment, cutting teeth  30  exist on all sides of the cutting head except a trailing surface  25 . Holes  32  are incorporated into the cutting head to collect chips of bone and to facilitate the cutting process.  
         [0038]      FIG. 5-13  are alternative embodiments of the cutting head of vibrating cutter  110 . All embodiments of vibrating cutter  110  could either be inserted while cutting, or alternatively could be inserted into disc space  5  while not activated by vibratory actuator  100  and then activated once in disc space  5  so that the anterior surface of superior vertebra  1  and inferior vertebra  2  would not be cut and only endplates  3  would be cut. Many features are demonstrated, but a combination of any of these features into a single cutting head can be utilized. Configurations are for demonstration only and are not intended to limit the scope of the cutting head geometry.  FIG. 5  shows a cutting head of rectangular cross-section with cutting teeth  30  on top and bottom surfaces. Side surfaces  29  do not incorporate cutting teeth.  FIG. 6  shows a cutting head with a circular shape with pyramidal teeth  32  on the top surface only. A cutting head with teeth on one surface only would permit cutting one endplate at a time and may require reinsertion after a 180 degree rotation of vibrating cutter  110  to cut an opposing endplate.  FIG. 7  shows a cutting head with a protrusion incorporated into top and bottom surfaces to create a space for a corresponding protrusion incorporated into an implant. Cutting teeth  34  are shown on top and bottom surfaces but not front surface  36  or trailing surface  25 .  FIG. 8  shows a cutting head with a substantially cylindrical shape to create a space for a correspondingly shaped implant such as a fusion cage. Cutting teeth  38  would be incorporated, but may or may not continue all the way to trailing surface  25 .  FIG. 9  shows a substantially wedge shaped cutting head to create a space for a correspondingly shaped implant which creates a lordosis or kyphosis angle in disc space  5 . Conical teeth  40  are incorporated in top and bottom surfaces, but may also be incorporated into side surface  42  and/or the front surface.  FIG. 10  shows a cutting head with a partial conical shape to create a space for a correspondingly shaped implant which creates a lordosis or kyphosis angle in the corresponding disc space  5 . Holes  46  are incorporated into the cutting surfaces to aid in cutting endplate bone material.  FIG. 11  shows a cutting head with a keel type protrusions  50  to create a space for a correspondingly shaped implant such as a disc replacement with a keel. Teeth  52  are incorporated into top, bottom, and protrusion surfaces and a portion of side surfaces. Surfaces  54  are devoid of cutting teeth to aid in insertion.  FIGS. 12 and 13  show a cutting head with a substantially hollow shape and holes  32  to aid in cutting and/or to aid in collection of bone material for grafting purposes. Interior surfaces  60  are meant to collect bone chips created in the cutting process. Front surface teeth  62  are incorporated in this embodiment and could also be incorporated in any of the preceding cutting head embodiments.  FIG. 13  is a reverse angle view of  FIG. 12  to show interior surfaces  60  and front surface teeth  62 .  
         [0039]      FIG. 14  shows a cutting head of vibrating cutter  110  and some of the possible motions of vibration possible. Vibrational actuator  100  will be capable of translating vibrating cutter  110  along, or rotating it about, axes X, Y or Z or any combination of these motions or orbital motion.  
         [0040]      FIG. 15  shows vibrating cutter  110  with a moveable protrusion cutter. A spacer  775  incorporating side walls  740 , a rear wall  745 , and a substantially flat surface  780  can be inserted into disc space  5  with a protrusion cutting head  785  oriented so that substantially flat surface  750  is parallel to substantially flat template surface  780 . Shaft  700  is rigidly connected to protrusion cutting head  785  and a driving end  715  and is constructed to be capable of rotating within hollow shaft  730  of template  775 . After insertion, handle  710  can be rotated through any angle A so that cutting teeth  760  cut a recess into endplates  3  which substantially match a corresponding shape in an implant. Template  775  may further incorporate a depth stop  720  to limit the depth of the protrusion cut in superior vertebra  1  and inferior vertebra  2  with respect to their anterior surface.  
         [0041]      FIGS. 16 &amp; 17  show another embodiment of vibrating cutter  110  with a moveable protrusion cutter similar to the embodiment shown in  FIG. 15 . A spacer  880  has an intervertebral portion  885  with side walls  800 , cutting teeth  810 , a substantially flat guide surface  805  and a depth stop  820 , is attached to a hollow shaft  840  with a slot  845 . A shaft  700  is rigidly connected to a protrusion cutting head  890  with a protrusion cutting surface  895  with cutting teeth  825 , and is also rigidly connected to a driving end  715 . A handle  710  is connected to driving end  715  by means of a shaft  705 . Shaft  700  is able to rotate within hollow shaft  840  when handle  710  is rotated. Spacer  880  is inserted into disc space  5  until depth stop  820  contacts the anterior surface of either superior vertebra  1  or inferior vertebra  2  or both. Spacer  880  is inserted with a protrusion cutting surface  895  oriented so that protrusion cutting surface  895  is substantially parallel to guide surface  805 . After insertion, handle  710  is rotated through an angle B so that cutting teeth  825  on protrusion cutting surface  895  cut a recess into endplates  3  which substantially matches a corresponding protrusion in an implant. A pin  850  moves within slot  845  which acts to limit the range of rotation of protrusion cutting head  890 .  FIG. 17  is a front view of the assembly shown in  FIG. 16 .  
         [0042]      FIGS. 18   a ,  18   b , and  18   c  show an alternative method of creating an intervertebral space. A sizer/introducer  615  with an elongated shaft  600  and an intervertebral head  605  with sloped front surface(s)  610  is first introduced into disc space  5 . Front surface(s)  605  may be in the form of a “bullet” tip. Vibrating cutter  110  is cannulated so that it fits over shaft  600 . In the figure, Vibrational actuator  100  is also cannulated, but this may not be necessary. Sizer/introducer  615  therefore functions as a guide to control the placement and orientation of the cut. The vibrational actuator  100  and vibrating cutter  110  assembly is slid over shaft  600  and cuts a space into superior vertebra  1  and/or inferior vertebra  2  as shown in  FIGS. 18   b  and  18   c . Vibrational cutter  110  may also incorporate a depth stop  602  to limit travel into disc space  3 .