Abstract:
A method and system for engaging an implant with a bone is disclosed. In one method incorporating principles of the invention, a bone is engaged with an implant by placing a first surface of an implant adjacent to a first bone portion, contacting the first bone portion with at least one first engagement member extending from the first surface, controlling an agitator to agitate the first surface of the implant and the at least one first engagement member, generating at least one first surface feature in the first bone portion with the agitated at least one first engagement member, stilling the first surface implant and the at least one first engagement member and settling the stilled at least one first engagement member into engagement with the at least one first surface feature.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to surgical methods and devices and, more particularly, to methods and devices used to facilitate engagement of devices with a bone. 
       BACKGROUND 
       [0002]    The spine is made of bony structures called vertebral bodies that are separated by soft tissue structures called intervertebral discs. The intervertebral disc is commonly referred to as a spinal disc. The spinal disc primarily serves as a mechanical cushion between the vertebral bones, permitting controlled motions between vertebral segments of the axial skeleton. The disc acts as a synchondral joint and allows some amount of flexion, extension, lateral bending, and axial rotation. 
         [0003]    The normal disc is a mixed avascular structure including two vertebral end plates, annulus fibrosis and nucleus pulposus. The end plates are composed of thin cartilage overlying a layer of hard, cortical bone that attaches to the spongy cancellous bone of the adjacent vertebral body. 
         [0004]    The discs are subjected to a variety of loads as the posture of an individual changes. Even when the effects of gravity are removed, however, the soft tissue connected to the spine generates a compressive force along the spine. Thus, even when the human body is supine, the compressive load on the third lumbar disc is on the order of 300 Newtons (N). 
         [0005]    The spinal disc may be displaced or damaged due to trauma or a disease process. A disc herniation occurs when the annulus fibers are weakened or torn and the inner material of the nucleus becomes permanently bulged, distended, or extruded out of its normal, internal annular confines. The mass of a herniated or “slipped” nucleus tissue can compress a spinal nerve, resulting in leg pain, loss of muscle strength and control or even paralysis. Alternatively, with discal degeneration, the nucleus loses its water binding ability and dehydrates with subsequent loss in disc height. Consequently, the volume of the nucleus decreases, causing the annulus to buckle in areas where the laminated plies are loosely bonded. As these overlapping plies of the annulus buckle and separate, either circumferential or radial annular tears may occur, potentially resulting in persistent and disabling back pain. Adjacent, ancillary facet joints will also be forced into an overriding position, which may cause additional back pain. 
         [0006]    Recently, efforts have been directed to replacing defective spinal column components including intervertebral discs. Some replacement components use a solid core of elastomeric material, such as polyolefin, to act as a compressible core between two metal endplates. The metal endplates are typically engaged to the adjacent intervertebral bodies by spikes which extend from the outer surface of the metal endplate. Engagement of the spikes is achieved by impacting the endplate so as to drive the spikes into the bony structure of the adjacent intervertebral body. Properly seating the endplate in this fashion, however, presents various problems. 
         [0007]    As an initial matter, access to the spinal area is generally achieved either through an anterior, posterior or lateral incision that is directly aligned with the area of the spine to be operated upon. Embedment of the endplate, however, requires a force to be applied orthogonal to the incision path. Thus, the impacting tool will normally contact the end plate at some angle off of the longitudinal axis of the spinal column. Therefore, the spikes on the endplate which are closest to the impacting tool may be fully engaged while those on the opposite side of the endplate are only partially engaged. 
         [0008]    Moreover, because the impact is provided at an angle, much of the force of the impact is wasted. Furthermore, the wasted impact tends to force the metal endplate away from the incision point and out of alignment with the spinal column. This problem is exacerbated by a recent trend toward minimally invasive surgery. Specifically, as the incision providing access to the spinal column decreases in size, the angular constraints on the tools and instruments used in the surgery become more restricted. 
         [0009]    A need exists for a system and method which allows endplates of an implant to be more easily attached to bone. A further need exists for a system and method which can be used in a minimally invasive surgery. It would be advantageous if the system and method could be used with a variety of geometric relationships between the location of an incision and the location of the implant. 
       SUMMARY 
       [0010]    A method and system for engaging an implant with a bone is disclosed. In one method incorporating principles of the invention, a bone is engaged with an implant by placing a first surface of an implant adjacent to a first bone portion, contacting the first bone portion with at least one first engagement member extending from the first surface, controlling an agitator to agitate the first surface of the implant and the at least one first engagement member, generating at least one first surface feature in the first bone portion with the agitated at least one first engagement member, stilling the first surface implant and the at least one first engagement member and settling the stilled at least one first engagement member into engagement with the at least one first surface feature. 
         [0011]    In accordance with another embodiment, an implant positioning tool includes a housing, an agitator located within the housing for providing a recurring pattern of movement and a shaft extending out of the housing and having a first end portion operably connected to the agitator and a second end portion configured to operably couple with an implant such that the recurring pattern of movement of the agitator causes the implant to move in a recurring pattern corresponding to the recurring pattern of movement of the agitator. 
         [0012]    The above-described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a cross-sectional view of an insertion instrument incorporating principles of the present invention; 
           [0014]      FIG. 2  shows a perspective view of one embodiment of a gripper that can be used with the insertion instrument of  FIG. 1  in accordance with principles of the present invention; 
           [0015]      FIG. 3  shows a perspective view of one embodiment of an artificial intervertebral disc that may be gripped using the gripper of  FIG. 2 ; 
           [0016]      FIG. 4  shows a cross-sectional view of the insertion instrument of  FIG. 1  with the trigger mechanism in a released position; 
           [0017]      FIG. 5  shows a cross-sectional view of the insertion instrument of  FIG. 1  with the trigger mechanism in a compressed position; 
           [0018]      FIG. 6  shows a cross-sectional view of the insertion instrument of  FIG. 1  with the trigger mechanism in a compressed position and the gripper of  FIG. 2  attached to the internal shaft of the insertion instrument; 
           [0019]      FIG. 7  shows a partial perspective view of the insertion instrument of  FIG. 1  and the gripper of  FIG. 2  snugly gripping the artificial intervertebral disc of  FIG. 3 ; 
           [0020]      FIG. 8  shows a cross-sectional view of the insertion instrument of  FIG. 1  with the trigger mechanism in a released position and the gripper of  FIG. 2  attached to the internal shaft of the insertion instrument such that the finger pairs or the gripper are forced toward each other; 
           [0021]      FIG. 9  shows a partial plan view of an intervertebral disc space created between two vertebrae which have been distracted in accordance with principles of the present invention; 
           [0022]      FIG. 10  shows a partial plan view of the intervertebral disc space created between the two vertebrae of  FIG. 9  with the insertion instrument of  FIG. 1  and the gripper of  FIG. 2  used to securely grip the artificial disc of  FIG. 3  and to position the artificial disc of  FIG. 3  within the intervertebral disc space in accordance with principles of the present invention; 
           [0023]      FIG. 11  shows a partial plan view of the intervertebral disc space and artificial disc of  FIG. 10  after at least some of the distraction force on the vertebrae has been reduced; 
           [0024]      FIG. 12  is a schematic partial plan view of the artificial disc of  FIG. 3  showing the movement of an engagement member when a movement vector of the artificial disc parallel to the axis of the insertion instrument is about ½ of the length of the footprint of the engagement member on the endplate of the artificial disc; 
           [0025]      FIG. 13  is a schematic partial plan view showing the area of bone that is swept by the movement of the engagement member of  FIG. 12 ; 
           [0026]      FIG. 14  is a schematic partial plan view of the artificial disc of  FIG. 3  showing the movement of an engagement member when a movement vector of the artificial disc parallel to the axis of the insertion instrument is significantly less than ½ of the length of the footprint of the engagement member on the endplate of the artificial disc; 
           [0027]      FIG. 15  is a schematic partial plan view showing the area of bone that is swept by the movement of the engagement member of  FIG. 14 ; and 
           [0028]      FIG. 16  shows a partial plan view of the intervertebral disc space and artificial disc of  FIG. 10  after the artificial disc has been embedded into the adjacent vertebrae and released. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  depicts a side cross-sectional view of an insertion instrument  100 . The insertion instrument  100  includes a body housing  102  and a sheath portion  104 . The sheath portion  104  includes an outer sleeve  106  which encloses an inner shaft  108  and which is retained by a retaining pin  110 . The outer sleeve  106  includes a tapered end portion  112 . The inner shaft  108  includes a female threaded end  114  and a male threaded end  116 . 
         [0030]    An internal compression spring  118  is fastened to the sheath portion  104  and held in place by a spring retaining screw  120  which is threadedly engaged with the female threaded end  114  of the inner shaft  108 . The spring retaining screw  120  includes a drive shaft  122  which extends along the axis of the insertion instrument  100 . Once the sheath portion  104  is assembled, it is inserted into the body housing  102  and retained within the body housing  102  with the retaining pin  110 . 
         [0031]    The body housing  102  includes a handle  124 , a handle transition  126 , a trigger mechanism  128 , and pivot pin  130 . The trigger mechanism  128  can be any type of trigger mechanism known in the art. The trigger mechanism  128  of  FIG. 1  pivots about the pivot pin  130  in the body housing  102 . 
         [0032]    The body housing  102  is configured to threadingly receive an agitator component  132  which includes a port  134  for the insertion of a power source. The power source may be a power cord or a battery pack. Energy from the power source is used to drive a transducer  136 . The transducer  136  is in operable contact with a driver  138  and armature  140 . When the agitator component  132  is threaded into the body housing  102  and the trigger mechanism  128  is in the position shown in  FIG. 1 , the drive shaft  122  is operably received within the armature  140 . 
         [0033]    The transducer  136  in this embodiment includes a piezoelectric driver which contains Thunder Technology, which is a high deformation Piezo electrical actuator, (described and illustrated in U.S. Pat. No. 5,632,841, U.S. Pat. No. 5,639,850 and U.S. Pat. No. 6,030,480, the disclosures of which are incorporated herein by reference). The transducer provides operating frequencies of between 40 kHz and 65 kHz, although other frequencies may be used. 
         [0034]      FIG. 2  shows a gripper  142  which includes a coupling portion  144 , a throat portion  146  and a shaft  148  in an unstressed condition. The coupling portion  144  includes a slit  150  and a slit  152  which extend through the coupling portion  144  and the throat portion  146  into the shaft  148 . The slits  150  and  152  define two opposing pairs of fingers  154  and  156  in the coupling portion  144  (only one finger of finger pair  156  is shown in  FIG. 2 ). The throat portion  146  tapers from a larger diameter at the coupling portion  144  to a smaller diameter at the shaft  148 . The shaft  148  includes a threaded inner bore  158  which is configured to be engaged with the male threaded end  116  of the inner shaft  108 . 
         [0035]    The coupling portion  144  of the gripper  142  is configured to mate with an artificial disc such as the artificial disc  160  shown in  FIG. 3 . The artificial disc  160  includes two endplates  162  and  164  which are separated by a core  166 . Each of the two endplates  162  and  164  include a number of engagement members  168 . In the embodiment of  FIG. 3 , the engagement members  168  are generally in the shape of a cone, with the apex  170  of the engagement members  168  spaced apart from the respective endplate  162  or  164 . In alternative embodiments, the engagement members may be pyramidal, conical, or another shape. Preferably, the portions of the engagement members farthest away from the endplates, such as the apex of the engagement members  168 , are relatively sharp. 
         [0036]    The endplates  162  and  164  further include four notches  172 ,  174 ,  176  and  178  and four notches including the notch  180  and three notches not shown) that are symmetrical and spaced apart from the notches  172 ,  174 ,  176  and  178  to form four notch pairs. By way of example, the notch  180  which is shown in  FIG. 3  in shadow form, is the symmetrical to and spaced apart notch for the notch  172 . Thus, the notch  172  and the notch  180  area notch pair. 
         [0037]    The eight notches,  172 ,  174 ,  176 ,  178 ,  180 , and the three notches not shown, are sized and shaped to snugly mate with the fingers in the finger pairs  154  and  156 . Additionally, the notches  172  and  176  define a ledge  182  which is sized for engagement with the width of the slit  152 . Moreover, the distance between each of the notches in the notch pairs is substantially the same as the distance between the opposing fingers of the finger pairs  154  and  156 . 
         [0038]    Operation of the insertion instrument  100  begins with the insertion instrument  100  in the condition of  FIG. 4 . In  FIG. 4 , the trigger mechanism  128  is not depressed. Accordingly, the trigger mechanism is maintained in the position of  FIG. 4  by the internal compression spring  118 , which is configured to bias the inner shaft  108  to the rear of the insertion instrument  100  which, in  FIG. 4 , is to the right. Specifically, the internal compression spring  118  forces the spring retaining screw  120  against the trigger mechanism  128 . 
         [0039]    Next, the operator applies a force to the trigger mechanism  128  in the direction of the arrow  184 . As the force applied to the trigger mechanism  128  increases above the force provided by the internal compression spring  118 , the trigger mechanism  128  pivots about the pivot pin  130  forcing the spring retaining screw  120  in the direction of the arrow  186 . As the spring retaining screw  120  moves in the direction of the arrow  186 , the internal compression spring  118  is compressed and the inner shaft  108  is forced in the direction of the arrow  186  to the position shown in  FIG. 5 . If desired, a locking mechanism may be provided to maintain the trigger mechanism  128  in the compressed position of  FIG. 5 . 
         [0040]    When the trigger mechanism  128  is fully compressed, the shaft  148  of the gripper  142  is inserted into the outer sleeve  106  of the insertion instrument  100 . The threaded inner bore  158  of the gripper  142  is then positioned about the male threaded end  116  of the inner shaft  108  and threaded onto the male threaded end  116  to the position shown in  FIG. 6 . In the position of  FIG. 6 , the trigger mechanism  128  is fully compressed and the threaded inner bore  158  of the gripper  142  is fully engaged with the male threaded end  116  of the inner shaft  108 . Additionally, the throat portion  146  of the gripper  142  is located adjacent to the tapered end portion  112  of the outer sleeve  106  and the slits  150  and  152  are in an uncompressed state. 
         [0041]    Next, the gripper  142  is engaged to the artificial disc  160 . This is accomplished by aligning the finger pair  154  with the notch pair  172  and  180  and the notch pair  182  and the symmetrical and spaced apart notch (not shown) for the notch  182 . Additionally, the finger pair  156  is aligned with the notch pair  176  and the symmetrical and spaced apart notch (not shown) for the notch  176 , and the notch pair  178  and the symmetrical and spaced apart notch (not shown) for the notch  178 . 
         [0042]    The gripper  142  is then pushed against the artificial disc  160 . This force causes the fingers in the finger pairs  154  and  156  to be forced apart as the slit  150  widens. Additionally, in this embodiment, the finger pairs  154  and  156  are forced apart as the slit  152  widens. As the finger pairs  154  and  156  encounter the eight notches,  172 ,  174 ,  176 ,  178 ,  180  and the three notches not shown, the gripper  142  moves toward its non-stressed condition with the slit  150  narrowing and the finger pairs  154  and  156  moving into the eight notches,  172 ,  174 ,  176 ,  178 ,  180  and the three notches not shown. Thus, the artificial disc  160  is firmly gripped by the gripper  142  as shown in  FIG. 7 . 
         [0043]    The operator now releases the trigger mechanism  128 . As the force applied to the spring retaining screw  120  by the trigger mechanism  128  decreases below the force provided by the internal compression spring  118  on the spring retaining screw  120 , the spring retaining screw  120  is forced in the direction of the arrow  188  as the internal compression spring  118  is decompressed and the inner shaft  108  is forced in the direction of the arrow  188 . As the spring retaining screw  120  moves in the direction of the arrow  188 , the drive shaft  122  is positioned within the armature  140  and the trigger mechanism  128  pivots about the pivot pin  130  in the direction indicated by the arrow  190 . 
         [0044]    Movement of the inner shaft  108  in the direction of the arrow  188  also forces the gripper  142  to be moved further into the outer sleeve  106 . Specifically, the tapered end portion  112  acts upon the throat portion  146  of the gripper  142  thereby forcing the slit  150  and the slit  152  toward a narrower configuration. Accordingly, the finger pairs  154  and  156  are forced in a direction further into the eight notches,  172 ,  174 ,  176 ,  178 ,  180  and the three notches not shown and the finger pairs  154  and  156  are forced toward the ledge  182 . 
         [0045]    By way of example,  FIG. 8  depicts the insertion instrument  100  with the trigger mechanism  128  in a non-compressed state and with the gripper  142  pulled further into the outer sleeve  106  than in the  FIG. 6 . Thus, the slit  152  is narrowed such that the finger pairs  154  and  156  are placed into contact with each other. Of course, when the artificial disc  160  is gripped by the gripper  142 , the ledge  182  maintains the finger pairs  154  and  156  spaced apart from each other. 
         [0046]    In this condition, the artificial disc  160  is securely gripped by the gripper  142 . The insertion instrument  100  is then used to implant the artificial disc  160 . In one method, the vertebrae  200  and  202  adjacent to an intervertebral disc to be replaced are distracted using a distractor (not shown) and the natural intervertebral disc is removed as shown in  FIG. 9 . The insertion instrument  100  is then used to position the artificial disc  160  in the intervertebral space between the vertebrae  200  and  202  as shown in  FIG. 10 . If desired, placement of the artificial disc  160  within the intervertebral space may be assisted by the use of guides. The guides may be integral with the distractor or separate components. 
         [0047]    Once the artificial disc  160  is at the desired location, the force exerted on the vertebrae  200  and  202  by the distractor (not shown) is reduced. This allows the soft tissue connected to the spine to force the vertebrae  200  and  202  toward each other until the vertebrae  200  and  202  are partially embedded onto the artificial disc  160  as shown in  FIG. 11 . The force exerted by the soft tissue on the spine is not, however, sufficient to fully embed the vertebrae  200  and  202  onto the artificial disc  160 . 
         [0048]    With the artificial disc  160  securely gripped by the gripper  142  and partially embedded into the adjacent vertebrae  200  and  202 , the agitator component  132  is activated. In this embodiment, the agitator component  132  generates a reciprocating movement of the drive shaft  122  along the axis of the insertion instrument  100  resulting in a repeated pattern of movement in the directions indicated by the arrows  204  and  206  in  FIG. 11 . Specifically, the movement of the drive shaft  122  is transferred to the inner shaft  108  through the female threaded end  114  of the inner shaft  108 . The inner shaft  108  in turn causes the gripper  142  to move in the repeated pattern of movement in the directions indicated by the arrows  204  and  206 . Therefore, because the artificial disc  160  is securely gripped by the gripper  142 , the artificial disc  160  also moves in the same pattern generated by the agitator component  132 . 
         [0049]    The resultant movement of the engagement members  168  on the artificial disc  160  is depicted in  FIG. 12 . As the agitator component  132  causes movement in the direction of the arrow  204 , the engagement member  168  moves from its original position to the position indicated by the engagement member  168 ′ which is offset from the original position of the engagement member  168  by ½ of the length of the footprint of the engagement member  168  on the endplate  162 . The footprint of the engagement member  168  on the endplate  162  along the axis of the insertion instrument is identified by the points “A” and “B” in  FIG. 12 . 
         [0050]    As the agitator component  132  causes movement in the direction of the arrow  206 , the engagement member  168  moves to the position indicated by the engagement member  168 ″ which is offset from the original position of the engagement member  168  by ½ of the length of the footprint of the engagement member  168  on the endplate  162  in a direction opposite to the offset of the engagement member  168 ′ from the position of the engagement member  168 . Accordingly, the amplitude of the movement in the axis of the insertion instrument  100  is equal to the length of the footprint of the engagement member  168  on the endplate  162  parallel to the axis of the insertion instrument  100 . 
         [0051]    Thus, as shown in  FIG. 13 , the above described movement of the engagement member  168  causes the engagement member  168  to sweep an area “C” of the adjacent vertebra  200  or  202 . The repeated movement of the engagement member  168  as pressure is applied to the vertebrae  200  and  202  by the soft tissue connected to the spine results in a scraping and/or compaction of the vertebra  200  or  202  at the contact point of the engagement member  168 . Accordingly, an area in the bone corresponding to the area “C” is either scraped away or compacted leaving a surface feature in the vertebra  200  or  202  in which the engagement member  168  remains. 
         [0052]    The final shape of the surface feature will depend upon the resiliency of the vertebral bone as well as the amplitude of the repeated movement and the size of the engagement member. Any resiliency of the vertebral bone will tend to reduce the size of the finally realized surface feature. Nonetheless, large movements of a particular engagement member results in a larger area of vertebral bone that is affected by the engagement member. For example, the amplitude of the movement of the engagement member  168  in  FIG. 14  is significantly less than ½ of the length of the footprint of the engagement member  168  on the endplate  162 . Thus, when moved between the positions of  168 ′ and  168 ″ of  FIG. 14 , an area in the bone corresponding to the area “D” of  FIG. 15  is either scraped away or compacted leaving a surface feature in which the engagement member  168  settles when the movement of the artificial disc  160  is stilled. 
         [0053]    The area of vertebral bone affected by the movement of the engagement member  168  in  FIG. 14  is substantially less than the area of vertebral bone affected by the movement of the engagement member  168  in  FIG. 12 . Thus, the smaller amplitude of movement depicted in  FIG. 14  provides a lesser amount of disturbance to the adjacent vertebra  200  or  202  along the axis of movement compared to the larger amplitude of movement depicted in  FIG. 14 . In the embodiment of  FIG. 1 , the amplitude of movement may be controlled by threading the agitator component  132  further into the body housing  102  for larger amplitudes or further out of the body housing  102  for smaller amplitudes. Alternatively, the amplitude may be a function of electrical power input to the transducer  136 . 
         [0054]    In alternative embodiments, more complex agitation patterns are employed. By way of example, in one embodiment the amplitude of movement is varied from a larger amplitude when the engagement member is near the surface of the adjacent vertebrae to a smaller amplitude as the engagement member is further embedded into the vertebrae. In a further embodiment, an engagement member is moved in a pattern that includes a cross-axial component as well as the above described axial component, thus affecting an area of bone that is larger than the engagement member in two different axes. 
         [0055]    In a further embodiment, the engagement member is moved in a pattern that includes a perpendicular movement component which is aligned with the longitudinal axis of the spine as indicated by the arrows  208  and  210  in  FIG. 11 . The perpendicular component may be in place of or in addition to the foregoing patterns of movement. Additionally, the perpendicular movement component in a pattern may be simultaneous with an axial component or components or sequential to an axial component or components. Perpendicular movement may be provided by a reciprocating rotary movement of the drive shaft  122  with some modification of the outer sleeve  106 . Further, the perpendicular component may be provided by the use of linkages or impact wedges near the tapered end portion  112 . 
         [0056]    Once the artificial disc  160  has been embedded into the adjacent vertebrae  200  and  202  to the desired depth, the agitator component  132  is deenergized thereby stilling the movement of the artificial disc  160 . As the movement of the artificial disc  160  is stilled, the engagement members  169  settle into the respective surface features generated on the adjacent vertebra  100  o  202 . 
         [0057]    Next, the gripper  142  is disengaged. With reference to  FIGS. 4-8 , the operator applies a force to the trigger mechanism  128  in the direction of the arrow  184  of  FIG. 4 . As the force applied to the trigger mechanism  128  increases above the force provided by the internal compression spring  118 , the trigger mechanism  128  pivots about the pivot pin  130  forcing the spring retaining screw  120  in the direction of the arrow  186 . As the spring retaining screw  120  moves in the direction of the arrow  186 , the internal compression spring  118  is compressed and the inner shaft  108  is forced in the direction of the arrow  186 . Thus, the throat portion  146  of the gripper  142  is moved in a direction out of the outer sleeve  106  from the position shown in  FIG. 8  to the position shown in  FIG. 6 . 
         [0058]    As the throat portion  146  moves out of the outer sleeve  106 , the finger pairs  152  and  154  are less constricted by the tapered end portion  112  of the insertion instrument  100 . Accordingly, the finger pairs  154  and  156  are resiliently forced in a direction away from the eight notches,  172 ,  174 ,  176 ,  178 ,  180  and the three notches not shown and the finger pairs  154  and  156  are resiliently forced away from the ledge  182 . The artificial disc  160  is thus only firmly gripped by the gripper  142 . Accordingly, by forcing the insertion instrument  100  away from the vertebrae  200  and  202 , the finger pairs  154  and  156  are forced apart as the slit  150  widens. As the finger pairs  154  and  156  are moved out of and away from the eight notches,  172 ,  174 ,  176 ,  178 ,  180  and the three notches not shown, the gripper  142  is disengaged from the artificial disc  160 . As the gripper  142  clears the artificial disc  160 , the gripper returns to its non-stressed condition with the slits  150  and  152  narrowing to the unstressed condition shown in  FIG. 2  and the artificial disc  160  remains embedded in the vertebrae  200  and  202  as shown in  FIG. 16 . 
         [0059]    While the present invention has been illustrated by the description of exemplary processes and system components, and while the various processes and components have been described in considerable detail, applicant does not intend to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will also readily appear to those ordinarily skilled in the art. By way of example, the gripper and inner shaft of an insertion instrument may be integrally formed. The invention in its broadest aspects is therefore not limited to the specific details, implementations, or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.