Patent Publication Number: US-2010114105-A1

Title: System and method for vertebral interbody fusion

Description:
BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates generally to the insertion of fusion cages, and more particularly, to systems and methods for implanting fusion cages with an inserter instrument for intervertebral disc replacement. 
     2. The Relevant Technology 
     Current cage inserter designs typically rely on a threaded connection between the fusion cage and the inserter. This connection type has its drawbacks, as the act of releasing the cage from the inserter requires a large number of revolutions to disengage the threaded member from the cage. This method of release is time consuming and the threaded hole needed in the cage causes high stress concentrations that can cause premature failure of the device. Additionally typical interfaces between the fusion cage and the inserter do not provide a truly locked configuration, allowing the fusion cage to rotate or become displaced while attached to the inserter. 
     Another technique utilizes an expandable collet inserter that provides a single-movement release that is superior to the threaded connection. However, the use of an expandable collet creates the possibility of exposing the cage attachment hole to large mechanical forces which can cause premature failure of the device. 
     As the above described instruments and techniques illustrate, the existing systems and procedures for inserting a fusion cage into intervertebral space, positioning of a cage between two vertebrae and releasing a cage may not be as effective as desired and may lead to further spinal surgeries. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
         FIG. 1  illustrates a perspective slightly proximal side view of an intervertebral assembly comprising a fusion cage and an inserter; 
         FIG. 2  illustrates a perspective view of an inserter comprising a proximal handle portion and an insertion component with a collapsible collet protruding from a hollow outer shaft of the insertion component; 
         FIG. 3  illustrates a perspective view of the inserter of  FIG. 2  with a toggle assembly in an outward position forcing the collapsible collet to protrude from the outer shaft and the locking sleeve in a locked outer position forcing the locking rod to protrude from the interference shaft controlling the collapsible collet; 
         FIG. 4  illustrates an exploded perspective view of the inserter of  FIG. 2 ; 
         FIG. 5  illustrates a blown up distal end perspective view of the inserter of  FIG. 2  with the collapsible collet within the hollow outer shaft; 
         FIG. 6  illustrates a blown up distal end perspective view of the inserter of  FIG. 2  with the collapsible collet protruding from the hollow outer shaft; 
         FIG. 7  illustrates a blown up distal end perspective view of the inserter of  FIG. 2  with a locking rod protruding from an interference shaft and the collapsible collet, controlling the collet, which is protruding from the hollow outer shaft; 
         FIG. 8  illustrates a perspective view of a fusion cage; 
         FIG. 9  illustrates a cross-sectional top view of the fusion cage of  FIG. 8 ; 
         FIG. 10  illustrates a cross-sectional view of an alternate embodiment of a fusion cage; 
         FIG. 11  illustrates a cross-sectional side view of the interaction between the fusion cage and the distal end of the inserter and the collapsible collet with the locking rod in the unlocked position; 
         FIG. 12  illustrates a cross-sectional side view of the interaction between the fusion cage and the distal end of the inserter and the collapsible collet with the locking rod in the locked position; 
         FIG. 13  illustrates a cross-sectional side view of the interaction between the cage and the distal end of the inserter, the collapsible collet, the locking rod in a locked position with the collet engaging the fusion cage and locking the cage to the inserter. 
         FIG. 14  illustrates a cross-sectional side view of the distal end of the inserter with the locking rod and collapsible collet retracted and the cage released from the inserter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to systems and methods for securing a fusion cage to and inserter and insertion of a fusion cage between two vertebrae. Those of skill in the art will recognize that the following description is merely illustrative of the principles of the invention, which may be applied in various ways to provide many different alternative embodiments. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts in the appended claims. 
     One embodiment of the present invention includes a fusion cage and an inserter. A method of securing a fusion cage to an inserter consists of forcing a collapsible collet to protrude from an instrument body by pressing an actuation assembly to an outward position. The collet inserts into the proximal end of the fusion cage. A locking rod of the instrument is forced through the collet to control the collet from collapsing. The actuator assembly is pressed to an inward position forcing the collet to retract against a reverse tapered aperture, locking the fusion cage to the inserter. 
     A method for positioning a fusion cage between two vertebrae consists of securing a fusion cage to an inserter. The inserter inserts the fusion cage into the intervertebral space. Osteogenic substances such as harvested bone chips, bone growth factors, hydroxyapatite, tri calcium phosphate, bone growth factors, demineralized bone matrix or the like are packed into a fusion cage cavity that is accessible through a first and a second aperture. The inserter releases the fusion cage after placement within the intervertebral space. 
     The following definitions should be used with regard to this application: 
     A “reverse tapered aperture” means a hole that increases in diameter when moving from the outside of a device to the inside of a device, either continuously (e.g., a conical taper or the like) or discontinuously (one or more steps up in the diameter). 
     An “insertion component” means a long, slender, distal end of a surgical instrument that is intended to be introduced into the body of a surgical patient. 
     “Semi-tubular” means approximately half of a tube after a cut along the length of the tube. 
     “Snap into engagement” means an engagement in which parts come into a predetermined relative position or orientation via deformation of at least one of element, followed by relaxation of the deformation such that there is physical interference tending to resist motion of the parts from the predetermined relative position or orientation. 
     “Trigger” means a member that is shaped and sized to receive contact and pressure from one or more fingers of a user. 
     Referring to  FIG. 1  a perspective view of an embodiment of a fusion cage  100  and an inserter  102  is shown. The inserter  102  includes a fusion cage interface  122  at a distal end allowing for a substantially complimentary fit with a proximal end  181  of the fusion cage  100 . The proximal end of the inserter  102  within a proximal handle portion  114  includes an actuator button  116  which, when pressed, forces a collapsible collet  120  (not shown in  FIG. 1 ) to protrude from the inserter distal end  122 . 
       FIGS. 2-7  illustrate an embodiment of an inserter with a proximal handle portion, an intermediate portion, and an insertion component. 
     Referring to  FIG. 2 , the inserter  102  comprises the proximal handle portion  114  with a first grip  101  and a second grip  103  each extending non-parallel from the longitudinal axis with the second grip  103  extending opposite the first grip  101 . The grips  101 ,  103  include handle grooves  164  which aid in the gripping of the proximal handle portion  114 . An intermediate portion  107  of the inserter  102  comprises a proximal hollow outer shaft  108  which may be encompassed by a locking sleeve  109 . The locking sleeve  109  comprises two semi-tubular portions comprising a first locking sleeve portion  110  and a second locking sleeve portion  111  with a first trigger  112  extending non-parallel from the first locking sleeve portion  110  and a second trigger  113  extending non-parallel from the second locking sleeve portion  111 . Each locking sleeve portion  110 ,  111  comprises a feature configured to snap into engagement either in an unlocked snap groove  117  (not shown in  FIG. 2 ), or a locked snap groove  118 . The snap grooves  117 ,  118  are positioned on the exterior of the proximal hollow outer shaft  108  proximate a tapered shaft  106 . The unlocked snap groove  117  is positioned proximate the locked snap groove  118  separated by some distance. The tapered shaft  106  is positioned at the distal end of the intermediate portion  107  of the inserter  102 . The tapered shaft  106  decreases in size toward an insertion component  105  of the inserter  102 . 
     An alternate embodiment (not shown) of the proximal handle portion may include a single grip extending in a single direction non-parallel from the longitudinal axis of the inserter. A further embodiment may also include a longer grip extending in a single direction non-parallel form the longitudinal axis of the inserter and a second shorter grip extending opposite the first grip. 
     An alternate embodiment for the locking sleeve (not shown) may include a single tubular component that encompasses an intermediate portion of the inserter. In addition the locking sleeve may include a single trigger (not shown) with a first trigger rod. 
     The insertion component  105  extends from the distal end of the tapered shaft  106  of the intermediate portion  107  along the same direction as the longitudinal axis of the intermediate portion  107 . The insertion component comprises a generally circular hollow outer shaft  104  comprising an outer wall defining a bore, and an inserter distal end  122  which interacts with the fusion cage  100 . 
     A collapsible collet  120  moves longitudinally independent from the hollow outer shaft  104 . The collet  120  may maintain an open configuration or a collapsed configuration. The collet  120  may protrude from within the hollow outer shaft  104  of the insertion component  105  of the inserter distal end  122  when the actuator button  116  is pressed. 
     Referring to  FIG. 3 , the inserter  102  is shown with the locking sleeve  109  in a locked position snapped into engagement in the locked snap groove  118 . Positioning the locking sleeve  109  in the locked position forces a locking rod  136  (not shown in  FIG. 3 ) to protrude out of the inserter distal end  122  from within the insertion component  105  as well as protrude from within the collet  120 , thereby controlling collapse of the collet  120 . 
     Referring to  FIG. 4 , the inserter  102  is shown in an exploded view exposing the individual parts. The proximal handle portion  114  further comprises a handle bore  162  extending lengthwise non-parallel to the handle grips  101 ,  103 . An actuator assembly  138  passes at least partially through the handle bore  162 . The proximal handle portion also includes an actuator shaft  156  which extends distally from the grips  101 ,  103  in a non-parallel fashion. The actuator shaft  156  includes a handle portion groove  160  and a handle portion rib  158  allowing for a slidable interface with the intermediate portion  107 . More specifically the proximal hollow outer shaft  108  engages the handle portion groove  160  and an upper slot interface  153  of the intermediate portion  107  engages a first handle portion rib  158  and a lower slot interface  155  of the intermediate portion  107  engages a second handle portion rib  159 . Each slot interface  153 ,  155  maintains a cavity between the proximal handle portion  114  and the intermediate portion  107  allowing for passage of a first trigger rod  115  through the intermediate portion  107 . In the preferred embodiment the proximal handle portion  114  engages the intermediate portion by means of welding or securely fastened by some other means well known, such that once the proximal handle portion  114  and the intermediate portion  107  are engaged each cannot be separated from the other. 
     The actuator assembly  138  includes a toggle assembly within the actuator body. The distal end of the actuator assembly  138  comprises the actuator button  116 . The proximal end of the actuator assembly  138  comprises an actuator dowel  139  which abuts a distal end of a plug  140 . 
     The intermediate portion  107  includes the proximal hollow outer shaft  108  with the slot interface  153  proximal the unlocked snap groove  117  which is proximal the locked snap groove  118 . The distal end of the intermediate portion includes the tapered shaft  106  decreasing in diameter toward the insertion component  105 . The plug  140  and a spring  148  are shaped to pass at least partially through the proximal hollow outer shaft  108  substantially along the same longitudinal axis of the inserter  102 . The plug  140  comprises a plug distal end  142  configured to abut a spring proximal end  152  of the spring  148 . The plug distal end  142  also engages the proximal end of an interference shaft  134 . The plug also includes an elongated plug body  144  which includes an elongated plug aperture  146  passing through the center of the plug body  144 . The elongated plug aperture  146  passes through the plug body  144  in a non-parallel fashion in regard to the longitudinal axis of the inserter  102  or the plug  140 . A plug bore  147  extends from the distal end of the plug  140  and passes through the plug  140  in communication with the elongated plug aperture  146 . 
     The spring  148  also includes a spring distal end  150  configured to abut the surface of the interior of the tapered shaft  106 . Abutment of the spring  148  against the plug distal end  142  and the interior of the tapered shaft  106  allows for compression of the spring  148  between the two surfaces. 
     The locking sleeve  109  at least partially encompasses the intermediate portion  107  with the first locking sleeve portion  110  and the second locking sleeve portion  111 . The first locking sleeve portion includes a first locking sleeve aperture  154  that accepts the first trigger rod  115  of the first trigger  112 . The first trigger rod  115  passes through the first locking sleeve aperture  154  which provides access to the upper slot interface  153 . The first trigger rod  115  passes through the upper slot interface  153  which provides access to the elongated plug aperture  146 . The first trigger rod  115  passes through the elongated plug aperture  146  which provides access to the lower slot interface  155 . The first trigger rod  115  passes through the lower slot interface  153  engaging the second locking sleeve portion  111  at the point the second trigger  113  and second locking sleeve portion  111  connect. 
     The interference shaft  134  is hollow, comprising an interference shaft wall that defines an interference shaft bore. The interference shaft  134  is positioned at least partially within the hollow outer shaft  104  along a longitudinal direction. The distal end of the interference shaft  134  comprises the collapsible collet  120 . A locking rod  136  is positioned at least partially within the interference shaft  134  along a longitudinal direction. The proximal end of the interference shaft  134  engages the plug distal end  142  passing longitudinally through the spring  148 . The locking rod  136  passes through the plug bore  147  engaging the first trigger rod  115  which is positioned through the elongated plug aperture  146 . 
     Referring to  FIG. 5 , the inserter distal end  122  includes an inserter distal wall  128  on opposite sides of an inserter trough  129  comprising a primarily rectangular cross sectional void with a trough base wall  130  and trough inner longitudinal walls  132 . The inserter trough  129  facilitates attachment of the fusion cage  100  to the inserter. The collet  120  resides within the hollow outer shaft  104 . 
     Referring to  FIG. 6 , the collet  120  includes collet grooves  121  allowing collapse of the collet and a collet proximal end  166  which tapers when moving proximally from the center of the collet  120 . The collet  120  protrudes from within the hollow outer shaft  104  when the actuator button  116  is pressed extending the actuator dowel  139  to an outward position, pushing the plug  140  distally. The plug  140  moving distally moves the interference shaft  134  distally causing the collet  120  to protrude from the hollow outer shaft  104 . 
     Referring to  FIG. 7 , the locking rod may protrude from within the interference shaft  134 . The locking sleeve moves distally from an unlocked position to a locked position by pushing the triggers  112 ,  113  distally which forces the locking rod  136 , connected to the first trigger rod, distally. The locking rod  136  controls the collet  120  from collapsing. 
     It is appreciated that the inserter  102  is comprised of many pieces and these pieces may be comprised of similar or many different materials. The inserter  102  and its pieces may be comprised of any metals, metal alloys, semi-rigid plastics or polyurethane. The interference shaft  134  and the collet  120  may be comprised of similar materials as the remainder of the inserter  102 ; however, the interference shaft  140  and the collet  120  may comprise metal, metal alloys and the like and may not consist of any elastomeric substances. It can be appreciated as well, that the pieces may also take on slightly different forms than depicted in the drawings such as straight, curved, bayoneted, offset, or the like, which assist in adapting the instrument for the access approach that the surgeon uses to get to the intervertebral space. Thus, the instruments of the present invention may be adapted to a variety of different surgical approaches. 
       FIGS. 8 and 9  illustrate an embodiment of a fusion cage comprising a cavity, a distal wall, lateral walls and a proximal portion including a head with a rectangular cross section. 
     Referring to  FIG. 8 , the fusion cage  100  comprises an outer wall which includes a distal wall  178  which may be an uninterrupted surface, an inserter interface which comprises a head  179  with a generally rectangular cross section, the head  179  protrudes from a proximal wall  180 , a shoulder  183  may be defined at the juncture of the head  179  and the proximal wall  180 , a first corrugated vertebra engaging surface  188  and a second corrugated vertebra engaging surface  189  extending substantially parallel to one another from the proximal wall  180  to the distal wall  178 . A first lateral wall  192  and a second lateral wall  194  are positioned opposite and parallel the first lateral wall  192 , each lateral wall  192 ,  194  extending longitudinally from the proximal wall  180  to the distal wall  178 . The distal wall  178  may include rounded edges or tapered edges at the junctures with the lateral walls  192 ,  194 . A fusion cage aperture  196  may extend longitudinally along the fusion cage from the corrugated vertebrae engaging surfaces  188 ,  189 . The lateral walls  192 ,  194  may include a plurality of pores  172 . The pores  172  may be the same size or may vary in size. The fusion cage  100  also comprises a fusion cage cavity  186  located centrally between the lateral walls  192  and the proximal wall  180  and the distal wall  178 , and in communication with the fusion cage aperture  196 . Osteogenic substances may be inserted into the fusion cage cavity  186  through the fusion cage aperture  196  or through the pores  172 . 
     Referring to  FIG. 9 , the head  179  of the fusion cage may comprise a generally circular reverse tapered aperture  170  which extends longitudinally from the proximal end of the fusion cage  100  to the fusion cage cavity  186 . The reverse tapered aperture  170  comprises a collet engagement surface  168  that extends in a substantially diagonal or distal-lateral direction. The reverse tapered aperture  170  may receive the collet  120  of the inserter  102  facilitating attachment of the fusion cage  100  to the inserter  102 . It can be appreciated that this reverse tapered aperture could take on many geometrical forms or engagement features to accomplish the same function of retaining the cage on the inserter via the collet. (e.g. a conical taper or stepped hole, etc) The fusion cage head  179  slides into the inserter trough  129  which may form a complimentary fit. A fusion cage head lateral wall  182  interfaces with the trough inner longitudinal walls  132  of the inserter as well as a fusion cage head base wall  184  interfaces with the trough base wall  130 . 
     Positioning bores  174 ,  176  are present on the fusion cage  100  and may be used to determine if the fusion cage  100  has been placed in the correct location between two vertebrae. A proximal positioning bore  174  is located on the first corrugated vertebra engaging surface  188  toward the proximal end of the fusion cage  100  between the lateral wall  192  and the fusion cage cavity  186 . A distal positioning bore  176  is positioned on the second corrugated vertebra engaging surface  189  toward the distal end of the fusion cage  100  between the opposite lateral wall  194  and the fusion cage cavity  186 . Tantalum wire markers are inserted into the positioning bores so that x-rays of the fusion cage  100  within the intervertebral space can detect them to facilitate correct positioning of the fusion cage  100 . However, it will be appreciated that any radio-opaque material or shape may also be used for insertion into the positioning bores  174 ,  176  to facilitate proper placement of the fusion cage  100  between two vertebrae. 
     The preferred embodiment of the fusion cage  100  is comprised of a carbon-fiber reinforced PEEK (polyetheretherketone). However, any biocompatible material may be used, including but not limited to stainless steels, titanium and its alloys, cobalt-chrome and its alloys, ceramics, polymers, biodegradable materials, allograft bone materials, or the like. 
     An alternate embodiment of a second fusion cage  200  is shown in  FIG. 10 . While most of the features remain constant with the previously disclosed fusion cage  100 , the second fusion cage  200  may comprise fewer pores  172  while maintaining a plurality of pores, and the distal end  178  may taper more abruptly toward the lateral walls  192 ,  194 . In addition the corrugated vertebrae engaging surfaces  188 ,  189  may include more or fewer ridges. 
     Another possible embodiment of the fusion cage may be a fusion cage wherein each lateral wall  192 ,  194  comprises a single pore (not shown). Further still another embodiment may include an aperture, a pore or other opening on the fusion cage distal wall  178  (not shown). 
       FIGS. 11 through 14  illustrate one method of implementing the present invention to attach a fusion cage to an inserter and to release a fusion cage from an inserter. Referring to  FIG. 11 , a fusion cage  100  is engaged with the inserter  102  at the inserter distal end  122 . The fusion cage head  179  is slidably placed into the inserter trough  129 . The collet  120  is forced distally by a user pressing the actuator button  116  which forces the toggle assembly to an outward position pushing actuator dowel  139  distally which forces the plug  140  to move distally compressing the spring  148  between the plug and the internal portion of the tapered shaft  106  which forces the interference shaft  134  distally causing the collet  120  to protrude from the inserter distal end  122 , and more particularly, the collet  120  to protrude from within the inserter trough  129 . The collet  120  is urged into a collapsed configuration as it is restricted by the reverse tapered aperture  170  to a smaller diameter as it is inserted into the fusion cage  120  reverse tapered aperture  170 . The collet  120  may enter at least a portion of the fusion cage cavity  186 . The collet  120  returns to its open configuration or original diameter after passing through the reverse tapered aperture  170 . 
     Referring to  FIG. 12 , the locking rod  130  protrudes distally from within the interference shaft  134  by a user thrusting the triggers  112 ,  113  distally which forces the locking sleeve from an unlocked position to a locked position (refer to  FIG. 3 ). Forcing the triggers  112 ,  113  distally forces the locking sleeve  109  to unsnap from engagement from the unlocked snap groove  117  and snap into engagement into the locked snap groove  118 . The first trigger rod  115  forces the locking rod  136  distally to protrude from the interference shaft  134  and more particularly from the collet  120 . The locking rod  136  controls collapse of the collet  120 . 
     Referring to  FIG. 13 , a user presses the actuator button  116  which forces the toggle assembly to an inward position proximally retracting the actuator dowel  139  allowing the spring  148  to expand forcing the plug  140  distally. The collet  120  is retracted to engage the reverse tapered aperture  170 . The locking rod controls collapse of the collet causing the collet proximal end  166  to engage the collet engagement surface  168  of the reverse tapered aperture  170  of the fusion cage  100 . The retraction of the collet forces the fusion cage head  179  fully engage the inserter trough  129 . The inserter distal wall  128  engages the fusion cage proximal wall  180 . The trough base wall  130  engages the fusion cage head base wall  184  and the trough inner longitudinal walls  132  engage the fusion cage head lateral walls  182 . The fusion cage  100  is incapable of being independently manipulated from the inserter  102  after the collet  120  engages the reverse tapered aperture  170  of the fusion cage  100 . 
     The fusion cage  100  is positioned into the intervertebral space by a user manipulating the inserter  102 . The vertebrae engaging surfaces  188 ,  189  may engage a superior and an inferior vertebra. Osteogenic substances may be inserted into the fusion cage cavity  186 . 
     Referring to  FIG. 14 , release of the fusion cage  100  is accomplished by retraction of the locking rod  136  from the collet  120 . A user pulls the triggers  112 ,  113  back from the locked position to the unlocked position wherein the locking sleeve  109  is unsnapped from engagement from the locked snap groove  118  and moves proximally and snaps into engagement in the unlocked snap groove  117 . Retraction of the locking rod  136  allows uncoupling of the collet  120  from the fusion cage  100  and more particularly collapse of the collet  120  through the reverse tapered aperture  170 . The spring  148  expands to its original size and presses against the interior tapered shaft  106  and the plug  140 . The plug is forced proximally which retracts the interference shaft  134 . The collet  120  collapses through the reverse tapered aperture  170  and retracts proximally into the hollow outer shaft  104 . The fusion cage  100  remains frictionally in place between two vertebrae as the user withdraws the inserter  102  from a surgical patient. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, above are described alternative examples of an inserter and fusion cages for spinal surgeries. It is appreciated that various features of the above-described examples of each can be mixed and matched to form a variety of other combinations and alternatives. It is also appreciated that this system should not be limited to a single method of use. This inserter and fusion cage attachment system may be used for any spinal surgery requiring fusion cage placement or replacement. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.