Abstract:
A system for performing bone arthrodesis includes an implant for bone arthrodesis and a bone fastening device. The implant includes a fastener with an elongated shaft having a head at one end and a bone-piercing point at the opposite end. A first washer has structure for engaging the head of the shaft so as to be polyaxially pivotable with respect to the head. A locking member has structure for engaging the shaft. The locking member can have a second washer pivotally engaged thereto. The bone fastening device can include an elongated cannula with a collet for detachably engaging the first washer and for advancing the first washer. Structure is provided for engaging the fastener and for advancing and rotating the fastener through the collet and through the first washer. The bone arthrodesis device further includes a lower end portion extending from the cannula. The lower end portion has structure for detachably engaging the locking member. The fastener, first washer, and locking member are aligned such that the advancing fastener will advance through the first washer, drill through the bone, and move into the locking member. A method for performing bone arthrodesis is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Utility patent application Ser. No. 10/683,076, filed Oct. 10, 2003, which claims the benefit of U.S. Provisional Application No. 60/417,543, filed Oct. 10, 2002. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to bone arthrodesis, and more particularly to bone fixation implants and systems and methods for installing such implants.  
       BACKGROUND OF THE INVENTION  
       [0003]     Bone arthrodesis or fusion is a process used to assist in the healing or stabilization of impaired bones or joints. In particular, facet arthrodesis is used to fuse the superior and inferior facet in spinal treatment operations. Prior art systems and methods have used bone screws which are screwed through the superior and inferior facets to immobilize the joint so as to permit the adjoined bone sections to fuse together. Wire has also been used to loop around the facets to immobilize the joint. The surgical procedures that must be performed to implant the screws or wires are difficult and time consuming. There is therefore a need for improved bone fixation implants, devices and methods.  
       SUMMARY OF THE INVENTION  
       [0004]     An implant for bone fixation comprises a fastener with an elongated shaft having a head at one end and a bone-piercing point at the opposite end. A first washer has structure for engaging the head of the shaft so as to be polyaxially pivotable with respect to the head. A locking member has structure for engaging the shaft. The locking member has a second washer pivotally engaged thereto. The shaft and the locking member can have cooperating threads. The locking member can be a nut. The second washer can be pivotally attached to the nut by a clip.  
         [0005]     The first washer and second washer can comprise angled contact surfaces. The contact surfaces can be serrated. One of the head and the first washer can have a convex surface. The other of the head and the first washer can have a cooperating concave surface. The convex surface is in contact with the concave surface to provide for polyaxial pivoting of the first washer with respect to the head. The first washer can comprise structure for engagement to a bone fastening device. The structure can comprise a circumferential groove that is adapted to receive a flange on the fastening device. The first washer can comprise rotational engagement structure. The rotational engagement structure can comprise depressions adapted to receive protrusions on a fastening device.  
         [0006]     The locking member can comprise structure for engaging the fastening device. The structure can comprise depressions adapted to receive protrusions on a lower end portion of the fastening device.  
         [0007]     A bone fastening device according to the invention can have an elongated cannula with a collet for detachably engaging a first washer and for advancing the first washer. The fastening device can further comprise structure for detachably engaging a fastener and for advancing the fastener through the collet and through the first washer. A lower end portion extends from the cannula. The lower end portion can have structure for detachably engaging a locking member. The fastener, first washer, and locking member are aligned such that the advancing fastener will advance through the first washer, through the bone, through the second washer and into the locking member.  
         [0008]     A system for performing bone arthrodesis includes an implant for bone fixation and a bone fastening device. The implant includes an elongated shaft having a head at one end and a bone-piercing point at the opposite end. A first washer has structure for engaging the head of the shaft so as to be polyaxially pivotable with respect to the head. A locking member has structure for engaging the shaft. The locking member can have a second washer pivotally engaged thereto. The bone fastening device can include an elongated cannula with a collet for detachably engaging the first washer and for advancing the first washer. Structure is provided for detachably engaging the fastener and for advancing the fastener through the collet and through the first washer. The bone fastening device further includes a lower end portion extending from the cannula. The lower end portion has structure for detachably engaging the locking member. The fastener, first washer, and locking member are aligned such that the advancing fastener will advance through the first washer, through the bone, through the second washer and into the locking member.  
         [0009]     A method for performing bone arthrodesis includes the steps of providing an implant for bone fixation, the implant comprising: a fastener with an elongated shaft having a head at one end and a bone-piercing point at the opposite end; a first washer having structure for engaging the head of the shaft so as to be polyaxially pivotable with respect to the head; and a locking member having structure for engaging the shaft. The locking member can have a second washer pivotally engaged thereto.  
         [0010]     The method further includes the step of providing a bone fixation device, the bone fixation device comprising: an elongated cannula having a collet for detachably engaging the first washer and for advancing the first washer, and structure for engaging said fastener and for advancing the fastener through the collet and through the first washer; a lower end portion extending from said cannula, said lower end portion having structure for detachably engaging the locking member. The fastener, first washer, and locking member are aligned such that the advancing fastener will advance through the first washer, through the bone, through the second washer and into the locking member.  
         [0011]     The method further includes the step of positioning the bone fixation device with the bone between the cannula and the lower end portion. The device is operated to advance the first washer to the bone. The device is then operated to advance the fastener through the first washer, the bone, and into the locking member.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     There is shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:  
         [0013]      FIG. 1  is a perspective view of a bone fastening device according to the invention.  
         [0014]      FIG. 1   a  is a perspective view of a bone fastening device having a protective cannula.  
         [0015]      FIG. 2  is a side elevation of a bone arthrodesis implant according to the invention.  
         [0016]      FIG. 3  is a side elevation of a fastener.  
         [0017]      FIG. 4  is a perspective view.  
         [0018]      FIG. 5  is a side elevation of a locking member and washer assembly.  
         [0019]      FIG. 6  is a perspective view.  
         [0020]      FIG. 7  is a perspective view, partially in phantom.  
         [0021]      FIG. 8  is a perspective view of a first, superficial washer.  
         [0022]      FIG. 9  is a bottom perspective view.  
         [0023]      FIG. 10  is a bottom perspective view of an alternative embodiment.  
         [0024]      FIG. 11  is a bottom perspective view, partially broken away.  
         [0025]      FIGS. 12   a - c  are cross-sectional views, partially broken away, showing alternative orientations.  
         [0026]      FIG. 13  is a perspective view of a collet.  
         [0027]      FIG. 14  is a schematic side elevation view showing a first mode of operation.  
         [0028]      FIG. 15  is a schematic side elevation view showing a second mode of operation.  
         [0029]      FIG. 16  is a schematic side elevation, partially broken away and partially in cross-section.  
         [0030]      FIG. 17  is a schematic perspective view, partially broken away.  
         [0031]      FIG. 18  is a schematic perspective view in a second mode of operation.  
         [0032]      FIG. 19  is a schematic perspective view, partially in phantom, in a subsequent mode of operation.  
         [0033]      FIG. 20  is a schematic perspective view in yet another mode of operation.  
         [0034]      FIG. 21  is a schematic cross-sectional view.  
         [0035]      FIG. 22  is a schematic cross-sectional view illustrating a final installation.  
         [0036]      FIG. 23  is a schematic perspective view showing bone fixation utilizing an implant according to the invention.  
         [0037]      FIG. 24  is a schematic cross section illustrating a bone fixation system and method, in a fist mode of operation.  
         [0038]      FIG. 25  is a schematic cross section illustrating a second mode of operation.  
         [0039]      FIG. 26  is a schematic cross section illustrating a third mode of operation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]     There is shown in  FIG. 1 a  bone fastening device  10  according to the invention. The device  10  has a main body  12  and an elongated housing  14  terminating in a lower end portion  16 . The device  10  has structure for holding a first washer  20  at a distal portion of the elongated housing  14  and a second washer  24  and locking member  28  in the lower end portion  16 . A handle  30  is provided to grip the device, and triggers  34  and  38  can be provided to operate the device during the implantation process. A guide knob  35  can be operated to rotate the housing  14  and attached lower end portion  16  to properly position the second washer  24 . A locking lever  32  can be provided to lock the device  10  on the bone after the first washer  20  and second washer  24  have been properly positioned. The locking lever  32  may be unlocked to allow repositioning of first washer  20  and second washer  24 . A knob  37  can be provided to manually advance the fastener and apply appropriate torque.  
         [0041]     A slidable protective cannula or sheath  39  may be used to facilitate insertion into the body and cover lower end portion  16 . In  FIG. 1   a  there is shown a bone fastening device  10  having a protective cannula or sleeve  39  for shielding the housing  14  and lower end portion  16  during the insertion process. A grip  41  can be used to pull back the cannula  39  prior to use. The housing  14 , lower end portion  16  and guide knob  35  can be detachable from the main body  12 . Another housing  14 , lower end portion  16  and guide knob  35 , with another implant, can be attached for reuse of the main body portion  12 .  
         [0042]     There is shown in  FIG. 2  an implant  40 . The implant  40  comprises a fastener having an elongated shaft  44  and a head  48 . The fastener engages the first washer  20  and the second washer  24  and locking member  28 . As shown in  FIG. 3 , the head  48  can have a convex surface  54  for use in engaging the first washer  20  as will be described below. Threads  58  are provided on the shaft  44  for purposes of engaging the locking member  28 . Other engagement structure is possible. A pointed end  62  is provided for piercing bone during the implantation process. Grooves or flutes  66  provide space for bone chips to disperse during insertion into locking member  28  and to carry bone debris away from the point  62  as it is progressing through the bone. Suitable structure such as hex opening  70  is provided for engagement of the fastener  44  to apply compressive and rotational forces during the implantation process. Depressions or other suitable structure can be provided to permit a fastening device to grip the head  48 .  
         [0043]     The second washer  24  and locking member  28  are shown in  FIGS. 5-7 . The second washer  24  can have suitable structure such as serrations  80  for engaging the bone surface. Alternative structure is possible. The second washer  24  is pivotal with respect to the locking member  28 . The locking member  28  can have suitable structure such as apertures  84 . Cooperating engagement structure such as clip  88  can be provided for extending through apertures  89  in the second washer  24  and engaging the apertures  84  such that the second washer  24  will engage the locking member  28 . A convex surface  92  on the locking member  28  can cooperate with a similar concave surface  96  on the second washer  24 . The clip  88  can be positioned in a suitable retaining groove  90  on the second washer  24 . An aperture  104  and slotted L-shaped groove  108  can be provided to engage corresponding protrusions on the lower end portion  16  to secure the locking member  28  to the lower end portion  16  of the fastening device  10 .  
         [0044]     The first washer  20  is depicted in  FIGS. 8-11 . The first washer  20  can have a concave surface  114  for cooperating with the convex surface  54  of the head  48  of the fastener  44 . An elongated opening  118 , which can be in the form of a tapered slot, permits the pivoting of the first washer  20  relative to the fastener  44 . The first washer  20  can have structure for allowing the washer to be engaged by the fastening device  10 . This structure can be a circumferential groove  124  which can be engaged by cooperating flange structure on the fastening device  10 . This will allow the first washer  20  to be advanced toward the surface of the bone. Additional structure such as depressions  130  can be provided for engagement by the fastening device  10  to permit rotation of the first washer  20 . This will assist in properly positioning the first washer  20 . The first washer  20  can have an angled contact surface  136  which will permit the first washer  20  to cooperate against bone surfaces such as facets which present significant angles. Additional structure can be provided for to promote engagement. This structure can include serrations  140  on the contact surface  136 . The opening  118  can expand wider in a fluted manner toward the contact surface  136  to permit greater pivoting.  
         [0045]     The manner of engagement between the fastener  44  and the first washer  20  and second washer  24  and locking member  28  is depicted in  FIGS. 12   a - c.  The pivoting motion of the first washer  20  is shown. This washer can tilt approximately 30° from a transverse section through the screw axis. More or less is possible depending on the bone system that is being fused. The second washer  24  is capable of tilting +45° to −20° from the transverse to the screw axis. More or less is possible.  
         [0046]     Suitable structure can be provided with the fastening device  10  for engaging the first washer  20 . There is shown in  FIG. 13 a  collet  140  although other holding structure is possible. The collet has distal circumferential flanges  144  which engage the groove  124  on the first washer  20 . Protrusions  148  are provided to engage the depressions  130  to permit the rotation of the first washer  20 . Elongated slots  152  provide leaf springs  153  for creating a spring action on the lower lips  144  such that the collet  140  can engage and disengage from the first washer  20  using moderate manual force.  
         [0047]     The manner of engaging the first washer  20  and second washer  24  to the bone is shown in  FIGS. 14-15 . The locking member  28  is engaged to the lower end portion  16  in a suitable slot. Protrusions in the lower end portion  16  can engage the apertures  104  in the locking member  28 . The bone is shown schematically as a superior facet  160  and inferior facet  164 . The first washer  20  is engaged to the collet  140 . The lower end portion  16  is positioned such that the second washer  24  rests against the inferior facet  164 . The pivoting of the lower washer  24  relative to the locking member  28  and lower end  16  permits the second washer  24  to match the incline portion  168  of the inferior facet  164 . The collet  140  is then lowered such that the first washer  20  engages the incline portion  172  of the superior facet  160 . The protrusions  148  engage the depressions  130  such that rotation of the collet  140  will rotate the first washer  20  to properly position the first washer  20  relative to the incline portion  172  of the superior facet  160 .  
         [0048]     The installation of the fastener  44  is shown in the sequence of  FIGS. 16-18 . The fastener  44  is held by a suitable engagement portion of the device  10  (not shown) and driven toward the superior facet  160 . The fastener  44  can be engaged such that the head  48  can be rotated and the point  62  can be driven into the facet  160 . Flutes can be provided on the pointed end  62  to remove bone debris as the fastener  44  is rotated and pushed into the bone. In this manner, the fastener  44  will drill through the superior facet  160  and inferior facet  164 . As the fastener  44  is advanced through the bone, it will engage the locking member  28 . The threads  58  will engage female threads in the locking member  28 . The fastener  44  will thereby be engaged to the locking member  28 , as shown in  FIG. 19 . The collet  140  can then be removed, as shown in  FIGS. 20 and 21 . The lower end portion  16  is then removed as the fastening device  10  is removed, as shown in  FIG. 22 . This results in a completed implant across the superior facet  160  and inferior facet  164 , as shown in  FIG. 23 .  
         [0049]     A bone fixation device  10  as used during an implantation procedure is illustrated in  FIGS. 24-26 . The device  10  has an elongated housing  14  in the general shape of a cannula. Within the housing is the collet  140 . The collet  140  has structure for engaging the first washer  20 . Any structure is possible, however, the collet  140  in  FIG. 24  has inwardly directed circumferential holding flanges  144 . The holding flanges  144  engage the groove  124  on the first washer  20 . The collet  140  further can have protrusions  148  which engage the depressions  130  in the first washer  20 . The first washer  20  is thereby held against movement out of the collet  140  and against rotation relative to the collet  140 . The spring force holding the first washer  20  in the collet  140  is such that a manual force can be used to remove the collet  140  from the first washer  20  after the first washer  20  has been secured to the bone.  
         [0050]     The collet  140  is mounted in the housing  14  so as to be axially movable therethrough. The collet  140  can have structure for slidably engaging a guide groove  222  or other suitable structure. The first trigger  34  can be operated to move the collet  140  and first washer  20  through the housing  14  from the position shown in  FIG. 24  to the position shown in  FIG. 25 . When gear  230  is rotated the shaft  210  is pulled away by the threaded end of the shaft  246 . The first washer  20  will be seated against the superior facet  160 , and the second washer  24  will be seated against the inferior facet  164 . The guide knob  35  can be rotated to properly position the second washer  24  if the orientation is not correct. The locking lever  32  can be operated to clamp the device to the facet.  
         [0051]     The helical gear  230  is then rotated by the action of the trigger  38 , which causes the mostly slidable hexagonal or flat faced shaft  210  to rotate. This rotates the extended threaded end of the shaft  246 , which is engaged to mating internal threads  250  on an interior surface of the collet  140 . The face of threaded end  246  includes structure for engaging the fastener  44 , such as a hexagonal tip. Rotation of the threaded end  246  will thereby rotate and advance the fastener  44 . The fastener  44  will advance through the first washer  20 , and through the superior facet  160  and inferior facet  164  due to the drilling action created by the forward and rotational movement of the fastener  44 . The fastener  44  will then advance through the second washer  24  and into the locking member  28 . The threads  58  on the fastener  44  will engage cooperating threads on an inside surface of the locking member  28 . The knob  37  can then be operated to properly torque the implant  40  including to fully seat fastener  44  with locking member  28 .  
         [0052]     The invention provides numerous advantages over prior art pedicle screw fixation systems. As the bone joint segments, such as the superior facet  160  and inferior facet  164 , are compressed between the first washer  20  and second washer  24 , there are no internal threads in the bone to raise stresses within the bone. The threads  58  are only on the lower end of the shaft  44  such that these threads engage only the locking member  28  and do not apply thread stresses to the interior of the bone. Also, as the implant is tightened using the rotational force, conventional torqueing mechanisms can be applied such that a known compressive force is applied to the joint. The first washer  20  and second washer  24  can be provided with varied angled contact surfaces to variously fit differing bone geometries for joining bone segments other than the facets. Also, the amount of tilt in the first washer  20  and second washer  24  relative to the fastener  44  can be adjusted depending upon the particular bone geometry that is being fused, owing to the pivotal and polyaxial motion that is permitted. The installation of the implant  40  is reversible. The compression of the implant washers  20  and  24  can be removed to allow repositioning prior to fastener  44  insertion. Accordingly, the invention provides great variability and flexibility, in addition to ease, control and consistency of installation.  
         [0053]     The various components of the invention are constructed with constructions of surgical grade plastics or metal, such as titanium. Different dimensions of the various components of the invention are within the scope of the invention.  
         [0054]     This invention can be embodied in other forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be had to the following claims rather than the foregoing specification as indicating the scope of the invention.