Abstract:
An expansion assembly expands a vertebral implant. The vertebral implant has an inner cylindrical assembly adapted for insertion into an outer cylindrical assembly having an outer wall. The vertebral implant is expandable along an implant axis defined by the outer and inner cylindrical assemblies. The expansion assembly comprises an axle having proximal and distal end portions and an axle axis defined between the proximal and distal end portions. The expansion assembly further comprises a gear arranged about the axle axis at the proximal end portion of the axle and adapted to rotate about the axle axis to cause the inner cylindrical assembly to expand the vertebral implant. The engagement assembly also comprising a first engaging portion adapted to engage the inner cylindrical assembly and a second engaging portion adapted to engage the gear externally of the outer wall of the outer cylindrical assembly.

Description:
CROSS REFERENCE 
     This application is a Continuation of U.S. Ser. No. 10/663,554, filed on Sep. 16, 2003 and incorporated by reference herein, which claims the benefit of U.S. Provisional Application No. 60/412,730 filed on Sep. 23, 2002 and incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns medical procedures and instruments used during surgery. More particularly, a novel apparatus and method is provided for adjusting an adjustable vertebral implant. 
     BACKGROUND 
     A variety of spinal injuries and deformities can occur due to trauma, disease or congenital effects. For example, one type of spinal deformity, a kyphosis, involves a prolapse of the vertebral column towards the front of the body, often caused by the destruction of the vertebral body itself. This destruction can be in the form of a trauma type injury, such as a fracture or burst injury to the vertebral body, or a non-traumatic deformity caused by a tumor or a degeneration of the bone in the vertebral body. 
     Treatment of a kyphosis in the thoracic or lumbar spine appears now to be best achieved through an anterior approach, particularly in order to avoid some of the more severe complications associated with support or replacement of a damaged vertebral body. In most treatments of a kyphosis, a high degree of anterior reconstruction of the spine is required, most frequently involving total removal of the damaged vertebral body. In a typical anterior approach, partial or total ablation of the vertebral body and the two adjacent vertebral discs is carried out. Following this vertebrectomy, a vertebral implant assembly may be used to restore the vertebral column to the correct orientation. 
     One implant that may be used is disclosed in U.S. Pat. No. 6,344,057 to Rabbe et al. (“Rabbe patent”), which is hereby incorporated by reference. The implant disclosed in the Rabbe patent is an adjustable vertebral implant assembly configured to span the void created by the removed vertebral body and discs. The assembly includes a thin-walled tubular body which defines a hollow interior and further includes endplates with end surfaces configured to engage the tubular body between the adjacent vertebrae. In some embodiments, the end surfaces defines a bore through the endplate. 
     Current surgical spinal reconstruction techniques can use a plurality of wrenches to expand or otherwise manipulate rotationally adjustable implants, such as the assembly disclosed in the Rabbe patent. However, a wrench requires lateral translation which, in the confined area of the wound, can require an enlarged wound and increased labor and time. It must also relocate and reattach to the implant after each turn, which is both difficult and time consuming. 
     SUMMARY 
     In one embodiment of the present disclosure, an expansion assembly expands a vertebral implant. The vertebral implant has an inner cylindrical assembly adapted for insertion into an outer cylindrical assembly having an outer wall. The vertebral implant is expandable along an implant axis defined by the outer and inner cylindrical assemblies. The expansion assembly comprises an axle having proximal and distal end portions and an axle axis defined between the proximal and distal end portions. The expansion assembly further comprises a gear arranged about the axle axis at the proximal end portion of the axle and adapted to rotate about the axle axis to cause the inner cylindrical assembly to expand the vertebral implant. The engagement assembly also comprising a first engaging portion adapted to engage the inner cylindrical assembly and a second engaging portion adapted to engage the gear externally of the outer wall of the outer cylindrical assembly. 
     In another embodiment, a method for installing a vertebral implant between adjacent vertebrae comprises providing a vertebral implant having an inner cylindrical body extending into an outer cylindrical body. The outer cylindrical body has an outer wall and the bodies defining an implant axis. The method further includes providing an expansion assembly. The expansion assembly comprises an axle having proximal and distal end portions and an axle axis defined between the proximal and distal end portions. The expansion assembly also includes a secondary gear assembly attached to the proximal end portion and a main gear assembly engaged with the secondary gear assembly externally of the outer wall. The method further includes engaging the main gear assembly with the inner cylindrical body and rotating the axle about the axle axis to cause the inner cylindrical body to move relative to the outer cylindrical body along the implant axis. 
     In still another embodiment, an instrument is adapted for installing a vertebral implant. The implant has at least one outer tubular assembly threadedly engaged with an inner tubular assembly. The instrument comprises an axle having proximal and distal ends and an axle axis defined between the proximal and distal ends. The instrument also comprises a gear assembly connected to the proximal end of the axle and adapted to rotate the inner tubular assembly to expand the vertebral implant. The inner tubular assembly is rotated without extending the gear assembly into the at least one outer tubular assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an perspective view of a destroyed vertebral body within a vertebral column (in shadow) and a vertebral implant assembly according to one embodiment of the present invention positioned within the vertebral column. 
         FIG. 2  a perspective view of a vertebral implant assembly coupled with a portion of an expansion apparatus according to one embodiment of the present invention. 
         FIG. 3  is a perspective view of an expansion apparatus according to an embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of a portion of the expansion apparatus of  FIG. 3 . 
         FIG. 5  is a partial cross-section of a portion of the expansion apparatus of  FIG. 3 . 
         FIGS. 6   a  and  6   b  are perspective views of a holding instrument used with the expansion apparatus of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a vertebral column  10  includes a damaged vertebra  12   a  (shown in phantom) extending between a vertebra  12   b  and a vertebra  12   c . An intervertebral disc  14   a  (shown in phantom) extends between vertebrae  12   a  and  12   b , and an intervertebral disc  14   b  (shown in phantom) extends between vertebrae  12   a  and  12   c . In a surgical excision, the vertebra  12   a  can be removed together with discs  14   a  and  14   b  creating a void between the two intact vertebra  12   b  and  12   c . This procedure may be performed using an anterior, anterolateral, or other approach known to one skilled in the art. A vertebral implant assembly  20  as described in the Rabbe patent can then be provided to fill the void between the two intact vertebrae  12   b  and  12   c.    
     Referring now to  FIG. 2 , the vertebral implant assembly  20  is shown as a turnbuckle in accordance with one embodiment of the present invention. The implant assembly  20  generally includes a threaded tubular body  22  extending between threaded endplate assemblies  24  and  26 . The threaded tubular body  22  is provided with a plurality of apertures  28  that may be used for installation of the assembly  20  and that may also provide an avenue for bone or tissue ingrowth to further enhance the stability of the replacement assembly after implantation. In the present embodiment, the opposite ends of the tubular body  22  are formed into external threads  30 . The threads  30  may extend from each opposite end over most or all of the length of the tubular body  22  and may be configured to threadedly engage endplate assemblies  24  and  26 . 
     The endplate assembly  24  may include a flange  32 , which may cover a substantial load-bearing area of the endplates of the adjacent intact vertebral bodies. A cylinder  34  may be integrally formed with flange  32  to extend toward the threaded tubular body  22  when the endplate assembly  24  is placed within the excised vertebral space. The cylinder  34  and flange  32  define a bore  36  there through. The inside surface of the bore  36  is provided with internal threads  38  which are configured to mate with the external threads  30  of the tubular body  22 . In one embodiment, the threads  38  extend along the entire length of the cylinder  34  and into the flange  32 . Endplate assembly  26  may be configured similar or identical to endplate assembly  24  and therefore will not be described in detail. The endplate assemblies  24  and  26  may further include one or more apertures  40  configured to engage a holding instrument (as described below for  FIGS. 6   a  and  6   b ). 
     In one specific embodiment, the external threads  30  on the threaded tubular body  22  may be cut in opposite directions (e.g., right handed and left handed) so that the endplates can be drawn together or apart by rotating only the body. Thus, as the body is rotated in one direction, the threads  30  at each of the ends engage the internal threads  38  of each of the end caps  24  and  26  in the proper direction to draw the end caps together. Alternatively, the handedness of the threads  30  can be the same at each end so that it is necessary to individually thread each end cap in opposite directions onto the tubular body  22 . The disadvantage of this arrangement is that it is more difficult to adjust the height of the total assembly  20  while maintaining the proper orientation of each of the endplate assemblies  24  and  26 . An advantage is that in situ the assembly is unable to unthread itself. Further details of the assembly  20  and its operation are described in the embodiments shown in the Rabbe patent. 
     The assembly  20  may be inserted into the vertebral column (as shown in  FIG. 1 ) and then expanded to achieve the desired fit and alignment between the adjacent intact vertebrae. In one embodiment, expansion of the assembly can be achieved by rotating the tubular body  22  using an expander apparatus  50  as shown in  FIG. 3 . 
     Referring now to  FIG. 3 , in accordance with one embodiment of the present invention, the expander apparatus  50  includes a handle section  52 , an extension section  54 , a main gear box  56  and an engager  58 . The expander apparatus  50  may allow the assembly  20  to be adjusted without the use of lateral movement, thereby reducing the size of a patient&#39;s wound and decreasing the time and labor involved to complete the procedure. 
     Referring to both  FIG. 3  and  FIG. 4 , the handle section  52  can receive and enclose a portion of the extension section  54 . In the present embodiment, the extension section  54  may comprise an outer casing  60  through which an interior axle  62  may extend. The handle section  52  may include a handle  64  that receives, surrounds and rotationally engages the outer casing  60  of the extension section  54  through one or more bushings  66 . It is understood that in other embodiments, the rotational engagement of the outer casing  60  may be accomplished using ball bearing assemblies and/or the material comprising the handle  64 . Although not shown, in some embodiments, the handle  64  may be separated into two independent portions, with one portion being fixed to the outer casing  60  to secure and position the expander apparatus  50  during use, and the other portion being free to rotate for providing the rotational force discussed below. 
     In the present embodiment, the handle section  52  may further include a distally located selector gear box  70 . The selector gear box  70  may include a set or plurality of gears  72   a ,  72   b ,  72   c  configured to selectively engage with the distal end of the interior axle  62  of the extension section  54 . Each of the gears  72   a ,  72   b , and  72   c  may be of a different size so that a user of the expander apparatus  50  may choose from a range of selectable gear ratios, enabling the user to achieve a desired speed or torque for adjusting the vertebral implant assembly  20 . The selector gear box  70  may be configured to engage with a cap member  74 . The cap member  74  can be both axially and rotationally movable about the handle  64  and can further include a gear selection member  76  which, as the cap member  74  is moved, can engage any of the different gears  72   a ,  72   b , or  72   c  to create the desired gear ratio. 
     Although the present embodiment depicts three gears, it is understood that in other embodiments a fewer or a greater number of gears may be used. Further, any of a variety of gear train systems may be employed incorporating a variety of gear components such as a planetary gear systems, a layshaft, a clutch, a worm gear system, a bevel gear system, a rack and pinion system, or other gear based systems. In the present embodiment, the cap member  74  rotates or translates about the handle  64  to select a particular gear, but other gear selection mechanisms can also be used. In some embodiments, the selector gear box may not be located in the handle section  52 , but rather, may be included in the extension section  54  or elsewhere in the expander tool  50 . 
     Although not shown, in another embodiment, the selector gear box  70  may be omitted and the distal end of the axle  62  may be fixedly engaged with the gear selection cap  74  and/or a rotating portion of the handle section  52 . In this embodiment, the rotation of the axle  62  may be directly driven by rotation of the gear selection cap  74 . In still another embodiment, the axle  62  may be driven by a motor coupled to the axle  62  or to the selector gear box  70 . 
     Referring now to  FIG. 5 , while one end of the extension section  54  engages with the handle section  52 , the opposite end may engage with the main gear box  56 . The main gear box  56  may include a main gear/tooth assembly  80  and a secondary gear assembly  82 . The main gear/tooth assembly  80  can be partially enclosed and secured within a casing  83 , and can include a gear section  84  coaxially attached to a toothed section  86 . The casing  83  may include a pin  88  about which the main gear/tooth assembly  80  can rotate. In the present embodiment, the rotational axis of the pin  88  and the gear section  84  may be aligned perpendicular to the rotational axis of the axle  62 , although different embodiments may have different arrangements. 
     The secondary gear assembly  82  may be attached to the proximate end of the interior axle  62 , opposite from the end engaged with the selector gear box  70 , and may rotate about the axis of the axle  62 . The secondary gear assembly  82  may engage with the gear section  84  of the main gear/tooth assembly  80  causing any rotational force from the axle  62  to be transferred to the main gear/tooth assembly  80 . 
     Referring to  FIGS. 2 and 5 , the main gear box  56  can be further connected to the engager  58 . The casing  83  of the main gear box  56  may be attached to a positioning mechanism  90 , which in the embodiment of  FIG. 2  is shaped like a semi-circle with opposing arc portions  92   a  and  92   b . The arc portions  92   a  and  92   b  can define a cross-section of an engagement area  91  into which the implant assembly  20  may be positioned. The positioning mechanism  90  is shaped to mate with the tubular body  22  of the implant assembly  20 , allowing the tubular body  22  to rotate while assisting in maintaining the general position and proximity of the engager  58  to the tubular body  22 . 
     As described above, the casing  83  may cover only a portion of the main gear/tooth assembly  80 . The other portion, which can include the tooth section  86 , may extend into the engagement area  91  of the engager  58 . The tooth section  86  may include a plurality of teeth  93  that are sized, spaced, and shaped to engage the apertures  28  on the tubular body  22  when the tubular body  22  is positioned in the engagement area  91 . With the endplate assemblies at least tentatively affixed to the adjacent vertebral endplates, the tubular body  22  can rotate as the tooth section  86  is rotated. Furthermore, the positioning mechanism  90  and the arrangement of the apertures  28  can minimize any translation of the tubular body  22 , ensuring that the next tooth  93  easily locates and engages the next aperture  28 , to thereby maintain the rotation. In the present embodiment, the teeth  93  are radially arranged on the tooth section  86  in a gear-like configuration. In other embodiments, a toothed belt or another gripping mechanism can be used to drive the rotation of the tubular body  22 . 
     Referring more specifically to  FIG. 5 , in some embodiments, the positioning mechanism  90  is shaped more like a “C.” In these embodiments, the positioning mechanism  90  also helps to prevent the engager  58  from accidentally disengaging from the replacement assembly  20 . In one embodiment, the opposing arc portions  92   a ,  92   b  are selectively pivotable about pins  94   a  and  94   b  with friction keeping the arc portions  92   a ,  92   b  either open or closed. In the open position, the tubular body  22  can be positioned in or removed from the engagement area  91 . In the closed position, the arc portions  92   a  and  92   b  aid in keeping the positioning mechanism  90  engaged to the tubular body  22  while the body rotates. It is understood, that other embodiments may use a clip, a spring, or some other means of engagement to selectively allow the positioning mechanism  90  to remain engaged. 
     In some embodiments, the positioning mechanism  90  may be configured to more securely maintain the desired position of implant assembly  20 . For example, the positioning mechanism  90  may extend laterally along the tubular body  22  to restrain the assembly  20  from pivoting about its longitudinal axis. Another example (e.g.  FIGS. 6   a  and  6   b ) may include a second positioning mechanism  90  extending from the casing  83  in which case the assembly  20  can be held in position by arc positions both above and below the tooth section  86 . 
     Referring now to  FIGS. 1-5 , in operation, once the implant assembly  20  is placed in position between the endplates of the two adjacent vertebrae  12   b  and  12   c  (as shown in  FIG. 1 ), the expander apparatus  50  may be positioned within the surgical area proximate to the implant assembly  20 . It is understood, however, that in some instances the expander apparatus  50  can be used to facilitate the placement of the assembly  20  inside the vertebral column  10 . The expander apparatus  50  is positioned so that the engager  58  is engaged with the tubular body  22  of the implant assembly  20 . Specifically, at least one of the teeth  93  may engage one of the apertures  28 . The handle  60  can extend away from the vertebral column  10 , for example, in an anterior surgical approach, the handle may be positioned in the anterior area of the patient, within easy reach of the surgeon. 
     After the expander apparatus is in place, the surgeon can rotate or axially translate the cap member  74  to engage the appropriate gear  72   a ,  72   b ,  72   c  to achieve the desired gear ratio, although it is understood that in some embodiments the selector gear box  70  can be omitted. The surgeon can then turn either the handle  64  or the rotatably movable portion of the handle  64  around the axis of the interior axle  62  to expand (or contract, if necessary) the implant assembly  20 . Specifically, the rotation of the handle  64  or handle portion is transferred through the gear box  70  to rotate the axle  62 . The axle, in turn, rotates the secondary gear assembly  82 , which rotates the gear section  84 . The rotation of the gear section  84 , causes the fixedly attached tooth section  86  to rotate which, in turn moves the teeth  93 . With the endplate assemblies  24  and  26  held immovably in place by compression of the vertebral endplates, by structural features of the endplate assemblies  24  and  26 , or by mechanical means, the movement of the teeth  93  can cause the tubular body  20  to rotate which may cause the endplate assemblies  24  and  26  to move relative to one another, thereby expanding, contracting, or otherwise adjusting the implant assembly  20 . 
     Referring now to  FIGS. 6   a  and  6   b , in this embodiment, a holding instrument  100  may be coupled to the expander apparatus  50  to hold the implant assembly  20  in position during the expansion, all the while minimizing backlash or lateral movement of the assembly  20 . The holding instrument can be attached to the extension section  54  by an attachment device  102  which may include one or more rings  104  configured for fastening to the outer casing  60 . The one or more rings  104  may be fixedly attached to the extension section with one or more fastening mechanisms  106  which can be, for example, screws. In one alternative embodiment, to avoid interference with the interior axle  62  running through the extension section  54 , the fastening mechanisms  106  may engage a protrusion (not shown) extending from the outer casing  60 . 
     A plurality of expansion members  108  may connect the attachment device  102  to a pair of alignment arms  110  and  112 . Each expansion member  108  may be a rigid bar pivotally connected at one end to the attachment device  102  and at the opposite end to one of the alignment arms  110  or  112 . In alternative embodiments, the expansion member may be a spring, an elastic member, or another mechanism capable of expanding with the alignment arms  110  and  112  as the implant  20  is expanded. An alignment member  114  may further extend between the alignment arms  110  and  112  and may be adjustable to maintain a relatively parallel alignment of the alignment arms. Each of the alignment arms  110  and  112  extend toward the engagement area  91  where the ends of each alignment arm  110  and  112  are configured with holding assemblies  116  and  118 , respectively. The holding assemblies  116  and  118  may be arc-shaped to accept the assembly  20  and may further include fasteners  120  for engaging the apertures  40  on the endplate assemblies  24  and  26  to maintain the assembly  20  in a generally rigid vertical position while the assembly  20  is expanded. The fasteners may be, for example, pins, screws, or clamps. In some embodiments, the holding assemblies  116  and  118  may fasten to the endplate assemblies  24  and  26  without engaging the apertures  40 . 
     Referring still to  FIGS. 6   a  and  6   b , in operation, once the implant assembly  20  is placed in position between the endplates of the two adjacent vertebrae  12   b  and  12   c  (as shown in  FIG. 1 ), the expander apparatus  50  with the attached holding instrument  100  may be positioned within the surgical area proximate to the implant assembly  20 . It is understood, however, that in some instances the expander apparatus  50  and holding instrument  100  can be used to facilitate the placement of the assembly  20  inside the vertebral column  10 . The expander apparatus  50  is positioned so that the engager  58  is engaged with the tubular body  22  of the implant assembly  20 . Specifically, at least one of the teeth  93  may engage one of the apertures  28 . To further secure the implant assembly  20 , the pins  120  may be engaged with the apertures  40  on the endplate assemblies  24  and  26 . The handle  60  can extend away from the vertebral column  10 , for example, in an anterior surgical approach, the handle may be positioned in the anterior area of the patient, within easy reach of the surgeon. 
     After the expander apparatus is in place, the surgeon can rotate or axially translate the cap member  74  to engage the appropriate gear  72   a ,  72   b ,  72   c  to achieve the desired gear ratio. It is understood that in some embodiments the selector gear box  70  can be omitted. The surgeon can then rotate either the handle  64  or the rotatably movable portion of the handle  64  along the axis of the interior axle  62  to expand (or contract, if necessary) the implant assembly  20 . Specifically, the rotation of the handle  64  or handle portion is transferred through the gear box  70  to rotate the axle  62 . The axle, in turn, rotates the secondary gear assembly  82 , which rotates the gear section  84 . The rotation of the gear section  84 , causes the fixedly attached tooth section  86  to rotate which, in turn moves the teeth  93 . 
     With the endplate assemblies  24  and  26  held immovably in place by the holding instrument  100 , the movement of the teeth  93  can cause the tubular body  20  to rotate, which in turn can cause the endplate assemblies  24  and  26  to move relative to one another, thereby expanding (or contracting, if necessary) the implant assembly  20 . As the implant assembly  20  expands, the expansion members  108  may pivot to allow the alignment arms  110  and  112  to move apart while remaining in relatively parallel alignment. As the alignment arms  110  and  112  move, the alignment member  114  may adjust to further preserve the parallel alignment of the alignment arms  110  and  112 . After the implant assembly  20  has attained the desired height, the pins may be removed from the apertures  40 , disconnecting the holding instrument  100  from the implant assembly  20 . 
     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.