Patent Publication Number: US-8523874-B2

Title: Instruments and techniques for separating bony structures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/441,689 filed May 20, 2003 now U.S. Pat. No. 7,749,231, which claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/382,408 filed on May 21, 2002 and also claims the benefit of the filing date of U.S. Provisional Application No. 60/411,562 filed on Sep. 18, 2002. The referenced applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Adjacent bony structures can require separation for appropriate treatment or repositioning of the bony structures. Separating the bony structures can facilitate insertion of instruments and implants into the space between bony structures. 
     For example, the spinal disc space between adjacent vertebrae can collapse completely or partially, causing pain and trauma for the afflicted person. Other conditions associated with the spinal column can also require access to a spinal disc space for appropriate treatment. Surgical techniques for treating such conditions can require the adjacent vertebrae to be distracted or spread apart to restore or partially restore the spacing, or to increase the spacing, between the adjacent vertebrae. 
     There remain various needs for instruments and techniques that can be employed for separating bony structures. The present invention is directed to meeting these needs, among others. 
     SUMMARY 
     The invention relates to instruments and techniques for separating adjacent bony structures. 
     According to one aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. 
     According to another aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The distal spreader assembly includes opposite bony structure contacting surfaces, at least one of which includes an etched bone contacting surface. 
     According to a further aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The spreader assembly includes opposite surfaces for contacting bony structures. The opposite surfaces each include bone engaging features for engaging the adjacent bony structure to maintain the spreader assembly in contact therewith. Bone engaging features may include any one or combination of pitting, knurling, serrations, teeth, ridges, barbs, spikes, peeks and valleys, grooves, concave curvature, and convex curvature. 
     According to another aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The spreader assembly includes first and second spreading members that are positionable adjacent one another in a low profile configuration for insertion into the space between the bony structures and thereafter movable away from one another to contact respective ones of the adjacent bony structures to separate the bony structures. The low profile arrangement can include, for example, nesting the spreading members, collapsing of the spreading members, overlapping the spreading members, and/or compressing the spreading members. 
     According to a further aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The spreader assembly includes spreading members having opposite surfaces for contacting the bony structure. The spreading members are engaged to the actuator assembly so that the spreading members remain parallel to one another as the spreading members are moved away from one another to spread the adjacent bony structure. The engagement of each of the spreading members to the actuator assembly can include a fastener movably received in a slot so that a connection location between the actuator assembly and the respective spreading member is variable within the slot. 
     According to a further aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The spreader assembly includes opposite spreading members for contacting the bony structure. The spreading members each have a length sufficient to extend in the space across a substantial portion of the adjacent bony structures. The spreading members each have a cross-sectional modulus or moment of inertia that limits deflection of the spreading member within an acceptable range when the spreading member applies a separating force to the adjacent bony structure. 
     In another aspect of the invention, a spreader instrument is provided with spreading members for contacting bony structures. The cross-sections of the spreading members provide a low profile configuration when the spreading members are positioned adjacent one another for insertion of the spreading members into the space between the adjacent bony structures. The length to depth ratio of the spreading members can also be sufficient to provide adequate resistance to bending of the spreading members. 
     According to another aspect, a method for separating adjacent vertebrae is provided. Spreading members are inserted into an at least partially collapsed disc space between the adjacent vertebrae. The spreading members are actuated to spread the adjacent vertebrae. The spreading members have a length sufficient to spread or distract the entire depth of the disc space between the vertebrae. Instruments are inserted into the disc space to perform surgical procedures while the spreading members maintain separation of the vertebrae. One or more implants can also be inserted in the disc space while the spreading members maintain separation of the adjacent vertebrae. 
     According to one aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The distal spreader assembly includes a pair of spreading members each having at least one support surface extending therealong adapted to guide a cutting instrument in a spinal disc space. 
     According to a further aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The distal spreader assembly includes a pair of spreading members each having a guide member. Disc space preparation, implants, and/or implant insertion instruments can be guided into the disc space between the guide members. 
     According to one aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The distal spreader assembly includes a pair of spreading members each having a pair of distal extension members positionable in the spinal disc space. For each spreading member, one of the distal extension members is longer than the other distal extension member. 
     According to another aspect, a spreader instrument is provided that includes a distal spreader assembly for insertion in the space between bony structures and a proximal actuator assembly for actuating the spreader assembly to separate the bony structures. The distal spreader assembly includes a pair of spreading members each having a pair of distal extensions positionable in the spinal disc space. Each spreading member includes a stepped region to increase the spacing between the spreading members. 
     These and other aspects of the invention will be apparent from the following description of the illustrated embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a diagrammatic illustration of a spreader instrument. 
         FIG. 2  is an elevation view of one embodiment of a spreader instrument having spreading members positioned in a space between adjacent bony structures in an unactuated state. 
         FIG. 3  is an elevation view of the spreader instrument of  FIG. 2  in an actuated state. 
         FIG. 4  is an elevation view of a portion of the side of the actuated spreader instrument opposite the side shown in  FIG. 3 . 
         FIG. 5  is a plan view looking toward the bottom of the spreader instrument of  FIG. 2 . 
         FIG. 6  is a perspective view of a distal spreader assembly comprising a portion of the spreading instrument of  FIG. 2 . 
         FIG. 7  is another perspective view of the distal spreader assembly of  FIG. 6 . 
         FIG. 8  is a sectional view through the spreading members of the distal spreader assembly of  FIG. 6 . 
         FIG. 9  is an elevation view looking at the side of a first spreading member of the distal spreader assembly of  FIG. 6 . 
         FIG. 10  is an elevation view looking at the contact surface of the spreading member of  FIG. 6 . 
         FIG. 11  is an elevation view looking at the side of the second spreading member of the distal spreader assembly of  FIG. 6 . 
         FIG. 12  is a perspective view of another embodiment of a distal spreader assembly. 
         FIG. 13  is another perspective view of the distal spreader assembly of  FIG. 12 . 
         FIG. 14  is a sectional view through the spreading members of the distal spreader assembly of  FIG. 12 . 
         FIG. 15  is an elevation view looking at the side of a second spreading member of the distal spreader assembly of  FIG. 12 . 
         FIG. 16  is an elevation view looking at the contact surface of the spreading member of  FIG. 15 . 
         FIG. 17  is an elevation view looking at the side of the first spreading member of the distal spreader assembly of  FIG. 12 . 
         FIG. 18  is an elevation view of another embodiment spreader instrument in an unactuated position. 
         FIG. 19  is an elevation view of the spreader instrument of  FIG. 18  in an actuated position. 
         FIG. 20  is an elevation view of the spreader instrument of  FIG. 18  in an actuated position and having an alternate distal end arrangement to provide greater spreading distance capability. 
         FIG. 21  is a plan view of the spreader instrument of  FIG. 18 . 
         FIG. 22  is a perspective view of one embodiment spreading member useable with, for example, the spreader instrument of  FIG. 18 . 
         FIG. 23  is a bottom plan view of the spreading member of  FIG. 22 . 
         FIG. 24  is a top plan view of the spreading member of  FIG. 22 . 
         FIG. 25  is a detail view of a portion of the spreading member of  FIG. 22 . 
         FIG. 26  is a perspective view of another embodiment spreading member useable with, for example, the spreader instrument of  FIG. 18 . 
         FIG. 27  is a bottom plan view of the spreading member of  FIG. 26 . 
         FIG. 28  is a perspective view of a pair of the spreading members of  FIGS. 26 and 27  in an operative orientation relative to one another. 
         FIG. 29  is an elevation view in partial section of one operative orientation for a pair of the spreading members shown in  FIGS. 22-25 . 
         FIG. 30  is an elevation view of another operative orientation for a pair of the spreading members shown in  FIGS. 22-25 . 
         FIG. 31  is a perspective view of the spreading members of  FIG. 30  positioned in a disc space between adjacent vertebrae of the spinal column. 
         FIG. 32  is a plan view looking toward the bottom of the upper spreading member of  FIG. 31  positioned in the disc space. 
         FIG. 33  is a perspective view showing insertion of a spinal implant into the disc space between the spreading members of  FIG. 31 . 
         FIG. 34  is a perspective view of another embodiment spreading member. 
         FIG. 35  is a perspective view of another embodiment spreading member. 
         FIG. 36  is a plan view looking toward the bottom of the spreading member of  FIG. 35 . 
         FIG. 37  is a plan view looking toward the bottom of another embodiment spreading member. 
         FIG. 38  is a perspective view of another embodiment spreading member. 
         FIG. 39  is a perspective view of the spreading member of  FIG. 38  guiding a cutting instrument. 
         FIG. 40  is a perspective view of another embodiment spreading member. 
         FIG. 41  is a perspective view of the spreading member of  FIG. 40  looking in a direction opposite that of  FIG. 40 . 
         FIG. 42  is a perspective view of another embodiment spreading member. 
         FIG. 43  is a bottom plan view of the spreading member of  FIG. 42 . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any such alterations and further modifications in the illustrated device and any such further applications of the principles of the invention as illustrated therein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Referring to  FIG. 1 , a diagrammatic illustration of one embodiment of a spreader instrument  10  for insertion into the space between adjacent bony structures and for spreading the adjacent bony structures is shown. Spreading instrument  10  includes a proximal actuator assembly  12  and a distal spreader assembly  14 . Actuator assembly  12  provides remote actuation of spreader assembly  14  when spreader assembly  14  is positioned within the space between adjacent bony structures. Actuator assembly  12  also releasably maintains spreader assembly  14  in the actuated position. Spreader instrument  10  can be used to access the space between adjacent bony structures in an open or minimally invasive procedure. Additionally, actuator assembly  12  can include an adjustment mechanism  16  to effect an adjustment of the actuated position of spreader assembly  14  achieved through actuator assembly  12 . 
     Proximal actuator assembly  12  includes any device or mechanism capable of adjusting the position or orientation of distal spreader assembly  14 . Actuator assembly  12  may include linkage systems, wire systems, gear systems, and flexible adjustment systems, for example. Actuator assembly  12  may include linear and/or rotationally moving elements. Actuator assembly  12  may be rigidly fixed to spreader assembly  14 , movably fixed to spreader assembly  14 , or a combination of rigid and movable fixation. Suitable examples of actuator assembly  12  components include solid shaft like elements, bar stock, tubular elements, rod-like elements, linkages, elastically-deformable members, and articulating connectors, for example. Actuator assembly  12  can be biased by a spring, resilient hinge or other means to a normal position in which spreader assembly  14  is unactuated, actuated, or at some position therebetween. 
     Adjustment mechanism  16  can position and/or maintain spreader assembly  14  in any one of a number of actuated states, and is provided with means for securing one or more components of actuator assembly  12  in a particular position. Such means can include a rod and stop member movably engageable along the rod, a geared mechanism, a force fit or wedge mechanism, a pivoting locking mechanism, a rotational locking mechanism, one or more clamping members, an interference fit between components of actuator assembly  12 , and an interference fit between one or more components connected to and extending between the components of actuator assembly  12 , for example. 
     Distal spreader assembly  14  can include a pair of spreading members movable away from one another by actuator assembly  12  to spread adjacent bony structures. The spreading members can be coupled to actuator assembly  12  for movement in parallel relation to one another, although non-parallel movement is also contemplated. Distal spreader assembly  14  can include a low profile arrangement in the unactuated state for insertion of the spreading members into a space between the adjacent bony structures. Such low profile arrangement can be provided by nesting the spreading members, collapsing of the spreading members, overlapping the spreading members, and/or compressing the spreading members. The spreading members of spreader assembly  14  can each be configured to conform to the profile of the bony structure of which it contacts. Each spreading member can include means for engaging the bony structure to resist movement of the spreading members relative to the bony structure. Such engagement means includes pitting, knurling, serrations, teeth, ridges, barbs, spikes, peeks and valleys, grooves, concave curvature, and convex curvature. 
     One embodiment of a spreader instrument  20  will be described with reference to  FIGS. 2-4 . This embodiment of spreader instrument  20  includes actuator assembly  21 , distal spreader assembly  90  and an optional adjustment mechanism  45 . Actuator assembly  21  includes a first handle  22  pivotally coupled to a second handle  24  about a fastener  26 . Other coupling arrangements are also contemplated, such as an integral hinge or separate hinge mechanism. A first spring member  42  extends along first handle  22  and is coupled thereto with pin  42   a . A second spring member  44  extends along second handle  24  and is coupled thereto with pin  44   a . Spring members  42 ,  44  are leaf springs that are interconnected at their distal ends to spring bias handles  22 ,  24  away from one another to an unactuated position, shown in  FIG. 2 . Handles  22 ,  24  are moved to an actuated position by moving handles  22 ,  24  toward one another against spring members  42 ,  44 , as shown in  FIG. 3 . 
     Adjustment mechanism  45  is provided to adjust and/or secure handles  22 ,  24  and thus spreader assembly  90  in any one of a number of actuated positions. Adjustment mechanism  45  includes a connecting member  46  pivotally coupled at a distal end  46   b  to second pin  44   a . Connecting member  46  extends through an aperture of a first handle extension  22   b  to proximal end  46   a , and pivots as handles  22 ,  24  move toward or away from one another. An adjustment member  48  located between handle extension  22   b  and proximal end  46   a  is movable along connecting member  46 . In the illustrated embodiment, connecting member  46  is threaded and adjustment member  48  is a hand knob threadingly coupled thereto. Proximal end  46   a  of connecting member  46  can be non-threaded and enlarged to retain adjustment member  48  on connecting member  46 . Adjustment member  48  contacts handle extension  22   b  to maintain handles  22 ,  24  and distal spreader assembly  90  in any one of a number of actuated positions. Adjustment member  48  can be threaded toward proximal end  46   a  of connecting member  46  in the direction opposite arrow P. This allows handles  22 ,  24  to move along connecting member  46  and return toward their unactuated position when released until either adjustment member  48  contacts handle extension  22   b  or the handles  22 ,  24  and spreader assembly  90  are completely unactuated. Adjustment member  48  can be threaded along connecting member  46  in the direction of arrow P toward handle extension  22   b  to engage or move handles  22 ,  24  toward one another for actuation. 
     Distal spreader assembly  90  includes a first spreading member  50  and a second spreading member  70 . First spreading member  50  includes a proximal portion  52  attachable to actuator assembly  21 . An extension member  54  extends distally from proximal portion  52 . Second spreading member  70  includes a proximal portion  72  attachable to actuator assembly  21 . An extension member  74  extends distally from proximal portion  72 . 
     As shown in  FIG. 4 , spreader instrument  20  is rotated 180 degrees about longitudinal axis L. First handle  22  is pivotally coupled at its distal end  22   a  to a proximal end  30   a  of a first link member  30 . Second handle  24  is pivotally coupled at its distal end  24   a  to a proximal end  28   a  of a second link member  28 . First link member  30  extends to a distal end  30   b , and second link member  28  extends to a distal end  28   b . Link members  28 ,  30  cross one another to form an X-shape in their actuated state as shown in  FIGS. 3 and 4 . Link members  28 ,  30  are pivotally couple to one another about central fastener  40  ( FIG. 2 ) of actuator assembly  21 . The overlapping portions of the crossed link members  28 ,  30  can be recessed so that the distal and proximal end portions of link members  28 ,  30  extend over one another, as shown with recessed portions  28   c  n  FIG. 4  and recessed portion  30   c  in  FIG. 3 . 
     Proximal portion  52  of first spreading member  50  includes a proximal slot  56  through which fastener  35  extends. Proximal portion  52  further includes a distal hole  58  through which fastener  39  extends. Fastener  35  rotatably and slidably couples proximal portion  52  to actuator assembly  21  at the connection between distal end  22   a  of first handle  22  and proximal end  30   a  of first link member  30 . Fastener  39  rotatably couples proximal portion  52  to distal end  28   b  of second link member  28 . Second spreading member  70  includes a proximal portion  72  attachable to actuator assembly  21 . Proximal portion  72  includes a proximal slot  76  through which fastener  33  extends. Proximal portion  72  further includes a distal hole  78  through which fastener  37  extends. Fastener  33  rotatably and slidably couples proximal portion  72  to actuator assembly  21  at the connection between distal end  24   a  of second handle  24  and proximal end  28   a  of second link member  28 . Fastener  37  rotatably couples proximal portion  72  to distal end  30   b  of first link member  30 . 
     When actuator assembly  21  is in an unactuated state as shown in  FIG. 2 , spreading members  50 ,  70  are positioned adjacent one another. As actuator assembly  21  is actuated by moving handles  22 ,  24  toward one another, spreading members  50 ,  70  can move away from and remain parallel during such movement. The rotatable and slotted engagement of proximal portions  52 ,  72  via fasteners  35 ,  33  in slots  56 ,  76 , respectively, allows the relative longitudinal position between actuator assembly  21  and spreading members  50 ,  70  to vary in accordance with the amount of actuation provided between spreading members  50 ,  70 . 
     In operation, distal ends  22   a ,  24   a  of handles  22 ,  24  move away from one another by the pivoting of handles  22 ,  24  about fastener  26 . In addition, distal ends  28   b ,  30   b  of link members  28 ,  30  move away from one another by the pivoting of link members  28 ,  30  about fastener  40 . This pivoting movement of the components of actuator assembly  21  causes the length of actuator assembly  21  to reduce along longitudinal axis L. Spreading members  50 ,  70  rotate about respective ones of the fasteners  39 ,  37 , respectively, as distal ends  28   b ,  30   b  of link members  28 ,  30  are moved away from one another. Fasteners  35 ,  33  rotate within and move distally in respective ones of the slots  56 ,  76  as distal ends  22   a ,  24   a  move away from one another. The movement of fasteners  35 ,  33  in slots  56 ,  76  accommodates the reduction in length of actuator assembly  21  along axis L, while the rotation of fasteners  35 ,  33  in slots  56 ,  76  allows spreading members  50 ,  70  to remain parallel to one another as actuator assembly  21  is actuated and unactuated. 
     As shown in  FIG. 5 , spreader instrument  20  can be provided with angled offsets in actuator assembly  21  and spreader assembly  90  to assist in keeping spreader instrument  20  out of the way of the surgeon. In  FIG. 5 , handles  22 ,  24  for a proximal portion  21   a  of actuator assembly  21  extending along axis A 1  and a distal portion  21   b  extending along axis A 2 . Link members  28 ,  30  also extend along axis A 2 . Axis A 1  forms angle C 1  with axis A 2 . Angle C 1  can vary from 180 degrees to 90 degrees or less. It is also contemplated that angle C 1  can range from 180 degrees to 135 degrees. One specific embodiment contemplates an angle C 1  of 170 degrees. Another specific embodiment contemplates an angle C 1  of 0 degrees 
     Proximal portions  52 ,  72  of spreading members  50 ,  70  of distal spreader assembly  90  extend along axis B 1 . Proximal portions  52 ,  72  are coupled to one side of actuator assembly  21  such that axis B 1  is offset from and extends parallel to axis A 2 . In one embodiment, it is contemplated that spreader assembly  90  can be coupled to the working side of spreading instrument  20  so that actuator assembly  21  is offset laterally from spreader assembly  90 , providing additional space in the surgeon&#39;s approach to the operative site. Extension members  54 ,  74  extend along an axis B 2  that forms angle C 2  with axis B 1 . Angle C 2  can vary from 180 degrees to 90 degrees or less. It is further contemplated that angle C 2  can vary from 180 degrees to 135 degrees. One specific embodiment contemplates an angle C 2  of 170 degrees. Another specific embodiment contemplates an angle C 2  of 180 degrees. 
     Referring to  FIGS. 6-11 , spreading member  50  includes an enlarged opening  56   a  about slot  56  so that the head of fastener  35  can be recessed at least partially therein. The shaft of fastener  35  extends through slotted portion  56   b . Similarly, spreading member  70  includes slot  76  with an enlarged opening  76   a  about slotted portion  76   b  so that the head of fastener  33  can be recessed at least partially therein. Hole  58  of spreading member  50  includes an enlarged opening  58   a  in which the head of fastener  39  can be recessed, and the shaft of fastener  39  extends through hole portion  58   b . Similarly, spreading member  70  includes hole  78  with an enlarged opening  78   a  about hole portion  78   b  so that the head of fastener  37  can be recessed at least partially therein. 
     Spreading member  50  includes a concavely curved end wall  60  extending from proximal portion  52  to extension member  54 . Spreading member  70  includes a concavely curved end wall  80  extending from proximal portion  72  to extension member  74 . End walls  60 ,  80  can abut against the bony structure adjacent the space in which extension members  54 ,  74  are inserted to limit the insertion depth of extension members  54 ,  74  into the space. 
     Extension member  54  and extension member  74  each include a configuration that allows the extensions members  54 ,  74  to be positioned adjacent one another in a low profile arrangement for insertion into the space between the adjacent bony structures. Extension member  54  includes a laterally oriented flange portion  54   a  and a vertically oriented web portion  54   b  extending along flange portion  54   a . Flange portion  54   a  includes a contact surface  54   c  opposite web portion  54   b . Flange portion  54   a  and web portion  54   b  define a receptacle  54   d . Extension member  74  includes a laterally oriented flange portion  74   a  and a vertically oriented web portion  74   b  extending along flange portion  74   a . Flange portion  74   a  includes a contact surface  74   c  opposite web portion  74   b . Flange portion  74   a  and web portion  74   b  define a receptacle  74   d . Receptacle  74   d  is sized to receive web portion  54   b , and receptacle  54   d  is sized to receive web portion  74   b , allowing extension members  54 ,  74  to be placed in a nested configuration when spreader instrument  20  is unactuated and spreading members  50 ,  70  are placed against or adjacent to one another. 
     Flange portion  54   a  includes a ramped surface  62  opposite contact surface  54   c  that transitions into proximal portion  52 , and web portion  54   b  includes a ramped surface  64  opposite contact surface  54   c  that transitions into proximal portion  52 . Similarly, flange portion  74   a  includes a ramped surface  82  opposite contact surface  74   c  that transitions into proximal portion  72 , and web portion  74   b  includes a ramped surface  84  opposite contact surface  74   c  that transitions into proximal portion  72 . The ramped transition surfaces facilitate the nesting relationship between extension members  54 ,  74  when proximal portions  52 ,  72  are positioned adjacent one another. 
     In one form, spreading member  50  and spreading member  70  are positioned adjacent one another and in contact with one another along their entire length in the low profile position. In another form, at least extension members  54 ,  74  are positioned adjacent to one another and in contact along their entire length in the low profile orientation. This low profile orientation facilitates positioning of spreading members  50 ,  70  as far as possible in the disc space to obtain an even distraction or spreading of the adjacent vertebrae in the distal and proximal regions of the disc space. 
     Contact surfaces  54   c ,  74   c  can have a profile that maximizes the surface area contact with the adjacent bony structure. For example, contact surface  54   c ,  74   c  can have a convex profile that matches the geometry of the portion of the endplates of vertebrae V 1  and V 2  along which the extension members  54 ,  74  are positioned, as shown in  FIGS. 2 and 3 . Such matching geometry maintains extension members  54 ,  74  in position relative to the vertebral endplate, and also spreads the distraction or spreading load over a greater area of the bony structure, reducing potential damage to the bony structure that might be caused by distraction or spreading forces concentrated on portions of the adjacent endplate. The matching geometry also provides a self-centering effect to assist in proper positioning of extension members  54 ,  74  in the space relative to the bony structures. 
     Contact surfaces  54   c ,  74   c  can be smooth or have surface features that engage the bony structure, such as the grooves forming the ridges shown in  FIGS. 2-11  that extend transversely to convex curvature of the respective bone contacting surface. Examples of other surface features include pitting, knurling, serrations, teeth, ridges, barbs, spikes, peeks and valleys, grooves, concave curvature, and convex curvature, for example. 
     In one specific embodiment, each extension member  54 ,  74  can be provided with a maximum thickness t of 6 millimeters, and receptacles  54   d ,  74   d  each have a depth of 3 millimeters. Thus, extension members  54 ,  74  can have an overall maximum height of 9 millimeters between contact surfaces  54   c ,  74   c  when spreader assembly  90  is in its unactuated position and spreading members  50 ,  70  are nested relative to one another. Thus, in the specific illustrated embodiment, the nested relationship provides at least a 25% reduction in height along the entire length of extension members  54 ,  74  than would be provided in a non-nested relationship. Extension members  54 ,  74  can have a width W of 8 millimeters, and web portions  54   b ,  74   b  occupy half of width W. Extension members  54 ,  74  can also be provided with a length D of 40 millimeters, or other length D such that the extension members  54 ,  74  extend across a substantial portion of a disc space providing even and complete separation of the adjacent vertebrae. It is to be understood that other embodiments contemplate other maximum heights, widths and lengths for extension members  54 ,  74 . 
     The moment of inertia and section modulus provided by extension members  54 ,  74  maintains deflection of extension members  54 ,  74  within acceptable limits even with long lengths D for extensions members  54 ,  74 . Accordingly, extension members  54 ,  74  can be provided with length D that extends substantially across the adjacent vertebral endplate, and uniform distraction or spreading of the vertebrae and force distribution along the vertebrae can be achieved. The low profile, nested configuration of extension members  54 ,  74  in the unactuated position facilitates insertion into a collapsed or partially collapsed disc space or through a small opening to the space between adjacent bony structures. 
     Referring now to  FIGS. 12-17 , another embodiment of a distal spreader assembly  190  is provided. Spreader assembly  190  can be mounted to actuator assembly  21  such as discussed above with respect to spreader assembly  90 . Spreader assembly  190  includes a first spreading member  150  and a second spreading member  170 . First spreading member  150  includes a proximal portion  152  attachable to actuator assembly  21 . An extension member  154  extends distally from proximal portion  152 . Second spreading member  170  includes a proximal portion  172  attachable to actuator assembly  21 . An extension member  174  extends distally from proximal portion  172 . 
     Proximal portion  152  includes a proximal slot  156  through which fastener  35  extends. Proximal portion  152  further includes a distal hole  158  through which fastener  39  extends. Fastener  35  rotatably and slidably couples proximal portion  152  to actuator assembly  21  at the connection between distal end  22   a  of first handle  22  and proximal end  30   a  of first link member  30 . Fastener  39  rotatably couples proximal portion  152  to distal end  28   b  of second link member  28 . Second spreading member  170  includes a proximal portion  172  attachable to actuator assembly  21 . Proximal portion  172  includes a proximal slot  176  through which fastener  33  extends. Proximal portion  172  further includes a distal hole  178  through which fastener  37  extends. Fastener  33  rotatably and slidably couples proximal portion  172  to actuator assembly  21  at the connection between distal end  24   a  of second handle  24  and proximal end  28   a  of second link member  28 . Fastener  37  rotatably couples proximal portion  172  to distal end  30   b  of first link member  30 . 
     Spreading member  150  includes an enlarged opening  156   a  about slot  156  so that the head of fastener  35  can be recessed at least partially therein. The shaft of fastener  35  extends through a slotted portion  156   b . Similarly, spreading member  170  includes slot  176  including an enlarged opening  176   a  about slotted portion  176   b  so that the head of fastener  33  can be recessed at least partially therein. Hole  158  of spreading member  150  includes an enlarged opening  158   a  in which the head of fastener  39  can be recessed, and the shaft of fastener  39  extends through hole portion  158   b . Similarly, spreading member  170  includes an enlarged opening  178   a  about hole  178  so that the head of fastener  37  can be recessed at least partially therein with the shaft extending through hole portion  178   b.    
     When actuator assembly  21  is in an unactuated state as shown in  FIG. 2 , spreading members  150 ,  170  are positioned adjacent one another. As actuator assembly  21  is actuated by moving handles  22 ,  24  toward one another, spreading members  150 ,  170  can move away from and remain parallel during such movement in the manner discussed above with respect to spreader assembly  90 , as shown in  FIG. 3 . 
     Spreading member  150  includes a concavely curved end wall  160  extending from proximal portion  152  to extension member  154 . Spreading member  170  includes a concavely curved end wall  180  extending from proximal portion  172  to extension member  174 . End walls  160 ,  180  can abut against the bony structure adjacent the space in which extension members  154 ,  174  are inserted to limit the insertion depth of extension members  154 ,  174  into the space. 
     Extension member  154  and extension member  174  each include a configuration that allows the extensions members  154 ,  174  to be positioned adjacent one another in a low profile arrangement for insertion into the space between the adjacent bony structures. Extension member  154  includes a lateral flange portion  154   a  and a web portion  154   b  extending along flange portion  154   a . Flange portion  154   a  includes a contact surface  154   c  opposite web portion  154   b . Flange portion  154   a  and web portion  154   b  define a receptacle  154   d . Extension member  174  includes a flange portion  174   a  and a web portion  174   b  extending along flange portion  174   a . Flange portion  174   a  includes a contact surface  174   c  opposite web portion  174   b . Flange portion  174   a  and web portion  174   b  define a receptacle  174   d . Receptacle  174   d  is sized to receive web portion  154   b , and receptacle  154   d  is sized to receive web portion  174   b , allowing extension members  154 ,  174  to be placed in a nested configuration when spreader instrument  20  is unactuated and spreading members  150 ,  170  are placed against or adjacent to one another. Web portions  154   b ,  174   b  are provided with a uniform height along the respective flange portion  154   a ,  174   a , allowing the height of the nested extension members  154 ,  174  to be minimized along the entire length thereof. 
     Flange portion  154   a  includes a ramped surface  162  opposite contact surface  154   c  that transitions into proximal portion  152 , and web portion  154   b  includes a ramped surface  164  opposite contact surface  154  that transitions into proximal portion  152 . Flange portion  174   a  includes a ramped surface  182  opposite contact surface  174   c  that transitions into proximal portion  172 , and web portion  174   b  includes a ramped surface  184  opposite contact surface  174   c  that transitions into proximal portion  172 . The ramped transition surfaces facilitate the nesting relationship between extension members  154 ,  174 . 
     Contact surfaces  154   c ,  174   c  can include a relatively flat profile along flange portions  154   a ,  174   a . In one embodiment, contact surfaces  154   c ,  174   c  includes a number of surface features that include pits formed by a chemical photo-etching process. The process can produce many various patterns, ranging from a very fine surface roughness to a very coarse surface roughness. The patterns of etching can be controlled by using computer-generated negatives of the desired pattern. By controlling the surface area affected by the photo-etching and the etching depth, the strength of the respective extension member  154 ,  174  can be maintained in close proximity to its original, unetched strength. In comparison, an extension member including surface features formed by mechanical cutting or abrasion requires a greater thickness to maintain the same bending strength after placement of the surface features than does an extension member with chemically etched surface features. Thus, the thickness of flange portions  154   a ,  174   a  can be minimized to provide a low profile spreader assembly with bone engagement structures on the spreading member for insertion into small spaces between adjacent bony structures. 
     In one specific embodiment, each extension member  154 ,  174  can be provided with a thickness t of 3.5 millimeters, and recesses  154   d ,  174   d  each have a depth of 2 millimeters. Thus, extension members  154 ,  174  can have an overall height of 5 millimeters between contact surfaces  154   c ,  174   c  when spreader assembly  190  is in its unactuated position and spreading members  150 ,  170  are nested relative to one another. Thus, in the specific illustrated embodiment, the nested relationship provides at least a 28% reduction in height than would be provided in a non-nested relationship. In the specific embodiment, extension members  154 ,  174  can have a width W of 5 millimeters, and web portions  154   d ,  174   d  occupy half of width W. Extension members  154 ,  174  can also be provided with a length D of 32 millimeters, or other length D such that the extension members  154 ,  174  extend across a substantial portion of a disc space providing even and uniform separation of the adjacent vertebrae across the disc space. It is to be understood that other embodiments contemplate other maximum heights, widths and lengths for extension members  154 ,  174 . 
     The moment of inertia and section modulus provided by extension members  154 ,  174  maintains deflection of extension members  154 ,  174  within acceptable limits even with long lengths D. The low profile unactuated height of extension members  154 ,  174  and their parallel relationship allow extension members to be completely inserted in the space between the adjacent bony structures before distraction or spreading. The controlled deflection of extension members  154 ,  174  provides uniform spreading or distraction of the vertebrae across the disc space, facilitating endplate and disc space preparation and implant insertion. 
     Referring back to  FIGS. 2-3 , techniques employing the spreader instrument will be described with reference to spreader instrument  20 , it being understood that the techniques described also have application with the other embodiments discussed herein and in surgical procedures other than spinal surgery. In  FIG. 2  spreader instrument  20  has a reduced profile configuration for insertion into a collapsed disc space D between vertebrae V 1  and V 2 . Actuator assembly  21  is actuated to move spreading members  50 ,  70  away from one another in parallel relation. In one embodiment, actuator assembly  21  moves spreading members  50 ,  70  away from one another in parallel relation while actuator assembly  21  simultaneously moves longitudinally relative to the spreading members  50 ,  70 . It should be understood, however, that aspects of the invention contemplate that the spreading members are not moved parallel to one another and/or are not parallel to one another. 
     The spreading members  50 ,  70  contact an endplate of a respective one of the vertebrae V 1  and V 2 . Spreading members  50 ,  70  are moved further away from one another with actuator assembly  21  to restore collapsed disc space D from its collapsed height H 1  to a restored height H 2 . Thereafter the surgeon can insert instruments and the like into disc space D to remove bone material, disc material and the like to prepare the disc space for subsequent procedures, such as the insertion of an interbody device, fusion device, graft material, or artificial disc, for example. Spreader instrument  20  can maintain disc space distraction during such procedures. Since, contact surfaces  54   c ,  74   c  occupy relatively small areas of the vertebral endplates, it is contemplated that the entire procedure can be conducted with spreader instrument  20  in the disc space. It is further contemplated that spreader instrument  20  can be easily and quickly repositioned in the disc space for completion of procedures in the areas previously occupied by the spreader instrument. 
     One specific application contemplates distracting or spreading adjacent vertebrae of the spine. Any number of approaches to the spine are contemplated, including anterior, posterior, lateral, postero-lateral, antero-lateral approaches, for example, and also in minimally invasive and open surgical procedures. Aspects of the spreader instrument embodiments discussed can be employed in spreader instruments adapted for endoscopic, laparoscopic, and/or thorascopic procedures. The spreader instrument can also be employed to spread adjacent bony structures in locations other than the spine. 
     In one embodiment, the spreading members are provided with a ceramic coating. A ceramic coating can provide a low friction surface treatment that reduces or eliminates glare from the distal spreader assembly, enhancing surgeon viewing of the operative site. It is further contemplated that the spreading instruments can be made from any material acceptable for fabrication of surgical instruments. 
     Another embodiment of a spreader instrument  220  will be described with reference to  FIGS. 17-20 . This embodiment of spreader instrument  220  includes an actuator assembly  221 , a distal spreader assembly  290  and an optional adjustment mechanism  245 . Actuator assembly  221  includes a first handle  222  pivotally coupled to a second handle  224  about a fastener  226 . A first spring member  242  extends between first handle  222  and second handle  224  along and about a pin  244 . Spring member  242  is a coil spring that biases handles  222 ,  224  away from one another so that spreader assembly  290  of spreader instrument  220  is biased to a normally closed position, as shown in  FIG. 18 . Handles  222 ,  224  are moved to an actuated position by moving handles  222 ,  224  toward one another against spring member  242 , compressing spring member  242  along pin  244  as shown in  FIG. 19 . 
     Adjustment mechanism  245  is provided to adjust and/or secure handles  222 ,  224  and thus spreader assembly  290  in any one of a number of actuated positions. Adjustment mechanism  245  includes pin  244  pivotally connected to handle  222  and extending through handle  224 . Spring member  242  extends about the portion of pin  244  between handles  222 ,  224 . An adjustment member  248  located on the end of pin  244  extending through handle  224  is movable along pin  244  to adjust and/or maintain the relative positioning between handles  222 ,  224 . In the illustrated embodiment, pin  244  can be threaded and adjustment member  248  can be a hand knob threadingly coupled thereto. The outer end of pin  244  can be non-threaded and enlarged to retain adjustment member  248  on pin  244 . 
     Adjustment member  248  can contact second handle  224  to maintain handles  222 ,  224  and distal spreader assembly  290  in any one of a number of actuated positions. Adjustment member  248  can be threaded toward the direction opposite arrow P to allow handles  222 ,  224  to return toward their unactuated position until either adjustment member  248  contacts handle  224  or the handles  222 ,  224  and spreader assembly  290  are completely unactuated. Adjustment member  248  can be threaded along pin  244  in the direction of arrow P toward handle  224  to maintain an actuated position or move handles  222 ,  224  toward one another for actuation. 
     First handle  222  is pivotally coupled at its distal end  222   a  to a proximal end of a first link member  230 . Second handle  224  is pivotally coupled at its distal end  224   a  to a proximal end of a second link member  228 . Link members  228 ,  230  cross one another to form an X-shape in their actuated state as shown in  FIGS. 19 and 20 . Link members  228 ,  230  are pivotally coupled to one another about central fastener  240  of actuator assembly  221 . The overlapping portions of the crossed link members  228 ,  230  can be recessed so that the distal and proximal end portions of link members  228 ,  230  can extend over and be aligned with one another, as shown in  FIG. 21 . 
     Distal spreader assembly  290  includes a first spreading member  250  and a second spreading member  270 . First spreading member  250  is attachable to a first coupling member  252  of actuator assembly  221 . Second spreading member  270  is attachable to a second coupling member  272  of actuator assembly  221 . Coupling member  252  includes a distal slot  256  through which fastener  235  extends. Coupling member  252  further includes a proximal hole through which fastener  239  extends. Fastener  235  rotatably and slidably couples coupling member  252  to a distal end of second link member  228  of actuator assembly  221 . Fastener  239  rotatably couples coupling member  252  to a proximal end of first link member  230 . Second coupling member  272  includes a distal slot  276  through which fastener  233  extends. Coupling member  272  further includes a proximal hole through which fastener  237  extends. Fastener  233  rotatably and slidably couples coupling member  272  to a distal end of first link member  230 . Fastener  237  rotatably couples coupling member  272  to a proximal end of second link member  228 . 
     When actuator assembly  221  is in an unactuated state as shown in  FIG. 18 , spreading members  250 ,  270  are positioned adjacent one another. As actuator assembly  221  is actuated by moving handles  222 ,  224  toward one another, spreading members  250 ,  270  can move away from one another and remain parallel during such movement. The rotatable and slotted engagement of coupling members  252 ,  272  via fasteners  235 ,  233  in slots  256 ,  276 , respectively, allows the relative longitudinal position between actuator assembly  221  and spreading members  250 ,  270  to vary in accordance with the amount of actuation provided, and for spreading members  250 ,  270  to remain parallel to one another during such movement. It should be understood, however, that other actuator assemblies  221  are contemplated, including those that provide non-parallel movement of spreading members  250 ,  270 . Actuator assembly  221  could also be configured to move spreading members  250 ,  270  through, for example, a scissors coupling arrangement between handles  222 ,  224 , a gear rack mechanism, or other actuator assembly arrangement discussed herein. 
     In operation, the distal ends  222   a ,  224   a  of handles  222 ,  224  move away from one another by the pivoting of handles  222 ,  224  about fastener  226 . In addition, the distal ends of link members  228 ,  230  move away from one another by the pivoting of link member  228 ,  230  about fastener  240 . This pivoting movement of the components of actuator assembly  221  causes the length of spreader instrument  220  to reduce along longitudinal axis L. Coupling members  252 ,  272  rotate about respective ones of the fasteners  239 ,  237 , respectively, as spreading members  250 ,  270  are moved away from one another. Fasteners  235 ,  233  rotate within and move proximally in respective ones of the slots  256 ,  276  as spreading members  250 ,  270  move away from one another. The movement of fasteners  235 ,  233  in slots  256 ,  276  accommodates the reduction in length of actuator assembly  221  along axis L, while the rotation of fasteners  235 ,  233  in slots  256 ,  276  and the rotation of fasteners  239 ,  237  allows spreading members  250 ,  270  to remain parallel to one another as actuator assembly  221  is actuated and unactuated. 
     In the unactuated position of  FIG. 18 , spreading members  250 ,  270  are positioned adjacent one another, and have an overall height H 3  that allows insertion of distal extension members  262 ,  282  of spreading members  250 ,  270 , respectively, into a spinal disc space or corpectomy space between adjacent vertebrae. In an actuated state, spreading members  250 ,  270  can be separated so that a height H 4  is provided between distal extension members  258 ,  278 . Height H 4  can correspond to a desired disc space height prior to disc space preparation, vertebral body preparation, and/or implant insertion. The configuration of actuator assembly  221  contemplates that handles  222 ,  224  are moved toward one another to move spreading members  250 ,  270  away from one another, which can limit the maximum distraction or separation height H 4  when the handles contact or are adjacent one another. 
     Spreading members  250 ,  270  can be removably coupled to coupling members  252 ,  272 , respectively so that spreading members  250 ,  270  can be readily interchanged with, for example, spreading members having different sizes and/or configurations. For example, as shown in  FIG. 20 , spreading members  350 ,  370  are attached to actuator assembly  221  and provide a maximum distraction height H 5  between distal extension members  362 ,  382 . Height H 5  is greater than height H 4  since each spreading member  350 ,  370  is provided with a stepped region  354 ,  384 , each of which includes a height H 6 . Thus, the amount of distraction available with spreading members  350 ,  370  is greater than that provided with spreading members  250 ,  270  by two times height H 6 . Spreading members with a stepped region can be employed in, for example, corpectomy procedures where the spreading distance needed between the spreading members is greater than that required in disc space procedures. 
     In one specific example, selecting one spreading member with a stepped region including a height H 6  provides a 15 millimeter spacing between the spreading members when the other spreading member includes no stepped region. If desired, the other spreading member can be replaced with a second spreading member including a stepped region including a height H 6  that provides an additional 15 millimeter spacing between the spreading members. Thus, an overall spacing of 30 millimeters is provided between the spreading members. The ability to select and employ spreading members with stepped regions of various heights, or with no stepped region, facilitates use of the spreading instrument in corpectomy procedures and other procedures requiring additional space or separation between the adjacent bony structures may be required. 
     As shown in  FIG. 21 , actuator assembly  221  can be provided with a linear configuration along its length. Spreading members  250 ,  270  can be provided in a generally U-shaped configuration. For example, spreading member  270  includes a pair of distal extension members  282 ,  284  extending from a body portion  271 . Spreading member  250  can be similarly provided with a first distal extension member (not shown) below and aligned with distal extension member  284 , and a second distal extension member  262  below and aligned with distal extension member  282 . Each of the spreading members  250 ,  270  of distal spreader assembly  290  can be offset to one side of actuator assembly  221  with, for example, an offset portion  274  extending between body portion  271  and a coupling portion  284  engaged with coupling member  272 . Similarly, spreading member  250  can include an offset portion extending between a body portion and a coupling portion  264  engaged with coupling member  252 . The offset of actuator assembly  221  relative to the spreading members of spreader assembly  290  facilitates access for disc space preparation, vertebral body preparation and implant insertion between the spreading members  250 ,  270  while spreading members  250 ,  270  are positioned in the space between vertebrae. 
     It is further contemplated that each of the handless  222 ,  224  can be provided with a distal portion  222   c ,  224   c  and a proximal portion  222   b ,  224   b , respectively. Proximal portions  222   b ,  224   b  can be pivotally coupled to respective ones of the distal portions  222   c ,  224   c  about pins  230 ,  231 , respectively. Pins  230 ,  231  can be configured to lock proximal portions  222   b ,  224   b  in the position shown in  FIG. 20 . When pins  230 ,  231  are pressed, proximal portions  222   b ,  224   b  can be pivoted about their connection with distal portions  222   c ,  224   c  in the direction of arrow  229  and away from spreader assembly  290  to further facilitate access to the operative site. 
     In  FIGS. 22-41  various embodiment spreading members are provided. These spreading member embodiments and the spreading member embodiments discussed above can be employed with any of the actuator assembly embodiments or configurations discussed herein. It is further contemplated that spreading member embodiments could be removably attached to an actuator assembly so that spreading members having various configurations and/or distraction characteristics can be readily employed by the surgeon during the surgical procedure or for different surgical procedures with the same instrument set or actuator assembly. It is further contemplated that the spreading member embodiments could be a permanent and/or integral portion of the spreading instrument. 
     Referring now to  FIGS. 22-25 , another embodiment spreading member  400  is provided that is attachable to, for example, actuator assembly  221 . Spreading member  400  includes a body portion  402  and a proximal coupling portion  404  offset from body portion  402  by offset portion  424 . A first extension member  406  and a second extension member  408  extend distally from body portion  402 . Body portion  402  further includes a proximal end wall  421  and an opposite distal end wall  422  having a concave surface profile configured to reside against or along the convex curvature of an adjacent vertebral body. Body portion  402  includes an outer surface  403  and an opposite inner surface  405  oriented toward the other spreading member when assembled with the actuator assembly. 
     Outer surface  403  and inner surface  405  are spaced from one another to provide a thickness or depth to body portion  402  that limits deflection upon application of a spreading load to the adjacent bony structure. For example, extension member  406  is spaced laterally from the connection of spreading member  400  with the actuator assembly  221 . Thus, extension member  406  is cantilevered laterally relative to extension member  408  by body portion  402 . Loads applied by extension member  406  will tend to bend or deflect body portion  402  such that extension members  406 ,  408  do not remain aligned with one another. Body portion  402  is provided with a thickness between outer surface  403  and inner surface  405  that limits the deflection of extension member  406  under the spreading loads to be encountered so that extension members  406 ,  408  remain aligned with one another to facilitate precise endplate preparation and implant insertion. 
     A guide member  410  extends along and forms an extension of the inner surface  405  of body portion  402  between a leading end  411  and a trailing end  412 . Leading end  411  is positioned distally of body portion  402  and extends between extensions  406 ,  408 . Trailing end  412  is positioned proximally of body portion  402 . In the illustrated embodiment, guide member  410  has a flat, plate-like surface profile opposite body portion  402 . As discussed further below, guide member  410  facilitates placement of disc space preparation instruments and implants between adjacent spreading members employing guide members  410 . 
     First extension member  406  and second extension member  408  are spaced by a distance W 1 , and each extension member  406 ,  408  can be provided with a width W 3 . In one embodiment, spreading member  400  is adapted for an anterior approach to the lumbar spine, and width W 1  can be about 27 millimeters and width W 3  can be about 3.5 millimeters. Other widths W 1  and W 3  are contemplated for anterior approaches to the lumbar spine, and for other approaches to the spine, and for approaches to other anatomical structures. Extension members  406 ,  408  can be provided with a tapered leading end to facilitate insertion into the spinal disc space, and a height that tapers from body portion  402  to the leading end thereof. Extension members  406 ,  408  extend along and below inner surface  405  of body portion  402  as shown in  FIGS. 22-23 , and define a space therebetween that can receive instruments and/or implants. 
     Each of the extension members  406 ,  408  can be provided with bone engaging features, such as teeth  414  shown in  FIG. 25 . In the illustrated embodiment, three teeth  414  are provided on each extension member  406 ,  408 . Teeth  414  are located so that when extension members  406 ,  408  are positioned in a spinal disc space and leading end wall  422  of body portion  402  is adjacent to or in contact with the vertebral body, teeth  414  can bite into or engage the cortical rim of the adjacent vertebral endplate as spreader instrument  220  is actuated to spread the adjacent vertebrae. Teeth  414  can anchor the spreader instrument to the vertebrae and resist movement of the spreader instrument relative to the vertebrae during the surgical procedure. In the illustrated embodiment, teeth  414  are V-shaped with a sharp outer end to penetrate into the adjacent bony structure. 
     Coupling portion  404  includes proximally opening channel having an entry portion  416  and a locking member receiving portion  418 . A locking member, such as locking members  253 ,  273  shown in  FIGS. 18-21 , include a first portion positionable through entry portion  416  and a larger, second portion positionable in receiving portion  418 . The larger portion is too large to pass through entry portion  416 . When it is desired to engage spreading member  400  to an actuator assembly, locking member  253 , for example, can be pressed downwardly so that its larger first portion is located out of the insertion path of coupling portion  404  into coupling member  252 . The smaller portion of locking member  253  is located in the insertion path, and entry portion  416  can slide over the smaller portion until the smaller portion of locking member  253  is positioned in receiving portion  418  and the larger portion is aligned with receiving portion  418 . Locking member  253  is then released and spring-biased to return the larger portion into receiving portion  418 , providing an interference fit therewith and locking spreading member  400  to actuator assembly  221 . 
     In  FIGS. 26 and 27  there is shown another embodiment spreading member  450  attachable to a spreader instrument, such as, for example, spreader instrument  220 . Spreading member  450  can be similar to spreading member  400  discussed above, and includes a body portion  452  having extension members  456 ,  458  extending from distal end wall  472  adjacent inner surface  455  of body portion  452 . An offset portion  474  extends between body portion  452  and a coupling portion  454 . Extension members  456 ,  458  can be provided with bone engaging features  464 . 
     A guide member  460  extends between a leading end  461  located distally of distal end wall  472  and an opposite trailing end  462  located proximally of proximal wall  471 . When compared to guide member  410  above, guide member  460  extends proximally a greater distance to provide a greater surface area along which to guide disc space preparation instruments and/or implant insertion instruments. In each embodiment, leading ends  411 ,  461  of guide members  410 ,  460  can extend into the disc space at least along the cortical rim of the adjacent vertebra. For spreading member  400 , trailing end  412  can be spaced about 42.5 millimeters from leading end  411 . For spreading member  450 , trailing end  462  can be spaced about 60 millimeters from leading end  461 . Other lengths between the leading ends and trailing ends of guide members  410 ,  460  are also contemplated, ranging from 7 millimeters to 80 millimeters or more, for example. 
     In  FIG. 28  a pair of spreading members  450 ,  480  are shown separated from one another in an actuated position without an actuator assembly. Spreading member  480  is a mirror image of spreading member  450 , and includes a body portion  482  having a distal end wall  499  and a pair of extension members  486 ,  488  extending distally from distal end wall  499 . A coupling portion  484  extends proximally from body portion  452 . Implants and implant insertion instruments can be guided into the disc space between spreading members  450 ,  480  along the flat surfaces of guide members  460 ,  490  adjacent the inner surfaces  455 ,  485 . 
     In  FIG. 29  a pair of spreading members  400 ,  430  are shown in partial section through guide members  410 ,  440 . Spreading members  400 ,  430  are separated from one another in an actuated positioned without an actuator assembly. Spreading member  430  is a mirror image of spreading member  400 , and includes a body portion  432  having a distal end wall  449  and a pair of extension members (only extension member  438  shown) extending distally from distal end wall  449 . A coupling portion  434  extends proximally from body portion  432 . Implants and implant insertion instruments can be guided into the disc space along the flat surfaces of guide members  410 ,  440 , which form angle A 3  therebetween. In the illustrated embodiment, angle A 3  is 0 degrees for parallel endplate preparation and implant insertion. In  FIG. 30 , angle A 4  is formed between guide members so that the spacing between guide members  410 ,  440  tapers distally for lordotic endplate preparation, implant insertion and restoration. In one embodiment, angle A 4  can be 8 degrees. Other angles are also contemplated based on the desired angle between the adjacent vertebral endplates. 
     When positioned adjacent the spinal column, as shown in  FIGS. 31 and 32 , distal end walls  422 ,  449  of spreading members  400 ,  430  can abut the adjacent vertebral body  500 ,  502 , respectively, with the extension members  406 ,  408  of spreading member  400  and the corresponding extension members of spreading member  430  in the spinal disc space  504 . Guide members  410 ,  440  have their leading ends, such as leading end  411  shown in  FIG. 32 , extending into the disc space  504  while trailing end  412  is positioned proximally of the vertebral bodies  500 ,  502 . The portion of the guide member extending into the disc space can protect the implant and/or the outer cortical bone from damage during insertion of the implant. Extension members  406 ,  408  can be centered about the sagittal plane  520 , or can be offset for an oblique approach or multiple approaches to the disc space. 
     As shown in  FIG. 33 , an implant  506  can be attached to a distal end  508  of an insertion instrument  510 . Spreading members  400 ,  430  are spread apart by an actuator assembly (not shown) to provide a desired spacing between vertebrae  500 ,  502 . Implant  506  is positioned between guide members  410 ,  440  and guided into disc space  504  therebetween as insertion instrument  510  is impacted or pushed forward to the desired location in disc space  504  between vertebrae  500 ,  502 . Implant  506  can further be guided laterally between extension members  406 ,  408  and also the extension members of spreading member  430  to maintain the insertion path into the disc space until the implant is fully seated. 
     The guide members of spreading members  400 ,  430 ,  450 ,  480  act as a ramp to facilitate distraction of the adjacent vertebrae with insertion of the implant. The implant enters the space between the guide members at their trailing ends, and is impacted or pushed toward the distal ends to distract the vertebrae. The guide members protect the cortical bone along which the guide member extends from damage during implant insertion, and can prevent the distal extension members from subsiding into the vertebral endplates by providing a greater load bearing area during distraction. The guide members can also reduce friction during implant insertion to facilitate implant placement. It is further contemplated that the guide members can be formed with or engaged with the distal extension members and the body portion of the adjacent spreading member to provide rigidity and strength to the guide member. The low profile of the guide members and separation between the distal extension members facilitates viewing of the operative space between the spreading members. 
     In  FIG. 34  there is shown another embodiment spreading member  550  useable with a spreader instrument, such as spreader instrument  220 . Spreading member  550  can be similar to spreading member  450  discussed above, and includes a body portion  552  having distal extension members  556 ,  558  extending from distal end wall  572 . An offset portion  574  extends between coupling portion  554  and body portion  552 . Extension members  556 ,  558  can be provided with bone engaging features  564 . 
     Coupling portion  554  can be provided with a tapered insertion portion  566  and a laterally extending locking member receiving portion  568 . Receiving portion  568  can receive a locking member to releasably engage spreading member  550  to a spreading instrument with a locking member, such as locking members  253 ,  273  discussed above. The tapered insertion portion  566  moves the locking member out of alignment with the passage into which coupling portion  554  is positioned. The locking member can be spring-biased to releasably engage coupling portion  554  in receiving portion  568 . 
     Spreading member  550  further includes a stepped region  560  that extends vertically between coupling portion  554  and body portion  552 . Stepped region  560  can be provided with a height H 6  between coupling portion  554  and extensions  556 ,  558 . Stepped region  560  provides greater separation between the distal extensions members of adjacent spreading members, thus allowing greater distraction distances between vertebrae to be obtained, as may be desirable in corpectomy procedures. 
     In  FIGS. 35 and 36  a spreading member  600  is provided that is adapted for an anterior-oblique approach to the spinal disc space. Spreading member  600  includes a body portion  602  and a pair of extension members  606 ,  608  extending distally from body portion  602 . An offset portion  624  extends to coupling portion  604 . Coupling portion  604  includes a detent  605  for receiving a spring-loaded ball to couple spreading member  600  to an actuator assembly. Other coupling arrangements discussed herein are also contemplated. 
     Spreading member  600  has a central axis  610  between and extending parallel to extension members  606 ,  608 . Offset portion  624  extends along an axis  612  oriented at angle A 5  to axis  610 . One embodiment contemplates that angle A 5  can be in the range from 0 degrees to 90 degrees. Another embodiment contemplates that angle A 5  can be in the range from 15 degrees to 60 degrees. In one specific embodiment, it is contemplated that angle A 5  can be about 30 degrees. 
     To accommodate an anterior oblique approach, extension member  606  can be longer than extension member  608  since extension member  606  is positioned anteriorly of extension member  608  in the disc space. One embodiment contemplates that extension member  606  is about 7 millimeters longer than extension member  608 . Another embodiment shown in  FIG. 37  contemplates a spreading member  650  having a configuration suited for an oblique approach in which extension members  656 ,  658  have the same length extending from body portion  652 . Spreading member  650  similarly includes a central axis  660  and an offset axis  662  extending along coupling portion  654  forming angle A 5  with central axis  660 . Spreading member  650  can also be inserted in an anterior-posterior orientation with at least a portion of the actuator assembly angled relative to axis  660 . 
     In  FIG. 38  there is shown another spreading member embodiment designated at  700 . Spreading member  700  includes a body portion  702  having a distal end wall  722 . First extension member  706  and second extension member  708  extend distally from and below end wall  722 . Extension members  706 ,  708  include bone engaging features  714 . An offset portion  724  extends between a coupling portion  704  and body portion  702 . A support surface  710  extends along extension member  708 , through body portion  702 , and along offset portion  724 . An opposite support surface  711  extends along extension member  706  and through body portion  702 . Support surfaces are open toward the upper sides of extension members  706 ,  708 . 
     As shown in  FIG. 39 , support surfaces  710 ,  711  are adapted to support at least a blade portion  734  of a cutting instrument  730 , such as a chisel. Blade portion  734  extends distally from a shaft portion  732 . Blade portion  734  is movable along support surfaces  710 ,  711  to remove, for example, bony material and/or other tissue material located between extensions  706 ,  708  and below support surfaces  710 ,  711 . Extension members  706 ,  708  remain in contact with and support the adjacent vertebrae as cutting instrument  300  is manipulated to remove bony material between extension members  706 ,  708 . 
     In  FIGS. 40 and 41  there is shown another spreading member embodiment designated at  750 . Spreading member  750  includes a body portion  752  having a distal end wall  772 . First extension member  756  and second extension member  758  extend distally from and are offset below end wall  772 . Extension members  756 ,  758  include bone engaging features  764  along a bone contacting surface thereof. An offset portion  774  extends between a coupling portion  754  and body portion  752 . A support surface  763  is defined by a receiving slot  760  extending through body portion  752  and above extension members  756 ,  758 . Receiving slot  760  is adapted to receive at least a blade portion of a cutting instrument, such as cutting instrument  730  discussed above. The lateral edges of receiving slot  760  are positioned between extensions members  756 ,  758  so that the bone material supported by extension members  756 ,  758  remains intact as the blade portion is moved within slot  760  to remove, for example, bony material and/or other tissue material located between extension members  756 ,  758  and below slot  760 . The implant can then be positioned in the prepared disc space in contact with the portions of the vertebral bodies removed with the cutting instrument. 
     It is further contemplated that slot  760  can be provided with a groove  761  therealong. Groove  761  can receive a guide member (not shown) on the cutting instrument to maintain movement of the cutting blade within slot  760  parallel to extension members  756 ,  758 . Groove  761  is formed in support surface  763 , although other locations about slot  760  are also contemplated. 
     Referring now to  FIGS. 42-43 , another embodiment spreading member  800  is provided that is attachable to, for example, actuator assembly  221 . Spreading member  800  includes a body portion  802  and a proximal coupling portion  804  offset from body portion  802  by offset portion  824 . An extension member  808  extends distally from body portion  802  adjacent a first side thereof. Body portion  802  further includes a proximal end wall  826  and an opposite distal end wall  822  having a concave surface profile configured to reside against or along the convex curvature of an adjacent vertebral body. Body portion  802  includes an outer surface  803  and an opposite inner surface  805  oriented toward a second spreading member when assembled with the actuator assembly, it being understood that the second spreading member provides a mirror image of spreading member  800  when assembled with the actuator assembly. 
     Outer surface  803  and inner surface  805  are spaced from one another to provide a thickness or depth to body portion  802  that limits deflection thereof upon application of a spreading load to the adjacent bony structure. A guide member  810  extends along and forms an extension of the inner surface  805  of body portion  802  between a leading end  814  and a trailing end  816 . Leading end  814  is positioned distally of body portion  802  and extends along distal end wall  822  between extension member  808  and a guide member extension  812 . Guide member extension  812  is positioned adjacent a second side of body  802  opposite the first side from which extension member  808  extends. Guide member extension  812  extends distally to mimic the shape and length of extension member  808 . Trailing end  816  is positioned proximally of body portion  802 . In the illustrated embodiment, guide member  810  has a flat, plate-like surface profile opposite body portion  802 . As discussed above, guide member  810  facilitates placement of disc space preparation instruments and implants between adjacent spreading members employing guide members  810 . 
     Extension member  808  extends from inner surface  805  and includes a thickness between an outer surface  830  and an inner surface  832  that limits or prevents bending of extension member  808  as it applies a spreading force to the adjacent vertebra. Extension member  808  further includes a length extending from distal end wall  822  that allows outer surface  830  to contact the cortical rim of the adjacent vertebral endplate to apply a spreading force thereto. However, the length is minimized to facilitate implant insertion and/or instrument manipulation laterally of extension member  808  in the direction opposite guide member extension  812 . Guide member  810  also extends distally for distal end wall  822  along the cortical rim of the adjacent vertebral endplate to facilitate passage of instruments and/or implants along the cortical rim into the disc space without engaging or catching and damaging the bony material at the cortical rim. In one specific embodiment, extension member  808  and guide member  810  extend distally about 4 millimeters from distal end wall  822 . Other embodiments contemplate other lengths greater than about 2 millimeters. 
     Guide member extension  812  includes an inner surface that lies in the same plane as inner surface  805 . This allows implants and/or instruments to be guided into the disc space between spreading members and along medial surface  809  of extension  808 . The implants and/or instruments can be provided with a width extending from medial surface  809  that is greater than the width of spreading member  800  between extension member  808  and guide member extension  812 . Accordingly, the implant and/or instruments are not constrained between distal extension members of spreading member  800 . It is further contemplated that extension member  808  can be provided with bone engaging features, such as teeth, surface roughenings or other surface features as discussed herein to resist movement of extension member  808  relative to the vertebral endplate. 
     Other forms for spreading member  800  contemplate a second extension member extending distally from body  802  along guide member extension  812 . The second extension member can be provided with a relatively short length to allow instruments and implants to be positioned distally thereof when the second extension member is in the disc space. 
     The instruments discussed herein can be provided as a kit including an actuator assembly and various pairs of spreading members removably attachable to the actuator assembly and from which the surgeon can select depending on the procedure. For example, the kit can include an actuator assembly and any one or combination of a set of single extension spreading members such as shown in  FIG. 6 ; one or more sets of double extension spreading members forming various angles between guide members such as shown in  FIGS. 29 and 30 ; one or more sets of spreading members without guide members and/or for various approaches to the disc space such as shown in  FIGS. 34-37 ; one or more sets of spreading members with an offset region such as shown in  FIG. 34 ; one or more sets of spreading members adapted to guide a cutting instrument, such as shown in  FIGS. 39 and 40 ; and one or more sets of spreading members with a single extension and guide member, such as shown in  FIGS. 42-43 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, and that all changes and modifications that come within the spirit of the invention are desired to be protected.