Patent Publication Number: US-11654033-B2

Title: Distractible intervertebral implant

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/411,005, filed Jan. 20, 2017, which is a continuation of U.S. patent application Ser. No. 14/950,740, filed Nov. 24, 2015, now U.S. Pat. No. 9,579,215, which is a continuation of U.S. patent application Ser. No. 14/143,529, filed Dec. 30, 2013, now U.S. Pat. No. 9,320,615, which is a continuation of U.S. patent application Ser. No. 13/170,557, filed Jun. 28, 2011, now U.S. Pat. No. 8,623,091, which claims the benefit of U.S. Provision Application Ser. No. 61/359,554, filed Jun. 29, 2010, the contents of all of which are hereby incorporated by reference as if set forth in their entirety herein. 
    
    
     BACKGROUND 
     Historically, after complete removal of a disc from between adjacent vertebrae, the adjacent vertebrae were fused together. This “spinal fusion” procedure, which is still in use today, is a widely accepted surgical treatment for symptomatic lumbar and cervical degenerative disc disease. More recently, disc arthoplasty may be utilized to insert an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae. Such a disc implant allows limited universal movement of the adjacent vertebrae with respect to each other. The aim of total disc replacement is to remove pain generation (caused by a degenerated disc), restore anatomy (disc height), and maintain mobility in the functional spinal unit so that the spine remains in an adapted sagittal balance. Sagittal balance is defined as the equilibrium of the trunk with the legs and pelvis to maintain harmonious sagittal curves and thus the damping effect of the spine. In contrast with fusion techniques, total disc replacement preserves mobility in the motion segment and attempts to mimic physiologic conditions. 
     SUMMARY 
     A distractible intervertebral implant configured to be inserted in an insertion direction into an intervertebral space that is defined between a first vertebral body and a second vertebral body is disclosed. The implant may include a first implant body and a second implant body. The first implant body may define an outer surface that is configured to face the first vertebral body, and an opposing inner surface that defines a rail. The second implant body may define an outer surface that is configured to face the second vertebral body, and an inner surface that defines a recess configured to receive the rail of the first implant body. The second implant body is configured to move along the vertical direction as the second implant body is translated over the first implant body and the rail is received by the recess, so as to distract the first and second vertebral bodies. 
     In another embodiment, the implant may include a first implant body and a second implant body. The first implant body may include a pair of first side regions, and may define an outer surface that is configured to face the first vertebral body. The second implant body may also include a pair of second side regions. Each second side region may have an anterior end that angles toward the first implant body as the anterior end extends in a direction opposite the insertion direction. The second implant body may define an outer surface that is configured to face the second vertebral body. The anterior ends of the second implant body are configured to contact the first side regions of the first implant body as the second implant body is translated over the first implant body to thereby cause the outer surface of the second implant body to move away from the outer surface of the first implant body. 
     In another embodiment, a method for inserting an intervertebral implant into an intervertebral disc space defined between first and second vertebral bodies is disclosed. The method may include the step of inserting a first implant body into the intervertebral space such that as the first implant body is being inserted at least one of the first and second vertebral bodies moves away from the other vertebral body. The first implant body may include an outer surface that faces the first vertebral body, and an inner surface. The method may further include inserting a second implant body into the intervertebral space by sliding the second implant body over the inner surface of the first implant body. The second implant body may cause at least one of the first and second vertebral bodies to move away from the other as the second implant body is being inserted. The second implant body may include an outer surface that faces the second vertebral body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of a preferred embodiment of the application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the distractable fusion implant and related instruments of the present application, there is shown in the drawings a preferred embodiment. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG.  1 A  is a front perspective view of an intervertebral space defined between a superior vertebral body and an inferior vertebral body; 
         FIG.  1 B  is a front perspective view of a distractible intervertebral implant inserted into the intervertebral space, the implant including an inferior implant body and a superior implant body; 
         FIG.  2 A  is a front perspective view of the inferior implant body of the distractible fusion implant shown in  FIG.  1 B ; 
         FIG.  2 B  is a front elevation view of the inferior implant body shown in  FIG.  2 A ; 
         FIG.  2 C  is a side elevation view of the inferior implant body shown in  FIG.  2 A ; 
         FIG.  2 D  is a front perspective view of the inferior implant body shown in  FIG.  2 A  with a first fixation member being inserted into a bore of the inferior implant body; 
         FIG.  3 A  is a bottom perspective view of the superior implant body of the distractible fusion implant shown in  FIG.  1 B ; 
         FIG.  3 B  is a front elevation view of the superior implant body shown in  FIG.  3 A ; 
         FIG.  3 C  is a side elevation view of the superior implant body shown in  FIG.  3 A ; 
         FIG.  3 D  is a front perspective view of the superior implant body shown in  FIG.  3 A  with a pair of locking screws being inserted into a pair of bores of the superior implant body; 
         FIG.  4 A  is a back perspective view of the superior implant body being slid onto the inferior implant body; 
         FIG.  4 B  is a front perspective view of the superior implant body fully slid onto the inferior implant body to define the distractible fusion implant; 
         FIG.  4 C  is a front perspective view of the implant shown in  FIG.  4 B  with three locking screws received within the bores of the superior and inferior implant bodies; 
         FIG.  4 D  is a top plan view of the implant shown in  FIG.  4 C ; 
         FIG.  4 E  is a cross-sectional view of the implant shown in  FIG.  4 D  through the line  4 E- 4 E; 
         FIG.  5 A  is a side elevation view of the inferior implant body being slid into the intervertebral space defined between the superior and inferior vertebral bodies to thereby partially distract the vertebral bodies away from each other; 
         FIG.  5 B  is a side elevation view of the inferior implant body affixed to the inferior vertebral body with a first fixation member and a ramp portion of the superior implant body contacting an edge of the inferior implant body as it is being slid onto the intervertebral space; 
         FIG.  5 C  is a side elevation view of the superior implant body further slid over the inferior implant body within the intervertebral space; and 
         FIG.  5 D  is a side elevational view of the superior implant body affixed to the superior vertebral body with second and third locking screws. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1 A , an intervertebral space  11  is defined between a superior vertebral body  12   a  and an inferior vertebral body  12   b . The superior vertebral body  12   a  generally defines an inferior endplate  13   a  or superior surface of the intervertebral space  11 , and the adjacent inferior vertebral body  12   b  defines a superior endplate  13   b  or inferior surface of the intervertebral space  11 . Thus, the intervertebral space  11  is disposed between the vertebral bodies  12   a  and  12   b . The vertebral bodies  12   a  and  12   b  can be anatomically adjacent vertebral bodies, or can remain after a discectomy has been performed that removed a vertebral body from a location between the vertebral bodies. As illustrated, the intervertebral space  11  is illustrated after a discectomy, whereby the disc material has been removed or at least partially removed to prepare the intervertebral space  11  to receive a disc implant that can achieve height restoration. The intervertebral space  11  can be disposed anywhere along the spine as desired. Moreover, the superior vertebral body  12   a  may be considered a first or a second vertebral body and the inferior vertebral body  12   b  may be considered a first or a second vertebral body. 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “inner” or “distal” and “outer” or “proximal” refer to directions toward and away from, respectively, the geometric center of the implant and related parts thereof. The words, “anterior”, “posterior”, “superior,” “inferior,” “medial,” “lateral,” and related words and/or phrases are used to designate various positions and orientations in the human body to which reference is made and are not meant to be limiting. The terminology includes the above-listed words, derivatives thereof and words of similar import. 
     Referring also to  FIG.  1 B , an intervertebral implant, such as a distractable intervertebral implant  10 , can be inserted into the intervertebral space  11  along a longitudinal insertion direction I, which can be a posterior direction in accordance with the illustrated embodiment or any other direction as desired. The distractable intervertebral implant  10  is described herein as extending horizontally along a longitudinal direction “L” and lateral direction “A”, and vertically along a transverse direction “T”. Unless otherwise specified herein, the terms “lateral,” “longitudinal,” and “transverse” are used to describe the orthogonal directional components of various components. It should be appreciated that while the longitudinal and lateral directions are illustrated as extending along a horizontal plane, and that the transverse direction is illustrated as extending along a vertical plane, the planes that encompass the various directions may differ during use. For instance, when the distractable intervertebral implant  10  is implanted into the intervertebral space  11  the transverse direction T extends generally along the superior-inferior (or caudal-cranial) direction, while the plane defined by the longitudinal direction L and lateral direction A lie generally in the anatomical plane defined by the anterior-posterior direction, and the medial-lateral direction. Accordingly, the directional terms “vertical” and “horizontal” are used to describe the distractable intervertebral implant  10  and its components as illustrated merely for the purposes of clarity and illustration. 
     Referring to  FIG.  1 B , the distractable intervertebral implant  10  includes a first or inferior implant body  18  and a second or superior implant body  14  that is coupled to the inferior implant body  18 . The distractable intervertebral implant  10  can further include at least one first fixation member  22 , illustrated as a first screw that couples the inferior implant body  18  to the inferior vertebral body  12   b , and at least one second fixation member, such as second and third fixation members  26  and  30  illustrated as screws, that couple the superior implant body  14  to the superior vertebral body  12   a . It should be understood that the fixation members  22 ,  26 , and  30  may be also be configured as nails, blades, or graft. The distractable intervertebral implant  10  defines an anterior end  42  and an opposed posterior end  46 . The anterior end  42  defines a trailing end of the distractable intervertebral implant  10  along the direction of insertion I, and the posterior end  46  defines a leading end of the distractable intervertebral implant  10  along the direction of insertion I. 
     The distractable intervertebral implant  10  may be partially or entirely formed from a metal, polymer, ceramic, allograft, or other artificial biomaterials such as beta-tricalcium phosphate. Suitable biocompatible materials or combinations of materials, may include PEEK, porous PEEK, carbon fiber-reinforced PEEK, titanium and titanium alloys, stainless steel, ceramic, polylactic acid, tantalum, magnesium, allograft, or other artificial biomaterials. The distractable intervertebral implant  10  presents an outer surface  19  that can be coated with any suitable material, such as hydroxyl apatite, beta-tricalcium phosphate, anodic plasma chemical treated titanium, or other similar coatings that improve osseointegration of the distractable intervertebral implant  10 . As shown, the assembled implant  10  may be generally rectangular in shape, though it should be understood that all geometries are imaginable. 
     Referring to  FIGS.  2 A- 2 D  the inferior implant body  18  includes a body portion  34  that defines a lower or inferior, or outer, engagement surface  38  configured to contact or otherwise face the superior endplate  13   b  of the inferior vertebral body  12   b , an opposing inner surface  40 , an anterior end  42 , and an opposing posterior end  46 . The body portion  34  further includes a plurality of engagement features  50 , illustrated as teeth, that extend transversely out from engagement surface  38  and can be angled toward the anterior end  42  of the body portion  34 . The engagement features  50  allow the inferior implant body  18  to easily translate along a posterior direction over the superior endplate of the inferior vertebral body during insertion of the inferior implant body  18  while at the same time provides immediate primary stability allowing the inferior implant body  18  to resist anterior migration. In other words, the engagement features  50  allow the inferior implant body  18  to easily slide in one direction, but if it were to slide in a second opposite direction, the teeth  50  would catch on the superior endplate  13   b  of the inferior vertebral body  12   b  to thereby prevent migration of the inferior implant body  18 . It should be understood that the engagement features  50  can be shaped in any manner as desired, such as teeth, spikes, pyramids, cones, undefined geometries, rough surface topography, or independent bodies such a metal spikes that are embedded into the body portion  34  may be used. 
     As shown in  FIGS.  2 A- 2 D , the body portion  34 , such as the inner surface  40 , includes a middle region  54  and a first side region  58  extending from opposite sides of the middle region  54 . The middle region  54  protrudes higher in the transverse vertical direction (or outwardly toward the superior implant body  14 ) with respect to the first side regions  58 , and thus provides a longitudinally elongate rail that the superior implant body  14  can translate longitudinally along. In this way, the inner surface  40  of the body portion  34  defines the rail. In accordance with the illustrated embodiment, the anterior end  62  of the middle region  54  is angled upwards toward the superior implant body  14  as it extends toward the posterior end  46  of the body portion  34 , and the posterior end  66  of the middle region  54  is angled upwards toward the superior implant body  14  as it extends toward the anterior end  42  of the body portion  34 . As shown in  FIG.  2 A , the body portion  34  defines a bore  72  that extends through the anterior end  62 . As shown in  FIG.  2 D , the bore  72  is configured to receive the first fixation member  22 . The first fixation member  22  can include a shaft  23  and a head  25  that is dimensioned larger than the shaft  23 . The bore  72  can likewise include a shaft-receiving region sized to receive the shaft  23 , and a head receiving region sized to receive the head  25  when the fixation member  22  is fully received by the bore  72 . The bore  72  can further be tapered and elongate along an angle toward the posterior end  46  of the body portion  34 , such that the fixation member  22  is also elongate along the angle toward the posterior end  46  of the body portion  34  when received in the bore  72 . The bore  72  can include a locking mechanism that engage a locking mechanism of the first fixation member  22 , for instance a thread, a locking pin, a ratchet, a rough surface, etc. along one or both of the shaft  23  and the head  25 . It should be understood that at least one or both of the shaft  23  and the head  25  can be substantially smooth and devoid of the locking mechanism. Likewise, at least one or both of the shaft-receiving region and the head-receiving region can be substantially smooth and devoid of the locking mechanism. 
     The middle region  54  further defines a top surface  76  and opposed side surfaces  78  that extend down from the top surface  76 . The side surfaces  78  extend toward each other as they extend down from the top surface  76 . That is, as the side surfaces  78  extend down from the top surface  76 , the direction in which the side surfaces  78  extend includes a lateral component that extends toward the other side surface  78 . Therefore, the side surfaces  78  and the top surface  76  define a dovetail shaped locking member. It should be understood, however, that the middle region may include configurations other than a dovetail shaped locking member. For example, the middle region may define an L-shaped locking member, a greater angulation longitudinal ratchet, etc. 
     As shown in  FIG.  2 A , the first side regions  58  include conical recesses  80  at their anterior ends. As shown, the conical recesses  80  are angled up as they extend toward the posterior end  46  of the body portion  34 . As will be described later, the conical recesses  80  allow the second and third fixation members  26  and  30  to be inserted into the superior implant body  14  of the distractable intervertebral implant  10  at a specified angle. 
     The inferior implant body  18  can further include at least one graft window  90  such as a plurality of graft windows  90  that extend through at least one or more of the middle region  54  and the first side regions  58 . Generally, each graft window  90  is elongate in the longitudinal direction, though it should be understood that any shape may be desired. The graft windows  90  are configured to receive autogenous bone graft or bone graft substitute such as Chronos, or DBM. For instance, the graft windows  90  may be pre-filled with the bone graft. 
     Referring to  FIGS.  3 A- 3 D, and  4 A- 4 E  the superior implant body  14  may be translated, for instance longitudinally, along the inferior implant body  18 . As shown, the superior implant body  14  includes a body portion  134  that defines an upper or superior, or outer, engagement surface  138  configured to contact or otherwise face the inferior endplate  13   a  of the superior vertebral body  12   a , an opposing interior surface  140 , an anterior end  142 , and an opposing posterior end  146 . The body portion  134  further includes a plurality of engagement features  150  that extend transversely out from the engagement surface  138  and can be angled toward the anterior end  42  of the body portion  134 . The engagement features  150  allow the superior implant body  14  to easily translate along a posterior direction under the inferior endplate of the superior vertebral body during insertion of the superior implant body  14  while at the same time provides immediate primary stability allowing the superior implant body  14  to resist anterior migration. In other words, the engagement features  150  allow the superior implant body  14  to easily slide in one direction, but if it were to slide in a second opposite direction, the engagement features  150  would catch on the inferior endplate  13   a  of the superior vertebral body  12   a  to thereby prevent migration of the superior implant body  14 . It should be understood that the engagement features  150  can be shaped in any manner as desired, such as teeth, spikes, pyramids, cones, undefined geometries, rough surface topography, or independent bodies such a metal spikes that are embedded into the body portion  134  may be used. 
     As shown in  FIGS.  3 A- 3 D , the body portion  134 , such as the inner surface  140 , includes second side regions  154  that define a longitudinally elongate middle recess  158  configured to receive the longitudinally elongate rail of the body portion  34 . The middle recess  158  extends into the body portion  134  from an inferior side of the superior implant body  14 , and generally acts as a groove or channel that receives the middle region  54  of the inferior implant body  18 . As shown, the middle recess  158  receives the middle region  54  of the inferior implant body  18  as the superior implant body  14  translates along the inferior implant body  18 . An anterior end  162  of the middle recess  158  defines a conical recess  166  that is angled downwards. That is, the anterior end  162  of the middle recess  158  extends down as it extends toward the posterior end  146  of the body portion  134 . Additionally, the anterior end  162  of the middle recess  158  defines a conical recess  166  that angles downward as it extends toward the posterior end  146  of the body portion  134 . As will be described, the conical recess  166  enables the first fixation member  22  to be removed from the inferior implant body  18  of the distractable intervertebral implant  10  if so desired. 
     The middle recess  158  further defines a top surface  168  and opposing side surfaces  170  extending down from the top surface  168 . The side surfaces  170  extend toward each other as they extend down from the top surface  168 . That is, as the side surfaces  170  extend down from the top surface  168 , the direction in which the side surfaces  170  extend includes a lateral component that extends toward the other side surface  170 . Therefore, the side surfaces  170  and the top surface  168  define a dovetail shaped channel that receives the dovetail shaped middle region  54  of the inferior implant body  18 . It should be understood, however, that the middle recess may include configurations other than a dovetail shaped channel. For example, the middle recess may define an L-shaped channel, a greater angulation longitudinal ratchet, etc. 
     The second side regions  154  each include an anterior end  172  and a posterior end  176  that are angled downwards. That is, the anterior end  172  of the second side regions  154  includes a surface that extend down or otherwise toward the inferior implant body  18  as they extend toward the posterior end  146  of the body portion  134 , and the posterior end  176  of the second side regions  154  extend down or otherwise toward the inferior implant body  18  as they extend toward the anterior end  142  of the body portion  134 . As shown in  FIG.  3 A , the body portion  134  defines a bore  180  that extends through each anterior end  172 . As shown in  FIG.  3 D , each bore  180  is configured to receive one of the second and third fixation members  26  and  30 . Like the first fixation member  22 , the second and third fixation members can include a shaft  23  and a head  25  that is dimensioned larger than the shaft  23 . The bores  180  can likewise include a shaft-receiving region sized to receive the shaft  23 , and a head receiving region sized to receive the head  25  when the fixation members  26  and  30  are fully received by the bores  180 . The bores  180  can further be tapered and elongate along an angle toward the posterior end  146  of the body portion  134 , such that the fixation members  26  and  30  are also elongate along the angle toward the posterior end  146  of the body portion  134  when received in the bores  180 . The bores  180  can include locking mechanisms that engage locking mechanisms of the second and third fixation members  26  and  30 , for instance threads, locking pins, ratchets, rough surfaces, etc. along one or both of the shafts  23  and the heads  25 . It should be understood that at least one or both of the shafts  23  and the heads  25  can be substantially smooth and devoid of the locking mechanisms. Likewise, at least one or both of the shaft-receiving regions and the head-receiving regions can be substantially smooth and devoid of the locking mechanisms. 
     As shown in  FIGS.  3 A and  3 D , the superior implant body  14  can further include at least one graft window  190  such as a plurality of graft windows  190  that extend through at least one or more of the second side regions  154  as well as through the portion of the body portion  134  in which the recess  158  is defined. Generally, each graft window  190  is elongate in the longitudinal direction, though it should be understood that any shape may be desired. The graft windows  190  are configured to receive autogenous bone graft or bone graft substitute such as Chronos, or DBM. For instance, the graft windows  190  may be pre-filled with the bone graft. 
     As shown in  FIG.  3 D , the second and third fixation members  26  and  30  may be inserted into the bores  180  of the superior implant body  14  once the superior implant body  14  is fully slid onto the inferior implant body  18 . The second and third fixation members  26  and  30  extend at an angle toward the posterior end of the distractable intervertebral implant  10 . The second and third fixation members  26  and  30  engage the inferior endplate of the superior vertebral body to thereby securely attach the distractable intervertebral implant  10  to the superior vertebral body. 
     As shown in  FIGS.  4 A- 4 E , when the superior implant body  14  is fully slid onto the inferior implant body  18 , the graft windows  190  of the superior implant body  14  align with the graft windows  90  of the inferior implant body  18 . Therefore, the graft windows  90  and  190  define transverse channels that extend through the assembled implant  10 . The graft windows  190  may be pre-filled with the bone graft. 
     As shown in  FIGS.  4 A- 4 D , the superior implant body  14  lockingly engages the inferior implant body  18  with respect to at least one or both of relative rotation and relative translation along a direction angularly offset with respect to the longitudinal insertion direction I when the recess  158  of the superior implant body  14  has received the rail of the inferior implant body  18 . In that regard, the dovetail shaped recess  158  of the superior implant body  14  engages the dovetail shaped middle region  54  of the inferior implant body  18  when the inferior implant body  18  is received by the superior implant body  14  to create a form fit between the superior and inferior implant bodies  14  and  18 . This form fit eliminates rotational degrees of freedom between the superior and inferior implant bodies  14  and  18 . Other interlocking features between the superior implant body  14  and the inferior implant body  18  are envisioned to prevent translation in the longitudinal direction, such as a snap-action mechanism (e.g. PE-inlay or Prodisc-L). A third body (e.g. splint, pin, screw, bolt, glue) that is inserted after intraoperative assembly of the superior and inferior implant bodies  14  and  18  may also be used. 
     As shown in  FIGS.  4 C- 4 E , the bores  72  and  180  are conical in shape. The conical shaped bores  72 ,  180  are configured to prevent the fixation members  22 ,  26 , and  30  from being over inserted into the bores, and allow for angle stable fixation. The angle stable fixation prevents the fixation members not only from being over inserted but also from backing out. Thus, as each bore  72  and  180  receives its respective fixation members  22 ,  26 , and  30  the heads of the fixation members  22 ,  26 , and  30  will eventually abut the walls of the bores  72  and  180  to thereby prevent further insertion of the fixation members  22 ,  26 , and  30 . Such a configuration allows for a more stable fixation of the fixation members  22 ,  26 , and  30 . Furthermore, the angle stable connection between the fixation member&#39;s head and its counter part allow it to bear a bending moment. 
     As shown in  FIG.  4 E , the distractable intervertebral implant  10  may include marker pins  200 , which may be used in case of a radiolucent base material that would not be visible in fluoroscopy/x-ray equipment. As shown, marker pins  200  may be buried within the body portion  34  of the inferior implant body  18 . The marker pins  200  may be radioopaque to allow easy identification of the distractable intervertebral implant  10  in fluroscopique images. It should be understood that the implant  10  may include any number of pins  200 , and that the pins  200  may also be buried within the superior implant body  14 . Furthermore, instead of radiopaque marker pins  200 , it may be possible to use polymers, ceramics, or biomaterials that include barium sulfate, or a similar substance. Barium sulfate (that is either homogeneously or inhomegeneously distributed in the base material) allows to make a radiopaque base material visible under fluoroscopy/x-ray equipment. 
     As shown in  FIGS.  5 A- 5 D , both the inferior implant body  18  and the superior implant body  14  may act as distractors as they are individually slid into the intervertebral space  11 . As shown, in  FIG.  5 A , as the inferior implant body  18  is positioned within the intervertebral space  11  at least one of the superior vertebral body  12   a  and the inferior vertebral body  12   b  moves away from the other such that the superior and inferior vertebral bodies are separated by a first distance F 1 . The first distance F 1  may be substantially equal to the transverse height of the inferior implant body  18 . Once the inferior implant body  18  is properly positioned and attached to the inferior vertebral body  12   b , the superior implant body  14  may be slid or otherwise translated over the inferior implant body  18  and into the intervertebral space  11 . As shown in  FIG.  5 B , the angled posterior ends  176  of the superior implant body&#39;s second side regions  154  contact respective second side regions  58  of the inferior implant body  18 . Because of the angled posterior ends  176  of the superior implant body  14 , the superior implant body  14  will move toward the superior vertebral body  12   a  as the superior implant body  14  is slid over the inferior implant body  18 , as shown in  FIGS.  5 B- 5 D  to thereby cause at least one of the superior vertebral body  12   a  and the inferior vertebral body  12   b  to move away from the other such that the vertebral bodies are separated by a second distance F 2  that is greater than the first distance F 1 . In this way, continuous distraction is achieved until the superior implant body  14  is fully assembled with the inferior implant body  18 . As shown in  FIG.  5 D , the superior implant body  14  may move a distance H in an upward direction once it has been fully slid onto the inferior implant body  18 . The distance H as well as the degree of distraction may depend on the angle at which the posterior ends  176  extend toward the anterior end of the superior implant body  14 . 
     In operation, the inferior implant body  18  is first inserted into the intervertebral space. Once properly placed, the first fixation member  22  may be inserted into the bore  72  of the inferior implant body  18  and driven into the inferior vertebral body. Next the superior implant body  14  is pushed into the intervertebral space or otherwise slid over the inferior implant body  18 . During insertion of the superior implant body  14 , the superior implant body  14  slides over the inferior implant body  18 . As described in relation to  FIGS.  5 A- 5 D , as the superior implant body  14  is sliding onto the inferior implant body  18 , the superior implant body  14  moves up toward the superior vertebral body. Therefore, a continuous distraction of the inferior and superior vertebral bodies is achieved until the distractable intervertebral implant  10  is fully assembled. The superior implant body  14  interlocks with the inferior implant body  18  and builds a solid construct. The assembled implant  10  withstands translation and rotation in all six degrees of freedom. 
     Once the assembled implant  10  is properly positioned, the second and third fixation members  26  and  30  may be inserted into the bores  180  of the superior implant body  14 . The second and third fixation members  26  and  30  engage the inferior endplate of the superior vertebral body to thereby securely attach the superior implant body  14  and therefore the distractable intervertebral implant  10  to the superior vertebral body. 
     Because the distractable intervertebral implant  10  may be placed into the intervertebral space  11  by first inserting the inferior implant body  18  and then the superior implant body  14 , the distractable intervertebral implant  10  may be inserted into the intervertebral space  11  either from the anterior end of the patient or from the posterior end of the patient. In other words, by positioning the distractable intervertebral implant  10  in pieces rather than as a fully assembled construct the surgeon will be capable of accessing the intervertebral space  11  from the posterior end of the patient which is usually difficult, due to the limited amount of space. It should be understood that any surgical approach (i.e. anterior, antero-lateral, lateral, extraforaminal, transforaminal, and posterior) may be considered. 
     It should be appreciated that the distractable intervertebral implant  10  described herein can be configured so as to provide a range of numerous possible geometries and angular relationships. For example, while the superior implant body  14  is described as having angled posterior ends that cause the superior implant body  14  to move upwards and thereby act as a distractor, it is possible to include an angled anterior end on the inferior implant body  18  to cause the superior implant body  14  to distract as it is inserted. Furthermore, it is envisioned that the superior implant body  14  could be inserted into the intervertebral space prior to the insertion of the inferior implant body  18 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. Furthermore, it should be appreciated that the structure, features, and methods as described above with respect to any of the embodiments described herein can be incorporated into any of the other embodiments described herein unless otherwise indicated. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present disclosure.