Abstract:
An inter-vertebral-body (IVB) spacer may include a skeletal body and a pair of interchangeable contact pads. The skeletal body may be made of a rigid material for providing structure support, and the pair of contact pads may be made of a softer material for contacting the endplates of the vertebral bodies. Advantageously, the IVB spacer may be strong enough to withstand the pressure applied between the vertebral bodies yet soft enough to protect the vertebral bodies from being eroded. Moreover, the IVB spacer may have an inter-pad angle, which may be adjusted to adapt to patients with various vertebral bone structures. The inter-pad angle of the IVB spacer may be adjusted by simply selecting and replacing one of the contact pads.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present invention relates generally to the field of medical devices used in spinal fusion surgery, and more particularly to inter-vertebral-body spacers. 
         [0003]    2. Description of the Related Art 
         [0004]    Spinal fusion (a.k.a. spondylodesis or spndylosyndesis) is a surgical technique used for joining two or more vertebrae. Spinal fusion surgery may be appropriate for patients who have neurological deficits or severe pain which has not responded to conservative treatment. For example, spinal fusion may be appropriate for patients who suffer from degenerative disc disease, spinal disc herniation, discogenic pain, spinal tumor, vertebral fracture, scoliosis, kyphosis, spondylolisthesis, spondylosis, posterior Rami syndrome, and/or other degenerative spinal conditions. 
         [0005]    There are two main types of spinal fusion—posterolateral fusion and interbody fusion. In posterolateral fusion, a bone graft may be placed between the transverse processes of two successive vertebrae of a patient. In interbody fusion, a bone graft may be placed between two successive vertebral bodies of a patient. The surgeon may remove the spinal disc positioned between the two vertebral bodies, and may then place a spacer between the two vertebral bodies to maintain spine alignment and disc height. After that, the surgeon may fill the spacer with the bone graft, which may promote the fusion between the endplates of the two vertebral bodies. 
         [0006]    Conventional spacers are generally made of one type of material, which may be either too hard for the endplates of the vertebral bodies or too brittle to withstand the pressure applied by the vertebral bodies. For example, a spacer made solely of rigid metallic material may be too hard for the endplates, and it may erode the endplates. For another example, a spacer made solely of plastic material may be too brittle to withstand the pressure applied by the vertebral bodies, and it may shatter shortly after installation. In either situation, the conventional spacers may cause internal injuries to the patient&#39;s body, and they may require frequent replacement. 
         [0007]    Moreover, some conventional spacers are not adjustable. If a conventional spacer does not fit the vertebral body structure of a particular patient, a surgeon will need to replace that spacer and try a new one. According to standard surgical procedure, the spacer should be discarded once it is unpacked and has made contact with the patient. Hence, a good number of conventional spacers may be discarded during the fitting process. Because conventional spacers are generally expensive to manufacture, the practice of discarding unused spacers may drive up the cost of spinal fusion surgeries. 
         [0008]    Thus, there is a need to provide inter-vertebral-body spacer with improved durability and adjustability. 
       SUMMARY 
       [0009]    The present invention may provide an inter-vertebral-body (IVB) spacer for use in spinal fusion surgery. The IVB spacer may be made of a rigid material for providing structural support and a softer material for contacting the endplates of the vertebral bodies. Advantageously, the IVB spacer may be strong enough to withstand the pressure applied between the vertebral bodies yet soft enough to protect the vertebral bodies from being eroded. Moreover, the IVB spacer may have an inter-pad angle, which may be adjusted to adapt to patients with various vertebral bone structures. The inter-pad angle of the IVB spacer may be adjusted by selecting and replacing one of the contact pads. As such, only a small portion of the IVB spacer will be discarded during the adjustment process while the majority portion of the IVB spacer will be fully utilized. Advantageously, the IVB spacer may help reduce overall equipment costs of the spinal fusion surgery and provide a better and more accurate and comfortable fit to the patient. 
         [0010]    In one embodiment, an inter-vertebral-body (IVB) spacer may be used for placement between first and second vertebral bodies, and the spacer may comprise a first pad having a first contact surface configured to contact the first vertebral body, a second pad having a second contact surface configured to contact the second vertebral body, and a skeletal body positioned between the first and second pads, and having a first frame configured to secure the first pad, support the first contact surface, and arrange the first contact surface along a first plane, a second frame configured to secure the second pad, support the second contact surface, and arrange the second contact surface along a second plane, such that the second plane forms an inter-pad angle with the first plane, and a plurality of pillars coupled between the first and second frames, and configured to maintain a distance between the first and second frames. 
         [0011]    In another embodiment, an inter-vertebral-body (IVB) spacer may be used for placement between first and second vertebral bodies, and the spacer may comprise a first thermal plastic pad having a first contact surface configured to contact the first vertebral body, a second thermal plastic pad having a second contact surface configured to contact the second vertebral body, a rigid skeletal body positioned between the first and second pads, and having a first frame configured to secure the first pad, support the first contact surface, and arrange the first contact surface along a first plane, a second frame configured to secure the second pad, support the second contact surface, and arrange the second contact surface along a second plane, such that the second plane forms an inter-pad angle with the first plane, and a plurality of pillars coupled between the first and second frames, and configured to maintain a distance between the first and second frames, and a stopper configured to be coupled to the rigid skeletal body and prevent the first and second thermal plastic pads from detaching from the first and second frames. 
         [0012]    In yet another embodiment, an inter-vertebral-body (IVB) spacer may be used for placement between first and second vertebral bodies, and the spacer may comprise a first thermal plastic pad having a first contact surface configured to contact the first vertebral body, a second thermal plastic pad having a second contact surface configured to contact the second vertebral body, a rigid skeletal body positioned between the first and second pads, and having a first frame configured to secure the first pad, support the first contact surface, and arrange the first contact surface along a first plane, a second frame configured to secure the second pad, support the second contact surface, and arrange the second contact surface along a second plane, such that the second plane forms an inter-pad angle with the first plane, and a plurality of pillars coupled between the first and second frames, and configured to maintain a distance between the first and second frames, a stopper configured to be coupled to the rigid skeletal body and prevent the first and second thermal plastic pads from detaching from the first and second frames, and an anchoring device disposed between the first and second frames of the rigid skeletal body, and configured to protrude the first and second thermal plastic pads and anchor the rigid skeletal body to the first and second vertebral bones. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Other systems, methods, features, and advantages of the present invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the present invention. In the drawings, like reference numerals designate like parts throughout the different views, wherein: 
           [0014]      FIG. 1A  shows a perspective view of an inter vertebral body (IVB) spacer being placed in between two vertebral bodies according to an embodiment of the present invention; 
           [0015]      FIG. 1B  shows a perspective view of the IVB spacer according to an embodiment of the present invention; 
           [0016]      FIG. 1C  shows a top view of the IVB spacer being placed on top of a vertebral body according to an embodiment of the present invention; 
           [0017]      FIGS. 2A-2E  show various perspective views of the IVB spacer including the assembly process of the IVB spacer according to an embodiment of the present invention; 
           [0018]      FIGS. 3A-3C  show various dimensions of the IVB spacer according to an embodiment of the present invention; 
           [0019]      FIGS. 4-6  show the side views of the IVB spacers with various inter-pad angles according to various embodiments of the present invention; 
           [0020]      FIGS. 7A-7C  show a perspective view, an exploded view, and a side view of an IVB spacer having an anchoring device according to an embodiment of the present invention; 
           [0021]      FIGS. 8A-8B  show the deployment of the anchoring device according to an embodiment of the present invention; 
           [0022]      FIGS. 9A-9B  show a perspective view and an exploded view of an IVB spacer according to an alternative embodiment of the present invention; and 
           [0023]      FIGS. 10A-10D  show various views of an alternative skeletal body according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Apparatus, systems and methods that implement the embodiment of the various features of the present invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate some embodiments of the present invention and not to limit the scope of the present invention. Throughout the drawings, reference numbers are re-used to indicate correspondence between reference elements. In addition, the first digit of each reference number indicates the figure in which the element first appears. 
         [0025]      FIG. 1A  shows a perspective view of an inter-vertebral-body (IVB) spacer  110  being placed in between two vertebral bodies  102  and  103  according to an embodiment of the present invention. Generally, the IVB spacer  110  may be used in inter-vertebral-body (interbody) fusion surgery for facilitating the fusion of two or more vertebral bodies. A patient may have a defective spinal column  101 , which may be caused by a damaged or degenerated inter-vertebral disc between a first vertebral body  102  and a second vertebral body  103 . To correct the defective spinal column  101 , a surgeon may remove the damaged or degenerated inter-vertebral disc and then insert the IVB spacer  110  in between the first and second vertebral bodies  102  and  103 . 
         [0026]      FIG. 1B  shows a perspective view of the IVB spacer  110  according to an embodiment of the present invention. Generally, the IVB spacer  110  may include a first (top) pad, a second (bottom) pad  140 , a skeletal body (case)  120 , and a stopper  150 . The first pad  130  may be used for contacting the first vertebral body  102 , while the second pad  140  may be used for contacting the second vertebral body  103 . The skeletal body  120  may be used for supporting the first and second pads  102  and  103 . The stopper  150  may be used for preventing the first and second pads  130  and  140  from being detached from the skeletal body  120 . Together, the skeletal body  120  and the first and second pads  130  and  140  may provide structural support and stabilization between the first and second vertebral bodies  102  and  103 . The skeletal body  120  may be made of non-brittle and/or rigid materials. The first and second pads  130  and  140  may be made of high endurance and corrosive resistance materials. Moreover, the first and second pads  130  and  140  may be made of a material having a modulus that is approximately the same as the modulus of the human bone. 
         [0027]    In one embodiment, for example, the skeletal body  120  may be made of metal, metal alloy, ceramic, pyrolictic carbon, and/or carbon fiber, while the first and second pads  130  and  140  may be made of ceramic, pyrolictic carbon, carbon fiber, and/or thermal plastic material. In another embodiment, for example, the skeletal body  120  may be made of titanium, titanium alloys, titanium oxide, cobalt chrome, 316L stainless steel, nitinol and/or nickel alloys, while the first and second pads  130  and  140  may be made of (polyether ether ketone) PEEK material and/or ultra high molecular weight polyethylene (UHMWPE). In yet another embodiment, for example, the skeletal body  120  may be made of titanium, while the first and second pads  130  and  140  may be made of PEEK material. 
         [0028]      FIG. 1C  shows a top view of the IVB spacer  110  being placed on top of the second vertebral body  103 . The IVB spacer  110  may have a front side  112  and a back side  114 . Particularly, the front side  112  may have a wide curvy profile aligning with the anterior ridge side of the vertebral body  103 , while the narrower back side  114  may have a linear profile aligning with the posterior ridge side of the second spinal segment  103 . The IVB spacer  110  may have one or more fusion channels, which may allow a bone putty material (autologous bone graft) to fill up a space between the first and second vertebral bodies  102  and  103 . For example, the IVB spacer  110  may have a first (left) fusion channel  113  and a second (right) fusion channel  115 , both of which may extend vertically through the IVB spacer  110 . Accordingly, the bone putty material may contact and connect the first and second vertebral bodies  102  and  103  by filling up the first and second fusion channels  113  and  115 . 
         [0029]      FIG. 2A  shows an exploded view of the IVB spacer  110 . Generally, the first and second pads  130  and  140  may share similar structural features. For example, the first pad  130  may have a first contact surface  232  for contacting the first vertebral body  102 , and the second pad  140  may have a second contact surface  242  for contacting the second vertebral body  103 . For another example, the first pad  130  may have a first assembly surface  237  for contacting one side of the skeletal body  120 , and the second pad  140  may have a second assembly surface  247  for contacting another side of the skeletal body  120 . The first contact surface  232  and the first assembly surface  237  may form a first insertion angle, while the second contact surface  242  and the second assembly surface  247  may form a second insertion angle. Together, the first and second insertion angles may be combined to form an inter-pad angle, which may exactly match or be substantially similar to a lordotic angle between the first and second vertebral bodies  102  and  103  of a particular patient. 
         [0030]    Moreover, the first pad  130  may have first and second fusion openings  233  and  235 , and the second pad  140  may have third and fourth fusion openings  243  and  245 . Together, the first and third fusion openings  233  and  243  may help define the first fusion channel  113 , while the second and fourth fusion openings  235  and  245  may help define the second fusion channel  115 . 
         [0031]    Furthermore, the first and second pads  130  and  140  may include one or more alignment devices and/or mechanisms, which may be used for aligning the first and second pads  130  and  140  with the skeletal body  120 . For example, the first pad  130  may have a first alignment bar  236 , and the second pad  140  may have a second alignment bar  246 . In one embodiment, each of the first and second alignment bars  236  and  246  may be implemented by a rectangular bar with a rectangular cross section. In another embodiment, each of the first and second alignment bars  236  and  246  may be implemented by a rectangular bar with a willow-tail cross section. 
         [0032]    The skeletal body  120  may be used for supporting and securing the first and second pads  130  and  140 . Generally, the skeletal body  120  may include a first (top) frame  222 , a second (bottom) frame  224 , and a plurality of pillars  226 , which may be coupled between the first and second frames  222  and  224 . The first frame  222  may be used for contacting and supporting the first assembly surface  237  of the first pad  130 , while the second frame  224  may be used for contracting and supporting the second assembly surface  247  of the second pad  140 . The plurality of pillars  226  may be used for providing structural support between the first and second frames  222  and  224 , such that the first and second frames  222  and  224  may maintain a constant and evenly distributed distance. 
         [0033]    To align the first pad  130  with the skeletal body  120 , the first frame  222  may have a first alignment trench for receiving and guiding the first alignment bar  236  of the first pad  130 . As shown in  FIG. 2B , the first alignment bar  236  may be inserted into the first alignment trench  223 . The first pad  130  may slide from the front side  112  to the back side  114  of the first frame  222 . Because of the willow-tail cross section, the first alignment trench  223  may prevent the first alignment bar  236  from moving in a direction that is perpendicular to the first frame  222 . That is, the first alignment trench  223  may allow the first alignment bar  236  to move only in a parallel direction with respect to the first frame  222 . 
         [0034]    To align the second pad  140  with the skeletal body  120 , the second frame  224  may have a second alignment trench for receiving and guiding the second alignment bar  246  of the second pad  140 . As shown in  FIG. 2C , the second alignment bar  246  may be inserted into the second alignment trench  225 . The second pad  140  may slide from the front side  112  to the back side  114  of the second frame  224 . Because of the willow-tail cross section, the second alignment trench  225  may prevent the second alignment bar  246  from moving in a direction that is perpendicular to the second frame  224 . That is, the second alignment trench  225  may allow the second alignment bar  246  to move only in a parallel direction with respect to the second frame  224 . 
         [0035]    The first and second pads  130  and  140  may be replaced and exchanged easily. As such, surgeons may optimize the result of interbody fusion procedures by trying and switching one of the first and second pads  130  and  140 . Particularly, surgeons may select the first or second pad  130  or  140  with the appropriate geometric properties and material characteristic. For example, surgeons may select the first and second pads  130  and  140  from a group of pads that have a specific range of insertion angles. For another example, surgeons may select the first and second pads  130  and  140  from a group of pads that have a specific shape and size. For yet another example, surgeons may select the first and second pads  130  and  140  from a group of pads that are made of a specific type material. As a result, surgeons may keep at least one of the two pads and the skeletal body  120  during the optimization process. Advantageously, less material may go into waste during the optimization process, and the equipment cost of the interbody fusion surgery may therefore be reduced. This process can be repeated after the interbody fusion surgery due to change in condition of the patient. Particularly, one of the first and second pads  130  and  140  may be removed and replaced by another pad, which may have similar or different geometric properties and material characteristics. 
         [0036]    After the first and second pads  130  and  140  are properly received, aligned, and secured by the respective first and second frames  222  and  224  of the skeletal body  120 , a partially assembled IVB spacer  250  may be formed. As shown in  FIG. 2D , the partially assembled IVB spacer  250  may be handled by a pair of surgical forceps  282 . In one embodiment, the skeletal body  120  may include a pair of manipulation trails to provide easy access for the pair of surgical forceps  282 . An insertion driver  286  may be used for inserting the partially assembled IVB spacer  250  into the space between the first and second vertebral bodies  102  and  103 . To cooperate with the insertion driver  286 , the skeletal body  120  may have a center member  228  coupled between the first and second frames  222  and  224 . The center member  228  may define an installation channel  227 , which may be used for receiving the insertion driver  286 . 
         [0037]    After the partially assembled IVB spacer  250  is properly placed between the first and second vertebral bodies  102  and  103 , the stopper  150  may be used for locking the first and second pads  130  and  140  in place. Generally, the stopper  150  may include a screw head  256 , a threaded shaft  254 , and a flange  252  coupled between the flange  252  and the screw head  256 . The threaded shaft  254  may be inserted into the installation channel  227  and engage an inner threaded section (not shown) therein. The screw head  256  may receive a locking force, thereby causing the threaded shaft  254  to further engage the installation channel  117 . When the threaded shaft  254  substantially engages the installation channel  117 , the screw head  256  may cause the flange  252  to push against the front sides of the first and second pads  130  and  140 . The flange  252  may block the first and second pads  130  and  140 , such that the first and second alignment bars  236  and  246  are stopped from sliding out of the first and second alignment trenches  223  and  225 . When the IVB spacer  110  is fully assembled, the flange  252  may prevent the first and second pads  130  and  140  from being detached from the first and second frames  222  and  224 . 
         [0038]    The first and second pads  130  and  140  may include one or more anchoring devices or mechanisms to restrain the movement of the IVB spacer  110  with respect to the first and second vertebral bodies  102  and  103 . In one embodiment, for example, the first contact surface  232  of the first pad  130  may have a first set of spikes (keels)  234 , and the second contact surface  242  of the first pad  140  may have a second set of spikes (keels)  244 . The first and second set of spikes (keels)  234  and  244  may incline or point away from the direction of insertion. 
         [0039]    Once the IVB spacer  110  is properly positioned between the first and second vertebral bodies  102  and  103 , the first set of spikes  234  may anchor the first pad  130  to the endplate of the first vertebral body  102 , while the second set of spikes  244  may anchor the second pad  140  to the endplate of the second vertebral body  103 . Accordingly, the first and second sets of spikes  234  and  244  may help stabilize the IVB spacer  110  between the first and second vertebral bodies  102  and  103 . Moreover, the first and second sets of spikes  234  and  244  may help align the first and second vertebral bodies  102  and  103  and hold them in place. Advantageously, the IVB spacer  110  may promote the stability between the first and second vertebral bodies  102  and  103 . 
         [0040]    After the IVB spacer  110  is properly positioned and anchored between the first and second vertebral bodies  102  and  103 , a surgeon may inject the bone putty into the IVB spacer  110  via the front openings of the skeletal body  120 . The bone putty may reach and contact the first and second vertebral bodies  102  and  103  via the first and second fusion channels  113  and  115 . The first fusion channel  113  may be a passage that may coincide with the first fusion opening  233  of the first pad  130 , a left segment of the top frame  222 , a left segment of the second frame  224 , and the third fusion opening  243  of the second pad  140 . Similarly, the second fusion channel  115  may be a passage that may coincide with the second fusion opening  235  of the first pad  130 , a right segment of the top frame  222 , a right segment of the second frame  224 , and the fourth fusion opening  245  of the second pad  140 . 
         [0041]    To prevent the bone putty from reaching the spinal cord, the skeletal body  120  may include a back stopper  229 , which may be used for stopping the bone putty from leaving the back side of the skeletal body  120 . After the bone putty substantially occupies the first and second fusion channels  113  and  114 , the first vertebral body  102  may be connected to the second vertebral body  103  by the bone putty. As a result, the interbody fusion between the first and second vertebral bodies  102  and  103  may take place. 
         [0042]    The discussion now turns to various dimensions of the IVB spacer  110 .  FIG. 3A-3C  show various dimensions of the IVB spacer. Referring to  FIG. 3A , the first pad  130  may have a first front thickness L 31 , which may range, for example, from about 1.5 mm to about 5.5 mm, and the second pad  140  may have a second front thickness L 41 , which may range, for example, from about 1.5 mm to about 5.5 mm. In one embodiment, the first front thickness L 31  may be about 3.5 mm, and the second front thickness L 41  may be about 3.5 mm. 
         [0043]    The skeletal body  120  may have a skeletal height L 21 , which may range from about 5 mm to about 15 mm, and a front skeletal width L 22 , which may range from about 15 mm to about 40 mm. In one embodiment, the skeletal height L 21  may be about 10 mm, and the front skeletal width L 22  may be about 30 mm. The front openings of the skeletal body  120  may each have a front opening width L 25 , which may range, for example, from about 12 mm to about 18 mm. In one embodiment, the front opening width L 25  may be about 15 mm. The installation channel  227  may have a diameter D 21 , which may range, for example, from about 2.5 mm to about 4.5 mm. In one embodiment, the diameter D 21  may be about 3.5 mm. 
         [0044]    Referring to  FIG. 3B , the first set of spikes  234  may each have a first spike height L 32 , which may range, for example, from about 0.5 mm to about 0.7 mm, and the second set of spikes  244  may each have a second spike height L 42 , which may range, for example, from about 0.5 mm to about 0.7 mm. In one embodiment, the first and second spike height L 32  and L 42  may each be about 0.6 mm. 
         [0045]    The flange  252  of the stopper  150  may have a flange thickness L 51 , which may range, for example, from about 0.5 mm to about 1 mm, and a flange height L 52 , which may range, for example, from about 5 mm to about 7 mm. In one embodiment, the flange thickness L 51  may be about 0.75 mm, and the flange height L 52  may be about 5.6 mm. The skeletal body  120  may have a skeletal body length L 23 , which may range, for example, from about 20 mm to about 30 mm. In one embodiment, the skeletal body length L 23  may be about 25 mm. The side openings of the skeletal body  120  may have a side opening width L 24 , which may range, for example, from about 15 mm to about 25 mm. In one embodiment, the side opening width L 24  may be about 25 mm. 
         [0046]    Referring to  FIG. 3C , the skeletal body  120  may have a back skeletal width L 27 , which may range, for example, from about 20 mm to about 30 mm. In one embodiment, the back skeletal width L 27  may be about 23 mm. The back openings of the skeletal body  120  may each have a back opening width L 28 , which may range, from about 7 mm to about 9 mm. In one embodiment, the back opening width L 28  may be about 8 mm. 
         [0047]    The discussion now turns to the adjustability of the inter-vertebral-body (IVB) spacer  110 .  FIGS. 4-6  show the side views of the IVB spacers  110  with various inter-pad angles according to various embodiments of the present invention. Referring to  FIG. 4 , the first pad  430  may have a first narrow insertion angle  402 , which may be formed between the first contact surface  432  and the first assembly surface  437 . The second pad  440  may have a second narrow insertion angle  404 , which may be formed between the second contact surface  442  and the second assembly surface  447 . The first and second narrow insertion angles  402  and  404  may each range, for example, from about 1 degree to about 7 degrees. In one embodiment, the first and second insertion angles  402  and  404  may each be about 3.5 degrees. 
         [0048]    After being secured by the skeletal body  120 , the first contact surface  432  of the first pad  130  may be arranged to align with a first plane  410 , and the second contact surface  442  of the second pad  440  may be arranged to align with a second plane  420 . Together, the first and second planes  410  and  420  may form a narrow inter-pad angle  401 , which may range, for example, from about 4 degrees to about 10 degrees. In one embodiment, the narrow inter-pad angle  401  may be about 7 degrees. Because the first assembly surface  437  is arranged to be substantially parallel with the second assembly surface  447 , the sum of the first and second narrow insertion angles  402  and  404  may determine the value of the narrow inter-pad angle  401 . Hence, by selecting the first and second pads  430  and  440  with narrow insertion angles, the IVB spacer  110  may adapt to patients with small lordotic angles between successive vertebral bodies. 
         [0049]    Referring to  FIG. 5 , the first pad  530  may have a first wide insertion angle  502 , which may be formed between the first contact surface  532  and the first assembly surface  537 . The second pad  540  may have a second wide insertion angle  504 , which may be formed between the second contact surface  542  and the second assembly surface  547 . The first and second wide insertion angles  502  and  504  may each range, for example, from about 5 degrees to about 10 degrees. In one embodiment, the first and second wide insertion angles  502  and  504  may each be about 7 degrees. 
         [0050]    After being secured by the skeletal body  120 , the first contact surface  532  of the first pad  530  may be arranged to align with a third plane  510 , and the second contact surface  542  of the second pad  540  may be arranged to align with a fourth plane  520 . Together, the third and fourth planes  510  and  520  may form a wide inter-pad angle  501 , which may range, for example, from about 10 degrees to about 20 degrees. In one embodiment, the wide inter-pad angle  501  may be about 14 degrees. Because the first assembly surface  537  is arranged to be substantially parallel with the second assembly surface  547 , the sum of the first and second wide insertion angles  502  and  504  may determine the value of the wide inter-pad angle  501 . Hence, by selecting the first and second pads  530  and  540  with wide insertion angles, the IVB spacer  110  may adapt to patients with large lordotic angles between successive vertebral bodies. 
         [0051]    Referring to  FIG. 6 , the first pad  530  may have the first wide insertion angle  502 , which may be formed between the first contact surface  532  and the first assembly surface  537 . The second pad  440  may have the second narrow insertion angle  404 , which may be formed between the second contact surface  442  and the second assembly surface  447 . 
         [0052]    After being secured by the skeletal body  120 , the first contact surface  532  of the first pad  530  may be arranged to align with the third plane  510 , and the second contact surface  442  of the second pad  440  may be arranged to align with the second plane  420 . Together, the third and second planes  510  and  420  may form an intermediate inter-pad angle  601 , which may range, for example, from about 7 degrees to about 15 degrees. In one embodiment, the intermediate inter-pad angle  601  may be about 10 degrees. Because the first assembly surface  537  is arranged to be substantially parallel with the second assembly surface  447 , the sum of the first wide and second narrow insertion angles  502  and  404  may determine the value of the intermediate inter-pad angle  601 . Hence, by selecting the first and second pads  530  and  440 , the IVB spacer  110  may adapt to patients with medium lordotic angles between successive vertebral bodies. 
         [0053]    In  FIGS. 7A-7C , an alternative inter-vertebral-body (IVB) spacer  700  is shown according to an alternative embodiment of the present invention. The alternative IVB spacer  700  may be similar to the IVB spacer  110 . For example, the alternative IVB spacer  700  may include a skeletal body  720 , which may have a first frame  722 , a second frame  724 , and a plurality of pillars  726  coupled between the first and second frames  722  and  724 . For another example, the alternative IVB space  700  may include a first pad  730 , which may be coupled to the first frame  722 , and a second pad  740 , which may be coupled to the second frame  724 . The first and second pads  730  and  740  may be used for contacting the first and second vertebral bodies  102  and  103 , respectively. The skeletal body  720  may be used for supporting the first and second pads  730  and  740 . 
         [0054]    The skeletal body  720  may be made of rigid materials, while the first and second pads  730  and  740  may be made of high endurance and corrosive resistance material. In one embodiment, for example, the skeletal body  720  may be made of metal, metal allowy, ceramic, pyrolictic carbon, and/or carbon fiber, while the first and second pads  730  and  740  may be made of ceramic, pyrolictic carbon, carbon fiber, and/or thermal plastic material. In another embodiment, for example, the skeletal body  720  may be made of titanium, titanium alloys, titanium oxide, cobalt chrome, 316L stainless steel, nitinol and/or nickel alloys, while the first and second pads  730  and  740  may be made of polyether ether ketone (PEEK) material and/or ultra high molecular weight polyethylene (UHMWPE). In yet another embodiment, the skeletal body  720  may be made of titanium, while the first and second pads  730  and  740  may be made of PEEK material. 
         [0055]    Despite the above similarities, the alternative IVB spacer  700  may be different from the IVB spacer  110  in at least one aspect. For example, the IVB spacer  700  may include an anchoring device  760 , which may be used for anchoring the IVB spacer  700  in between two successive vertebral bodies. The anchoring device  760  may be an anchoring clip, which may be positioned in the center of the skeletal body  720 . The anchoring device  760  may be positioned between the first and second frames  722  and  724  of the skeletal body  720 . More specifically, the anchoring device  760  may be disposed within a center compartment  729 , which may be positioned adjacent to the first and second fusion channels  711  and  713 . The anchoring device  760  may be held by the center compartment  729 , such that the anchoring device  760  may be restrained from having any lateral or longitudinal movement in relative to the skeletal body  720 . 
         [0056]    The anchoring device  760  may include a first keel section  764 , a second keel section  766 , a first lever  765  coupled to the first keel section  764 , a second level  767  coupled to the second keel section  766 , and a flexible hinge  762  coupled between the first and second levers  765  and  767 . The flexible hinge  762  may allow a relative movement between the first and second keel sections  764  and  766 . More specifically, the first and second keel sections  764  and  766  may move away from each other when a pair of deployment forces is directed against the first and second inner surfaces  761  and  763 . The first and second keel sections  764  and  766  may resume to their original positions when the pair of deployment forces is removed. 
         [0057]    The keels of the first and second keel sections  764  and  766  may incline or point towards the direction of insertion of the IVB spacer  700 . When deployed, the keels of the first and second keel sections  764  and  766  may engage the first and second vertebral bodies  102  and  103 , respectively. As a result, the keels of the first and second keel sections  764  and  766  may anchor the IVB spacer  700  to the first and second vertebral bodies  102  and  103  and prevent the IVB spacer  700  from moving towards the posterior side of the first and second vertebral bodies  102  and  103 . 
         [0058]    After the first and second pads  730  and  740  are properly aligned, received, and secured by the skeletal body  720 , the anchoring device  760  may be inserted into the skeletal body  720 . For example, the anchoring device  760  may be inserted into the skeletal body  720  via the installation channel  727 . Next, the stopper  750  may be coupled to the installation channel  727 . The stopper  750  may have a screw head  758 , a threaded section  754  coupled to the screw head  758 , a flange  752  coupled between the threaded section  754  and the screw head  758 , and a deployment head  756  coupled to the threaded section  754 . 
         [0059]    The screw head  758  may be used for receiving a locking force, which may cause the threaded section  754  to be substantially engaged to the installation channel  727 . The flange  752  may be used for preventing the first and second pads  730  and  740  from being detached from the skeletal body  720 . The deployment head  756  may be used for deploying the anchoring device  760 . Advantageously, the stopper  750  may be used for simultaneously locking the first and second pads  730  and  740  and deploying the anchoring device  760 . 
         [0060]    When the IVB spacer  700  is being properly positioned between the first and second vertebral bodies  102  and  103 , the anchoring device  760  may be deployed.  FIGS. 8A-8B  show the process of deploying the anchoring device  760  according to an embodiment of the present invention. Initially, the deployment head  756  of the stopper  750  may contact the first and second inner surfaces  761  and  763  of the anchoring device  760 . As the screw head  758  receives the locking force  801 , the threaded section  754  may be substantially engaged to the installation channel  727 . 
         [0061]    The substantial engagement between the threaded section  754  and the installation channel  727  may create an insertion force  802 , which may push the deployment head  756  against the first and second inner surfaces  761  and  763  of the anchoring device  760 . As a result, the deployment head  756  may assert the pair of deployment forces  803  and  804  against the first and second inner surfaces  761  and  763 , respectively, thereby pushing the first and second keel sections  764  and  766  away from each other. 
         [0062]      FIG. 8B  shows a side view of the IVB spacer  700  when the anchoring device  760  is deployed. At the deployed state, the first keel section  764  may protrude from the first frame  722  of the skeletal body  720  and then from a first slot  735  of the first pad  730 . Similarly, the second keel section  766  may protrude from the second frame  724  of the skeletal body  720  and then from a second slot  745  of the second pad  740 . The keels of the first and second keel sections  764  and  766  may incline or point towards the insertion direction of the IVB spacer  700 . 
         [0063]    Upon engaging the first and second vertebral bodies  102  and  103 , the keels of the first and second keel sections  764  and  766  may prevent the IVB spacer  700  from moving towards the posterior side of the first and second vertebral bodies  102  and  103 . The anchoring device  760  and the first and second pads  730  and  740  may cooperate with one another to substantially stabilize the IVB spacer  700  in between the space defined by the first and second vertebral bodies  102  and  103 . The stability provided the IVB spacer  700  may advantageously enhance the quality and rate of interbody fusion. 
         [0064]      FIGS. 9A-9B  show a perspective view and an exploded view of an IVB spacer  900  according to an alternative embodiment of the present invention. Generally, the IVB spacer  900  may include a first ellipsoidal pad  930 , a second ellipsoidal pad  940 , a skeletal body  920 , a stopper  950 , and an anchoring device  960 . The skeletal body  920  may be coupled between the first and second ellipsoidal pads  930  and  940 . The anchoring device  960  may be positioned within the skeletal body  920 , and it may be deployed when the stopper  950  is substantially engaged to the skeletal body  920 . 
         [0065]    The first and second ellipsoidal pads  930  and  940  may be similar to the first and second pads  130  and  140  as discussed in  FIGS. 2A-2E . For example, the first ellipsoidal pad  930  may have a first contact surface and a first assembly surface, and the second ellipsoidal pad  940  may have a second contact surface and a second assembly surface. The first and second contact surfaces may each have a set of spikes inclining or pointing away from the direction of insertion. As such, the set of spikes may be used for anchoring the respective first or second ellipsoidal pads  930  or  940  to the endplates of the vertebral bodies. 
         [0066]    The first ellipsoidal pad  930  may have a first alignment bar  936  formed on the first assembly surface, and the second ellipsoidal pad  940  may have a second alignment bar  646  formed on the second assembly surface. The first and second alignment bars  936  and  946  may be received and secured by the skeletal body  920 . As such, the first and second ellipsoidal pads  930  and  940  may be attached to the skeletal body  920 . Moreover, the stopper  950  may be used for preventing the first and second ellipsoidal pads  930  and  940  from being detached from the skeletal body  920 . 
         [0067]    Before the stopper  950  is substantially coupled to the skeletal body  920 , the first and second ellipsoidal pads  930  and  940  may be slid in and out of the skeletal body  920  relatively easily. The first and second ellipsoidal pads  930  and  940  may come with different insertion angles and/or sizes to accommodate patients with various vertebral body structures. A surgeon may adjust the IVB spacer  900  by simply switching one of the first and second ellipsoidal pads  930  and  940 . That is, the surgeon does not need to discard the whole IVB spacer  900  during the adjustment process. 
         [0068]    Advantageously, most parts of the IVB spacer  900  may be fully utilized, and the equipment costs of the spinal fusion may be reduced. Moreover, the first and second ellipsoidal pads  930  and  940  may each have a shape that matches the footprint of the endplates of the vertebral bodies. Therefore, the first and second ellipsoidal pads  930  and  940  may provide good contact with the vertebral bodies. 
         [0069]    As shown in  FIGS. 10A-10D , the skeletal body  920  may have a first (top) ellipsoidal frame  1022 , a second (bottom) ellipsoidal frame  1024 , a pressure redistribution member  1026  coupled between the first and second ellipsoidal frames  1022  and  1024 . The first ellipsoidal frame  1022  may define a first alignment trench  1023  for receiving and guiding the first alignment bar  936  of the first ellipsoidal pad  930 . Similarly, the second ellipsoidal frame  1024  may define a second alignment trench  1025 , which may be used for receiving and guiding the second alignment bar  946  of the second ellipsoidal pad  940 . 
         [0070]    The skeletal body  920  may include a center member  1030 , which may be coupled between the first and second ellipsoidal frames  1022  and  1024 . The center member  1030  may define an installation channel  1032  for engaging the stopper  950 . Moreover, the center member  1030  may help define the first and second fusion channels  1013  and  1015  by dividing both the first and second ellipsoidal frames  1022  and  1024  in the middle. Furthermore, the center member  1030  may have a center compartment  1034  for placing the anchoring device  960 . 
         [0071]    The pressure redistribution member  1026  may be used for implementing the shock absorbing functionality of the spinal disc. Particularly, the pressure redistribution member  1026  may balance and evenly distribute the pressure received by the first and second ellipsoidal frames  1022  and  1024 . As such, the IVB spacer  900  may protect the vertebral bodies from sudden and/or uneven impact redistributing the pressure evenly across the surfaces of the vertebral bodies. The pressure redistribution member  1026  may be implemented by various structures. 
         [0072]    In one embodiment, for example, the pressure redistribution member  1026  may be implemented by a set or stack of wave lines or structures, which may function as a contiguous pressure redistributor between the first and second ellipsoidal frames  1022  and  1024 . The set of wave lines may have an up and down configuration in the shape of a wave or a curve. The stack of wave lines may be substantially rigid with little to no displacement. Alternatively, the stack of wave lines may be adjustable, replaceable, and/or removable. As such, the height of the pressure redistribution member  1026  may have an adjustable range of about 2%. Each of the wave lines may contact with one or more wave lines at one or more locations. The stack of wave lines may form a mesh cylindrical membrane surrounding a cylindrical space defined by the first and second ellipsoidal frames  1022  and  1024 . Advantageously, the cylindrical membrane may help retain the bone putty within the first and second fusion channels  1013  and  1015  during the spinal fusion process. In another embodiment, for example, the pressure redistribution member  1026  may be implemented by a series of helicoidal wave lines. 
         [0073]    Exemplary embodiments of the invention have been disclosed in an illulstrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents.