Abstract:
Intervertebral implants and associated methods of implantation and treatment are provided. In one aspect, an intervertebral implant for positioning between an upper vertebra and a lower vertebra is provided. The implant includes an upper endplate, a lower endplate, and at least one support having a variable stiffness positioned between the upper and lower endplates. In some instances, the implant includes a sensing element for monitoring a characteristic of the intervertebral implant, a processor for determining a desired stiffness of the supports based on the characteristic monitored by the sensing element, and an actuator for adjusting the stiffness of the supports to the desired stiffness. In another aspect, a prosthetic device for a spinal joint is provided. In yet another aspect, a method of treating a motion segment of a vertebral column is provided.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the present disclosure relate generally to intervertebral implants and associated methods of implantation and treatment. 
       BACKGROUND 
       [0002]    Within the spine, the intervertebral disc functions to stabilize and distribute forces between vertebral bodies. It comprises a nucleus pulposus which is surrounded and confined by the annulus fibrosis. 
         [0003]    Intervertebral discs are prone to injury and degeneration. For example, herniated discs typically occur when normal wear or exceptional strain causes a disc to rupture. Degenerative disc disease typically results from the normal aging process, in which the tissue gradually loses its natural water and elasticity, causing the degenerated disc to shrink and possibly rupture. Intervertebral disc injuries and degeneration may be treated by fusion of adjacent vertebral bodies or by replacing the intervertebral disc with an implant, also known as a prosthesis or prosthetic device. Generally, fusion of the adjacent vertebral bodies prevents movement between the adjacent vertebrae and the range of motion provided by the natural intervertebral disc. Some implants, on the other hand, preserve at least some of the range of motion provided by the natural intervertebral disc. 
         [0004]    Although existing devices and methods associated within intervertebral implants have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. The devices and methods in this disclosure overcome one or more of the shortcomings of the prior art. 
       SUMMARY 
       [0005]    In one aspect, a spinal implant is provided. 
         [0006]    In a further aspect, an intervertebral implant for positioning between an upper vertebra and a lower vertebra is provided. The intervertebral implant comprises an upper endplate for engaging the upper vertebra and a lower endplate for engaging the lower vertebra. At least one support having a variable stiffness is positioned between the upper endplate and the lower endplate. The intervertebral implant also includes at least one sensing element for monitoring a characteristic of the intervertebral implant. A processor is in communication with the at least one sensing element for determining a desired stiffness of the at least one support based on the characteristic monitored by the sensing element. An actuator in communication with the processor adjusts the stiffness of the at least one support to the desired stiffness based on a signal received from the processor. 
         [0007]    In some instances, the supports include a magnetorheological fluid. In that regard, in some instances the actuator controls a viscosity of the magnetorheological fluid of the supports. In some embodiments, the actuator includes a power supply for producing an electromagnetic field through the magnetorheological fluid to control the viscosity. In some instances, the characteristic monitored by the at least one sensing element is a load, acceleration, or rotation related to the intervertebral implant. In some instances, the supports include a temperature-activated metal alloy. In one particular embodiment, the temperature-activated metal is Nitinol. Accordingly, in some embodiments the actuator delivers an electric current to the temperature-activated metal to control the stiffness of the supports. In some instances, the processor continuously determines the desired stiffness of the supports and the actuator continuously adjusts the stiffness of the supports to the desired stiffness. In that regard, in some embodiments the actuator adjusts the stiffness of the supports to the desired stiffness within 10 ms of receiving the signal from the processor. 
         [0008]    In a further aspect, a prosthetic device for treating a spinal joint is provided. The prosthetic device comprises a first endplate having a first engagement surface and a second endplate having a second engagement surface. A plurality of supports having a variable stiffness are positioned between the upper endplate and the lower endplate. The prosthetic device also includes at least one sensor for monitoring a characteristic of the prosthetic device, at least one processor in communication with the at least one sensor for determining a desired stiffness for each of the plurality of supports based on a value of the characteristic monitored by the at least one sensor, and at least one actuator for adjusting the variable stiffness of each of the plurality of supports to the desired stiffness based on a signal received from the processor. 
         [0009]    In some instances, the sensors, processors, and/or actuators are positioned at least partially within the endplates of the prosthetic device. In some embodiments, the actuator comprises a power supply that is in communication with the at least one sensor and the at least one processor. In one particular embodiment, the power supply is a rechargeable battery. In some instances, at least one of the plurality of supports includes a magnetorheological fluid and the at least one actuator produces an electromagnetic field to control a viscosity of the magnetorheological fluid. In that regard, in some embodiments the actuator produces a magnetic field to control the viscosity of the magnetorheological fluid. In some instances, the characteristic monitored by the at least one sensor is a load on the prosthetic device. In that regard, in some embodiments the desired stiffnesses for the supports as determined the processor are inversely proportional to the load on the prosthetic device as measured by the sensors. In some embodiments, at least one of the plurality of supports comprises a temperature-activated metal and the actuator controls a voltage supplied to the temperature-activated metal to control the stiffness of the support. 
         [0010]    In another aspect, a method of treating a motion segment of a vertebral column is provided. The method includes providing a self-adjusting intervertebral implant and implanting the self-adjusting intervertebral implant within the motion segment of the vertebral column. In some instances the implant includes at least one support having a variable stiffness, at least one sensing element for monitoring a load on the intervertebral implant, a processor for determining a desired stiffness for the at least one support based on the load on the intervertebral implant, and an actuator in communication with the processor for adjusting the stiffness of the supports to the desired stiffness. 
         [0011]    Additional aspects and features of the present disclosure will be apparent from the detailed description and claims as set forth below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagrammatic side elevation view of an adult human vertebral column. 
           [0013]      FIG. 2  is a diagrammatic side elevation view of a portion of the vertebral column of  FIG. 1 , depicting an intervertebral implant according to one aspect of the present disclosure positioned between two adjacent vertebrae. 
           [0014]      FIG. 3  is a diagrammatic perspective view of the intervertebral implant of  FIG. 2 . 
           [0015]      FIG. 4  is a diagrammatic partial cutaway perspective view of the intervertebral implant of  FIGS. 2 and 3 . 
           [0016]      FIG. 5  is a diagrammatic front view of the intervertebral implant of  FIGS. 2-4 . 
           [0017]      FIG. 6  is a diagrammatic partial cutaway rear view of the intervertebral implant of  FIGS. 2-5 . 
           [0018]      FIG. 7  is a diagrammatic partial cutaway of the intervertebral implant similar to that of  FIG. 6 , but showing a lateral side view of the intervertebral implant. 
           [0019]      FIG. 8  is a diagrammatic lateral side view of the intervertebral implant of  FIGS. 2-7   
           [0020]      FIG. 9  is a diagrammatic partial cutaway top view of the intervertebral implant of  FIGS. 2-8 . 
           [0021]      FIG. 10  is a diagrammatic bottom view of the intervertebral implant of  FIGS. 2-9 . 
           [0022]      FIG. 11  is a diagrammatic partial cutaway phantom perspective view of the intervertebral implant of  FIGS. 2-10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    For the purpose of promoting an understanding of the principles of the present disclosure, reference is made to the specific embodiments illustrated in the drawings, and specific language is used to describe the embodiments. It is nevertheless understood that no limitation of the scope of the present disclosure is intended. Any alterations and further modifications of the described embodiments, and any further applications of the principles of the present disclosure as described herein, are fully contemplated, as would occur to one skilled in the art to which the invention relates. 
         [0024]      FIG. 1  illustrates a lateral view of a portion of a spinal column  10 , illustrating a group of adjacent upper and lower vertebrae V 1 , V 2 , V 3 , V 4  separated by natural intervertebral discs D 1 , D 2 , D 3 . Although the illustration generally depicts the lumbar region, it is understood that the devices, systems, and methods of this disclosure also may be applied to all regions of the vertebral column, including the cervical and thoracic regions. A vertebral joint comprises two adjacent vertebrae separated by an intervertebral disc.  FIG. 2  illustrates an exemplary vertebral joint  12  including an upper vertebra  14  and a lower vertebra  16 . In this illustration, instead of a natural intervertebral disc, an intervertebral implant  100  is disposed in the disc space S between the upper and lower vertebrae  14 ,  16  created by removal of the natural disc. 
         [0025]    Referring generally to  FIGS. 2-11 , the intervertebral implant  100  will be discussed in greater detail.  FIG. 2  is a diagrammatic side elevation view of the intervertebral implant  100  positioned between two adjacent vertebrae  14 ,  16  of a vertebral joint  12 .  FIG. 3  is a diagrammatic perspective view of the intervertebral implant  100 .  FIG. 4  is a diagrammatic perspective view of the intervertebral implant  100  similar to that of  FIG. 3 , but with partial cutaway to illustrate additional aspects of the intervertebral implant  100 .  FIG. 5  is a diagrammatic front view of the intervertebral implant  100 .  FIG. 6  is a diagrammatic partial cutaway rear view of the intervertebral implant  100 .  FIG. 7  is a diagrammatic partial cutaway of the intervertebral implant  100  similar to that of  FIG. 6 , but showing a lateral side view of the intervertebral implant.  FIG. 8  is a diagrammatic lateral side view of the intervertebral implant  100  from the direction substantially opposite to that of  FIG. 7 .  FIG. 9  is a diagrammatic partial cutaway top view of the intervertebral implant  100 .  FIG. 10  is a diagrammatic bottom view of the intervertebral implant  100 .  FIG. 11  is a diagrammatic partial cutaway phantom perspective view of the intervertebral implant  100 . 
         [0026]    Generally, the intervertebral implant  100  is sized to fit within the disc space S in a manner similar to that of a natural intervertebral disc, as shown in  FIG. 2 . The intervertebral implant  100  provides support and stabilization to the vertebrae  14 ,  16 . In addition, the intervertebral implant  100  allows the upper vertebra  14  to move relative to the lower vertebra  16  to preserve at least some movement in the vertebral joint  12 . In some instances, the intervertebral implant  100  has a variable stiffness to control the amount or degree of movement between the vertebrae  14 ,  16  and/or the amount of support provided to the vertebral joint  12 . Further, in some embodiments the intervertebral implant  100  continuously self-adjusts its stiffness as necessary to maintain a desired amount of motion and support to the vertebral joint  12 . In some embodiments, the stiffness of the intervertebral implant  100  is adjusted in the sagittal, axial, and/or coronal planes to provide the desired amount of motion and/or support. 
         [0027]    Referring more specifically to  FIG. 3 , in the illustrated embodiment the intervertebral implant  100  includes an upper endplate  102 , a lower endplate  104 , and four supports  106 ,  108 ,  110 , and  112  extending between the upper and lower endplates. The upper endplate  102  is configured to engage the upper vertebra  14  in some instances. To that end, the upper endplate  102  includes an engagement surface  114  for engaging the endplate of the upper vertebra  14 . As discussed in greater detail below, the engagement surface  114  includes various features for enhancing the engagement with the upper vertebra in some embodiments. Referring to  FIG. 5 , opposite the engagement surface  114 , the upper endplate  102  includes an inner surface  116 . In the present embodiment the inner surface  116  is substantially planar and the supports  106 ,  108 ,  110 , and  112  extend from the inner surface  116  towards the lower endplate  104 . The upper endplate  102  has a thickness  117  between the engagement surface  114  and the inner surface  116 . In some embodiments, the thickness  117  of the upper endplate  102  is sufficient to allow one or more electronic components of the intervertebral implant to be positioned therein. In some instances, the thickness  117  is between about 2 mm and about 25 mm, and in some instances between about 5 mm and about 15 mm. 
         [0028]    Similarly, the lower endplate  104  is configured to engage the lower vertebra  16  in some instances. To that end, the lower endplate  104  includes an engagement surface  118 , best viewed in  FIG. 10 , for engaging the endplate of the lower vertebra  16 . In some embodiments, the engagement surface  118  also includes various features for enhancing the engagement with the lower vertebra. Referring again to  FIG. 5 , opposite the engagement surface  118 , the lower endplate  104  includes an inner surface  120 . In the illustrated embodiment, the inner surface  120  is substantially planar and the supports  106 ,  108 ,  110 , and  112  extend from the inner surface  120  towards the upper endplate  102 . The lower endplate  104  has a thickness  121  between the engagement surface  118  and the inner surface  120 . In some embodiments, the thickness  121  of the lower endplate  104  is sufficient to allow one or more electronic components of the intervertebral implant to be positioned therein. In some instances, the thickness  121  is between about 2 mm and about 25 mm, and in some instances between about 5 mm and about 15 mm. 
         [0029]    Referring to  FIGS. 3-8 , the supports  106 ,  108 ,  110 , and  112  extending between the upper endplate  102  and the lower endplate  104  control the amount of cushioning or support provided by the intervertebral implant  100  and/or the amount of motion allowed by the implant. In some instances, the supports  106 ,  108 ,  110 , and  112  allow the intervertebral implant  100  to compress or elastically deform under compressive loads. Further, in some instances the supports  106 ,  108 ,  110 , and  112  allow the intervertebral implant  100  to expand or elastically stretch in response to a force that pulls the endplates  102 ,  104  away from one another. Further, in some instances, the supports  106 ,  108 ,  110 , and  112  allow both compression and expansion of the intervertebral implant. In some instances, a portion of the intervertebral implant  100  is compressed while another portion of the intervertebral implant is expanded. For example, when positioned in the cervical spine, a posterior portion of the implant  100  may be compressed during extension of the vertebral joint while an anterior portion of the implant is expanded. As another example, in a lateral bending to the patient&#39;s right side, the lateral right side of the implant  100  may be compressed while the lateral left side of the implant is expanded or stretched. 
         [0030]    In some embodiments of the present disclosure, the supports  106 ,  108 ,  110 , and  112  continually adjust the amount of the support and/or motion of the implant  100  based on parameters associated with the patient&#39;s physical activity. For example, in some instances the supports  106 ,  108 ,  110 , and  112  adjust the based on an anatomical load imparted on the implant. In other embodiments, the adjustment is based on acceleration, motion, pressure, and/or other parameters associated with the vertebral joint. In some instances, the stiffness of the supports  106 ,  108 ,  110 , and  112  is adjusted in order to adjust the support provided by the implant and/or the motion allowed by the implant. In that regard, the stiffness of the supports  106 ,  108 ,  110 , and  112  is adjusted in a different manner depending on the type of support utilized. In accordance with the present disclosure support  106  and support  108  represent two different types of support and each will be described in greater detail below. The supports  110  and  112  are representative of a generic support and, therefore, will not be discussed in great detail below. In some embodiments, the supports  110  and  112  are substantially similar to the support  106  and/or the support  108 . In that regard, in some instances the implant  100  includes all of the same type of supports. In other instances, the implant includes at least two different types of support in accordance with the present disclosure. In some instances, the implant combines one or more of the supports of the present disclosure with previously known implant features and/or supports. 
         [0031]    Referring more particularly to  FIG. 6 , the support  106  generally comprises a shock absorber having a magnetorheological fluid  140  disposed therein. The magnetorheological fluid  140  has variable viscosity. In particular, the viscosity of the magnetorheological fluid  140  varies based on the strength of the magnetic field applied to the fluid. The greater the magnetic field applied to the magnetorheological fluid  140 , the greater the viscosity of the fluid. As illustrated, the magnetorheological fluid  140  comprises a plurality of ferrous particles  142  suspended in a carrier fluid  144 . In some instances, the carrier fluid  144  is a silicon based fluid and the ferrous particles are iron particulate. Under the presence of a magnetic field the ferrous particles  142  are polarized and form a chain-like formation within the carrier fluid  144 . Generally the ferrous particles  142  form along the direction of the magnetic flux passing through the magnetorheological material  140 , such that the strength of the ferrous particle chain is directly related to the strength of the magnetic field. 
         [0032]    As shown, the magnetorheological material  140  is positioned within a cylinder  146  of the support  106  that mates with a rod  148 . In some embodiments, the cylinder  146  is substantially fixed with respect to the upper endplate  102  and the rod  148  is substantially fixed with respect to the lower endplate  104 . In that regard, the cylinder  146  is partially imbedded within the upper endplate  102  in the present embodiment. In some instances, the cylinder  146  is integrally formed with the upper endplate  102 . Similarly, in some embodiments the rod  148  is partially imbedded within the lower endplate  104  and is integrally formed with the lower endplate in some instances. 
         [0033]    Together, the cylinder  146 , rod  148 , and magnetorheological fluid  140  act as a shock absorber for the implant  100 . By adjusting the viscosity of magnetorheological fluid  140  the stiffness of the support  106 , and in turn the implant  100 , is adjusted. Thus, in some embodiments the implant  100  includes electronics  150 , as seen in  FIG. 4  for example and discussed in greater detail below, for controlling and producing a magnetic field for adjusting the viscosity of the magnetorheological fluid  140 . In some instances, the electronics  150  produce an electric current in a portion of the upper end plate  102  and/or cylinder  146  that generates a corresponding magnetic field through the magnetorheological fluid  140 . In that regard, in some instances the electronics  150  determine the appropriate amount of electric current to be provided to achieve a desired viscosity at least partially based on an attribute associated with the patient&#39;s activity. For example, in some instances the electric current is determined by the electronics based on a load on the implant, an acceleration of a portion of the implant, and/or a pressure on the implant. The viscosity of the magnetorheological fluid  140  is capable of changing within a few milliseconds (generally less than 10 milliseconds) of being subjected to the magnetic field generated by the electric current from the electronics. Accordingly, in some embodiments the implant  100  is capable of approximately real time adjustment of the stiffness of the support  106  based on the patient&#39;s physical activities and/or attributes associated with the patient&#39;s activity. 
         [0034]    Referring more particularly to  FIGS. 4 and 9 , the electronics  150  include a processor  152  (“processor” is understood to include microprocessors) that is connected to a pair of power supplies  154  and  156 , a pair of load sensors  158  and  160 , and four microelectromechanical systems (“MEMS”) devices  160 ,  162 ,  164 , and  166 . As illustrated in  FIG. 4 , the electronics  150  are all positioned within the upper endplate  102  in the present embodiment. In that regard, as illustrated by  FIG. 3 , in some instances the electronics  150  are entirely enclosed within the upper endplate  102 . In other embodiments, however, one or more of the electronic components  150  are positioned outside of the upper endplate  102  and/or co-planar with an outer surface of the upper endplate. While the electronics  150  are shown as being disposed entirely within the upper endplate  102 , in other embodiments the electronics  150  are positioned partially or entirely within the lower endplate  104 . Further, in some instances electronics are positioned in both the upper and lower endplates  102 ,  104 . In that regard, in one particular embodiment the electronics may be hard-wire connected through a wire extending through the support  108 . 
         [0035]    In some embodiments, the processor  152  receives signals from the load sensors  158  and  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166  and determines the amount of voltage or current necessary to produce a magnetic field to adjust the viscosity of the magnetorheological fluid  140  to a desired level. Based on the processor&#39;s  152  determination, the appropriate amount of current is provided from one or more of the power supplies  154 ,  156 . In some instances, the processor  152  continually monitors the signals received from the load sensors  158  and  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166  and continually dictates the appropriate current to be provided by the power supplies  154 ,  156  such that the support  106  provides the appropriate amount of stiffness at all times. In that regard, in some particular aspects the stiffness of the support  106  is adjusted within 10 ms of the processor  152  requesting a change in the stiffness. Also, in some embodiments the processor  152  is configured to associate data from the load sensors  158  and  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166  with typical activities of the patient, such as walking, sitting, standing, running, laying down, kneeling, and/or other activities. Based on the associated activity as determined by the processor, a corresponding current is generated to incite the appropriate amount of stiffness in the support  106 . 
         [0036]    As mentioned, the processor  152  determines the appropriate amount of stiffness for the support  106  and the corresponding amount of current based on signals received from the load sensors  158  and  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166 . The load sensors  158 ,  160  monitor forces on the implant  100  resulting from loads on the vertebral joint and relay the corresponding loading information to the processor  152 . The MEMS devices  160 ,  162 ,  164 , and  166  monitor aspects of the implant and/or vertebral joint such as accelerations, rotations, and/or other motions. In that regard, the MEMS devices  160 ,  162 ,  164 , and  166  send the resulting data to the processor  152  for consideration. While two load sensors and four MEMS devices have been disclosed, in other embodiments other combinations of load sensors and/or MEMS devices are utilized including only load sensors or only MEMS devices. Further still, in some instances only a single sensing element (load sensor or MEMS device) is utilized. 
         [0037]    In order to save battery power and/or computing power, in some instances signals from the load sensors  158  and  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166  are conditioned or filtered before being sent to the processor  152 . For example, in some instances a sufficient change in the force as measured by the load cells must occur before a signal is sent to the processor. In other instances, a threshold level of acceleration must be detected by the MEMS devices before a signal is sent to the processor. In this manner, the processor  152  may only be utilized when a change sufficient to trigger a change in the stiffness of the support  106  has been detected. In other instances, the load sensors  158  and  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166  continuously send all information to the processor  152  for consideration. 
         [0038]    Supplying the power requirements for the processor  152  and the implant  100  in general are the power supplies  154  and  156 . In that regard, the power supplies  152  and  154  generate the electrical currents that induce the magnetic fields that change the viscosity of the magnetorheological material  140  in some instances. In other instances, the power supplies  152  and  154  generate the electrical currents that change the material properties of the support  108  as discussed below. In some embodiments, the power source supplies  154 ,  156  are batteries. In this manner the electronics  150  may be internally powered. The batteries are lithium iodine batteries similar to those used for other medical implant devices such as pacemakers in some instances. It is understood that the battery may be any type of battery suitable for implantation. In some instances the battery is rechargeable. In that regard, in some specific embodiments the battery may be recharged by an external device so as to avoid the necessity of a surgical procedure to recharge the battery. For example, in one embodiment the battery is rechargeable via inductive coupling. 
         [0039]    It is also contemplated that at least some of the electronic components be self-powered and not require a separate stored-energy power supply. For example, in some embodiments the load sensors  158 ,  160  and/or the MEMS devices  160 ,  162 ,  164 , and  166  are piezoelectric such that signals detected by these components or other signals provide power to the sensor. In other embodiments, the electronic components utilize energy harvesting to recharge the power supplies  154 ,  156  or store energy for use by the electronic components. Energy harvesting in this context is understood to be energy generated by the patient&#39;s motion or natural body that is captured by the implant  100  for use in powering the electronics. Additional and/or alternative sources of power may be utilized in other embodiments. In that regard, while two power supplies are illustrated, it is understood that in other embodiments a single power supply or a greater number of power supplies may be utilized. 
         [0040]    Referring more particularly to  FIG. 6 , the support  108  is generally shaped like a bellow. In that regard, the support  108  includes a plurality of alternating protrusions  168  and recesses  169  on its outer surface and a generally cylindrical core  170 . The bellow shape of the support  108  allows it to be flexible in some instances. In that regard, the support  108  is formed of a temperature-activated metal alloy in some embodiments. The mechanical properties of the metal alloy are dependent upon its temperature. In some instances, the metal alloy becomes stiffer as its temperature increases. One specific example of such an alloy is Nitinol. Accordingly, in some embodiments the stiffness of the support  108  increases as the temperature of the support increases. In some embodiments, a current is introduced into the support  108  to control the temperature of the metal alloy. Generally, an increase in the current results in an increase in the stiffness of the support  108 . Similarly, a decrease in the current passing through the support reduces the stiffness of the support  108 . Accordingly, by controlling the amount of current passing through the support  108 , the stiffness of the support and, in turn, the implant is controlled. Thus, in some embodiments the electronics  150  of the implant  100  are utilized in a substantially similar manner as that described above with respect to the support  106 . For example, the processor  152  determines the current to be applied to the support  108  based on a desired stiffness for the support. In some instances, this determination is based on a physical activity and/or a measurable attribute associated with the patient&#39;s physical activity. In this manner, the support  108  is utilized to provide continuous adjustment of the stiffness of the support  108  based on the patient&#39;s physical activities and/or attributes associated with the patient&#39;s activity. In some embodiments, the inner core or inner surface of the support  108  is not cylindrical. In one particular embodiment, the inner portion of the support  108  includes a plurality of alternating protrusions and recesses corresponding to the protrusions  168  and recesses  169  of the outer surface. 
         [0041]    In some embodiments, the supports  106 ,  108 ,  110 , and  112  allow the implant  100  to facilitate motion in vertebral joint  12 , including but not limited to flexion, extension, lateral bending, rotation, and translation between the vertebrae  14 ,  16 . Accordingly, in some instances the supports  106 ,  108 ,  110 , and  112  allow corresponding motion between the endplates  102  and  104 . Thus, in some embodiments, supports  106 ,  108 ,  110 , and  112  allow the endplates  102 ,  104  to translate with respect to one another in the anterior-posterior direction, the lateral directions, and/or the inferior-superior direction. Further, in some embodiments the supports  106 ,  108 ,  110 , and  112  allow the endplates  102 ,  104  to rotate with respect to one another. In other embodiments, the supports  106 ,  108 ,  110 , and  112  limit motion of the implant  100  and, therefore, the vertebral joint  12  in one or more directions. In that regard, the supports  106 ,  108 ,  110 , and  112  entirely prevent or limit movement in a particular direction and/or permit movement in the particular direction up to a certain level. Accordingly, in some embodiments the supports  106 ,  108 ,  110 , and  112  include a hard stop that prevents movement beyond the desired amount. 
         [0042]    In some instances, the maximum amount or range of movement allowed by the supports  106 ,  108 ,  110 , and  112  is varied over time. For example, in some instances it is desirable to further limit motion of the implant  100  in one or more directions and/or provide more rigid support to the vertebral joint over time due to the patient&#39;s physical conditions or other factors. In other instances, it is desirable to allow greater range of motion in one or more directions and/or provide less rigid support to the vertebral joint over time or after a set period of time after implantation. As discussed above, the amount of movement or range of motion allowed by the supports  106 ,  108 ,  110 , and  112  is determined by a processor or other control mechanism in some embodiments. Accordingly, in some instances the processor or other control mechanism is reprogrammed or otherwise configured to facilitate the change in the range of motion of the device. 
         [0043]    In the present embodiment, the supports  106 ,  108 ,  110 , and  112  are equally spaced about the outer portion of the prosthetic device. In particular, the supports  106  and  108  are positioned on the lateral portions of the implant  100 , while the supports  110  and  112  are positioned on the anterior and posterior portions of the implant. Further, each of the supports  106 ,  108 ,  110 , and  112  extend generally at an oblique angle with respect to the inner surfaces  116  and  120  of the upper and lower endplates  102 ,  104 . For example, referring more specifically to  FIG. 5 , as shown therein the support  106  extends at an angle  122  from the inner surface  116  of the upper endplate  102  and interfaces the inner surface  120  of the lower endplate  104  at an angle  124 . In the present embodiment, the angles  122  and  124  are supplementary angles. However, in some embodiments, the angles  122  and  124  are not supplementary. Generally, each of the angles  122  and  124  is between about 30 degrees and about 150 degrees. In some rare embodiments the angles  122 ,  124  may be outside of these ranges. Accordingly, in some instances the support  106  engages the inner surface  116  of the upper endplate  102  at a position closer to a midpoint of the implant than the position where the support engages the inner surface  120  of the lower endplate  104 . Further, in some instances the support  106  extends substantially perpendicular to both the upper endplate  102  and the lower endplate  104 . 
         [0044]    Similarly, the support  108  extends at an angle  126  from the inner surface  116  of the upper endplate  102  and extends at an angle  128  from the inner surface  120  of the lower endplate  104 . The angles  126  and  128  are supplementary angles in the present embodiment, but are not supplementary in all embodiments. Generally, each of the angles  126  and  128  is between about 30 degrees and about 150 degrees. In some rare embodiments the angles  126 ,  128  may be outside of these ranges. Accordingly, similar to the support  106 , in some instances the support  108  engages the inner surface  116  of the upper endplate  102  at a position closer to a midpoint of the implant than the position where the support  108  engages the inner surface  120  of the lower endplate  104 . Further, in some instances the support  108  extends substantially perpendicular to the inner surfaces  116 ,  120  of both the upper endplate  102  and the lower endplate  104 . 
         [0045]    Referring to  FIG. 8 , the supports  110  and  112  also extend at angles  130  and  132  from the inner surface  116  of the upper endplate  102 , respectively. The supports  110  and  112  extend at angles  134  and  136  from the inner surface  120  of the lower endplate  104 , respectively. Similar to the supports  106  and  108  above, angles  130 ,  132  and angles  134 ,  136  are supplementary angles, respectively, in the present embodiment. However, in other embodiments the angles may not be supplementary. Generally, each of the angles  130 ,  132 ,  134 , and  136  is between about 30 degrees and about 150 degrees. In some rare embodiments the angles  130 ,  132 ,  134 , and  136  may be outside of these ranges. Accordingly, in some instances one or both of the supports  110  and  112  engage the inner surface  116  of the upper endplate  102  at a position closer to a midpoint of the implant than the position where the support  110  or  112  engages the inner surface  120  of the lower endplate  104 . Further, in some instances one or both of the supports  110  and  112  extend substantially perpendicular to the inner surfaces  116 ,  120  of both the upper endplate  102  and the lower endplate  104 . 
         [0046]    While the present embodiment of the intervertebral implant  100  includes the four supports  106 ,  108 ,  110 , and  112 , in other embodiments the intervertebral implant includes a greater or less number of supports. In that regard, in some instances the intervertebral implant includes three supports. In one such embodiment, two of the supports are positioned adjacent a posterior portion of the device and equally spaced laterally from a midline of the implant, while the third support positioned adjacent an anterior portion of the device and substantially centered on the midline. In another embodiment, two of the supports are positioned adjacent an anterior portion of the device and equally spaced laterally from a midline of the implant, while the third support positioned adjacent a posterior portion of the device and substantially centered on the midline. Generally, any number of supports may be utilized. 
         [0047]    Further, in some embodiments multiple implants  100  may be implanted into a single patient at multiple levels of the spine. In some embodiments, the multiple implants  100  form a networked implant system. For example, in some instances the effect of stiffening a support of one of the implants is considered at each level where an implant is positioned. By taking into account more than one level of the spine where an implant is positioned instead of only the single level of a particular implant, a global support for the spinal column is established. In this manner, the networked implants prevent the implants from working against one another. In such situations, the implants  100  communicate with one another via wireless telemetry or other suitable means. In some instances, each of the implants communicates with a remote device that then controls the corresponding attributes of each of the implants. Accordingly, in some instances a patient begins with only a single implant, but then is implanted with another implant later. In such situations, the initial implant may not be configured for communication with the new implant, but would be configured for communication with the remote device such that the old and new implants could be networked together. In that regard, it is contemplated that the remote device may be programmable and/or backwards compatible to communicate with implants previously implanted. 
         [0048]    In some instances, the implant includes memory for storing performance data for the implant. In that regard, the implant may also include a wireless telemetry component so that the stored data may be communicated to an external receiver. In some instances, the external receiver also includes a memory unit. In that regard, the memory unit of the external receiver may be adapted for multiple uses. First, the memory unit may be adapted for permanent storage of the performance data obtained from the implant. Thus, the memory unit may store data obtained at various times from the implant so the data may later be reviewed, compared, or analyzed. Second, the memory unit may be adapted for temporary storage of performance data obtained from the implant. In this case, the memory unit will store the data until it is either discarded or transferred for permanent storage. For example, the data may be transferred from the memory unit of the external receiver via a networking interface to a network or computer for permanent storage. In some instances, such a networking interface provides a means for the external receiver to communicate with other external devices. The type of network utilized may include such communication means as telephone networks, computer networks, or any other means of communicating data electronically. 
         [0049]    In some instances, the networking interface of the external receiver could obviate the need for the patient to even go into the doctor&#39;s office for obtaining implant performance data. For example, the patient could utilize an external receiver to obtain the usage data from the implant on a scheduled basis (e.g. daily, weekly, monthly, etc.). Then, utilizing the networking interface the patient could send this data to the treating medical personnel. The networking interface may be configured to directly access a communication network such as a telephone or computer network for transferring the data. It is fully contemplated that the computer network be accessible by treating medical personnel for reviewing implant performance data of the patient without requiring the patient to make an actual visit to the doctor&#39;s office. In some instances, the networking interface is similar to the CareLink system from Medtronic, Inc. 
         [0050]    It is also contemplated that any communication between the external receiver and the computer network may be encrypted or otherwise secured so as protect the patient&#39;s privacy. It is also contemplated that the networking interface may be configured for communication with a separate device that is adapted for accessing the communication network. For example, the networking interface may be a USB connection. The external receiver may be connected to a personal computer via the USB connection and then the personal computer may be utilized to connect to the communication network, such as the internet, for transferring the data to a designated place where the treating doctor may receive it. 
         [0051]    Further, supports in accordance with the present disclosure may be utilized in combination with other spinal implant motion preserving features. For example, in some instances one or more supports are utilized in combination with a ball-and-socket articulating joint of the implant. In one embodiment, the one or more supports are positioned around the ball-and-socket joint. In that regard, the supports are utilized to control the movement and/or support provided to the vertebral joint by the implant. In some instances, the supports are utilized to limit movement of the implant in a particular direction or orientation. 
         [0052]    The upper and lower endplates assemblies  102 ,  104  are formed of suitable biocompatible materials. In instances, metals such as cobalt-chromium alloys, titanium alloys, nickel titanium alloys, and/or stainless steel alloys are utilized. Ceramic materials such as aluminum oxide or alumnia, zirconium oxide or zirconia, compact of particulate diamond, and/or pyrolytic carbon are suitable in some instances. In some embodiments, polymer materials are utilized, including any member of the polyaryletherketone (PAEK) family such as polyetheretherketone (PEEK), carbon-reinforced PEEK, or polyetherketoneketone (PEKK); polysulfone; polyetherimide; polyimide; ultra-high molecular weight polyethylene (UHMWPE); and/or cross-linked UHMWPE. 
         [0053]    Further, the exterior engagement surfaces  114 ,  118  of the upper and lower endplates  102 ,  104  include features or coatings (not shown) that enhance the fixation of the implanted prosthesis in some embodiments. For example, the surfaces  114 ,  118  are roughened such as by chemical etching, bead-blasting, sanding, grinding, serrating, and/or diamond-cutting in some instances. All or a portion of the exterior surfaces  28 ,  34  may also be coated with a biocompatible and osteoconductive material such as hydroxyapatite (HA), tricalcium phosphate (TCP), and/or calcium carbonate to promote bone in growth and fixation. Alternatively, osteoinductive coatings, such as proteins from transforming growth factor (TGF) beta superfamily, or bone-morphogenic proteins, such as BMP2 or BMP7, may be used. Other suitable features may include spikes, ridges, keels, fins, posts, or other bone engaging protrusions for initial fixation of the intervertebral implant  100  and/or to prevent migration in the lateral or anterior/posterior directions. In some instances, the exterior surfaces  114 ,  118  include serrations, diamond cuts, and/or other surface textures. 
         [0054]    In the illustrated embodiment of  FIGS. 2-11 , the implant  100  includes elliptical, oval, or oblong endplates  102 ,  104  as viewed from the top or bottom of the intervertebral implant ( FIGS. 9 and 10  for example). In other embodiments, the endplates have other shapes, including rectangular, rectangular with curved sides, kidney shaped, heart shaped, square, oval, triangular, hexagonal, or any other shape suitable for mating with the vertebrae  12 ,  14 . Further, in the illustrated embodiment of  FIGS. 2-11 , the engagement surfaces  114 ,  118  extend relatively parallel to one another. However, in other embodiments, the surfaces  114 ,  118  are angled with respect to each other to accommodate a desired lordotic or kyphotic angle. In that regard, the specific lordotic or kyphotic angle may be selected based on the level of spine in which the implant  100  is to be inserted. In some instances, the outer profile of the implant  100  is tapered, angled, or wedge shaped to create the desired lordotic or kyphotic angle. In some embodiments, the lordotic and kyphotic angles are created by utilizing one or more angled, tapered, or wedge shaped endplate assemblies. In that regard, the thickness of the endplate may vary along the length and/or width of the prosthetic device to achieve the angled orientation. 
         [0055]    In other embodiments, the endplates  102 ,  104  have substantially planar surfaces  114 ,  118  and substantially constant thicknesses, but are positioned at a lordotic or kyphotic angle due to the orientation of the supports positioned between the endplates. In some instances, the supports have a neutral position that positions the endplates in a lordotic or kyphotic angle. In some instances, the supports are biased towards the lordotic or kyphotic neutral position. In some embodiments, the relative heights of the supports are controlled by a processor and/or actuator to achieve the desired lordotic or kyphotic angle. In that regard, the processor and/or actuator will direct one or more of the supports to have an increased or decreased height relative to one or more other supports. 
         [0056]    Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. Accordingly, all such modifications and alternative are intended to be included within the scope of the invention as defined in the following claims. Those skilled in the art should also realize that such modifications and equivalent constructions or methods do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. It is understood that all spatial references, such as “horizontal,” “vertical,” “top,” “upper,” “lower,” “bottom,” “left,” and “right,” are for illustrative purposes only and can be varied within the scope of the disclosure. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.