Abstract:
In a spinal implant device, a frictionless pivot member is used to interconnect multiple links and produce a scissor jack-like device with minimal frictional wear characteristics. The device is attached to at least two vertebrae, wherein a first device segment is attached to a first vertebra and at least one additional device segment is attached to at least one additional vertebra. The implanted device functions to control and dampen the movement between the attached vertebral bodies.

Description:
REFERENCE TO PRIORITY DOCUMENT 
       [0001]    This application claims priority of co-pending U.S. Provisional Patent Application Ser. No. 60/874,195, filed Dec. 11, 2006. Priority of the aforementioned filing date is hereby claimed and the disclosures of the Provisional Patent Application is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to methods and devices that permit dynamic stabilization of the bony elements of the skeleton. The devices permit adjustment and maintenance of the spatial relationship(s) between neighboring bones. Depending on the specifics of the design, the motion between skeletal segments may be limited or enhanced in one or more planes. 
         [0003]    Spinal degeneration is an unavoidable consequence of aging. The disability produced by the aging spine has emerged as a major health problem in the industrialized world. Alterations in the anatomical alignment and physiologic motion that normally exists between adjacent spinal vertebrae can cause significant pain, deformity, weakness, and catastrophic neurological dysfunction. The traditional surgical treatment of spinal disease is decompression of the neural elements and complete immobilization of the involved bony spinal segments. Over time, an extensive array of surgical techniques and implantable devices has been formulated to accomplish this goal. 
         [0004]    The growing experience with spinal fusion has shed light on the long-term consequences of vertebral immobilization. It is now accepted that fusion of a specific spinal level will increase the load on, and the rate of degeneration of, the spinal segments immediately above and below the fused level. As the number of spinal fusion operations have increased, so have the number of patients who require extension of their fusion to the adjacent, degenerating levels. The second procedure necessitates re-dissection through the prior, scarred operative field and carries significantly greater risk than the initial procedure while providing a reduced probability of pain relief. Further, extension of the fusion will increase the load on the motion segments that now lie at either end of the fusion construct and will accelerate the rate of degeneration at those levels. Thus, spinal fusion begets additional fusion surgery. 
         [0005]    In view of the proceeding, there is a growing recognition that segmental spinal fusion and complete immobilization is an inadequate solution to abnormal spinal motion and vertebral mal-alignment. Correction of the abnormal movement and preservation of spinal mobility is a more intuitive and rational treatment plan. 
         [0006]    The vast experience gained in the implantation of mobile prostheses in the hip, knee, shoulder, ankle, digits and other joints of the extremities has shown that the wear debris produced by the bearing surfaces and the loosening that occur at the bone-device interface are major causes of implant failure. The latter is at least partially caused by the former, since it&#39;s been shown that the particulate debris from the bearing surfaces promote bone re-absorption at the bone-device interface and significantly accelerates device loosening. In the long term, the degradation products of the implant materials may also produce negative biological effects at distant tissues within the implant recipient. 
         [0007]    While ceramic and polymer implant components produce wear debris, these degradation products are usually deposited as insoluble particles around the implant thereby limiting the extent of potential toxicity. In contrast, metallic degradation products may be present as particulate and corrosion debris as well as free metals ions, composite complexes, inorganic metal salts/oxides, colloidal organo-metallic complexes and other molecules that may be transported to distant body sites. In fact, studies have revealed chronic elevations in serum and urine cobalt and chromium level after prosthetic joint replacement. Given the known toxicity of titanium, cobalt, chromium, nickel, vanadium, molybdenum and other metals used in the manufacture of orthopedic implants, the tissue distribution and biologic activity of their degradation products is of considerable concern. Host toxicity may be produced directly by the reactive metallic moieties as well as by their alterations of the immune system, metabolic function, and their potential ability to cause cancer. These issues are thoroughly discussed in the text “Implant Wear in Total Joint replacement” edited by Thomas Wright and Stuart Goodman and published by the American Academy of Orthopedic Surgeons in 2000. The text is hereby incorporated by reference in its entirety. 
         [0008]    Unlike joints in the extremities, proper function of the spinal joints (i.e., inter-vertebral disc and facet joints) returns the attached bones to the neutral position after the force producing the motion has dissipated. That is, a force applied to the hip, knee or other joints of the extremities produces movement in the joint and a change in the position of the attached bones. After the force has dissipated, the bones remain in the new position until a second force is applied to them. In contrast, the visco-elastic properties of the spinal disc and facet joint capsule dampen the force of movement and return the vertebral bones to a neutral position after the force acting upon them has dissipated. 
         [0009]    Prosthetic joint implants that attempt to imitate native spinal motion have usually employed springs, polyurethane, rubber and the like to recreate the visco-elastic properties of the spinal joints. When subjected to the millions of cycles of repetitive loading that is required of a spinal joint prosthesis, all implants to date have been plagued by excessive wear and degeneration secondary to the fairly modest wear characteristics of these elastic elements. Thus, in addition to the wear debris generated by the bearing surface(s), the elastic materials used to dampen spinal motion will produce a second source of degradation products. Given the number of joints in the spine and the extensive potential application of replacement technology in these joints, it is critical that the wear debris from the implanted prosthesis be minimized. 
       SUMMARY 
       [0010]    The preceding discussion illustrates a continued need in the art for the development of mobile prostheses with a reduced wear profile. This development would maximize the functional life of the prostheses and minimize the production of toxic degradation products. 
         [0011]    In a first embodiment, a frictionless pivot member is used to inter-connect multiple links and produce a scissor jack-like device with minimal frictional wear characteristics. The device is attached to at least two vertebras, wherein a first device segment is attached to a first vertebra and at least one additional device segment is attached to at least one additional vertebra. The implanted device functions to control and dampen the movement between the attached vertebral bodies. Multiple methods of device attachment are shown. 
         [0012]    In a second embodiment, the frictionless pivot member is used to manufacture an orthopedic device capable of at least partially replacing the function of a natural inter-vertebral disc. In a third embodiment, the frictionless pivot member is used to construct a connector that is used to inter-connect at least two bone screws that are connected to at least two vertebral bones. The inter-connector will function to control and dampen the movement between the attached vertebral bodies. 
         [0013]    In other embodiments, devices are constructed out of malleable slats that are attached to the vertebral bodies in unique configurations. The devices control and dampen vertebral movement in one or more planes of motion. In a final embodiment, a device with a pyramidal articulation is used to interconnect the vertebral bodies. The device is adapted to resist motion and dampen the movement between the attached vertebral bodies. 
         [0014]    In one aspect, there is disclosed an implant adapted to dynamically stabilize two or more vertebral bodies, comprising: a first attachment member adapted to attach onto a first vertebral body; at least one second attachment member adapted to attach onto at least one additional vertebral body; at least one linkage member coupled to the attachment members; and at least one pivotable bearing mechanism that connects the linkage members and the attachment members, wherein: A) the pivotable bearing mechanism contains at least two rotatable members that pivot around a common central axis but do not directly contact one another; and B) the pivotable bearing mechanism contains at least one malleable member that connects the rotatable members and reversibly returns the bearing mechanism to a neutral position after the dissipation of a force acting upon it. 
         [0015]    Other features and advantages will be apparent from the following description of various embodiments, which illustrate, by way of example, the principles of the disclosed devices and methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0016]      FIG. 1  shows perspective views of an exemplary embodiment of a dynamic orthopedic implant. 
           [0017]      FIG. 2  shows various views of the orthopedic implant attached to the vertebral bones. 
           [0018]      FIG. 3A  shows an assembled view of a portion of the implant. 
           [0019]      FIG. 3B  shows an exploded view of a portion of the implant. 
           [0020]      FIG. 4  shows a perspective view of an embodiment of an articulation member. 
           [0021]      FIG. 5  shows the articulation member in partial cross section. 
           [0022]      FIG. 6  shows another embodiment of an articulating member. 
           [0023]      FIG. 7A  shows an embodiment of an articulating rod. 
           [0024]      FIG. 7B  shows the rod of  FIG. 7A  in cross-section. 
           [0025]      FIG. 8  shows another embodiment of an articulating rod. 
           [0026]      FIGS. 9-14B  show additional embodiments of orthopedic implants. 
           [0027]      FIGS. 15A and 15B  show modular attachment members. 
           [0028]      FIG. 16  shows a perspective view of an interspinous device that is configured for placement between the spinous processes of two adjacent vertebral bones. 
           [0029]      FIG. 17  shows an exploded view of the device of  FIG. 16 . 
           [0030]      FIG. 18  shows a cross-sectional view of the device implanted on the vertebral bones. 
           [0031]      FIGS. 19-21  show another embodiment of an interspinous device. 
           [0032]      FIGS. 22-26  show another embodiment of an interspinous device. 
           [0033]      FIG. 27  shows another embodiment of a vertebral implant. 
           [0034]      FIG. 28  shows the device of  FIG. 27  in an exploded state. 
           [0035]      FIGS. 29A and 29B  show the device in cross-section. 
           [0036]      FIG. 30A  shows the vertebral bodies in partial flexion. 
           [0037]      FIG. 30B  shows the vertebral bodies in full flexion. 
           [0038]      FIG. 31  shows another embodiment of a flex member. 
           [0039]      FIG. 32A  shows the vertebral bodies in partial flexion. 
           [0040]      FIG. 32B  shows the vertebral bodies in full flexion. 
           [0041]      FIGS. 33 and 34  illustrate perspective and cross-sectional views of another embodiment of an interspinous device. 
           [0042]      FIG. 35  illustrates a coronal section through an embodiment of a mobile implant device. 
           [0043]      FIGS. 36A-36B  show another embodiment of an implant device. 
           [0044]      FIGS. 37-40B  illustrate multiple embodiments of mobile devices that are placed within the disc space between two vertebral bodies and used to at least partially replace and/or augment the function of the native disc. 
           [0045]      FIG. 41  illustrates a perspective view of the a dynamic rod. 
           [0046]      FIG. 42  shows the dynamic rod in an exploded state. 
           [0047]      FIG. 43  shows an exemplary bone screw assembly. 
           [0048]      FIG. 44  shows cross-sectional views of the dynamic rod. 
           [0049]      FIG. 45  shows a flexible pivot of the dynamic rod. 
           [0050]      FIGS. 46-49  show a dynamic rod assembly that includes two rod members that are movably attached to one another via a dynamic pyramidal connector. 
       
    
    
     DETAILED DESCRIPTION  
       [0051]      FIG. 1  shows perspective views of an exemplary embodiment of a dynamic orthopedic implant. The implant can be anchored across multiple levels of vertebral bones via one or more anchor devices, such as bone screw assemblies  105  that anchor into the vertebral bones. The configuration of the bone screw assemblies  105  can vary. In an embodiment, the bone screw assemblies are polyaxial bone screw assemblies each having a housing that can be locked to a bone screw. It should be appreciated that other types of bone screw assemblies can be used.  FIG. 2  shows various views of the orthopedic implant attached to the vertebral bones. For clarity of illustration, the vertebral bones are represented schematically and those skilled in the art will appreciate that actual vertebral bones may include anatomical details not shown in  FIG. 1 . 
         [0052]    With reference to  FIGS. 1 ,  2 , and  3  the implant includes a connecting mechanism  107  ( FIG. 3A ) that employs one or more articulating members  110  that provide an articulating connection between two or more rods  120  over multiple vertebral levels. The rods  120  are adapted to extend across the vertebral midline when the implant is positioned on the spine. Opposite ends of the rods  120  are attached to respective anchor devices  105 . The articulating members  110  and the rods  120  are adapted to rotate around a central axis in response to the application of a rotational load. The connecting mechanism  107  can be fixedly attached to one or both of the rods  120  such that the entire device is a unitary device. Alternately, the connecting mechanism  107  can modularly attach to one or both of the rods  120 , as described more fully below. Moreover, the rods  120  can be articulating or can be solid rods of fixed size and shape, as described more fully below. 
         [0053]      FIG. 3A  shows an assembled view of the implant while  FIG. 3B  shows an exploded view of the implant. The connecting mechanism  107  includes the articulating members  110  that are interconnected via elongate link members  305 . The link members  305  can move relative to one another as a result of articulation of the articulating members  110 . In this regard, the articulating members  305  are adapted to provide frictionless or near frictionless movement about an axis of rotation, such as the axis of rotation A show in  FIG. 3A . The axis of rotation extends through a central, longitudinal axis of the articulation member. In the embodiment shown in  FIGS. 3A and 3B , the rods  120  are elongated sleeves that are adapted to receive an elongated rod therein. It should be appreciated that the rods  120  can be solid rods, sleeves, articulating rods, etc. In addition, the rods  120  can be replaced with another implant device other than a rod. 
         [0054]      FIG. 4  shows a perspective view of an embodiment of an articulation member  110 .  FIG. 5  shows the articulation member  110  in partial cross section. With reference to  FIGS. 4 and 5 , each of the articulating members  110  is formed of a plurality of sections  410  and  420 . The articulating member  110  permits the attached link members  305  ( FIG. 3A ) to rotate about the longitudinal axis of the articulating member. In one embodiment, the rotational range is +30 to −30 degrees, although it should be appreciated that the rang can vary. The articulating member  110  is a flexure based bearing, utilizing internal flexible slats  1110  contained within a cylindrical housing, to provide precise rotation with low hysteresis and no frictional losses. The bearing is stiction-free, requires no lubrication, and is self-returning. The articulating member can resist rotational movement away from a neutral state and the extent of resistance to rotation is directly related to the extent of rotation. The extent of resistance to rotation can be a pre-determined property of the device. In one embodiment, the articulation member is has high radial stiffness, high axial stiffness and is frictionless (hence, no particle wear debris). An exemplary articulating member of the type shown in  FIGS. 4 and 5  is distributed by Riverhawk Company of New York under the name FREE FLEX PIVOT.  FIG. 6  shows another embodiment of an articulating member  110 . The embodiment of  FIG. 6  comprises several sections formed of a plurality of internal, interconnected structures that are adapted to move and/or deform relative to one another. 
         [0055]    As mentioned, the rod  120  can be a solid device of fixed shape or it can be an articulating device adapted to change shape in response to loads.  FIG. 7A  shows an embodiment of an articulating rod  120  formed of interconnected rod sections including an articulating member  705  that is constructed in a manner similar to the articulating member  110 . The articulating member  705  permits the rod sections to rotate about the axes of the central articulating member  705 .  FIG. 7B  shows a cross-sectional view of the articulating member  705 , which comprises several sections formed of a plurality of internal slats that are adapted to deform in response to the rotational movement of central member  705  relative to ends  706 .  FIG. 8  illustrates an alternative embodiment of an articulating rod. The rod contains three solid segments that contain end recesses adapted to accept an articulation member  110 . In the assembled state, a first articulation member  110  provides rotational movement between the first and second rod segments and a second articulation member  110  provides rotational movement between the second and third rod segments. 
         [0056]    The implant can use various configurations of the connecting mechanism  107 . The connecting mechanism can employ various quantities of articulating members  110  that are linked to one another via link members  305  arranged in various structural and geometric configurations.  FIG. 9  shows an embodiment that includes several articulating members  110  that are linked together in series via several link members  305 . The articulating members  110  are arranged in an undulating pattern between a pair of rods  120 .  FIG. 10  shows another embodiment of an implant. In this embodiment, one of the rods  120  is directly connected to two articulating members  110  while the opposite rod  120  has a direct connection to a single articulating member  110 . A pair of in-between articulating members  110  are linked by link members  305  that cross over one another. 
         [0057]      FIG. 11  shows another embodiment of an implant wherein four articulating members  110  are interlinked by link members  305  arranged in a cross-wise fashion. The articulating members  110   a  and  110   b  are slidably positioned in slots to permit sliding translation of the articulating members  110   a  and  110   b  within the slots and relative to the rod  120   a . The implants can have several connecting mechanisms  107  that each extend across one or more vertebral levels. For example,  FIGS. 12 and 13  shows an implant with two connecting mechanisms  107  that each extend across a vertebral level. The geometric arrangement of the linking arms and the articulating members can be the same between different levels or it can vary between levels. 
         [0058]    In certain circumstances, it may be desirable to provide one or more rods  120  that extend parallel to the vertebral midline.  FIG. 14A  shows an embodiment of an implant with rods  120  that are parallel to the vertebral midline along opposite sides of the vertebral midline. The implant also includes a cross-member  1405  that extends across the vertebral midline and connects at opposite ends to the rods  120 . 
         [0059]    As mentioned, an embodiment of the connecting mechanism  107  is adapted to modularly attach to a rod  120  or to another device. This permits multiple connecting mechanisms to be removably attached to one another over several vertebral levels. For example, the embodiment of  FIG. 10  has at least one modular attachment member  1005  that removably attaches to a rod  120  or to another type of device. The modular attachment member  1005  can be configured to removably attach to a rod or another type of device using various mechanisms.  FIGS. 15A and 15B  show top and side views of an embodiment of the attachment member  1005 . The attachment member  1005  has a receiving cavity  1505  that is sized and shaped to removably receive a rod  120 . It should be appreciated that the attachment member  1005  can have various types of structures that are adapted to removably receive or mate with a rod or other device. 
         [0060]    Spinous Process Devices 
         [0061]      FIGS. 16-26  show various flexible pivoting interspinous devices that can be attached onto the spinous processes and/or lamina of neighboring vertebral bones.  FIG. 16  shows a perspective view of an interspinous device that is configured for placement between the spinous processes of two adjacent vertebral bones.  FIG. 17  shows an exploded view of the device of  FIG. 16 .  FIG. 18  shows a cross-sectional view of the device implanted on the vertebral bones. The device includes an articulating central region  1605  that is sized and shaped to fit between the spinous processes of the two adjacent vertebral bodies. The device further includes a pair of attachment regions  1610  each adapted to attach and anchor onto the spinous process of a vertebral body. The central region  1605  can have a variety of shapes and sizes for placement between the spinous processes. The attachment regions  1610  can also have various sizes and shapes for attachment to the spinous processes. 
         [0062]    The attachment regions are attached to a pair of threaded screws  1615  (threads not shown) that are attached the spinous processes. As shown in  FIG. 18 , the screws  1615  have shank regions that extend into the spinous processes. It should be appreciated that means other than screws can be used to attach the attachment regions to the spinous processes. The central region  1605  of the device limits the extent of vertebral extension at the implanted level. The malleable nature of the device resists vertebral extension and rotation. The device also resists anterior or posterior displacement of one vertebral level relative to the other. While the illustrated embodiment will permit anterior flexion alone, additional members  110  may be added in the desired plane to produce additional rotational planes. 
         [0063]    With reference to the exploded view of  FIG. 17 , the central region  1605  includes a pair of arms  1705  that are movably attached to articulation locations or articulation points  1710 . The articulation points  1710  provide means of movement of the arms  1705  about the articulation points. The articulation points  1710  can be conventional pins that serve as hinges, or the articulation points can be articulation members of the type shown in  FIGS. 5-6 . The articulation points  1710  are cylindrically shaped and rotatably positioned in openings  1712  in the attachment regions  1610  and in the arms  1705  to provide rotational movement therebetween. The arms  1705  are attached to a housing  1720  having an opening that receives a flexible pivot member  1725  that has a construction similar to or the same as the articulation members shown in  FIGS. 5-6 . The pivot member  1725  serves as a central flexible pivot between the spinous processes. When implanted as shown in  FIGS. 16 and 18 , the device allows vertebral movement in certain planes while limiting vertebral motion. 
         [0064]      FIGS. 19-21  show another embodiment of an interspinous device that is configured for placement between the spinous processes of two adjacent vertebral bones.  FIG. 19  shows a perspective view of the device mounted on vertebral bones while  FIG. 20  shows a lateral view of the device mounted on vertebral bones.  FIG. 21  shows cross-sectional views of the device. As in the previous embodiment, the device includes an articulating central region  1605  that is sized and shaped to fit between the spinous processes of the two adjacent vertebral bodies. The device further includes a pair of attachment regions  1610  each adapted to attach and anchor onto the spinous process of a vertebral body. In this regard, the attachment regions  1610  are sized and shaped to at least partially encircle the spinous processes in an anterior-posterior direction. The attachment regions  1610  are contoured to provide a relatively smooth fit when placed on the spinous processes. 
         [0065]    The central region  1605  can have a variety of shapes and sizes for placement between the spinous processes. The central region  1605  includes an articulating member  1620  positioned between the spinous processes. The articulating member  1620  can have a structure as shown in  FIGS. 5-6 . The articulating member is configured to provide a point of articulation between the vertebral bones. It should be appreciated that additional points or locations of articulation can be provided, such as in the previously-described embodiment. The central region  1605  further includes a pair of plate members  1625  that abut the spinous processes in the implanted device. 
         [0066]      FIGS. 22-25  show various views of another embodiment of an interspinous device that is configured for placement between the spinous processes of two adjacent vertebral bones. The device includes an articulating central region  1605  that is sized and shaped to fit between the spinous processes of the two adjacent vertebral bodies. The device further includes a pair of attachment regions  1610  each adapted to attach and anchor onto the spinous process of a vertebral body. In this regard, the attachment regions  1610  are sized and shaped to be positioned along the sides of the spinous processes. The attachment regions  1610  can have a clamp-like or “u”-shaped configuration that is positioned over the sides of the spinous processes. 
         [0067]      FIG. 26  is a cross-sectional view that illustrates how attachment screws attach the device to the spinous processes. A pair of bone screws  1615  extend through the attachment regions  1610  and into the spinous processes. The screws engage the interior aspect of the spinous processes at an angle to the long axis of the spinous processes. The screws follow a trajectory that preferably aims the screw tips towards the vertebral midline M. An additional screw  1607  ( FIGS. 23 ,  25 ) can be inserted into the anterior-superior lip of the spinous processes. 
         [0068]    With reference still to  FIGS. 22-25 , the device has at least one, and preferably three, points or locations of articulation. The articulation is provided by one or more flexible pivot members  2205  located in the central region  1605 . The pivot members can have a construction as shown in  FIGS. 5-6 . 
         [0069]    There are now described and illustrated additional embodiments that use flexible plank members  200  to produce mobile devices with minimal frictional contact.  FIG. 27  shows a first embodiment of such a device. As in the previous embodiments, the device includes an articulating central region that is sized and shaped to fit between the spinous processes of the two adjacent vertebral bodies. The device further includes a pair of attachment regions each adapted to attach and anchor onto the spinous process of a vertebral body. The central region uses flexible plank members comprised of elongate, planar elements that can flex. The device has a cross member that attaches at opposite end to bone screw assemblies. The device can attach to the spinous processes using screws. While illustrated as attaching onto the spinous process using screws positioned along the long axis of the spinous process, the device may be alternatively attached to the bone using any of the previously illustrated fixation methods or any other applicable method that is known in the art.  FIG. 28  shows the device of  FIG. 27  in an exploded state.  FIGS. 29A and 29B  show the device in cross-section. 
         [0070]    The device includes attachment members  210 ,  220 , and  230  that fit between the spinous processes. The attachment members are inter-connected by the flexible plank members  200 . A first member  210  is affixed onto one vertebra while a second member  220  is attached onto a second vertebra. A member  230  is placed within the space between the spinous processes at a distance from each of members  210  and  220  and attached to the former by two side flexible plank members  200  and to the latter by a central flexible plank member  200 . The configuration of flexible plank members and attachment members permit particular movements and limit other types of movement. It should be appreciated that the quantity and shape of the flexible plank members can vary. 
         [0071]    In specific, significant movement of the vertebra towards each other is prevented by the interaction of members  210  and  220 . That is, vertebral extension is limited by the collision of member  210  and  220  with one another. Alternatively, member  230  may be enlarged and sized to limit vertebral extension by directly maintaining the distance between the spinous processes of the two vertebras. The members are sized and shaped to provide a level of movement therebetween. The movement of the vertebra away from one another is permitted but reversibly opposed by the action of flexible members  200 . The anterior translation of upper vertebra relative to the lower vertebra is prevented by the interaction of member  210  and  220 . Lateral flexion of the vertebral bodies is permitted to a limited degree. Vertebral rotation is limited by the shape of the flexible members  200  since rotation requires flexure of members  200  towards one of the long sides of each plank member. Rotation is also opposed by the collision of the medial surface of each of the laterally-placed members  200  and the lateral surfaces of medially-placed member  220 . The foregoing is illustrated in cross-section in  FIG. 30A  where the vertebral bodies are in partial flexion and in  FIG. 30B  where the vertebral bodies are in full flexion. Note that the amount of rotation does not vary with the extent of flexion. 
         [0072]      FIG. 31  shows another embodiment of the flex member  220 . This embodiment has a “V”-shaped configuration with a thickness defined by side walls  2205 . Along at least a portion of the member  220 , the side walls  2205  are non-parallel. For example, this embodiment has side walls  2205  that converge towards one another while the side walls  2205  of member  220  of the previous embodiment are parallel and non-convergent. With this modification, the present embodiment recreates physiologic spinal motion by allowing the extent of vertebral rotation to increase with progressive vertebral flexion. This is illustrated in cross-section in  FIG. 32A  where the vertebral bodies are in partial flexion and in  FIG. 32B  where the vertebral bodies are in full flexion. Note that the distances between the medial edge of each of members  200  and lateral side walls  2205  of member  220  increase with flexion and permit a greater range of vertebral rotation. 
         [0073]      FIGS. 33 and 34  illustrate perspective and cross-sectional views of another embodiment of an interspinous device. Like the prior two embodiments, attachment members  210 ,  220 , and  230  are inter-connected by flexible plank members  200  that extend between the attachment members. A member  210  is affixed onto one vertebra while member  220  is attached onto a second vertebra. Unlike the prior embodiments, the device is attached to the vertebral bone using bone screws or similar fasteners that attach onto the pedicle portion of the vertebrae. A bone screw also attaches to the spinal process. The member  230  is placed at a distance from each of members  210  and  220  and attached to the former by two side flexible plank members  200  and to the latter by a central flexible plank member  200 . The device is functionally similar to the prior two embodiments. 
         [0074]    There are now described multiple embodiments of mobile devices that are placed within the disc space between two vertebral bodies and used to at least partially replace and/or augment the function of the native disc. Each of these embodiments uses one or more of the flexible pivot members (articulation members) such as the type shown in  FIGS. 5 and 6 .  FIG. 35  illustrates a coronal section through embodiment of such a mobile device. The device contains a top surface  440 , a bottom surface  442 , cylindrical members  444  and  446 , link members  448  and  450  as well as multiple flexible pivot members of the type shown in  FIGS. 5 and 6 . The cylindrical members  444  and  446  slidably reside within cylindrical channels in the upper surface of member  442 . The articulations between the cylindrical members and cylindrical channels permit extension and anterior flexion of the implanted device and the attached vertebral bodies. In addition, the actions of the flexible pivot members  110  permit relative vertical movement of surfaces  440  and  442  and impart a shock-absorbing quality to the device. Finally, movement in the coronal plane recreates the lateral flexion movement of the natural disc but rotation is effectively prevented. 
         [0075]      FIG. 36A  is another embodiment that is similar to the previous embodiment. This embodiment is structured such that it is effectively one half of the previous embodiment. The device is particularly useful in the correction of vertebral coronal plane mal-alignment (i.e., scoliosis).  FIG. 36B  shows a mal-aligned vertebral segment and  FIGS. 36C  shows the segment with the device of  36 A implanted. The device is adapted to re-align the mal-aligned vertebral segment when positioned between the vertebral bodies. As in the previous embodiments, the top and bottom surfaces can move relative to one another in response to loads. Further, device attachments onto the sides of the vertebral bones provide additional points of fixation. 
         [0076]      FIGS. 37-40  illustrate multiple embodiments of mobile devices that are placed within the disc space between two vertebral bodies and used to at least partially replace and/or augment the function of the native disc. Each device embodiment uses one or more flexible plank members with a central mobile surface assembly  330  positioned therebetween. The assembly  330  is adapted to articulate in response to loads to provide relative movement between the flexible plank members.  FIG. 37  shows a perspective view of one embodiment while  FIG. 38  illustrates additional views of the embodiment.  FIG. 39  shows an exploded view of the central mobile surface assembly  330 . An upper segment  310 , middle segment  320  and lower segment  325  are interconnected by flexible plank members  315  as shown and collectively make up the upper one-half of assembly  330 . The flexible plank members  315  are spaced from one another to provide space for relative movement and articulation of the plank members  315 . The lower one-half of the assembly is similarly configured but the moving members are situated perpendicular to the upper one-half of the assembly.  FIGS. 40A and 40B  show alternative mobile assembly embodiments. 
         [0077]      FIGS. 41 to 55  show a dynamic rod. The rod is adapted to be linked at opposite ends to bone screw assemblies which attach to vertebral bones. The rod is dynamic in that it can change shape in response to loads. The device is preferably attached to bone using a screw assembly such as shown in the example of  FIG. 43 .  FIG. 41  illustrates a perspective view of the device while  FIG. 42  shows the device in an exploded state. The opposed ends of the device each have a head that couples to the bone screw assembly. 
         [0078]      FIG. 44  shows cross-sectional views of the device. In use, each end  500  is paced within a receiving porting of a bone screw assembly (such as shown in  FIG. 43 ). After the devices are placed into the desired position, the locking screw of the screw assembly is tightened thereby locking both spherical segments  505  of ends  500  relative to the remainder of the screw assembly. Each end segment  505  is rigidly affixed to the end segments  507  of flexible pivot  509  ( FIG. 45 ). The middle segment  511  of pivot member  509  is rigidly affixed to the middle segment  515  ( FIG. 45 ). The configuration allows the movement of middle segment  515  relative to immobilized end segments  505  based on the action of flexible pivot  509 . Each of rectangular rod  520  can move relative to one another in the direction of the long axis of the rods. 
         [0079]    In another embodiment,  FIGS. 46-49  show a dynamic rod assembly that includes two rod members  4610  that are movably attached to one another via a dynamic pyramidal connector. The connector is formed of two pieces  4615  and  4620  that can slidably move relative to one another in a male-female relationship.  FIG. 47  shows the device with the pieces  4615  and  4620  separated from one another. The piece  4620  is formed of a plurality of interconnected plank members that can flex relative to one another so as to change the shape of the piece  4620 . The piece  4620  fits into a cavity within the piece  4615 , as shown in the cross-sectional views of  FIGS. 48 and 49 . When positioned in the cavity, the planks of piece  4620  expand outward such that the piece  4620  is retained within the cavity. Movement of the male member relative to the female member is at lease partially resisted by the action of the plank members. 
         [0080]    The disclosed devices or any of their components can be made of any biologically adaptable or compatible materials. Materials considered acceptable for biological implantation are well known and include, but are not limited to, stainless steel, titanium, tantalum, shape memory alloys, combination metallic alloys, various plastics, resins, ceramics, biologically absorbable materials and the like. Any components may be also coated/made with osteo-conductive (such as deminerized bone matrix, hydroxyapatite, and the like) and/or osteo-inductive (such as Transforming Growth Factor “TGF-B,” Platelet-Derived Growth Factor “PDGF,” Bone-Morphogenic Protein “BMP,” and the like) bio-active materials that promote bone formation. Further, any surface may be made with a porous ingrowth surface (such as titanium wire mesh, plasma-sprayed titanium, tantalum, porous CoCr, and the like), provided with a bioactive coating, made using tantalum, and/or helical rosette carbon nanotubes (or other carbon nanotube-based coating) in order to promote bone in-growth or establish a mineralized connection between the bone and the implant, and reduce the likelihood of implant loosening. Lastly, the system or any of its components can also be entirely or partially made of a shape memory material or other deformable material. 
         [0081]    Although embodiments of various methods and devices are described herein in detail with reference to certain versions, it should be appreciated that other versions, embodiments, methods of use, and combinations thereof are also possible. Therefore the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.