Abstract:
Devices and methods for spinal fixation employ at least first and second plates that are configured to allow progressive sliding advancement of the plate members toward one another and limit movement of the plate members away from one another after installation. A spring member associated with one bone plate may engage toothed section(s) on the other bone plate. The bone plates may each have arms that are spaced from one another and engaged by corresponding arms on the other bone plate. There may be more than two bone plates, with multiple restricted movement regions.

Description:
BACKGROUND  
       [0001]     Spinal plates have been developed for stabilization of various portions of the spine after various surgical procedures, particularly spinal fusion procedures. Conventional spinal fixation plates typically take the form of a unitary plate with a pair of bone screw openings at opposing ends. The plate is placed over an excavated bone graft-receiving site in the vertebral column, in which a bone graft is located for fusion to adjacent vertebrae, and secured in place with bone screws. These prior art spinal fixation plates fix the adjacent vertebrae on opposite sides of the bone graft-receiving site a set distance relative to one another.  
         [0002]     While the fixation plates discussed above are suitable for some situations, they also pose some difficulty in practice due to their lack of adjustability to a particular patient&#39;s needs. In particular, such fixation plates have a predetermined length with a predetermined spacing between the screw holes. As such, when a fixation plate with a different spacing is required for a particular patient, another fixation plate must be made available. As the particular needs of a patient may not be known prior to surgery, this necessarily means that multiple sizes of plates must be kept in ready inventory. In response to this, some forms of variable length fixation plates have been proposed, with varying degrees of success. The variable length devices allow the surgeon to adjust the length of the device during surgery, and then to fix that length via suitable locking mechanisms. However, even with variable length devices, the overall length of the device is fixed during surgery and does not change post-operatively.  
         [0003]     It has been recognized that it may be beneficial to subject the bone graft to compression over time as the graft fuses to the vertebrae. Use of the conventional fixed length or variable length spinal plates discussed above generally precludes compression of the bone graft beyond any initial compression achieved during the surgical procedure. As such, there remains a need for additional approaches to spinal fixation, advantageously approaches that allow the bone graft to be progressively compressed between adjacent vertebrae over time.  
       SUMMARY  
       [0004]     The present invention is directed to various embodiments of a bone fixation device and methods of use, typically for spinal fixation. One specific embodiment employs at least first and second bone plate members adapted to be secured to bone portions, such as adjacent vertebrae. The bone plate members are configured to allow progressive sliding advancement of the plate members toward one another and limit movement of the plate members away from one another after installation. For example, a spring member associated with one bone plate members may engage toothed section(s) on the other bone plate member. The spring member may be a generally U-shaped spring member abutting the first and second plate members and distinct therefrom. The bone plate members may each have arms that are spaced from one another and engaged by corresponding arms on the other bone plate member. The arms may engage in a male/female relationship, and the distal portions of the male arms may be substantially enclosed by the corresponding female arms. The centerlines of the arms may be substantially aligned when joined. There may be more than two bone plate members, with multiple restricted movement regions. Various combinations of these aspects may also be employed as is appropriate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  shows one embodiment of the present invention attached to a cervical portion of a spinal column.  
         [0006]      FIG. 2  shows one embodiment of the present invention attached to thoracic and/or lumbar portion of a spinal column.  
         [0007]      FIG. 3  shows an exploded view of a bone plate device according one embodiment of the present invention.  
         [0008]      FIG. 4  shows the bone plate device of  FIG. 3  in a partially-engaged configuration.  
         [0009]      FIG. 5  shows one embodiment of a “female” bone plate portion.  
         [0010]      FIG. 6  shows one embodiment of a “male” bone plate portion.  
         [0011]      FIG. 7  shows one embodiment of a spring member.  
         [0012]      FIG. 8  shows another embodiment of a spring member.  
         [0013]      FIG. 9  shows yet another embodiment of a spring member.  
         [0014]      FIG. 10  shows another bone plate device according to another embodiment of the present invention, having guide rails and slots.  
         [0015]      FIG. 11  shows a close up of a toothed section according to one embodiment of the present invention.  
         [0016]      FIG. 12  shows an exploded view of one multi-level embodiment of the bone plate device.  
         [0017]      FIG. 13  shows an exploded view of another multi-level embodiment of the bone plate device.  
         [0018]      FIG. 14  shows the device of  FIG. 13  in an assembled state.  
         [0019]      FIG. 15  shows one embodiment of a “female” bone plate portion suitable for use in the bone plate device embodiment of  FIG. 13 .  
         [0020]      FIG. 16  shows an exploded view of yet another multi-level embodiment of the bone plate device, displaying one approach to reversing the male/female relationship with respect to the embodiment of  FIG. 12 . 
     
    
     DETAILED DESCRIPTION  
       [0021]     One embodiment of the present invention is directed to a bone plate device for fixing vertebrae in the spinal column of a patient. One embodiment the device, generally designated  30  in  FIG. 1 , includes a male bone plate  40 , a female plate  80 , and a spring lock member  100 . The male bone plate  40 , disposed in the inferior position in  FIG. 1 , includes a generally U-shaped body with two arms  60   a,   60   b  and an intervening base section  42 . The base section  42  includes two holes  44  for receiving anchoring bone screws  5 , which may advantageously be counter-sunk. In addition, the base section  42  may include a third hole  46  for securing a locking ring or other device (not shown) that acts to retain the bone screws  5  in place once they are fully installed. The base section  42  has top  40 T and bottom surfaces  40 B, which may be flat or advantageously slightly curved to match the orthodic curve of the installation site, as desired. The arms  60   a , 60   b  extend from the base section  42  and may advantageously be disposed symmetrically about a midline of bone plate  40 , which advantageously coincides with the longitudinal axis  32  of the overall bone plate device  30 . In addition, arms  60   a , 60   b  have conceptual centerlines  68   a , 68   b  that are spaced from each other a distance D MC  and advantageously run generally parallel to longitudinal axis  32 . With respect to the longitudinal axis  32 , the arms  60   a , 60   b  have respective inner surfaces  66  and outer surfaces  67 . The inner surfaces  66  include respective sections  70   a , 70   b  having a plurality of teeth  72  therein, sometimes referred to herein as the toothed sections  70   a , 70   b . The teeth  72  of the toothed sections  70   a , 70   b  advantageously have a non-symmetric profile with a generally flat proximal face  74  disposed generally perpendicular to the longitudinal axis  32  and an outwardly angled distal face  75 . As can be seen, these toothed sections  70   a , 70   b  may be disposed proximally from the distal end portions of the arms  60   a , 60   b . The arms  60   a , 60   b  may have variable thickness, such as being thicker in a portion  62  proximal to the base section  42  and thinner in a section  64  distal from the base section  42 , with an optional shoulder  63  formed at the change in thickness. The section of the arms  60   a , 60   b  extending from proximate the toothed sections  70   a , 70   b  distally to their tips advantageously has a uniform thickness. The inside surfaces  66  of the arms are advantageously joined by a curved portion  43  of the base section  42  corresponding to the inside center of the overall U-shape.  
         [0022]     The female bone plate  80 , disposed in a superior position in  FIG. 1 , includes a generally U-shaped body with two arms  90   a , 90   b  and an intervening base section  82 . The base section  82  includes two holes  84  for receiving bone screws  5 , which may advantageously be counter-sunk. In addition, the base section  82  may include a third hole  86  for securing a locking ring or other device (not shown) that acts to retain the bone screws  5  in place once they are fully installed. The base section  82  has planar top  80 T and bottom surfaces  80 B, which may be flat or advantageously slightly curved to match the orthodic curve of the installation site, as desired. The arms  90   a , 90   b  extend from the base section  82  and may advantageously be disposed symmetrically about a midline of the superior bone plate  80 , which advantageously coincides with longitudinal axis  32  of the overall bone plate device  30 . In addition, arms  90   a , 90   b  have conceptual centerlines  98   a , 98   b  that are spaced from each other a distance D FC  and advantageously run generally parallel to the longitudinal axis  32 . Each arm  90   a , 90   b  includes a bay  92  that is intended to receive the distal portion  64  of a corresponding arm  60   a , 60   b  of the male bone plate  40 , and therefore generally corresponds in cross-sectional shape thereto. With respect to the longitudinal axis  32 , the arms  90   a , 90   b  have respective inner surfaces  90   SI  and outer surfaces  90   SO . In addition, the arms  90   a , 90   b  have respective top surfaces  90 T and bottom surfaces  90 B, which advantageously continue the shape of top and bottom surfaces  80 T, 80 B of base section  82 . A groove  94  may be formed on the inner surfaces  90   SI  that extends along one arm  90   a , across the distal curved surface  83  of the base section  82 , and along the other arm  90   b . Near each end of the groove  94 , a small passage  93  connects the groove  94  to the corresponding bay  92 . If desired, top surface  90 T may include a notch  96  extending outwardly from the longitudinal axis  32  a short distance, proximate the terminal ends of the groove  94 . The groove  94  is intended to accept the spring lock member  100 , as discussed further below. Advantageously, the arms  90   a , 90   b  may have relatively uniform thickness, such as a thickness corresponding to that of the base section  82  of the superior bone plate  80 . In addition, it should be noted the inside surfaces  90   SI  of the arms  90   a , 90   b  are advantageously spaced a distance apart of D SI , which is smaller than distance D T  separating the toothed sections  70   a , 70   b  of the inferior bone plate  40 .  
         [0023]     The spring lock member  100 , or simply spring member, is advantageously generally U-shaped, with respective pawl barbs  102   a,   102   b  extending outward from the longitudinal axis  32  on each end of the U-shape. The material of the spring member  100  may taper towards the distal portion of the U-shape if desired, for added flexibility. Each pawl barb  102   a  , 102   b  , or simply pawl, advantageously has non-symmetric profile with a generally flat proximal face  104  extending generally perpendicular to the longitudinal axis  32 , and a sloped distal face  105  that is angled outward and backward to the proximal side of the spring member  100 .  
         [0024]     The spring member  100  is mated to the female bone plate  80  by inserting the spring member  100  in the groove  94 , with the barbs  102   a  , 102   b  facing outward. The optional notches  96  proximate the terminal portions of the groove  94  aid in seating the barbs  102   a  , 102   b  properly. It should be noted that the tips of the barbs  102   a  , 102   b  are intended to extend through the passages  93  and into the corresponding bays  92 . The inherent spring force of the spring member  100  helps urge the barbs  102   a  , 102   b  into position. As such, it may be advantageous for the spring member  100 , when in a natural unconstrained state, to have a slightly flatter U-shape, but be required to assume a narrower U-shape by interaction with the superior bone plate  80  (e.g., by being restrained by the groove  94 ).  
         [0025]     With the spring member  100  in place, arms  60   a , 60   b  of the male bone plate  40  are inserted into the bays  92  of arms  90   a , 90   b  of the female bone plate  80 . Advantageously, the two bone plates  40 , 80  are somewhat loosely coupled at this point, such that they can be moved both toward and away from each other. Such a condition may be achieved, for example, by having the pawls  102   a  , 102   b  of the spring member  100  bear against the inner surfaces  66  of the arms  60   a , 60   b  distally from the toothed sections  70   a , 70   b . For ease of reference, this configuration may be referred to as the pre-installation configuration. The bone plate device  30  may be shipped from the manufacturer in this pre-installation configuration, or the bone plate device  30  may be assembled to this configuration after shipment, but prior to or during surgery.  
         [0026]     In use, a surgical site is opened and prepared in any known fashion. At an appropriate point in the procedure, such as shortly after a bone graft implant is placed in position, the bone plate device  30  is installed by securing the bone plates  40 , 80  to their respective vertebrae V 1 ,V 2  using bone screws  5  and holes  44 , 84 . During installation, the length of the bone plate device  30  may be adjusted by sliding the bone plates  40 , 80  relative to each other. Advantageously, during installation, the bone plates  40 , 80  are moved toward each other so that pawls  102   a  , 1   02   b  of the spring member  100  engage some of the teeth  72  of the toothed sections  70   a , 70   b  , such as the distal most teeth  72 . For ease of reference, this configuration may be referred to as the partially-engaged configuration. In this partially-engaged configuration, the bone plates  40 , 80  have limited ability to move apart due to the engagement of the pawls  102   a  , 102   b  and the toothed sections  70   a , 70   b . However, the bone plates  40 , 80  may be moved closer together in a progressive ratcheting fashion due to the interaction of the angled faces  75 , 105  of the pawls  102   a  , 102   b  and the teeth  72 . During this forward or closing movement, the end portions of the spring member  100 , proximate the pawls  102   a  , 102   b  , are deflected inward toward the longitudinal axis  32  until the next tooth  72  is passed, at which point the inherent spring force of the spring member  100  urges the pawls  102   a  , 102   b  outward to “lock-in” the incremental movement. Thus, the surgeon is able to adjust the bone plate device  30  to the desired initial length prior to closing the surgical site.  
         [0027]     Post-operatively, the bone plate device  30  described above is able to continue to shorten (i.e., the proximal portions  48 , 88  of the bone plates  40 , 80  are allowed to move toward each other) incrementally, but is limited in its ability to lengthen, thereby helping to ensure proper compression of the bone graft. Of course, as the bone plate device  30  continues to shorten, the bone plates  40 , 80  will at some point reach a point of maximum movement toward each other. For example, the tips of arms  90   a , 90   b  may abut against the shoulders  63  formed on arms  60   a , 60   b  where the arms  60   a , 60   b  change thickness, thereby preventing further shortening of the bone plate device  30 . For ease of reference, this configuration may be referred to as the fully-engaged configuration.  
         [0028]     As can be seen in  FIG. 3 , with arms  60   a , 60   b  engaging arms  90   a , 90   b  , the “female” arms  90   a , 90   b  advantageously extend farther inward toward the longitudinal axis  32  than the “male” arms  60   a , 60   b  , and also advantageously extend farther outward away from the longitudinal axis  32  than the centerlines  68   a , 68   b  of their counterpart arm  60   a , 60   b . In some embodiments, the arms  90   a , 90   b  may advantageously extend at least as far outward as their counterpart arm  60   a , 60   b  , and optionally farther outward. Indeed, in some embodiments, the female arms  90   a , 90   b  may substantially circumferentially enclose the distal portions  64  of the male arms  60   a , 60   b . Further, it should be noted that in some embodiments the distance D FC  between the centerlines  98   a , 98   b  of arms  90   a , 90   b  is advantageously approximately equal to distance D MC  associated with centerlines  68   a , 68   b  of arms  60   a , 60   b . While not required in all embodiments, the advantageous spacing and/or general alignment of the arms  60   a , 60   b  , 90   a , 90   b  discussed above allows the curved sections  43 , 83  of the bone plates  40 , 80  to help define a generally oval visualization port  34  through the bone plate device  30 , thereby allowing the surgeon to easily view the bone graft between the vertebrae V 1 ,V 2 . Advantageously, this visualization port  34  exists in the pre-installation, partially-engaged, and fully-engaged configurations. The width W O  of the visualization port  34  in a direction generally transverse to a theoretical line connecting the two curved surfaces  43 , 83 , such as along the longitudinal axis  32 , is advantageously approximately equal to the distance D T  between the toothed sections  70   a , 70   b  in the same direction.  
         [0029]     In some embodiments, the spring member  100  may have an additional proximal portion that acts to retain the bone screws  5  in place once they are fully installed. This additional portion may, if desired, take the form of two curved fingers  108  that approximate a split circle. The fingers  108  may sit in a suitable recess in the proximal portion  82  of bone plate  80 , and flex inwardly when the bone screws  5  are installed, but spring back out to retain the bone screws  5  with the bone plate  80  and help prevent backing out of the bone screws  5  after they are fully installed. As such, it may be advantageous for the bone screws  5  to include small circumferential shoulders on their heads. Backing out refers to inadvertent removal or significant loosening of the bone screws  5  while installed in the patient; intentional loosening and/or removal of the bone screws  5  by, e.g., a surgeon, is not considered backing out. In other embodiments, the end portions of the spring member  100 , proximate the pawls  102   a  , 102   b , may optionally include small inwardly extending tabs  110  that may include small holes  112 . Pulling inward on such tabs  110 , such as with appropriate retaining ring pliers extending through the holes  112 , disengages the pawls  102   a  , 102   b  in the event such is needed to intentionally spread apart the bone plates  40 , 80 . Alternatively, some embodiments allow the pawls  102   a  , 102   b  to be disengaged by inserting a suitable tool into notches  96  and/or passages  93 . In still other embodiments, the legs of the spring member  100  may include small outwardly protruding bumps  114 , disposed closer to the base of the U than the pawls  102   a  , 102   b  , that help retain the spring member  100  with the bone plate  80  by resting in corresponding depressions (not shown) in the arms  90   a , 90   b.    
         [0030]     The interconnection between the bone plates  40 , 80  may, in some embodiments, further include inter-engaging rails  65  and slots  95  that help guide the sliding movement of the bone plates  40 , 80 . In this vein, the distal portion  64  of arms  60   a , 60   b  of bone plate  40  may include rails  65  that extend generally parallel to axis  32 , and are advantageously located along centerlines  68   a , 68   b . These rails  65  mate with corresponding slots  95  in the arms  90   a , 90   b  of bone plate  80 . Alternatively, the rail  65  and slot  95  positions may be reversed.  
         [0031]     The teeth  72  of the toothed sections  70   a , 70   b  discussed above have been assumed to be regularly spaced and disposed essentially contiguously, with the base  76  of one tooth  72  abutting the base  76  of the adjacent tooth  72 . However, such an arrangement is not required in all embodiments. In some embodiments, the teeth  72  may be spaced apart some amount, so that a significant space  78  exists between the bases  76  of adjacent teeth  72 . See  FIG. 11 . When a pawl  102   a  , 102   b  of spring member  100  is disposed in this space  78 , the bone plates  40 , 80  may move relative to each other, both forward and backward, some small limited amount. With such an arrangement, small movements by the patient that might otherwise cause the bone plate device  30  to ratchet to the next shorter increment are allowed without causing such ratcheting. Such spaces  78  may be limited to being not more the size of the base  76  of the teeth  72 , so that, in effect, the toothed section  70   a , 70   b  has the appearance of every other tooth  72  being removed. Other tooth profiles and tooth/teeth configurations are also possible, such staggering teeth  72  on the different toothed sections  70   a , 70   b  , curved profiles for the teeth  72 , and the like.  
         [0032]     The discussion above has been in terms of a bone plate device  30  having two bone plates  40 , 80  for fixing two adjacent vertebrae V 1 ,V 2 . However, some embodiments of the bone plate device  30  may have more bone plates for fixing together more than two vertebrae. For example, the multi-level bone plate device  30 ′ of  FIGS. 12-14  has three bone plates for fixing three adjacent vertebrae V 1 ,V 2 ,V 3 . Two of the bone plates, the upper and lower bone plates  80 ′, 80 ″, may be as described above for bone plate  80 . The other bone plate, the center bone plate  120 , may be somewhat similar to bone plate  40  described above, but with four arms  60 ′, two on each end. Thus, the center bone plate  120  of such an embodiment has four arms  60 ′ with four corresponding toothed sections  70 ′, and two curved sections  43 ′. For such a bone plate  120 , the terms “proximal” and “distal” are with reference to the midline thereof perpendicular to the longitudinal axis  32 ′ of the overall bone plate device  30 ′. In addition, such a device  30 ′ may have two spring members  100 ′ similar to spring member  100  discussed above. For such a configuration, the upper and lower bone plates  80 ′, 80 ″ move toward the center bone plate  120  from generally opposite directions along the longitudinal axis  32 ′ of the bone plate device  30 ′. To use such a multi-level device, the upper bone plate  80 ′ is secured to an upper vertebrae V 1 , the center bone plate  120  is secured to a middle vertebrae V 3 , and the lower bone plate  80 ″ is secured to a lower vertebrae V 2 . The installation and movement limiting action of such a device  30 ′ is substantially as described above.  
         [0033]     It should be understood that the male/female relationship of the embodiments discussed above may be reversed without departing from the scope of the present invention. For example, another embodiment of a multi-level bone plate device is shown in  FIG. 16 . This multi-level embodiment of the bone plate device  30 ″ is similar to that described immediately above, but with the male/female relationship reversed for the connection between center bone plate  120 ′ and lower bone plate  40 ′. Thus, the center bone plate  120 ′, has two male arms (like arms  60   a , 60   b ) extending toward upper bone plate  80 ′, and two female arm (like arms  90   a , 90   b ) extending toward lower bone plate  40 ′.  
         [0034]     The bone plates  40 , 40 ′, 80 , 80 ′, 80 −, and spring members  100 , 100 ′ may be made from any material or materials, such as titanium, poly-ether-ether-ketone (PEEK), or the like, compatible for use in an animal body over significant periods of time. Bioabsorbable and/or resorbable materials may alternatively used.  
         [0035]     The various embodiments of the bone plate device  30 , 30 ′, 30 ″ may be used in various locations in the animal body, including without limitation anterior or lateral locations on the cervical, thoracic, and lumbar portions of the spinal column.  
         [0036]     Other embodiments of the present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The terms “upper”, “lower”, “inner”, “outer”, and the like are terms to describe the relative positioning of different elements, and are used in a general sense. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.