Abstract:
The present invention relates to a bone plate designed to secure locking screws inserted into the plate at various angles. The interior wall surface of the plate apertures include a series of protruding threaded ridges interspaced by relief notches. The threaded ridges and intermediate relief notches of the bone plate in combination with the threaded ridges and intermediate relief notches of the locking screw head allow the locking screw to bypass or “lump” threads of the bone plate. Thus, the locking screw can be inserted into the bone plate at a first angle and part-way through its advancement along the threads of the bone plate that angle can be changed. The second angle can either be greater than the first with respect to an orientation perpendicular to a longitudinal axis of the bone plate, or less than. This gives the physician a great amount of flexibility during a surgical procedure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application also claims priority from U.S. Provisional Application Ser. No. 61/175,855, filed May 6, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related generally to implantable orthopedic implants. More specifically, the present invention is related to implantable orthopedic bone plates used to reinforce fractured bones. 
         [0004]    2. Background of the Invention 
         [0005]    Orthopedic bone plates play a critical role in the healing process of broken bones. Once a bone has been fragmented, it is ideal for the broken bone fragments to be joined back together under compression to promote improved healing. The bone plate is a critical device that is used as a stabilizing bar to bridge the gap between bone fragments. 
         [0006]    During surgery, a bone plate is inserted next to the fragmented bone of a patient. Compression screws are first placed through the bone plate. They are anchored into each of the bone fragments and tightened, pulling the bone fragments together under a compression load and against the plate. Once the compression screws are set in place, locking bone screws are inserted through the bone plate and anchored into the fragmented bone. The locking screws in conjunction with the bone plate secure the bone fragments together the compression created by the compression screws and ensure that they do not move. However, high tensile stresses are created when the bone fragments are fixated with the locking screws. These tensile stresses could damage the fragile bone fragments and impair the healing process. Bone plates, therefore, are a key element in the bone healing process. 
         [0007]    Bone fragmentation, however, is unpredictable. As a result of a traumatic experience, a bone may fragment in multiple erratic locations and present itself in random orientations. Every patient&#39;s bones are unique; no two bones will fragment in the same manner in the same orientation. Nevertheless, traditional bone plate technology makes it difficult for a bone plate to be oriented in such a manner as to be utilized correctly for every trauma situation. Bone plates are rigid braces, typically composed of metal, which have historically been designed with fixed threaded holes through which some bone screws may not properly align with the matching bone fragment. In that respect, early bone plate technology comprised bone plates with preexisting threaded holes in combination with threaded locking screws. These earlier bone plates often lacked the ability to secure bone fragments that were not aligned under the threaded screw holes. That is because the preexisting threaded holes of earlier bone plate technology confined the angle through which the locking screw could be advanced into a bone fragment. 
         [0008]    For example, with the earlier bone plate and screw technology, the physician could only advance the screw along the pre-defined orientation of the threads in the bone plate. This limitation often created a problem for the physician in that only bone fragments that presented themselves directly under a threaded aperture in the bone plate could be secured together. Examples of these earlier bone plate and locking screw devices are disclosed in U.S. Pat. No. 5,709,686 to Talus et al.; U.S. Pat. No. 6,206,881 to Frigg et al.; and U.S. Pat. No. 6,306,140 to Siddiqui, the disclosures of which are incorporated herein by reference. 
         [0009]    In an effort to increase the degree of freedom in healing fractured bones, bone plates were developed with locking screws that can be inserted at different angles through the plate. One such improvement was the development of a bone plate with a tappable contact region as disclosed in U.S. Pat. No. 6,955,677 by Dahners. The disclosure of this patent is incorporated herein by reference. The &#39;677 patent discloses a bone screw with a threaded head that is intended to penetrate into the hole of the bone plate in a tapping fashion. A drawback to this invention, however, is that it utilizes a softer bone plate material which lacks rigidity and stiffness to bear high tensile loads. Over time the softer material of the bone plate can yield to tensile stresses, resulting in possible movement of the bone fragments, which is detrimental to proper healing of the bone fragments. 
         [0010]    Accordingly, an orthopedic device is needed that expands the possible locking screw insertion angles in anchoring bone fragments to promote bone healing. 
       SUMMARY OF THE INVENTION 
       [0011]    In that light, the present invention is directed to an orthopedic bone plate system comprising a compression screw, a locking screw, and a bone plate with a plurality of complex locking screw apertures. The inner wall of the bone plate is provided with a plurality of thread columns separated from each other by relief notches. Likewise, the head of the locking screw is provided with a plurality of thread columns separated from each other by relief notches. When the thread columns of one are aligned with the relief notches of the other, it is possible to impart a lateral force to the screw. This force causes the screw threads to jump either up or down one row of threads on the bone plate to alter the angular orientation of the bone screw with respect to its original orientation when its threaded engagement with the bone plate began. That way, the present bone plate system increases the number of possible locking screw insertion angles even after the screw is partially threaded into the bone plate and the bone undergoing repair. This results in a desirable compression fit between plate and bone that would otherwise not be possible. 
         [0012]    Therefore, it is now possible to secure bone fragments in compression with a bone plate using greater angular orientations for the bone screw. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a perspective view of the orthopedic bone plate system  10  of the present invention. 
           [0014]      FIG. 2  is an enlarged view of two complex bone plate apertures of the present invention as shown in  FIG. 1 . 
           [0015]      FIG. 3  is an enlarged top view of a complex bone plate aperture of the present invention. 
           [0016]      FIG. 4  is a perspective view of a locking screw embodiment of the present invention. 
           [0017]      FIG. 4A  is an enlarged perspective view of the locking screw head as shown in  FIG. 4 . 
           [0018]      FIG. 5  depicts a cross-sectional view of the present invention with locking screws inserted through the bone plate of the present invention. 
           [0019]      FIG. 6  is a schematic view depicting the advancement of a screw through a threaded aperture of a bone plate at a first angle. 
           [0020]      FIG. 7  is a schematic view showing the threads of the screw of  FIG. 6  having “jumped” a row of threads in the bone plate to change the orientation of the screw to a second, different angle. 
           [0021]      FIG. 8  is a schematic view showing the locking screw being threaded into the plate at the second angle depicted in  FIG. 7 . 
           [0022]      FIG. 9  is a perspective view of a compression screw. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    Turning now to the drawings,  FIG. 1  is a perspective view of an orthopedic bone plate system  10  according to the present invention. The bone plate system  10  comprises a bone plate  12  and at least one locking screw  14 . If desired, at least one compression screw  15  can also be included. 
         [0024]    The bone plate  12  has a longitudinal axis A-A, an axis B-B ( FIG. 3 ) which is oriented 90 degrees from axis A-A, a bone contacting bottom side  20  and a top side  22 . At least one complex aperture  24  extends through the bone plate  12  from the top side  22  to the bottom side  20 . The complex aperture  24  is designed to receive either the locking screw  14  or the compression screw  15 . In this embodiment, the complex aperture  24  is comprised of at least one set of two immediately adjacent apertures  26 ,  28 . The apertures  26 ,  28  do not overlap, thereby providing the complex aperture  24  as an oval shaped opening.  FIG. 2  shows an enlarged perspective view of the complex aperture  24 . 
         [0025]    The plan view of the complex aperture  24  illustrated in  FIG. 3  shows that apertures  26 ,  28  have a center-to-center distance d along the longitudinal axis A-A that is greater than the diameter d 1  of the head of the locking screw  14  ( FIG. 4A ) or d 2  of the head of the compression screw  15  ( FIG. 9 ). That way, the adjacent apertures  26 ,  28  of the complex aperture  24  define a relief-space  30  disposed between them. Preferably, the relief-space  30  is configured as either a straight slot, or as a constricted or “waisted” slot centered along axes A-A and bisected by axis B-B. 
         [0026]    A compression ramp surface  38  emerges into the complex aperture  24  from opposite sides of the wall  34  of the bone plate  12  to provide part of the boundary for the relief-space  30 . Preferably, the compression ramp surfaces  36  are non-threaded and ramp into the open relief space  30  of the complex aperture  24  along both the axis B-B perpendicular to the longitudinal axis A-A of the bone plate  12  and into the open space of the openings  26 ,  28  themselves. The ramp surfaces  36  slope downwardly and inwardly from the bone plate top side surface  22  into the opening of the complex aperture  24 . At the relief space  30 , the distal end of each of the ramps  38  meets a substantially vertical surface  40  which extends to the bone plate bottom side  20 . At the openings  26 ,  28 , the ramps  38  meet threaded surfaces of the openings. Vertical surface  40  can be planar or have a beveled contour that ramp into the open spaces  30  and into each of the apertures  26 ,  28  of the complex aperture  24 . 
         [0027]    The downwardly and inwardly sloping ramps  38  act as compression structures for the locking screw  14 . As the locking screw  14  is threaded into one of the apertures  26  or  28  comprising the complex aperture  24  and moves in a downwardly direction, the underside of the locking screw head  16  compresses against the ramp surface  38 . The downwardly sloping inclination of the ramp  38  causes the screw head  16  to slide down the ramp  38 , creating a frictional fit and prohibiting advancement of the locking screw  14  further into the complex aperture  24 . 
         [0028]    A series of threads that are generally indicated by numerical designation  31  in  FIGS. 1 and 2  protrude from the plate walls defining the apertures  26 ,  28 . The plate threads  31  are aligned in a spiral extending from adjacent to the top side  22  toward the bottom side  20 . The spiral of the plate threads  31  has a pitch that ranges from about 0.1 mm. to about 1.0 mm. 
         [0029]    The plate threads  31  are also orientated in thread columns  32 ,  33 , etc. ( FIGS. 6 to 8 ). Each thread column  32 ,  33  extend along the interior aperture wall surface  34  from the top side  22  to the bottom side  20  of plate  12 . The thread columns  32 ,  33  are preferably spaced apart from each other by a distance ranging from about 0.10 mm. to about 0.500 mm. 
         [0030]    The space between each thread column  32 ,  33  is defined as an aperture relief notch  36  in the form of an indentation into the wall of the bone plate  12  defining the apertures  26 ,  28  of the complex aperture  24 . Each complex aperture  24  may comprise multiple relief notches  36  having exemplary shapes including curved, squared-off or as a key slot. In that manner, the threads  31  of the bone plate  12  provide both spiral and columnar structures. 
         [0031]    As shown in  FIGS. 4 and 4A , the locking screw  14  is comprised of a bulbous head  16  and an elongated shaft  18 . The locking screw head  16  is comprised of locking threads that are generally indicated by numerical designation  45 . The threads have a pitch similar to that of the threads  31  of the bone plate  12 . The screw threads  45  are also aligned in a series of threaded columns  52 ,  54 ,  56 ,  58 , etc. When viewed from the side, the locking threads  45  are separated from each other by a “V” cutout  47 . It is in the space provided by the V-cutouts  47  that the threads  31  of the bone plate  12  reside as the screw  14  is threaded into the bone plate. A screw relief notch  60  is provided between adjacent columns of locking threads  45 . The relief notches  60  extend from the locking screw head proximal end to the locking screw head distal end adjacent to the threaded shaft  18 . 
         [0032]      FIG. 5  illustrates two exemplary orientations of locking screws  14  threaded in the bone plate  12 . The right one is at about 90 degrees with respect to the longitudinal plane of the bone plate  12  while the left locking screw  14  is at an insertion angle of about 10° in relation to the longitudinal plane. Insertion angles can range from about 1° to about 45°, however, they preferably range from about 10° to about 40°, and more preferably from about 15° to about 35° from perpendicular. This figure is an exemplary illustration of the many orientations that the locking screw  14  can be inserted into the bone plate  12 . 
         [0033]      FIGS. 6 ,  7  and  8  illustrate how the present bone plate  12  and locking screw  14  system  10  allows the threads of the locking screw head  16  to bypass or “jump” threads on the bone plate. That the threads of the locking screw head  16  are capable of “jumping” threads of the bone plate  12  is made possible by the incorporation of the respective relief notches  36 ,  60  in both the bone plate apertures  26 ,  28  of the complex aperture  24  and in the locking screw head  16 . 
         [0034]    As  FIG. 6  shows, as the locking screw  14  is threaded into the bone plate  12 , screw threads in column  46  and  48  reside between thread columns  32  and  33 , respectively, of the bone plate. In other words, the threads of the bone plate columns  32 ,  33  reside in the cutouts  47  provided between the thread columns  46 ,  48  of the screw  14 . 
         [0035]    In particular, screw thread  46 A resides between bone plate threads  32 A and  32 B and screw thread  46 B resides between bone plate threads  32 B and  32 C. In the adjacent column, screw thread  48 A resides between bone plate threads  33 A and  33 B and screw thread  48 B resides between bone plate thread  33 B and  33 C. The relief notch  36  of the bone screw  12  resides between screw thread columns  32  and  33  and relief notch  60  of the plate  12  resides between plate thread columns  46  and  48 . This alignment of the screw threads disposed between threads of the bone plate  12  is a typical configuration as the locking screw  14  is threaded into the bone plate in a customary manner. In particular, since the plate threads have a pitch, plate thread  33 A is at a slightly lower elevation than plate thread  32 A as the screw  16  is advancing into the bone plate. That is regardless whether the locking screw  14  is at an initial orientation perpendicular to the longitudinal plane of the plate as in the right-hand screw shown in  FIG. 5  or at some other angular orientation as shown in the left-hand screw in that drawing. 
         [0036]      FIG. 7  illustrates how the locking screw threads bypass or “jump” levels of bone plate threads. As the figure shows, a lateral force  100  has been applied to the locking screw head  16 . This lateral force  100  is illustrated by showing that the longitudinal axis of the screw  16  has deviated an angle α. This angle is measured by the difference between the longitudinal axis  102  of the screw prior to the lateral force  100  in relation to the orientation of the axis  104  after the lateral force. In practice, the lateral force  100  would be imparted to the screw as the screw is simultaneously being threaded into the bone plate. 
         [0037]    As a result of the lateral force  100 , exemplary locking screw thread  46 A has moved laterally and downwardly, bypassing or “jumping” from where it would have resided between bone plate threads  33 A and  33 B had the lateral force  100  not occurred to being angled toward a position residing between bone plate threads  33 B and  33 C ( FIG. 8 ). This lateral force can only be exerted against the screw  14  when its columns of threads reside in the notches  36  of the bone plate  12 . That is when the leading edge of a screw thread, for example threads  46 A and  46 B, is not engaged with either thread column  32  or  33  of the bone plate. However, the trailing edge of the screw threads  46 A,  46 B are still disposed between bone plate threads  32 A,  32 B and  32 B,  32 C, respectively. Otherwise, the bone screw  14  would be capable of simply “falling” through the bone plate every time the columns of threads  52 ,  54 ,  56 ,  58 , etc. on the screw  14  are in alignment with the relief notches  36  of the plate  12 . 
         [0038]    Further, the width of each thread  45  comprising the thread columns  52 ,  54 ,  56 ,  58 , etc. of the screw  14  are laterally from about 0.5 to 2 millimeters wider than the width of the bone plate relief notches  36 . This is illustrated in  FIG. 7  where exemplary screw thread  46 A has its leading edge just beginning to reside between the edges of plate threads  33 B,  33 C before the trailing edge of that thread has left the edges of plate threads  32 A,  32 B. That is from a longitudinal perspective with respect to the edges of the threads of the plate  12  and of the screw  14  as shown by dashed lines  106  and  108 . 
         [0039]    It should be pointed out that while the present plate and screw system  10  permits the physician to change the angle of the screw  14  part way through it being screwed into the plate  12 , that should not be viewed as limiting. Additionally, the screw  14  could be oriented with the threads of the bone plate  12  in the orientation shown in  FIG. 8 . That is in a “jumped” or cross-threaded orientation from the beginning. Furthermore, even though the sequence of drawings of  FIGS. 6 to 8  shown that the angle α can be increased so that the screw ends at a greater angle of inclination that which it was first oriented ( FIG. 6 ), the angle could also be decreased. That would be where even though the screw is being tightened by being rotated to the right, the angle of inclination or pitch of its threads is in an upwardly or horizontal orientation instead of a downwardly direction as shown in  FIG. 8 . This structure provides the physician with a large amount of flexibility in repairing a fractured bone with the present system  10 . 
         [0040]    The compression screw  15  illustrated in  FIG. 9  can also be used with the bone plate  12  of the present invention. The compression screw  15  has shaft threads  15 A that are helically disposed around the shaft  15 B. An unthreaded head  15 C is affixed to the proximal end of the shaft  15 B. 
         [0041]    The bone plate  12  and locking and compression screws  14 ,  15  are preferably made from Ti 6Al-4V. However, other biocompatible materials, not limited to other titanium alloys, stainless steel or polymers, i.e., PEEK could also be used. 
         [0042]      FIG. 1  further illustrates that the bone plate can comprise a threaded aperture  110  adapted to receive only one screw or an overlapping threaded aperture  112 . The overlapping threaded aperture is similar to that described in U.S. Pat. No. 7,695,472 to Young, which is incorporated herein by reference. The complex aperture  112  comprises at least two overlapping holes having an offset of a given distance between centers thereof, wherein any two immediately adjacent overlapping holes comprise a compression ramp extending from an oval shaped opening at the top side of the plate downwardly and inwardly part way through the plate thickness to a threaded lower portion having an hourglass shape extending from where the compression ramp ends at the hourglass shape to the bottom side of the bone plate with threaded surfaces of the overlapping holes meeting each other at a threaded overlap forming the hourglass shape, wherein the threaded lower portion is adapted to lock with threads of a corresponding bone screw in one or the other of the overlapping holes. The overlapping holes can be formed either normal to the top side of the plate or at an angle offset from normal. In either embodiment  110 ,  112 , the aperture has a relief notches disposed between columns of threads as described with respect to the complex aperture  24 . 
         [0043]    It is appreciated that various modifications to the inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention.