Abstract:
An interlocking bone plate system includes an outer bone plate for being arranged outside a broken bone, an inner bone plate for being installed inside the medullary cavity of the broken bone, and screws for being inserted through and engaged with the outer bone plate and the broken bone and then engaged with the inner bone plate so as to interlock the out and inner bone plates together. The inner bone plate provides an added support in addition to the support provided by the outer bone plate, enhancing the structural strength of the whole bone fixation structure and lowering the risk of failed surgery.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to orthopedic instruments and more particularly, to an interlocking bone plate system for rigidly affixing bone segments. 
     2. Description of the Related Art 
     Conventionally, a bone plate and screws are used in surgery for fixation of a comminuted or osteoporotic fracture. By means of the engagement force between the screws and the bone and the friction force between the bone plate and the bone, the bone plate is affixed to the surface of the bone at one side. This fixation method is not stable due to the fact that when the load from the patient during a movement of the patient is greater than the friction force between the bone plate and the surface of the bone, the bone plate may be forced to display, biasing the screws. Further, if the bone plate is not closely matched in configuration with the bone, or if the screws are fastened excessively tight or the bone bears an excessive load, bone repositioning after surgery may be destructed. 
     Due to the aforesaid drawbacks of conventional surgery, a new locking plate is created for healing a broken bone. A locking plate of this design has an inner thread in each screw hole thereof for engagement with an outer thread around the periphery of the head of each screw. Thus, when a locking plate is locked to a broken bone by screws, the locking plate is not kept in direct contact with the surface of the broken bone, minimizing bone contact surface area, avoiding periosteal compression, facilitating quick bone healing and enhancing structural stability. 
     However, the biodynamic effect of the fixation of the aforesaid new locking plate is still obscure. Further, a locking plate system of this design is quite expensive and requires a specifically designed surgical implement during surgery. Further, if the bone receives an excessive muscle tension or load after surgery, the fixation cannot sustain inverse deformation of the bone, leading to surgical failure. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide an interlocking bone plate system for healing a broken bone, which provides a highly stable fixation structure. 
     To achieve this object of the present invention, an interlocking bone plate system is adapted for fixation of a fracture of a bone comprising a diaphysis, two epiphysises at two distal ends thereof, two metaphysises respectively connected between the diaphysis and the two epiphysises, an outer bone wall and a medullary cavity surrounded by the outer bone wall. The interlocking bone plate system comprises an outer bone plate attached to the bone adjacent to a predetermined area of an outer surface of the bone and comprising at least one first through hole, an inner bone plate set in the medullary cavity of the bone corresponding to the outer bone plate and comprising at least one second through hole corresponding to the at least one first through hole of the outer bone plate, and at least one screw for locking the outer bone plate and the inner bone plate to the bone. Each screw comprises a head for engaging in one the first through hole, and a shank engageable through the outer bone wall of the bone into one the second through hole. Thus, the inner bone plate gives an added support, enhancing the structural strength and lowering the risk of failed surgery. 
     Other advantages and features of the present invention will be fully understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference signs denote like components of structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of an interlocking bone plate system in accordance with a first embodiment of the present invention. 
         FIG. 2  is an elevational view of the first embodiment of the present invention, illustrating the interlocking bone plate system affixed to a bone. 
         FIG. 3  is a schematic side view, partially in section, of the first embodiment of the present invention, illustrating the interlocking bone plate system affixed to the bone. 
         FIG. 4  is an exploded view of an interlocking bone plate system in accordance with a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     By ways of the following examples in conjunction with the annexed drawings, the technical contents and features of the present invention will be fully understood. 
     An interlocking bone plate system  10  is shown for healing a broken bone of a patient, more particularly, for fixation of a comminuted or osteoporotic fracture. As shown in  FIG. 2  and  FIG. 3 , the structure of a bone  1  is symmetric. In the drawings, only one end of the bone  1  is shown for explanation. As illustrated, the bone  1  mainly comprises a diaphysis  2 , two epiphysises  3  at the two distal ends thereof, two metaphysises  4  respectively connected between the diaphysis  2  and the two epiphysises  3 , a bone wall  5 , and a medullary cavity  6  surrounded by the bone wall  5 . In this embodiment, the interlocking bone plate system  10  is affixed to one end of the bone  1 , comprising an outer bone plate  12 , an inner bone plate  14  and a plurality of screws  16 . 
     As shown in  FIGS. 1-3 , the outer bone plate  12  is arranged at a location outside the bone  1 , and configured subject to the configuration of the bone  1 . The outer bone plate  12  is kept in proximity to a predetermined area of the outer surface of the bone  1  at a predetermined distance, comprising a plurality of first through holes  121  and a first inner thread  122  in each of the first through holes  121 . Specifically speaking, the outer bone plate  12  defines a diaphysis portion  18 , an epiphysis portion  20  and a metaphysis portion  22 . The diaphysis portion  18  is shaped like an elongated bar, having at least one first through hole  121  provided thereon. In this first embodiment, as shown in  FIG. 1 , four first through holes  121  are spacedly arranged on the diaphysis portion  18  in a line. The epiphysis portion  20  comprises a forked structure consisting of three protruding lugs  201 , and at least one first through hole  121 . In this first embodiment, as shown in  FIG. 1 , one first through hole  121  is located on one of the three protruding lugs  201 . The metaphysis portion  22  is located between the diaphysis portion  18  and the epiphysis portion  20  and integrally joined with the diaphysis portion  18  and the epiphysis portion  20 . The metaphysis portion  22  has at least one first through hole  121  provided thereon. In this first embodiment, as shown in  FIG. 1 , one first through hole  121  is provided on the metaphysis portion  22 . 
     Referring to  FIGS. 1 and 3  again, the inner bone plate  14  is shaped like an elongated bar and mounted inside the medullary cavity  6  of the bone  1  corresponding in location to the outer bone plate  12 . The length of the inner bone plate  14  is slightly greater than that of the outer bone plate  12  so that one end of the inner bone plate  14  can be kept in proximity to one epiphysis  3  of the bone  1  in the medullary cavity  6 . The inner bone plate  14  comprises at least one second through hole  141  and a second inner thread  142  in each second through hole  141 . In this first embodiment, totally eight second through holes  141  are provided on the inner bone plate  14 . 
     Each of the screws  16  comprises a head  161 , a shank  162 , a first outer thread  163  extending around the periphery of the head  161 , and a second outer thread  164  extending around the periphery of the shank  162 . As shown in  FIG. 3 , the screws  16  are respectively inserted through the outer bone plate  12 , the bone  1  and the inner bone plate  14 . The heads  161  of the screws  16  are respectively set in the first through holes  121 . By means of threading the respective first outer threads  163  into the respective first inner threads  122 , the heads  161  of the screws  16  are respectively engaged into the first through holes  121 . By means of the respective second outer threads  164 , the shanks  162  of the screws  16  are driven through and engaged with the bone wall  5  of the bone  1 . Further, by means of threading the respective second outer threads  164  into the respective second inner threads  142 , the shanks  162  of the screws  16  are respectively engaged into the second through holes  141 . Thus, the outer bone plate  12  outside the bone  1  and the inner bone plate  14  in the medullary cavity  6  are spacedly and interconnectedly secured together. 
     Based on the aforesaid technical features, the interlocking bone plate system of the present invention comprises an inner bone plate set in the medullary cavity for fixation with an outer bone plate outside the bone to be healed. Through the dual support design, the outer and inner bone plates of the interlocking bone plate system effectively share the tension force received by the bone after surgery. When the bone receives a great load pressure, the inner bone plate can additionally provide a support against the compression force, enhancing the structural strength of the fixation. This design of interlocking bone plate system has a structural strength five times greater than similar conventional bone plate systems. Thus, the interlocking bone plate system of the present invention can bear a high load, preventing inverse deformation of the bone and lowering the risk of failed surgery. Further, performing a surgical operation using the interlocking bone plate system of the present invention does not require any other particular surgical implements. 
       FIG. 4  illustrates an interlocking bone plate system  30  in accordance with a second embodiment of the present invention. This second embodiment is substantially similar to the aforesaid first embodiment with the exception that the first through hole  321  at the metaphysis portion  42  of the outer bone plate  32  and the first two first through holes  321  at the diaphysis portion  38  of the outer bone plate  32  adjacent to the metaphysis portion  42  each define a first peripheral edge  323  and three first positioning portions  324  located on the first peripheral edge  323 ; the three second through holes  341  of the inner bone plate  34  corresponding to the first through hole  321  at the metaphysis portion  42  of the outer bone plate  32  and the first two first through holes  321  at the diaphysis portion  38  of the outer bone plate  32  adjacent to the metaphysis portion  42  each define a second peripheral edge  343  and three second positioning portions  344  located on the second peripheral edge  343 . The interlocking bone plate system  30  further comprises an anchor member  44 , which comprises three first anchoring portions  441  and three second anchoring portions  442 . 
     Each of the first anchoring portions  441  corresponds to one respective first positioning portion  324  of one of the respective first through hole  321 . Each of the second anchoring portions  442  corresponds to one respective second positioning portion  344  of one of the respective second through hole  341 . As shown in  FIG. 4 , the first anchoring portions  441  and the second anchoring portions  442  are shaped like a block, specifically a sharp-edged block, thus, the anchor member  44  exhibits a triangular cross section. The first positioning portion  324  and the second positioning portions  344  are notches, specifically are sharp notches. The anchor member  44  is detachably insertable through one first through hole  321  and the corresponding second through hole  341 . Thus, the first through hole  321  at the metaphysis portion  42  of the outer bone plate  32  and the first two first through holes  321  at the diaphysis portion  38  of the outer bone plate  32  adjacent to the metaphysis portion  42  and the corresponding second through holes  341  allow insertion of respective screws  36  and selectively insertion of the anchor member  44 . When the inner bone plate  34  is set in the medullary cavity  6  of the bone  1 , the anchor member  44  can be inserted through one first through hole  324  and the broken zone of the bone into the corresponding second through hole  341  to temporarily secure the inner bone plate  34  and the outer bone plate  32  in a proper angle and position, and then respective screws  36  can be fastened to the outer bone plate  32  and the inner bone plate  34  to fixedly fasten the outer bone plate  32  and the inner bone plate  34  to the bone, and then the anchor member  44  can be removed from the outer bone plate  32  and the inner bone plate  34  for insertion of one screw  36  as a substitute. Thus, the interlocking bone plate system  30  is accurately and conveniently affixed to the fracture area of the bone. 
     Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.