Abstract:
A bone plate having a plurality of openings for receiving a compression bone screw or a cortical screw. An end cap, threadably insertable in the opening and having a layer of polymeric material interposed between the end cap and the top of the head such that the compression of the polymeric material would allow slight axial movement of the screw. Alternatively, a locking ring adapted to attach to the head of the screw and having shape complimentary to the features formed on the head. The locking ring and the bone screw being assembled together and being insertable in the bone simultaneously using a dedicated instrument. Compression may be applied to a bone fracture by turning the bone screw alone after the locking ring has reached its final axial position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/925,457 filed Apr. 19, 2007, the disclosure of which is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to an apparatus and method for the treatment of fractures of the proximal femur including the neck of the femur and the intertrochantric region. 
         [0004]    2. Brief Description of the Prior Art 
         [0005]    In treatment of the fracture of the femoral neck it is necessary to maintain angular stability of the head fragment to maintain an anatomical reduction postoperatively. It is also desirable to compress fracture site intra-operatively and then to stabilize the bone fragments by not allowing any further axial or angular movement. Since axial movement of the bone fragment resulting in shortening of the neck of the femur will result in reduced physical functioning, particularly in younger patients, it is desirable to stabilize the fracture postoperatively. 
         [0006]    Many locking plates are available that allow stabilization of bone fragments. Conventional locking plates (also known as bone plates) have a plate that is attached to the fragments of the fractured bone via screws that are inserted in the bone through screw holes in the plate. The screws of the conventional locking plates have threads on the head portion in addition to the threads on the shaft. The threads on the head portion have a greater core diameter than the threads on the shaft but both threads have same pitch. When the screw is advanced in the bone and the head of the screw is in the screw hole of the bone plate, the threads on the screw head engage matching threads in the screw hole. This locks the screw in place and prevents it from moving in the axial direction post operatively. However, such bone plate system cannot be used to compress the fracture site. In another conventional bone plate system used for femoral neck fracture a compression screw is used. The compression screw head does not have the threads and therefore may be rotated further after its head has reached the final axial position thereby compressing the fracture site. A separate end cap is then screwed in the compression screw hole of the bone plate to prevent the screw from moving back in the axial direction. 
         [0007]    These bone plate systems require a separate step of installing an end cap to prevent post operative axial movement of the screw. Therefore, there is a need for further improvement in bone plate systems to provide an easy to use plate system that facilitates intra-operative compression and at the same time provides angular and axial stability post operatively. 
         [0008]    As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a bone plate for use with fractures of the femur. Screws attach the bone plate to the femur. The compression screws that are inserted in the neck of the femur may be parallel to the axis of the neck of the femur. Inserting the bone screws in the neck region of the femur provides compression and angular and rotational stability to the head of the femur. Cortical interlocking type screws may be used in a distal portion of the bone plate in the subtrochantric shaft region of the femur. The compression screws stabilize bone fragments when used with end caps and prevent the shortening of the femoral neck resulting in improved postoperative function of the hip. The end cap may be inserted in a threaded plate hole and contact the top of each screw. A polymer buffer may be placed in the screw hole between the end cap and the head of the compression screw. The polymer buffer may allow small movement of the screw. 
         [0010]    In use, the compression bone screw is inserted in the screw hole and screwed into the neck of the femur until the underside of the bone screw sits on the flat face formed in screw hole. Next, the screw is rotated further to apply compression to the fracture site. Once the desired amount of compression is applied, the end cap is inserted in screw hole. The end cap prevents the screw from moving back in the axial direction. 
         [0011]    In another embodiment, a compression screw having a different head design is used with a split locking ring. The locking ring has a smooth circular outer surface that fits in the screw hole. The inner surface of the locking ring has a saw blade like or similarly functioning geometry. The saw blade geometry on the inner surface is preferably asymmetric. The compression screw head has a saw blade geometry that can mate with the saw blade geometry on the inner surface of the locking ring. 
         [0012]    In use, the screw and the split locking ring are assembled together and inserted into the screw hole. The assembly of the screw and the locking ring is then screwed into the bone using a dedicated insertion instrument that holds and rotates the screw and the locking ring simultaneously. When the head of the screw reaches the terminal axial position in the screw hole, both the screw and the locking ring can be rotated further to apply compression to the fracture site. After the compression is applied, the screw alone is turned. The locking ring is thereby clamped between the head of screw and the bone plate. This results in fixing the screw in place such that the screw can not back out in axial direction. 
         [0013]    In yet another embodiment, a compression screw having a different head design is used with a locking ring. The locking ring has a threaded circular outer surface that fits in the screw hole. The top wall of the locking ring projects towards the center of the screw hole and has a hexagonal internal periphery. The bottom surface of the top wall has ridges. The screw has a head that has an outer peripheral surface that slidably fits into the locking ring. The top surface of the head of the screw has depressions that correspond to the ridges. Thus, when the screw is assembled in locking ring, the ridges sit in the depressions. The top surface of the screw head also has a hexagonal depression to allow engagement of a suitable screw driver. 
         [0014]    In use, the compression screw and the locking ring are assembled together and inserted into the screw hole. The assembly of the screw and the locking ring is then screwed into the bone using a dedicated insertion instrument that holds and rotates the screw and the locking ring simultaneously. When the head of the screw reaches the terminal axial position in the screw hole, the screw can be rotated further to apply compression to the fracture site. When the screw is rotated further the ridges loose contact with the depressions. This forms a small gap of approximately 0.1-0.4 millimeters between the screw and the locking ring. As soon as the body weight is applied post-operatively, the femoral head fracture fragment presses the screw back to the lateral side until the movement is stopped by the locking ring. The polymer buffer may also be used with any of the above described embodiments. 
         [0015]    In one aspect the present invention provides a bone plating system having a bone plate having a plurality of openings. The system includes at least one bone screw for insertion in the opening and into a bone and having a head. Depressions are formed on a top surface of the head, and a locking ring adapted to attach to the head and having ridges that have shape complimentary to the depressions is provided. The locking ring fits in the depressions when the locking ring is attached to the head. The locking ring and the bone screw are assembly together and simultaneously inserted in the opening using a dedicated instrument. 
         [0016]    In another aspect, a bone plating system includes a bone plate having a plurality of openings. The system also has at least one bone screw capable of being received through the opening and into a bone. The head of the bone screw has an asymmetric saw blade geometry formed on the periphery. A locking ring having an asymmetric saw blade geometry matching the asymmetric saw blade geometry formed on the periphery of the head is provided. The locking ring and the bone screw are assembly together such that the saw blade geometry on the locking ring is in engagement with the saw blade geometry on the head, and the assembly is inserted in the opening using a dedicated instrument. 
         [0017]    In yet another aspect, a bone plating system includes a bone plate having a plurality of openings and at least one bone screw capable of being received through the opening and into a bone. The bone screw having a head adapted for fitting in the opening when the bone screw is fully inserted in the bone, the head of the bone screw and the opening in the bone plate having complementary shape such that the bone screw when seated in the opening has angular stability. At least one end cap is fixedly inserted in the opening, and a layer of polymeric material is interposed between the end cap and the top of the head such that the compression of the polymeric material would allow slight axial movement of the screw. 
         [0018]    In yet another aspect, a method of fusing fractures of femoral neck using a bone plate is disclosed. The method includes placing a bone plate on the femur, and inserting an assembly of a bone screw and a locking ring in an opening in the plate. Thereafter, simultaneously threading the locking ring and the bone screw in the femur and further threading the bone screw in the femur to compress the fracture. A space is created between the locking ring and the bone screw allowing the bone screw to move towards the locking ring when the joint is loaded. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]      FIG. 1  is an anterior elevation view of a bone plate mounted on a femur. 
           [0020]      FIG. 1A  shows another embodiment of a bone plate that may be mounted on the femur. 
           [0021]      FIG. 2  shows an isometric sectional view of a screw hole in the bone plate of  FIG. 1  with a bone screw and an end cap inserted therein. 
           [0022]      FIG. 3  is an isometric view of a first locking ring embodiment. 
           [0023]      FIG. 4  shows a sectional view of the bone plate of  FIG. 1  with a locking ring and a screw installed therein. 
           [0024]      FIG. 5  is a lateral view of a portion of a bone plate assembly showing the bone plate, a screw and the locking ring of  FIG. 3 . 
           [0025]      FIG. 6  is a sectional view of the bone plate of  FIG. 1  with a second embodiment of a locking ring and a screw installed therein. 
           [0026]      FIG. 7  is another sectional view of the embodiment of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION  
       [0027]      FIG. 1  shows a bone plate  20  mounted on a femur  22 . Any one of the compression screws disclosed hereafter may be used with the bone plate  20 . In  FIG. 1 , compression screws  24 A attach the bone plate  20  to the head  33  and neck  31  of femur  22 . Screws  24 A may be used to attach bone plate  20  to the femur via screw holes  26  in plate  20 . Cortical screws  25  may be used to attach a distal portion  27  of bone plate  20  to the subtrochantric shaft of the femur  22 . In the preferred embodiment these are locking screws. The compression screw  24 A may provide angular and axial stability to the fractured bone pieces. The compression screws  24 A may be cannulated or non-cannulated. The compression screws  24 A may also provide rotational stability. Rotational stability may be achieved by inserting at least two compression screws  24 A through the screw holes  26  and into the neck  31  of the femur  22 . The compression screws  24 A that are inserted in the neck  31  of the femur  22  may be parallel to the axis of the neck  31  of the femur  22 . Cortical interlocking type screws  25  may be used in plate holes  29  in the subtrochantric shaft region of the femur  22 . The cortical interlocking screws  25  may have threads (not seen in the figures) on the periphery of the head portion for engaging threads in hole  29 . The cortical interlocking type screws  25  may be used to prevent the backout of the screws  25  and the bone plate  20 . The compression screws  24 A stabilize the neck fracture head fragment and thereby prevent the shortening of the femoral neck  31  resulting in improved postoperative function of the hip.  FIG. 1A  shows a plate  20 A. Plate  20 A is a variation of design of plate  20 , and includes a slot  21 . A guide wire may be inserted through slot  21  and into the head  33  of femur  22 . The guide wire may be used to position the plate  20 A in a desired alignment on the surface of the femur  22 . Any one of the compression screws disclosed hereafter may be used with the bone plate  20 A. 
         [0028]      FIG. 2  shows the screw hole  26  in the bone plate  20  with bone compression screw  24  and an end cap  28  inserted in the screw hole  26 . The bone compression screw  24  may be a cannulated screw. However, non-cannulated screws may also be used. In a preferred embodiment, the screw hole  26  has a first threaded section  30  having a larger diameter and a second section  32  having a smaller diameter. A flat face  34  is formed at the junction of the first threaded section  30  and the second section  32 . Threads (not seen in the figures) may be formed on all or portion of the inner periphery of the first threaded section  30 . Inserting one bone compression screw  24  in the neck region of the femur  22  provides angular stability to the head  33  of the femur  22 . One or two or three or more bone compression screws  24  may be inserted in the neck region of the femur  22 . Inserting more than one bone compression screw  24  provides rotational stability to the head  33  of the femur  22 . An end cap  40  may be inserted in screw hole  26  on top of each compression screw  24 . A polymer buffer  44  may be placed in the screw hole  26  between the end cap  40  and the head of the compression screw  24 . The polymer buffer  44  may allow small movement of the compression screw  24 . 
         [0029]    In use, the bone compression screw  24  is inserted in the screw hole  26  and screwed into the neck  31  of the femur  22  until the underside of the bone compression screw  24  sits on the flat face  34  formed in screw hole  26 . Next, the compression screw  24  is rotated further to apply compression to the fracture site. Once desired amount of compression is applied, the end cap  40  is inserted in screw hole  26 . End cap  40  has threads (not seen in the figures) on its periphery that mate with the threads in the screw hole  26 . End cap  40  is screwed into the screw hole  26  till its bottom is on top of the top surface of the head of the compression screw  24  that was previously installed in that screw hole  26 . Thus, the end cap  40  prevents the compression screw  24  from moving back in the axial direction. Optionally, the polymer buffer  44  may be placed over the compression screw  24  prior to installing the end cap  40 . Cortical bone screw  25  are also installed in screw holes  29  and screwed into the subtrochantric shaft region of the femur  22 . The screws  24  and  25  stabilize the bone fracture. The end cap  40  and the bone plate  20  also provide angular stability. 
         [0030]    In another embodiment a compression screw  50  of a different head design is used with a split locking ring  52 .  FIG. 3  shows the locking ring  52 .  FIG. 4  shows a cross sectional view of the bone plate  20  with the locking ring  52  and the compression screw  50  installed therein.  FIG. 5  is a top view of a portion of a bone plate assembly showing the bone plate  20 , the compression screw  50  and the locking ring  52 . The locking ring  52  has a smooth circular outer surface  54  that fits in the screw hole  26 . The inner surface  56  of the locking ring  52  has a saw blade like geometry. The saw blade geometry on the inner surface  56  is asymmetric. The compression screw  50  has a head  58  that has an outer peripheral surface  60  with a saw blade geometry that can mate with the saw blade geometry on the inner surface  56  of the locking ring  52 . The top surface  62  of the screw head  58  has a hexagonal depression to allow engagement of a suitable screw driver. Other known shapes for the depression and corresponding screwdriver may also be used. 
         [0031]    In use, the compression screw  50  and the split locking ring  52  are assembled together and inserted into the screw hole  26 . The assembly of the compression screw  50  and the locking ring  52  is then screwed into the bone using a dedicated insertion instrument that holds and rotates the compression screw  50  and the locking ring  52  simultaneously. When the head of the compression screw  50  reaches the terminal axial position in the screw hole  26 , both the compression screw  50  and the locking ring  52  can be rotated further to apply compression to the fracture site. After the compression is applied, the compression screw  50  alone is turned. This makes the compression screw  50  rotate in relation to locking ring  52  which results in partial disengagement of saw blade geometry on the inner surface  56  of the locking ring  52  from the saw blade geometry on the outer peripheral surface  60 . Since the saw blade geometries on both these surfaces are asymmetrical, the disengagement results in spreading of the locking ring  52 . The locking ring  52  is thereby clamped between the head of compression screw  50  and the bone plate  20 . This results in fixing the compression screw  50  in place such that the compression screw  50  can not back out in axial direction. To remove the compression screw  50 , compression screw  50  is rotated in the opposite direction. This results in the engagement of the saw blade geometries on the on the inner surface  56  of the locking ring  52  and the outer peripheral surface  60 . Next, the compression screw  50  and the locking ring  52  may be removed simultaneously using the dedicated instrument. 
         [0032]    In yet another embodiment a compression screw  70  of a different design is used with a locking ring  72 .  FIGS. 6 and 7  show the bone plate  20 , compression screw  70  and the locking ring  72  assembled together. The locking ring  72  has a threaded circular outer surface  74  that fits in the screw hole  26 . The top wall  76  of the locking ring  72  projects towards the center of the screw hole  26  and has a hexagonal internal periphery. The bottom surface  78  of the top wall  76  has ridges  80 . The compression screw  70  has a head  82  that has an outer peripheral surface  84  that slidably fits into the locking ring  72 . The top surface  86  of the head of the compression screw  70  has depressions  87  that correspond to the ridges  80 . Thus, when the compression screw  70  is assembled in locking ring  72 , the ridges  80  sit in the depressions  87 . The top surface  86  of the screw head  82  also has a hexagonal depression to allow engagement of a suitable screw driver. Other known shapes for the depression and corresponding screwdriver may also be used. The external surface of the locking ring  72  may have threads (not seen in the figures) that engage threads in the screw hole  26 . 
         [0033]    In use, the compression screw  70  and the locking ring  72  are assembled together and inserted into the screw hole  26 . The assembly of the compression screw  70  and the locking ring  72  is then screwed into the bone using a dedicated insertion instrument that holds and rotates the compression screw  70  and the locking ring  72  simultaneously. When the head of the compression screw  70  reaches the terminal axial position in the screw hole  26 , the compression screw  70  can be rotated further to apply compression to the fracture site. When the compression screw  70  is rotated further the ridges  80  loose contact with the depressions  87 . This forms, for example, a small gap of approximately 0.1-0.4 millimeter between the compression screw  70  and the locking ring  72 . As soon as the body weight is applied post-operatively, the femoral head fracture fragment presses the compression screw  70  back to the lateral side until the movement is stopped by the locking ring  72 . 
         [0034]    To remove the compression screw  70 , compression screw  70  is rotated in the opposite direction. This results in the engagement of the ridges  80  in the depressions  87 . Next the compression screw  70  and the locking ring  72  may be removed simultaneously using the dedicated instrument. 
         [0035]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.