Abstract:
A device for treating bone fractures and/or for fixing surgical implants, surgical threads or tissues in or on the bone comprising a closing element and a rivet. The rivet includes a shaft extending from a rear end to a front end coaxial to a central axis and having a through-hole extending coaxially therethrough. The shaft of the closing element is coaxially displaceable in the through-hole and the head of the closing element can be axially brought to rest on the front shaft end. The rivet also comprises at least two grooves on the outside, these grooves extending from the front shaft in the direction of the rear end, parallel to the central axis.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a device for the treatment of fractures of bones and/or for fixing surgical implants, surgical threads, or tissues in or on the bone.  
         BACKGROUND OF THE INVENTION  
         [0002]    For the surgical treatment of fractures of bones or for fixing surgical implants, threads, or tissues in or on the bone, even rivets, in particular blind rivets, can be used. Particularly suitable are rivets with closing heads formed of separate anchoring tongues spread relatively wide. Such blind rivets are disclosed in the non-medical area, e.g. in UK Patent Application No. GB 2,054,082 to Tucker Fasteners. The anchoring tongues are formed by axial tearing of the wall of the rivet shaft at the front end of the blind rivet by means of a pyramid-shaped, sharp-edged closing head which is drawn into the hollow cylindrical rivet shaft from the front end. At least one disadvantage of these types of blind rivets is their limited application to soft materials and the necessity of high closing forces for forming the closing head on the blind rivet.  
           [0003]    A need exists for an improved medically applicable fixation means, in particular a surgically applicable blind rivet which provides materials with high strength, e.g. titanium, and can be fixed by means of closing forces acceptable in surgery. A need also exists that the device be suitable for the treatment of fractures of bones and/or for fixing surgical implants, surgical threads, or tissues in or on the bone.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention generally relates to a device comprising a closing element with a shaft and at the end position a head which is fixedly connected to the shaft or, for example, can be connected by means of a thread connection, to the shaft, and a rivet which comprises, coaxial to a central axis, a rivet shaft and a through-hole coaxially penetrating the rivet.  
           [0005]    The shaft of the closing element can be displaced coaxially in the through-hole so that the head can be brought axially to lie at the front shaft end. The head and shaft of the closing element can be structured in two parts or as one part. Furthermore, the rivet shaft includes two grooves which extend from the front shaft end parallel to the central axis over a length L in the direction of the rear end of the rivet. The grooves serve as theoretical break points so that on further displacement of the closing element in the direction of the rivet head the rivet shaft is divided by the head of the closing element into anchoring tongues on a part of its overall length. In one preferred embodiment, the ratio of the length L to the overall length of the rivet shaft is between 20% and 90%.  
           [0006]    In another preferred embodiment of the device according to the invention, the rivet shaft includes at least one slot, each slot having a first end intersecting the front shaft end and extending into the through-hole and a second end extending parallel to the central axis into a groove. In another embodiment, the rivet includes at its rear end a rivet head which can be fixedly connected to the rivet or, for example, can be connected to the shaft by means of a thread connection.  
           [0007]    In another embodiment of the device according to the invention, the characteristic values of the rivet material lie within a range of the ratio of tensile strength to elongation at break of 10:1 to 50:1, preferably 10:1 to 30:1.  
           [0008]    In still another embodiment of the device according to the invention, the geometric dimensions of the rivets are chosen so that the ratio of the outer diameter da of the rivet shaft to the diameter d of the through-hole lies in a range from 1.1:1 to 2.5: 1, preferably from 1.5:1 to 2:1. The ratio of the radial depth t of the grooves to the wall thickness of the rivet shaft lies suitably in a range from 1:1.2 to 1:2.5, preferably from 1:1.7 to 1:2.3. The wall thickness can be determined from the difference of the outer diameter da and the diameter d. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein:  
         [0010]    [0010]FIG. 1 is a top view of the device according to the invention,  
         [0011]    [0011]FIG. 2 is a longitudinal cross-sectional view through the embodiment of the device according to the invention represented in FIG. 1,  
         [0012]    [0012]FIG. 3 is a cross-sectional view taken along line I-I of FIG. 2,  
         [0013]    [0013]FIG. 4 is a perspective view of the device of FIGS.  1  to  3 .  
         [0014]    [0014]FIG. 5 is a longitudinal cross-sectional view of another embodiment of the device according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Referring to FIG. 1, a rivet  2  and a closing element  1  according to one embodiment of the device according to the invention are represented. The rivet  2  has a central axis  6  and comprises a cylindrical rivet shaft  3  running parallel to the central axis  6 . In a preferred embodiment, the cylindrical rivet shaft is not necessarily required to be circularly cylindrical. A rivet head  4  is fixedly connected to the rivet shaft  3 , and a cylindrical through-hole penetrates the rivet  2  coaxially along the central axis  6 . The rivet shaft  3  has an outer diameter da and includes grooves  9  which run parallel to the central axis  6 , and extend from the front shaft end  7  over a length L, and have a depth t from the outer circumferential surface  14 . The depth t is determined so that the wall thickness, defined by the diameter da and d and the depth t, on closing of the rivet  2  with the closing element  1  allows a separation of the rivet  2  into separate anchoring tongues  13  (FIG. 4) on the part to be closed. In a preferred embodiment, the number of anchoring tongues  13  corresponds to the number of grooves  9  introduced on the outer circumferential surface  14  of the rivet  2 .  
         [0016]    The grooves serve as theoretical break points so that on further displacement of the closing element in the direction of the rivet head the rivet shaft is divided by the head of the closing element into anchoring tongues on a part of its overall length. In this embodiment, the ratio of the length L to the overall length of the rivet shaft may be between 20% and 90% so that the anchoring tongues can expand radially to a surface F which can be 3 to 20 times the cross-sectional surface of the rivet shaft. The number of the grooves distributed uniformly on the circumference of the rivet shaft may be in a range of 3 to 8, preferably 3 to 5. From the number of grooves the number of anchoring tongues in the fixed rivet also follows. In the embodiment of the rivet  2  represented here, the wall thickness of the rivet shaft  3  corresponds to 14% of the outer diameter da. From the front apical face  15  of the rivet shaft  3 , slots  12  penetrate into the rivet shaft  3  parallel to the central axis  6 . The slots run, on one side, at the front shaft end  7  into the through-hole  5  and, on the other side, parallel to the central axis  6  into the grooves  9 .  
         [0017]    The closing element  1  comprises a shaft  10  parallel to the central axis  6  and at the end position a head  11  is disposed which runs in the form of a wedge into the shaft  10 . The closing of the rivet  2  is accomplished after the introduction of the rivet  2 , e.g. into a bone plate and a bone (not represented) by means of the closing element  1 . The head  11  of the closing element  1  has a diameter D which is greater than the diameter d of the through-hole  5  so that the head  11  of the closing element  1  is pressed into the inner cone  8  (FIG. 2) of the through-hole  5  by means of a tractive force exerted on the shaft  10 . On pressing the widening wedge-like head  11  of the closing element  1  into the inner cone  8  (FIG. 2) in the through-hole  5 , the wall  20  (FIG. 2) of the rivet shaft  3  is expanded and on further pressing of the head  11  of the closing element  1  separated into the anchoring tongues  13  (FIG. 4) at the theoretical break points formed by the grooves  9 .  
         [0018]    Referring to FIG. 2, a cross-section of the rivet is represented which corresponds to the above-described embodiment of the device according to the invention. The rivet  2  comprises a central axis  6 , a circularly cylindrical rivet shaft  3  with a front shaft end  7  intersecting the central axis  6 , and at its rear end  18  intersecting the central axis  6  at the end position a rivet head  4 , also circularly cylindrical. At the front shaft end  7  there is a front apical face  15  perpendicular to the central axis  6 . The rivet head  4  runs against the front shaft end  7  directed convexly or tapering in the form of a wedge into the rivet shaft  3  and also convexly or tapering in the form of a wedge into the rear apical face  19  of the rivet  2 . The rear apical face lies at the end position at its rear end  18 . A through-hole  5  penetrates coaxially to the central axis  6  and the rivet  2  from the front shaft end  7  up to the rear end  18 . The through-hole  5  runs at the front shaft end  7  with the inner cone  8  expanding into the front apical face  15 . Parallel to the central axis  6 , grooves  9  are introduced which penetrate from the front shaft end  7  up to a length L (FIG. 1) into the rivet shaft  3  and have a V-shaped cross-section (FIG. 3) perpendicular to the central axis  6 . Moreover, slots  12  penetrate into the rivet shaft  3  from the front apical face  15  also parallel to the central axis  6 . These slots  12  have a rectangular cross-section (FIG. 1) perpendicular to the central axis  6  and have a wedge-like structure parallel to the central axis  6 . The slots  12  run parallel to the central axis  6  and run into the front apical face  15 , into the outer circumferential surface  14 , and into the grooves  9 . The tearing of the rivet shaft is promoted by these slots.  
         [0019]    [0019]FIG. 4 shows the rivet  2  with central axis  6 , rivet head  4 , expanded rivet shaft  3 , and closing element  1  in the closed state of the rivet  2 . The rivet shaft  3  is expanded to the length L (FIG. 1) and comprises three anchoring tongues  13 .  
         [0020]    In one preferred embodiment, the rivet may have the following geometric dimensions: the outer diameter da of the rivet shaft may be 2 to 12 mm, preferably 3 to 8 mm; diameter d of the through-hole may be 1 to 8 mm, preferably 1.5 to 5 mm; wall thickness of the rivet shaft may be 0.2 to 4 mm, preferably 0.5 to 2 mm; and radial depth t of the grooves may be 0.1 to 3 mm, preferably 0.2 to 1 mm. In another embodiment of the device, the geometric dimensions of the rivets are selected so that the ratio of the outer diameter da of the rivet shaft to the diameter d of the through-hole is in a range from 1.1:1 to 2.5:1, preferably from 1.5:1 to 2:1.  
         [0021]    The ratio of the radial depth t of the grooves to the wall thickness of the rivet shaft may be in a range from 1:1.2 to 1:2.5, preferably from 1:1.7 to 1:2.3. The wall thickness can be determined from the difference of the outer diameter da and the diameter d. In an additional embodiment, the grooves may have a triangular cross-section perpendicular to the central axis where the apical angle of the triangle in the base of the groove lies within a range of 30° to 80°, preferably of 40° to 70°.  
         [0022]    The rivet material is preferably metallic and may include the following materials or alloys: a) materials based on iron, preferably steel, b) materials based on titanium, preferably Ti CP and titanium alloys, c) materials based on cobalt, preferably cobalt alloys, d) materials based on tantalum, preferably tantalum alloys, and e) materials based on zirconium, preferably zirconium alloys. In another embodiment, the rivet may be made from a material having the following physical properties or characteristics: the ratio of tensile strength (Rm in N/mm2) to elongation at break (A5 in %) is between 10:1 to 50:1, preferably between 10:1 to 30:1.  
         [0023]    Referring to FIG. 5, an embodiment of the rivet  2  is represented which is distinguished from the forms of embodiment represented in FIGS. 1 and 2 only in the fact that the rivet  2  includes no rivet head  4  (FIGS. 1 and 2) at its rear end  18 . Furthermore, the closing element  1  penetrates the rivet  2  only on a part of its overall length and is structured with a hole  21  penetrating the closing element  1  coaxially. The hole is provided at its end  22  lying axially opposite the head  11  with a coaxial inner thread  23 . A Kirschner wire  24  can be screwed into this inner thread and can be screwed out of the inner thread  23  once again after the closing of the rivet  2 .  
         [0024]    It will be appreciated that a more homogeneous introduction of force into the bones is possible as compared to the use of screws, and generally a more stable anchoring can be produced compared to bone screws, even with poor bone quality.  
         [0025]    While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein. Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.