Abstract:
An osteosynthetic device, particularly a condylus screw, which is composed of a female-type part and a shank part which each have a flanged portion. At least one flanged portions is a separate part and is formed as a ring-shaped bearing component which forms a bearing seat for a spherically-shaped end portion of the female-type part and/or the shank part and wherein the bearing is movably supported on the female-type and/or the shank part.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to an osteosynthetic condylus screw generally for use with a bone nail. In certain types of fractures the condylus screw can be used without the bone nail.  
           [0002]    A supracondylar or retrograde bone nail is disclosed in U.S. Pat. No. 6,010,505. It has an elongate shank which is shaped relatively short as compared to other femoral nails and is driven in through a bore which distally opens out between the condyli and, for the rest, follows the bone channel. To take good care of a fracture in the condylus region, a so-called condylus screw is provided which can be passed through a transverse bore of the bone nail. The condylus screw has a female-type portion and a shank portion which are screwed together. At each end, the portions have a flange-like extension which bears on the bone side which faces it. Such a screw makes it easy to efficiently compress the bone fragments and retain them on the nail. The latter normally is designed as a so-called locking nail.  
           [0003]    The extent to which the flanged-like extension bears on the bone depends on the position exhibited by the ends of the condylus screw, and the outer contour of the bone. It might readily happen that only small surface regions will bear thereon, thus producing an undesirably high contact pressure.  
         SUMMARY OF THE INVENTION  
         [0004]    It is the object of the invention to provide an osteosynthetic device which avoids the disadvantage described and which allows optimum adaptation to the bone.  
           [0005]    In the screw of the present invention, at least one flanged portion is shaped as a separate part and is in the form of a ring-shaped bearing component which is movably supported on a spherically-shaped end portion of the female-type part or the shank part of the condylus screw. The movable, preferably pivotable, bearing of the flange-like portion provides for movability in all directions so that optimum adaptation is made to the prevailing surface conditions and, thus, minimal contact pressure is applied to the bone surfaces.  
           [0006]    Various constructional measures are possible to join the flange-like portion to the ball-shaped end portion. According to the invention, one design feature provides that the bearing part be shaped so as to allow it to snap onto the ball-shaped end portion. However, care has to be taken that the snap-on connection be designed so as to prevent it from inadvertently getting separated while or after the screw is mounted. In particular, the two elements must not snap out in the direction of pull.  
           [0007]    According to the invention, a particularly simple constructional version consists in that some sort of bearing socket is provided which has a slot, which permits resiliently widening the bearing socket. However, there is possibly a danger here that a tensile load also effects widening. Therefore, another aspect of the invention provides that the slot be shaped in such a way that the ends of the bearing socket which face the slot can be moved away from each other only to a limited degree. Such a slot, for example, may be of an S or Z shape. As soon as the motion to move apart the ends of the ring-shaped bearing socket exceeds a preset extent portions of the slot will bear on the slot and prevent any widening.  
           [0008]    As in the case which is known from the prior art, the side of the bearing part, which faces the bone, can be of a planar shape. The opposite side preferably is of a rounded contour to prevent lesions to the tissue.  
           [0009]    An alternative option also consists in the bearing socket or bearing ring not being slotted, but providing axially parallel webs which are conformed to the ring-shaped bearing part in their circumferential spacing and define some part of the bearing socket-like recess. The raised webs grip around the ball-shaped end portion and land in place in a slightly springable way while the end portion is being inserted. After being mounted, the webs prevent the end portion from getting out of the bearing ring.  
           [0010]    The inventive screw or the inventive osteosynthetic device, for example, may be used with a supracondylar nail, but also with any other locking nail. However, it is also possible to use the osteosynthetic device herein with no bone nail if there is an appropriate attendance situation, i.e., in an appropriate fracture.  
           [0011]    The invention will now be explained in more detail with reference to an embodiment shown in the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows a side view of a shank portion of a condylus screw according to the invention;  
         [0013]    [0013]FIG. 2 shows a longitudinal section through the illustration shown in FIG. 1;  
         [0014]    [0014]FIG. 3 shows a side view of a female-type part of a condylus screw according to the invention;  
         [0015]    [0015]FIG. 4 shows a section through the female-type part of FIG. 3;  
         [0016]    [0016]FIG. 5 shows a plan view of the bearing socket for the condylus screw according to the invention;  
         [0017]    [0017]FIG. 6 shows a section through the illustration of FIG. 5 taken along lines  6 - 6 ;  
         [0018]    [0018]FIG. 7 shows a section through the distal femur part with a supracondylar nail and a condylus screw according to the state of the art;  
         [0019]    [0019]FIG. 8 shows a plan view of a bearing part of another embodiment of the invention;  
         [0020]    [0020]FIG. 9 shows a side view of the bearing part of FIG. 8; and  
         [0021]    [0021]FIG. 10 shows a section through the bearing part of FIG. 8 taken along lines  10 - 10 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Initially, it should be noted that the drawings are not to scale.  
         [0023]    Referring to FIG. 7, the distal region of a femur  10  is shown which receives a bone nail  12 . It is inserted through a bore which is subcondularly made in a retrograde way. This is explained in detail in U.S. Pat. No. 6,010,505 the teachings of which are incorporated herein by reference.  
         [0024]    The distal region of bone nail  12  is provided with three transverse bores. FIG. 7, the state of the art, further makes it evident that the condylus region of the femur is damaged by an obliquely extending fracture having a fracture line  32 . Two bone screws  34 ,  36  are passed through two of the three transversal bores and serve to anchor nail  12  in femur  10 . A condylus screw  38 , which is composed of a shank part  50  and a female-type part  42 , is passed through the distal transverse bore. The two parts  42 ,  50  are screwed onto each other (with the thread not being shown). The female-type part  42  and the shank part  50  have flange-like heads which are followed by conical portions  44 . A condylus screw  38  helps to accomplish a compression. The flange-like heads are rigidly connected to the parts associated therewith. The parts of the condylus screw shown in FIGS.  1  to  6  are of a similar structure, but are configured in a particular way. This will be described in greater detail below.  
         [0025]    The shank part of the preferred condylus screw of the present invention is indicated by  60  and is shown in FIGS. 1 and 2. It has a smooth, cylindrical shank portion  62 , a threaded end portion  64 , and a ball-shaped or ball section-shaped head  66 . Shank part  60  is axially traversed by a through bore or cannulation  68 . There is a hexagonal socket  70  in the head  66  for engagement with a tool for rotating the shank. The shank part  60  has a conical portion  72  near the head  66 .  
         [0026]    A female-type part  74  is illustrated in FIGS. 3 and 4. In the preferred embodiment, it has a conical threaded portion  76  having a female-type thread and a ball-shaped or ball section-shaped head  78  with a hexagonal socket  80 . Female-type part  74  also has a through axial bore  82 . As can be seen the shank part  60  and female-type part  74  are shown at different scales because the female-type part is screwed onto threaded portion  64  when in use with the free end of the conical portion  76  being of a diameter which is equal to the diameter of smooth shank portion  62 .  
         [0027]    In the preferred embodiment, a bearing disc  86  the contour of which can be seen from FIGS. 5 and 6 is snapped onto the ball-shaped heads  66  and  78 . The bearing disc or bearing cup  86  is circular at its circumference and has an inner globular or ball-shaped bearing portion  88 . Its dimensions are such that the ball-shaped head  66  of shank part  60  or the ball-shaped head  78  of the female-type part  74  can be received in an approximately or close fitting relationship. This enables bearing disc  86  to pivot to any side on the head associated therewith. According to FIG. 7, it can be seen that this would allow the bearing disc  68  to optimally bear on the condylus portion of the femur  10 .  
         [0028]    As can be seen from FIG. 5 the bearing disc  86  has a through Z-shaped slot  90 . This slot permits the bearing disc  86  to be snapped onto head  66  and  78  when the ends of the ring-shaped bearing disc  86  which face the slot are slightly moved apart. It is understood that the bearing disc  86  is made of an appropriate resilient material. It further can be seen that the shape which preferably is non-linear of the S or Z shaped slot  90  prevents the ends of bearing disk  86  from being moved apart by more than the width dimension of the slot  90 . Hence, the female-type part or shank part may apply a pressure, which is not insignificant, to the bearing disk  86  during compression with the parts not being separated from each other.  
         [0029]    It can be seen from FIG. 6 that the side of bearing disc  86  which faces the bone is planar as is shown at  92 . The opposite side has a rounded contour which consists of a flanged portion  94  adjoining the surface  92  and a collar portion  96  towards the other side of the disc  86 .  
         [0030]    Two or three condylus screws may be used instead of one screw if this is made necessary by the fracture which is being treated.  
         [0031]    Another embodiment of the bearing component  86   a  is shown in FIGS.  8  to  10  which has a ring-shaped portion  100  which is comparable to ring-shaped portion  94  of bearing component  86  of FIGS. 5 and 6. Four webs  102  are formed out of ring-shaped portion  100  which extend away from the ring-shaped portion  100  in a nearly axially parallel relationship and are disposed at spacings of approximately 90°. Rounded depressions  104  are formed between them. The depressions are semi-circular in the side view (FIG. 9). The projections or webs,  102  along with ring-shaped portion  100 , define a bearing socket  88   a . Socket  88   a  is interrupted by depressions  104  in the area of webs  102 . A ball-shaped end portion such as end portion  66  of FIGS.  1  to  4  may be inserted into the bearing socket via the region of webs  102 . This causes webs  102  to be resiliently deformed slightly radially towards the outside and, subsequently, will be snapped over the final portion so that the bearing component  86   a  is captively secured on the end portion. For the rest, the function of the bearing element  86   a  fully corresponds to that of bearing element  86 .  
         [0032]    The screw illustrated in FIGS. 1 through 6 and  8  through  10  is adapted to be used to attend the various cases of bones fractures, even with no bone nail as is shown in FIG. 7, for example. If it is employed in the situation shown in FIG. 7 the screw  38  would be replaced with the screw of the present invention. Screws  34 ,  36  of FIG. 7 can also be replaced with the screw of the present invention. The heads of the screw shown in FIGS. 5, 6, and  8  to  10  allow the screws to optimally bear on the bones because they are pivotable. This is not ensured, for example, by the heads of screws  34 ,  36  in FIG. 7.