Abstract:
A supracondylar bone nail has an elongated shank with a distal end and a proximal end and has two bends in the M-L plane. Both bends are in the same direction with screw holes between the distal tip of the nail and the first bend.

Description:
BACKGROUND OF THE INVENTION 
     The invention refers to a supra condylus bone nail. 
     Frequently, in cases of fractures of the femur bone, nails are applied which are driven into the intramedullary bone canal from proximal. It is also known to apply so-called locking nails which have transverse bores to be fixed on both sides of the fracture. Fractures in the condylus area of the bone necessitate a very long bone nail. Furthermore, the danger exists that the bone is pierced through in the area of the condylus by which cartilage is damaged. 
     OBJECTS OF THE INVENTION 
     An object of the invention is a supra condylus bone nail. 
     Another object of the invention is a method of repairing a fracture of a femur with a particular locking nail of the invention. 
     SUMMARY OF THE INVENTION 
     The bone nail according to the invention has an elongated shank which is relatively short if compared with known femur nails. The maximum length is for example 230 mm. The bone nail according to the invention is driven into a bore which ends at the distal end between the condylii and which follows the intramedullary canal. For the drilling of the bore and the insertion of the nail it is necessary to bend the knee and to laterally displace the patella. For the surgical operation this does not meet any obstacle. In view of the function of the knee the position of the bore is not critical since it is located remote from the sliding areas of the condylii on the plateau of the tibia. 
     According to the invention the bone nail includes two bends. The first begins at a distance from the distal end of about a quarter or a third of the length of the nail. The angle for example is 8°. The second bend begins in the last third of the nail length if looking from the distal end and has approximately an angle of 3° Both bends are lying in a plane parallel to the sagittal plane of the human body. Furthermore, the nail according to the invention has transverse bores in the distal and the proximal portion, with the bores extending transverse to the mentioned plane wherein the nail is bent. The bores are adapted to accommodate bone screws. 
     The bone nail according to the invention can be applied to fractures in the condylus area, with at least one screw being adapted to fix segments of the fracture in the distal area of the nail. 
     The diameter of the nail according to the invention which is approximately between 10 and 12 mm may be held constant for different lengths. Preferably, according to an embodiment of the invention a set of bone nails can be provided having the same diameter, however, a different length, with the length difference occurring only in the proximal portion behind the second bend while the remaining portion is approximately 120 to 130 mm if looking from the distal end and remains substantially constant. 
     According to another embodiment of the invention, the frontal side of the proximal portion of the shank has a skid-shaped flattening. This facilitates the driving and sliding in of the nail and avoids undesired damage to the bone. 
     According to another embodiment of the invention the shank is solid. Therefore, it is extremely stable in view of rotational and bending forces. 
     In order to allow application of a condylus screw in case of a fracture of the condylus portion, an embodiment of the invention provides that the condylus screw has a nut which is threaded onto a threaded portion of the shank of the condylus screw. Nut and head of the screw can be relatively thin. By means of such a condylus screw, segments of the fracture can be effectively compressed and retained at the nail. 
     The shank of such a condylus screw is preferably smooth. According to an embodiment of the invention the shank of the condylus screw is conically enlarged toward the end of the shank, and the nut includes a conical extension wherein an inner thread is formed to accommodate the threaded portion of the screw shank. 
     For the guidance of the condylus screw, in particular for threading the nut on the screw shank, an embodiment of the invention provides that the shank and shank head have an axial throughbore. A guiding lance may be threaded through the throughbore which allows a threading of the nut. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention is explained in more detail with accompanying drawings. 
     FIG. 1 shows diagramatically the distal portion of a femur including a bone nail according to the invention. 
     FIG. 2 shows a bottom view of the femur of FIG. 1. 
     FIG. 3 shows a front view of the distal portion of a femur with a bone nail according to the invention. 
     FIG. 4 shows a lateral view of the bone nail according to the invention. 
     FIG. 5 shows a cross-section through a condylus screw for a bone nail of FIG. 4. 
     FIG. 6 shows a cross-section through a nut for the screw of FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 the distal portion of a femur 10 is shown which accommodates a bone nail 12. The bone nail 12 is inserted through a bore 14 which is made from below the condylus retrograde (see FIG. 2). 
     In a plane parallel to the sagittal plane, the bone nail 12 which is solid and made of body compatible metal or metal alloy has a distal portion 16, an intermediate portion 18 and a proximal portion 20. Distal portion 16 and proximal portion 20 have three transverse bores 22 and two transverse bores 24, respectively. Between the portions 16, 20 a first bend 26 is provided with an angle of about 8°. A weaker bend is located between portion 18 and portion 20 as shown at 28. This bend has an angle of approximately 3°. 
     At its distal end, the bone nail 12 has diametrically opposed recesses 30 for the engagement of a driving instrument. Furthermore, the distal end may have an axial threaded bore (not shown). It also serves for the engagement with a driving or retracting instrument. In FIG. 3 it can be seen that the condylus portion of the femur 10 has a oblique fracture. The fracture line is designated with 32. Two bone screws 34, 36 having a drill tip are extended through two of the three transverse bores 22 and serve for the fixation of the bone nail 12 in the femur, with the lower screw 36 penetrating both segments of the fracture. A particular condylus screw 38 is extended through the distal transverse bore 22. The structure of the screw is explained in more detail with FIGS. 5 and 6. The condylus screw 38 has a thin smooth shank 40 which conically enlarges towards a head 42 as shown at 44. The head 42 is relatively thin and has a large diameter. The head 42, furthermore, has an inner hexagon 46 for a corresponding rotary tool. At the free end shank 40 has an outer threaded portion 48. 
     A nut 50 in FIG. 6 has a flat head 52 similar to head 42 and an inner hexagon 54. A conical extension 56 joins to head 52 which is hollow and has an inner threaded portion 58 by which nut 50 can be threaded onto a threaded portion 48 of the condylus screw. As can be seen in FIG. 5, shank 40 and also head 46 are provided with a throughgoing axial bore 60 for the accommodation of a guiding lance. 
     As can be seen in FIG. 3 by means of the condylus screw shown in FIGS. 5 and 6 a compression force can be exerted onto the fracture segments. The diameter of shank 40 is such that it can be extended through the bores 22 with relatively small clearance. 
     In FIG. 4 the bone nail 12 is more clearly illustrated as to the dimensions thereof. It can be seen furthermore that the proximal end of nail 20 is pointed as shown at 52. Furthermore, it has a flattening 54 frontally faced which forms a skid for the introduction of nail 12. It is again mentioned that the nail 12 may have different lengths. From the distal end up to the bend 28 all nails have the same length independent of their total length. Merely the portions between bend 28 and the proximal end in a set of nails will have different lengths. The diameter of nail 12 is constant for all lengths.