RELATED APPLICATION DATA
 The present application is a continuation of the U.S. National Stage designation of co-pending International Patent Application No. PCT/CH2003/000184, filed Mar. 21, 2003, the entire content of which is expressly incorporated herein by reference thereto.
FIELD OF INVENTION
 The invention relates to an intramedullary nail for use in treating bone fractures, e.g., the distal tibia. More particularly, the present invention relates to an intramedullary nail having at least two intersecting transverse boreholes, wherein the axes of the two boreholes intersect at a point that is offset from the central longitudinal axis of the nail.
BACKGROUND OF THE INVENTION
 The state of the art already includes intramedullary nails that have two intersecting transverse boreholes at the same height, so that the same intramedullary nail can be used both for a right and for a left tubular bone.
 The disadvantages of this prior known arrangement is that the two (or even more) holes intersect and their axis of intersection lies on the longitudinal axis of the nail, with the result that a relatively large quantity of material is taken from the cross section of the intramedullary nail, which in turn leads to considerable mechanical weakening of the intramedullary nail at this point.
 The invention is intended to remedy this situation. The invention is based on the problem of creating an intramedullary nail with two (or more) intersecting transverse boreholes that has improved mechanical strength compared to the state of the art described above, but which does not require the size of the cross section of the intramedullary nail to be increased.
SUMMARY OF THE INVENTION
 The invention solves the specified task by providing an intramedullary nail having a proximal end, a distal end, a central longitudinal axis, and a plurality of transverse boreholes, each having a hole axis and defining a virtual borehole cylinder having a cylinder axis corresponding to the hole axis of the defining transverse borehole. The borehole cylinders of at least two of the transverse boreholes mutually penetrate one another and the cylinder axes of the two mutually penetrating borehole cylinders intersect at a point that does not lie on the central longitudinal axis of the nail.
 One variation of this invention is that the cylinder axes of the two mutually penetrating borehole cylinders meet at an intersection point P which is at a distance d>0 from the longitudinal axis. The distance d relative to the diameter D of the intramedullary nail is advantageously in the range 0.0001 D<d<0.6000 D, preferably in the range of 0.2 D<d<0.5 D.
 One further variation is that the cylinder axes of the two mutually penetrating borehole cylinders are skewed and have a shortest distance x between them, where x>0. The length x in this system should be less than half the total of
the two diameters of the mutually penetrating borehole cylinders to enable the two borehole cylinders to be penetrated. The segment S of the length x representing the shortest distance between the two cylinder axes can run parallel or at an angle to the longitudinal axis, and the shortest distance y between the segment S and the longitudinal axis is greater than zero. The distance y is advantageously less than D/2, but greater than 0.4 D.
 In a further embodiment, the cylinder axes of the two mutually penetrating borehole cylinders lie in a plane orthogonal to the longitudinal axis.
 In another embodiment, the cylinder axes of the two mutually penetrating borehole cylinders lie in a plane that intersects the longitudinal axis at an angle a, wherein 0°<a<60° and preferably 0°<a<30°. The advantage of this slanted arrangement compared to the orthogonal arrangement is to be found in the potentially longer bearing length of the screw to be inserted into the borehole cylinder, which leads to greater stability. A further advantage is improved fracture treatment.
 In a further embodiment, the cylinder axes of the two mutually penetrating borehole cylinders intersect at an angle |3, wherein 30°<|3<90°, and preferably 50°<|3<80°. Selection of the ideal angle will lead to optimisation of the wall thickness of the intramedullary nail.
 In a preferred embodiment, the mutually penetrating borehole cylinders are provided with two separate entrance points into the intramedullary nail, but only one common exit from the intramedullary nail. The advantage of this system compared to one with four openings is that this system has less material loss, i.e. greater strength of the intramedullary nail.
 The diameter DB of the mutually penetrating borehole cylinders advantageously measures at most 0.6 times, but preferably at most 0.5 times of D.
 In a further embodiment, the intramedullary nail is provided with a longitudinal hole coaxial to the central longitudinal axis. The bigger the diameter is of this hollow relative to the diameters of the borehole cylinders, the greater can be the angle between the mutually penetrating cross holes, without any impairment to the cross section area of the intramedullary nail, i.e. without any lessening of the strength of the intramedullary nail.
BRIEF DESCRIPTION OF THE DRAWINGS
 The invention and refinements of the invention are described in more detail in the following on the basis of partially schematic illustrations of several embodiments.
 FIG. 1 shows a front and rear view of the intramedullary nail with two intersecting transverse boreholes;
 FIG. 2 shows a front view of the intramedullary nail with a schematic, perspective view of the borehole cylinders;
 FIG. 3 shows an orthogonal cross section through the intramedullary nail according to FIG. 2 in the range of the intersecting transverse boreholes; and
 FIG. 4 shows a schematic perspective view of two mutually penetrating borehole cylinders with skewed cylinder axes.