Abstract:
A locking nail for treating fractures of tubular bones has two parallel cross-bores that are axially spaced apart provided on the distal end of said nail and optionally at least one additional cross-bore is provided on the proximal end thereof for receiving bone screws. The nail includes a groove which is parallel to a longitudinal axis of the nail is formed into the outer side of the nail. The groove extends into the distal bores on both sides and merges into the bore. The longitudinal axis of the groove intersects the axis of each cross-bore.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a bone nail and a targeting device for locating cross-locking holes in the bone nail. 
   Locking nails to care for fractures in cylindrical hollow bones are widely used. Their utilization is described, for example, in “The Journal of Trauma” of 1993, Vol. 35, No. 5, pp. 772 to 775. It is the typical of such locking nails that two cross-bores are disposed at the distal end and at least one cross-bore is disposed at the proximal end. Bone screws are passed through the cross-bores. They are screwed into the corticalis at opposed sides. This secures the locking nail axially and against a rotation. 
   A problem in employing such locking nails is how to identify the position of the cross-bores to drill a hole in the corticalis in the right place from outside. A number of aim-taking apparatus has become known, which work with X-rays to identify the position of the cross-bores relative to an aiming or targeting apparatus. Therefore, it is possible to drill a hole in the bone in the right place by means of the targeting apparatus and a so-called drilling sleeve or targeting sleeve. In most cases of the known targeting instruments are firmly connected to the proximal end of the nail. Such an instrument is shown in U.S. Pat. Nos. 5,176,681 and 5,454,813. Thus, the position of the cross-bores may already be preset in an approximately precise way. However, it should be considered that the presumed position of the cross-bores does not coincide with the real one because of the curvature of the bone and the possible torsion of the nail while it is driven in. 
   Although the position of the cross-bores may be determined by means of X-rays in a relatively precise way using X-rays is not always the best means of choice because it could cause harm to both the patient and surgeon. Therefore, it has also become known to employ targeting apparatus not including X-raying equipment. As mentioned earlier the approximate position of the cross-bores already results from the distance at which the holes are spaced from the proximal end and the circumferential position results from given markings at the proximal end of the locking nail, which cause the targeting apparatus to be connected to the nail in a given rotational position. As explained earlier, however, it is impossible to precisely identify the position of the cross-bores only in a mechanical way by using the known means. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to provide a locking nail which makes it possible to easily determine the position of the distal cross-bores even without using X-raying equipment. 
   According to the invention, an axially parallel groove is formed in the outside of the nail. It extends at either side of at least that cross-bore which is positioned nearest to the distal end of the nail. The longitudinal axis of the groove intersects the axis of the bone nearly perpendicularly. In an aspect of the invention, the groove is preferably U-shaped in cross-section and is preferably rounded at bottom. Preferably, the groove extends beyond the two cross-bores in the distal and proximal directions. The maximum width of the groove may be smaller than the diameter of the cross-bores. Preferably, the distal end of the locking nail is of a cylindrical shape. The end may be hollow or massive depending on choice. 
   Conventional targeting apparatus are located axially and with respect to their relative rotational position at the proximal end of the locking nail. Hence, the position of the outermost distal cross-bore may be preset in a nearly approximate way. This can be done in the same way in the inventive locking nail. After the approximate position is found a hole may be cortically drilled in the bone following an incision puncture. However, it is only the associated bone wall which is drilled open. Subsequently, a drill smaller in diameter or a wire pin or the like is passed through the hole in the bone. The operator may now make out by sensing whether the pin may be readily inserted by passing it through the distal cross-bore. If this is not the case he may find out whether he has got the inner end of the pin into the groove. He can find it out particularly by slightly turning the locking nail by means of the targeting apparatus which is still mounted on the nail. This enables him to adjust the rotational position of the locking nail with regard to the hole drilled in the bone already. Now, in order to obtain an alignment of the cross-bore towards the bone hole also in an axial direction the nail is driven in slightly more or is pulled out a little bit by means of the targeting apparatus until the right position of the cross-bore is adjusted. 
   It is very unlikely that the locking nail will be deformed in the region between the two distal cross-bores to such an extent that the original position of the two cross-bores relative to each other would be changed. Hence, once the position of the first cross-bore is determined the position of the second bore is fixed as well. Therefore, the inventive locking nail can be used the threadably connect the distal end of the locking nail in a simple way with no recourse to X-raying equipment. 
   However, the invention provides a suitable targeting apparatus with a view to readily localizing the second cross-bore in the locking nail as well in order that the second hole may be drilled in the bone in the right place. It has a handle portion which is adapted to conventionally be connected to the proximal end of the locking nail in order to fix it to the locking nail in the axial and rotational directions. Connectable to the handle portion is also an targeting bar, which is releasably mountable on the handle portion, but is located, when mounted, in an axially and rotationally stable condition. The targeting bar extends in parallel with and at a distance from the locking nail when the latter is mounted on the handle portion. Thus, the targeting bar externally extends in parallel with the length of the bone of which requires to be cared for. Distally, the targeting bar has two cross-bores the distance between which corresponds to the cross-bores of the locking nail. Still, they are larger in diameter as is known as such in order to receive a drilling or aiming sleeve. What is substantial for the invention, however, is that the distal portion of the targeting bar is made of a resilient material, preferably an appropriate plastic material which preferably is PTFE. 
   The distal portion is preferably formed cylindrically. On the contrary, the proximal part of the targeting bar consists of a relative rigid material which is a metal, for example, to permit its rotationally stable reception in the handle portion. 
   According to the above-described procedure, when a bone screw is screwed into the most distally located cross-bore of the locking nail the distal bar may be slipped subsequently onto the shank of the screw-driver which is still connected to the bone screw. The proximal end of the targeting bar, however, is connected to the handle portion of the targeting apparatus in its given rotational position. If a torsion of the locking nail has occurred while it was driven in the targeting bar will automatically undergo a torsion, too. This torsion will take place, first and foremost, in the resilient distal portion, the consequence of which is that also the second cross-bore of the aim-taking bar is now aligned more precisely towards the second cross-bore of the aim-taking nail. There is a similar case when the nail has been bent in the bone. The distal bar portion will then be subjected to bending as well. Therefore, it is now possible to drill the second hole in the bone by means of the second cross-bore of the distal portion and to insert the second bone screw subsequently. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained with reference to the drawings. 
       FIG. 1  is a schematic perspective view of a targeting apparatus according to the invention and a bone nail in a cylindrical hollow bone which is schematically outlined; 
       FIG. 2  is an schematic perspective view of the aim-taking apparatus of  FIG. 1  in its complete shape; 
       FIG. 3  is a side view of the targeting bar of the aim-taking apparatus of  FIGS. 1 and 2 ; 
       FIG. 4  is a side view of the handle portion which is modified as compared to one of  FIGS. 1 and 2 ; 
       FIG. 5  shows a part of the handle portion of  FIG. 4  in a side view according to arrow  5 ; 
       FIG. 6  shows a section through the representation of  FIG. 5  along lines  6 — 6 ; 
       FIG. 7  shows a section through the targeting bar of  FIG. 3  along the lines  7 — 7 ; 
       FIG. 8  shows the distal end of the locking nail according to the invention; 
       FIG. 9  shows a section through the nail portion of  FIG. 8  along lines  9 — 9 ; and 
       FIG. 10  shows a section through the nail portion of  FIG. 8  along lines  10 — 10 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a cylindrical hollow bone  10  is outlined which requires to be cared for by means of a locking nail  12  which is only outlined as well. A targeting apparatus  14 , which is outlined in  FIG. 1 , has a handle portion  16  to which the proximal end of nail  12  is connected in an axially and rotationally stable way. The type of connection is not shown. It is known per se. A targeting bar  18 , which consists of a distal portion  20  and a proximal portion  22 , extends in parallel with nail  12 . Proximal portion  22  is a metallic square. Distal portion  20  is cylindrical and is formed from an elastic plastic material such as PTFE. Portions  20 ,  22  are interconnected in an appropriate way which, however, is not shown. Seated in a rotationally stable way on portion  22  of targeting bar  18  is a fixing ring  24  which, however, is axially displaceable with the axial position being locatable by means of a fixing screw  26 . Handle portion  16  has a bifurcated portion  28  where the gap between its legs is sized so as to fittingly receive square portion  22 . Another fixing screw  30  serves for locating square portion  22  in bifurcated portion  28 . 
   As is evident from  FIG. 2  locking nail  22  is provided with two distal cross-bores as is known as such. This is more obvious from the representation of  FIG. 8 . The distal portion of the locking nail is indicated by  32  and the cross-bores are given the reference numbers  34  and  36 . What is apparent from a consideration of  FIGS. 2 and 8  to  10  is that the distal portion  32  has externally formed therein a groove  40  which runs in an axially parallel direction thereto and extends beyond bores  34 ,  36  in the distal and proximal directions, respectively. Its extension along the two sides of bores  34 ,  36  is 5 mm, for example. In addition, groove  40  extends into bores  34 ,  36 . It is evident from  FIGS. 9 and 10  that the groove is approximately U-shaped in cross-section and is rounded at bottom. It is slightly smaller in width than the diameter of cross-bores  34 ,  36 . 
   Targeting bar  18  is shown in a slightly more distinct way in  FIGS. 3 and 7 . It can be seen, for instance, that square portion  22  is partly embedded in the material of distal portion  20 . On the distal side, distal portion  20  has two cross-bores  42 ,  44 . The distance of their axes corresponds to the distance of the axes of cross-bores  36 ,  34  (the drawings not being to scale). The diameter of cross-bores  42 ,  44  is larger than the diameter of cross-bores  34 ,  36  because they also require to receive a sleeve through which a drill can be introduced, reference to which will be made further below. 
   Handle portion  16   a  of  FIG. 4  distinguishes itself from the one of  FIGS. 1 and 2  in that it is angle-shaped. It has a cone  50 , onto which the locking nail (not shown) is slipped, at the right-hand upper end of handle  48 . The other mounting of the locking nail is not described as was mentioned earlier. 
   Like handle portion  16 , handle portion  16   a  has a bifurcated portion  28  to fittingly receive square portion  22 . Referring to  FIG. 5 , a threaded through cross-bore  52  can be seen for receiving the fixing screw  30  of  FIG. 2 . 
   Handle portion  16   a  has an oblique through bore  54  above bifurcated portion  28  with no reference being made to its function. 
   When an implantation is made and cross-bores  34 ,  36  of locking nail  12  are discovered subsequently the distance of these cross-bores from the proximal end is known for the nail which is not yet driven in. Therefore, targeting bar  18  may be mounted in its axial position in such a way that its cross-bores  42 ,  44  are aligned towards the presumed position of the locking nail which was implanted or towards its cross-bores  34 ,  36 . In practice, however, the real position of cross-bores  34 ,  36  may deviate therefrom because locking nail  12  has been bent or there is a torsion. In any case, the targeting procedure is initially based on the presumed position. In this position, a hole  58  is drilled in bone  10  by means of a drill  56  of  FIG. 1 , i.e. merely in the associated wall of the bone. Targeting bar  18  will then be removed. After this, the operator manually introduces a drill which is smaller in diameter (he perhaps used a 5.5 mm drill before the succeeding drill and the pins are 3.5 mm in diameter) into the bone hole until it feels the nail. If the operator does not feel the cross-bore  34  he slightly rotates nail  12  until the operator makes out groove  40  by sensing. Nail  12  is then moved on and back until it is possible to further introduce the drill shank or wire pin with ease. After this, a hole may also be drilled in the opposed corticalis and the bone screw may be screwed in subsequently. The shank of the screw-driver remains on the screw, and targeting bar  18  is then located in handle portion  16  and  16   a , respectively, in a repeatable position. This will possibly torsion or deform distal portion  20  if the nail also sustained a deformation or torsion while being driven in. Second cross-bore  42  of distal portion  20  is then precisely aligned with second cross-bore  36  of nail  12  so that a hole may also be drilled now in the corticalis for the second cross-bore  36  for a subsequent screw-connecting operation by means of the second bone screw which is not shown. 
     FIG. 2  is intended to merely outline the interaction of targeting screw  18  and cross-bores  34 ,  36  of nail  12  by means of pins  60 ,  62  which are shown. 
   Subsequently, locking nail  12  may also be locked in a manner which is known per se. It is unlikely that a deformation has occurred in this region. Hence, a hole provided on targeting bar  18  (not shown) coincides with the proximal cross-bore of nail  12  in any case. Thus, no difficulties will be encountered by the operator. 
   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.