Abstract:
A locking nail for treating fractures of tubular bones has at least one cross-bore is provided at one end for the reception of a bone screw. The nail has a female thread at the end with the cross-bore for connection to a nail retention screw. The nail has an anti-rotation feature to anti-rotationally secure the rotational position of a joining sleeve which joins a targeting apparatus relative to the locking nail.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a locking nail to treat fractures of tubular bones. The invention also relates to an aiming or targeting apparatus for a locking nail. 
   Locking nails for treating fractures of, for example, a femur, humerus and tibia, are known. It is common for locking nails to have cross-bores at the distal end and at least one cross-bore at the proximal end. Typically, bone screws are passed through the cross-bores which screws have been screwed into the corticalis at the opposite side of the bone. The bone screws secure the locking nail axially and rotationally. If supracondylar nails are used condylus screws may also be passed through the cross-bores. 
   A problem in employing locking nails, when inserted, is how to identify the position of the cross-bores to drill a hole into the corticalis in the proper place from outside. A number of aiming or targeting apparatus have become known, which work with X-rays to identify the position of the cross-bore relative to the targeting apparatus. Therefore, it is possible to drill a hole into the bone in the proper place by use of the targeting apparatus and a so-called drilling sleeve or aiming sleeve. In most cases, known targeting apparatus are firmly connected to the end of the nail used to drive in the nail. 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 will not coincide with the real one because of the curvature of the bone and the possible torsion the nail undergoes while it is driven in. 
   The disadvantage of using the targeting apparatus working with X-rays is that both the operator and patient are exposed to a radiation dose. Therefore, targeting apparatus are known that do not use radiography, but allow for the identification of the location of the cross-bore mechanically. Such are shown in U.S. Pat. Nos. 5,176,681, 5,334,192 and 6,039,739. Since it is necessary for the targeting apparatus to be connected to the locking nail it has hitherto been impossible to identify the location of cross-bores and to introduce bone screws for those positioned close to the nail end. This is why cross-bores always need to be at a minimum distance from the end of the locking nail. 
   SUMMARY OF THE INVENTION 
   It is the object of the invention to provide a locking nail and a targeting apparatus which, using a simple method to make it possible to safely identify cross-bores close to the end of the locking nail and to introduce bone screws or condylus screws therein. 
   The locking nail of the present invention is provided, at one of its ends, with at least one cross-bore for the reception of a screw, particularly a condylus screw or a bone screw. The end with the cross-bore is provided with a female thread which serves for connection to a nail retention screw. The locking nail is further designed to locate the rotational position of a joining sleeve or adaptor of a targeting apparatus relative to the locking nail. The cross-bore located most closely to the end of the locking nail may be at a small distance from the nail end. The nail retention screw of the targeting apparatus is threaded onto the locking nail in an axial direction. The radial location of the targeting apparatus is performed via a joining sleeve of the targeting apparatus, which, when loaded on the nail retention screw, is located in the required rotational orientation, relative to the locking nail. Thus, the inventive locking nail is configured such as to locate the targeting apparatus axially and rotationally independently of each other. To this end, it is sufficient to provide a small distance between the end of the locking nail and the cross-bore. 
   To locate the rotational position of the joining sleeve or adaptor relative to the locking nail, the end of the locking nail adjacent the at least one cross-bore preferably has one or more recesses and/or projections on its face. In the preferred embodiment three recesses be provided on the face in which adjacent recesses enclose an angle of about 90° or 180° with each other. Thus, the third recess is spaced at 90° to the middle of the three recesses and thus 180° from the first recess. If only two recesses are provided they would be at 90° from each other. The effect of recesses disposed in this way is that a joining sleeve or adaptor having corresponding projections may engage the recesses only in exactly one position. Any other arrangement of projections and recesses that locate the joining sleeve in a distinct position relative to the locking nail is feasible as well. Also, it is possible to locate the joining sleeve in a position and in its other position turned through 180°. 
   According to the invention, the object is also attained by having a targeting apparatus which couples to the adaptor or sleeve. The targeting apparatus has a nail retention screw which engages the joining sleeve. The nail retention screw, at its ends facing the locking nail, is provided with two extensions which project in an axial direction. The space or recess between the extensions, when in a predetermined position, opens a cross-bore in the locking nail. In the inventive targeting apparatus, the nail retention screw is introduced into the nail bore to an extent such as to close the cross-bore disposed closest to the end of the nail by the nail retention screw extensions, but is left open by orienting the space between the extensions parallel to the cross-bore. At the other end, the nail retention screw also has a bearing surface extending in an axial direction. The joining sleeve or adaptor is further provided with key and recess to anti-rotationally secure the joining sleeve with respect to the locking nail in the predetermined position of the nail retention screw. In the targeting apparatus of the present invention, the joining sleeve is secured from rotation with respect to the locking nail. If the joining sleeve or adaptor is brought to the anti-rotationally secured position the nail retention screw is automatically brought to its predetermined position in which the extensions open the cross-bore. 
   Preferably, the extensions of the nail retention screw are provided with a thread on the outside. The bottom between the extensions is rounded and the free ends of the extensions are rounded. The nail retention screw is fixed by threading to the end of the locking nail adjacent the at least one cross-bore with the space between the extensions aligned with the cross-bore. The extensions are shaped such that a Kirschner wire introduced through the extensions after drilling may remain in the bore if the nail retention screw is removed, and is merely urged to the edge thereof is the screw rotates. 
   Preferably, the nail retention screw has a circumferential projection at the end facing the locking nail. A circumferential groove is provided between the portion having the extensions and the projection. The joining sleeve has three recesses adjacent ones of which enclose an angle of about 90° or 180° with each other on the face and, in the inserted position, engage the recesses on the locking nail. 
   The bearing surface of the nail retention screw is preferably formed as a flattened area or groove. However, it is also possible to provide the shank of the nail retention screw with a plurality of flat surfaces in a region. 
   It is preferred that a bore in the sleeve wall and a pin inserted therein are provided as a driver for the central bore in the joining sleeve. The pin inserted in the bore extends perpendicularly and at a distance from a central longitudinal axis of the joining sleeve. The two ends of the pin are held in place in the wall of the joining sleeve. The joining sleeve or adaptor further is provided with orientation recesses for a handle portion of the targeting apparatus. The handle portion is preferably provided with spring detent for location of the handle axially and rotationally of relative to the orientation recesses on the sleeve. To this end, the handle portion preferably has a bore into which a spring-biased stud projects for engaging one of the orientation recesses on the joining sleeve. 
   The handle portion further is provided with an arresting or locking screw which, when in a threaded-in position, presses and locks the stud against the orientation recess of the joining sleeve or adaptor. 
   For location in the joining sleeve in an axial direction, the nail retention screw, at its end facing away from the locking nail, is provided with a threaded portion which projects beyond the end of the joining sleeve when it is in its fully inserted position. To locate the joining sleeve in an axial direction, a nut which presses the joining sleeve against the locking nail is screwed onto the threaded portion of the nail retention screw. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in more detail below with reference to an embodiment. In the drawings: 
       FIG. 1  shows the distal end of a locking nail; 
       FIG. 2  shows a nail retention screw in a first side view; 
       FIG. 3  shows a nail retention screw of  FIG. 2  in a second side view; 
       FIG. 4  shows a section along line  4 — 4  of  FIG. 3 ; 
       FIG. 5  shows a joining sleeve as seen from a first side view; 
       FIG. 6  shows a joining sleeve of  FIG. 5  as seen from a second side view; 
       FIG. 7  shows a joining sleeve of  FIG. 5  as seen from a third side view; 
       FIG. 8  shows a section along line  8 — 8  of  FIG. 5 ; 
       FIG. 9  shows an exploded view of the nail retention screw and joining sleeve; 
       FIG. 10  shows a section along line  10 — 10  of  FIG. 9 ; 
       FIG. 11  shows an exploded view of the nail retention screw and joining sleeve in a perspective view; 
       FIG. 12  shows a sectional representation of the targeting apparatus placed on top of the locking nail; 
       FIG. 13  shows a handle member of the targeting apparatus of  FIG. 12 ; and 
       FIG. 14  shows a handle member mounting on the joining sleeve. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows the distal end of a locking or supracondylar nail  10 . The locking nail is provided with four cross-bores  12 ,  14 ,  16  and  18  which serve for receiving bone screws and/or condylus screws to locate the locking nail both axially and radially in the bone. On the end face  19 , locking nail  10  is provided with two recesses  20  the nearest one of which is shown and the second being spaced around the nail from the other at an angle of 180° in  FIG. 1 . In the preferred embodiment, recess  20  is of a rectangular shape. In the locking nail illustrated, the cross-bore  18  is at a distance of 6 mm from the free end of the nail. Not shown in  FIG. 1  is a female thread which is provided inside the locking nail and which from the end  19  of the locking nail extends beyond the beginning of the cross-bore  18 . 
     FIG. 2  shows a nail retention screw  22 . The end  24  is provided for connection to locking nail  10 . End  24  has a male thread  26  which corresponds to the abovementioned female thread of locking nail  10 . The end  24  has two extensions  28  and  30  which define a recess  32  therebetween. Extensions  28 ,  30  project in axial direction and form a U-shaped end of the nail retention screw. A circumferential groove  34  is provided which adjoins the threaded portion and is followed by a circumferential projection  36 . 
   The opposite end of nail retention screw  22  is provided with a threaded portion  38 . The thread  38  is interrupted in the area of the flattened portion  40 . Hence, the thread  38  also includes a part threaded portion.  FIG. 3  shows a plan view of the flattened portion  40 . A section along line  4 — 4  of  FIG. 3  is illustrated in  FIG. 4 . The sectional representation  4  makes it apparent that the region  24  is separated by a partition or wall  42  from the shank of the nail retention screw. 
   The joining sleeve or adaptor of the present invention will now be described in greater detail with reference to  FIGS. 5 through 8 . The joining sleeve  44  has a cylindrical shank with a first portion  46  and a second portion  48  which has a larger radius than that of first portion  46 . In the preferred embodiment, the transition area  50  between the first and second portions has a conical configuration. The inner diameter of an internal bore of the joining sleeve matches the outer diameter of the nail retention screw so that sleeve  44  may be slid onto nail retention screw  22 . 
   The end of the first portion  46  is provided with three projections  52 ,  54  and  56 . The projections  52  through  56  correspond with recesses  20  in the locking nail. The projections  52 ,  54  and  56  are arranged in a semicircular segment so that projections  52  and  54  enclose an angle of 90°, projections  54  and  56  also enclose an angle of 90°, and projections  56  and  52  enclose an angle of 180°. 
   The outer surface of second portion  48  has provided therein location elements or orientation recesses  58 ,  60  and  62 . Each orientation recess has a funnel-shaped area  64  with a central through bore  66 . 
   A through bore  68  is provided in the wall at the end of the second portion  48 . The through bore  68  is spaced from the central longitudinal axis  70  of the sleeve by the distance  72  and extends perpendicularly to axis  70 . As shown in  FIG. 10 , a pin  76  is pressed into the through bore  68  and intersects the inner bore  73  of sleeve  44  and reduces the diameter thereof. The cross-section of sleeve bore  73  with pin  68  inserted corresponds to flattened portion  40  of nail retention screw  22 . 
   As shown in  FIGS. 6 and 7 , the second portion  48  also has provided therein wrench-engaging surfaces  74  for an open-ended wrench or the like. 
     FIG. 9  shows an end of a locking nail  77  having a cross-bore  78 . The end of the locking nail is provided with a female thread  80  as can be seen from the sectional representation of  FIG. 10 . Also provided are recess  81  which are similar to recess  20  of  FIG. 1  but oriented at 90° on end  77 . The nail retention screw  22  is screwed into the end of locking nail  77  by means of its male thread  26 . Pin  76  is pressed into bore  68  of joining sleeve  44 . As described above, pin  76  reduces the inner bore  73  diameter of the sleeve  44  as can be seen from  FIG. 10 . If joining sleeve or adaptor  44  with the pin  76  pressed in a bore  68  is slid onto nail retention screw  22  it can only be slid on if the pin  76  bears on the flattened portion  40 . Retention sleeve  44  thus assembled on screw  20  is appropriately oriented by the projections  54  and  56  engaging the recesses  81  on the end of the locking nail. Each recess  81  corresponds to a projection  54  and  56  here. The interaction between the projection and the recess allows the joining sleeve and, hence, the nail retention screw to be located only in a single position on the locking nail. In this position, the recess  32  nail retention screw  22  is aligned with cross-bore  78  so that the bore is open. 
   Joining sleeve or adaptor  44  is secured by a nut  82  which is screwed onto the threaded portion  38  of the nail retention screw to axially lock the screw  22  within sleeve  44 . 
     FIG. 12  shows a cross-section through the whole targeting apparatus in its assembled position. Locking nail  10  has screwed thereon, on end  19 , the nail retention screw  22  on top of which joining sleeve  44  is located. Joining sleeve  44  is secured on screw  22  by the nut  82 . The extension  28 ,  30  of nail retention screw  22  are oriented in such a way that the cross-bore located closest to the end is open and aligned along the imaginary line  84 . The second portion  48  of joining sleeve  44  has coupled to the outer circumference thereof a handle member  86  of the targeting apparatus. The handle member  86  is secured both axially and rotationally on sleeve  44 . The handle member  86  has a first portion  88  which, in the preferred embodiment, is configured to be grasped and has a targeting bore  90  for receiving an aiming or drilling sleeve. The cantilevered part  92 , when pressed down, secures a sleeve inserted in the aiming bore  94  in its inserted position. Such a system is shown in U.S. Pat. No. 6,039,739. 
   Referring to  FIGS. 13 and 14 , first portion  88  is connected to a tubular locating device  96  via any convenient method. In the preferred embodiment, the locating device  96  has a tongue  98  via which fits in to a recess in the handle member for this connection. The locating device  96  has a central bore  100  the inner diameter of which corresponds to the outer diameter of the sleeve  44  in at second portion  48 . A spring-biased stud  99  extends into the bore  100  and has a rounded tip extending into the bore  100  and cooperates with the funnel-shaped indentations of the location elements or orientation recesses  58 ,  60  and  62  to form a snap connection. The stud  98  snaps into one of the marking recesses  58 ,  60  and  62  on the joining sleeve  44 . If the stud  99  has not snapped into a marking recess it will be pressed outwardly against the spring tension and the locating element  96  may be moved axially and rotationally on the joining sleeve. 
   The stud  99  which is snapped in is secured via a locking screw  102 . Locking screw  102  has a shank  104  which is screwed into the bore of the stud  99  via a thread. When in its screwed-in position, the shank  104  bears on the stud  99 , pressing it against joining sleeve  44 . 
   A circumferential step  106 , which cooperates with a circumferential projection of the locating device  96 , secures the stud  99  and prevents it from being pushed too far into the opening  100 . 
   To allow for a better orientation of the device, individual marking recesses  58 ,  60  and  62  may be labeled to make it evident to which of the cross-bores the targeting bore  90  is directed. After the targeting device  86  is oriented the locking screw  102  secures it in position. Thus, for example, when position in recess  60  opening  94  is aligned with cross-bore  16  of nail  10 . When positioned in recess  62  it is aligned with cross bore  18  etc. 
   An insertion of a condylus or locking screw into the cross-bore disposed closest to the border is effected by means of a Kirschner wire which, for example, is 1.8 mm in diameter. After a hole is drilled, e.g. by means of a drill preferably 5 mm in diameter, the Kirschner wire is introduced, allowing the targeting apparatus to be removed. If the condylus screw were inserted prior to the removal of the targeting apparatus nail retention screw  22  could no longer be unscrewed from the locking nail because the extensions  28 ,  30  thereof are blocked by the condylus screw. However, the extensions are rounded to such an extend that the Kirschner wire is forced aside in the cross-bore, thus allowing the nail retention screw to be unscrewed with the wire in place. Subsequently, the condylus screw is introduced into the cross-bore via the Kirschner wire and is screwed in place. 
   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.