Abstract:
A device to establish a connection of portions of a broken bone includes a base body adapted to receive a bone nail. A clamping holder has a receptacle to receive a fixation rod. A bearing element mounts the clamping holder on the base body for spherically displacement. A tensioning rod connection has a tensioning rod on which the base body, the clamping holder and the bearing element are arrangeable in a row for tensioning relative to each other. In a first connection state the tensioning rod connection is released so that the fixation rod and base body are adjustable relative to each other. In a second connection state there is sufficient closing tension in the tensioning rod connection to form a stable non-positive locking connection between the fixation rod and the base body. The clamping holder and the bearing element are in positive engagement in the first connection state with the tensioning rod passing through a through-opening of the clamping holder with sufficient play for spatial guiding in all directions.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a U.S. National Stage of International Application No. PCT/EP2006/002951, filed Jan. 19, 2007, designating the United States and claiming priority to German application DE 20 2005 005 444.5, filed Apr. 1, 2005. 
     BACKGROUND 
     The invention concerns a fixation device for the stable connection of at least two bone portions of a broken bone, including at least one base body for tightly receiving at least one bone nail, at least one fixation rod which can be connected to the base body by means of a clamping joint, base body and fixation rod being released in a first connection state of the fixation device for adjusting their relative position and rigidly connected to each other by non-positive locking in a second connection state for fixing the adjusted position, a clamping holder which is mounted with adjustable angle on the base body and which receives a fixation rod for altering and adjusting its position in a receptacle, a bearing which mounts the clamping holder on the base body, and a connection to a tensioning rod on which the base body, the rod clamping holder and the bearing for the clamping holder are arranged in a row for tensioning relative to each other, wherein on the one hand the released connection is made when the tensioning rod connection is released, and on the other hand the stable non-positive locking connection is made when there is sufficient closing tension in the tensioning rod connection, wherein the rod clamping holder is formed by a holder which spherically displaces the fixation rod and which is guided in all spatial directions in a region for displacing and maintaining the set position on the base body, wherein the clamping holder and at least one bearing element of the bearing connecting the clamping holder to the base body are in a positive engagement which produces the spatial guidance, the tensioning rod passing through the bearing element. The invention also relates to a fixation element of such a device and a kit receiving its components in a sterile package. 
     A generic device which is also referred to as a fixator serves to make a fixation connection between bone portions in order to treat fractures. In particular, such fixators are applied in the case of fractures of the radius involving the wrist. Bone nails introduced into the bone portions must be rigidly connected to at least one fixation rod in order to allow the bone portions to grow together in the correct position relative to each other. According to the arrangement and alignment of the bone nails and the area to be bridged, the fixation rod must be capable of being aligned. In the aligned position, it must be capable of rigid connection to the base bodies which in turn can be fixed to the bone nails in a stable rigid connection. 
     A number of requirements are made of the fixators. High stability must be guaranteed. Fixed bones must not change their position relative to each other even when the fixator is worn for several weeks. This requires high stability particularly in the connections of individual components. The fixator is to be capable of being handled easily in order to shorten the operation time. Also, it is to be relatively light in weight. The fixation device is also to be cheaply available. This is especially important particularly with a view to disposable use when this is worthwhile compared with treating the components for reuse. Thus fixators which should be used several times as a result of high purchase costs are frequently not returned after they are used, so that a loss is incurred as a result. Also, special procedures and measures are necessary particularly for sterilisation in case of reuse. 
     Known fixators do not meet the above requirements. Fixation elements of a generic fixator include a base body having a rod clamping bearing which is spherically displaceable for positioning a fixation rod, wherein parts of the fixation element are connected by means of a tensioning rod (U.S. Pat. No. 5,393,161 A). A clamping holder ball is encased in a hinge joint. Consequently the fixation element is bulky, and handling is made more difficult. For the construction of a fixation device, screw clamps for bone nails and screw connections for fixation rods are necessary in addition. Fixation elements known from US 2003/109879 A1 are displaceable in only two planes for positioning a fixation rod in a screw connection. For displacement in other planes, additional parts with additional screw connections are provided. Clamping elements are arranged on different bearing axes. Other clamping holder devices having several screw connections on different bearing axes are relatively hard to handle when they are released, they tend to become released in the tensioned state, and they are made with relatively heavy clamping parts from metal. Fixators according to US 2003/109879 A1 and other known fixators provide one screw connection each for a number of bone nails and fixation rods. With these devices, handling is made particularly difficult, as a result of the plurality of screw connections there is a susceptibility to instability, and relatively solid metal elements are used for the screw connections in order to increase the rigidity of the connection. 
     SUMMARY 
     It is the aim of the invention to design a fixation device in such a way that it is particularly easy to handle and cheaply available with relatively few components, wherein the rigidity of the connection can be guaranteed particularly high and reliable over a long period of time. Nevertheless it should be possible to make the components of the device from lightweight material and cheaply in mass production, in particular from plastic parts made by injection moulding. If necessary, manufacture should be so cheap that the product is usable as a cheap disposable product, in order to simplify the procedures in particular in a hospital by avoiding return, reprocessing and sterilisation of already used fixators. 
     The aims of the invention are achieved in conjunction with the features of the fixation device of the kind mentioned hereinbefore by the fact that the clamping holder is lined up on the tensioning rod, comprising a through-opening which is designed in such a way that the tensioning rod passes through the through-opening with sufficient play in the through-opening for spatial guidance of the clamping holder. A number of advantages are gained with the solution of the invention. Due to the three-dimensional guiding of movement and capacity of the clamping holder for displacement, adjustment and connection of the fixation element to fixation rods is particularly simplified and facilitated. Also, this contributes to a particular extent to the rod and base body or clamping bearing not being braced with forces transverse to the tensioning rod in the state of force-locking connection. This increases the strength and stability of the device to a particular extent. With regard to a simple shape, it is particularly advantageous that the clamping holder for the clamping rod forms a bearing which as such is movable as a unit in three dimensions, that is, in all spatial directions. The tensioning rod connection is particularly simple because portions to be clamped including the clamping holder which is guided and displaceable on the base body in all spatial directions are released by one and the same pull rod of the tensioning connection and attached to each other in a rigid connection. Tensioning force is applied uniformly to different parts of the tensioning combination, namely both for fixing the fixation rod in its clamping holder and for fixing the clamping holder of which the angle is spatially adjustable in a bearing element on the base body. The shape of connection and construction according to the invention allows the components to be made relatively simple. The manufacturing costs of the component parts remain low. Compared with traditional devices, the expenditure for component parts is considerably reduced with respect to number, handling and use. In particular, parts to be made by shape cutting chipping technology are avoided, and lightweight components preferably consisting of plastic injection mouldings are used instead. 
     A fixation element according to the invention which is particularly universally usable is achieved by the fact that on the tensioning rod are placed in a row at least one base body and on the base body opposite each other two rod clamping holders with their bearing portions. Appropriately, with this design the base body is formed by a cross-shaped element including a cylindrical longitudinal body portion which comprises bearing surfaces at its ends for a clamping holder each, and a transverse body portion which receives at least one bone nail. This shape of the base body, of which the longitudinal body portion has the tensioning rod passing through it, has relatively large resistance cross-sections for compression and/or bending loads, so that the tensioning connection is particularly firm and stable. Appropriately, along the extent of the transverse body portion in the latter is formed a through-slot which receives bone nails in regions of the transverse body portion projecting from the longitudinal body portion. This leads both to a spatially particularly favourable arrangement of the bone nails and a particularly effective and pronounced transmission of tensioning force along the longitudinal body portion. Also the result is that tightening for tensioning the connection is associated with only a relatively low tightening torque. 
     Due to the measures according to the invention, a fixation element including the base body and at least one rod clamping holder held thereon by means of the tensioning rod connection can be handled particularly easily and placed on appropriately two bone nails as a compact part joined together in a simple combination by itself. 
     Advantageously, the tensioning rod connection is formed by a screw/shank connection. This appropriately comprises two screws with a longitudinal shank which are screwed to each other in a passage in the base body, so that a tensioning rod which works by shortening is formed already by a few turns of the two screws relative to each other. The portions which are thus clamped are subjected to clamping pressure uniformly in a straight line. Instead, for example a continuous tensioning rod, which at least one end ends in a screw connection with a nut that can be tightened, can be used. 
     One particular design of the invention consists in that the tensioning rod connection, in addition to its function for fixing the rod holder and the rod, forms a tensioning means which in the released connection state lets at least one bone nail movably engage in a base body which is manufactured in one piece preferably from lightweight material such as plastic, while it fixes the bone nail to the base body in a non-positive locking stable relationship in the non-positive locking connection state. 
     Advantageously, in the base body is formed at least one slot for adjustably receiving and fastening a bone nail by clamping, the base body being elastically deformed in the region of the slot upon tensioning the tensioning rod connection. Appropriately, the slot in the base body and at least one bone nail received by it are given dimensions such that in the released state of the tensioning rod connection the bone nail is received by the slot in a clamping/sliding fit for adjusting the connecting position between bone nail and base body. In this embodiment the base body can be mounted particularly easily and reliably on bone nails. 
     According to the invention the rod clamping holder can advantageously be designed as an independent clamping element which in the released state of the tensioning rod connection receives at least one fixation rod in a press fit. Particularly advantageously, the clamping holder can be designed as an independently acting clamping element which receives the fixation rod in an elastic press fit due to the materials. The fixation rod can be moved at least in the axial direction against static friction for positioning. Also the rod clamping holder can appropriately be designed in such a way that the receptacle for the fixation rod comprises an opening through which the rod passes in the released state of the tensioning rod connection into a fit produced by at least one displaceable latch element. This facilitates handling substantially, as the fixation rod due to this measure is put in a position for adjustment by a click connection. Escape of the rod in the direction of insertion is prevented by this means. Nevertheless it remains movable in at least one dimension for adjustment. 
     In a further, particularly preferred embodiment of the invention, the three-dimensionally movable rod clamping holder comprises at least two through-openings, wherein a first opening is formed by a central axial through-opening through which the tensioning rod of the tensioning rod connection is passed, leaving sufficient radial play for the three-dimensional movement, and at least one second opening passes through the holder transversely to the axial opening and without intersecting the latter and forms the clamping receptacle for the fixation rod. 
     Appropriately, the holder which is guided three-dimensionally on the base body comprises spherical surface sections with which it is mounted in positive engagement between annular bearing elements in a row on the tensioning rod of the tensioning rod connection, wherein one bearing element is arranged on the base body which is held on the tensioning rod. A particularly advantageous measure consists in that the central through-opening of the clamping holder is expanded in the region of at least one spherical surface of the bearing in order to provide a spherical holder displacement region which is limited thereby. To keep the number of components particularly low, the clamping holder is appropriately formed by a one-piece ball. Advantageously, such a holder is designed with a rod clamping receptacle which on the holder surface forms an open slot for receiving the fixation rod. 
     In order to particularly strengthen the non-positive locking connection, a measure according to the invention consists in that at least one portion of the clamping surfaces of the fixation device is structured. Appropriately, the structuring comprises roughening, grooves, knobs and/or a corresponding means for producing particularly intimate engagement. 
     Due to the measures according to the invention, a relatively small number of components which can be kept ready in particular as cheap lightweight components in the form of a compact kit in a sterile package is achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further preferred features, embodiments and possibilities of the invention are apparent from subsidiary claims and the description. Particularly preferred practical examples are described in more detail with the aid of the drawings. The drawings show: 
         FIGS. 1 and 2  in an axonometric view and in an exploded view, a fixation device according to the invention with two fixation elements connected by two fixation rods, 
         FIG. 3  in an axonometric view, a fixation device according to the invention with two fixation elements connected by only one fixation rod, and 
         FIGS. 4 and 5  in an axonometric view and in an exploded view, a fixation device according to the invention with two connecting rods and two fixation elements which receive bone nails in a different arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of a fixation device  1  according to the invention can be seen from  FIGS. 1 and 2 . This is composed of two fixation elements  11  according to the invention, bone nails  7  to which the elements  11  are applied, and two fixation rods  6 . This is a fixator which with the two fixation rods  6  bridges a bone joint, e.g. a wrist, on the outside in order to make a fixation connection between broken bone portions. The fixation elements  11  are designed to match each other. The fixation rods  6  are shown in parallel alignment in  FIGS. 1 and 2 . But the device according to the invention allows them to be adjusted with a large deviation from parallel alignment as well. The bone nails  7  for the fixation element  11  each stand in a line which runs at least almost parallel to the fixation rods  6 . 
     The fixation element  11  comprises a cross-shaped base body  2  which is made in one piece by a plastic part formed by injection moulding and to a certain extent is inherently deformable against the elastic return force of the materials for making clamping connections. For manufacture of the injection moulding, a high-strength plastic having a relatively low specific gravity is used. Such a body can be made with high precision with accurate shape and size. 
     The base body  2  which has a symmetrical cross shape is formed by a circular cylindrical longitudinal body portion  201  and a transverse body portion  202  which as a unit has an oval shape and with its ends projects perpendicularly from the cylinder body portion  201 . The dimensions of the cross-sections of the portions  201  and  202  which are each perpendicular to the long direction in which they extend are of the same order of magnitude. In the transverse body portion  202  is formed a flat through-slot closed at the edges for forming a receptacle  22  for a pair of bone nails  7 . The slot receptacle  22  extends with the transverse body portion  202 , wherein the slot with its flat surface is perpendicular to the central longitudinal axis  20  of the longitudinal body portion  201  and open at free narrow sides of the transverse body portion  202  for placing on the bone nails  7 . The longitudinal body portion  201  has an axial through-bore  23  through which is passed a tensioning rod  501  of a tensioning connection  5 . 
     The fixation element  11  is formed as a unit by a captive arrangement in a row of the base body  2 , two rod clamping holders  3  and clamping holder bearing elements  41 ,  42  of a bearing  4  on the tensioning rod  501 . The rod clamping holders  3  enclose between them the base body  2 , and this arrangement is encompassed in positive engagement with two bearing ring elements  42  in the form of calotte-shaped caps between their concave ring sides. 
     The two rod clamping holders  3  are designed to match each other. The clamping holder  3  is formed by a one-piece clamping ball  30  which has an axial central through-opening  33  in the form of a bore. The through-opening  33  merges with a concave annular recess  34  at each of its opening ends. Each ball  30  which is made of high-strength plastic is received in positive engagement by the bearing  4 . Each bearing  4  has a bearing element  41  each formed at the end of the longitudinal body portion  201  in the form of a calotte-shaped recess  413  forming a concave bearing ring, and an associated bearing element  42 . Each bearing element  42  has a through-hole  421  with which it is fitted on the tensioning rod  501  at the end of the latter. The bearing element  42  is formed, on its side facing towards the bearing ball  30 , with a concave annular recess  423  which corresponds to the concave annular recess  413  of the bearing element  41 . 
     The clamping holder bearing ball  30  is further designed with a slot receptacle  31  for receiving and holding the fixation rod  6 . The slot receptacle  31  extends in a ball secant region in the equatorial plane of the ball without intersecting the axial through-opening  33  of the ball  30 . The slot receptacle  31  is expanded at its bottom to match the circular cross-section of the fixation rod  6 , forming a seat  311  through which the fixation rod  6  passes at its end. Furthermore, the walls of the slot  31  form latch elements  312  which are expandable against the elastic return force of the material in order to let the fixation rod  6  latch in the seat  311  in clamping relationship. The receiving cross-sections of the slot receptacle  31  and the material elasticity of the bearing ball  30  are selected such that the rod  6  is automatically held by clamping in the latched position, wherein it is movable axially and rotationally against clamping friction force for positioning and adjustment. Also, the bearing ball  30  in its equatorial plane is divided by a gap  301  into two halves which are held together in one piece by a wall web  302  only on the ball side opposite the slot receptacle  31 . The gap  301  is formed by a notch. The one-piece bearing ball  30  can be handled particularly easily. Instead, it is also possible to make the ball halves completely separate from each other. 
     The through-opening  33  passes through the gap  302 . As a result, the ball halves are tensioned relative to each other with a uniform and relatively small tensioning force of the tensioning rod connection  5  for fixing the rod  6  in the slot receptacle  31 . The tensioning force exerted via the bearing elements  41 ,  42  in the process also clamps the bearing ball  30  between the bearing elements  41 ,  42 , so that at the same time the ball  30  is fixed in position easily and very stably. The diameter of the bearing ball  30  is only slightly larger than the cross-sectional diameter of the cylindrical longitudinal body portion  203  and of the bearing element  42 . Consequently, the bearing balls  30  form highly effective clamping elements in the arrangement in a row on the tensioning rod  501  when they are pulled towards each other by the tensioning rod  501 . 
     The tensioning rod  501  of the tensioning connection  5  of each fixation element  11  is formed by set screws  51  and  52  which can be screwed axially to each other at their bottom ends. For this purpose set screw  51  is provided with an external thread at its bottom end, and set screw  52  is provided with an internal thread at its bottom end. The set screws  51 ,  52  have heads  53  each with an internal polygonal recess for applying a screwdriver. On the bearing elements  42  are formed, in each case on the side facing away from the bearing ball  30 , recesses in which the screw heads  53  engage for tensioning the parts arranged in a row on the tensioning rod  501  relative to each other. 
     The bearing ball  30  of each clamping holder  3  is thus mounted in positive engagement between the bearing rings  41 ,  42  in such a way that it is guided and three-dimensionally displaceable in its seat in the bearing elements  41 ,  42  when the tensioning connection  5  is sufficiently undone. To obtain a sufficiently large and limited spherical displacement range, the axial through-opening  33  is given sufficiently large dimensions, and the concave annular recesses  34  are expanded outwardly in a cone shape from the opening  33 . 
     Advantageously and appropriately, the displacement range is selected so large that, starting from the position shown in  FIG. 1  in which the two base bodies  2  with the axes  20  of their longitudinal body portions  201  are aligned parallel in one plane, the longitudinal body portions  201  or their axes  20  when the rods  6  intersect with each other can be torsionally rotated or pivoted relative to each other by at least 90° about an imaginary unidirectional axis  10  comprising the centres M 1  and M 2  of the cross pieces. The two axes  20  can therefore be moved at least into a position perpendicular to each other. In the process the imaginary axis  10  is not fixed, but can be moved in all spatial directions out of the basic position shown in  FIG. 1 . 
     The slot  22  in each base body  2  and the identical bone nails  7  received by it in a pair have dimensions such that the bone nails  7  are received in clamping relationship against the elastic return force of the wall material of the base body  2  in a sliding fit even when the tensioning connection  5  is fully undone. On the slot  22  at the centre of the cross piece of the base body is formed a recess  24  oriented perpendicularly to the axial through-bore  23  and having a shape corresponding to the polygonal recess in the screw head  53 . By inserting and turning the rotating tool with which the tensioning connection  5  is also tensioned, the slot  22  can be expanded slightly against the elastic return force of the material of the slot wall in order to place the fixation element  11  easily on the pair of bone nails. In the process the two bone nails  7  each come to lie in the slot region which extends in the ends of the transverse body portion  202  projecting from the longitudinal body portion  201 . The arrangement of the bone nails  7  in the ends of the transverse body portion  202  which project from the longitudinal body portion  201  leads to particularly effective clamping in the tensioning combination according to the invention. As a result, the central region of the receiving slot  22  between the nails  7  is uniformly and markedly elastically pressure-deformable in the direction of the tensioning rod  501  during tensioning. Also, the shape of the parts of the base body cross piece paired with the plastic materials used forms optimally working cross-sections for permanently and stably tensioning the tensioning rod connection  5 . 
     The surgical technique for applying the fixation device according to the invention proves to be particularly simple and reliable. After two pairs of bone nails  7  have been placed substantially in a line in the usual manner with screw-in tool and drilling jig, the fixation element  11  is fitted onto each pair of nails. A screwing tool is inserted in the recess  24  and turned into a position such that the slot  31  is expanded for fitting. In the turned-back position of the tool it is removed, and the fixation element sits sufficiently tight for adjusting by shifting its position, but slidably on the bone nails  7 . After both fixation elements  11  have been applied to the associated bone nails  7 , the two fixation rods  6  are inserted. The bearing balls  30  are open with their slot recesses  31  on the side which faces away from the bone portions to be joined, and they can easily be displaced three-dimensionally into lockable positions for inserting and displacing the rods  6 . In the process the rods  6  first pass with their ends into captive click-latch positions in which they remain displaceably for adjustment by the fact that they are movable on the one hand axially and rotationally by the automatic clamping action of the elastic clamping ball  30  and on the other hand by spherical displacement of the ball  30  in the bearing  4 . With the capacity for universal displacement for adjustment combined in one unit according to the invention, the two fixation rods  6  are kept largely tension-free in relation to each other. Here it is highly advantageous that both the bone nails  7  and the fixation rods  6  are displaceable for adjustment by the automatic clamping action in the slot receptacle  22  of the base body  2  and in the slot receptacle  31  of the bearing ball  30  without affecting the tensioning connection  5 . But also it is possible to tighten the tensioning rod connections  5  slightly in order to superimpose an additional component for adjustment on the inherent clamping actions. For fully fixing the parts relative to each other, the tensioning rod connection  5  is tensioned by tightening and tensioning the tensioning rod  501  to a given torque. This is achieved according to the invention by the fact that all clamping actions on the fixation element  11  are accomplished uniformly with only the one tensioning rod connection  5 . 
     In  FIG. 3  can be seen a fixation device  1 . 2  according to the invention, which is assembled from the same components as the fixation device  1 . 1  of  FIGS. 1 and 2 . Fixation elements  12  of this arrangement are formed by the fact that the base body  2  and the rod clamping holder  3  are placed on the tensioning rod at only one end of the cylindrical longitudinal body  201 . On the other side the recess  413  in the bearing element  41  serves to receive the screw head  53 . Appropriately, a tensioning rod  501  with screw elements  51 ,  52  is used, which allow the tensioning length to be altered within a wide range, in order to be used both for the device as in  FIGS. 1 and 2  and for the device as in  FIG. 3 . 
       FIGS. 4 and 5  show a fixation device  1 . 3  according to the invention in an embodiment having a modified fixation element  13 . 
     At one end of the arrangement of the fixation rods  6  extending substantially parallel to each other is arranged the fixation element  11 , as described for  FIGS. 1 and 2  The fixation rods  6  are connected at their other ends to the modified fixation element  13 . The latter is designed like the fixation element  11 , with the exception that, instead of the longitudinal body portion  201 , there is provided a longitudinal body portion  203  which remains free from a transverse portion and is instead provided with an additional oval longitudinal body portion  204 . The latter extends parallel to the body portion  203  to which it is connected by an attachment piece  131 . In the body portion  204  in the direction in which it extends is formed a slot receptacle  25  for a pair of bone nails  7 . The design of this slot with tool recess  24  corresponds to the design of the slot in the portion  202  of the other fixation element  11 . As can be seen from  FIGS. 4 and 5 , the fixation element  13  serves to receive a pair of bone nails  7  which stand transversely, in particular at least almost in a line perpendicular to the rods  6 . 
     In the practical example of  FIGS. 4 and 5 , the body portion  204  has been made separate and connected by a screw connection  26  to the attachment piece  131  formed integrally on the body  203 . The screw connection  26  is also used to fix the bone nails  7 , as in the slot receptacle  22 , in the slot receptacle  25 .