Abstract:
Disclosed is a spring for a device for stabilizing bones. The spring is designed as a leg spring that includes a spring coil with at least one turn and, at the end, a first and a second leg, which project beyond the periphery of the turn. At its end, at least one leg includes a rod-shaped end piece that has a three-dimensional structure in the form of a turn or a peripheral leaf or lip. Also disclosed is a device for stabilizing bones, which includes a spring, a bone plate that includes means for securing the bone plate to the three-dimensional structure in the form of a turn or a peripheral leaf or lip, and a clamping element that has at least one hole for accepting a bone fixation element as well as a channel through which one of the two legs of the spring can be guided.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The invention relates to a spring for stabilizing human or animal bones, to a device for stabilizing human or animal bones, and to a method for stabilizing long tubular bones or the vertebral column. 
         [0003]    2. Brief Description of Related Art 
         [0004]    A device for stabilizing the vertebral column is known from the document WO 02/102259 SENGUPTA. This device includes at least two pedicle screws, a spring element between the pedicle screws, and on each pedicle screw, a securing mechanism for securing the spring element to the pedicle screws. The spring element has a substantially straight end piece at each end and a central C-shaped or coil-shaped section arranged between the end pieces. On the straight end pieces, sleeves are attached, which increase the outer diameter of the end pieces, so that the end pieces can be secured in the pedicle screws. The securing mechanism consists of an open channel arranged at the end on the head of the pedicle screws for receiving an end piece of the spring element, a cap which is slid partially over the head and the end piece, and a nut by means of which the cap can be secured on the head of the pedicle screw and at the same time the end piece can be secured in the channel. Since, particularly in animals, in the lumbo-sacral portion of the vertebral column, only minimal space conditions for the implant exist, the voluminous form, in particular of the securing mechanism between the spring element and the pedicle screws of the aforementioned device, is disadvantageous. 
         [0005]    An implant for the articulated connection of two vertebral bodies is known from US-A 2005/209694 LOEB. This known implant includes a spring element with a straight end piece at each end of the spring element and a central coil-shaped section. The end pieces each have a longitudinal hole for passing a bone securing element through it. However, the end pieces are connected rigidly to the central section, so that the bone fixation elements cannot be angled relative to a plane defined by the central axis of the coil-shaped section. The disadvantage of this embodiment therefore is that the bone securing elements as a result cannot be attached selectively in the pedicles and/or the laminas of the vertebral bodies, as a result of which the possibilities for the securing of the implant to the vertebral bodies are considerably reduced. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The purpose of the invention is to provide a remedy for this. The invention is based on the problem of producing a spring and a device for stabilizing bones, which allows a translational and rotational motion of at least one bone plate relative to the spring of the device, and thus allows the selective anchoring of the device by means of bone securing elements, for example, bone screws, in the laminas or in the pedicles of the vertebral bodies. 
         [0007]    The invention solves the posed problem with a spring for stabilizing bones as disclosed and claimed herein, with a device for stabilizing bones as disclosed an claimed herein, and with a method for stabilizing long tubular bones or the vertebral column as disclosed and claimed herein. 
         [0008]    The advantages achieved by the spring according to the invention are substantially that the spring can be made from a spring wire and a thread can be applied directly to the spring wire. As a result, an implant having a minimum volume is produced, so that the implant can be attached in the lumbo-sacral area of the vertebral column of dogs, for example, without limiting the movements of the animal. In addition, by means of a simple threaded connection, a bone plate can be attached to at least one leg, wherein, due to the translational and rotational mobility of the bone plate relative to the spring, the entire implant can be shortened, lengthened or twisted, so that the position of the bone securing element which can be introduced into the plate hole of the bone plate, for example, the position of a bone screw, can be selected after the introduction of the implant by the surgeon. 
         [0009]    The advantages achieved by the device according to the invention are substantially that:
   due to the translational and rotational movability of at least one bone plate relative to the spring, the device can be shortened, lengthened or twisted, so that the bone securing elements can be anchored in a desired position selectively in the pedicles and/or in the laminas of the vertebral bodies. As a result, the surgeon is given the possibility of setting the bone screws and the implant in such a manner that the bone screws are not pulled out even in the case of the great forces that occur in the lumbosacral area of the vertebral column, in particular in running or jumping dogs. Due to the threaded connection between at least one end piece of the spring and at least one bone plate, it becomes also possible to angle the bone plates and screws relative to the spring;   in the human and animal body, only a minimal space requirement (volume) for the device is needed;   relative to the spring of the device, axial slippage of the bone plates is not possible, even in the case of high stresses;   due to the threaded connection, a stable securing of the bone plate to the spring of the device is possible, even in the case of a small outer diameter of the end piece and a small bone plate;   the spring, in the case of a design as a leg spring, has a preferred swivel plane for the bone plates attached to the legs, so that the elastic resistance of the spring can be dimensioned for a defined movement, for example, extension and flexion of the vertebral bodies stabilized by the device, whereas considerably smaller or larger spring forces can act in the case of a torsion movement or a lateral bending of the vertebral bodies relative to one another; and   improvement, respectively promoting of callus formation in the case of long tubular bone fractures.   
 
         [0016]    Additional embodiments of the invention can be commented on as follows:
   The peripheral lamella or lip can have one or more threaded segments or, in an alternative embodiment, can be arranged in a plane perpendicular to the axis of the straight end piece. In further embodiments, several peripheral laminas or lips can be provided, which are arranged in several planes perpendicular to the axis of the straight end piece.   The first and second leg can comprise, at the end, a straight, preferably circular cylindrical end piece with a thread.   In a special embodiment, the spring coil has a variable pitch, which is implemented preferably in the form of only one turn of the spring coil. In an additional embodiment, the spring is produced from a spring wire which is wound around a central axis of the spring coil, and at least one leg in the direction of its free end is convergent relative to a plane that is perpendicular to the central axis, towards the other leg. In an additional embodiment, at least one leg is angled, relative to a plane perpendicular to the central axis, towards the other leg.   
 
         [0020]    By means of these three embodiments, the variable pitch of one or both legs, in particular, can be arranged so that the straight end pieces come in contact substantially in a narrow axial region of the central axis of the spring coil. The bone securing means used for attaching the spring to bones can as a result be arranged in the immediate vicinity of a plane perpendicular to the central axis of the spring coil, so that the spring coil is stressed only in the turn direction upon bending and an unintentional deformation of the spring coil can be prevented. 
         [0021]    Suitable materials for the spring are: stainless steel, nitinol, titanium, a titanium alloy, preferably TiAlNb, plastics, preferably fiber-reinforced plastics, or ceramic materials which allow a greater stiffness of the spring compared to plastics. 
         [0022]    In an additional embodiment, the spring is produced from a hollow spring wire. The central fibers of the spring wire contribute nothing or only little to the bending stiffness, so that, due to the hollow formation, the bending stiffness is not decreased, but the dead weight is reduced. 
         [0023]    In an additional embodiment, the spring is made from a spring wire having a preferably rectangular cross-sectional area that is flattened in the area of the spring coil. The advantage of this embodiment consists of the different bending stiffness of the spring wire in different directions. 
         [0024]    In an additional embodiment, the spring coil is designed as a cone-shaped coiled spiral. 
         [0025]    In an additional embodiment, the spring is made from a spring wire with a wire axis, and the sections of the wire axis, which are straight in the area of the first and second end piece of the first and second leg, enclose, viewed in a plane perpendicular to the central axis of the spring coil, an angle alpha which, in the unstressed state of the spring, is between 135° and 225°. 
         [0026]    The advantage of this embodiment is that the end sections of the leg, which are provided for the attachment of the spring to the bone, can be aligned in a position that is suitable with regard to the anatomy. 
         [0027]    In an additional embodiment, the leg spring can be prepared from a spring wire having a diameter d between 2.0 mm and 4.0 mm, preferably between 3.3 mm and 3.7 mm. 
         [0028]    In an additional embodiment, the spring coil has several spring turns. Due to the larger number of spring turns, the leg spring can allow an increased relative movement of the vertebral body, under the same stress. 
         [0029]    In an additional embodiment, the spring coil is made from a spring wire with a wire axis, wherein the wire axis of the spring wire coils in the area of the spring coil with a diameter D around the central axis, which is at least 12 mm, preferably at least 15 mm and typically 20 mm. 
         [0030]    In a particular embodiment, the spring coil is made from a spring wire with a wire axis, wherein the wire axis of the spring coil coils in the area of the spring coil with a diameter D around the central axis, which is at most 25 mm, preferably at most 22 mm. 
         [0031]    The invention moreover relates to a device for stabilizing bones in the human or animal body. In this device, the first and/or the second bone plate can have a cavity with an inner thread which can engage with the outer thread on the end piece of the first and/or the second leg. Each of the two bone plates can be moved towards the spring in translation or rotation relative to the longitudinal axis of the corresponding end piece. The bone plates can therefore be brought independently of one another each into an appropriate position on a vertebral body. The surgeon can therefore decide immediately before producing the bores for securing the bone securing elements in the bone, for example, in the vertebral bodies, whether the bone securing element should be anchored in the cortex, for example, in the lamina or in a pedicle of a vertebral body. 
         [0032]    In an additional embodiment, the plate hole in the first and/or in the second bone plate has a hole axis, and the longitudinal axis of the cavity is arranged perpendicularly to the hole axis. 
         [0033]    In an additional embodiment, the device includes a first and a second bone plate and, in addition, at least one clamping element with at least one hole for receiving a bone securing element and a channel for the passage of one of the two legs of the leg spring. The advantage of this embodiment is that the legs of the spring, in addition, can be attached to the bone surface, for example, to a vertebral body, in such a way that the leg spring can be secured against rotation. The device can be attached in such a manner to the bone, for example, to the vertebral bodies, that the bone screws are not pulled out, even in the case of great forces such as those that can occur in running or jumping dogs. 
         [0034]    In an additional embodiment, at least one of the bone plates includes a first section having at least one plate hole, which is connected to an end piece of a leg, and a second section having at least one plate hole, wherein the second section is angled relative to the first section. The advantage of this embodiment is that the bone securing elements can be positioned optimally with regard to the anatomy. 
         [0035]    In an additional embodiment, the plate hole, in the first section, has a hole axis, and the second section is angled relative to a plane orthogonal to the hole axis. 
         [0036]    The first section and the second section can also be in a planar arrangement. 
         [0037]    In an additional embodiment, the clamping element is designed as a clip, so that the end piece of a leg can be snapped into the channel in the clamping element. In this manner, the bone plates, at the end first, can be secured to the bone, and subsequently the clamping elements located at appropriate sites between the bone plates and the central section of the spring can be attached on or to the bone. 
         [0038]    In an additional embodiment, the spring is made from a material that is different from the bone plates. 
         [0039]    In addition, the device according to the invention can also comprise bone screws. The bone screws can each have a screw head which can be locked in a plate hole. 
         [0040]    The device according to the invention is used for stabilizing vertebral bodies or for the temporary stabilization of a joint. For example, a joint on which a partial or complete abrasion of the collateral ligaments has taken place can be stabilized temporarily. Another use for the temporary stabilization of a joint exists in the case of bone defects resulting from the removal of a tumor. 
         [0041]    The device according to the invention can moreover be used for treating a fractured bone and also for treating osteoarthritis or pseudarthrosis. The device according to the invention can be used preferably on the knee joint or on finger joints. 
         [0042]    The spring according to the invention can also be used for treating a fractured bone, or osteoarthritis or pseudarthrosis, wherein the spring is used for the external securing. 
         [0043]    The spring can be attached, for example, to a plaster cast or it can be attached in the form of an external fixation by means of bone securing elements to the bone. 
         [0044]    The invention also relates to a method for stabilizing a long tubular bone or the vertebral column, having the steps of:
   i) producing an incision in the area of the bone section to be treated, more specifically a dorsal or posterior incision in the area of the vertebral bone section;   ii) preparing the epaxial muscles and the osseous attachment sites for securing the implant;   iii) performing a lateral retraction of the muscle masses;   iv) introducing an implant through the incision;   v) securing the implant to the bone section, or to the vertebral bodies, and   vi) closing the incision.   
 
         [0051]    In a particular embodiment of the method according to the invention, step i) is preceded by the following additional steps:
   diagnosing the degree and type of compression by means of an imaging investigation and/or   determining the maximum stretching and bending of the vertebral column segment to be treated.   
 
         [0054]    In an additional embodiment of the method according to the invention, after step v), the additional step of:
   performing a surgical decompression within the vertebral column channel can be carried out.   
 
         [0056]    In the method according to the invention, a device according to the invention can be implanted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0057]    The invention and variants of the invention are explained in further detail below in reference to partially diagrammatic representations of several embodiment examples. 
           [0058]      FIG. 1  shows a side view of an embodiment of the device according to the invention implanted on a lumbosacral vertebral column section of a dog in a side view; 
           [0059]      FIG. 2  shows a top view of an additional embodiment of the devices according to the invention implanted on a lumbosacral vertebral column section of a dog in a dorsal view; 
           [0060]      FIG. 3  shows a side view of an embodiment of the spring according to the invention; 
           [0061]      FIG. 4  shows a top view of the embodiment of the spring according to the invention according to  FIG. 3 ; 
           [0062]      FIG. 5  shows a side view of a bone plate according to the embodiment of the device according to the invention according to  FIG. 1 ; 
           [0063]      FIG. 6  shows a top view of the bone plate according to the embodiment of the device according to the invention according to  FIG. 1 ; 
           [0064]      FIG. 7  shows a section through a clamping element according to the embodiment of the device according to the invention according to  FIG. 2 ; 
           [0065]      FIG. 8  shows a top view of a clamping element according to the embodiment of the device according to the invention according to  FIG. 2 ; 
           [0066]      FIG. 9  shows a top view of a bone plate according to another embodiment of the device according to the invention; 
           [0067]      FIG. 10  shows a side view of a bone plate according to yet another embodiment of the device according to the invention; 
           [0068]      FIG. 11  shows a side view of a bone plate according to an additional embodiment of the device according to the invention; 
           [0069]      FIG. 12  shows a view of another embodiment of the device according to the invention implanted on a tubular bone; and 
           [0070]      FIG. 13  shows a top view of a spring according to another embodiment of the device according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0071]      FIG. 1  is a representation of an embodiment of the device  1  according to the invention for stabilizing the vertebral column, for example, the last lumbar vertebral body  41  relative to the sacrum  42 , for example, of a dog, wherein each device  1  is arranged on one side of the spinous processes of the vertebral body. Each of the two devices  1  includes a spring  2  ( FIGS. 3 and 4 ) which is designed as leg spring  14  and which, at the end, includes a first leg and a second leg  15   a ,  15   b , a first bone plate  7  arranged on the first leg  15   a  ( FIGS. 5 and 6 ), and a second bone plate  8  arranged on the second leg  15   b  ( FIGS. 5 and 6 ). The first bone plate and the second bone plate  7 ,  8  each have a plate hole  10  for receiving a bone securing element  11 , so that the spring  2  can be attached by means of the bone fixation element  11  inserted in the plate holes  10  of the first and second bone plates  7 ,  8 , for example, on the last lumbar vertebral body  41  and on the sacrum  42 . The first leg and the second leg  15   a ,  15   b  each have an end piece  5 ,  6 , each of which is connected by means of a threaded connection  17  to one of the bone plates  7 ,  8 . 
         [0072]    By securing the spring  2 , for example, on the last lumbar vertebral body  41  and on the sacrum  42 , a resistance is opposed by the spring  2  against the great forces occurring in the lumbosacral area of the vertebral column, particularly in running and jumping dogs, so that painful impacts or contacts between the last lumbar vertebral body  41  and the sacrum  42  can be prevented. 
         [0073]    Brief description of the implantation of the device according to the invention: 
         [0074]    First, the degree and the type of the compression of the spinal cord are diagnosed by an imaging investigation. In addition, the maximum stretching and bending of the vertebral column segment to be treated can subsequently be determined. For the introduction, positioning and securing of the device, the dorsal or posterior access is used. Before that, a bilateral preparation of the epaxial muscles and a surgical preparation of the osseous attachment sites are carried out. The lateral retraction of the muscle masses is established by the self-holding retractors. The pedicle, the transverse processes and the spinous processes are now exposed and they allow the securing of the implant with bone securing elements, preferably with bone screws having the necessary different angles relative to the device. A surgical decompression within the vertebral column channel is then also possible. After securing the implant, the incision is closed again. 
         [0075]      FIG. 2  shows a use of another embodiment of the device  1  according to the invention, also in the lumbosacral area of the vertebral column, which differs from the embodiment according to  FIG. 1  only in that each of the two devices  1  includes, in addition, a clamping element  20  ( FIGS. 7 and 8 ), each being attached to one of the legs  15   a ,  15   b  and secured by means of an additional bone fixation element  11  to the last lumbar vertebral body  41  and on the sacrum. 
         [0076]    In  FIGS. 3 and 4 , an embodiment of the spring  2  is represented. The spring  2  is designed as a leg spring  14 , and it includes a spring coil  30  coiled around a central axis  16 , a first end  3  and a second end  4 . The spring coil  14  is made from a spring wire  31  and includes in each case a preferably circular cylindrical leg  15   a ,  15   b  arranged at the end. The spring coil  30  has, for example, one spring turn. The spring wire  31  can have a circular cylindrical design with a diameter d. The wire axis  32  of the spring wire  31  is coiled in the area of the spring coil  30  with a diameter D in a helical pattern around the central axis  16  of the spring coil  30 , and at the transitions, it transitions tangentially towards the legs  15   a ,  15   b  into a respective straight section in the area of the legs  15   a ,  15   b . The leg spring  14  is also referred to as screw-like coiled bending springs, wherein a torque exerted on the legs  15   a ,  15   b  acts around the central axis  16  of the spring coil  30  as a substantially constant torque on the spring wire  31  in the entire area of the spring coil  30 . The projections of the sections of the wire axis  32  of the spring wire  31 , which are straight in the area of the legs  15   a ,  15   b , into a plane perpendicular to the central axis  16  of the spring coil  30 , enclose an angle alpha which, in the unstressed state of the spring  2 , can be between approximately 135° and approximately 225°, and which in the present embodiment is approximately 165°, for example. The legs  15   a ,  15   b  thus form levers, which can be turned relative to one another against the elastic resistance of the spring  2 , so that the angle alpha is increased or decreased. When the legs  15   a ,  15   b  are rotated under the action of a force relative to one another, the spring wire  31  is bent in the area of the spring coil  30 , i.e. inward or outward. The spring  2  is made from a material that is different from the first and the second bone plate  7 ,  8  and can be made from a titanium alloy, preferably from TiAlNb, a plastic, a ceramic material or from nitinol. Furthermore, the legs  15   a ,  15   b , on their end pieces  5 ,  6 , each have a thread  12 , so that the legs  15   a ;  15   b  of the spring  2  can be secured in a rigid manner on the first and second bone plates  7 ,  8  ( FIGS. 5 and 6 ). The diameter d of the spring wire  31  can be between 2.0 mm and 4.0 mm. A typical value for the diameter d is 3.5 mm. In the area of the spring coil  30 , the diameter D enclosed by the wire axis  32  of the spring wire  31  is typically 20 mm. 
         [0077]    The spring coil  30  has a variable pitch, so that on the first end and the second end  3 ,  4  of the spring  2 , the wire axis  32  of the spring wire  31  is located substantially in a plane perpendicular to the central axis  16  of the spring coil  30 . In this way, it is possible to achieve that the straight end pieces  5 ,  6  of the first and of the second leg  15   a ,  15   b  come to be located substantially in a narrow axial area of the central axis  16  of the spring coil  30 . 
         [0078]    As shown in  FIGS. 5 and 6 , the first and the second bone plates  7 ,  8  have a cuboid design and they each comprise a top side  34 , a bottom side  35 , two long side surfaces  36   a ,  36   b  and two short side surfaces  37   a ,  37   b . Each of the first and second bone plates  7 ,  8  includes a plate hole  10  which passes through the first bone plate and the second bone plate  7 ,  8  from the top side  34  to the bottom side  35 . Moreover, each one of the first and second bone plates  7 ,  8  comprises a cavity  18  penetrating from a short side surface  37   b  into the bone plate  7 ,  8 . The cavity  18  is designed as a blind hole with a longitudinal axis  21  which is perpendicular to the hole axis  25  of the plate bore  10 , and it has an inner thread  13  which matches the outer threads  12  on the end pieces  5 ,  6  of the legs  15   a ,  15   b , so that in each case one of the first and second bone plates  7 ,  8  can be secured by means of a threaded connection  17  to an end piece  5 ,  6  of a leg  15   a ,  15   b . The first and second bone plates  7 ,  8  can be produced from a biocompatible stainless steel, for example, an austenitic stainless chromium-nickel-molybdenum steel, titanium or a titanium alloy, for example, Ti-6Al-7Nb. 
         [0079]      FIGS. 7 and 8  show an embodiment of the clamping element  20  ( FIG. 2 ). The clamping element  20  includes a three-dimensional body  50 , which is produced, for example, as a cuboid body having a top side  51 , a bottom side  52  and four side walls  53   a ,  53   b ,  53   c ,  53   d . The clamping element  20  is designed as an elastic clip and includes a plate hole  10  having a hole axis  25 , hole which passes through the three-dimensional body  50 , and a channel  22  having a hole axis  25  skewed relative to the channel axis  28 , hole which also passes through the three-dimensional body  50 . The channel  22  is suitable for receiving a leg  15   a ,  15   b  of the leg spring  14  and includes a channel wall that is open at the periphery towards the bottom side  52  of the clamping element  20 . The hole axis  25  and the channel axis  28  are a distance apart which is measured so that plate hole  10  and the channel  22  do not interpenetrate. The plate hole  10  passes through the three-dimensional body  50  from the top side  51  thereof to the bottom side  52 , while the channel  22  passes through the three-dimensional body  50  from a first side wall  53   c  to a facing second side wall  53   d . The channel  22  narrows towards the bottom side  52  of the clamping element  20  in such a manner that a leg  15   a ,  15   b  of a spring  2  can be snapped into the channel  22  from the bottom side  52  of the clamping element  20 . If the spring  2  has to be secured by means of an additional clamping element  20  to the vertebral column, then an additional clamping element  20  can be simply placed on said vertebral column, without having to be slid painstakingly over the length of the legs  15   a ,  15   b  of the spring  2 . Furthermore, the spring  2  can be introduced into the human or animal body before the setting of the bone securing elements  11 , so that the positions of the bone fixation elements to be secured subsequently on the vertebral bodies can be determined easily by the surgeon. 
         [0080]    In  FIGS. 9 to 11 , additional embodiments of the bone plates  7 ,  8  are represented, which differ from the embodiment represented in  FIGS. 5 and 6  only in that the first and/or the second bone plate  7 ,  8  comprise(s), in addition to a first section  23  having a plate hole  10 , which can be connected to an end piece  5 ,  6  of a leg  15   a ,  15   b , a second section  24  having a plate hole  10 , wherein the second section  24  is angled relative to the first section  23 .  FIG. 9  shows an embodiment of the first and/or the second bone plate  7 ,  8 , wherein the first section and the second section  23 ,  24  are in a planar arrangement. In the embodiment of the first and/or the second bone plate  7 ,  8  shown in  FIG. 10 , the first section and the second section  23 ,  24  are angled relative to one another so that the hole axis  25  of the plate hole  10  in the first section  23  and the hole axis  25  of the plate hole  10  in the second section  24  converge towards the bottom side  35  of the first and/or the second bone plate  7 ,  8 , while in the embodiment of the first and/or the second bone plate  7 ,  8  represented in  FIG. 11 , the first section and the second section  23 ,  24  are angled with respect to one another in such a manner that the hole axis  25  of the plate hole  10  in the first section  23  and the hole axis  25  of the plate hole  10  in the second section  24  diverge towards the bottom side  35  of the first and/or the second bone plate  7 ,  8 . 
         [0081]    The embodiments of the bone plates  7 ,  8  represented in  FIGS. 9 to 11  are suitable as well for the stabilization of vertebral column segments or of joints. 
         [0082]    In  FIG. 12 , a use of the device  1  according to the invention for treating a fractured bone is represented. Here, a respective device  1  is arranged on the medial and on the lateral side of the fractured bone. Each one of the two devices  1  includes a spring  2  whose first leg  15   a  is connected by means of a threaded connection  17  to a first bone plate  7 , wherein the two first bone plates  7  are each secured with a bone securing element  11  to the proximal bone fragment  43 . Similarly, the second legs  15   b  of the spring  2  are each connected by means of a threaded connection  17  to a second bone plate  8 , wherein the second bone plates  8  are each attached to a bone securing element  11  on the distal bone fragment  44 . If the surgeon so desires, the springs  2  arranged on the medial side and the lateral side of the bone fragments  43 ,  44  can have a different spring constant and, in addition, one or more clamping elements  20  ( FIGS. 7 and 8 ) can be mounted on the springs  2 . 
         [0083]    The embodiment of the spring  2  represented in  FIG. 12  differs from the embodiment represented in  FIGS. 3 and 4  only in that the spring  2  designed as a leg spring  14  has several spring turns in its helical section  30 . 
         [0084]    Although, as described above, different embodiments of the present invention are present, they should be understood in such a way that the different features can be used both individually and also in any desired combination. 
         [0085]    The invention is therefore not limited to the above-mentioned particularly preferable embodiments.