Abstract:
A modular bone plate is provided including at least a first and a second member each having a top surface and a bottom surface, the first member comprising a male connection portion with a single hole extending from the top surface to the bottom surface and the second member comprising a female connection portion with a single hole extending from the top surface to the bottom surface, wherein the male connection portion is insertable into the female connection portion such that the holes overlap and wherein an anchor or a plug member is insertable into the holes when they overlap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and wholly incorporates by reference U.S. provisional application No. 61/497,972 to Biedermann filed on Jun. 17, 2011 (Atty Docket No. MD 11-P28350US00). 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a modular bone plate and to a connector piece for a modular bone plate. 
       BACKGROUND OF THE INVENTION 
       [0003]    U.S. Pat. No. 5,484,439 describes a modular implant for use in stabilizing femoral bone disorders. In one embodiment the implant has an upper side plate with a widened head and an angled barrel and a lower side plate adapted to be engaged with the upper side plate in a tongue and groove configuration. 
       SUMMARY OF THE INVENTION 
       [0004]    The object underlying the invention is to provide an improved modular bone plate that can be realized for various clinical applications and that is easy to assemble while providing a strong and durable construct. 
         [0005]    The object and further developments are addressed by a modular bone plate described according to the various embodiments described herein. 
         [0006]    The bone plate according to the invention comprises at least two members each having a top surface and a bottom surface and that can be connected together. The members include a male connection portion with a single hole extending from the top surface to the bottom surface and a female connection portion with a single hole extending from the top surface to the bottom surface. The male connection portion is insertable into the female connection portion so that the holes overlap and wherein an anchor or a plug member is insertable into the holes when they overlap. 
         [0007]    By means of the modular construction bone plates according to specific clinical requirements and adapted to a specific anatomical situation can be easily designed. 
         [0008]    There is only one hole of engagement in the male connection portion. The engagement portion of the male portion is relatively short. This makes the adjustment and engagement step easy to perform. 
         [0009]    The modular bone plate may be designed pivotable such that an angle between the members to be connected can be selected. The members may be locked with respect to each other in the angled configuration. 
         [0010]    In a further development there are additional points of engagement realized by a male portion in the female portion and a female portion in the male portion. This allows a more even load distribution between the members to be connected. 
         [0011]    Locking and non-locking screws may be used with the modular bone plate. The locking screws make use of a locking cap that is screwed into the hole. This renders the construct more stable and increases the stiffness. The plate portions can be clamped together also without screws using a plug member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further features and advantages of the invention will become apparent from the description of embodiments with reference to the accompanying drawings. In the drawings: 
           [0013]      FIG. 1   a  shows a perspective view of a modular bone plate assembly according to a first embodiment; 
           [0014]      FIG. 1   b  shows an exploded view of the modular bone plate assembly according to the first embodiment; 
           [0015]      FIG. 1   c  shows a cross sectional perspective view of the modular bone plate assembly to the first embodiment; 
           [0016]      FIG. 1   d  shows a cross sectional view of the bone plate assembly according to the first embodiment; 
           [0017]      FIG. 2   a  shows a perspective view of a ball locking cap from the top; 
           [0018]      FIG. 2   b  shows a perspective view of the ball locking cap from the bottom; 
           [0019]      FIG. 3   a  shows a perspective view of a male end piece of the modular bone plate according to the first embodiment; 
           [0020]      FIG. 3   b  shows a perspective view of a female end piece according to a first embodiment; 
           [0021]      FIG. 4  shows a perspective view of a female/male connector piece according to a first embodiment; 
           [0022]      FIG. 5   a  shows a top view of a modular bone plate assembly in a second angled embodiment that has an angled configuration; 
           [0023]      FIG. 5   b  shows a cross sectional top view of the modular bone plate assembly according to the second embodiment; 
           [0024]      FIG. 6  shows a cross sectional top view of an angled male/female connector piece in a second embodiment; 
           [0025]      FIG. 7   a  shows a perspective view of a modular bone plate system according to a third embodiment; 
           [0026]      FIG. 7   b  shows a side view of the modular bone plate assembly according to the third embodiment; 
           [0027]      FIG. 7   c  shows a cross sectional side view of the modular bone plate assembly according to the third embodiment; 
           [0028]      FIG. 7   d  shows a cross sectional perspective view of the modular bone plate assembly according to the third embodiment; 
           [0029]      FIG. 7   e  shows an exploded view of the modular bone plate assembly according to the third embodiment; 
           [0030]      FIG. 8   a  shows a perspective view of the female/male connector piece (4.5 mm to 2.5 mm) according to a third embodiment; 
           [0031]      FIG. 8   b  shows a side view of the female/male connector piece (4.5 mm to 2.5 mm) according to a third embodiment; 
           [0032]      FIG. 9   a  shows a perspective view of the female/male connector piece (3.5 mm to 2.5 mm) according to a fourth embodiment; 
           [0033]      FIG. 9   b  shows a side view of the female/male connector piece (3.5 mm to 2.5 mm) according to a fourth embodiment; 
           [0034]      FIG. 10   a  shows a perspective view of a modular bone plate assembly according to a fourth embodiment; 
           [0035]      FIG. 10   b  shows a side view of the modular bone plate assembly according to the fourth embodiment; 
           [0036]      FIG. 11   a - e  show perspective views of a humerus expandable plate according to a fifth embodiment; 
           [0037]      FIG. 12   a - e  show exploded views of the humerus expandable plate according to the fifth embodiment; 
           [0038]      FIG. 13   a - e  show perspective top views of the humerus expandable plate according to the fifth embodiment; 
           [0039]      FIG. 14   a - e  show perspective bottom views of the humerus expandable plate according to the fifth embodiment; 
           [0040]      FIG. 15  shows a top view of a modular hard angle bone plate according to a sixth embodiment; 
           [0041]      FIG. 16   a - i  show top views of hard angle connector pieces having angles from 0° to 90°; 
           [0042]      FIG. 17   a - i  show perspective views of hard angle connector pieces shown in  FIG. 16   a - i;    
           [0043]      FIG. 18   a  shows a perspective view of a female/male connector piece according to a fifth embodiment (angle 45°); 
           [0044]      FIG. 18   b  shows a cross sectional top view of the female/male connector piece according to the fifth embodiment (angle 45°); 
           [0045]      FIG. 19   a  shows a perspective view of a female/male connector piece in a sixth embodiment (angle 90°); 
           [0046]      FIG. 19   b  shows a cross sectional top view of the female/male connector piece in the sixth embodiment (angle 90°); 
           [0047]      FIG. 20   a - e  show perspective views of a modular T-plate according to a seventh embodiment; 
           [0048]      FIG. 21   a - e  show exploded views of the modular T-plate according to the seventh embodiment; 
           [0049]      FIG. 22   a - e  show perspective views of a modular Y-plate according to an eighth embodiment; 
           [0050]      FIG. 23   a - e  show exploded views of the modular Y-plate according to the eighth embodiment; 
           [0051]      FIG. 24   a - c  show perspective front views of a modular bone plate having interchangeable heads according to a ninth embodiment; 
           [0052]      FIG. 25   a - c  show exploded views of the modular bone plate according to the ninth embodiment; 
           [0053]      FIG. 26   a  shows a perspective view of a modular bone plate assembly according to a tenth embodiment in a first orientation; 
           [0054]      FIG. 26   b  shows a perspective view of the modular bone plate assembly according to a tenth embodiment in a second orientation; 
           [0055]      FIG. 27  shows a perspective view of a double latch connector according to the second embodiment; 
           [0056]      FIG. 28   a  shows a perspective view of a female/male connector according to a seventh embodiment in a first orientation; 
           [0057]      FIG. 28   b  shows a perspective view of the female/male connector according to the seventh embodiment in a second orientation; 
           [0058]      FIG. 29  shows a cross sectional side view of the modular bone plate assembly according to the tenth embodiment; 
           [0059]      FIG. 30   a  shows a perspective view of a modular bone plate according to an eleventh embodiment; 
           [0060]      FIG. 30   b  shows an exploded view of the modular bone plate according to the eleventh embodiment; 
           [0061]      FIG. 30   c  shows a cross sectional perspective view of the modular bone plate according to the eleventh embodiment; 
           [0062]      FIG. 31   a  shows a perspective view of a modular bone plate assembly according to the eleventh embodiment; 
           [0063]      FIG. 31   b  shows a cross sectional perspective view of the modular bone plate assembly according to the eleventh embodiment; 
           [0064]      FIG. 31   c  shows an exploded view of the modular bone plate assembly according to the eleventh embodiment. 
           [0065]      FIG. 32   a  shows a side view of a modular bone plate assembly according to the twelfth embodiment; 
           [0066]      FIG. 32   b  shows an exploded view of the modular bone plate assembly according to the twelfth embodiment; 
           [0067]      FIG. 32   c  shows a perspective view of the modular bone plate assembly according to the twelfth embodiment; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0068]    A first embodiment of the modular bone plate assembly will now be described with reference to  FIGS. 1 to 4 . As can be seen in particular in  FIGS. 1   a  to  1   d,  the modular bone plate assembly includes a plate member  1  having a top side  1   a  and a bottom side  1   b.  The modular bone plate  1  comprises a female end piece  2  (see  FIG. 3   b ), a male end piece  3  (see  FIG. 3   a ) and referring to  FIGS. 1   a  to  1   d,  a plurality of female/male connector pieces  4  (see  FIG. 4 ). 
         [0069]    The modular bone plate assembly  1  further comprises bone anchoring elements, for example—bone screws  5  having a threaded shank  51  for anchoring the bone anchoring element  5  in a bone and a substantially ball-shaped head  52  with an engagement structure  55  for engagement with a tool, for example a screwdriver. It is also possible to provide other bone anchors, for example bone nails having a threadless shank or having barbs. Furthermore, the bone anchoring element  5  may comprise a through bore hole  54  i.e. a channel (see  FIG. 1   c ) for inserting, for example, bone cement. Further, a substantially cylindrical insert  6  is provided having an outer thread which is adapted to fit with an inner thread of the female end piece  2  or a female connection portion or female part of the female/male connector piece  4 . The outer thread may also fit with an inner thread of the male end piece  3  (not shown) or a male connection portion or male part of the female/male connector piece  4  (not shown). The insert functions as a locking cap or locking element for locking the head  52  of the bone screw  5 . 
         [0070]    The male end piece  3  which is substantially formed by a plate comprises a through hole  31 , the female end piece  2  comprises a through hole  21  and the female/male connector piece comprises a first through hole  41  and a second through hole  42  (see  FIGS. 3   a  to  4 ). The through hole  31 , the through hole  21 , the through hole  41  and the through hole  42  have to be understood as circumferentially closed openings. 
         [0071]    The female end piece  2  is substantially cylindrical and the hole  21  comprises a portion  22  with an internal thread. Further, the female end piece  2  comprises a recess  23  which is provided in the side wall of the female end piece  2  and is in communication with the hole  21 .The recess  23  extends about the half of the circumference of the side wall of a female end piece  2  and is adapted to accommodate the male portion of the female/male connector piece  4 . The recess  23  extends from the outside into the hole  21 . Thereby a lug or pocket is formed which is adapted to engage a male portion having a tongue or projection. 
         [0072]    The main body of the male end piece  3  is substantially cylindrical and has an extension  32  to one side adapted to the contour of the recess  23  of the female end piece  2 . The extension  32  may be formed as tongue or projection which is adapted to engage a female portion having a recess, a lug or a pocket. A portion  33  of the hole  31  of the male end piece  3  is beveled and therefore conical on the top side. Further, a spherical bottom seat  34  is provided for accommodating the head  52  of the bone screw  5 . 
         [0073]    The female/male connector piece  4  is an integral combination of the male end piece  3  and the female end piece  2  connected by a middle portion  43 . The female connection portion of the female/male connector piece  4  hereby comprises a through hole  41  having an inner thread  46  and a recess  45  extending about the half of the circumference of the sidewall of the female connection portion of the female/male connector piece  4 . The recess  45  is in communication with the hole  41 . The male connection portion of the female/male connector piece  4  is formed by a lug portion  44  having a through hole  42  in its middle. The hole  42  has a circumferential beveled portion  47  as the beveled portion  33  of the male end piece  3  and a spherical bottom seat  47   a  as the spherical bottom seat  34  of the male end piece  3 . 
         [0074]    As can be seen in  FIG. 1   a  to  FIG. 1   c,  the recess  23  of the female end piece  2  or the recess  45  of the female/male connector piece  4  serves for accommodating the male end piece  3  or the male connection portion of the female/male connector piece  4  such that in an assembled state the respective holes of male and female connection portions overlap. 
         [0075]    The extended side  32  of the male end piece  3  is adapted to fit into the recess  23  of the female end piece or the recess  45  of the female/male connector piece. Thereby, the portion  32  of the male end piece  3  or the male portion  44  of the female/male connector piece  4  serves as a tongue portion  32 ,  44  and the recess  23  of the female end piece  3  or the recess  45  of the female/male connector piece  4  serves as a lug portion  23 ,  45 , respectively. When the male portion is inserted into the female portion, it forms a seat for the ball-shaped head  52  of the bone screw  5  that allows orientation of the bone screw  5  at an angle with respect to the straight position, as shown for example in  FIG. 1   a.    
         [0076]    As can be seen from  FIG. 1   b  and  FIG. 1   c  referring to the modular bone plate assembly  1 , three female/male connector pieces  4 , one female end piece  2 , and one male end piece  3  are connected to each other. The loose connection of these parts is locked by the bone anchoring elements  5 . The threaded shaft  51  of the bone anchoring element  5  extends through the hole  31  of the male end piece  3  or the hole  42  of the female/male connector piece  4  or through the hole  41  of the female/male connector piece  4  and the hole  42  of a further female/male connector piece  4  or through the hole  42  of the female/male connector piece  4  and the hole  21  of the female end piece  2 . The lower area of the screw head  52  thereby contacts the spherical portion  34  of the male end piece  3  or the spherical portion  47   a  of the male portion of the female/male connector piece  4 . By contacting the spherical portion  34  or  47   a  on the one hand and the inner portion of the hole  21 , i.e. the inner thread of the female end piece  2  or the inner surface  41 , i.e. the inner thread of the female portion of the female/male connector piece  4  on the other hand, both portions are centered by the bone anchoring element  5  or another locking element (see  FIG. 2   a, b ). 
         [0077]    A further possibility to lock the female parts and the male parts to each other is to provide a ball locking cap  7 , as can be seen from  FIG. 2   a  and  FIG. 2   b . The ball locking cap  7  comprises an upper threaded portion  71  and a lower rounded substantially spherical portion  72  which is adapted to cooperate with the spherical portions  34  of the male end piece  3  or the spherical portion  47   a  of the female/male connector piece  4 . The rounded portion  72  thereby substitutes the lower portion of the head  52  of the bone screw  5  and ensures the centering function as described above. The ball locking cap  7  further comprises an engagement portion  73  for being engaged by a tool to screw the ball locking cap  7  into the inner thread  22  of the female end piece of the inner thread  46  of the female/male connector piece or the inner thread  22  of the female end piece  2 . 
         [0078]    A second embodiment of the modular bone plate assembly will now be described with reference to  FIGS. 5   a  to  6 . As can be seen in particular in  FIG. 5   a  and  FIG. 5   b  the modular bone plate has an angled configuration. Referring to  FIG. 6  the tongue portion  44  of the female/male connector piece  4 ′ in the second embodiment is identical to the tongue portion  44  of the female/male connector piece  4  in the first embodiment. As can be seen in particular in  FIG. 6  the lug portion  45 ′ which is adapted to accommodate the tongue portion  44 ′ or the male end piece  3  comprises a circular portion  45   a ′ and two straight portions  45   b ′ that include an angle with respect to each other, which is about 40° in this embodiment. Other angles are also suitable here, for example 10°, 90° or 120°. In  FIG. 6  the angle between the straight portions  45   b ′ and a middle axis of the female/male connector piece  4 ′ are each 20°. But these two angles may also be different from each other to define a preferred orientation. 
         [0079]    By this configuration the female/male connector pieces  4 ′ which are connected to each other can be rotated relative to each other in a plane parallel to the surface of the modular bone plate to achieve an angled configuration. 
         [0080]    A third embodiment of the modular bone plate assembly will now be described with reference to  FIGS. 7   a  to  9   b . The modular bone plate  1 ″ is provided in a cascaded form. Referring to  FIGS. 7   a  to  7   d  the modular bone plate  1 ″ as a whole decreases in thickness from the left side of the Figures towards the right side of the Figures. Only the top surface  1   a ″ of the modular bone plate  1 ″ is lowered referring to  FIG. 7   a  in two steps by means of two inclined portions  431 ″ of the female/male connector pieces  4 ″, which can be seen in  FIG. 7   e.    
         [0081]    As can be seen from  FIGS. 8   a  and  8   b , the female/male connector piece  4 ″ according to the third embodiment differs from the first embodiment in that the middle portion  43 ″ comprises an inclined portion  431 ″ which is provided on the top side of the middle portion  43 ″ and in that the diameters of the two holes provided at the male and female connection portions of the female/male connector piece  4 ″ differ from each other. As in the first embodiment the female connection portion of the female/male connector piece  4  hereby comprises a through hole  41 ″ having an inner thread  46 ″ and a recess  45 ″ extending about the half of the circumference of the sidewall of the female connection portion of the female/male connector piece  4 ″. The recess  45 ″ is in communication with the hole  41 ″. The male connection portion of the female/male connector piece  4 ″ is formed by a lug portion  44 ″ having a through hole  42 ″ in its middle. The male and female connection portions of the female/male connector piece  4 ″ may be formed according to the corresponding portions according to the first embodiment. 
         [0082]    As can be seen from  FIGS. 9   a  and  9   b , the female/male connector pieces  4 ″ and  4 ′″ only differ from each other by the dimensions. The female/male connector piece  4 ″ is a 4.5 mm to 3.5 mm connector; the female/male connector piece  4 ′″ is a 3.5 mm to 2.5 mm connector, as can be seen in  FIGS. 9   a ,  9   b . These mm-values refer to the diameter of the holes. Therefore, this bone plate can be used with screws having different shaft diameters and/or head diameters. 
         [0083]    A fourth embodiment of the modular bone plate assembly will be described referring to  FIGS. 10   a  to  10   b . The modular bone plate  1 ′″ according to the fourth embodiment is also provided in a cascaded form. Opposite to the third embodiment referred to in  FIG. 10   a  the modular bone plate  1 ′″ decreases in thickness from the center of the bone plate towards either side by means of inclined portions  431 ′″ corresponding to the inclined portions  431 ″ according to the third embodiment. 
         [0084]    A fifth embodiment of the modular bone plate assembly is described with reference to the  FIGS. 11 to 14 . The plate is a humerus expandable plate  1 ″″. 
         [0085]    By the modular system, the length of the modular bone plate  1 ″″ can be chosen as desired. As can be seen in particular from  FIG. 12   a - e  the modular bone plate  1 ″″ comprises a main body having a plurality of holes for connecting the plate to a bone and none (a), one (b), two (c), three (d) or four (e) female/male connector pieces having a middle portion comprising a hole and one male end piece  3 ″″. With this system it is possible to combine one type of head with a plurality of connector pieces to provide a plate with a desired length. As can be seen from  FIG. 13 , the thickness of the main body or of the bone plate may vary or as can be seen from  FIG. 14 , the main body may be bent or angled. 
         [0086]    A sixth embodiment of the modular bone plate assembly will be described with reference to  FIGS. 15 to 19   b . The modular bone plate  1 ′″″ is a hard angle construct or fixed angle construct. The modular bone plate  1 ′″″ is a combination of the pieces shown in  FIG. 16   a - i  and  FIG. 17   a - i  is referring to the parts shown in  FIG. 16  and  FIG. 17 ,  FIG. 16   a  corresponds to  FIG. 17   i ,  FIG. 16   b  corresponds to  FIG. 17   h ,  FIG. 16   c  corresponds to  FIG. 17   g ,  FIG. 16   d  corresponds to  FIG. 17   f ,  FIG. 16   e  corresponds to  FIG. 17   e ,  FIG. 16   f  corresponds to  FIG. 17   d ,  FIG. 16   g  corresponds to  FIG. 17   c ,  FIG. 16   h  corresponds to  FIG. 17   b  and  FIG. 16   i  corresponds to  FIG. 17   a . The angled construction is achieved, as shown in  FIGS. 18 to 19  by providing the recess  45 ″″ in the female portion into which the male portion is inserted at an angle with respect to the longitudinal axis of the connector pieces. 
         [0087]    The angles 0° ( FIGS. 16   e ;  17   e ), 30° ( FIGS. 16   d, f;    17   d, f ), 45° ( FIGS. 16   c, g;    17   c, g ), 60° ( FIGS. 16   b, h;    17   b, h ) and 90° ( FIGS. 16   a, i;    17   a, i ) are shown. Other angles are also possible. By connecting these parts according to the above mentioned lug-tongue-principle a configuration shown in  FIG. 15  is achievable. The configuration is locked by bone screws or with ball locking caps as described above. In a further modification, the female portion may also have in addition the angled construction according to  FIGS. 5 to 6  that allow variations from the fixed angle. As can be seen from  FIGS. 18   a, b  and  19   a, b,  the angled configuration is achieved by providing the recess  45 ″″ of the female connection portion of the female/male connector piece  4 ″″ at the desired position at the circumference of the outer wall of the female connection portion.  FIGS. 19   a, b  show the 90° angle version as shown in  FIGS. 16   a, i  and  17   a, i.    
         [0088]    A seventh embodiment of the modular bone plate assembly is shown in  FIGS. 20 and 21 . The bone plate is a T-plate with a T-shaped head, applicable for example, to the wrist. The plate as a whole may be constructed in an angled or bent way. 
         [0089]    An eighth embodiment of the modular bone plate assembly is shown in  FIGS. 22 and 23 . The bone plate is a Y-plate with a Y-shaped head, applicable, for example, to the elbow. 
         [0090]    A ninth embodiment of the modular bone plate assembly will be described with reference to the  FIGS. 24 and 25 . The only difference referring to the other embodiments is the exchangeable head which can be seen in  FIG. 24   a - c  for example. In  FIG. 24   a  a straight head with six holes, in  FIG. 24   b  a straight head having four holes and in  FIG. 24   c  a head having four holes two of which are inclined are shown. 
         [0091]    A tenth embodiment of the modular bone plate assembly  10 ′″ is shown in  FIG. 26   a  to  FIG. 29 . 
         [0092]    As can be seen from  FIGS. 27 to 28   b  the connection between the male and female part is realised by a double latch connector. The female connecting piece  2 ′ according to a second embodiment comprises the recess  23 ′ and further a second recess  24 ′ which is positioned referring to  FIG. 27  above the recess  23 ′ in the conical portion of the female end piece  2 ′. The male portion of the female/male connector piece  4 ″″″ according to a seventh embodiment comprises a projection  432 ″″″ which is attached to the middle portion  43 ″″″. The projection  432 ″″″ which extends over the whole width of the middle portion  43 ″″″ is adapted to match with the second recess  48 ″″″ of another female/male connector piece  4 ″″″. This provides additional preliminary fixation when the bone screw or the locking cap is not yet inserted and may create a more stable construct once the screw and/or cap is locked. 
         [0093]    An eleventh embodiment of the modular bone plate  10 ″″ and the modular bone plate  100  will be described with reference to  FIGS. 30 to 31 . The difference referring to the above-mentioned embodiments is that the male portion comprises an internal thread  101 ″″ in the hole and the female portion of the female/male connector piece is threadless. The connection can be fixed with an ordinary screw  7 ′. The plate is also suitable for being used with ordinary bone screws without ball-shaped head. 
         [0094]    The connector piece may also be a longer piece with one or several additional holes and a female and a male portion at the ends. 
         [0095]    A twelfth embodiment of the modular bone plate  10 ′″″ will be described with reference to  FIGS. 32  a to  32   c . The difference to the tenth embodiment is that the projection  432 ′″″″ is attached at the middle portion  43 ′″″″ of a first member such that an upper face of the projection  432 ′″″″ is flush with an upper face of the middle portion  43 ′″″″. The second recess  48 ′″″″ is attached to a middle portion  43 ′″″″ of a second member such that it matches with the projection  432 ′″″″. This provides the same advantages as the tenth embodiment and facilitates manufacturing. Further, a second projection may be attached to the middle portion of the first member such that a lower face of the projection is flush with a lower face of the middle portion. The corresponding third recess is provided at the second member. 
         [0096]    The features of the embodiments can be combined among each other. 
         [0097]    The parts of the bone plate are made of biocompatible materials such as biocompatible metal or metal alloys such as titanium, stainless steel, Ni—Ti alloys, for example Nitinol, or biocompatible plastic materials, such as PEEK (polyetheretherketone). The parts may all be of the same material or of different materials.