Abstract:
A bone interface anchor for use with an elongated stabilization member, the anchor having: a receptor having a retaining device for receiving the elongated stabilization member; a compression assembly for securing the elongated stabilization member within the receptor; bone fixation screws which secure the anchors relative to bone segments of the human spine, 
     the receptor having a surface forming a mating cooperation with the screw such that the receptor can be variably positioned relative to the screw, a lock member to fix the screw relative to the receptor, and the retaining device having a retaining member between the elongated stabilization member and the interior of the receptor.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to a bone interface anchor for use with elongated stabilization members, and to an elongated stabilization member. 
       BACKGROUND 
       [0002]    In prior art EP-A-0 755 228 discloses a stabilization member and a bone interface anchor, wherein the stabilization member is a rod. The anchor has a retaining member which has a channel which is adapted to receive said rod and compression means for compressively securing the stabilization member in the retaining member with the compression means. With a downward compression force can be applied on the rod to bias it against a screw head. 
         [0003]    EP-A-0 934 027 describes a multi-axial bone crew assembly, which comprises a crown member for engagement with the bone crew. With a compression member a rod is pressed against said crown member and said crown member is pressed against the head of a bone screw. 
         [0004]    EP-A-1 240 875 discloses a spinal osteosynthesis member which has inside a U-shaped opening of the connector a ring cable of coming into contact with the head of a bone screw. A rod is inserted into the U-shaped opening and biased with a locking member against said ring to the head of a pedicle screw. 
         [0005]    Similar polyaxial fixing systems are known from WO 02/02024, WO 2005/016161 and WO 2006/083773. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention relates to a bone interface anchor for use with elongated stabilization members. The invention also relates to an elongated stabilization member useful in bone and especially spinal repair processes. The elongated stabilization member comprises a composite rod having a uniform cross-section essentially throughout its length and said rod having first and second segments each of which has a different modulus of elasticity. The stabilization member of the present invention has the advantage that it can approach the modular elasticity of bone without any danger of breakage. It further provides limited motion to the connected bones and can fulfill the biomechanical requirement which are needed to increase the muscle as well as the strength of the bones to which the muscles are connected. The rod can have variable stress characteristics throughout its length and a uniform cross-section essentially throughout its length. The uniform cross-section makes it possible to use the rod with almost any of the standard connectors. As the rod is made from composite it has the advantage of enhanced imaging throughout the length of the rod. The invention is especially useful for treatment of spinal bone cancer which requires radiation treatment in addition to stabilization, wherein it facilitates proper dosage of radiation adjoint to the implant. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0007]      FIG. 1  is an exploded perspective view of the components of the bone interface anchor and the elongated stabilization member according to one exemplary embodiment of the invention, 
           [0008]      FIG. 2  is a cross-sectional view of the anchor and stabilization member in the assembled state, 
           [0009]      FIG. 3  is a side view of the anchor according to an alternative embodiment of the invention, 
           [0010]      FIG. 4  is a partial cross-sectional view of the anchor as shown in  FIG. 3 , 
           [0011]      FIG. 5  is another partial cross-sectional view of the anchor as shown in  FIG. 3 , 
           [0012]      FIG. 6  is a cross-section of the anchor taken along line VI-VI shown in  FIG. 3 , 
           [0013]      FIG. 7  is a side view of the anchor according to an alternative embodiment of the invention, 
           [0014]      FIG. 8  is a partial cross-sectional view of the anchor as shown in  FIG. 7 , 
           [0015]      FIG. 9  is another partial cross-sectional view of the anchor as shown in  FIG. 7 , 
           [0016]      FIG. 10  is a cross-section of the anchor taken along line X-X shown in  FIG. 7 , 
           [0017]      FIG. 11-19  cross-sections of the elongated stabilization member, 
           [0018]      FIG. 20  is a perspective view of a transverse connector, 
           [0019]      FIG. 21  is a perspective view of a part of a transverse connector 
           [0020]      FIG. 22  is an exploded perspective view of the part shown in  FIG. 21 , 
           [0021]      FIG. 23  is a cross-sectional view of the part shown in  FIG. 23 , 
           [0022]      FIG. 24  is another exploded perspective view of the part shown in  FIG. 21 , 
           [0023]      FIG. 25  is a perspective view of a transverse connector having two longitudinal elements connected via an articulation, 
           [0024]      FIG. 26  is another perspective view of the transverse connector shown in  FIG. 25 , 
           [0025]      FIG. 27  is another perspective view of the transverse connector shown in  FIG. 25 , 
           [0026]      FIG. 28  is a perspective view of a part of the connector shown in  FIG. 25 , 
           [0027]      FIG. 29  is an exploded perspective view of the part shown in  FIG. 28 , 
           [0028]      FIG. 30  is a perspective view of another part of the connector shown in  FIG. 25 , 
           [0029]      FIG. 31  is a side view of the part shown in  FIG. 30 , 
           [0030]      FIG. 32  is another view of the part shown in  FIG. 30  and 
           [0031]      FIG. 33  is an exploded perspective view of the part shown in  FIG. 30 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0032]      FIGS. 1 and 2  show the components of the bone interface anchor  1  and a stabilization member, especially a rod R which, as shown in the drawings, is straight throughout its length, is clamped as shown in  FIG. 2 . The components of the anchor  1  include a compression member, especially a nut  10 , a receptor  18 , a crown member  12  and a bone screw  2 . The nut  10  is disposed within a bore  4  of the receptor  18  for engagement with the rod R and bias the rod R against a crown member  12  which engages a head  14  of the screw  2  at a concave surface  9  ( FIG. 1 ). The invention is disclosed with a bone screw, but other bone fixation members could be used instead. 
         [0033]    The receptor  18  has a threaded portion  7  configured to engage the nut  10  which has a corresponding outer thread  22 . The nut  10  also includes a tool recess  11  which can be a hex recess. 
         [0034]    The rod R is locked between the nut  10  and the crown member  12 . The upper side of the crown member  12  has a groove  5  which engages the rod R. This groove  5  increases the contact surface to the rod R and therefore the crown member  12  can be better propagate forces. The rod R is gripped tighter and with less deformation. The rod R as illustrated in  FIG. 1  has a round cross section. It is envisioned that the rod R can have other cross sections, wherein the groove is made correspondingly. 
         [0035]    The crown member  12  has a bottom surface  6  which is vex and especially spherical. This surface  6  engages the concave surface  9  of the screw head  14  which is preferably spherical as well. The surfaces  6  and  9  are glide and lock surfaces. Further glide and lock surfaces are a convex surface at the bottom of the screw head  14  and a concave surface  3  at the bottom of the bore  4 . Within the concave surface  3  there is an opening  15  for receiving the screw  2 . The screw  2  has a shank  29  with a recess  17 . The diameter of the shank  29  at the recess  17  is smaller than the diameter of the opening  15 . The opening  15  can be round or oval. 
         [0036]    When the nut  10  is not tightened, the receptor  18  is pivotable with respect to the longitudinal axis of the screw  2 . In order to fix the rod R, the surgeon tightens the nut  10 . The pressure between the nut  10 , the rod R, the crown member  12 , the screw head  14  and the bottom of the receptor  18  secures the assembly regardless of the angle between the screw  2  and the receptor  18 . 
         [0037]    The fixed rod R not only connects the vertebra to be fused, it is well exerts stable pressure upon the crown member  12 . In order to have enough friction between the surface  3  of the receptor  18 , the crown member  12  is made with a comparatively large mass. Furthermore, the crown member  12  has the shape of a saddle and engages the rod R with a comparatively large surface. The crown member  12  can therefore without much loss propagate the force to the screw head  14  and therefore effects a solid fixation regardless of the angle between the screw  2  and the receptor  18 . It has been shown that the anchor is especially suitable for a rod R made from a composite material, and especially a composite material with carbon fibers disposed therein. When the rod R is made from a composite material, there is almost no friction between the nut  10  and the rod R. Therefore, almost all of the pressure from the torque exerted on the nut  10  is upon the rod R and upon the threads of the anchor. When the rod R is made of titanium, there is considerably more friction between the nut  10  and the rod R and this friction absorbs part of the torque and part of the pressure, placing less stress on the threads and less pressure on the rod R. 
         [0038]    The rod R is especially suitable in combination with the anchor, when it contains fibers  30  and especially carbon fibers as illustrate in  FIGS. 11 to 19 . These fibers  30  not only affect stiffness between vertebrae, but at the same time the fibers  30  propagate the pressure from the nut  10  to the crown member  12 . The fibers  30  make the crown member  12  word biomechanically, because they transmit the force to the crown member  12 . The rod  10  is preferably anisotropic and has both the ability to exert a steady pressure and a control motion between fused vertebral bones. 
         [0039]    The  FIGS. 3 to 6  disclose an anchor  1 ′ which has a screw  2 ′, provided with a collar  23  disposed within a recess  21 . The collar  23  is provided with a comparatively large surface.  FIGS. 7 to 10  show an alternative anchor  1 ″ which has a thread  24  which is made corresponding to the thread  25  of the receptor  18 ″. 
         [0040]    The rods R as illustrated in  FIG. 11  has a first segment A, a second segment B and a third segment C which have different moduli of elasticity. The modulus of elasticity in the second segment B is lower than in the segments A and C. The rod R may have more than three segments or only two segments as illustrated in  FIG. 12 . 
         [0041]    The reinforcement of the rod R with fibers  30  helps to eliminate creep and spreads the load more evenly over a larger area. With the different moduli of elasticity it is possible to control motion between fused vertebral bones. The rod R can provide limited motion to the fused bones which helps to increase the muscle as well the strength of the bones to which the muscles are connected. 
         [0042]    The sections A and C as shown in  FIG. 11  contain plies  26 ,  27  and  28  made from fibers  30  and especially carbon fibers. The fibers  30  of the ply  26  and ply  28  are mainly parallel to the longitudinal direction of the rod R, whereas the fibers of the ply  27  are crossed and oblique to the longitudinal direction of the rod R. The plies  26  and  28  effect therefore a higher stiffness than the ply  27 . 
         [0043]    The plies  26 ,  27  and  28  can be arranged in a sandwich design as illustrated in  FIGS. 13 to 19 .  FIG. 13  shows a segment with plies  26  and  27  which are parallel to each other and which are disposed alternatively. The segment as shown in  FIG. 13  has therefore a stiffness which is between the high stiffness of segment A and the lower stiffness of segment B. 
         [0044]      FIG. 14  shows a segment made with plies  26  and has therefore a comparatively high stiffness, whereas the segment shown in  FIG. 15  is made with segments  27  and has therefore a comparatively low stiffness. 
         [0045]      FIGS. 16 to 19  show other possibilities to make segments with different moduli of elasticity. 
         [0046]      FIGS. 20 to 24  disclose a transverse connector  31  comprising a rod  32  made from a carbon composite material, two stiffener  33  and  34  and two connectors  35 . The rod  32  is clamped at its ends with nuts  37  which exert a pressure force on the stiffness  33  and  34  as well as on the rod  32 . The connectors  35  could be the tulip anchors as shown in  FIGS. 1 to 10  and the rod  32  could be a rod R as disclosed in  FIGS. 11 to 19 . 
         [0047]    The stiffeners  33  and  34  are made from a stable metal preferably of titanium. As shown in  FIG. 20 , the stiffeners  33  and  34  can be different, for example differently long. The transverse connector  31  can for example have a higher stiffness in the area of the stiffener  33  than in the area of the stiffener  34 , as the stiffener  33  is longer than the stiffener  34 . The stiffener  33 ′ as shown in  FIGS. 21 to 24  has a hole  39 , which lowers the stiffness compared with a stiffener without this hole. 
         [0048]    The rod  32  preferably contains carbon fibers  30  as shown in  FIGS. 11 to 19 . A part of these fibers have a direction which is oblique to the longitudinal direction of the rod  32 . These fibers have the effect that they prevent deformation of the rod  32  due to the pressure of the nut  10 . The cross-section of the rod  32  does therefore essentially not change when the rod is clamped with a comparatively high pressure. The cross-section even does not change later when the connector is implanted. The same feature relates to the rod R shown in  FIGS. 11 to 19 . 
         [0049]      FIGS. 25 to 33  show a transverse connector  40  comprising a first longitudinal element  41 , a second longitudinal element  3 , an articulation  43 , which connects the elements  41  and  42  and two clamps  47 . With the clamps  47  and the nuts  48  the transverse connector  40  is connected with stabilization rods as shown in  FIGS. 1 and 2 . The element  42  comprises an oblong hole  49  which allows to vary the angel between the two elements and the distance. Within a hole  51  a ring  50  is pivotably disposed which is made of a metal, for example titanium. The elements  41  and  42  are made of a carbon fiber composite material. The part  41  is as well made of a composite material and has at its ends a hole  54  and in another hole a pivotable ring  53 , made of a metal and especially titanium. The rings  50  and  53  are disposed at the ends where the nuts  48  and clamps are arranged. 
       LIST OF REFERENCE NUMBERS 
       [0050]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                  1 
                 bone interface anchor 
               
               
                  2 
                 screw 
               
               
                  3 
                 surface 
               
               
                  4 
                 bore 
               
               
                  5 
                 groove 
               
               
                  6 
                 surface 
               
               
                  7 
                 thread 
               
               
                  8 
                 surface 
               
               
                  9 
                 surface 
               
               
                 10 
                 compression means 
               
               
                 11 
                 tool recess 
               
               
                 12 
                 crown member 
               
               
                 13 
                 channel 
               
               
                 14 
                 screw head 
               
               
                 15 
                 opening 
               
               
                 16 
                 thread 
               
               
                 17 
                 recess 
               
               
                 18 
                 receptor 
               
               
                 19 
                 tool recess 
               
               
                 20 
                 opening 
               
               
                 21 
                 recess 
               
               
                 22 
                 thread 
               
               
                 23 
                 collar 
               
               
                 24 
                 thread 
               
               
                 25 
                 thread 
               
               
                 26 
                 ply 
               
               
                 27 
                 ply 
               
               
                 28 
                 ply 
               
               
                 29 
                 shank 
               
               
                 30 
                 fibers 
               
               
                 31 
                 transverse connector 
               
               
                 32 
                 longitudinal element (rod) 
               
               
                 33 
                 stiffener 
               
               
                 34 
                 stiffener 
               
               
                 35 
                 connector (anchor) 
               
               
                 36 
                 thread 
               
               
                 37 
                 nut 
               
               
                 38 
                 bore 
               
               
                 39 
                 hole 
               
               
                 40 
                 transverse connector 
               
               
                 41 
                 first longitudinal element 
               
               
                 42 
                 second longitudinal element 
               
               
                 43 
                 articulation 
               
               
                 44 
                 nut 
               
               
                 45 
                 disk 
               
               
                 46 
                 screw 
               
               
                 47 
                 clamp 
               
               
                 48 
                 nut 
               
               
                 49 
                 oblong hole 
               
               
                 50 
                 ring 
               
               
                 51 
                 hole 
               
               
                 52 
                 hole 
               
               
                 53 
                 ring 
               
               
                 54 
                 hole 
               
               
                 A 
                 segment 
               
               
                 B 
                 segment 
               
               
                 C 
                 segment 
               
               
                 R 
                 rod