Abstract:
A fixation element for use in orthopedic surgery, particularly spinal surgery is disclosed. The fixation element is capable of being screwed, hooked, or otherwise attached to a bone, and is configured to accommodate two or more rods or other elongated members. The head of the fixation elements thus has multiple places for positioning a rod, either vertically or horizontally spaced from each other.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    A variety of implants are known in the art for attaching an elongated member, e.g. an elongated bar or rod, to one or more bones for the purpose of correcting deformity, promoting healing, or other therapeutic uses. Among such devices are those disclosed in U.S. Pat. No. 5,005,562 to Cotrel, U.S. Pat. No. 5,797,911 to Sherman et al., and U.S. Pat. No. 6,280,442 to Barker et al. In those devices, a U-shaped head is provided for accommodating an orthopedic rod, such as that used in corrective spinal surgery. A threaded element or hook connects the U-shaped head to a bone portion, and a set screw locks the elongated rod within the U-shaped head.  
         SUMMARY OF THE INVENTION  
         [0002]    In one embodiment, an apparatus is disclosed which comprises a one-piece head portion having one or more channels, with the channels being configured so that a plurality of elongated members (e.g. spinal rods) may be connected to the head via one or more of the channels. At least one holder is connected to the head portion and holds at least one of the elongated members within their respective channels, and an attachment portion is provided connected to the head portion for connecting the head portion to a bone. There may be two substantially parallel channels in the head portion, with the head portion being substantially W-shaped. Such a pair of channels can have approximately the same width or radius, or one of the channels can have a width or radius larger than the other. A female thread can be formed in each of such channels, with set screws provided as the holders. The attachment portion may be integral with or may be movably connected with the head portion. If they are movably connected, the attachment portion may be rotatably or multi-axially connected with the head portion.  
           [0003]    Another embodiment of an apparatus according to the invention comprises a head portion having first and second outer legs and at least one post between the legs, a first channel between the first leg and the post, and a second channel between the second leg and the post. A first thread is formed on the first leg and the post, and a second thread is formed on the second leg and the post. First and second set screws are provided, with the first set screw adapted to be threaded in the first thread to close the first channel, and the second set screw adapted to be threaded in the second thread to close the second channel. A bone connection portion is connected to the head portion, whereby the apparatus is connected to a bone. The apparatus can further comprise a first elongated member, such as a spinal rod, such that at least a portion of the first elongated member occupies at least a portion of the first channel. The first set screw provides a clamping force to hold the elongated member with respect to the head portion. A second elongated member can also be provided such that at least a portion of the second elongated member occupies at least a portion of the second channel in the head portion, and the second set screw provides a clamping force to hold the second elongated member with respect to the head portion.  
           [0004]    A method is also disclosed, comprising providing a bone-engaging apparatus having an upper head portion and at least one lower attachment portion, with the head portion having a plurality of channels for receiving one or more elongated members; connecting the attachment portion of the apparatus to a bone; inserting an elongated member into one of the channels; and connecting a holder to said head portion to hold said elongated member in said channel. The holder connecting step can include threading a set screw into the channel into which the elongated member has been inserted until the set screw exerts a clamping force on said elongated member sufficient to lock it with respect to the head portion. The method may further include inserting a second elongated member into one of the channels. The channel into which the second elongated member is inserted can be previously occupied or unoccupied by an elongated member. An additional holder may be provided, if necessary, for the second elongated member. For example, a set screw may be threaded into the channel into which the second elongated member has been inserted until it exerts a clamping force on the second elongated member. The method may also include adjusting the bone prior to insertion of the first elongated member, and further adjustment of the bone prior to insertion of the second elongated member. The relative position of the attachment portion and the head portion may be adjusted prior to a time when the elongated member(s) are locked with respect to the apparatus.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a front elevational view of a first embodiment of a bone fixation element according to the invention.  
         [0006]    [0006]FIG. 2 is a side view of the embodiment shown in FIG. 1.  
         [0007]    [0007]FIG. 3 is a cross-sectional view taken along the lines  3 - 3  and viewed in the direction of the arrows of the embodiment shown in FIG. 1.  
         [0008]    [0008]FIG. 4 is a partial cross-sectional view of a further embodiment of a bone fixation element according to the invention.  
         [0009]    [0009]FIG. 5 is a partial cross-sectional view of another embodiment of a bone fixation element according to the invention.  
         [0010]    [0010]FIG. 6 is a partial cross-sectional view of yet another embodiment of a bone fixation element according to the invention.  
         [0011]    [0011]FIG. 7 is a partial cross-sectional view of another embodiment of a bone fixation element according to the invention.  
         [0012]    [0012]FIG. 8 is a partial cross-sectional view of a still further embodiment of a bone fixation element according to the invention.  
         [0013]    [0013]FIG. 9 is a partial cross-sectional view of another embodiment of a bone fixation element according to the invention.  
         [0014]    [0014]FIG. 10 is a side view of yet another embodiment of a bone fixation element according to the invention.  
         [0015]    [0015]FIG. 11 is a side view of another embodiment of a bone fixation element according to the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated, as would normally occur to one skilled in the art to which the invention relates.  
         [0017]    Referring now generally to FIG. 1, there is shown one embodiment of a fixation element  10  according to the present invention. In that embodiment, fixation element  10  includes a head portion  12  and an attachment portion  14 . Although fixation element  10  is depicted as a bone screw, with a threaded attachment portion  14 , one of ordinary skill in this art will appreciate that threaded attachment portion  14  could be replaced with a U-shaped or L-shaped hook element adapted to be fixed to a part of a bone, such as a pedicle or spinous process of a vertebra, or with another device allowing connection to a bone.  
         [0018]    In the embodiment shown in FIG. 1, head portion  12  is substantially in the shape of a W, having two outer legs or legs  16 ,  18 , and a post  20  between legs  16 ,  18 . Leg  16  and post  20  form a first channel  22 , and leg  18  and post  20  form a second channel  24 . Channels  22  and  24  are preferably substantially straight and substantially parallel, and have a lower surface  26 ,  28 , which may be curved or form a part of a cylinder. Channels  22  and  24  are sized and shaped to accommodate a rod or other elongated element R. In one particular embodiment, channels  22  and  24  are sized to accommodate rods of the same size, as for example where the radius of curvature of surfaces  26  and  28  are equal.  
         [0019]    Channels  22  and  24  are bounded by wall sections  32  and  34 , and  36  and  38 , respectively. Wall section  32  is an inner part of leg  16 , wall sections  34  and  36  form sides of post  20 , and wall section  38  is an inner part of leg  18 . Wall sections  32  and  34  include a female thread  40 , and wall sections  36  and  38  include a female thread  42 . Threads  40  and  42  are adapted to accommodate set screws, such as that denoted as  44  in FIG. 1, and threads  40 ,  42  and set screws  44  are holders that close channel  22  and hold or lock a rod or other elongated member therein. The size of the set screw needed to close channel  22  will, of course, depend on the characteristics of thread  40 , just as thread  42  will determine the size of the set screw for channel  24 . If an alternative holder is desired (such as a cam lock, a sliding member, a cap or nut with threads or a bayonet-lock), threads  40  and/or  42  may be altered, removed, or replaced with other features (e.g. grooves, external threads or the like) that permit connection to such holders.  
         [0020]    Further, in the above-described embodiment it is preferred that there be a set screw  44  and compatible threads (e.g. threads  40 ,  42 ) for each channel, i.e. a first set screw  44  for channel  22  and a second set screw  44  for channel  24 . It would be possible to use one or more holders of another type, e.g. caps or nuts, to contain or lock multiple rods or other elongated members within their specific channels. For example, a cap or nut that surrounded and connected to legs  16  and  18  of head portion  12  would close both channels  22  and  24  and keep elongated member(s) therein. In that case, there would be one holder to hold one or more elongated members within their respective channels, whereas with set screws several holders (i.e. set screws) may be needed to hold several elongated members within their respective channels. It will also be observed that not all holders elements need be the same, but that screws, nuts, caps, sliders or cams can be combined for use with a given head portion.  
         [0021]    In the embodiment of fixation member  10  in which channels  22  and  24  accommodate rods of the same size, the widths of the channels (i.e. the respective distances between walls  32  and  34  and between walls  36  and  38 ) will be approximately equal, and may accommodate identical set screws. On the outsides of legs  16  and  18  are found indentations  46  and  48 , respectively. Indentations  46  and  48  are adapted to accommodate a holding or twisting tool, such as a screwdriver. In one embodiment, indentations  46  and  48  are substantially circular, and may have a slightly tapered opening, so that a projection on a gripping or screwing tool that has a circular or other shape can easily be inserted into indentations  46  and  48 .  
         [0022]    In the embodiment of FIG. 1, attachment portion  14  may be formed integrally with head portion  12 , or may be made separately from head portion  12  and fixedly attached to head portion  12  after manufacture. Attachment portion  14  is a threaded member in the illustrated embodiment, having threads  50  adapted for insertion into a bone. Attachment portion  14  is illustrated as having a flattened end  52 , but it will be understood that end  52  may also be pointed and/or self-tapping. Fixation element  10  may also be cannulated, i.e. having an aperture  54  extending from end  52  of attachment portion  14  to the top of post  20  of head portion  12 . The embodiment of FIG. 1 also shows attachment portion  14  along a medial axis (i.e. equidistant from the outside edges of legs  16  and  18 ) of head portion  12 . As shown and described below with respect to other embodiments, attachment portion  14  may be placed to one side of a medial axis, for example directly beneath one of channels  22  and  24 .  
         [0023]    In use, access to an orthopedic surgical site is obtained in a known manner. A drill or similar device is used to make a hole in a bone. For convenience, use of fixation element  10  will be described with respect to spinal surgery, although it is understood that the present invention may be used with other bony tissue or another surgical site. After a hole is drilled in a vertebra, attachment portion  14  of fixation element  10  is inserted, and fixation element  10  is rotated so that fixation element  10  is screwed into the hole. The surgeon continues turning fixation element  10  until it is in a desired position, e.g. head portion  12  is at a desired height from the surface of the vertebra, and channels  22  and  24  are oriented as the surgeon desires for a rod. When used in spinal surgery, commonly fixation element  10  will be threaded into the bone until most or all of thread  50  is within the bone, and channels  22  and  24  are oriented substantially along the spinal column or along a desired orientation of one or more spinal segments.  
         [0024]    One or more rods or other elongated members can then be connected to fixation element  10 . As shown in FIG. 1, rod R is placed in channel  22 , and set screw  44  is screwed into internal thread  40  to close channel  22  and hold or lock rod R therein. Of course, rod R may also be placed in channel  24 , in substantially the same manner as described above. If two rods are used, one rod may be placed in each of channels  22  and  24  and held or locked therein with set screws, as described above.  
         [0025]    In a minimally-invasive procedure, access to the surgical site is available through one or more small openings through the skin and/or other soft tissues. Instruments suited to minimally-invasive procedures are inserted through such an opening and moved to the surgical site, where the steps described above are performed. Although this invention can be used in a variety of surgical techniques, it has been found to have significant application in minimally-invasive spinal surgery. In such procedures, it can be difficult to use screws or hooks that accommodate only a single rod or other elongated member, because of the rigidity of the corrective rod that must be implanted and because of the relative lack of mechanical advantage to adjust the spine when it is not exposed. Using the present invention, a surgeon can insert a screw or hook minimally-invasively, perform a degree of adjustment to the spine and connect a first rod that may be somewhat less rigid than is normally used in corrective spinal surgery (e.g. scoliosis-correcting surgery). The first rod holds the affected spinal segment(s) sufficiently while another, more-rigid rod is prepared and the spine adjusted to its final, corrected position. The second rod is then inserted and locked into the screws or hooks, and the surgery is completed. In some cases, it is contemplated that use of yet additional rods or other elongated members or additional spine-adjustment steps may be indicated or necessary, and thus screws or hooks that accommodate three or more rods come within the spirit of the invention.  
         [0026]    Several other embodiments are described below. For convenience, features or aspects that are identical or similar in two or more embodiments disclosed herein are denoted in the description and drawings by numbers sharing their last two digits.  
         [0027]    An alternative embodiment of a fixation member  110  is depicted in FIG. 4. Fixation element  110  is substantially the same as fixation member  10  with the exception that fixation member  110  has one channel (e.g. channel  124 ) that will accommodate a rod larger than the other (e.g. channel  122 ) will accommodate. Lower surface  126  of channel  122  has a smaller radius than bottom surface  128  of channel  124 , and the distance between walls  132  and  134  of channel  122  is smaller than the distance between walls  136  and  138  of channel  124 . A smaller set screw or other holding or locking element may be used in channel  122  compared to that used in channel  124 . In other respects, fixation element  110  is essentially the same as fixation element  10 .  
         [0028]    Fixation element  110  may be used where it is preferred to have two rods of different diameters in a particular orthopedic construct. In the spinal surgical field, for example, it is common to reposition (distract, compress, rotate, or otherwise adjust relative location) vertebrae prior to or during implantation of a supporting or corrective apparatus. Connecting a smaller, less-rigid rod to fixation element  110  as described above will allow some holding or support of a spine that has been adjusted, while still allowing the surgeon to readjust the spine and/or contour a larger, more-rigid rod for providing the main support or correction to the spine.  
         [0029]    Fixation element  110  may be placed in a vertebra as described above with respect to fixation element  10 . A first rod R 1  of relatively smaller diameter may be placed in channel  122 , and held with a set screw  144 . The surgeon can then perform additional or new repositioning procedures if he or she chooses, and may bend the locked rod in the process. While the relatively smaller rod R 1  is holding the vertebra as desired, the surgeon can contour a larger rod R 2  or perform other surgical procedures while the spine is held by the relatively smaller rod. The relatively larger rod R 2 , once prepared as the surgeon desires, can then be inserted into channel  124  of fixation element  110 , and locked with another set screw  144   a.    
         [0030]    It will be noted that in the illustrated embodiments of fixation elements  10  and  110 , the attachment portion  14 ,  114  is substantially centered between legs  16  and  18 . The present invention includes embodiments in which attachment portion  14  may be nearer to one leg or another, or it may be directly beneath one of channels  22  or  24 , or have some other non-symmetrical configuration.  
         [0031]    Turning now to FIG. 5, there is shown a fixation element  210 . Fixation element  210  is similar to fixation element  10 , except head portion  212  and attachment portion  214  are not initially integral with or fixed to each other. Rather, attachment portion  214  is separate from head portion  212 , and is rotatable with respect to head portion  212 . Like fixation element  10 , fixation element  210  includes head portion  212  having two channels  222  and  224 . The channels have wall sections  232 ,  234 ,  236  and  238  that are threaded with threads  240 ,  242 . One of the channels, e.g. channel  222 , communicates with a hole H that extends from the top to the bottom of head portion  212 . Toward the bottom end of head portion  212 , a groove  258  is set, essentially surrounding hole H.  
         [0032]    Attachment portion  214  in this embodiment is a bone screw having bone threads  250  and a head  260 , although it will be understood that hook could be provided on attachment portion  214  instead. Head  260  is substantially cylindrical, with a flange  262  at the top of head  260 , and an internal print  264  within head  260  to enable attachment portion  214  to be screwed into a bone.  
         [0033]    Fixation element  210  is assembled by inserting head  260  of attachment portion  214  into hole H of head portion  212  through the bottom end of head portion  212 . A C-shaped snap ring  266  is provided to retain attachment portion  214  within head portion  212 . Snap ring  266  has an inner diameter larger than the diameter of head  260 , but smaller than the diameter of flange  262  of head  260 . The outer diameter of snap ring  266 , in its non-stressed state, is slightly larger than the diameter of groove  258  in head portion  212 . Thus, attachment portion  214  is rotatable with respect to head portion  212 , but not necessarily multi-axially moveable with respect to head portion  212 .  
         [0034]    To use fixation element  210 , a hole in a bone (e.g. a vertebra) is prepared as described above. The assembled fixation element  210  is then coupled to the bone, by inserting the attachment portion  214  into the hole and screwing it into the bone. Attachment portion  214  may be screwed in to a point where the bottom of head portion  212  contacts bone and flange  262  presses against snap-ring  266 , effectively holding attachment portion  214  with respect to head portion  212 . Alternatively, attachment portion  214  can be screwed in to a lesser degree, with rotation of head portion  212  with respect to attachment portion  214  being inhibited or prevented by insertion of one or more rods into one or both channels  222 ,  224 . Once such rod(s) are inserted into one or both of channels  222  and  224  they are locked therein, as described above with respect to fixation element  10 .  
         [0035]    Referring now to FIG. 6, there is shown an embodiment of a fixation element  310 . Fixation element  310  is very similar to fixation element  210 , except that attachment portion  314  is configured so that its connection with head portion  312  is a multi-axial connection. A preferred configuration for the connection between head portion  312  and attachment portion  314  is disclosed in U.S. Pat. No. 6,280,445 to Barker et al., the entirety of which is incorporated by reference. Accordingly, attachment portion  314  includes a rounded head  360  that sits within hole H of head portion  312 , and is retained therein by a C-shaped snap ring  366  seated in groove  358 . A crown member  370  sets atop the head  360  of attachment portion  314 .  
         [0036]    Fixation element  310  is connected to a bone in essentially the same fashion as fixation element  210  described above. After attachment portion  314  is screwed into the bone, head portion  312  may be adjusted multi-axially with respect to attachment portion  314 . A rod is introduced into channel  322 , and any further multi-axial adjustments of head portion  312  with respect to attachment portion  314  can be made. A set screw  344  is threaded into threads  340  communicating with channel  322 . Locking down set screw  344  presses the rod down on crown member  370 , which locks head  360  of attachment portion  314  between crown member  370  and snap ring  362 . In a particular embodiment, head  360  may have ridges  372  that are somewhat harder than the material of crown member  370 , so that crown member  370  and head  360  are locked together by ridges  372  biting into crown member  370 .  
         [0037]    Referring now to FIG. 7, a further embodiment of a fixation element  410  is disclosed. Fixation element  410  includes a head portion  412  and an attachment portion  414 . In fixation element  410 , head portion  412  and attachment portion  414  may be integral or initially fixed with each other (as in fixation member  10 ), rotatable with respect to each other (as in fixation member  210 ), or multi-axially connected (as in fixation member  310 ). Head portion  412  includes an underside  456  having an approximately anatomically-shaped curvature. In a specific embodiment, the curvature has a concave aspect that approximates the curvature of a side of a vertebra. In another embodiment, the curvature may have a concave aspect in a first cross-section and a convex aspect in a second cross-section, e.g. one perpendicular to the first cross-section. Extending from surface  456  is a prong or spike  474 . Spike  474  is intended to be inserted into the bone tissue when fixation element  410  is attached to a bone, to provide yet further stability to the implant construct. In other respects, fixation element  410  can have any of the features or attributes of fixation elements  10 ,  110 ,  210 , and/or  310 .  
         [0038]    Referring now to FIG. 8, fixation element  510  in yet another embodiment is disclosed. Fixation element  510  may include attributes or features from any of fixation elements  10 ,  110 ,  210 , and/or  310 , wherein an attachment portion  514  is not centered with respect to head portion  512 , or is beneath one channel (e.g. channel  522 ) of head portion  512 . In addition, fixation element  510  includes a second attachment portion  514   a  connected to head portion  512 . In a specific embodiment, head portion  512  can include a hole H′ communicating with channel  524  and extending from bottom surface  556  through head portion  512 . Attachment portion  514   a  can be similar to attachment portion  214  or  314 , in which case the features of fixation elements  210  and/or  310  providing for connection between the respective attachment portions and head portions would be included in fixation element  510 . Alternatively, attachment portion  514   a  may be a standard bone screw with a curvate head  562  and an internal print  564 , that could rest against the lower edge of the hole H′. In that case, an additional hole  580  may be provided that communicates with hole H′, and is threaded to accommodate a set screw (not shown) therein, which can lock attachment portion  514   a  within hole H′ in a desired orientation.  
         [0039]    Fixation element  510  is attached to a bone in substantially the same fashion as described above, except an additional hole must be drilled in a bone to accommodate attachment portion  514   a . As one example, attachment portion  514  can be threaded into the bone, and attachment portion  514   a  can then be threaded into the second hole in the bone and used to make adjustments in the positioning of fixation element  510  with respect to the bone. One or more rods may be inserted in channels  522  and  524 , and fixation element  510  locked with respect to the rods by threading set screws down on them, as described above.  
         [0040]    Referring now to FIG. 9, there is shown an embodiment  610  of a fixation element. Fixation element  610  has a U-shaped head portion  612  with a single channel  622  therethrough, and is connected to an attachment portion  614  which in a specific embodiment is a threaded screw portion. Walls  632  and  634  of channel  622  include threads  640  for accommodating a set screw  644 . Walls  632  and  634  are of a height that enables insertion of two separate rods within channel  622  of head portion  612 . Thus, for a fixation element  610  intended to accommodate two rods of 5.5 mm diameter, the height of walls  632  and  634  would be at least 11 mm plus the height of set screw(s)  644 . With reference to FIG. 9, rod R 1  is placed within channel  622 , followed by a set screw  644 , screwed into thread  640 . A second rod R 2  would be placed atop set screw  644 , and a second set screw  644  would be threaded into threads  640  to lock the second rod R 2  with respect to head portion  612 .  
         [0041]    The diameters of rods R 1  and R 2  could be equal or they may be different to provide adjustability and stability prior to final locking down as described above. It will also be noted that a configuration of head portion  612  to accommodate two rods may be combined with a multi-axial head portion/attachment portion connection (such as those shown in U.S. Pat. No. 5,797,911 to Sherman et al. and U.S. Pat. No. 6,280,445 to Barker et al., the entireties of which are incorporated herein by reference), or could be rotational with respect to each other as shown above with respect to fixation member  210 . Further, although channel  622  is shown as extending from a back or proximal surface of head portion  612  toward attachment portion  614 , it will be understood that channel  622  could extend laterally, i.e. from a side surface of head portion  612  toward an opposite side surface. Two rods or other elongated members could then be inserted into channel  622  from the side and fixed with respect to head portion  612  substantially as described above, or as described further below with respect to FIGS. 10 and 11.  
         [0042]    Yet a further embodiment is shown in FIG. 10. A fixation element  710  is provided with a head portion  712  and an attachment portion  714 . In this embodiment, head portion  712  has channels  722  and  724 . Channel  722 , like channel  22  in FIG. 1, is substantially straight, extends through head portion  712 , and is open to the back (i.e. the portion opposite attachment portion  714 ) of head portion  712 . Channel  724  is also substantially straight and extends through head portion  712 , but channel  724  opens to the side of head portion  712 . Thus, head portion  712  has one channel that is “back-loading” for one elongated member (e.g. rod R 1  in FIG. 4 or  9 ) and “side-loading” for another elongated member (e.g. rod R 2  in FIG. 4 or  9 ).  
         [0043]    Head portion  712  may also include a hole  782  from the back of head portion  712  to channel  724 . Hole  782  may be internally threaded and accommodate a set screw  784 , which is used to lock a rod within channel  724 . In one embodiment, set screw  784  has a threaded portion  786 , and may also have a conically-shaped or tapered end portion  788 . It will be understood that any of several types of holder or locking member, including a set screw  744  (threaded into hole  782  or into channel  724  from the side of head portion  712 ) or other holder(s) described above, can be used. Channel  722  is configured to accommodate a holder such as set screw  744  or other holder(s) described above.  
         [0044]    Head portion  712  is shown in this embodiment to be fixed with respect to attachment portion  714 , with attachment portion  714  substantially in the middle of head portion  712 . Of course, attachment portion  714  may be rotatably or multi-axially connected to head portion  712 , or located toward one side of head portion  712 , or multiple attachment portions  714  may be provided, as described in detail above.  
         [0045]    Another embodiment of a fixation element  810  is shown in FIG. 11. Fixation element  810  is much like fixation element  710 , with the exception that both channels  822  and  824  are open to the sides of head portion  812  of fixation element  810 . In one particular embodiment, holes  882   a  and  882   b  are provided to communicated with channels  822  and  824 . Holes  882   a  and  882   b  may be internally threaded (as described above) to accommodate set screws such as  884   a  and  884   b , or may be configured to accommodate alternative holders, as described above. As with fixation element  710 , attachment portion  814  of fixation element  810  may be rotatably or multi-axially connected to head portion  812 , or located toward one side of head portion  812 , or multiple attachment portions  814  may be provided, as described in detail above.  
         [0046]    The implants described above are preferably made from a biocompatible material such as stainless steel, titanium, plastics or other sturdy biocompatible and/or resorbable materials. The elongated members may be flexible or rigid rods, cables or similar items. It is envisioned that well-known open and minimally-invasive surgical procedures may be used to implant embodiments of the present invention.  
         [0047]    The size of the implants described above may be identical or similar to implants currently used in spinal and other orthopedic surgeries. It has been found that the implants described above may have particular application to smaller vertebrae or other bones (e.g. those in children or other small persons, or adult cervical vertebrae), since one implant attaching to a bone can accommodate two rods or other elongated members. Accordingly, these implants may be made in standard and smaller sizes for such uses.  
         [0048]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. For example, while the embodiments described above have two channels (e.g. channels  22  and  24 ) for accommodating longitudinal supports, the present invention contemplates fixation elements with head portions having a larger number of channels or that can accommodate more than two rods or other support members. Further, it will be seen that aspects of one embodiment described above can be incorporated into another of the embodiments. For example, the “stacked rod” feature of fixation element  610  could be included with fixation element  10 . In that case, one of the channels of fixation element  10  would be of a height sufficient to place one rod atop another in that channel, as described with respect to fixation element  610 . Still further, it will be seen that the channel or channels may be differently oriented, as for example opening to the side of the head portion.