Abstract:
A multi-axial bone fixation implant includes an elongated member, one or more bone anchor assemblies, and stabilizer members fitted within the elongated member. A bolt having a bone-threaded end and a machine-threaded end and an enlarged medial portion is also provided. The bolt is anchored into a bone, and its machine-threaded end passes through the elongated member and the stabilizer, and is engaged by a coupled washer and nut. The washer includes an oblong aperture, and the nut includes a projecting sleeve. The sleeve is inserted into the washer and expanded, and the washer retains the sleeve without impairing relative rotatability or translatability of the nut and washer. When locked by the nut and washer, the enlarged portion of the bolt is forced against the stabilizer, which locks against the elongated member. The elongated member can be fixed with respect to the anchor at an infinite number of multi-axial angles.

Description:
This application is a continuation of U.S. patent application Ser. No. 09/978,932, filed Oct. 16, 2001, now issued U.S. Pat. No. 6,689,133, which is a continuation of application Ser. No. 09/526,188, filed Mar. 15, 2000, now issued as U.S. Pat. No. 6,315,779; which claims benefit of provisional application No. 60/149,774, filed Aug. 19, 1999, and provisional application No. 60/129,587 filed Apr. 16, 1999. 

   FIELD OF THE INVENTION 
   The present invention relates to an orthopedic implant assembly for use in stabilizing bone members in a desired spatial relationship and correcting bone mis-alignment disorders. In particular, the invention concerns a multi-axial spinal fixation system incorporating an elongated member such as a plate. 
   BACKGROUND OF THE INVENTION 
   In the art of orthopedic surgery, and particularly in spinal surgery, it has long been known to affix an elongated member, such as a plate or rod, to bones in order to hold them and support them in a given position. For example, in a procedure to fuse damaged, diseased, malformed or otherwise abnormal vertebrae, the vertebrae are positioned in a corrected position by a surgeon. An elongated plate is placed adjacent to the vertebral bone, and bone anchors, such as specially-configured screws or bolts, are employed to secure the plate to the bones. With such anchors placement is accomplished by drilling one or more holes in the bone(s), and threading the anchors into the holes. As examples, see U.S. Pat. No. 5,676,666 to Oxland et al., U.S. Pat. No. 5,613,967 to Engelhardt et al., and U.S. Pat. No. 5,603,713 to Aust et al. An anchor can be connected to the bone, as by threading into a vertebral hole, through a plate, or alternatively the plate can be placed in position over or around the anchor after the anchor is connected to the bone. The anchor and plate are then secured to each other to minimize or prevent relative movement. In this way, bones may be spinal held and/or supported in proper alignment for healing. 
   It has been found desirable for implant systems to have the capability for angular orientation of a bolt or other anchor in multiple planes relative to the elongated member or other fixation mechanisms of the implant system. Such features enable bone anchors to be placed at angles which are optimal for anchoring, thus reducing the chance of loosening, pull-out or other movement of the anchors while not compromising the optimal positioning of the fixation plate. Additionally, such systems alleviate awkwardness frequently found in spinal surgery due to uneven bone surfaces and the abnormality to be corrected and generally require less adjustment to the implant, rendering corrective surgery easier for the surgeon and less traumatic for the patient. 
   Various approaches have been used to achieve such multi-axial capability. For example, U.S. Pat. No. 5,735,853 to Olerud discloses an implant device in which a bone bolt can occupy different angular positions in relation to a plate by providing a compressible spherical collar which snap-fits around the bolt, which collar is rotatable and tiltable in a spherical opening in a plate insert. The compression fit of the bolt and collar within the plate can present difficulty in assembling the apparatus, particularly in a fluid-prevalent environment. 
   Another approach is shown in U.S. Pat. No. 5,304,179 to Wagner, which shows a bone screw fixed inside a bushing at an angle with respect to the longitudinal axis of the bushing. The bushing is rotatable within a portion of a connector angled with respect to the axis of the adjoining rod-based instrumentation. The connector is rotatable around the instrumentation axis. The Wagner system permits only discrete positions of a bone screw in three-dimensional space to be achieved, and the bushings add extra length and profile to the construct, as well as extra parts for the surgeon to handle and arrange. 
   A third approach is shown in U.S. Pat. No. 5,984,924 to Asher et. al., which shows a bone alignment system having an elongated bone alignment member sandwiched between two pairs of washers. Each such pair of washers have corresponding surfaces that mate together in a “ball and socket” configuration to potentially occupy a plurality of positions. When the shaft of a bone anchor extends through each washer pair, and also through an aperture of the elongated member, the washer pairs enable the shaft to be oriented at various angles relative to the elongated member. This approach also requires a plurality of small parts for handling and assembly during surgery. Further, since the washers in that system lie outside of the elongated member, they increase the thickness of the overall construct, with the attendant increase in the difficulty of use in a small surgical space and in the potential for patient discomfort. 
   There is therefore a need remaining in the art for a multi-axial bone anchor system which minimizes the number of parts used to engage a bone anchor to an elongated member such as a spinal plate in various angular orientations. There is also a need for a lower-profile, smaller-dimensioned multi-axial bone anchor that allows the positioning of the bone anchor to be adjustable through a continuous range of spatial angles and linear positions with respect to the elongated member. 
   SUMMARY OF THE INVENTION 
   The present invention provides, in one embodiment, an orthopedic implant system including a plate member for placement adjacent and along one or more bones, such as vertebrae, and having a longitudinal axis. The plate member includes at least one slot substantially parallel to the plate axis, which slot includes a channel portion that extends through substantially the entire longitudinal dimension of the plate member. Also provided is a stabilizer including an opening therethrough substantially bounded by a wall, the opening having a longitudinal axis and the stabilizer further including at least one finger portion extending laterally with respect to the opening axis, wherein said finger portion is received within the plate channel so that the stabilizer opening communicates with the plate slot. A bone bolt having a bone engaging portion, an intermediate portion and a threaded post portion extends through the stabilizer opening and the plate slot so that the bolt&#39;s intermediate portion is adjacent the wall of the stabilizer. Additionally, a washer having a rounded top surface, a bottom surface, and an aperture therethrough adapted for fitting around a portion of the bolt, as well as a nut separate from the washer and having a body portion, a skirt portion, a threaded hole extending through the body portion for threaded engagement with the bolt are provided, and the nut and the washer are coupled together prior to engagement with the bolt. 
   The nut and the washer may be rotatable with respect to each other and translatable with respect to each other. The nut may include a sleeve portion partially within the nut&#39;s skirt portion and substantially concentric with the nut&#39;s hole. Additionally, the washer can include an undercut having a first diameter within the washer&#39;s aperture, and the nut and the washer are coupled together by inserting the sleeve portion into the aperture and expanding a part of the sleeve portion, which may be an end of the sleeve portion, to a second diameter greater than the diameter of the undercut. The expansion can be caused by swaging, flaring, or other processes. 
   Other features, advantages and objects will be evident from the following specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing illustrating an embodiment of the orthopedic implant of the present invention, implanted in vertebrae. 
       FIG. 2  is a perspective view of one embodiment of the system of the present invention. 
       FIG. 3  is a sectional view of the embodiment of the invention illustrated in  FIG. 2  taken along line  3 - 3  in  FIG. 2  and viewed in the direction of the arrows. 
       FIG. 4   a  is a top view of one embodiment of an orthopedic plate used in the present invention. 
       FIG. 4   b  is a side elevational view of the embodiment of the orthopedic plate illustrated in  FIG. 4   a.    
       FIG. 4   c  is a cross-sectional view of the embodiment of the orthopedic plate illustrated in  FIG. 4   a , taken along the line  4   c - 4   c  in  FIG. 4   a  and viewed in the direction of the arrows. 
       FIG. 4   d  is a top view of a second embodiment of an orthopedic plate used with the embodiment of the invention illustrated in  FIG. 1 . 
       FIG. 4   e  is a side elevational view of the second embodiment of the orthopedic plate illustrated in  FIG. 4   d.    
       FIG. 5   a  is a top view of one embodiment of a stabilizer used with the embodiment of the invention illustrated in  FIG. 2 . 
       FIG. 5   b  is a cross-sectional view of the embodiment of the orthopedic stabilizer illustrated in  FIG. 5   a , taken along the line  5   b - 5   b  in  FIG. 5   a  and viewed in the direction of the arrows. 
       FIG. 6  is a top view of the embodiment of the orthopedic plate illustrated in  FIG. 4   a , shown with embodiments of the stabilizer illustrated in  FIG. 5   a  fitted therein. 
       FIG. 7  is a side view of an embodiment of a bone bolt used with the embodiment of the invention illustrated in  FIG. 2 . 
       FIG. 8   a  is a top view of one embodiment of the washer used in the embodiment of the invention illustrated in  FIG. 1 . 
       FIG. 8   b  is a bottom view of the embodiment of the washer illustrated in  FIG. 8   a.    
       FIG. 8   c  is a cross-sectional view of the embodiment of the washer illustrated in  FIG. 8   a , taken along line  8   c - 8   c  in  FIG. 8   a  and viewed in the direction of the arrows. 
       FIG. 9   a  is a side elevation view of one embodiment of a nut used in the embodiment of the invention illustrated in  FIG. 2 . 
       FIG. 9   b  is a top view of the embodiment of the nut illustrated in  FIG. 9   a.    
       FIG. 9   c  is a cross-sectional view of the embodiment of the nut illustrated in  FIG. 9   a , taken along line  9   c - 9   c  in  FIG. 9   b  and viewed in the direction of the arrows. 
       FIG. 10   a  is a top view of one embodiment of the washer-nut combination used in the embodiment of the invention illustrated in  FIG. 2 . 
       FIG. 10   b  is a side elevational view of the embodiment of the washer-nut combination illustrated in  FIG. 10   a.    
       FIG. 10   c  is a bottom view of the embodiment of the washer-nut combination illustrated in  FIG. 10   a.    
       FIG. 10   d  is a cross-sectional view of the embodiment of the washer-nut combination illustrated in  FIG. 10   a , taken along line  10   d - 10   d  in  FIG. 10   b  and viewed in the direction of the arrows. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   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 are also included. 
   Referring generally to  FIGS. 2-3 , one embodiment of the orthopedic implant system  520  of the present invention is illustrated. In that embodiment, implant system  520  includes an elongated member such as a bone plate  522 , a pair of bone anchor assemblies  524  and a set of supports or stabilizers  526 . Differing numbers of any of these elements may be utilized without departing from the scope of this invention. For example, a plurality of elongated members  522  can be used in conjunction with each other, or a greater or lesser number of bone anchor assemblies  524  may be used, depending upon the configuration of the elongated member, the medical problem to be addressed, and/or any other factors. The present invention contemplates at least one elongated member  522 , one bone anchor assembly  524 , and one stabilizer  526  for each bone anchor assembly  524 . 
   Referring now generally to  FIGS. 4   a - 4   c , there is shown an embodiment of bone plate  522 . Plate  522  has a generally rounded-rectangular or oval shape, an upper surface  523  and a lower surface  523   a . Plate  522  further includes one or more elongated slots  530  therethrough from upper surface  523  to lower surface  523   a , which extend along a longitudinal axis of plate  522 . Slots  530  have a generally open geometry enabling bone anchor assemblies  524  to be placed at any of an infinite number of positions within slots  530 . In the illustrated embodiment, slots  530  within plate  522  have an upper portion  530   a  adjacent to upper surface  523 , a medial portion  530   b , a longitudinal channel  530   c , and a lower portion  530   d  adjacent to lower surface  523   a  of plate  522 . Slot portions  530   a - 530   d  generally have a non-uniform width (i.e. the horizontal dimension in  FIG. 4   c ). Plate  522  can also include one or more cross members  531  to separate medial portions  530   b  and create a multiple slot configuration, thereby providing added rigidity and dimensional stability to bone plate  522  without compromising the open geometry, but the upper portion  530   a , channel  530   c  and lower portion  530   d  are continuous through the longitudinal dimension of plate  522 . Upper portion  530   a  is further partially bounded by ledge  532 , and channel  530   c  is partially bounded by ledge  535   a  and ceiling surface  535   b . Bone plate  522  is of sufficient length to bridge one or more vertebrae  521  for which stabilization is required, as will be appreciated, and various dimensions of the plate and its features, as well as numbers of slots, are within the scope of the present invention. 
     FIGS. 4   c  and  4   d  illustrate an alternative embodiment of bone plate  622 , which is different from plate  522  only insofar as plate  622  and its internal features, including slot portions  530   a - 530   d , are bent or curved. The curved plate  622  offers surgeons added convenience in situation where the bone members  521  have to be retained in an arc, e.g. maintaining the normal lordotic or kyphotic curves of the spine. 
   Referring now generally to  FIGS. 7-10 , there is shown an embodiment of a bone anchor assembly  524  of the present invention, which can be used with elongated member  522 . Generally, bone anchor assembly  524  includes an anchoring member such as bone bolt  540 , an arcuate washer  542 , and a nut  544 . In the illustrated embodiment, washer  542  and nut  544  are affirmatively coupled so that they cannot be easily separated, yet they are rotatable and translatable with respect to each other. 
     FIGS. 7 and 7   a  show one embodiment of bone bolt  540 , in which bolt  540  includes a bone-engaging portion  546  with a cancellous thread  548 , a proximal portion or post  550  having a machine threaded section  552  and a tool engaging recess  553 , and an intermediate portion  554 . In one particular embodiment, thread  548  adjoins the intermediate portion  554  and root diameter  548   a  of thread  548  increases in continuous fashion as thread  548  approaches intermediate portion  554 , thus providing a substantially smooth junction with intermediate portion  554 . Intermediate portion  554  includes a rounded upper section  555  and one or more flattened areas  556 , the latter being provided for insertion or removal of bolt  540  with respect to a bone. In the illustrated embodiment, upper section  555  has a spherical configuration, and flattened areas  556  are uniformly spaced in a hexagonal arrangement around the circumference of the intermediate portion  554 . Tool-engaging recess  553  is provided for engagement with a tool to enable threading bolt  540  into a bone. Recess  553  may be of any suitable configuration, such as hexagonal or hexalobed, and in the illustrated embodiment, recess  553  is hexagonal. Bolt  540  further includes a cannula  558  through its entire length. Cannula  558  enables bolt  540  to be advanced to the surgical site over a guide wire (not shown), and further allows flow of blood or other bodily fluids through bolt  540 , which may provide speedier healing. 
     FIGS. 8   a  and  8   b  show an embodiment of arcuate washer  542  of the present invention. Washer  542  has a generally cylindrical body  560 , a rounded head  562 , a substantially flat undersurface  563 , and an aperture  566  disposed therethrough. Viewed from the top, aperture  566  is oblong or oval in shape and has a minor axis  564  and a major axis  565 . Aperture  566  is bounded by inner wall sections  568  and  570 . In the illustrated embodiment, wall section  568  is decreasingly tapered from head  562  toward undersurface  563 , and wall section  570  is substantially cylindrical. The diameter of aperture  566  at the lowest portion of wall section  568  is smaller than the diameter of inner wall  570 , with the result that the junction of wall sections  568  and  570  form a step or undercut  569 . Alternate configurations of wall sections  568  and  570  that form a similar undercut, are also possible. For example, inner walls  568  and  570  may be spherical or conical or a combination thereof. 
   Referring now generally to  FIGS. 9   a - 9   c , nut  544  includes tabs  576 , a skirt portion  577 , a body portion  578 , and an downwardly-projecting sleeve portion  579 . Nut  544  also includes an aperture  580  extending longitudinally through body portion  578  and sleeve portion  579 . Tabs  576  extend upward in an inward incline from body portion  578  and, in the illustrated embodiment, define a passageway  581  that communicates with aperture  580 . Body portion  578  includes a conventional outer torque application surface which is capable of being coupled to torque applying tools. In this embodiment, body portion  578  is configured as a hexhead, but any known configuration of the nut portion  578  that will allow application of torque to nut  544  can be used. Aperture  580  is substantially cylindrical with a female thread  582  formed therein. Thread  582  in aperture  580  is configured to threadably receive machine threaded section  552  of post  550 . Passageway  581  has a diameter substantially similar to the root diameter of machine-threaded section  552  of bolt  540 . 
   Skirt portion  577 , in the illustrated embodiment, is integral with and extends below body portion  578 , and is substantially conical in shape, with a substantially conical inner surface  584  extending around sleeve portion  579 . It will be appreciated that other geometric shapes could also be used for skirt portion  577  and or inner surface  584 . In the illustrated embodiment, sleeve portion  579  extends integrally from approximately the junction of skirt portion  577  and body portion  578  to beyond the lower edge of skirt portion  577 . Sleeve portion  579  is adapted to be received in aperture  566  of washer  542 , and thus has an outer diameter slightly smaller than minor axis  564  of aperture  566 . 
   In a specific embodiment of the present invention shown in  FIGS. 10   a - 10   d , arcuate washer  542  and nut  544  are coupled so that they are rotatable and translatable relative to each other, but are not easily disconnected or uncoupled. The coupling in this embodiment is accomplished by first inserting sleeve portion  579  of nut  544  into aperture  566  of arcuate washer  542  such that the inner surface  584  of skirt portion  577  is proximate to head  562  of arcuate washer  542 . A lower part of sleeve portion  579  is swaged or otherwise expanded to form a flared edge  579   a  around substantially the entire circumference of sleeve portion  579 . Sleeve portion  579  can be swaged or expanded by any conventional method. The resultant flared edge  579   a  has a diameter smaller than that of wall section  570  of washer  542 , but larger than that of the smallest portion of wall section  568 , so that flared edge  579   a  is retained within aperture  566  of washer  542  by undercut  569 . So coupled, arcuate washer  542  and nut  544  can fully rotate relative to each other, and they can further move translationally along the major axis  565  with respect to each other. 
   Coupling washer  542  and nut  544  in this manner reduces the number of components to be handled by the surgeon, thereby increasing ease of use. Additionally, the coupled washer-and-nut component is larger than either separate component, which further improves handling of the implant and lessens the likelihood of dropped, misthreaded, or otherwise misused parts. It will be appreciated that other ways of coupling washer  542  and nut  544  can be used, such as expanding a medial part of sleeve portion  579  rather than an end part, or by providing additional conventional structure for coupling two parts, such as spring-loaded latches or ball-detent structure, clamps or other similar holding structures. 
   Referring now generally to  FIGS. 5   a  and  5   b , implant system  520  includes one or more stabilizers or supports  526 . In the illustrated embodiment, stabilizer  526  has an elongated-octagon shape with a substantially flat upper surface  591 , laterally-extending finger portions  592  and a rounded lower surface  593 . Stabilizer  526  also includes an opening  594  therethrough from upper surface  591  to lower surface  593 . Opening  594  is bounded, in a particular embodiment, by a top wall section  595 , a medial wall section  596 , and a lower wall section  597 . In a specific embodiment, top wall section  595  is decreasingly tapered from upper surface  591  toward medial wall section  596 , which is substantially cylindrical. Lower wall section  597  is substantially conical so as to receive rounded upper section  555  of bolt  540  and permit multi-axial motion of bolt  540  with respect to stabilizer  526  and plate  522 , as further described below. 
   Other wall configurations are contemplated as being within the scope of the present invention. For example, wall sections  595 - 597  could form a single conical wall bounding bore  594 . Further, other configurations of stabilizer  526  are contemplated as within the scope of the present invention, including those disclosed in U.S. Provisional Applications Ser. Nos. 60/129,587 and 60/149,774, which applications are incorporated by reference herein. 
     FIG. 1  shows one embodiment of an orthopedic implant  520  of the present invention fixed to a series of vertebrae  521  for stabilizing or restraining vertebrae  521  in a desired positional relationship. In particular, each of the two bone anchor assemblies  524  is optimally aligned to the respective geometry of a bone  521 , which may cause assemblies  524  not to be parallel to each other or orthogonal to the bone plate or elongated member  522 . The washer  542  and nut  544  of the present invention enables each of the bone screws  540  to be secured to the bone plate  522  regardless of the angular offset from an axis that is substantially normal to a surface of the bone plate. The bone plate  622  as shown is curved in the longitudinal direction for better adaptation to the natural contour of the bone members  521 . In other applications, a curved plate may not be necessary. Since plates  522  and  622  are used in substantially the same way, for the sake of clarity the use of the present invention will be described with respect to plate  522 . 
   Referring now generally to  FIGS. 1 to 3 , one way of assembling and using the illustrated embodiment of implant  520  is as follows. Plate  522  is pre-prepared by placing one or more stabilizers  526  inside plate  522  and within channel  530   c , which preparation can occur during or after manufacture of plate  522  and stabilizers  526 , or shortly before beginning the implant procedure. Stabilizer  526  is fitted into channel  530   c  within plate  522  such that finger portions  592  of stabilizer  526  abut ledges  535  and are adjacent to ceiling surface  535   b . Referring to  FIGS. 6   a  to  6   d , one or more stabilizers  526  may be inserted into channel  530   c  via an open end of plate  522 . Stabilizers  526  can be placed at any longitudinal position along channel  530   c , so that bolt  540  can be fixed to plate  522  at any longitudinal position along plate  522 . 
   After the surgeon has drilled one or more holes into bone or bones  541 , bolt(s)  540  are threaded into the hole(s) via cancellous threads  548  of bone-engaging portion  546 , but not to cover flattened areas  556  of bolt  540 . Plate  522  with inserted stabilizer(s)  526 , is placed over bone bolts  540 , so that intermediate portions  554  are within bore  594  of a respective stabilizer  526 , and proximal portions  550  extend through the upper surface  523  of plate  522 . Plate  522  can then be adjusted both translationally (by moving bolts along slot  530  and associated stabilizer  526  along channel  530   c ) and multi-axially (by pivoting plate  522  and stabilizer  526  on upper surface  555  of intermediate portion  554 ) with respect to bolts  540 . The rounded upper surfaces  555  of intermediate portions  554  of bone bolts  540  are able to articulate within bore  594  and wall portions  597  and  598  of stabilizers  526 , and bone bolts  540  may thereby form any of a variety of angles with respect to plate  522 . It will be seen with reference to the embodiment of the invention illustrated in  FIG. 3  that lower surface  593  of stabilizer  526  does not approach flattened areas  556  or bone-engaging thread  548  of bolt  540 . 
   When the desired positioning of the vertebrae  541  and the plate  522  with respect to bolts  540  is achieved, a coupled washer  542  and nut  544  are threaded onto proximal portion  550  of each bone bolt  540 , so that proximal portion  550  extends through aperture  566  of washer  542  as well as threaded aperture  580  and passageway  581  of nut  544 . Since inner wall section  568  of washer  542  is tapered, washer  542  can occupy various angular positions relative to proximal portion  550  of bolt  540  as washer  542  and nut  544  are threaded thereon. As the coupled washer  542  and nut  544  approach plate  522  along proximal portion  550 , washer  542  is rotated if necessary with respect to bolt  540  and plate  522  to assume a position with respect to plate  522  such that oblong aperture  566  accommodates the angular off-set between post  550  and elongated member  522 . Such a position is achieved when the undersurface  563  of washer  542  rests substantially squarely on upper surface  523  of plate  522  when plate  522  is oriented as desired with respect to bolt  540 . 
   Further tightening of nut  544  causes skirt portion  577  to firmly engage and bear against a portion of head  562 , providing secure, tight contact between inner surface  584  of skirt portion  577  and head  562  of washer  542 . Such tightening of nut  544  on proximal portion  550  forces intermediate portion  554  of bolt  540  against wall portion  597  of stabilizer  526 , and upper surface  591  and finger portions  592  against ceiling surface  535   b  inside plate  522 , securely locking plate  522  to bolt  540 . 
   Tabs  576  of nut  544  may lodge under the machine thread on proximal portion  550  of bolt  540 , providing substantial resistance or interference fit against backward rotation or other movement of nut  544 . Any part of proximal portion  550  that remains above tabs  576  is broken or cut off or sheared away to minimize irritation to surrounding tissues. 
   In the above description, embodiments incorporating the washer-nut combination  541  are described. It should be understood that other embodiments incorporating separate arcuate washers  542  and nuts  544  are within the scope of the present invention, as for example the embodiments disclosed in U.S. Provisional Application Ser. Nos. 60/129,587 and 60/149,774, which applications are incorporated by reference into the present disclosure in their entirety. Further, it is contemplated that differing sizes of parts or of apertures within parts are within the scope of the present invention. 
   The parts of the implant system of the present invention may be made available in kits. Such kits may include, for example, a set of elongated members  522  and  622  of various lengths and having differing numbers or orientations of slots and/or bores. Sets of washers, bolts, screws and nuts and washer-nut combinations as disclosed herein can also be provided. Further, tools such as wrenches and screwdrivers compatible with the parts of the implant system of the present invention may also be included. It will be appreciated that the parts of the present invention should be constructed of biocompatible materials such as stainless steel, titanium, titanium alloys, certain plastics, or other known materials. 
   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.