Abstract:
A surgical system comprising:
       an object to be secured to bone, the object comprising an opening extending therethrough; and   a sleeve/expander construction for securing the object to bone, the sleeve/expander construction comprising:
           a sleeve adapted for positioning through the opening in the object and into the bone, the sleeve comprising:
               a shank having a distal end and a proximal end and an opening extending from the distal end to the proximal end, wherein the opening narrows toward the distal end of the shank, and further wherein the distal end of the shank is slit so as to form a plurality of radially-expandable segments; and   an enlarged head formed at the proximal end of the shank, the enlarged head being formed so as to be radially-expandable; and   
               an expander adapted for positioning through the opening in the sleeve, the expander being sized so as to (i) radially expand the distal end of the sleeve so that the sleeve is secured to the bone, and (ii) radially expand the enlarged head of the sleeve so that the sleeve is secured to the object, whereby to secure the object to the bone.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS 
     This patent application: 
     (1) is a continuation-in-part of pending prior U.S. patent application Ser. No. 10/554,379, filed Oct. 25, 2005 by Barry T. Bickley et al. for FIXATION AUGMENTATION DEVICE AND RELATED TECHNIQUES, which in turn claims benefit of:
         (a) International (PCT) Patent Application No. PCT/US04/14640, filed May 10, 2004 for FIXATION AUGMENTATION DEVICE AND RELATED TECHNIQUES, which itself claims benefit of U.S. Provisional Patent Application Ser. No. 60/468,829, filed May 8, 2003 for FIXATION AUGMENTATION DEVICE; and   (b) U.S. Non-Provisional patent application Ser. No. 10/246,304, filed Sep. 18, 2002 for FIXATION AUGMENTATION DEVICE AND RELATED TECHNIQUES; and       

     (2) claims benefit of prior U.S. Provisional Patent Application Ser. No. 60/925,729, filed Apr. 23, 2007 by Barry T. Bickley et al. for METHOD AND APPARATUS FOR ATTACHING AN OBJECT TO BONE. 
     The five above-identified patent applications are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to surgical methods and apparatus in general, and more particularly to surgical methods and apparatus for securing an object to bone. 
     BACKGROUND OF THE INVENTION 
     In many situations an object may need to be secured to bone. By way of example but not limitation, where a bone is fractured, it may be desirable to stabilize the bone with a bone plate which extends across the fracture line. By way of further example but not limitation, where two separate bones need to be secured together (e.g., in the case of a spinal fusion), it may be desirable to secure the two bones to one another with a bone plate which extends from one bone to the other. By way of still further example but not limitation, where soft tissue needs to be attached (or re-attached) to bone (e.g., in the case of a ligament repair or reconstruction), it may be desirable to capture the soft tissue to the bone using a fixation plate. 
     In all of the foregoing situations, as well as many others which are well known to those skilled in the art, a plate or other object needs to be secured to bone. Such attachment is most commonly effected by using a surgical screw which passes through a hole in the plate (or other object) and into the bone. 
     When using a surgical screw to secure a plate to bone, the plate is first aligned with the bone. Then a hole is drilled into the bone, by passing a drill through a pre-existing hole in the plate and into the bone. Next, the bone hole may be tapped. Then the surgical screw is passed through the hole in the plate and into the hole in the bone, whereby to secure the plate to the bone. 
     One problem which can arise during the foregoing procedure is that the hole in the bone may become stripped as the screw is inserted into the bone. When this occurs, the screw can no longer obtain adequate purchase in the bone, thereby undermining plate fixation. A screw having inadequate purchase is sometimes referred to as a “spinner”. Spinners can occur for many reasons, including (i) inadequate bone quality, (ii) over-tightening of the screw, (iii) an error when drilling the hole in the bone, (iv) an error when tapping the hole in the bone, etc. As noted above, spinners generally result in inadequate fixation. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to address the foregoing deficiencies of the prior art, by providing a new and improved method and apparatus for securing an object to bone. 
     More particularly, the present invention provides a new and improved fixation system for securing an object to bone. 
     In one preferred form of the present invention, the new fixation system comprises a plate which is to be secured to bone, and a sleeve and a screw for securing the plate to the bone. The plate comprises an opening which extends through the plate. The plate is placed against the bone and then a drill is used to form a hole in the bone beneath the opening. A sleeve is passed through the opening and into the hole in the bone. The sleeve and plate are formed so that the sleeve (and the recipient bone hole) can be disposed at any one of a variety of angles relative to the plate. A screw is then passed through the sleeve, radially expanding the sleeve so that the sleeve is simultaneously secured to both the bone and the plate. 
     In one preferred form of the invention, there is provided a surgical system comprising: 
     an object to be secured to bone, the object comprising an opening extending therethrough; and 
     a sleeve/screw construction for securing the object to bone, the sleeve/screw construction comprising:
         a sleeve adapted for positioning through the opening in the object and into the bone, the sleeve comprising:
           a shank having a distal end and a proximal end and an opening extending from the distal end to the proximal end, wherein the opening narrows toward the distal end of the shank, and further wherein the distal end of the shank is slit so as to form a plurality of radially-expandable segments; and   an enlarged head formed at the proximal end of the shank, the enlarged head being formed so as to be radially-expandable;   the sleeve being sized so that when the sleeve is positioned through the opening in the object and into the bone, at least a portion of the radially-expandable segments extend into the bone beyond the cortical bone/cancellous bone interface; and   
           a screw adapted for positioning through the opening in the sleeve, the screw being sized so as to (i) radially expand the distal end of the sleeve so that the sleeve is secured to the bone, and (ii) radially expand the enlarged head of the sleeve so that the sleeve is secured to the object, whereby to secure the object to the bone.       

     In another preferred form of the invention, there is provided a surgical system comprising: 
     an object to be secured to bone, the object comprising an opening extending therethrough; and 
     a sleeve/expander construction for securing the object to bone, the sleeve/expander construction comprising:
         a sleeve adapted for positioning through the opening in the object and into the bone, the sleeve comprising:
           a shank having a distal end and a proximal end and an opening extending from the distal end to the proximal end, wherein the opening narrows toward the distal end of the shank, and further wherein the distal end of the shank is slit so as to form a plurality of radially-expandable segments; and   an enlarged head formed at the proximal end of the shank, the enlarged head being formed so as to be radially-expandable; and   
           an expander adapted for positioning through the opening in the sleeve, the expander being sized so as to (i) radially expand the distal end of the sleeve so that the sleeve is secured to the bone, and (ii) radially expand the enlarged head of the sleeve so that the sleeve is secured to the object, whereby to secure the object to the bone.       

     And in another preferred form of the invention, there is provided a method for securing an object to bone, the method comprising the steps of: 
     providing an object having an opening extending therethrough, and providing a sleeve/expander construction for securing the object to bone, the sleeve/expander construction comprising:
         a sleeve adapted for positioning through the opening in the object and into the bone, the sleeve comprising:
           a shank having a distal end and a proximal end and an opening extending from the distal end to the proximal end, wherein the opening narrows toward the distal end of the shank, and further wherein the distal end of the shank is slit so as to form a plurality of radially-expandable segments; and   an enlarged head formed at the proximal end of the shank, the enlarged head being formed so as to be radially-expandable; and   
           an expander adapted for positioning through the opening in the sleeve, the expander being sized so as to (i) radially expand the distal end of the sleeve so that the sleeve is secured to the bone, and (ii) radially expand the enlarged head of the sleeve so that the sleeve is secured to the object, whereby to secure the object to the bone;       

     positioning the object against the bone; 
     placing the sleeve through the opening in the object and into the bone; and 
     positioning the screw in the sleeve so as to secure the sleeve to the bone and to the object, whereby to secure the object to the bone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be read in conjunction with the attached drawings wherein like numbers refer to like parts, and further wherein: 
         FIG. 1  is a schematic view showing one preferred form of the novel fixation system of the present invention; 
         FIGS. 2 and 3  are schematic views showing one preferred form of the plate; 
         FIG. 4  is a schematic view showing an alternative form of plate and sleeve; 
         FIGS. 5-10  are schematic views showing one preferred form of the sleeve; 
         FIGS. 11-14  are schematic views showing one preferred form of the screw; 
         FIGS. 15-20  are schematic views showing the plate being secured to a bone using a plurality of sleeve/screw constructions; 
         FIGS. 21-25  are schematic views showing another preferred form of the plate; 
         FIGS. 26-28  are schematic views showing another preferred form of the sleeve; 
         FIG. 29  is a schematic view showing another preferred form of the screw; 
         FIG. 30  is a schematic view showing a rod for use with the sleeve/screw construction of the present invention; 
         FIG. 31  is a schematic view showing another form of rod for use with the sleeve/screw construction of the present invention; 
         FIG. 32  is a schematic view of a plate for capturing a rod against bone; 
         FIG. 33  is a schematic view of a “tulip” mount which may be secured to a bone using the sleeve/screw construction of the present invention; 
         FIGS. 34 and 35  show the sleeve being mated with the tulip mount, and the screw being mated with the sleeve, respectively; 
         FIG. 36  is a schematic view showing a hybrid tulip mount/sleeve construction; and 
         FIG. 37  is a schematic view showing a screw being mated with the hybrid tulip mount/sleeve construction shown in  FIG. 36 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Looking first at  FIG. 1 , there is shown a novel fixation system  5  which generally comprises a plate  10  which is to be secured to bone, and a sleeve  15  and a screw  20  for securing plate  10  to the bone. 
     Plate  10  is shown in detail in  FIGS. 2 and 3 . Plate  10  generally comprises a distal surface  25  ( FIG. 3 ) for positioning against bone, a proximal surface  30  ( FIG. 2 ), and at least one opening  35  formed in the plate. Opening  35  is preferably in the form of a bore-counterbore configuration, i.e., a bore  40  opens on distal surface  25 , a counterbore  45  opens on proximal surface  30 , and an annular flange  50  is formed at the intersection of bore  40  and counterbore  45 . As will hereinafter be discussed in further detail, bore  40  is sized to receive the shank of sleeve  15 , and counterbore  45  is sized to receive the head of sleeve  15 , with annular flange  50  serving to support the head of sleeve  15  and prevent the head of the sleeve from passing through the plate. 
     Opening  35  is preferably dimensioned, and one or more of the plate surfaces defining opening  35  are preferably appropriately radiused, and counterpart portions of sleeve  15  are preferably appropriately radiused, in order to permit sleeve  15  to extend through plate  10  at a range of different angles as will hereinafter be discussed in further detail. See, for example,  FIG. 1 , where sleeve  15  is shown extending through plate  10  at an acute angle. 
     A raised rim  55  is preferably formed on proximal surface  30  adjacent to opening  35 . Raised rim  55  helps to present a smooth interface between the elements of the system and the surrounding tissue, particularly when sleeve  15  and screw  20  are placed at an acute angle relative to the plane of plate  10  (i.e., at an angle significantly off the perpendicular, such as is shown in  FIG. 1 ). In addition, raised rim  55  also provides an enlarged contact surface for the head of sleeve  15 , particularly when sleeve  15  and screw  20  are placed at an acute angle relative to the plane of plate  10  (i.e., an angle significantly off the perpendicular). See, for example,  FIG. 1 . 
     Depending on the intended use of plate  10 , more than one opening  35  may be provided. By way of example but not limitation, where plate  10  is intended to be used as a fracture fixation plate or as a spinal fusion plate, at least one (and preferably two or more) openings  35  are formed in plate  10  on either side of the bone separation line (e.g., the fracture line, the vertebral body abutment lines, etc.), such that plate  10  can be secured to bone on each side of the bone separation line. By way of further example but not limitation, where plate  10  is intended to be used to secure soft tissue to bone, plate  10  might include only one opening  35 . 
     If desired, opening  35  in plate  10  and head  65  of sleeve  15  may be formed with non-circular (e.g., oval) shapes (as seen in top view) so as to provide an anti-rotation contact between the sleeve and the plate. Furthermore, if desired, opening  35  in plate  10  can have a slot-like configuration (as seen in top view), so as to allow a degree of longitudinal freedom when determining where to place sleeve  15  through opening  35  in plate  10 . See  FIG. 4 . 
     Sleeve  15  is shown in detail in  FIGS. 5-10 . Sleeve  15  generally comprises a shank  60 , a head  65  and an opening  70  extending along the length of sleeve  15 . 
     Shank  60  comprises a screw thread  75  on its outer surface. Screw thread  75  is preferably configured to facilitate the gripping entry of sleeve  15  into bone when the sleeve is turned into bone. Such screw threads may be self-drilling, in which case it may not be necessary to pre-drill a hole in the bone. Furthermore, the threads may be self-tapping, or they may not be self-tapping, in which case it may be necessary to tap a bone hole before inserting the sleeve into that bone hole. Sleeve  15  may be formed with threads having a reverse face so as to aid in backing the sleeve out of the bone, in the event that the same should be desired (e.g., in the case of a revision). 
     A plurality of slits  80  extend through the side wall of shank  60  at the distal end of shank  60 . Slits  80  permit shank  60  to expand radially when screw  20  is disposed in opening  70 , as will hereinafter be discussed in further detail. 
     Head  65  includes a plurality of longitudinally-extending slots  85 . Slots  85  permit sleeve  15  to be held against rotation as screw  20  is turned into the sleeve, as will hereinafter be discussed in further detail. Slots  85  also permit head  65  to expand when screw  20  is turned into the sleeve, whereby to facilitate head  65  gripping adjacent portions of plate  10 , as will hereinafter be discussed in further detail. Additionally, the head of sleeve  15  can be formed with a beveled edge so that it stands less proud when the sleeve is inserted into plate  10  at an angle which is relatively far off the perpendicular. 
     Opening  70  comprises a bore-counterbore-counterbore configuration. More particularly, and looking now at  FIG. 10 , a bore  90 , terminating in a tapered portion  92 , communicates with distal slits  80 . A counterbore  95  communicates with bore  90 . An annular flange  100  is formed at the intersection of bore  90  and counterbore  95 . Another counterbore  102  communicates with counterbore  95  and opens on the proximal end of sleeve  15 . An annular shoulder  103  is formed at the intersection of counterbore  95  and counterbore  102 . As will hereinafter be discussed, counterbore  95  is sized to receive the shank of screw  20 , and counterbore  102  is sized to receive the head of screw  20 , with annular shoulder  103  serving to support the head of screw  20 . However, sleeve  15  and screw  20  are sized so that when screw  20  is received in opening  70  of sleeve  15 , engagement of the shank of screw  20  with tapered portion  92  of sleeve  15  will radially expand the distal end of sleeve  15  so as to grip the bone. Furthermore, sleeve  15  and screw  20  are also sized so that when the head of screw  20  is seated in counterbore  102 , screw  20  will radially expand head  65  of sleeve  15  so as to grip plate  10 . 
     It should be appreciated that (i) the size and shape of the head of screw  20 , (ii) the size and shape of counterbore  102 , and (iii) the size and shape of slots  85  in the head of sleeve  15 , can all be combined so as to “tune” the degree of expansion of head  65  of sleeve  15 , whereby to regulate the force with which the sleeve is secured to plate  10 . 
     In addition to the foregoing, and as will hereinafter be discussed in further detail, sleeve  15  is preferably sized so that, when sleeve  15  is deployed in a plate  10  and into a bone, the distal end of shank  60  will extend beyond the cortical bone/cancellous bone interface, so as to provide enhanced stabilization. 
     Thus, advancing screw  20  into sleeve  15  radially expands both the distal and proximal ends of sleeve  20 , such that the sleeve is simultaneously secured to both the bone and the plate, as will hereinafter be discussed in further detail. 
     Bore  95  is preferably threaded so as to securely receive the shank of screw  20 . 
     A radially-extending detent  105  is preferably formed in the side wall of counterbore  102 , in order to receive a counterpart locking finger (see below) of screw  20 , whereby to releasably lock screw  20  to sleeve  15 , as will hereinafter be discussed in further detail.
         Screw  20  is shown in detail in  FIGS. 11-14 . Screw  20  generally comprises a shank  110 , a head  115  and an opening  120  extending longitudinally into screw  20 . Shank  110  comprises a thread  125  on its outer surface. As noted above, head  115  includes a radially-extending locking finger  130  for seating in the radially-extending detent  105  formed in sleeve  15 , whereby to releasably lock screw  20  to sleeve  15 , as will hereinafter be discussed in further detail. Opening  120  has a non-circular cross-section (e.g., hexagonal), in order that screw  20  can be rotatably driven by an appropriate driver. Preferably screw  20  is sized so that when it is seated within sleeve  15 , the distal end of the screw projects out of the distal end of the sleeve (see  FIG. 1 ).       

     Sleeve  15  and screw  20  can be used to secure a plate to bone. By way of example but not limitation, sleeve  15  and screw  20  can be used to secure plate  10  to a fractured bone so as to stabilize that bone. In this circumstance, plate  10  extends across the fracture line, with each end of the plate being secured to the bone using a sleeve/screw construction. Significantly, each sleeve/screw construction can be oriented at a different angle relative to plate  10 , so as to better distribute load and/or apply a compressive force. 
     More particularly, and looking now at  FIG. 15 , there is shown a bone B having a fracture F. In order to stabilize fracture F, a plate may be secured to the bone on either side of fracture F. To this end, and looking now at  FIG. 16 , plate  10  is positioned against bone B, and then a hole H is drilled into the bone beneath of the openings  35  which is to receive a sleeve/screw construction. This is done by passing a drill through opening  35  in plate  10  and into the bone. Due to the construction of plate  10  and sleeve  15 , bone hole H can be set at any one of a number of different orientations relative to plate  10 , e.g., bone hole H can extend at an acute angle relative to the plane of plate  10  (see, for example,  FIG. 16 ) or bone hole H can extend at a right angle to the plane of plate  10  (not shown). This construction allows the surgeon to select the most desirable orientation for the bone hole, taking into account factors such as bone quality, force distribution, angle of approach, etc. 
     Once bone holes H have been drilled in bone B, sleeves  15  are advanced through plate openings  35  and into bone holes H ( FIGS. 17 and 18 ). This is done by turning sleeve  15  with an appropriate rotational driver. Sleeve  15  is advanced until shank  60  is disposed in bone B and head  65  is seated in plate counterbore  45 . At this point, sleeve  15  will serve to provide some degree of attachment of plate  10  to bone B, by virtue of the engagement of screw threads  75  with bone B and head  65  with counterbore  45 . 
     As noted above, sleeve  15  is preferably sized so that, when sleeve  15  is deployed in a plate  10  and into bone B ( FIG. 17 ), the distal end of shank  60  extends beyond the cortical bone/cancellous bone interface I, so as to provide enhanced stabilization, as will hereinafter be discussed in further detail. 
     Next, screw  20  is advanced down opening  70  in sleeve  15  ( FIGS. 19 and 20 ). As this occurs, sleeve  15  can be held against rotation using sleeve slots  85 . The advancing screw  20  causes sleeve  15  to be radially expanded, so that the sleeve is simultaneously secured to both bone B and to plate  10 . More particularly, the distal end of the sleeve&#39;s shank  60  is expanded so that the sleeve engages the cancellous portion of bone B, the proximal end of the sleeve&#39;s shank  60  engages the cortical portion of bone B, and the sleeve&#39;s head  65  engages plate  10 . Significantly, sleeve  15  is sized so that the distal end of the sleeve mushrooms open beyond the cancellous bone/cortical bone interface I, making a tight securement between plate  10  and bone B. 
     Screw  20  is advanced until locking finger  130  seats in sleeve detent  105 , thereby releasably locking the screw in position relative to the sleeve. Engagement of locking finger  130  in sleeve detent  105  also serves as an indicator, with tactile feedback, that the screw has been advanced to the proper extent (and not overtightened) relative to the sleeve. 
     Significantly, inasmuch as sleeve  15  opens laterally and presents a substantially larger profile than screw  20  alone, the disposition of the combination of sleeve and screw in the plate and the bone provides much better contact with the plate and the bone, thereby enhancing securement and shear resistance. This is particularly true since the distal end of sleeve  15  opens just beyond the cortical bone/cancellous bone interface I, so that plate  10  is secured to bone B under tension. In addition, since screw  20  is being advanced into sleeve  15  and not directly into the bone, there is little likelihood that the screw will lose its purchase and become a spinner. Furthermore, in the unlikely event that the screw should become a spinner, the situation can be easily rectified by removing screw  20  from sleeve  15  and removing sleeve  15  from the bone and plate  10 . This leaves the host bone in condition for the procedure to be repeated with a new sleeve and/or a new screw, reusing the same bone hole. 
     Additional Constructions 
     It is possible to modify the constructions described above without departing from the scope of the present invention. 
     By way of example but not limitation, plate  10  might be formed with a non-rectangular and/or curved configuration, so as to seat more securely against a curved bone surface. See, for example,  FIGS. 21-25 , which show one such construction for plate  10 . 
     By way of further example but not limitation, sleeve  15  might be formed with ribs (or other lateral projections)  75  instead of a screw thread  75 . See, for example,  FIGS. 26-28 , which show a sleeve  15  formed with ribs  75 . In this case, sleeve  15  might be set with a mallet driver, etc., rather than with a rotational driver. Where sleeve  15  is formed with ribs  75 , ribs  75  may be given a profile to facilitate insertion and impede withdrawal from the bone, e.g., sloped leading edges  135  and sharp rims  140 . 
     Also by way of example but not limitation, screw  20  may be sized to terminate within sleeve  15  rather than extend out the end of sleeve  15 . Furthermore, the screw thread  125  of screw  20  might be replaced by ribs (or other lateral projections)  125  for engaging the interior side wall of sleeve  15 . See, for example,  FIG. 29 , which shows such a ribbed construction. In this case, or in other cases, the interior side wall of sleeve  15  might not be threaded. Additionally, screw  20  can be cannulated, so as to facilitate delivery over a guidewire. 
     Furthermore, sleeve  15  might be formed without a counterbore, and screw  20  might be formed without an enlarged head, in which case the screw would essentially constitute a threaded pin to be seated within a sleeve bore. 
     Additionally, the positions of detent  105  and finger  130  may be reversed, i.e., finger  130  may be formed on sleeve  15  and detent  105  may be formed on screw  20 . Additionally, more than one detent and/or finger may be provided, e.g., the apparatus may comprise one finger and multiple detents. 
     Also, screw  20  and sleeve  15  may be pre-assembled (either at the time or manufacture or in the operating room) so as to constitute a single unit. 
     It should also be appreciated that the present invention may be used to secure a rod (or the like) to bone. By way of example but not limitation, the rod could be a spinal rod (or other surgical rod) used to stabilize a plurality of vertebral bodies relative to one another. In this case, a portion of the rod might be modified so as to be analogous to plate  10  (e.g., so as to provide one or more openings  35  through the rod for receiving a sleeve  15  and screw  20 ). See  FIG. 30 , where a rod  141  is provided with one or more openings  35  therethrough. Where the rod has a relatively narrow diameter, and looking now at  FIG. 31 , a portion of rod  141  might be flattened and/or laterally expanded so as to provide an enlarged surface area  142  for receiving openings  35  to receive sleeve  15 . However, where the rod has a relatively large diameter, openings  35  may be formed in the rod without requiring any flattening and/or lateral expansion of the rod. 
     Alternatively, an adapter might be provided to secure the rod to bone. In this case, and looking now at  FIG. 32 , plate  10  could function as a rod mount, preferably with a groove  143  on the underside of the plate to capture the rod to the bone. In this case, it may be necessary to position openings  35  in plate  10  so that a sleeve  15  passing through openings  35  pass alongside a rod captured in the groove. See  FIG. 32 . 
     Additionally, the novel sleeve/screw construction can be used to secure a tulip-shaped mount to the bone, with the tulip-shaped mount being used to secure a rod to the bone. More particularly, and looking now at  FIG. 33 , a tulip-shaped mount  144  is shown, wherein the tulip-shaped mount has an opening  35  for securing the tulip-shaped mount to bone and a slot  145  for receiving a rod. 
     In use, tulip-shaped mount  144  is positioned alongside bone. A hole is drilled in the bone via opening  35  formed in tulip-shaped mount  144 . Sleeve  15  is advanced through opening  35  ( FIG. 34 ) and into the hole formed in the bone. Next, screw  20  is advanced through sleeve  15 , causing sleeve  15  to be radially expanded, so that the sleeve is simultaneously secured to both the bone and to tulip-shaped mount  144  (see  FIG. 35 ). With tulip-shaped mount  144  secured to the bone, a rod may be positioned in the slot  145  of tulip-shaped mount  144 , whereby to stabilize the bone(s). If desired, tulip-shaped mount  144  may be provided with a threaded cap (not shown) which can be positioned superior to the rod using threads  150 , so as to securely hold the rod in place within slot  145  of tulip-shaped mount  144 . 
     Looking next at  FIGS. 36 and 37 , it should also be appreciated that sleeve  15  can be formed integral with tulip-shaped mount  144 . 
     Materials 
     The various components can be formed out of any material or materials consistent with the present invention. Thus, for example, some or all of the components may be formed out of implantable metals (e.g., surgical grade stainless steel, titanium, Nitinol, etc.), implantable plastics, implantable absorbables, etc. 
     Modifications 
     It will be understood that many changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the principles and scope of the present invention.