Abstract:
A bone screw is provided having first and second threaded portions of different diameter separated by a middle portion that is unthreaded so that the bone screw may be inserted into a pair of adjacent bone fragments and used to compress the fragments together by driving the screw into a hole drilled in the fragments. An installation tool is also disclosed for threadably engaging one end of the bone screw and is used to initially drive the screw into the bone hole. Thereafter, a screwdriver may be inserted through the tool and into engagement with a recess in the bone screw and may be used to drive the screw fully into the bone and to separate the bone screw from the installation tool. A method of installation is further provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/861,818 to Frenk et al, filed Jun. 4, 2004, which is a continuation of International Application No. PCT/CH01/00698 to Frenk et al., filed Dec. 4, 2001, the entirety of both applications is hereby incorporated by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a bone screw for connecting two bone fragments, to a device for implanting such a bone screw, and to a method for setting, compressing and/or fixing bone fragments. 
     BACKGROUND OF THE INVENTION 
     Bone screws are used in various ways in osteosynthesis, for example, for setting bone fragments, as compression screws or for fixing bone fragments. 
     A bone screw with two axially terminal threaded segments and a middle threadless segment is known from U.S. Pat. No. 5,019,079 to Ross. The diameter of the middle segment corresponds essentially to the external diameter of the external thread at the distal threaded segment, but is larger than the core diameter of the external thread at the proximal threaded segment, so that the middle segment can be used for laterally stabilizing the two bone fragments of the fracture. It may be a disadvantage of this particular construction of bone screws that the two external threads have different pitches, so that the different steps for the implantation, the setting the bone fragments, the compression of the bone fragments and the recessing of the screw head cannot be carried out separately from one another. 
     SUMMARY OF THE INVENTION 
     Pursuant to the invention, this objective is accomplished with a bone screw, and with a device for implanting such a bone screw, as well as with a method for setting, compressing and/or fixing bone fragments. 
     The inventive bone screw comprises essentially two threaded segments, which are disposed coaxially with the longitudinal axis and terminally at the bone screw, the pitches S V  and S H  of the front and rear segments respectively, which may be identical or may be different from one another. After these two bone fragments have been set and compressed, wherein only the front threaded segment is screwed into the distal bone fragment while the rear threaded segment is screwed, for example, into an implantation instrument and not yet into the proximal bone fragment, the bone screw can be screwed further into the bone fragments, until the rear threaded segment also is recessed completely in the proximal bone fragment. This can be accomplished without at the same time changing the position of the bone fragments relative to one another and without changing the compression of the two bone fragments. The two threaded segments are constructed so that the external diameter of the front threaded segment is smaller than or equal to the core diameter of the external thread at the rear threaded segment. 
     An advantage of the inventive bone screw and the inventive device are that due to the pitch of the external thread at the front threaded segment and at the rear threaded segment being the same, the steps of setting the bone fragments, compressing the bone fragments, and recessing the head of the screw can be carried out separately and in a controlled manner. 
     Because the rear threaded segment is configured with a core diameter, which may be larger than or equal to the external diameter of the front threaded segment, interaction of the rear threaded segment with the thread already cut in the bone fragments for the front threaded segment can be avoided. 
     Preferably, the external threads at the front and rear threaded segments are self-cutting threads. 
     A preferred embodiment of the inventive bone screw includes, between the two threaded segments, a middle, threadless segment, which has an external diameter, which is smaller than or equal to the core diameter of the external thread at the front threaded segment. With that, the front threaded segment can be screwed completely into the distal bone fragment and the borehole in the proximal bone fragment does not have to be enlarged relative to the borehole in the distal bone fragment for setting and compressing the bone fragments. Compared to embodiments of known bone screws, the front threaded segment of which directly adjoins the rear threaded segment in the axial direction and for which the borehole in the proximal bone fragment would have to be enlarged so that the front threaded segment can be screwed only into the distal bone fragment, a higher stability of the connection between the bone screw and the proximal bone fragment can furthermore be attained with the present device. 
     The inventive device serves for setting, compressing and fixing bone fragments by means of a bone screw and includes a surgical implantation instrument, which has a central borehole through which a screwdriver can be passed, extending coaxially through the implantation instrument. Furthermore, the central borehole is expanded from the front end of the implantation instrument up to a depth T, so that a shoulder is formed at the depth T. In the expanded part of the central borehole, there is an internal thread, which is complementary to the external thread of the rear threaded segment of the bone screw, so that the rear threaded segment of the bone screw can be screwed into the central borehole up to a depth T. The depth T is selected so that T may be greater than L, where L is the length of the rear threaded segment of the bone screw. With that, it can be achieved that the rear threaded segment of the bone screw can be screwed completely into the central borehole of the implantation instrument. However, T may also be equal to or less than L, which may have the effect of partially inserting the rear threaded segment of the bone screw into the central borehole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and further developments of the invention are explained in even greater detail in the following by means of the partially diagrammatic representations of several examples. In the drawings, 
         FIG. 1  shows a cross-sectional view of an embodiment of the inventive bone screw; 
         FIG. 2  shows a cross-sectional view of the embodiment shown in  FIG. 1 , an implantation instrument, and a screwdriver; 
         FIG. 3A  shows a side view of an embodiment of a compression sleeve; 
         FIG. 3B  shows a cross-sectional view of the compression sleeve of  FIG. 3A ; 
         FIG. 3C  shows an enlarged partial cross-sectional view of the compression sleeve of  FIGS. 3A-3B ; 
         FIG. 4A  shows a side view of an embodiment of a cannulated screwdriver; 
         FIG. 4B  shows a cross-sectional view of the screwdriver of  FIG. 4A ; 
         FIG. 5A  shows a side view of an embodiment of a protection handle; 
         FIG. 5B  shows a cross-sectional view of the protection handle of  FIG. 5A ; 
         FIG. 6A  shows a side view of a coupling member for use with the protection handle of  FIGS. 5A-5B ; 
         FIG. 6B  shows a cross-sectional view of the coupling member of  FIG. 6A ; 
         FIG. 7A  show a side view of an embodiment of a combi-instrument; 
         FIGS. 7B-7C  show cross-sectional views of the combi-instrument of  FIG. 7A ; 
         FIG. 8A  shows a cross-sectional view of a compression sleeve for use with the combi-instrument of  FIG. 7A ; 
         FIG. 8B  shows an enlarged cross-sectional view of the compression sleeve of  FIG. 8A ; 
         FIG. 9A  shows a side view of a handle for use with the combi-instrument of  FIG. 7A ; 
         FIG. 9B  shows a cross-sectional view of the handle of  FIG. 9A ; 
         FIG. 10A  shows a side view of a cannulated screwdriver and locking collar for use with the combi-instrument of  FIG. 7A ; 
         FIG. 10B  shows a cross-sectional view of the cannulated screwdriver and locking collar of  FIG. 10A ; 
         FIG. 10C  shows an enlarged side view of the engagement portion of the cannulated screwdriver of  FIGS. 10A-10B ; 
         FIG. 10D  shows a cross-sectional view of the engagement portion of  FIG. 10C ; 
         FIG. 11A  shows a side view of a locking ring for use with the combi-instrument of  FIG. 7A ; 
         FIG. 11B  shows a cross-sectional view of the locking ring of  FIG. 11A ; 
         FIG. 12A  shows a side view of a locking collar for use with the combi-instrument of  FIG. 7A ; 
         FIG. 12B  shows an end view of the locking collar of  FIG. 12A ; 
         FIG. 12C  shows a cross-sectional view of the locking collar of  FIG. 12A ; 
         FIG. 13A  shows a side view of an embodiment of a compression sleeve having a hex-shaped inlet for use with a plastic-sealed screw; 
         FIG. 13B  shows an enlarged side view of the compression sleeve of  FIG. 13A ; 
         FIG. 13C  shows an enlarged partial cross-sectional view of the compression sleeve of  FIG. 13A ; 
         FIG. 14A  shows a side view of a plastic seal for use with a screw; and 
         FIG. 14B  shows a cross-sectional view of the plastic seal of  FIG. 14A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of the inventive bone screw  1  is shown in  FIG. 1 . This bone screw  1  includes a rear threaded segment  7  with an external thread  9 , which has a core diameter D KH , an external diameter D HS  and a pitch S H , a middle, threadless segment  6  with an external diameter D MS , which adjoins the rear threaded segment  7  coaxially with the longitudinal axis  2 , and a front threaded segment  5  with an external thread  8 , which has a core diameter D KV , an external diameter D VS  and a pitch S V . The two threaded segments  5 ,  7  have different diameters, that is, the core diameter D KH  of the rear threaded segment  7  is larger than or equal to the external diameter D VS  of the front threaded segment  5 . The pitches of the two external threads  8 ,  9  may be identical, or may be different from one another. Moreover, the lead of the front threaded segment  5  may be equal to or different from the lead of the rear threaded segment  7 . The external diameter D MS  of the middle segment  6  is smaller than or equal to the core diameter D KV  of the front threaded segment  5 . Moreover, at the front end  3  of the bone screw  1  and at the transition between the rear threaded segment  7  and the middle segment  6 , several indentations  23 , distributed over the periphery of the two threaded segments  5 ,  7  which may be aligned axially, are disposed with cutting edges  12  essentially parallel to the longitudinal axis  2 , so that these two external threads  8 ,  9  are constructed as self-cutting threads. At the rear end of  4  of the bone screw  1 , means  11  for accommodating a screwdriver, for example, a hexagonal recess, Torx® or Phillips, are disposed coaxially. Moreover, the bone screw  1  is equipped with a central borehole  10 , which extends from the front end  3  up to the rear end  4  and serves, for example, for accommodating a guiding wire (not shown). 
     In  FIG. 2 , the inventive device is shown together with a bone screw  1 , a portion of the rear threaded segment  7  is screwed into the implantation instrument  15  and the front threaded segment  5  of which is screwed completely into the distal bone fragment  14 . The implantation instrument  15  includes a continuous central borehole  17 , which is expanded from the front end  18  up to a depth T and, in expanded part  24 , has an internal thread  20 , which is complementary to the external thread  9 . At the depth T, between the expanded part  24  of the central borehole  17  and the narrower part  25  of the central borehole  17 , there is a shoulder  22 , against which the rear end  4  of the bone screw  1  rests when the rear threaded segment  7  is screwed completely into the implantation instrument  15 . A screwdriver  16  can be passed through the narrower part  25  of the central borehole  17  from the rear end  19  of the implantation instrument  15 , so that the screwdriver  16  can be introduced into the means  11 , which are disposed at the rear end  4  of the bone screw  1  for accommodating a screwdriver and the bone screw  1  can be rotated by means of the screwdriver  16  relative to the implantation instrument  15 . 
     For setting, compressing and fixing the two bone fragments  13 ,  14 , a borehole  21 , passing through the proximal bone fragments  13  and into the distal bone fragment  14 , may be produced. The diameter of the borehole  21  corresponds to the core diameter D KV  ( FIG. 1 ) of the external thread  8  at the front threaded segment  5  of the bone screw  1 . Borehole  21  may be optional, however, particularly when bone screw  1  is self-drilling. 
     At the start of the implantation process, the rear, threaded segment  7  of the bone screw  1  is screwed completely and up to a depth T in the internal thread  20  into the central borehole of the implantation instrument  15 . By rotating the implantation instrument  15  about the longitudinal axis  2 , the bone screw may then screwed into the pre-drilled boreholes  21  in the two bone fragments  13 ,  14 . Since the rear threaded segment  7  of the bone screw  1  is taken up completely in the implantation instrument  15 , the external thread  9  of the rear threaded segment  7  cannot engage the proximal bone fragments  13 , so that, as the implantation instrument  15  is rotated, only the front threaded segment  5  of the bone screw  1  can be screwed into the distal bone fragment  14 . In this phase, the front end  18  of the implantation instrument  15  assumes the task of a screw head, so that, after the bone screw  1  has been brought into the two bone fragments  13 ,  14  far enough that the front end  18  of the implantation instrument  15  lies against the proximal bone fragment  14 , the two bone fragments  13 ,  14  are moved towards one another by rotating the implantation instrument  15  further. As soon as the two bone fragments  13 ,  14  are in contact with one another, compression of the two bone fragments  13 ,  14  commences. As soon as the desired compression of the two bone fragments  13 ,  14  has been reached by rotating the implantation instrument  15  further, the screwdriver  16  is inserted through the central borehole  17  in the implantation instrument  15  into the means  11  for accommodating the screwdriver and the bone screw  1  is rotated further with the screwdriver  16 , so that, while the implantation instrument  15  is held in place, the bone screw  1  is screwed out of the internal thread  20  at the front end  18  of the implantation instrument  15  and the rear threaded segment  7  is screwed into the proximal bone fragment  13 , until the rear threaded segment  7  is brought completely beneath the surface of the proximal bone fragment  13 . Since the two bone fragments  13 ,  14  are not moved relative to one another during this last process, the compression may be unchanged after the rear, threaded segment  7  is driven into the proximal bone fragment  13 . 
     Preferably, the bone screw  1  is used where a screw head would interfere, for example, for fractures in the vicinity of a joint, for intraarticular fixation such as scaphoid fractures, for small fragments and for fixations in the vicinity of sinews, nerves and vessels. Bone screw  1  may also be used in conjunction with or adjacent to a bone plate (not shown). 
       FIGS. 3A-3C  show an embodiment of a compression sleeve  30  for use with a bone screw  1 . As seen in the side view of  FIG. 3A , compression sleeve  30  may have a leading end  32 , a trailing end  34 , and a gripping portion  36  disposed near the trailing end  34 . As seen in the cross-sectional view of  FIG. 3B , compression sleeve  30  may have a bore  38  running through the sleeve  30 , and extending between leading opening  40  and trailing opening  42 . An enlarged view of the leading end  32  of the compression sleeve  30  is seen in  FIG. 3C . Internal threads  44  may be disposed at and/or near the leading end  32  and leading opening  40  of the sleeve  30 . Sleeve  30  may also have a shoulder  46  disposed adjacent internal threads  40 . Shoulder  46  may be sized to prevent a bone screw  1  from protruding too far into the bore  38  of sleeve  30 . Shoulder  46  may be positioned within bore  38  such that the rear threaded segment  7  of bone screw  1  can fully engage the internal threads  40 . Compression sleeve  30  may be used in a substantially similar manner as implantation instrument  15 , discussed supra. 
       FIGS. 4A-4B  show an embodiment of a screwdriver  50  for use with a bone screw  1 . As seen in the side view of  FIG. 4A , screwdriver  50  may have an engaging end  52 , a trailing end  54 , and indicia  56   a ,  56   b ,  56   c . Screwdriver  50  may also have a depressed section  58  at or near the trailing end  54 , which may aid in engaging a handle. As seen in the cross-sectional view of  FIG. 4B , screwdriver  50  may have a bore  60  running between a leading opening  62  and a trailing opening  64 . Screwdriver may also have an engaging portion  66  for engaging a bone screw  1  in a similar manner to that described supra in relation to screwdriver  16 . Engaging portion  66  may be of any chosen shape to effectively engage a bone screw  1 . 
     Indicia  56   a ,  56   b ,  56   c  may aid in determining the depth of insertion of a bone screw  1  in a bone or tissue. When inserted into a compression sleeve or other implantation instrument, indicia  56   a ,  56   b ,  56   c  may be fully or partially visible during use. As the engaging portion  66  of the screwdriver  50  engages a receiving portion (an embodiment of which is shown as means  11  above) of a bone screw  1 , the bone screw  1  is further inserted in a bone or tissue, and may become disengaged with the internal threads  40  of a compression sleeve  30 . As the screwdriver  50  is inserted farther into the bore  38  of sleeve  30 , the indicia  56   a ,  56   b ,  56   c  may progressively become covered, such that as indicia  56   c  becomes covered by sleeve  30 , the bone screw  1  may be fully inserted into a bone or tissue. 
       FIGS. 5A-5B  show an embodiment of a handle  70  for use with an instrument described herein. As seen in the side view of  FIG. 5A , handle  70  may have a gripping portion  72 , and a coupling member  74  having an leading opening  76  and expandable fingers  82 . Coupling member  74  may be a separate and distinct component (as shown in  FIGS. 6A-6B ), and may be at least partially inserted into a compression sleeve  30  via opening  42 . Expandable fingers  82  may be beneficial to resiliently contract within bore  38  of compression  30  to create a more secure fit. As seen in the cross-sectional view of  FIG. 5B , handle  70  may also have a bore  78  for receiving coupling member  74 . Receiving portion  74  may also have a bore  80  for receiving a portion of a guide wire (not shown) therethrough. 
       FIGS. 6A-6B  show an embodiment of a coupling member  74  in more detail. As seen in the side view of  FIG. 6A  and cross-sectional view of  FIG. 6B , coupling member  74  may have leading opening  76 , a trailing opening  86 , with a bore  80  extending therebetween. Coupling member  74  may also have a leading end  85  and a trailing end  86 . Bore  80  may be sized and dimensioned to fit a guide wire (not shown). 
     In use, handle  70  may be beneficial to provide a safe and ergonomic way for a user to insert bone screw  1  into a bone segment. First, a guide wire may be inserted into a bone segment at a desired location. The compression sleeve  30 , with bone screw  1  already engaged with internal threads  40 , may be engaged with handle  70 , and thereafter inserted over the guide wire, such that the front end  3  of the bone screw  1  is adjacent the bone surface. In this arrangement, the coupling portion  74  engages the compression sleeve  30  via its trailing opening  42 , and the free end of the guide wire is housed in the bore  78  of handle  70 . Bone screw  1  may then be inserted into the bone surface with the exposed, free end of the guide wire safely housed in the handle. After the bone screw  1  is inserted into the bone surface to a desired depth, the handle  70  and coupling portion  74  may be disengaged from the compression sleeve  30 , and the screwdriver  50  may be brought into engagement to further insert the bone screw  1  into the bone surface and/or disengage the bone screw  1  from the compression sleeve  30 . Thus, the configuration and removable engagement of handle  70  with compression sleeve  30  offers protection to the user from the free end of the guide wire, and also provides an ergonomic method to insert bone screw  1  at least partially into a bone surface. 
       FIGS. 7A-7C  show an embodiment of another type of instrument, combi-instrument  100 , that may be used with a bone screw  1 . As seen in the side view of  FIG. 7A , and cross-sectional views of  FIGS. 7B-7C , combi-instrument  100  may have a handle  110 , a locking collar  115 , a locking ring  120 , a compression sleeve  130  having a gripping portion  135  and a shaft portion  140 , a screwdriver  150  having a leading portion  158 , and a bore  160  extending therethrough. 
     In use, combi-instrument  100  may function in a substantially similar manner to that of the other devices described herein. One difference between the combi-instrument  100  and other devices described herein is that combi-instrument  100  may have a selective engagement feature that allows a bone screw  1  to be at least partially inserted with and without the use of screwdriver  150 . As described in more detail below, the selective locking arrangement between locking collar  115  and locking ring  120  may selectively determine whether the compression sleeve  130  is fixed in relation to the handle  110  and screwdriver  150 . As bore  160  may pass all the way through the combi-instrument  100 , a guidewire (not shown) may be utilized for more precise and accurate placement and use of the instrument  100 . 
       FIGS. 8A-8B  show an embodiment of a compression sleeve  130  for use with combi-instrument  100 . Compression sleeve  130  may be substantially similar in design and function to compression sleeve  30  and implantation instrument  15  described supra. Compression sleeve  130  may have a bore  131  extending between a leading opening  133  and a trailing opening  132 . Sleeve  130  may also have a gripping portion  135  and a shaft  140 . As with compression sleeve  30  discussed above, sleeve  130  may also have internal threads  134  for engaging a bone screw  1 , and a shoulder  136  for restricting movement of a bone screw  1  within bore  131 . Compression sleeve  130  also may have an auxiliary shaft portion  139 , which is either polygonal or otherwise non-circular in shape, for receiving a locking ring  120  such that when locking ring  120  is received on the auxiliary shaft, the locking ring  120  cannot rotate relative to the compression sleeve  130 . As such, compression sleeve  130  and locking ring  120  are rotationally fixed during use, although locking ring  120  may be slidably associated with the auxiliary shaft portion  139 . 
       FIGS. 9A-9B  show an embodiment of a handle  110  for use with combi-instrument  100 . Handle  110  may have a bore  111  extending between a leading opening  113  and a trailing opening  114 . Handle  110  may also have a gripping portion  190 , with indentations  192  for enhancing a user&#39;s gripping abilities. Handle  110  may further have an enlarged chamber  112 , at least partially concurrent with bore  114 , that may receive at least a portion of a locking collar  115 . Handle  110  preferably is fixedly attached to locking collar  115  by way of fasteners (not shown) inserted into fixation holes  194 . 
       FIGS. 10A-10D  show an embodiment of a cannulated screwdriver  150  for use with the combi-instrument  100 . Screwdriver  150  may be substantially similar to screwdrivers  16 ,  50  described above. Screwdriver  150  may have a leading end  152 , a trailing end  154 , a bore  156 , and a leading portion  158  at and/or near the leading end  152 . As seen in  FIGS. 10A-10B , screwdriver  150  may be sized to interact with locking collar  115 . Leading portion  158  is shown in more detail in  FIGS. 10C-10D . Leading portion  158  may have an engaging portion  157  for engaging a bone screw  1 . Leading portion  158  may also have a bore  159  coaxial with but of a reduced diameter than bore  156  of screwdriver  150 . Leading portion  158  may also be a separate and distinct component of screwdriver  150 , and accordingly may be a least partially inserted into bore  156  of screwdriver  150 . Any and all of the characteristics of leading portion  158  may also be used with screwdriver  16 ,  50 . Screwdriver  150  may be fixedly attached to handle  110  during use. 
       FIGS. 11A-11B  show an embodiment of a locking ring  120  for use with combi-instrument  100 . As seen in the side view of  FIG. 11A  and the cross-sectional view of  FIG. 11B , locking ring  120  may have indentations  122  to assist gripping, a first end  124 , a second end  126 , a first opening  125 , and a second opening  123 . Locking ring  120  may also have locking elements  127   a ,  127   b  protruding within the cavity  129  of locking ring  120 . Locking elements  127   a ,  127   b  may engage indentations  118  of locking collar  115 , as discussed below. Locking ring  120  may have one, two, three, or more locking elements. Inner surface  121  of locking ring  120  preferably corresponds to the shape and dimensions of auxiliary shaft portion  139  of compression sleeve  130 . 
       FIGS. 12A-12C  show an embodiment of a locking collar  115  for use with combi-instrument  100 . As seen in the side view of  FIG. 12A , the front view of  FIG. 12B , and the cross-sectional view of  FIG. 12C , locking collar  115  may have an insertion end  117  for insertion into a handle  110 , and an engaging end  119  for engaging a locking ring  120 . Locking collar  115  may also have a bore  116  extending between ends  117 ,  119 . As seen in detail in  FIG. 12B , the engaging end  119  of locking collar  115  may have a plurality of indentations  118  disposed around bore  116 . Some indentations  118  may engage locking elements  127   a ,  127   b  of locking ring  120 . Locking collar  115  is fixedly attached to handle  110  by way fasteners being inserted into fixation holes  196 , which may align with the fixation holes  194  of handle  110 . Fixation holes  194 ,  196  may be threaded. 
     Locking collar  115  may also have indicia  191   a ,  191   b ,  191   c , which may be utilized in a substantially similar manner as indicia  56   a ,  56   b ,  56   c  of screwdriver  50  (discussed supra), such that as the insertion of the bone screw  1  in a bone or tissue progresses, indicia  191   a ,  191   b ,  191   c  are progressively covered up. Indicia  56 ,  191  may be different colors to indicate the level of insertion of bone screw  1 . Indicia  56 ,  191  may be spaced apart as a variety of distances. Indicia  56 ,  191  are preferably spaced apart at about 2 mm. 
     The engagement and release of locking collar  115  with locking ring  120  will now be described. After the bone screw  1  is threaded attached to compression sleeve  130  by engaging internal threads  134  with the rear threaded segment  7  of bone screw  1 , the combi-instrument  100  is arranged such that the locking elements  127  of the locking ring  120  engage indentations  118  of the locking collar  115 . In this configuration, the entire combi-instrument  100  is essentially an integral tool. The combi-instrument  100  is then rotated and/or otherwise manipulated to insert bone screw  1  into a bone or tissue to a desired depth, but preferably such that the leading end  133  of the compression sleeve  130  is near the bone or tissue surface. At this point, the locking ring  120  may be slid toward the distal end of the device, such that locking elements  127  become disengaged with indentations  118  of locking collar  115 . Locking ring  120  preferably is slid in this direction to the point that it abuts compression sleeve  130 . After locking ring  120  is disengaged, handle  110  (with screwdriver  150  and locking collar  115  fixedly attached) may be rotated to further insert the bone screw  1  into a bone or tissue, while concurrently disengaging the rear threaded segment  7  from the internal threads  134  of the compression sleeve  130 . This is achieved because the engaging portion  157  of the screwdriver  150  is now allowed to engage the bone screw  1  and rotate free of the compression sleeve  130  within its bore  131 . 
       FIGS. 13A-14B  show another embodiment of a compression sleeve  200  and an embodiment of a plastic seal  220  for use with a bone screw  1 , and in accordance with the overall objectives of the invention described herein. As seen in the side view of  FIG. 13A , the enlarged side view of  FIG. 13B , and partial cross-sectional view of  FIG. 13C , compression sleeve  200  may have a bore  202  extending between leading opening  204  and trailing opening  206 . Bore  202  may have more than one diameter. Compression sleeve  200  may also have a shaft portion  208 , and a tip portion  209  having a leading end  210 . As seen in more detail in  FIGS. 13B-13C , tip portion  209  may have a hex-shaped inner surface  212  for receiving a portion of a plastic seal  220  (see  FIGS. 14A-14B , infra). Inner surface  212  may be other shapes as well suitable for restricting rotational movement of a plastic seal  220  within the tip portion  209 . Tip portion  209  may also have a ring  214  disposed near the leading end  210  for elastically securing a portion of a plastic seal  220 . Ring  214  may be elastically deformable so as to allow a portion of a plastic seal  220  to engage the ring  214  while still allowing the plastic seal  220  to slide past the ring and further into the bore  202 . 
       FIGS. 14A-14B  show an embodiment of a plastic seal  220  for use with compression sleeve  200  and bone screw  1 . As seen in the side view of  FIG. 14A , and the cross-sectional view of  FIG. 14B , seal  220  may have a leading end  222 , an insertion end  224 , with a bore  226  extending between leading opening  230  and trailing opening  228 . Seal  220  may also have a bulbous leading portion  234  for receiving a portion of a bone screw  1 . The inner surface of the leading portion  234  may have a shoulder  232 , similar in design and function to shoulder  22 ,  46 ,  136  described above. The inner surface of leading portion  234  may or may not be threaded. In one embodiment, the inner surface is not threaded, and bone screw  1  is inserted into the leading portion  234  by axial force. In another embodiment, inner surface is threaded, and bone screw  1  may be threadedly received within leading portion  234 . Seal  220  may also be molded over at least a portion of bone screw  1 . Seal  220  may also have a hex-shaped outer surface  236  at or near the insertion end  224 , which may be inserted into the hex-shaped inner surface  212  of compression sleeve  200 . Other shapes other than hex-shaped surfaces may be utilized. Seal  220  is preferably made of plastic, and is preferably a single-use, disposable element. 
     In use, bone screw  1  is inserted into the leading opening  230  of seal  220 , and the insertion end  224  is inserted within the leading opening  204  of compression sleeve  200 , such that the hex-shaped outer surface  236  of the seal  220  engages the hex-shaped inner surface  212  of the compression sleeve  200 . Bone screw  1  may then be partially inserted into bone or tissue to a desired depth. Bone screw  1  may then be engaged by a screwdriver via bore  206  of compression sleeve  200  to insert screw  1  further into bone or tissue, and concurrently disengaging bone screw  1  with seal  220 . Bone screw  1  may be engaged as such until the bone screw  1  is completely disengaged with seal  220 . Plastic seal  220  may then be removed from compression sleeve  200  and discarded. 
     Bone screw  1  may be fully or partially inserted into instrument  15  or compression sleeve  30 ,  130 ,  200  prior to engagement with a bone surface. Threaded portions of bone screw  1  may have a variety of pitches, lengths, diameters, and different threaded segments on a bone screw  1  may have the same or different pitches, lengths, and diameters. Various combinations of characteristics will be appreciated by those skilled in the art. 
     It is expressly contemplated that characteristics from some embodiments may be combined, integrated, or interchangeable with characteristics from other embodiments. In this sense, the described components of the instruments described herein are “modular” in nature. Such combinations will be appreciated by those skilled in the art, in addition to modifications thereof. 
     While the invention has been shown and described herein with reference to particular embodiments, it is to be understood that the various additions, substitutions, or modifications of form, structure, arrangement, proportions, materials, and components and otherwise, used in the practice and which are particularly adapted to specific environments and operative requirements, may be made to the described embodiments without departing from the spirit and scope of the present invention. Accordingly, it should be understood that the embodiments disclosed herein are merely illustrative of the principles of the invention, and that various modifications may be made by those skilled in the art which will embody the principles of the invention and fall within the spirit and the scope thereof.