a preferred embodiment of the inventive bone screw 1 is shown in fig1 . 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 fig2 , 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 ( fig1 ) 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 ). fig3 a - 3c show an embodiment of a compression sleeve 30 for use with a bone screw 1 . as seen in the side view of fig3 a , 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 fig3 b , 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 fig3 c . 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 . fig4 a - 4b show an embodiment of a screwdriver 50 for use with a bone screw 1 . as seen in the side view of fig4 a , 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 fig4 b , 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 . fig5 a - 5b show an embodiment of a handle 70 for use with an instrument described herein . as seen in the side view of fig5 a , 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 fig6 a - 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 fig5 b , 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 . fig6 a - 6b show an embodiment of a coupling member 74 in more detail . as seen in the side view of fig6 a and cross - sectional view of fig6 b , 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 . fig7 a - 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 fig7 a , and cross - sectional views of fig7 b - 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 . fig8 a - 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 . fig9 a - 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 . fig1 a - 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 fig1 a - 10b , screwdriver 150 may be sized to interact with locking collar 115 . leading portion 158 is shown in more detail in fig1 c - 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 . fig1 a - 11b show an embodiment of a locking ring 120 for use with combi - instrument 100 . as seen in the side view of fig1 a and the cross - sectional view of fig1 b , 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 . fig1 a - 12c show an embodiment of a locking collar 115 for use with combi - instrument 100 . as seen in the side view of fig1 a , the front view of fig1 b , and the cross - sectional view of fig1 c , 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 fig1 b , 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 . fig1 a - 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 fig1 a , the enlarged side view of fig1 b , and partial cross - sectional view of fig1 c , 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 fig1 b - 13c , tip portion 209 may have a hex - shaped inner surface 212 for receiving a portion of a plastic seal 220 ( see fig1 a - 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 . fig1 a - 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 fig1 a , and the cross - sectional view of fig1 b , 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 .
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 .