fig1 shows a drilling tool guide according to the present invention for use with a guide wire . the guide has a hollow sleeve 10 with a bore 12 of preferably cylindrical cross - section . the rear end 14 of the sleeve 10 is preferably threaded on its outer surface to screw to a hollow endcap 16 . preferably , another portion 17 of the outer surface of sleeve 10 is threaded to screw to a separate drill guide ( not shown ). a bore 18 extends through the front tip 20 of the sleeve 10 . preferably , the tip bore 18 is sized to guide a drilling tool , such as a threaded guide wire or a kirschner wire , but may have a diameter appropriate to other tools such as drill bits or fixation pins . the outer diameter of tip 20 is preferably as narrow as practical to seat closely around a drilling site , but still maintain the structural integrity needed to guide a spinning tool . also , serrations 22 preferably line the front side of the tip 20 to frictionally grip a bone surface during drilling to prevent the drilling guide from sliding on the bone &# 39 ; s slippery periosteum , a fibrous membrane that covers the surface of the bone . the preferred embodiment is handheld . it has a handle 24 secured to sleeve 10 by two pins 26 . in this embodiment , the pins 26 penetrate the wall of the sleeve 10 , but do not extend beyond the interior surface of the wall of sleeve 10 . the handle 24 also has an alignment bore 28 . the alignment bore 28 is sized to receive a parallel guide - wire that has already been inserted into a bone . preferably , the alignment bore 28 extends in parallel to the intended drilling axis at a predetermined distance therefrom . a plunger 30 slides telescopically within the sleeve 10 . the main body 32 of the plunger 30 is preferably narrower than the sleeve bore 12 . a plunger bore 34 extends axially through the length of the plunger 30 and is shaped to receive and guide a spinning tool . this bore is axially aligned with the tip bore 18 of sleeve 10 in order to guide the tool along a straight line into the bone . moreover , the plunger 30 and the sleeve 10 together protect tissue surrounding the drilling site . the rear of the plunger 30 terminates in a platform 36 . platform 36 is adapted to abut the front of a spinning drill chuck , so that the chuck can force the plunger 30 forward and deeper into the sleeve 10 . the platform 36 also provides a surface that a user can grasp to pull the plunger 30 backwards , extending the drilling guide . the forward end of the plunger 30 is divided into a plurality of resilient fingers 38 . in the preferred embodiment , finger heads 40 on the fingers 38 naturally form a slightly larger diameter than that of the sleeve bore 12 . most preferably , the fingers are tapered to produce a constant deflection along their lengths when a force is applied to their tips , producing fairly uniform bending moments throughout each finger . thus , when the fingers 38 are inserted within the sleeve bore 12 , the inner wall of the sleeve 10 biases the fingers 38 inwardly . this fit permits the plunger 30 to telescope within the sleeve 10 under friction , so the plunger 30 and the sleeve 10 retain their relative telescopic position after they have been partially collapsed . as explained above , a front end of the hollow endcap 16 is screwed to the rear 14 of the sleeve 10 . a rear endcap bore 42 , behind the threaded portion , has an inner diameter that approximately matches the outer cross - section of the main body 32 of the plunger 30 . when the endcap 16 is screwed onto the rear 14 of the sleeve 10 , it prevents the finger heads 40 from retreating backwards beyond the endcap bore 42 . thus , the telescoping sleeve 10 and plunger 30 of this embodiment may only extend up to a predetermined maximum , as shown in fig1 . this maximum extension should be at least as long as the portion of a drilling tool that protrudes from a chuck , and preferably at most as long as that portion of the tool . a scale 44 graduates the outside of the plunger 30 and indicates the amount by which the guide has been collapsed . fig1 shows numerical markings at every 10 units , and graduations 44 at every 2 units . the graduations 44 in this embodiment are read against the rear end 46 of the endcap 16 , although other embodiments can employ alternative forms of scale indicators . in the illustrated , maximally extended position , the scale 44 reads zero . as the plunger 30 is introduced further into the sleeve 10 , the endcap rear end 46 indicates a higher number . fig2 shows a drilling tool 48 , in this case a self tapping , surgical guide - wire according to the invention . the front tip 50 of the guide wire 48 preferably has sharp facets and ends at an acute point for cutting through bone . in the illustrated embodiment , the guide wire 48 has self - tapping threads 52 , but other embodiments , such as kirschner wires , pins , and drill bits , may not exhibit this feature . to facilitate the use of the guide wire 48 , indicia 54 marks the portion of the guide wire 48 to be inserted into the chuck of a drill . the distance from this indicia 54 to the tip 50 of the wire 48 preferably equals the fully extended length of the guide . thus , if a surgeon properly loads the wire 48 into a chuck and aligns the front of the chuck with the indicia 54 , the portion 55 of the wire protruding from the drill will be as long as the extended drilling - guide . if the surgeon places serrated tip 30 against a bone , as the surgeon drills the tool 48 into a bone through the drilling guide , the scale 44 indicates the length of the portion of the tool 48 that extends beyond the tip 20 of the sleeve 10 , the frontmost part of the guide , and thus the scale 44 indicates the length of the wire 48 presently drilled into the bone . if an intermediate object is placed between the tip 30 and the bone , the penetration depth indicated includes the part of the intermediate object through which the wire 48 is currently passed . fig3 shows the guide wire 48 of fig2 being implanted into a bone 56 . after having closed a drill chuck 58 of drill 60 around the wire 48 so that the tip of the chuck 48 aligns with indicia 54 , the surgeon has slid guide wire 48 into the guide . in the figure , the serrations 18 at the front tip 20 of the sleeve 10 rest against the proximal bone - cortex 62 or its periosteum . in the illustrated use , guide wire 48 is being implanted at a predetermined distance from , and parallel to , a parallel guide - wire 64 that has already been implanted . the alignment bore 28 has been slid over the parallel wire 64 as shown . as the surgeon operates the drill 60 , the chuck 58 pushes the platform 36 and the plunger 30 forward , gradually collapsing the guide . the surgeon may monitor the progress of the wire 48 with lateral x - ray imaging . at any point during the insertion of the wire 48 , the current depth of the wire is indicated on the scale 44 . the surgeon stops drilling when the tip 50 of wire 48 reaches the appropriate depth within the bone 56 . this is usually when the wire 48 reaches the distal bone - cortex 66 , which is visible under lateral imaging . the surgeon may read the indicated depth at this point . otherwise , the surgeon may read the depth after detaching the drill 60 and removing the drilling guide , provided that a mechanism retains the sleeve 10 and the plunger 30 in relative stasis , as does the frictional association between the plunger fingers 38 and the inner wall of sleeve 10 . as a result of its construction , during insertion , the drilling guide provides simultaneous support for the guide wire 48 , implantation depth indication , and protection of surrounding tissue . certain procedures require a surgeon to use a separate , specialized drill - guide . one percutaneous procedure necessitates screwing a bullet nosed insert , called a trocar , into a drill guide , piercing the patients skin with the trocar far enough so the trocar touches bone , and unscrewing the trocar prior to drilling when the separate drill - guide is firmly seated against the skin . in an embodiment of the invention adapted for this procedure , the threaded portion 17 of the sleeve 10 is sized to screw into the separate drill guide from where the trocar was removed . in the preferred embodiment , the sleeve 10 , the plunger 30 , and the endcap 16 have round cross - sections . fig4 shows an alternative embodiment with a plunger 68 of noncircular cross - section . the square cross - section in the figure is seen from a forwardly facing view taken through endcap 70 . in this embodiment , the inner cross - section of the sleeve , hidden from view behind the endcap 70 , preferably also matches the noncircular shape of the plunger 68 . embodiments with noncircular cross - sections prevent relative rotation between the plunger 68 and the sleeve 10 . because the plunger 68 is not round , the endcap 70 is preferably fixed to the sleeve in a manner different from screwing a threaded endcap onto a threaded sleeve , as is preferred in embodiments of circular cross - section . the endcap 70 can be secured to the sleeve by bonding or with other fasteners , for instance . other noncircular embodiments , for example , have a key fixed to the sleeve or the plunger and slidably engaging a slot in the other of the two . this key in slot arrangement also limits rotation while permitting telescopic movement of the drilling guide . in another embodiment , shown in fig5 the plunger 30 is rearwardly biased , preferably by a spring 72 disposed inside the sleeve 10 that presses against a front surface of the plunger 30 . a drilling guide of this embodiment automatically extends when pressure on the platform 36 is removed . thus , if a surgeon has partially drilled a hole , but decides to realign it , the drilling guide will still indicate the current depth of the tool 48 while the surgeon partially or wholly retracts the tool from the bone 56 . this feature is especially useful when larger drill bits are used . in embodiments comprising a sleeve and a plunger , the sleeve need not be at the front of the drilling guide . further embodiments may place the plunger at the front , to abut the bone , and the sleeve at the rear , to abut the drill . still further embodiments may have a workpiece - abutment member and a chuck - abutment member with different shapes and mechanisms than those of the sleeves and plungers described . also , as stated above , the invention may be tailored to accept other drilling tools including other types of guide wires , kirschner wires , pins , and drill bits , and the tip 20 may be adapted to abut other types of workpieces such as skin .
a surgical drilling guide for guiding a drilling tool , measuring its penetration depth , and protecting surrounding tissue . the guide has a sleeve and a plunger that telescopes within the sleeve . the plunger and the sleeve have axial bores adapted to slidably receive a portion of the tool that protrudes beyond a drill chuck . the extended length of the drilling guide is substantially as long as the length of the protruding portion of the tool , and a maximum extended length of the guide is preferably as long as the protruding portion . as the tool in drilled into a workpiece , the chuck collapses the drilling guide . gradations on the side of the guide indicate workpiece - penetration depth .