Field of the Invention This invention relates generally to orthoped surgical devices and in particular, to fixation screws f stabilizing fractured bones.

Background of the Invention

Over the years various devices and methods have be developed for attending to fractured bones in an effort achieve an effective healing of the fracture. The probl is ensuring that the splintered bone segments are "fixe in a sufficiently secure position to prevent slippage separation of the fractured segments during the heali process. The most common means for securing fractures an external fixation device which extends into or throu the bone fragments substantially orthogonal to the plane the fracture. The fixation device is preferably direct inwardly into the fractured bone so as to pierce the out cortex of the fractured bone, cross the medullary cana and imbed its point in the opposite cortex. While su devices were historically used to temporarily stabilize t bone in preparation for a more permanent device, orthoped physicians subsequently found these pins to be just effective for stabilizing the bone during the enti healing process. Since then, these fixation devices ha found general acceptance and are now widely used througho the world.

Early fixation pins were configured with smoot cylindrical shafts which were passed through pre-drill holes. As these early pins had no threads about the shafts, the pins did not utilize a threaded engagement the bone fragments. Rather, the pin was snugly fit with the pre-drilled hole merely to minimize slippage separation. More contemporary fixation pins have employ a plurality of threads secured about a smooth, cylindric shaft in order to improve upon the "fixed" nature of t

pin within the fractured bone. Many were configured wi self-tapping threads, thereby eliminating the need to tap hole in the bone first. After a hole was drilled, t fixation pins were advanced into the hole, simultaneous tapping the sides thereof.

More modern fixation pins further improve upon t fixation process by eliminating the need to pre-drill fixation hole in the bone. These pins consist of slender configured metal shafts which have a set of drilling tee at a first end and a recess at the other end for receivi an operating tool. The tool assists in rotating the p within the bone in order to advance or retract the p therein. Many fixation pins of this type incorporate pointed spade configuration at the drilling end wherein o or more obtuse, wedge-shaped, spade surfaces are position on opposite sides of a longitudinal axis with knife edg to scrape away the bone when the pin is turned. Thes fixation pins also employ self-tapping threads positione along the shaft proximate to the sloping surfaces of th drilling teeth and extend for a distance sufficient to fi the bone on"opposite sides of the fracture.

Despite the improvement over earlier devices, ther are some disadvantages inherent with some of the self drilling, self-tapping fixation pins presently available First of all, it is difficult to construct drilling teet out of suitably acceptable materials wherein the drillin teeth are sufficiently sharp to maintain the necessary pi advancement rate required by the self-tapping threads. A ineffectively slower advancement rate is achieved wit simultaneous drilling of the bone hole in contrast to tha achieved if a self-tapping pin were advanced in a pre drilled hole. As a result, the threads tapped into th bore created by the drilling teeth are partially strippe away due to the slower advancement rate. To avoid thi problem, some orthopedic surgeons, in treating a fracture bone, use only a self-tapping fixation screw and therefor

pre-drill a bore into the bone. Following the creation o an acceptable bore, the orthopedid surgeon directs th fixation screw through the bone cortex on one side of th marrow, through the marrow, and then into the bore create in the bone cortex on the other side of the marrow.

A second problem develops with such slow advancemen rates - that of excessively high temperatures resultin from the frictional engagement of the pin with the bone a the fixation pin is inserted. Often a portion of bon tissue, local to the bore, is exposed to excessive heat Since bone cells are highly vulnerable to severe hea buildup and have been shown to die at temperatures as lo as 105°F, the use of self-drilling fixation pins sometime results in a small region of dead bone tissue surroundin the pin, sometimes causing the pin to become unsecured. I such events, it is necessary for the stabilization proces to be repeated to the discomfort and inconvenience of th patient.

While pre-drilling the fixation holes generall overcomes this problem, it results in a more time consumin surgical procedure. Not only is the additional pre drilling step involved, but since the orthopedic surgeon i unable to see the interior portions of the pre-drilled hol after the drill bit is removed, the manner in which th fixation screw is advanced occurs solely by feel. Th interior surfaces of the bone table, adjacent the marrow are of a generally porous nature, making it difficult t slide a sharp point over the porous surface. Suc circumstances further complicate the use of a self-tappin fixation pin not employing self-drilling means.

Recently there have been developed other variations o fixation pins, such as the cannulated fixation scre disclosed in U.S. Patent No. 4,537,185 to Stednitz ("th '185 patent") . The fixation device disclosed in the '18 patent is a self-tapping, self-drilling, orthopedi fixation screw for use with a guide pin. The manner i

which the cannulated fixation screw is used is significa because of its ability to overcome previous difficulties accurately directing a fixation screw into a predetermin location. The conventional guide pin, having a relative long thin shaft with threads and drilling teeth at one en is first directed into the fractured bone so as penetrate two or more of the fractured segments whi maintaining a certain length of shaft outside the bon The cannulated fixation screw includes an axial openi extending the entire length therethrough, wherein t opening has a diameter slightly larger than the diameter o the shaft of the guide pin. With such an arrangement, th fixation screw can be placed over the protruding end of th guide pin and rotated, by way of a separate advancing tool into the bone area surrounding the guide pin. The drillin teeth on the fixation screw provide an opening large enoug for the fixation screw to advance when the screw i rotated.

The cannulated fixation screw of the '185 paten further consists of a shaft having a plurality of straigh axial flutes defining one side face of several drillin teeth, positioned at the forward end of the screw, and als the cutting face of the self-tapping threads is dispose proximal to the drilling teeth. The flutes consist of tw perpendicular surfaces, a first surface being aligne coplanar with a diameter of the shaft. Separating th flutes are a plurality of lands defined by decreasin height threads which assist in exposing the first flut surface in order to provide a self-tapping surface. A with most conventional self-tapping screws, the fixatio screw of the '185 patent includes a lead angle o incomplete thread heights, formed adjacent the drilling en of the screw, which provide a gradual increase in th height of the threads carved out in the bone up to th maximum thread height.

The device of the '185 patent is somewhat limited b

itε positioning of the cutting edge of the flutes coplanar alignment with the diameter of the shaft. Such configuration creates a neutral rake angle for tapping t hole through which the screw is directed. Neutral ra angles sometimes result in less accurately develop threads in the side walls of the bone while requiri greater force in advancing the fixation screw.

Another problem with cannulated fixation screws, su as that disclosed in the '185 patent, is the disposal bone chips developed adjacent the drilling teeth. Whi theoretically the chips are removed from the bone directing the chips outwardly through the flutes and t threads, as a practical matter, not all are removed. So remain at the end of the bore during advancement of t fixation screw due to clogging of the flutes or thread thereby impairing the drilling process.

Still another problem exists with the current fixati screws, wherein the self-tapping threads are position immediately adjacent the drilling teeth. The absence of transition zone between the two features increases t likelihood "of excessive heat build-up by precluding t ability of the surrounding bone to momentarily cool aft being drilled before the self-tapping operation begin Furthermore, the employment of self-tapping screws about constant minimum diameter further increases heat build- by making it more difficult to advance the fixation screw

It would therefore be a novel improvement to provide fixation device having self-tapping threads defined by cutting face with positive rake angles in order to increa its effectiveness. It would be another improvement ov the prior art to provide for tapered threads along portion of the self-tapping threads to assist in t advancement process and contribute to the reduction of he build-up. In addition, it would be a novel improvement provide a means for more effectively removing bone chi away from the drilling end of the fixation screw in ord

to improve the drilling process. Furthermore, it would a significant improvement over the prior art to provide fixation screw which employs a transition zone between t drilling teeth and the self-tapping threads in order further reduce the build-up of heat in the fractured bon Finally, it would be a significant improvement to provi other means incorporated within the fixation screw reduce heat buildup and thereby minimize bone cel destruction during the fixation process. -.nfflTnarY of the Invention

The present invention provides a system fo penetrating fractured bones for the purposes of mor effectively stabilizing the fractured segments an enhancing the healing process. The present system include a fixation device which is configured to more effectivel pierce the outer cortex of a fractured bone, cross th medullary canal, and imbed its point in the opposit cortex, in conjunction with an improved guide pin. Th present system also includes a guide pin having a partiall non-circular configuration which, when used in conjunctio with the fixation device, permits the effective passage o bone chips through an interior portion of the fixatio device.

The fixation device of the present system comprises metal cannula defined by a hollow cylindrical shaft havin a drilling means at one end, an operating tool receivin means at the other end and a plurality of thread therebetween. One preferred embodiment of the cannula i advantageously constructed of titanium, although othe materials are contemplated. Titanium is readily acceptabl by body tissue as it is sufficiently porous about it exterior surface to permit bone growth to extend into th surface, thereby providing a more effective stabilizatio system. The drilling portion of the cannula comprises one o more drilling teeth, each having cutting surface

positioned obliquely with first and second directions in diametric plane extending axially through the cannul Positioned distally from the drilling portion, t receiving portion consists of a polygonally-sided rece aligned concentrically with the hollow portion of t cannula. The receiving portion is configured so as accept an operating tool which can be used to rotate t cannula, thereby advancing or withdrawing the cannu within the fractured bone. Intermediate the drilling portion and the receivi portion is the main body of the shaft characterized fir by a featureless length of cylindrical shaft and second a plurality of self-tapping threads. Intersecting portion of the threads is at least one flute which defined by two substantially orthogonal surfaces. T flute is advantageously provided with an elongate sl which penetrates the wall of the cannula so as to provi fluid communication between the flute and the interi hollow portion of the cannula. In one preferred embodiment, the threads a configured ^" with a non-circular circumference so that minimum area of contact is maintained between the threa and bone as the cannula is rotated within the bone. eliminating a circular surface normally associated wi prior art devices, the build-up of heat in bone significantly reduced. In another preferred embodiment, transition zone is provided between the drilling porti and the beginning of the threads which permits the bone momentarily cool between the drilling and tapping actio In still another embodiment, a portion of the threads a tapered so as to provide a more gradual development threads, thereby reducing the force necessary to advan the cannula and further reducing heat build-up.

The flute comprises a cutting surface and a tangenti surface positioned substantially orthogonal to the cutti surface, although more acute angles are contemplated.

one preferred embodiment the cutting surface is position obliquely with the diametric plane such that a positi rake angle is formed which improves upon the cutting acti of the self-tapping threads. The elongate slot positioned along a portion of the tangential surface. Wi such an arrangement, the bone chips generated by t rotating self-tapping threads may be passed through t slot and into the interior hollow portion of the cannula.

The present system also includes an improved guide pi consisting of an elongate solid shaft, having one or mor drilling teeth and self-tapping threads at a first end, an a cross-section partially defined by a non-circula circumference. The guide pin is provided with a non circular surface which, together which the interior hollo portion of the cannula, define a pathway through which bon chips may easily pass. Such an arrangement mor effectively disposes of the bone chips and reduces th accumulation thereof about the threads of the cannula.

With the present system, the bone stabilizing proces is advantageously improved by providing a cannula and guid pin which cooperate to reduce the build-up of heat to th bone and, consequently, the amount of bone cells destroyed thereby improving upon the "fixed" nature of the system In addition, the force necessary to advance the cannula i reduced due to the effective disposal of bone chips and th improved configuration of the drilling teeth and the self tapping threads. Finally, the present system i advantageously constructed of titanium or like metal whic develops a more secure engagement and acceptance of th cannula in the bone by permitting bone growth directl into the surface of the cannula. Other advantages of th present system may be appreciated by reference to th attached drawings and the detailed description below. Brief Description of the Drawings Figure 1 is a perspective view of one preferre embodiment of the invention showing a first preferre

fixation device and a guide pin, wherein the fixati device is a cannula.

Figure 2 is a side elevation view of the fir preferred cannula of Figure 1. Figure 3 is a cross-sectional end view of the fir preferred cannula taken along line 3-3 of Figure 2, showi the polygonal circumference and the flute.

Figure 4 is an enlarged segmented view of the cannu of Figure 2 illustrating the two ends of the cannula. Figure 5 is a first end view of the cannula tak along line 5-5 of Figure 4.

Figure 6 is a second end view of the cannula tak along line 6-6 of Figure 4.

Figure 7 is an enlarged perspective view of the tip the first preferred cannula illustrating the drilling tee and the beginning portions of the self-tapping threads.

Figure 8 is an enlarged perspective view of one of t drilling teeth of Figure 7.

Figure 9 is a segmented side view of the guide pin. Figure 10 is a cross-sectional view of the fixati system taken along line 10-10 of Figure 1, showing t guide pin shaft and the first preferred cannula cooperation.

Figure 11 is a perspective view of the seco preferred fixation device, wherein the fixation device is partial cannula.

Figure 12 is a elevational view of the partial cannu of Figure 11, shown partially in cross-section.

Figure 13 is an elevational view of the parti cannula of Figure 11 but illustrated at a 90° orientati therefrom, shown partially in cross-section.

Detailed Description

Reference is now made to the accompanying drawin wherein like elements are referred to with like numeral Referring now to Figure 1, the present invention is system 10 for stabilizing fractured bones which consists

a guide pin 12 and a cannula 14. Initially it i noteworthy that while the following description is directe to use of the present system 10 in bone reparatio procedures, it is contemplated that it may be used in othe circumstances requiring the fastening of discreet elements The guide pin 12 of the present invention 10 i defined by an elongate shaft 16 provided with a pluralit of threads 17 and a drilling means 18 positioned at forward end thereof for drilling a guide hole into fractured bone in a predetermined location. The guide pi 12 will be described more fully below in association wit Figure 7.

The cannula 14 is defined by an elongate cylindrica shaft having an axial aperture (not shown) extendin therethrough. One preferred embodiment of the cannula 1 is constructed of titanium due to its acceptability to bod tissue. With long term uses, a titanium cannula provide for more effective fixation. However, where temporary use are contemplated, other cannula materials such as stainles steel are employed. In still other embodiments, a titaniu nitrate coating is provided about the exterior surface o the cannula to further enhance the durability of th fixation device.

As shown in Figure 1, the guide pin 12 is configure to slidably receive the cannula 14 about its shaft 18. While the preferred embodiment of the cannula 14 i intended for use with a guide pin 12 for stabilizin fractured bones, similar embodiments of the cannula may b used in other applications requiring improved self-tappin and self-drilling means alone or in conjunction with other components.

As shown in Figure 2, the cannula 14 comprises a drilling means 22 positioned at a forward end thereof, a self-tapping threading means 24, positioned adjacent the drilling means 22, and a receiving means 26, positioned distally from the drilling means 22, for receiving an

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operating tool (not shown) . The operating tool is used advance or withdraw the cannula 14 within a fractured bon Intersecting the self-tapping threading means 24 preferably a single flute 28 extending from a first poi on the cannula, proximate the drilling means 22, to generally featureless mid-portion 30 of the cannula 1 Disposed within a portion of the flute 28 is an elonga slot 32 penetrating the outer wall of the cannula 14 a providing fluid communication between the exterior of t cannula 14 and the interior of the cannula 14, as discuss further below. Separating the drilling means 22 from t self-tapping threading means 24 is a transition zone defined by a tapered section of the cylindrical shaft.

Referring now to Figure 3, a cross-sectional view the cannula 14, taken about a mid-portion of the sel tapping threading means 24, can be seen. Longitudinal traversing the entire cannula 14 is an axial aperture defined by a cylindrical interior surface 41 of the cannu 14. As indicated above, the axial aperture 40 is in flu communication with the exterior of the cannula 14 throu the elongate slot 32 disposed within the flute 28, as we as through opposite ends of the cannula 14.

In one preferred embodiment, a circumferential surfa C of the self-tapping threaded means 24 is defined by non-circular contour which, in the preferred embodimen comprises a plurality of contiguous planar surfaces 46 form a hexagonal contour. By providing a non-circul circumference, the present invention eliminat substantially 360" contact of the cannula 14 to the bo thereby reducing the build-up of heat normally associat with the circular circumferences of the prior art device Advantageously, with the present invention, bone contact maintained only with axial intersections 48 of t contiguous planar surfaces 46. It is contemplated th other embodiments of the cannula 14 will have oth polygonally-shaped circumferences, such as pentagons

octagons, etc.

As viewed in Figure 3 , the cross-section configuration of the cannula 14 is further defined by t flute 28 which axially intersects the self-tappi threading means 24. In the preferred embodiment, the flu 28 comprises two abutting surfaces, the first surface bei a cutting surface 50 and the second surface being tangential surface 52 positioned substantially orthogon to the cutting surface 50. The elongate slot 32 disposed within the tangential surface 52 and is position such that a side wall 53 thereof is aligned coplanar wi the cutting surface 50. The flute 28 functions to perm the rearward passage of bone chips, generated by t tapping action of the advancing cannula 14, away from t threading means (not shown) . As such, the bone chips ar directed through the elongate slot 32 and into the axia aperture 40. As the cannula 14 is rotatingly advance further into the bone, the bone chips directed into th axial aperture are forced out through the receiving mean and away from the fractured bone in a manner described mor fully below ^" .

The cutting surface 50 of the flute 28 provides means for tapping threads into the opening created in th bone by the advancing cannula 14. As shown in Figure 3 one preferred embodiment of the cutting surface 50 i positioned parallel with a first diametric plane P extending substantially orthogonal to the tangentia surface 52. The cutting surface 50 is also positione oblique to a second diametric plane P' extending through a outer edge 54 of the cutting surface 50. A positive rak angle 55 is thereby defined by the intersection of th cutting surface 50 with the second diametric plane P'. I is worth noting that a positive rake angle advantageousl improves the effectiveness of the tapping action b reducing the blunt effects of a cutting surface positione at a neutral rake angle, i.e., where a cutting surface i

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aligned with the second diametric plane P' . However, it contemplated that a neutral rake angle or even a negati rake angle can be used if desired. In one preferr embodiment, the positive rake angle 55 is about 6-10 although any positive angle will be effective.

Referring now to Figure 4, other significant aspec of the present invention may be described. There it may seen that the receiving means 26, positioned at t rearward end of the cannula 14, comprises a recess disposed within an enlarged collar 58 integral with t mid-portion 30 of the cannula 14. The recess 56 is align concentrically with the axial aperture 40 extendi therethrough as shown more clearly in Figure 5. The rece 56 is configured to receive a compatibly-configur operating tool required to advance and withdraw the cannu 14 from a fractured bone. In one preferred embodiment, t recess 56 has a hexagonal perimeter which accepts operating tool similarly having a hexagonal perimeter.

Referring back to Figure 4, it can be seen that t drilling means 22 is positioned at the forward end of t cannula 14 ^" and preferably comprises one or more drilli teeth 60 each having a planar cutting face 62 defined by forward cutting edge 63 and an outer cutting edge 64. Figure 4, it is illustrated that the outer cutting edge is positioned oblique to a longitudinal axis extendi through the cannula 14. With this oblique arrangemen positive cutting action is achieved, similar to th achieved by the cutting surface 50 of the flute 2 whereby a cutting edge is presented rather than a cutti face. However, where neutral or negative cutting action desired, the cutting face 62 may be position alternatively. When the cannula 14 is rotatingly advanc forward, bone chips are generated by the drilling actio These bone chips are directed into the axial aperture and are directed out of the recess 56. With such arrangement, the amount of bone chips which accumula

adjacent to the drilling means 22 is significantly reduce thereby facilitating the drilling process and furth reducing the build-up of heat to the bone.

Rearwardly adjacent the drilling means 22 is t transition zone 34 which effectuates a reduction potential heat buildup by separating the drilling operati from the tapping operation. The transition zone 34 essentially featureless and is defined by a short taper section of cylindrical shaft. During surgical advanceme of the cannula 14 within a fractured bone, the transiti zone 34 provides an opportunity for the adjacent bone momentarily cool following drilling action and precedi tapping action. It is to be noted that other embodimen having no transition zone 34 are contemplated where it not necessary to reduce local heat build-up.

Continuing axially along the cannula 14, the sel taping threading means 24 is shown comprising a plurali of helical threads 65 having thread heights H and a minim diameter D coincidental with the outer diameter of t featureless mid-portion 30. At a first forward portion the threading means 24 are a plurality of lead-in threa 66 defined by rearwardly-increasing thread heights developed at a lead angle 68. The lead-in threads 6 provide gradual tapping of the bone opening created by th drilling teeth 60 as the cannula 14 is advanced into th bone. In one preferred embodiment, the lead angle 68 i 15°, but other angles are contemplated.

In one preferred embodiment, a second forward portio of the self-tapping threading means 24 is defined by plurality of tapered threads 72 having a taper angle 73 wherein the tapered threads 72 are defined by a rearwardly increasing minimum diameter D' extending from th transition zone 34. In one preferred embodiment, the tape angle 73 is 2°, but other angles are contemplated. In th preferred embodiment, one or more of the lead-in threads 6 have tapered characteristics reflective of the tapere

threads 72. The remaining threads 65 of the threadi means 24 (those not tapered) are characterized by constant minimum thread diameter D. The incorporation the transition zone 34 and the tapered threads 72 on o preferred embodiment of the cannula 14 provides for significant reduction in heat build-up local to the cannu 14.

Intersecting the self-tapping threading means 24 the flute 28 defined in Figure 4 by the cutting surface and the tangential surface 52. Traversing a portion of t flute 28 is the elongate slot 32 disposed within t tangential surface 52 and extending inwardly toward t axial opening 40. As indicated above, the bone chi generated by the self-tapping threads 65 are direct rearwardly along the flute 28 and through the elongate sl 32 into the axial aperture 40. The bone chips then ex the recess 56 and away from the cannula 14. With such arrangement, the amount of bone chips which accumula between individual threads is significantly reduce thereby facilitating the tapping process and furth reducing the build-up of heat to the bone.

Referring now to Figures 5 and 6, further details the drilling teeth 60 may be more fully appreciated. Whi one or more drilling teeth 60 are contemplated, in t preferred embodiment the cannula 14 is provided with thr drilling teeth 60 spaced radially at substantially equ distances apart. As indicated above, the cutting face of each drilling tooth comprises two cutting edges, t forward cutting edge 63 and the outer cutting edge 6 wherein the outer cutting edge 64 is positioned oblique the longitudinal axis. In Figure 6, it can be seen th the forward cutting edge 63 is also positioned oblique with a third diametric plane P" passing through the seco cutting edge 64. It is therefore intended that the cutti face 62 be preferably positioned oblique to the thi diametric plane P" in two directions, thereby presenting

sharper cutting surface and eliminating the blunt effec of a cutting surface otherwise aligned coplanar with P ^, .

A noteworthy aspect of the present fixation system is that the maximum thread heights of all threads 6 whether tapered or not, are constant about a sing revolution. In other words, a single thread has constant maximum thread height between the cutting surfa 50 of the flute 28 and the tangential surface 52 thereo as shown in Figure 6. The increase in thread height H' the lead in threads 66 occurs incrementally wherein increase takes place in successive threads only at t cutting surface 50 of the flute 28.

In Figure 7, it can be seen that the circumference the drilling means 22 comprises a circumferential surfa C. Each drilling tooth 60 is therefore defined intersection of the cutting face 62, the circumferenti surface C , the interior surface 41 of the axial apertu

40 and an inclined contact surface 80. The intersection the inclined contact surface 80 with the cutting face 6 defines the forward cutting edge 63 while the intersectio of the circumferential surface C and the cutting face 6 defines the outer cutting edge 64 (shown more clearly i

Figure 8) . It is important to note that the drilling teet

60 are defined by surfaces other than the cutting surfac 50 of the flute 28. As such, the drilling teeth are space radially about the cannula 14 so as to be out of alignmen with the cutting surface 50, thereby reducing local stres to the cannula 14.

Still referring to Figure 7, the transition zone 3 separates an initial section 82 of lead-in threads 66 at a axial distance 84 from the drilling teeth 60. It i readily apparent that the lead-in threads 66 hav incomplete thread heights with frusto-conical contours thereby providing a gradually increasing height of th tapped threads in the bone.

Referring now to Figure 9, the details of the guid

pin 12 may be more fully appreciated. The guide pin comprises the shaft 16 having the threads 17 and drilling means 18 positioned at a forward end thereof. guide pin drilling means 18 comprises preferably one more drilling teeth 90 each having a cutting edge 92 having configurations similar to those integral w conventional guide pins in the field of orthope medicine.

Adjacent the drilling teeth 90 are the self-tapp threads 17 followed by a forward section 94 of the shaft defined by a cylindrical configuration to support the se tapping threads 17. Rearwardly adjacent the forward sh section 94 is a central section 96 of the shaft 16 defi by a non-circular cross-section. As illustrated in Fig 10, the central section 96 of one preferred embodiment the guide pin 12 has a triangular cross-section consist of three intersecting planar surfaces 98. It will appreciated that an interior passageway 100 is defined the exterior surface of the guide pin shaft 96 and interior surface 41 of the axial aperture 40 of the cann 14. As described above, the bone chips generated dur the drilling and tapping operations are directed thro the axial aperture 40 along the passageway 100 outwardly away from the cannula 14. Specifically, the b chips generated by the drilling action are immediat directed into the axial aperture 40 adjacent the drill means 22. The bone chips generated by the tapping act are directed into the elongate slot 32 (shown in Figure of the flute 28 and then further directed into the ax aperture 40. It is to be noted that the guide pin cent shaft section 96 may be configured with any non-circu circumference so as to provide a passageway adjac thereby. For instance the central shaft section 96 may polygonally shaped or elliptically shaped. Having described in detail the guide pine 12 and cannula 14, the manner in which they cooperate in

present system 10 may be discussed. Referring back Figure 1, use of the system 10 preferably includes t steps of inserting the guide pin 12 in a designat location within a fractured bone so that an end portion 1 of the shaft 12 protrudes from the bone. The guide pin preferably directed sufficiently into the bone so that portion of the shaft 12 extends inwardly beyond t fracture. The cannula 14 is then placed over the e portion 102 of the guide pin and advanced into the bone using an operating tool which also slips over the end o the guide pin 12 and engages the rearward end of th cannula 14. By rotating the cannula 14 in a preferabl clockwise direction, the drilling means 22 of the cannul 14 creates an opening in the bone concentric with the guid pin 12. The cannula 14 is advanced at least until th drilling means 22 engage a portion of the bone entirel inward of the fracture. The cannula 14 is further advance until the bulbous receiving means 26 tightly engages a exterior surface of the bone, thereby drawing the fracture bone segments together. After the cannula 14 is advance sufficiently so as to stabilize the fractured bone t assist bone healing, the guide pin 12 is withdrawn leavin the cannula 14 remaining in place. Depending on the need of the practitioner, the cannula 14 may be maintaine permanently or temporarily in place within the bone.

It is also contemplated that the cannula 14 of th present invention may be used without a guide pin 12. I those instances, the cannula 14 is placed at a designate location on the bone and rotatingly advanced using th operating tool so that the drilling means 22 creates a hol in the bone while the threading means taps a plurality o threads in the hole. The bone chips generated by th drilling action are directed into the interior axia opening 40, as described above. It may be necessary, wher a guide pin is not used, to provide a starter hole in th bone before inserting the cannula 14 therein. The starte

hole will then act as a guide for the accurate advanceme of the cannula 14.

Referring now to Figures 11-13, a second preferr embodiment of the present invention may be described. Figure 11, it can be seen that the second preferr fixation device is defined by a partial cannula 1 comprising an elongate cylindrical shaft having a drilli means 122 at a first end, self-tapping threading means 1 adjacent the drilling means 122 and a receiving means 1 at a second end thereof. Intersecting the self-tappi threading means 124 is at least one flute 128 extendi from a point adjacent the drilling means 122 to a mi portion 130 of the cannula 114, wherein the flu incorporates an elongate slot 132 therein. In Figure 12 it can be seen that the flute 1 comprises two abutting surfaces positioned substantial orthogonally with each other; the first being a cutti surface 150 for the self-tapping threading means 124. T other surface is a tangential surface 152 having the sl 132 disposed therein. The mid-portion 130 of the cannu 114 is defined by an essentially featureless ^~ section cylindrical shaft. Separating the drilling means 122 fr the threading means 124 in one preferred embodiment is transition zone 134 defined similarly by an essential featureless section of cylindrical shaft.

The drilling means 122 of the second preferred cannu 114 comprises one or more drilling teeth 160 which a configured similarly to the drilling teeth presently fou on conventional self-drilling devices commonly available the art. An example is the drilling teeth of the gui pin described above (see the text in association wi Figure 9) . However, it will be appreciated from Figure that the configurations of the threading means 124, t receiving means 126 and the flute 128 are preferab identical with the analogous components on the fir preferred cannula 14 (see Figures 2-8) .

It is important to note that the flute 128 does n extend forward into the drilling means 122, but terminat proximate to the forward end of the threading means 12 As such, the drilling teeth 160 are not formed by a surface of the flute 128. Furthermore, because t threading means 124 is configured identically with t threading means of the first preferred embodiment, t circumference of the threads in the second preferr embodiment have a non-circular contour and have consta maximum thread heights throughout each 360* revolution thread.

Referring now to Figure 13, it may be appreciated tha the partial cannula 114 has a different interio configuration than the cannula 14 of the first preferre fixation device. Extending axially through a portion o the partial cannula 114 is an axial aperture 140 whic extends from a point adjacent the forward end of th threading means 124 to the receiving means 126. I contrast to the first preferred cannula 14, the axia aperture 140 of the partial cannula 114 does not exten through the drilling means 122. As such, the drillin teeth 160 are configured differently from the firs preferred cannula 14 because they are not partially forme by an interior surface of an axial opening (see the abov text in association with Figure 7) . In addition, th partial cannula 114 cannot be used with a guide pin, bu rather is used independently in orthopedic surgica procedures for the treatment of bone fractures.

When bone chips are generated by radial advancement o the second preferred cannula 114 into a working material they are disposed of by guiding them along the flute 128 through the slot 132 and into the axial aperture 140 fo transmission out of the receiving means. The partia cannula 114 has the advantage of offering a fixatio device which is used independent of a guide pin that stil provides more effective disposal of bone chips than th

present self-drilling screws found in the art. addition, heat build-up is significantly reduced providing non-circular circumferences, tapered threads a a transition zone, as more fully described above association with the first preferred cannula 14. It also important to note that the present invention shou not be limited to bone reparation procedures but may utilized in other circumstances where it is desired fasten segmented elements. The present invention may be embodied in oth specific forms without departing from its spirit essential characteristics. The described embodiment is be considered, in all respects, only as illustrative a not restrictive, and the scope of the invention i therefore, indicated by the appended claims rather than the foregoing description. All changes which come with the meaning and range of equivalency of the claims are be embraced within their scope.