CA2696138A1 - Highly-versatile variable-angle bone plate system - Google Patents

Abstract

A bone plate system for internal fixation of bone fractures includes a bone plate having a plurality of bone plate holes. The holes are constructed to receive either a non?locking, locking, or variable angle locking bone screw. The holes have discrete columns of thread segments arranged around the inner surface of the hole for engaging threads on the heads of locking and variable angle locking bone screws. Conventional locking bone screws engage the bone plate coaxially with the central axis of the bone plate hole. Variable angle locking bone screws can engage the bone plate at a selectable angle within a range of angles relative to the bone plate. The head of the variable angle locking screw is at least partially spherical, and the thread thereon has a profile that follows the arc-shaped radius of curvature of the spherical portion of the screw head.

Description

HIGHLY-VERSATILE VARIABLE-ANGLE
BONE PLATE SYSTEM
C'ross Reference To Related Applications [00011 This clainis the benetit of U. S. Provisional Application N'o.
60!95_5,ti06, filed August 1'), 1-007, and is a continuation-in-part of pending U.S. Patent Ap'plication No. 10/763,689, filed Januai-y 26, 2004. The entire contents of botli applications are expressly incorporated liereiii by reference thereto.

Field of the Invention 100021 The invention relates to a bone plate system for intei-tial botie fraeture fixatioii.
More particularly, the invention relates to a bone plate system that includes bone plates having bone plate holes constructed to receive non-locking, locking, or variable-angle locking bone screws.

Backcuound of the Ii,avention [00031 Bone plate systenis for the internal fixation of bone fractures are well known.

Conventional bone plate s-vstenls are particularly well-suited to promote the healin, of a fracture. A bone screw (also known as a bone anchor) is insci-ted tlu=oLigh a bone plate hole (also kiiown as an anchor hole) and is thi=e.aded into bone to cotnpress.
neutratize, buttress, tension bend, and/or bridge the fracture ends toLether and dravv the boneagainst the plate.

These screws, which at=e not secured to the bone plate (and are hereinafter referred to as "non-locking screws"). can be threaded into bone at various angles relative to the botle plate, Howevcr, because the screws are not secured to the bone plate, the angular relationships betwe.en the plate and screws are not fixed and can change intraoperatively and%or postoperatively. That is, dynamic loading on the bone anci bone plate from physiological conditions can c-ause the screws to loosetl or back out with respect to the plate. Tl1is can lead to poor aligtuiient and poor clinical results. ~

[0004] Scc,urtng the screws to the plate provides a fixed an~ular relationship between the screws and plate and reduces the incidence of loosening. (_)ne kno -Ii embodiment oF
screws that can be secured to the bone plate has a screw tluead on an outer surface of the screwhead. The thread on the screwhead mates with a corresponding thread on the ituier surfaee of a bone plate hole to lock the sc.rew to the plate. These sere~,vs'{which are hereinafter referred to as "loc);.ing sc.re~vs") are typically insel-teci coaxiafly with the central axis of the hole. Because the relationship betwecn locking screws atid the plate is fixed, locl:inc, screNvs provide high resistance to shear, torsional, and bending forces. However, locl:ing screws are litnited in their ability to compress bone fragments, which affects liealin(y.
[0005] In stun, therefore, an illterfzice formed by a locking sereNvand bone plate has hi.gh resistance to shear forces so as to niaintain stability at the screw/plate intei-face, but has limited ability to compress bone fragtnents, while an interface fornied by a non-loc.kina bone screw and bone plate effectivelv compresses bone fragments, but has lo~i resistance to shear forces that can lead to screws loosening or backina, out. Accordingly, a hone plate systeni that combines non-lockino screws NG-ith lockinL, screws is desirable in niany clinical sttUatlOns.

-[00061 A known bone plate systenl that can accotluliodate both loeking and non-locking screws includes a bone plate having a plurality of threaded lilate holes for receiving locking screws and a plurality of tion-tlu=eaded plate lioles for receiving noii-locking screws. However, the non-lockin, screws in this known systeni are only used temporarily to keep the plate in plaee while- the locking screws are insei-ted. The non-loc.king screws are renloved after the locking screws have been inserted. Thus, the long term benefits of conibining non-loc.king screws with locking screws are not obtained. 0007 another lulo~~~n bone system that acconiniociates bot [--~ ] plate h types of screws includes a bone plate with partially threaded plate holes. The partially tlu-eaded holes receive either lockinc, or iion-locking screws. Because the plate holes are only partially tlireaded.
however, locl:ing screws may not be able to maintain the fixed angular relationship between the sc.reN.\-s and plate while under pllysiological loads. Specifically, the locking serews within the plate are only partially surrounded by tlireads and thus only partially secured. Uiider high sti=ess and loading conditions, the locking plate hole may distort and allo~N;
the fixed angular relationship between the locking screw azid plate to c.hange. This caii resLdt in a loss of fixatioti or plate orientation. Additionally, because of the plate hole cleonietry. translation of the plate with non-locking screws is limited to one direction only. This inav be disadvanta~?eous in l.ione fracttu-e reduction and inanipulation.

[00081 Still another known bone plate system that acconnnodates both tvpes of screws includes a bone plate with threaded ancl non-threaded plate holes .~
The tlu=eaded plate holes rec.eive lockiiig screws, and the non-threacled plate holes receive nOn-locking screws, each intended to remain inserted while the plate is implanted.
However,''because locking screws are effective only when used Nvith threaded holes, a disadvantage'of this system is that the number and location of threaded holes in the plate may not be as desired for a par-ticular suroical procedtire. For example, there may be otie or more non-tlveade~d holes at locations vvhere a surgeon would prefer a tlireaded hole for inseiiion of a locking s cre'vv.

[00091 Further to the l.noxvn bone plate systems nientioiied above, it is often desirable for a surgeon to be able to iiisert a locking bone screw through a bone plate hole at a surgeon-selected angle relative to the bone plate. A number of so-c.alled "polyaxial'' bone plate systems are l:nown. Many use a bushing located in a plate hole to lock the deoree of , _ -,--- - , -- -- - _ ~ `
screw angulation relative to the plate. In one such tivstem, the bushilic, is rotatable within the plate hole. A so-called "variable-angle locking" screw is tlu-eaded into hone through the bushing and plate hole. As the screw is tlireaded into bone, the tlu=eaded'tapered head of the screw enaages a tlu=eaded internal surface of the bushing to expand the b!ushing against the iiulcr surface or wall of the plate hole, thercby friction locking the screw at the desired angle relative to the bone plate.

[00101 In another known Polyaxial bone plate system, a bushing!is seated at a desired angle in a plate hole. A fastening screw having an expandable head with a threaded recess is insertecl tlu=ougli the bushing and threaded into bone. A locking screw is then tltreaded into the recess of the screwliead to expand the head outward against the bush~ng to lock the selected angle of the screw relative to the bone plate.

[001.] In still another known polvaxial bone plate system, an elpanclable ring is positioned in the plate hole. As a bone scre,,v -ith a tapereci liead engagzs the ring and is threaded i,nto bone, the riiig expands against the iniier surface or wall ofthe hole to lock the selected angle of the screw relative to the bone plate.

100121 However, these polyaxial bone plate systems have multiple components that can be cumbersome and tedious to manipulate durincl surgery and more harticularly, for exanlple, it is possible that the bushint; or expandable rin may pop out durinc, surgery.
[0013] In view of the foregoing, it vvould be desirable to be able to provide an improved bone plate system that overcomes the deficieiicies and disadvaiitages of known bone plate systems.

Suniniarv of the hnvention [0014] The im'ention provides a highly-versatile variable-angle lione plate systeni for fixing boiie fractures. The system includes bone plates having a pluralitv of bone plate hotes that pass completely through the bone plate. from a top surtace of the plate to a bottom bone-contactin~ surface of the plate. The holes are constructed advantabeouslv to receive ~
e.ither a non-locking, lockina, or variable-angle lockinc, bone screw. Instead of serew, threads as is known in conventional bone plate holes, the iruler surface of the pla~te lioles has discrete coluiruis of teeth or thread segments for engaging compatibly dimensioned and configured threaded lZeads of locking aild variable-angle locl:ing bone screws.

[0015] The invention advantageously peruiits conventional non-iockin, bone screws of cotnpatible size and screwllead shape to be used in the bone plate holes.
Non-locking bone screws have a tlireaded shaft for engaginu bone and a screwhead havin(y no me.ans or structures t:e.ga., tlu=cads j tllereon for sec.urino or locking to the hone plate. A non-locking screw nlav be received in the bone plate hole at anv desired angle. whereupon the shaft of the = ' screw is driven iiIto the l.ione until the head of the screw is seated as desi,red in the bone plate hole.

C00161 The invention also advantageously pernlits conventional ocking bone screws of compatible size, screwhead shape, and screwllead thread to be used in the bone plate holes. These locking bone screws have a threaded shaft for engaging boine and a screw tlu=ead on an outer surface of the screwhead that can advantageouslv engage the columns of threacl segments in the bone plate hole. Locking bone screws are received in the bone plate holes coaxial to the c.entral axis of the hole. That is, for example, if the central axis of the hole is perpendicular to the top surface of the bone plate, a locking bone~l screw is received in - - -- -_ _ _ a bone plate hole of the invention at about a 90 degree angle with respect to the top surface.
The sliaft of the lockinb screv,, is driven into bone until the screwhead eiigages the bone plate hole, whereupon the screwhead threads en~~age the coluinns oftlu=ead se! -ments in the bone plate hole. The screw is then driven until the screwhead is tlu=eaded as d~,esired iiito the bone plate hole, which fixes the screw to the plate.

[0017] A variable-angle locking bone screw according to the inv'ention is inserted tlu=ough a bone plate hole and locked to the bone plate at a selectable an2le within a ranue of selectable angles. The range of selectable angles in one e.ivbodinient for~',ms a cone of abotlt 30 degrees about the central =axis of the hole. In other ,~-ords, the angle cif the screw can vary from 0 degrees to al.iout 15 degrees in any direction away fronl the. c.zntral axis of the hole.
Variable-angle locking screws of the invention advantageouslv do not reduire a bushing, a . ~
conipression cap an evpandable ring, or an expandable head to lock the angular position of the screw relative to the bone plate.

(0O18] Variable-an~le loca:ing screws of the invention advantaQzoLisly have a head that is at least partially spherically-shape.d. The spherically-shaped portion of the head has an extertial screw thread on its outer surface. The profile of the screw tllread follows the arc-shaped (i.e., non-linear) outer radius of curvature of the spherically-shaped pot-tion. Each thread peak and each thread trouCIh (or crest and root in thread terminolo',gy, respectively) lies ~

on a respective raditis of curvature coinciding with or parallel to!concentric. with (i.e., having the saine center as) the radius of c.urvature of the spherically-shaped poi-~ion of the screwhead. In other words, the peaks may lie on a"rriajor" radius of curwature, whieh coiricicles Nvith the radius of curvature of the spherically-shaped portion.
while the troughs lie on a"nlinor" radius of curvature, wherein the mqjor and minor radiuses of curvature have the same center, thus forming concentric circles. Note that this radius of eutwature center is not necessarily the cetlter of the screNvhead. In one e.nlbodiment, the tlvead profile lias proiile lines that intersect the center of the radius of ctirvature of the screwhead.
Profile lines represent an extension of the longitudinal axis of a cuttin- bit of a thread~i c-utter as the cutting ~
bit contacts a surface in which a threact is cut, Conventional locking screwheads, in contrast, have tlu-ead peaks and troughs (viewecl in protile) that lie on respective substantially straight, parallel lines, and the profile lines of those peaks and troughs extend parallel to each otlier and do not intersect the center of the radius of curvature of the screwhead.
(except perllaps the profile line of one peak or trough that happens to be aligned with the cetiter).

[0019] To facilitate tlireaditlg into botie, each of the bone screws! mav be self-tapping and/or self-drilling. Eacli of the bone screws also may be canllular for iiisertion of a guide wire to ouide screw placement.

[00201 Bone plates of the invention are not limited to any particular shape, size, or configuration. For exatnple, in one enlbodiment, the bone plate has a lie~ad portion and a shaft portion. The head portion is configured and climensionecl to conforrn to a inetaphysis of a bone, and the shaft portion is configtued and dimensioned to conform to a diaphysis of a bone. In another exaniple embodinient, the head portion lias a curved su.rface and includes an anterior fork substantially parallel to an anterior side of the shaft port~ion and a posterior fork extending out from a posterior side of the shaft portion. In still anotlier example embodiinent, the head portion flares outurard from the shaft portion and is ctirved, tapered, and tw isted.

[00211 Bone plate holes of the invention are not linlited to any pLirticular nuliiber or ar7=angement. Optionally, bone plate holes of the invention may have elongated non-ttueaded portions toincrease the versatility of placin non-locl:in" screws. Bone plates oftlic invention mav also optionally have suture lioles and conventional thread~iect and/or ' non-tlu=e.aded screw holes, although neither type of conventional hole is iecessary nor recommended.

[0022] The invention also provides a method of bone fi=acture fiYation. The method includes positioning a bone plate against botie, selectin- a bone plate hole ior insertin, there tlixou,li a bone sc.re~v, selecting a non-locking, locking, or variable-angle lockin, bone screw, ~ ~

inserting the selected bone screw tlirouuh the selected bone plate hole and, if applicable.
,.

selecting an insertion angle 1~vith respect to the central axis of the hole, aild drivin~,= the screw into the bone until the screwhead is seateci in or secured to the boneplate hole to either compress the botie plate against the bone or fix the relationship be.tweenlthe sez=e-,v and the bone plate. The bone screws remain in the bone for substantially as lon - as the bone plate is implaiited.

Brief Description of the Drawings [0023] The above anct other advantages of the invention ~vilt be apparent upoti consideration of the following detailed description, taken in coiljunction! ~v-ith the accompanying drawings. in which like reference characters refer to like parts tlu=oughout, and in which:

[0024] FIG. 1 is ati elevational viev,7 of a conventional non-lockiiag bone screw;
[0025] FIG. 2 is an elevational vieN-v of a conventional locking bone screw;

[0026] FIGS. 3A and 'IB are elevational and cross-sectional views of the head of a conventional lockinc, bone screw:

[0027] FIG. 3C is an enlarged, partial cross-sectional view of thel loc-Icing bone screw of FIGS. 3 A and 3B;

[0028] FIG. 4A is a perspective view of a rack and pinion gear;

[0029] FIG. 4B is an elevational ti=ont view of the pinion gear of''FIG. 4A;
[0030] FIG. 4C is an enlargeil sectional vie\v of the pinion gear o~,f FIG.
=IB;

[0031] FIG. _5A is a perspective view of a variable-angle lockingscrew according to the -invention:

[0032] FIGS. 5B and tiC' are front elevational and cross-se-ctiolial!, views, respectively, of the head of the vas=iable-anule lockinc, screw of FIG. 5A;

[0033] FIG. 6 is a cross-sectional view of another embodiment of a variable-ancle locking screw according to the invention; [0034] FIG. 7 is a c.ross-sectional view of a still another embodiiiient of a variable-angle locking screwhead accordinc, to the invention;

[0035] FIG. 8 is a perspective view of a poi-tion of a bone plate \vith conventional loc.kin,. non-locking, and combination lockina/non-locking bone plate llloles;

[00361 FIGS. 9A and 9B are perspective vieNvs of an embocliine t of a bone plate hole according to the invention;

[0037] FIGS. l0A-C and 1OD-F are top, cross-sectiotial, and pe.rspective, respectively, of two similar embodinients of a bone plate hole accordingito the invention;
[0038] FIG. 11 is a cross-sectional vie,,v of a bone plate hole according to the inveiltion;

[0039] FIG. 12 is an enlarged, partial cross-sectional profile vie~N,, of a eoh.ulin of thread segnients of the bone plate hole of FIG. 11;

[0040] FIG. 1 31 is a perspective view of au einbodinlent of a bone plate system show'iiig the r~aiige of selectable aiigles of a variable-angle locl:in~,~
screw accordiiicy to the invention:

[0041] FIGS. 14A and 14B are perspective and elevational front'views, respectively, of an embodinient of a bone plate systenl showing non-lockiiig, locking.~and variable-angle locl.ing screws used with a bone plate according to the invention;

[0042] FIGS. 15A and 15B are perspective ancl clevational front views, respectively, of a non-locking sc-rew inserted through a bone plate hole accordiiig to tlle inveution;

[0043] FIGS. 16A and 17B are perspective ancl elevational front ~views, respectively, of a locking screw driven into a bone plate llole according to the invention;

[00=14] FIGS. 17A and 17B are perspective ancl elevational front views, respec-tively, of a variable-ancrle locacing screw driven into a bone plate hole according to the invention;
[0045] FIGS. 18P.,B,C -?-',A,B,C are top, cross-sectional, and perspective views, respectively. of various features of a boiie plate hole accorcling to the invention; [0046] FIGS. 24A-D are top, cross-sectional, top perspective, an,i bottom perspective views, respectively, of a bone plate hole according to the invention:

[0047] FIGS. 25A-C. 26A-C, and ?7A-D are various perspective! views of drill auides uscd with a bone plate according to the inventlon;

[0048] FIG. 28 is a perspective view of an etnbodiment of a bone plate according to the invention;

[0049] FIGS. ?9A-C are perspective, front elevational, and top vi ews, respectively, of another etnbodinient of a bone plate ac.cordinb to the invention;

[0050] FIG. 310 is a perspective view of the underside of a bone. p'late according to the invention;

[0051] FIG. i 1 is a perspective view of a botie plate applied to abone fracture according to the invention;

[0052] FIGS. 32-34 are cross-sectional views of three respective eniboditnents of a Oe locking bone screw according to the invention; and screwhead of a variable-ang [0053] FIG. 35 is an enlarced partial cross-sectional view of a sci=ewhead of a variable-angle locking bone screw according to the invention.

Detailed Description of the Invention [00541 A bone plate system accordiiig to the invention includes a bone plate, variable-angle locking screws, non-locking screws, and optionally lockilig screws. The bone plate advantageously has botic plate holes having discrete columns of tln-ead segments ~
aroUuld an inner surface of the hole. The bone plate tnay also have cotnbination bone plate holes that have a portion with columns of tlu=eaci sepments and a portiotl iwithout thread segments o,r threads. Both tvpes of bone plate holes advantageouslv are constructed to receive non-locking, locl:ing. and variable-angle locking screws. Optionally, bone plates of the invention tnay additionally have suttn=e holes, and while unnecessary!, conventional threaded holes, smooth holes (i.e., holes without thread segnlents or tlire~ads) and/or combination holes thereof.

[0055] FIG. 1 shovvs a typical non-locking bone screw 100, also known as a cortex screw. Gcnerally. anv surgical bone screw havinc.; a non-tlireaded head 102 with a generally smooth surface atld of an appropriate size and geometrv for a selected plate hole caii be used with the invention. The shapeof licad 1022 inav be, for exampte, conicallv tapered, straight-.

sided, spherical, hemispherical, etc. Non-locking screw 100 has a shaft 104 that is at least partialIy tlueailed for attacliiiieizt to boile. The leiigfh of shatt 101 aiid tlie tlii=eacl configuration (e.g., pitch, profile, etc.) of shaft tlu=ead 107 can vary depeilding on the application. As is known in the art, tip 106 and shaft threads 107 inay, be self-tapping and/or setf-clrilling to facilitate implantation into bone. Head 102 and shaft 104 may also have a cannula 108 for receiving a guide wire to aid in proper placenient. [0056]
FIG. 2 shows a typical lockinc, screw 200. Generally, any surgical bone serew having a tlireade.d head ''0? can be used witli the invention provided that~, head 202 is of an appropriate size ancl cTeometry- for a selected plate hole and that tlu=eads 2103 niate with the colunans of thre=ad segments in the plate hole. The shape of head 202 is typieally c.onically, tapered_ but also n1ay- be, for exarnple, straight-sided, Lockin- screw 200 has a shaft 204 that is at least partially ttvcaded for attacluiieiit to bone. The length of sliaft 04 and the tlu=ead configuration (e.g., pitch, profile, etc.) of shaft. thread 207 can vary deheilding on the .
application. As is known in the art, tip ?06 and shaft tlireads 207 mav be self-tapping and/or sclf-drilling to facilitate implantation into bone. Heacl 2_02 and sliaft 20~
niav also be c=aiuiular for receiving a-tiide wire to aid in proper placement.

1~

[0057] FIGS. 3A atid 3B show liead 302 of a typical loc.king sc-rew 300. The profile of tliread 303 on head 302 includes tliread peaks 310 and troughs 312 coiuiected to eac.h other by flanks 3 11, two acljoining flanks 311 forming, a tlu=ead angle 317, as s~hown in FIG. 3C.
Head 302, which is conically shaped as is usual on known lockinc, scre~us is typically oriented such that tlu=ead peaks 310 lie on a straight line, stich as lines 30) or 31 5, and threacl troughs 312 lie on another straight line, suc.h as lines 314 or 316, whereiii the pairs of liries ( 313, 314) aiid (315, 316) are parallel to each other. Furthennore, the thread profile -lines-of each tlveatFpeak -) 10 and eaeh thread trough 3 )-1-2 -extend-parallellrto eaeli other and perpetldicular or normal to the central axis 319 of the screw, as represented by trougli profile lines 318a-e shown in FIG. 3B. Profile lines 318a-e are fornled by eltending the longitudinal axis 301 of a cutting bit 30~ of a thread cutter as the cuttinc, bit contacts the outer surface of head 302 to cut tliread 303. A typical locking screw also has a constant thread pitcli (the distance frorn peak to peak, trough to troubh, or protile line to profile li~ie ) as nleasured alon~
the central axis (e.o., 319).

[0058] A variable-ana1e locking screw according to the inventioi~i has a screwhead that is at least partially splierical. The spherically-shaped por-tion of the llead has a thread on an outer- scirface thereof wllich is preferably a double lead tlu=ead. The tliread has a profile that follows the arc-shaped (i.e., non-linear) radius of eurvature of the spherically-shaped portion of the head. Note that the thread pitch is constant as measured along:
the radius of ctuvatlire. but var=ies froni narrow-to-wide-to-narrow as riie-asurecl along 'the central axis of the screw froni one end (e.g., the top) of tlle spherically-shaped portion of the head to the other end the bottom) (see, e.~.. FIGS. 3?-35 and the description thereof tiirther below), This tl-iread profile allo\,vs the variable-angle locking screw to enciade a boiie plate hole of the 1~

invention at a selectable anole within a range of anales while advant.agecusly niaintaining the saine degree of contact with the bone plate regardless of the angle chosen.
That is, the angle of the screw with respect to the central axis of the bone plate hole within~
the pennissible range of anblcs does tiot affect the engagetnent of the screwliead tlu=ead with respect to the imler surface of the plate hole. A tight lock is advantageously obtained l?e.tween the screw and the bone plate regardless of the angle (within the rancye of angles) at which the screw is inserted into the bone plate hole, because the threads on the spherically-shaped portion of the _,e the columns of thread seametits ptei tsely the same iiiatulei; ensuritib a screWllead engag good fit.

[00591 Some of the advantageous features of the bone plate syste;rn of the invention inay be explained with the aid of an analobv witli rack and pinion gears. ~
Altllough bone plate systetiis and rack and pinion gears are very niuch unrelated (rack and piiiion gears are used, for exatnple, in autoniotive steerintz mecllanisms ancl locotnotive and railcar drive rnechanisms ), the bone plate system of the invention shares an analo2ou s concept. As shown in FIGS. 4A-C, rack and pinion -ear 400 has a rack 420 having teeth 421 and a circular pinion 422 havina teeth 423. Rotational nlotioti applied to pinion 4?22 caluses racl. 420 to translate while, conversely, linear motion or translation of rack 420 causes pinion 422 to rotate.

[0060] The analogous concept is the arrangement of teeth 42-3 around the radius of curvature 425 oC pinion 4?2. Gear teetli 423. shown in profile in FIGS. 4B and 4C. are equally angularly spaced and follow radius of curvatu,re 425. Moreover,~ each tooth 42 ' ) is oriented such that a line bisectitia the tooth 423, as represented by line 417. intersects the center 41-6 of the radius of curvature =}?~, which fornis a circle havim; a adius 424.

Similarly, a line bisecting any space 4.28 between adjacent teeth 423, as i-epresented by line 429, also intersects center 426. The thread profile of the head of a variable-angle lockin-screw (viewed in a direction perpendicular to the central axis of the screw ) according to the invention is analocous to that of the sectional profile vievv of the pinion teeth 4213 and spaces 428 of FIG. 4C.

[0061] FIGS. 5A-C show an embodiment of a variable-angle lockina screw according to the invention. Variable-angle locking screw 500 has a partially-spherical head 502 and a ~ "' _ ~ ead 502 preferably shaft .,04. Head -~(1_-lias a-tlu~ead-5~3; and ~haft 5(:1d h~~s a tlu~ead ~()7: I~

has a recess 509 for receiving a tool to drive and extract the screw iiito and out of bone and into and out of a bone plate hole. Preferably, tip 506 and shaft tliread 507 are self-tapping and/or self-drilling to facilitate implantation into bone. Head 502 and sh!aft 504 mav be cannular tor receiving a gtiide wire to aid in proper placemeiit. FIGS. 513 and 5C show the profile of thread 503, Nvhich advantageously follows the radius oi'curvatilre 5?5. In one enibodiment, the radius is about 2 nun, Respective peaks 510 and trou-1is 512 of tliread 503 as seen in profile are preferably separated by equal angiilar increments.
Peaks 510 and troughs 51 2 are connected by flanks 511 at tliread angles 517, whic.h in this embodinient, are preferablyabout 60 degrees. The tlu=ead profile lines 51 8a-f extend tlu=oiiali trouphs 51? and result in a series of lines that intersect the center 526 of the radius of ctn=vature 525. Profile lines 518a-f are formed by extendinu the longitudinal axis 501 of a cutti ng bit 505 of a thread cutter as the cutting bit contacts the oute.r spherical surface of heacl 502 to cut tlu=ead 503. In this embodiment, cutting bit 505 is al~vays normal to the outer spherical surface of head 502 as thread 503 is cut. Also in this embodiment, tlie radius of curvature is isucli that the radius center 526 lies on the central axis 51.9 of screw 500. De.peiiding on the 1en-th of the radius atid the dimensions of the screw, center 526 may or may- rtot lie on the central axis of the screw. Moreover, as the radius increases while the dirnensions of the screw remain constant, the radius eenter will rnove outside the screwhead, as sho-~vn, for example, in FIG. 6.

[0062] FIG. 6 shows another etnboc[ime.nt of a variable-angle locking screw of invention. In this embodiment, sc.rewhead 602 of variable-angle locking'screw 60011as a larger radius of curvature 6?5 thati screw 500. This results in troUgh profile lines 618a-f intersecting radius of curvature center 626, vvhich is a distance 630 (measured perpetidiciilarly) from central axis 619 of sci=evv 600. If, for example, radlitts 624 is 10 mn-i, distance 630 iiiay be abottt 8.2 mni for a 2.4 nini screw (the 2.4 tnm refer s to the major dianleter of shafit 604), Note, however, that as the radius of curvature increases, the screwhead bec.oines less and less spherical in shape, causing the tlu=ead profile to become niore and more aligned with a straight line (such as, e.g.. lines 313-316) as in known locking screvvheads.

[0063] FIG. 7 shows still another embodiment of a variable-angle locking screwhead in accordance vvith the invention. Screwhead 702 lias a central axis 719,41u=ead 703, and a recess 701) for receivinc, a driving.'extracting tool. As in previous emboditnents, the profile of thread 703 advantageously follows the are-shaped (i.e., non-linear) radius of curvature 725 and includes thread peaks 710, troughs 7121, and 1lard:s 711. However, u'nli.ke previous embodinients, the tlu=ead profile lines do not intersect tlie center of the raclius of curvature.
Instead, the thread profile Iines, represented by trough profile lines 718a-'f, extend parallel to each other and perpendicular to central axis 719. Tllese lines extend in this nlaruier because of the way in wliicll cutting bit 705 of a thread c.utter coritaets the outer spherical surface of head 702 to cut thread 70 3, lines 718a-f representinc, eaterisions of longitudinal axis 701 of cuttin- bit 705. Functionally, this difference results in a less ideal sc.rewhead/hole tlu-ead engabement. However, screwllead 702 is cui-rently easier to fabricate than screwhcad 502, [00641 FIG. 8 shows a bone plate 800 having conventional bone 'Plate holes including locking bone platc holes 832. non-locking bone plate lioles 834, and a conibination locking/non-locking bone plate hole 836. Each type of hole extetids frotil the top surface 837 complete.lv through to the bottonl bone-engaging stirface 839. L-ocking hlate holes 832 have . ~ ~ , tlu=eads 833 extendinc, around the inner surface of the hole for engabinc the tht=eads around the head of a locking bone screw. Conventional locking plate ho1es mav have tl-n=eads 833 extenciing completely through from top surface 837 to bottonl surface 839, as sho%\-n, or may alternatively have ttireads extending for only a portion of the vertical distance between the top and bottom stzrfaces of the bone plate. Non-locking plate holes 834 have non-tlueaded or smooth inner surfaces 835 for accommodating the head of a non-loeking~ bone screw.
Conlbination loeking/non-locking plate hole 836 increases the versatilitv of the bone plate by allowing the surgeon to use either a locking screw or a non-loeking screNw through the hole, Combination hole 836 has one end with tlu-eads 833 around the inner sur~face of the hole for receiving a lockino botie screw and the other end with a smooth or non-threaded iiuier surfac.e 835 for alternatively receiving a non-lockinc, bone screw.

[00651 FIGS. 9A and 9B show bone plate 900 having bone plate holes 940 in accordance with the invention. Instead of a lzelical tlu=ead around the iru%er surface 9'~ of the plate holes as in conventionallockinc, screw bone plate holes, bone plate~
holes of the invention have disc.rete, vertical c-oluinns 942 ofpreferably thread segments arran,ed arouuld the iiuier surface of the hole. The thre:aci segnient c.olumns, if e\panded to jo,in each other (i.e,, if extended completely arouncl inner surface 935), would form a helical tlu-eacl. The columns cztend in a direction from upper surface 937 to lower stu=face 9339 and are spaced preferably equidistantly apart around the iruier surface of the hole. The riumber of tliread segnients 92 1 per colunln can vary dependinc,r on the surgical applicatiori Lu1d the dimcnsions of the bone plate and bone screw (e.g., plate thickness and tlu-ead pitch).
However, each column should have at least two thread segments and preferably more to~ensure a fixed an-ular relationship between the screw and the plate.

[0066] Note that instead of tlu-ead segments, c.olunins 9}.) alternatively may have a pluralitv of teeth foi=ined thereori. The coliunns of teeth, if expanded to j'.n each other (i.e., ~

ifextended completely around inner surface 935), will not form a helical thread, but a series of concentric rid(jes and grooves perpendicular to the ccntral axis of the bone plate hole.
While such colui7uis of teeth can also receive non-locking, locking, and yariable-angle locking bone screws, the engagement of the teeth with the screwlicad tlu~eads of the locking aiid variable-angle locking bone screws is less ideal thail the cngageineni of tliread segments with the screwhead tlu-eacis of the locking and variable-anole locl:itlo botie screws.

[0067] Bone plate holes of the invention pre.ferably have four coh unns 942 of tlu-ead se,ments, as shown in FIGS. 9A and 9B. However, bone plate holes of tlie invention alternatively may have otlier nunlbers of columns of thread sepments.

[0068] For elainple; as illusti-ated in the two embodiments of FIGS. l0A-C

and l OD-F, respectively, bone plate holes 1040A atld 1040D of respectiv e bone plates 1000A
and 1000D each have six c.oluiluls of thread segnients (note that becausel of the perspective shown, only tliree columns are visible in FIGS. 1 OC atzd 1 OF). The difference between tliread seginent cohunns 1042A and tlire.ad segnient columns 1042D is that the column widtli 1041 A of tlu=ead se,ments 1042A is about twice that of column width 104 1 D of tliread segments 1042D. More than six columns of tlu-ead segments is not reconlmended, becattse of the increased risk of cross-threading the screwhead threads with the tlread se~,rnient coltnluis. Conversely, bone plate lioles of the invention having fewer than three columns of thread segrnents is also not recommended bec.ause of the increased likeliihood of insufficient stability at the bone/plate interface.

[00691 FIG. 11 shoN.vs a cross-section of a bone plate hole according to the invention.
Bone plate hole 1140 is formed in and extends completely through a bone plate 1100 from an tipper surface 1137 to a lower lione-eiigagiiig surface 1139. Hole 1040 lias ari inner surface 1 1-3) 5 con7prising a top portion 1144, a iniddle portion 1146, and a bottoni pot-tion 1148. Top portion 1144 extends from upper surface 11 57 to middle portion 1146.
Middle portion 1146 extends l~rom top portion 1144 to bottoin portion 11~48 and preferably has the smallest diaineter of the hole. And bottom portion 1148 extends from iniddle portion 1146 to lo~N~er surface 1139. Top portion 1144 is unthreaded, has a preferably smooth iiuier surface 1143, and is preferably conically tapered inward toward the lower surface. Bone plate hole 1140 has a shoulder 1145 at the interseetion of top portion 1144 and middle portion 1 146 (which is the top of the first tliread segment in eachl column).

Shoulder 1145 znay serve as a stop for the screwhead of a non-locking botie screw inserted tlirougli liole 1140 and, in one enlbodinient, is angled stich that it forms an angle of about 60 degrees with the central axis of the liole-. Note that innet= surface 1 143 oi= upper surface 11 37 may serve as a stop for the scre~,vliead of a non-locking bone screw depeiiding on the size and shape of the head. Bottonl portion 1148 also lias a preferably smooth inner surface 1149 and is preferably tapered inward toward the upper surface in the I:orm of an tindercut sphere. In one embodimeiit of tlie invention, the radius of the tindercut sphere is ablout 1.75 mm. For a bone plate tbickness of about 2 nini, for exanlple, the top portion may extend about 1 nim and the niiddle and bottom portions eac-1i nlav estend about 0.5 nim.

[0070] In this embodiment, middle portion 1146 of bone plate h'ole 1140 has four discrete columns of tliread semients 1142 on inner surface 1135. Each column 1142 is preferably ine.lined inward toivard lower surface 1 139 at an angle 1 150 iileasured with respect to the c.entral axis 1 1 19. In one embodiinent, angle 1150 is preferably about 15 degrees, Eacli column 1142 also preferably 11as four or five thread segnients 1121. Otlier embodiments may liave more or less tht=ead segnlents as described above. For a bone plate hole accoinmodatin(y, a 2.4 nun variable-angle locking screw, the columii width 1141 of each thread segment is preferably about 0.35 mm. Other enibodinlents may liave otlier colunln widths, ciepending on the application.

[0071] FIG. 12 shows a cross-sectional profile of a portion of a column 1242 of thread segments 1221. (Note that a cross-sectional profile of an alterative column of teetli, as described above, appears the same as the tlu=ead se-inents.) In FIG. 12, two of the five tliread seoi~iients 1221 of coluinn 1242 are shown. Colutnn 1242 of tluead se0ments is preferably iticlined to~vard the lower surface of the boile plate at angle 1250. In one embodiment, angle 1250 is about 15 degrees. As seen in profile, colunui 1242 of tluead segments 1221 includes peaks (or ci-ests) 1210 and troughs (or roots) 1212 connected to' each otber by flai-Lk-s 1211 at tllread angles 1217. Peaks 1210 pre:ferably have a length'1252, which in one embodiment is about 0.04 nlm. Trou~ahs 1212 preferably have a radius 1254, which in one embodiment is about 0.03 nini. Ansale 1217 is preferably about 60 deujrees, and the bisection of trouuhs 1212, as represented by trough profile litie 1218, occurs at ananble 1256 of prefe,rably about 30 degrees as rneasured frorn a flarik- 12.11. Other embbdimcnts of bone plate hole thread-scgnlent coltunns alternatively may have other values of colunln incline angle, peak leiigths, trough i-adiuses, thread angles, and bisection angles (which are a ftinction of thread an-le ). [0072] Advanta(yeously, variable-angle locking batle scre -s of the invention caii be driven into bone and secttred to the bone plate at a selectable angle withi.'~n a range of selectable angles. FIG. 1') shows an embodiinent of the invention in wllich bone plate 1300 has bone plates holes 1340 constructed in accordance witb. the invention'L
Each hole 1 340 can advantageously receive a variable-angle locking screw 1-3E0; also constrlLcted in accordaiice with the invention, at a selectable angle in anv direction withiil a range of anales. The ranae . ~ ~

of angles foi-ms a cone having an angle 1362, which in this embodiine.nt~is about 30 degrees.
In other words, variable-amle loc.kino screw 1360 can be inserted into alhole 1 340 and secured to bone plate 1 300 at a selectable angle ranging tiom 0 degrees to 15 degrees in anv direction with respect to central axis 1 319 of bone plate 1340. [0073] FIGS.
14A-17B show an advantageous feattue of a bone plate hole construeted in accordance with the invention. Bone plate 1400 has at least tliree bone plate holes 14=I0. Each hole 1440 has Iour columns of tlu=ead segments 154) LAnd can advantageously receive any one of a non-locking, locking, or variable-aiigle locking bone screw.

[0074] As shown in FIGS. 14A, 14B, 15A, and 15B, a conventional non-locking bone screw 14100 can be insei'ted tlu=ough one of bone plate holes 144(:).' Non-lockinu, bone screw 14100 has a non-threacled screwhead 14102 aiid a tlireaded shanl<~
14104. eac.h appropriately sized and configured for use ',Vith hole 1440. Note that non-lockina bone screw 14100 does not llave to be inserted througli hole 1440 coaxially vvith the central axis of the liole. but may instead be inserted throuah hole 1440 at a selectable ani.,le, as shown in FIG. 14B. FIG. 15B shows that screwhead 14102 does not engage the ci.~ltnns of tlu=ead segments 15421. but instead contacts shoulder 1545 of hole 1440 when fli,llv seated therein.
[0075] FIGS. 14A, 14B. 16A, and 16B show conventional lockiti;,, bone screw inserted though a second bone plate hole 1440. Locking bone screw 1421100 has a screNvllead 142102 with a tlu-ead 14203 on an oute.r surface therefore. Bot~h the screwhead and thread are appropriately sized and dimensioned such that thread 14203 can threadingly eii(.;age and mate with colunins of thread sei;nieiits 1542. _Iri oider to prolierly engage and mate with colunuls of tluead segments 1542, locking bone screw 14200 should be inseried througli hole 1440 coaxially with central axis 1419 of the hole. Screw 14200 also has a threaded shank 14204 for engaging bone. Shank 14204 is also appropriately sized and dimeiisioned for insertion through llole 1440.

[0076] FIGS. 14A, 14B, 17A. aild 17B show variable-angle loc.king bone screw inserted through a third botle plate hole 1440. Variable-angle locking bone screw 1460, constructed in accordance with the invention, has a threade.d s11ai-i1: 144, and a parCially-sphei-ical head1402 Nvith thread 1403 on an outer sLirface thercof.
Screwhead thread 1403 has a profile that advantageously fol lows the arc-shaped (i.e'., non-linear j radius of curvature of the sphericallv-shaped portion of head 140?. Screw 1460 is shown inserted iiito the third hole 1440 non-coaxially witli the central axis 1719 with thi~,ead 140 3 sec.urely engaging coltuYuis of tlu-ead segments 1542.

[0077] FIGS. 1 SA-24C illustrate various features of ati etnbodinient of a bone plate liole ac.eorclitig to the inventio,n. Other than the foriiiation of columns around the iiu-ier surfac.e of the hole, at least sonie of these features need not be used in alternative embodiments of a bone plate liole according to the invention. Also note ithat the order in which these, teature.s are described and shown does tiot irnply the order or steps of a particular process for fabricatiuo a bone plat hole of the invetrtion. As is apparent to those of ordinaiy skill in the ail, there is more than one way in which holes of the invention can be fabricatecl.
[0078] A bone plate hole of the invention typically starts with a circular start hole 186,. as shown in FIGS. 18A-C. Start hole 1865 has a central axis 1819 and extends completely through a bone plate 1800 fi=om upper surface 1837 to lovver 'sw-face 1839. In one embodiment, the diameter ofthe start liole is about 2:2 iiiin:

[0079] FIGS. 19A-C show an inner surface profile of a bone plate hole ~vitholrt other features, The profile of hole 1965 in bone plate 1900 includes ail inwarcllv tapering top portiori 1944, a protruding, in~vardly tapering iniddle portion 1946, and a spherically undercut bottoiii portion 1948. In one embodiment, the middle and bottoin portions of the hole each extend alona the central axis 1919 by about 1 mm, and the radius of the spherical undercut is about 1.75 nim.

[0080] Another feature is an optional "X l:ey" cutout 2065, shon FIGS. 20A-C..
X key cutout 2065 is preferably pressed, cut, or stamped coinpletely thro:ugh the bone plate about the same central axis 1819 as stat=t hole 186~. In one enibodinient;
eacll leg of the "X"
has a width of about 1.5 mm and ternlinates in an arc-shape having a radius of about 0.7-5 in.
ln this same einbodiinent, the span betvveen the ends of collinear legs is about 4.25 mm. The X key cutout fornls a c.loverleaf design iiitended to accomniodate a drill guide having a complementary drill-guide tip de.sibn, as described fi.u-ther belo\v with respect to FIGS. 2-5,A-27D.

[00811 Anotlier feature is a preferably 12-degree relief cut 2165, as shown in FIGS. 2 1A-C (without any other hole features). Relief cut 2165 inc.ludes ei(Flit svnlmetrically ctit sections 2166, two sections per quadrant, in which each section incliiles itiward at about 12 de(-,rees froiii the upper strface 21 3 7 of the bone plate. The relief cutlis iuade completely through the bone plate. In one einliocliinent, eacli relief eut axis ? 119 is about 1.1 innl frozn central axis 1819 of the bone plate hole.

[00821 FIGS. 22A-C show a hole profile with top portion 1944, iiliddle portiou 1946, bottoinportion 1948, 1 key ciitout 2065, relief cut 1.16-5, and four colunuls 21242 fornied therein that have not yet had teeth or thread seQinents eut into tliein. Col~iitnns 22421 are forined bv removing axial sections from the inner surface of the middle portion of the liole, [00831 A thread cutting process forms the thread seunients in columns 2742.
Note that if middle portion 1946 had not had the columns fornled therein, the tilu=ead ctiittinc, process would have cut a helical thread 2367 in and completely around tlle inner surface of iniddle por-tion 2346 of hole 2365 as showti in FIGS. 23 A-C. The tliread profile (i.e.. the peaks, taoughs, flanks, and tlie angles formed by adjacent flanks) of the tllread segments is preferably the same as the profile described above for the columns of thread sec-nients shown in FIGS. 1 l and 12.

[00841 As described previously, instead of forniiiig tluead segme~nts in colunnis 2242, teeth may be fornied alternatively therein. Teeth are tormed by cutting grooves in the colunni that are perpendicular, or at least substantially ~-perpendicular. to the central axis of the hole. Note that if middle portion 1946 had not had the columns forni;ed tlierein, the roove cutting process would have fornled a concentric, parallel series of alternating grooves and ricl,-es.

?4 [00851 FIGS. 24A-D shokv a completed embodiment of a bone plate hole according to the invention. Hole 2440 includes colunins of thread seginents 2442, X key cutout 2065, and relief cut 2165. FIG. 24C shows top surface 2437 ofllole 2440, whi!le FIG.
24D sliows bottom surface 2439 of hole 2440 that is intended to contact, be adjacentlto, or face the bone.
(0086] FIGS. 25A-27D sho~v another advantagzous feature of th~ invention in connection with drill guides. One enibodiment of a drill guide construct'ed in accordance Nvit11 the invention is shown in FIGS, 25A-26C, and another enlbodiment is sliown in F1GS.27A-D. (0087] FIG. 25A shows drill guide 2570, \N-hich has a tip 2571 arici a handle 257 3. As shown in FIG. 25B, tip 2571 has four equidistantly spaced and rounded vings or sections 2572 forming a cloverleaf design an=anged around a drill shaft flor guiding a drill. a ~
bone screw, and/or a drivin~~; extracting tool through a bone plate 2500 ai'~id into bone at a selectable aiigle. VVings 2572 are sized and conligtued to fit snugly witliin the X key etrtouts 1965 of bone plate holes 2540. This allows drill guide 2570 to be inserted coaxially into a bone plate hole 25=10 (i.e., coaxially with the central axis of a bone plate hole) and to be easily held in place whilea hole is drilled into the bone and!or a bone'scre~,v is driven into the bone. Note tliat, alternatively, configurations otlier than the cloverleaf design and X key cutouts can be used for tip 2571 and holes 2540. respectively. As sho~vri in FIG. 25C, handle 2573 can swivel 360 deurees about tip 2571 and the central axis of the hole 2540 in which tip 2571 is inserted.

(0088] FIG. 26A sliows clrill guide 2570 having a slot 2675 throti ,h vvhich drillings ~vithin a range of selectable angles can be made. In this embodimetit, the selectable andles range from 0 degrees to 15 degrees. The ability ot'handle 2573 to s~,vive1 360 degrees thus -,~

provides a 30 degree coiie of angulation around the central axis of the hole.
Drill guide 2570 lias niarkings ?674a-d along slot 2675, which in this cmbodiment indicate 0.
5, 10, and 15 degrees, respectively, with respect to the central axis of the hole. Other einbodinlents rnay have other angle ranges and/or other markings of selectable angles. FIGS. 26A
and 26B
show a drill bit 2676 being guided through drill guide 2570, tlu=ough boiie plate 2500, and into bone 2678 at the uppei-nlost angle setting 2674a, which in this eniboldiinent is 0 degrees with respect to the central axis of the bone plate hole (i.e., eoaxial). FIG', ?6C shows drill Iiit "'676 being guided through clrill guide 2570, tlu=ou-h bone plate ?5flll and into bone 2678 at the lowernlost angle setting 2674d, wliich in this embodiment is 15 dearees with respect to the central axis of the bone plate hole or 75 cleurees with respect to the top surface 2637 of bone plate 2500.

[0089] FIGS. 27A-D show another embodirne.nt of a drill guide in accordance Nvith the invention. Drill guide 2770 has a funilel-shaped guide 2777 with a ti,p 2771A at one end, a coaxial guide 2779 with a tip '?77l B at the opposite end, and a liandle 2773 there between.
Tips 2771A and 2771B each have four equid,istantly spaced and rounded~ wings or sections 2772 forniing a cloverleaf design around a drill shaft for guidinc~y a drill, a bone screw, and/or a driving/extrac.ting tool 2776 tlifou,:,h a bone plate and into bone. Wings ?772) are sized ancl c.onfioured to fit snugly within the X kev cutouts 1965 of b'one plate holes of the invention (e.g., bone plate holes ?540). This allows either end of driil guide 2770 to be inserted coaxially into a bone plate hole (i.e., coaxially witli the central aais of the bone plate hole) and to lie easily held in place while a hole is drilled into bone and/or a bone screw is driven into bone. Note tliat, alternatively, configurations other than the eloverleaf design and X key cutouts can be used for tips 2771A and 2771 B and holes of the invention, respectively.

?6 Unlike handle 257 ') of drill guide 2570. handle 2773 does not swivel about either tip 2771A
or 2771 B. Instead, funnel-shaped guide ?777 has a funnel-shaped bore 2775 extending there through and centered about the central axis of the boiie plate hole in which tip 2771A is inserted. Bore 2775 provides a coile of angulation. wllich in this eiiibociiiiiient is 30 degrees.
With funnet-shaped guide 2777 inserted in a boiie plate hole of the inventioii, and thus locked in a fixed position, drilling can be advantageously made at a selectable angle in any direction ranginc, froin 0 iiegrees to 15 dec,rees with respect to the central axis of the hole. At the opposite end of drill guide 2770, coaxialguide 2.779 hasbore 2778 e"tending there tlu=ough. With coaxial guide ?779 inserted in a boiie plate hole of the invention, bore 2778 can be used to guide a clrill bit or driving/extracting tool 2776 coaxial to the central axis of the hole. Coaxial guide ?779 also has an optional measurenie.nt gauge 2774 to lielp determine penetration deptlis.

100901 FIG. 28 shows a bone plate c-onfiguration in accordance vvith the invention.
Bone plate 2800 is shaped and contigured for, but not liniited to, frac:tures of the lateral proxiinal tibial plateau. Bone plate 2800 has a head portion 2880 configured and diniensioned to confoi-in to the metapliysis of the lateral proxinial tibia, Lind a shatt portion 288-1 configured and diniensioned to conforni to a diaphysis of tlae lateral proximal tibia. Bone plate 2800 further has an upper surface 2837 and a plurality of boiie plate holes 2840 that eltend completely tlirotigh the boiie plate, froni upper surface 2837 to the bottoin surface. Each hole 2840 llas four colunlns of tli-read segnlents 2842 and can advantage.ouslv receive either a non-locking, locking, or variable-anule lockin, bone screw accordino to the invention. Sliaft portion 288-1 also has several fic,ure-eight shaped combination lioles 2884 for increased versatility, vvhere one portion 2885 of the til-ure-eivht has preferably four columns of t1u=ead segments and the other poi-tion 2886 is preferably sniooth and unthreaded. Portion 2886 can receive a non-loclcinc, bone screw, while portion 2885 can advantageouslv receive either a non-locl:in,, lockin~, o:r variable-angle ~
lockinc, boiie screw. The ability to use variable anaie locking screws in shaft portion 2882 is particularly useful when the far cortex of part of the diaphysis is rnissing'or severely danlaged since fixation Nvith non-locking screws is problematic because of the c.onclition of the far cortex. The pai-ticular type and placenlent of bone plate holes n-la of course vary.
100911 F1GS, 29A-C' show another botie platecoritiguration in ac'cordance with the invention (this is same bone plate sho,,vn in FIGS. '' 5-27 ). Bone plate 29~~00 is shaped and confiUure.d for, but not liniited to, fi=actures of the distal radius. Bone plate 2900 has a head ~

portion 2980 conli-ured and diinensioned to conform to the metaphysis of the distal radius, and a shaft portion 21982 conficured and dimensioned to confoi-m to a diaphysis o1 the distal radius. Bone plate 2900 I'urther has an upper surface ?9 3 ) 7, a lower surfa~e 2939, and a plurality of bone plate holes 2940 that extend completely tlu=ouCIh the bone pl=ate, fioni upper surface 2937 to lower surface ^9;9. Each hole 2940 has preferably tuur coltunns of tluead seL,inents 2942 and can advantageously receive either a non-locking, locl:inc, or variable-angle locking bone screw according to the invention. Shaft portio~i N8? also has several combination boles 2984 and 2989 for increased versatility. Hole portion's 298>
of the --ments 2942 and the other combination holes have preferably four columns of thread seg portions '_'886 ancl 2887 are preferably sniooth and tultlireaded.
Portions~?886 and 2887 c-an receive a non-locking boile screNv. while portions 2855 can advantageou5ly receive either a non-lockinty, lockinL, or variable-anwle lockinc, bone screw. In one embbdiine.nt, the lengtli 2990 of boiie plate 2900 is about 65 nini, the width 2992 of head portion 2980 is about `
,

2 2.2 mm and the angle ?994 at which head portion 2980 i~ inclined upward with respect to shaft portion '.QS2 is about 25 degrees.

[0092] As shoNvn in FIG. 30, bone plates of the invention preferably may be shaped to liniit andior mininiize contact between the lower surface or underside of the boiie plate and the bone. Limiting and/or nlinimizinc contact between the boiie plate antl bone lias a nuniber of biolobical and mechanical advanta~es including reduced damage to bl0od supply and easier plate removal. One way to limit and/or mininlize contact between,a boiie plate 3000 and boiie is to provide plate 3000 -,vit:h radiused or scalloped cutouts 3099 on lower strface 3039 between bone plate holes. Other ways are disclosed in U.S.
Patents Nos. 5,151,103: 5,05 3,036; 5,002,544, and 4,838.252. The contents of these patents are incorporated herein by referetice.

[0093] FIG. 31 shows an embodiment of the boiie plate systenl of the invention as applied to a bone fracture. Bone plate 2900 is shown attaclied to fracttred bcme 3178 via four variable-angle locking screws 3160 inserted at various selectable an('--rles through bone plate 1loles 2940 of head portion 2980 and attached to bone plate 2900 via the columns of thread segments in holes 2940. The columns of tlu=ead segnierits on the iiuler surface of bone plate holes 2940 interact ancl mate with the tlu-ead on the spherically-sha ped head of variable-an(ile 1ockinL, screws 3160 generally analogous to a rack-and-pinion, allciwin~~ the variable-angle screws 3 160 to be secured in plate holes ?940 at a variety of angles.
Variable-an-le lockin- screws i 160 are constructed in accordance with the invention ana rnay be, for ~
exaniple, variable-anule locking screws 500, 600, and/or 700. Bone plate 2900 is also attached to bone 3 178 via non-locking boiie screw 3110O inserted through portion 2987 of boiie plate llole. 2989. Bone plate 2900 is iiirther attached to boiie 3178 via a pair of ~9 conventional locking bone screws 31200 inse,rted through respective portions 2985 of bone plate holes 2984 and secureci to the bone plate via the colunins of thread segnlents in portion 2985. The colunlns of tliread segnients in the bone plate holes nu'ate with the tt-ireaded heads of the locking screws to secure the locking screws to the bone ptate. Note that variable-angle lockinc, screws of the invention could have been used~i in place of lockin~
screws 31?00, Note ftu=ther that not all botie plate lioles need to be used 'in eacli application.
Variable-angle locking screws 3160, non-locking screw 31100. and locking screws 31200 remain inserted tlu-oughbone plate 2900 and iiito bone 3 178 for as lonu as plate 2900 remains iinplanted.

[0094] Returning to the serewhead thread features of variable-angle locking bone screws constructed in accordance with the invention, FIGS. 3?-3=4 shoNN- t1vee enlbodiinents of a variable-angle locking screw screwhead that illtistrate the varying th~read pitches (e.g., the peak to peak distance) as ineasured along the central axis of each sc.rew.
The following table lists the size of the variable-angle screw to whicll the iltustrated scri ewhead belongs and the varying pitches (all dimensions in nzillinieters).

FIG. 32 FIG. 33 FIG. 34 Shaft cliaineter: 5.0 3. ~ '-.4 Screwhead diameter: 6.5 4.5 3.0 Pitch: 32P01 = 0.90 33P01 - 0.76 34P01 = 0.56 32P02 = 0.95 33P02 = 0.79 34P02 = 0.59 32P0 3= 0.99 3 3P0 3= 0.80 34P03 = 0.60 32P04 = 1.00 33P04 = 0.79 34P04 = 0.58 321?0; = 0.99 33M = 0.75 34P0; = 0.5-5

3 3P06 = 0.68 34P06 = 0.49 32P06 = 0.95 32P07 =0.90 3 3P07 =0.60 3 4P0 7= 0.41 3'?P0S = 0.82 3?P09 = 0.7?

Other embodiments of variable-angle lockin- bone screws of the inveiltion inav have other varying tllreaci pitches.

[0095] Note that in each case, the aiigular distance between adjacent thread peaks (or aqjac.ent thread troughs) as measured along the radius of curvature is coqstant, as illustrated in FIG. 35. That is, each anc'ular distance 35AD between adjacent tluead peaks 3510 as meastu=ed along the radius of curvature 3525 is the same -- in cotitrast to tliread pitches 35Pp l- 3 5Ph5 wllich, as illustrated in FIGS. 321-34, varv as measured along or parallel to ceritral axis 3519.

[0096] By eombining variable-angle loeking screws, locking screws. and non-locking sc.rews on the same bone plate using the saine type of bone plate hole, the invention provides a novel miYed fiaation. With non-lockinoserews, fracture reduction is h'eld by friction bettiveen the bone plate and bone. This friction is generated by tightenin~
tkle non-locking i and bone leads to screws in bone. However, microinotion between the non locking screws~

bone resorptioiz and consequently loss of re.duction. Additionally, insertilon of the non-locking screws requires bone to withstand the stresses of screw ti,rhtening, which creates hicyh stress in bone surrounding the non-locking screws. Orilinarilv, the high stress can cause the non-locking screw tlu=eads to strip (i.e., tlireads in bone fail in shear) ancUor creep in bone (since boiie is a viscoelastic- material). Eidier one of tllese phenomcnon also results in loss of reduction.

[0097] By adding at least one locking or variable-angle locking screw, loss of reduction is miniinized or eliminated. Specifically, by securing the locking screws to the bone plate and not the tione, the effect of the viscoelastic behavior ofboiie is reciueed, the ~1 tlireads do not strip, and microinotion is prevented. The attaclunent betNveen the locking screws and the bone plate is a higli strength conlieetion of fixed angle coiistruct in which the lockinc, screw has to cut sidewavs through the bone to fail. [0098] Using variable-anCT le screws provides an even greater advantage than the locking scre,,vs. because the variable.-angle scrcNvs mav be secured at a niore desirable angle than the locking screws.

[0099] Nloreover, as nlanagemcnt of certain peri-articular fractw=es typically involves insertion of screws at various angles tivith respect to the bone plate, and iii view of the iniportance of maintaining the initial angular relationships between the iildividual screws and the bone plate, the highly-versatile bone plate systein of the invention is harticularlv well-suited for these clinical applications. [0100] Note that the features described and illustrated here.in mav be used singularly or in combination with other features and embodiments of bone plate systems.

[0101] The invention has thus been described above in c.onnectio:n with the preferred e.nibociiments. The invention is not, however, limited to these enibodimznts.
which are only eaamples of the invention. Persons skilled in the art will appreciate that'various niodifications can be made ~vithin the scope of the invention, ancl the inv~'~~ention is limited onlv by the claims ~vhich follow.

Claims (25)

What is Claimed is:

1. A bone plate system for securing a bone plate to bone, the system comprising a bone screw having a central axis and comprising:
a shaft configured and dimensioned to engage the bone;
a head having a spherically-shaped portion having a radius of curvature, the head having a thread on an outer surface of the spherically-shaped portion, the thread having a profile comprising peaks, troughs, and flanks, the flanks connecting the peaks and troughs, wherein the peaks and troughs lie on respective non-linear curves parallel to or concentric with the radius of curvature.

2. The system of claim 1 wherein the thread profile has profile lines that intersect the center of the radius of curvature, the profile lines representing extensions of the longitudinal axis of a cutting bit of a thread cutter as the cutting bit contacts the outer surface of the spherically-shaped portion of the head.

3. The system of claim 1 wherein the thread profile has profile lines that intersect a point located no more than 10 mm away from the central axis measured perpendicularly to the central axis, the profile lines representing extensions of the longitudinal axis of a cutting bit of a thread cutter as the cutting bit contacts the outer surface of the spherically-shaped portion of the head.

4. The system of claim 1 wherein the thread profile has profile lines that extend perpendicular to the central axis, the profile lines representing extensions of the longitudinal axis of a cutting bit of a thread cutter as the cutting bit contacts the outer surface of the spherically-shaped portion of the head.

5. The system of claim 1 further comprising a bone plate having a top surface, a bottom surface, and a plurality of holes extending from the top surface through to the bottom surface.

6. A bone plate system for securing a bone plate to bone, the system comprising a bone plate having an upper surface, a lower bone-engaging surface, and a hole extending there through from the upper surface to the lower surface, the hole having an inner surface, wherein:
the bone plate has a plurality of discrete columns of teeth or thread segments arranged around the circumference of the hole on the inner surface of the hole, each column extending in a direction from the upper surface to the lower surface;
the hole is configured and dimensioned to receive a non-locking bone screw, a locking bone screw, or a variable-angle locking bone screw; and the columns of teeth or thread segments are configured and dimensioned to engage a thread on a head of the locking bone screw or the variable-angle locking bone screw.

7. The bone plate system of claim 6 wherein the bone plate has four discrete columns of teeth or thread segments arranged around the circumference of the hole on the inner surface of the hole.

8. The bone plate system of claim 6 wherein the plurality of discrete columns of teeth or thread segment are spaced equidistantly apart on the inner surface of the hole.

9. The bone plate system of claim wherein each column of teeth or thread segments inclines inward toward the lower surface at an angle of about 15 degrees.

10. The bone plate system of claim 6 wherein the bone plate has a top portion, a middle portion, and a bottom portion forming the hole, the top portion extending from the upper surface to the middle portion, the middle portion extending between the top portion and the bottom portion, and the bottom portion extending from the middle portion to the lower surface, wherein the middle portion has the plurality of discrete columns of teeth or thread segments arranged on the inner surface of the hole.

11. The bone plate system of claim 10 wherein the top portion of the hole is unthreaded or has a smooth inner surface.

12. The bone plate system of claim 10 wherein the top portion of the hole is conically tapered inward toward the lower surface.

13. The bone plate system of claim 10 wherein the bottom portion of the hole is unthreaded.

14. The bone plate system of claim 10 wherein the bottom portion is tapered or curved inward from the lower surface to the middle portion.

15. The bone plate system of claim 10 wherein the discrete columns of teeth or thread segments form a shoulder at the intersection of the top portion and the middle portion of the hole.

16 The bone plate system of claim 6 further comprising a bone screw comprising a head and a threaded shaft, the threaded shaft configured and dimensioned to fit through the hole and to engage the bone.

17. The system of claim 16 wherein the hole has a central axis and the bone screw is a locking bone screw with a thread on an outer surface of the head configured and dimensioned to engage the plurality of columns of teeth or thread segments coaxial to the central axis.

18. The system of claim 16 wherein the bone screw is a non-locking bone screw with no screw threads on an outer surface of the head, the head configured and dimensioned to contact the uppermost teeth or thread segments nearest the upper surface.

19. The system of claim 16 wherein the bone screw is a variable-angle locking bone screw, the head having a spherically-shaped portion having a radius of curvature, the head also having a thread on an outer surface of the spherically-shaped portion, the thread configured and dimensioned to engage the plurality of columns of teeth or thread segments, the thread having a profile comprising peaks, troughs, and flanks, the flanks connecting the peaks and troughs, wherein the peaks and troughs lie on respective non-linear curves parallel to or concentric with the radius of curvature.

20. A method of bone fracture fixation comprising:
positioning a bone plate against bone, the bone plate having a plurality of bone plate holes, each hole extending completely through the bone plate;
selecting any one of a non-locking, locking, or variable-angle locking bone screw for insertion through any one of the bone plate holes and into the bone;
selecting any one of the bone plate holes for inserting there through the selected bone screw; and inserting the selected bone screw through the selected bone plate hole and into the bone.

21. The method of claim 20 wherein the selecting of any one of a non-locking, locking, or variable-angle locking bone screw comprises selecting a locking or variable-angle locking bone screw, the method further comprising engaging threads on the screwhead of the locking or variable-angle locking bone screw with columns of teeth or thread segments located on an inner surface of the selected bone plate hole.

22. The method of claim 20 wherein the inserting the selected bone screw comprises inserting the selected bone screw through the selected bone plate hole and into the bone non-coaxially with respect to the central axis of the bone plate hole.

23. The method of claim 20 wherein:
the selecting any one of a non-locking, locking, or variable-angle locking bone screw comprises selecting a variable-angle locking bone screw;
and the inserting the selected bone screw comprises inserting the selected variable-angle bone screw through the selected bone plate hole and into the bone at any angle within a range of angles in any direction from a central axis of the selected hole.

24. The method of claim 10 further comprising:
inserting a portion of a drill guide having rounded corners within corresponding scalloped cutouts in the selected hole;
selecting a desired angle within a range of angles permitted by the drill guide at which to insert a bone screw through the selected hole and into the bone, the portion of the drill guide inserted into the selected hole remaining in a fixed position in the selected hole regardless of angle selected.

25. A method of fabricating a hole in a bone plate of a bone plate system for internal bone fracture fixation, the method comprising:
drilling a start hole completely through a bone plate from an upper surface to a lower surface of the bone plate, the start hole having a central axis, and the bone plate having an inner surface around the circumference of the hole:
forming a top portion, a middle portion, and a bottom portion in the inner surface around the hole, the top portion extending from the upper surface to the middle portion. the middle portion extending from the top portion to the bottom portion. and the bottom portion extending from the middle portion to the lower surface, the middle portion forming a smaller diameter of the hole than the top and bottom portions;
removing a plurality of axial sections from the inner surface of the middle portion of the hole to form a plurality of columns on the inner surface of the middle portion; and forming a plurality of grooves in each of the columns.