CA2129974A1

CA2129974A1 - Bone cement having chemically joined reinforcing fillers

Info

Publication number: CA2129974A1
Application number: CA002129974A
Authority: CA
Inventors: Francis W. Cooke; Thomas R. Marrero; Hirotsugu K. Yasuda
Original assignee: Individual
Current assignee: ORTHOPAEDIC RESEARCH INSTITUTE Inc; University of Missouri System
Priority date: 1992-02-20
Filing date: 1993-01-06
Publication date: 1993-09-02
Also published as: AU3433393A; WO1993016661A1; EP0626834A1; US5476880A; US5336699A; AU664235B2

Abstract

Improved polymeric orthopaedic compositions are disclosed wherein sized, functional fibers are incorporated into a physiologically acceptable matrix. The compositions of the invention can be fabricated in the form of particulate powders (10) adapted for reinforcement of bone cements (14), continuous media (12) for such cements (14), and orthopaedic implant coatings (16). A complete implant attachment system is also provided, made up of a fiber reinforced implant coating (16), and a compatible fiber reinforced cement (14). In preferred forms, the fibers (20) have a layer of sizing (22) thereover which is chemically joined both to the surface of the fibers (20) and to the surrounding matrix, and the fibers (20) are present at a level of at least about 6 volume percent. If desired, sized radiopaque particles (24) may be incorporated into the compositions of the invention. The fibers (20) are advantageously polymeric in nature and of intermediate stiffness, whereas the matrix fraction is preferably polymethylmethacrylate.

Description

W~3 93tl6661 2 1 2 ~ ~ 7 ~ P~ S93/~00~6 BONE CEMENT HAVING CHEMICALLY
JOINED REINFORCING FILLERS

5 Back~round of the Invention l. Field of the Invention This invention relates to improved polymeric orthopaedic compositions such as particulate powders, cvntinuous media for bone cements, finished bone cements and orthopaedic implant coatings which are characterized by an amount of physiologically acceptable polymeric matrix with sized fibers dispersad in the matrix such that ~:the sizing layer on the fibers is chemically joined to the surface of the fibers and to the matrix material. In 15preferred forms, sized radiopa~ue particles can also be added to the orthopaedic compositions.

2. Descri~tion of the Prior Art S1:arting ~n the mid-1930s and con~inuing through khe middle part of the 1950s, the ~rthopaedic implantatic>n 20 ~of artificial femoral heads, i.e., the ball og~ the hip .
j oint, was achieved primarily by impaction of the stem of : ~ the implant into the medullary (marrow) ca~rity of the emur. Although this procedure achieved some degree of succe5s in that it increased the mobility of certain 25~patients sufferirlg from hip joint deterioration or mal-function, the procedure ` had maJny shortcomings, The princ:ipal problem encountered was traced to loosening of the implan t in~ a relatively f ew years, thus compromising the patient ' s mobility and oftentimes causing ~ignif icant 3 0paln .
;~ In the l~te 1950s, I~r. John Charnley in England proposed use of a mortar or grouting agerJt f or c~merlting an orthopaedic appliance to a pati~nt ' s bone structure using pol~ethyl~s~thacrylate (P~) as the grout agentO
35The P~ mortar ~aterial served to ~ill all o~ the ~paces WO93/16661 2 12 9 9 7 '-~ PCT/~'S93/~^')56 between the stem of the implant and the surrounding bone.
In particular, it was determined that the P~MA grouting agent could be forced into the tiny interstices of the porous bone. This resulted in a mechanical lock of the grout agent to the bone. Another advantage of the PMMA
system was the fact that mobilization of the patient following implantation could be accomplished at an earlier date following surgery, and the functional lifetime of the implant was greatly enhanced.
10The success obtained in hip surgery using PMMA
encouraged orthopaedic surgeons to develop implant attach-ment techniques for other prostheses such as the a~etabu-lar or cup sid~ of the hip joint and for the femoral, ~; tibial and patella components of total knee repla~ements.
Although the life time of these prosth~ses has markedly improved and the range of patients for which the surgery . is deemed appropriate has greatly increased, difficulties still remain . There is still a tendency f or the cement marltle which surrounds the prosthesis to fail by brittle ,:
~racture and fatigue and,. thereby, to 105e its ability to ransmit load from the implant t~ the bone structure .
This loss c:~f load transfer capability in turn was found to cause loosening o~ the prosthesis with concomitant j oint dysfunction, failure of the metal prosthesis itself by 25 : virtue of lo~;s o~ support, and finally pain during patient ac:tivity because of gross movement of the prosthesis.
Efforts to remedy these problems have not met with a great deal of success. One attempt involved ncreasing the thickness of the cement mantle. Another 3 0 proposal chose to proceed in the opposite direction by signif icantly decreasing the thickness of the ~nantle .
Thorough cleaning and lavage of the bony surfaces ih order to promote interdigitation and better m~chanical locking ~: of the c:em~nt with the interstices of the bon~ structure was also tried. Other res~archers suggested pressuriza-~ ' ' .

W093/16S61 2 ~ 3~ ? PCT/~S93/00056 tion of the cement during insertion to further promote introduction of the cement into the interstitial spaces of the bone. Grouting guns were used to eliminate seams and laps in the cement mantle. Finally, incorporation of strong reinforcement fibers in the cement was tried, including 316 type stainless steel wir~s, cobalt-chromium-molybdenum implant alloy wires, glass fibers, aramid fibers and polye~-hylene terephthalate (PET). These prior procedures di~ not adequately solve the problem for wo basic reasonsD First, prior researchers failed to appre-ciate that although cement reinforcement was desirable, their reinforcem~nts (except PET) were so rigid and stiff that they actually bridged bone interstices impeding ~ull ~- filling of the in'erstitial ca~ities. Sesondly~ these lS sama researchers made no attempt to chemically couple the fi~ers to the matrix polymer. Consequently, little or no load was trans~erred to the fibers and they were unable to participate in load bearing. Accordingly, the fibers ; conferred little improvement in strength or crack resis-tance to the cement.
An exemplary effort in this respect was the attempt in the early 1980s to reinfQrce bone cement materials with carbon fibers. The fibers were added to the powder mix so that upon consolidation of the bone c~ment, the fibers were only dispers~d in the matrix phase ~, -but not in the original P~MA particles. Carbon fiber addition had little, if any, beneficial ef~ect on the toughness ~f the bone cement because the fibers were not coupled to the matrix. ~urther, thes~ very sti~ fibers yreatly impeded the intrusion of the ce~ent into th~ small bony interstices~ This product ha~ subsequently been removed ~rom the market.

~ , W093/~666l PCT~'S93/r~56 ~ I 2 9 g~ 4_ Summary of the Invention The shortcomings of prior orthop~edic composi-tions and cements have now been oYercome by th~ present invention wherein sized fibers designed to enhance the functional properties of orthopaedic compositions are incorporated into and chemically joined with a polymeric matrix. The principles of the invention can be employed in the fabrication of particulate powders adapted for use in bone cements, continuous media for such cements, and in coatings for ort~opaedic implants.
: In preferred forms, the fibers have a layer of siæing ~h~reover which are chemically joined to the surface of the fibers, and also to the surrounding matrix.
: The fibers are broadly present in such orthopaedic compo-sitions at a level of at lest 6 volume percent, and have an average leng~h of from about 1 ~m to about 2 cm. Pre-: ferred fibers are selected from the group consisting of polyaramids, polyesterc, polyalkenes and polyamids~ The matrix phase is advantageously selected from the group consisting of a substituted ~r unsubstituted acryl~te, .
most particularly polymethylmethacrylate. A variety o~
sizing agents can be employed, particularly those from the group consisting of ethyl silane, methylmethacrylate, ethylmethacrylate, ethylene, propylene and methane.
: 25 ~ In preparing a particulate powder in accordance with the invention, the fibers are initially sized with ; MM~ using glow discharge polymerization, whereupon the ~: : fibers are dispersed in liquid MMA monomer subjected to addition polymerization. The resulting bulk material is thén reduced to a powder.
' Fabrication of a bone cement involves placin~
: the pr~viously prepared powder in MM~ monom~r also having a quantity o~ previously sized reinforcing fibers therein, ~ollowed by polymerizatisn of the monsmer. This creates .

WO~3/166~1 2 1 2 ~ 9 7 1 PCT/~IS~3/00056 --5-- .
a continuous poly~eric medium with the fiber-reinforced powder particles dispersed therein.
The fabrication of implant coatings is similar, Pxcept that such coatings generally do not contain the particulate powder fraction. Rather, th~se coatings comprise a continuous polymeric phase ~e.g., PMMA) having previou~ly sized reinforcing fibers therein. The coatings are adapted for applica~ion and chemical joinder to the outer surface of a rigid implant, in such fashion that the : 10 reinforcing fibers thereof extend outwardly from the : coating surface.
A complete implant installation system is made : up of a previously ~oated implant together with a bone ~:~ cement. In practice, a precoated orthopaedic implant is inserted into a previously reamed and cement-filled bone cavity. The sized fibers reinforcing both the continuous media and the cement and the c~ntinuous phase of the coating, and the fibers protrudin~ from the reinforcing cement particles, extend acros~ the coating/~one cement : 20 interface to enhance the bonding and chemical joinder between the coating and cemen~. The implant is thus firmly held in place.
: :
Brief Descrie~ion of the Drawin~s Figure l is a schematic, greatly enlarged cross-sectional view of a part of a sized fiber forming a part of a reinforced orthopaedic composition;
Fig. 2 is a ~reatly enlarged, schematic cross-, sectional representation of a PMMA powder particle with , reinforci~g fibers within the particle and especially adapted for incorporation in a bone cement composition, ~ . with the way in which certain of the ~ibers protrude : ~ through th~ ou~er surface of the particle being illus-; trated;
~,, .

W093/166~)1 2 1 ~ 9 ~ 7 ~ PCT/~S93~0~6 ~ig. 3 is a greatly enlarged, sche~atic cross-sectional representation of a reinforced bone cement containing the partic~late powder of the invention dis-persad in a continuous medium along with radiopa~ue particles;
Fig. 4 is a greatly enlarg~dt srhematic fragmen-tary cross-sectional view showing a rigid implant with a sized fiber reinforced PMMA coating thereover, and with the coated implant imbedded in a quan ity of bone cement of the type deplcted in Fig. 3, and further showing the interface between the implant coating and bone cement; and Fig. 5 is an enlarged, schematic, fragmentary cross sectional r~presentation of a rigid implant in a ~ bone cav? ty and illustrating the way in which bone cem~nt : 15 is used to firmly af~ix the implant to the interstices of t~e bone.

Detail~ D~$cr~io~ o$ th~ Pref~rr~ gmboq~ts A key principle of the pre~ent invention resides in the provision of a multiple-use orthopaedic composition broadly including an amount of a physiologically accept-: able polymeric matrix material with a quantity of siz d fibers dispersed in the matrix material. Such an ortho-paedi composition can be fabricated as a particulate ~25: powder 10 adapted for placemen~ in a continuous medium 12 to form a bone cement 14; as a continuous fluid medium 12 useful in a bone cemen~ context; or as a coating 16 for application to an orthspaedic appliance 18.
In general, the orthopaedic o~p~siti3ns o~ the invention includ~ fibers 20 having a layer of siæing ~aterial 22 thereover which is chemically joined ~o the : surface of the~fibers, with the sizing material on the ibers also being chemically joined to ~h~ matrix.
. Generally, ~he fibers are present in the orthopaedic c~mpositions at a level of at l~a~t about 6 volume percent ~ .
, Sl~BSlll''U~ ~HE-~

W093/16661 _7_ 212 9 9 ~ ~ PCT/~IS93JOOQ56 and have an average leng~h of from about l ~m to about 2 cm. The siæing material may be directly joined to the fibers, or u~e ~an be made of a coupling agent different from the matrix, such as a silane. The fibers are advan-tageously polymeric and are formed of a rel~tively hish ~trength polymer of in~ermediate s~iffness.

Particul~t~ Po~r In one specific aspect of the invention, the orthopaedic compositions may be fabricated as powders especially adapted for use in bone cements. In such a : ¢on~ext/ the particles of the powder would have an av~rage size of from absut 5 to lOO ~m, and are broadly made up of . the polymeric matrix ~nd sizsd fibers. Advantageously the .
fiber are of polymeric character and are selected from the group consisting of aramids~ polyesters, polyalkenes and polyamids. The fibers should ha~a a diameter of from ~: about ~ ~m to lOO ~m, and more preferably at least certain : of the fibers shsuld have a diameter of from about 2-15 ~m. ~he length of the fibers is variable, dependi~g upon desired end use~
Rarticularly good results have been found by using fibers having a stiffness ldefined as the product of the tensile elastic modulus of the fibers and the area ~ moment o~ inertia of the fibers) of from about l.O x 10-13 : to~l50 x 10-13 Nm2, and more preferably ~rom about ~0 x lOl3 m to 75 x lO-13 Nm2. The room temperature fatigue strength of the ~ibers should be at least about 7 NPa at 106 cycles, mor~ pre~erably at least about 30 NPa at lO6 cycles.
In the speci~ic context of par~iculat~ p~ders, 'the ~ibers should be present at a level of from about 6-70 . volume perc~nt, most preferably about 50 Yolume percent.
: . The matrix component is advan~ageously a substi-, tuted or unsubs~ituted acrylate, esp~cially polymethyl-,: , .

5UBS~ITI)TE SHEET

WO93/166~ 2 9 ~ 8- PCT/~IS93/~56 methacrylate having a viscosity average molecular weight of not less than about l x 105 g./mole.
As indicated, the fibers forming a component of the particles should be sized. The sizing agent is normally selected from the group consisting of ethyl silane, methyl~et~acryl~te, ethylmethacrylate, e~hylene, propylene and methane. The most preferred sizing agents are the a~rylates, specifically methylmethacrylate.
If desired, a radiopaque agent 24 may be added to the particulate powder, and in such a case the radi-opaque agent would have sizing material chemically joined thereto. The preferred radiopa~ue agent is zirconium dioxide, present at a level hetween 1-15% by weight of the ; ~ powder. Barium sulfate is also acceptable. The radi-; 15 opaque powder desir~bly has a diameter of about 1 ~m, although other sizes may be used.
In fabrication procedures, the sizing material is first chemically joined o the poIymeric fibars. ~he technique to accomplish this is normally selected fr~m the 0 group :consisting of glow discharge induc~d reaction, : ultraviolet induced reaction, free-radical induced reac-: tion, and catalytic reaction. The preferred technique is glow discharge induced reaction.
In the pref erred procedure, the properl y sized poly~eric fibers are introduced into a r~3action vessel :which is then e~acuated to a level of from about 0~l3 to : : I3 Pa to degas the ~ibers. A flowing stream of sizing :; agent is then~ introduced into the evacuated reaction v~ssel and maintained at a pressure of from about l~3 to 133 PaO Best re~ults are obtain~d if the sizing agent pres ureiin the reaction vessel~is maintained at a level o~ from about 7-35 Pa. ~ethylmethacrylate in the gaseous state i. the preferred sizing agent.
During the sizing procedure, the fibers in the 3 5 reac~ion vessel are suitably agitated, as by rotation or SUBSTI~UTE SH~EI

~093/16~61 2 1 2 9 ~ 7 j~ PCTJUS93/00056 sh~kîng of the vessel, to assure exposure of all fiber c.~face~ to the sizing agent. A hiyh frequency electro-m~netic field, such as is created by a microwave unit, is then applied ~o the contents of the vessel~ It is pre-ferred that the field have a frequency of up to about lO0 MHz (more preferably from about 5-15 MHz) at a power l~vel of at least about 20 W. This treatment of the fiber~ in the pres~nce of the sizing agent causes glow discharge polymerization of the sizing a~ent on th~ surfaces of the fibers. The time o~ exposure is variable dependent upon the quantity o~ fibers being processed and the surface area and density thereof. In one exemplary case, 30 ::: minutes o~ exposure time is appropriate, for a 0.05 kg quantity of fib~rs having a diameter of about lO ~m and a density of about 1 g./cm3. Proper equivalent exposure :~ . times may be employed for other quantities and types of fibers~ Sizin~ of the fibers with MMA using glow dis-charge polymerization causes the MMA molecules to become :chemically joined to the surface molecules of the poly-, ~ ~
: meric fibers~ .
Following sizing, the fi~ers may be mixe~ with matrix. Typically, the fibers are- initially mixed with monomer, and the mixture subjected to polymerization. For ex~mple, where liquid methylmethacrylate is used as the 25 ~ monomer, poly~erization may be accomplished using conven-tional addition polymerization techniquPs. For example, the MMA may be caused to polymerize by addition of a uitable amoun~ of an initiator such as benzoyl peroxide, Polymerization of~the MMA in the presence of the sized fibers causes the ~MA during ~such polymerization to chemically ~join with the sizing on the fibers and thus produ ~ a strong chemical coupling of the r~sultant polymethylmethacrylate to the acrylate sizing on the fibers.

~ .

~ :

WO 93/16S61 ~ ~ 2 ~, 3 7 ~ PCT/~'S93/0 ~6 The penultimate step in preparation of the particula~e powder involves reducing the bulk reinforced polymer t~ the desired particle size. As indicated, the powder should have an average particle size of from about 5-100 ~m. A proportion of very fine powder, less than 0.1 ~m, is als~ desirable. The powdered material is produced by milling relatively large pieces of the sized fiber reinforced polymer. Mixing or grinding of the polymer has the adv~ntage that some of the ends of the reinforcing fibers are exposed during fracturing of the bulk polymer as schematically depicted in Fig. 2. Reducing the temper-ature during milling to 0C or less facilitates brittle f,racture of the bulk polymer and exposure of fiber ends.
~: The fiber reinforced powder made up of particles such as illustrated in Fig. 2 is next blended with an additional quanti~y of sized fibers which may constitute from about 1% to about 15% by weight of the mixture. If . a~radiopaque agen~ is used, it may also be combined with the~powder and additional sized fibers. Best results are 0 ~btained if the radiopaque agent is also sized using glow :
discharge polymerization and a sizing agent of the same type:as used ~or sizing the polymeric fibers. Thus, if MMA i5 used to size the f ibers, MMA should also be used to size the radiopaque agent. Bulk polymer reduction and the addition of extra fiber serves to create final powder particles having reinforcing fibers extending through and :at least partially out of the p~rticles, as shown in Fig.
2. Fibers of this type are important in the production of bone cements, as will be described.
~; 30 ~':1 ~ ' : I
Co~ti~uou~ Me~lum for ~o~ C~
The sa~e general principlas described previously ¢an also be employed in the ~abrication of aon~inuous .

~93/16661 2 1 2 3 9 7 ~1 PCT/~S93/00056 media used in bone cements~ Again, such media broadly ir.clude a polymeric matrix wi~h sized fibers therein.
For purposes of continuous bone cement media, the same fibers described with ref~rence to the particu-late powder may be employed. However, the fiber content Of such media will generally be lower than the fiber content of the powder, i.e., the media should contain from about 6-20 volume percent of sized fibers. Moreover, in this context the length of the fibers may be greater, with ; 10a leng~h of up to about 5 mm having been found to be : suitable.
Similarly, the polymeric matrix fraction of the ,ontinuous medium is the same as that used in connection with the powders, although there will be correspondingly a greater proportion of matrix present in the continuous media, as compared with the particulate powder product.
The sizing materials and sizing techniques desc~ibed previously are also used in the creation of the continuous media products of the invention. ~f radiopaqu~
;20~ ~ agents are to be used in the continuous media, the same considerations, techniques and ingredients previously detailed, are us~d.

Bone ~
25~A complet~ bone cement m~y be prepared by the mix~ure o~ a particulate powder ~including fibers extend-: ing partially out~of the particles~ and continuous~medium ~ade in accordanc~ with the invention. The final cement should contain ~fro~ about 55-80% by weight powdPr, with ~ :, 30the balance being continuous medium~
Generally speaking, t~e final bone cement and continuous medium are created simultan~ously by the mixing o~ a precursor monomer to constitu~e ~he continuous medium, with the appropriate quantity of pr viously 35prepared powdex. For example, the appropriate quantity of W093/16661 2~299 1 ~ --12-- Pcr/us93/~ ~6 MMA monomer may be mixed with the particulate powder, with the MMA then being subjected to final polymerization.
Where MM~ is used, small amounts of additi~es may be used -to promote room temperature polymerization. Exemplary additi~es are accelerators (e.g., N,N-dimethyl paratoluid ine), initiators (P.g., benzoyl peroxide~ and stabilizers (e.g., hydroquinone). Typically, the mixture and polymer-ization of precursor monomer and powder is done just prior to u~e of the cement for attachment of an orthopaedic implant.
During incorporation of the sized fiber-rein-forced powder into the continuous medium, the liquid ~recursor monomeric material, the latter contact~ the polymerized matrix of the particles, thereby solubilizing at least a part of the surfaces of the particles, so that there is intermixing of the precursor monomer undergoing ~: polymerization to form the continuou~ medium, with the previously polymerized matrix. This intermixing contrib-: ~ utes to the s ability and strength of the bone cement, and 0 increases the functional life thereof.
The proportion of fibers in the complete bone cement, and the ratio of particulate powder to continuous `: :
medium, influence the viscosity of the cement. According-:ly, these parameters may be adjusted within the ranges dsscribed so as:to achieve the proper ~iscosity required or ease of use in a surgical context~ In many cases, it is desirable to effect mixing of the cement components in : : a ~vacuum mixer, cr to use other precautions to minimize bubble entrapment~. The full strengthening effect of the sized reinforced fibers is best realized when the size andnumber of entrapped bubbles are reduced to a minimum.
The resulting bone cement ~hus comprises fiber-reinforced continuous mediumiof physiologically acceptable polymeric material, with par~iculate powder di~persed ~herein and made up of polymeric matrix and reinforcing ~,j, . '"!' .'' ' ~"' ' ' '~"'' ~093/166~1 21 2 9 9 7 ~ PCT/~iS93/000~6 fibers extending through and at least partially out of ~he particles. The polymeric material of the continuous medium is chemically joined at the particle/continuous medium interface 24a with both the reinforcing fibers thereof and the fibers extending from the powder particles to cr~ate a cement of enhanced str~ngt~. Whe~e radiopaque agents are employed in the particles and/or continuous medium, such would also of course be present in he final cement. Inasmuch as the previously described particulate powder and continuous media are used in the preparation of the final bone cement, the parame~ers discussed above pertaining to fibers, sizing agent~ and matrices apply to tpe finished bone cement as well.

Coatina for_OrthoPa~fli~ Im~la~t The ~undamental orthopaedic compositions of the : inv~ntion can also be modified to obtain coating~ adapted ~: for direct application to an orthopaedic applian~e or i~plant, such as a metallic or polymeric prosthetic hip ~ implantO Broadly speaking, such coatings include a physiologically acceptable polymeric continuous phase with sized reinforcing fiber~ dispersed in the continuous phase. When such coatings are applîed over the outer surfaces of an implant or appliance, the coatings are : 2S : chemically joined with the surf~ce, thereby maximizing the strength of the composite.
Insofar as the ~iber component of such coatings is concerned, the parame~ers described above respecting the continuous medium for bone cements are ~ully applica-ble. Similarly, the continuous pha~e portion o~ the ~ coatings are the same as those used in the continuous : media for bone cements.
Following the fiber si~in~ operati~n~ the fibers - are mixed with precursor monomer, and mo~t preferably : 35 liguid MM~ for polymerization using conventional tech-SuBsTlTlJT S~EET

WO93/16661 ~ 9~ 14- PCT/~'S93/~ ~6 ni~ues, preferably addition polym~rization. The MMA may be caused to polymerize through use of an initiator such as benzoyl peroxide~ If desired, the implant may be provided with a roughenPd surface which enhances adher nce of the coating thereto. Alternately, the sizing agent used in preparation of the coating reinforcement may be applied directly to the outer surface of the impla~t, using the techniques described previously. In this fashion, the sizing agent is chemically joined with the outer surface of the implant and the coating to be applied thereo~er.
The coatings may be applied to the implants well p~ior to actual use thereof. For example, the manufactur-er of a metal or polymeric implant may coat its implant : 15 product at the time of fabrication, and the coated ortho-paedic device may then be shelved until needed. Addition-~:~ ally, afker such implant coating, the outer surface of the coating may be etched with MMA monomer or othPr suitable : etchant, either in liquid or vapor form. From about O.l 20~ ko 1 mm of the surface of the coating is desirably re-mo~ed, to expose the ends of sizad fibers, so that such fibers will extend across the interface 25 between the implant coa~ing and bone cement.
,, Ortho~eai~ I~ELlant Installatio~ ~Yste~
The in~ention ultimately provides a greatly improved system for the permanent implantation of ortho-paedic devices. Such a syst~m includes the described oating on the surface of the orthopaedic device, together with bone cement serving to contact and adhere to a bone , surface whil~ al50 contactin~ the implant oatin~.
During orthopaedic urgery, involving, f or - ~ ~:; example, a hip joint replacement where there has been a r~cture of the upper end o~ the f emllr, the f emoral head i!3 remcved by a saw or o~her equivalerlt dev~ce which ::
' . ' .

SUBS~TU ~ E SH~

~093/16661 2 1 2 ~ ~ 7 ~ PCT/~'S93J00~5~

produces a smooth cut, thUs exposing the spongy bone and marrow cavity within the hard cortical bone. The marrow cavity is then reamed to remove spongy bone and marrow to an extent that the rigid, previously coated and etched implant may be inserted into the cavity along with an appropriate quantity of bone cement.
The preferred bone cement previously described made up of the continuous medium and particulate powder is : then injected into the reamed bone cavity to fill the ~anal with bone cement. The rigid, precoated orthopaedic implant is then in erted into the cement-filled bone cavity. There is a firm chemical joinder of the oated Lmplan~ to the bone structure not only because of the :~ presence of the cem nt initially introduced into the bone cavity, but also by virtue of the fact that the cement has completely filled the interstices of the internal bone structure 26 as is illustrated in Fig. 5. The reinforcing fibers in the bone cement are of sufficient flexibility that they do not impede free flow of the cement composi-20 ~ tion into the small interstices of he bone structure, or :: bridge openings lead-ing to such interstices, as has occurred with prior fiber-reinforced orthopaedic cements.
Fig. 4 illustrates an implant disposed within a bone cavity, and held therein by the system of the inven-25: tion. ~s depicted, the sized fibers reinforcing both thecontinuous medium of the cement and the implant coating, as well as the fibers protruding from the particles, extend across the coating/bone cement interface 25 to enhance the bonding and chemical joinder between the coating and cement.

Alter ~
For certain orthopaedic applications, it may not .~ be necessary to incorporate sized fiber~ in the powder ~ 3S particles ~s previously described and sp~cifically illus-:
:

SllBSTlTlJTE SHEET

WO93/16661 PCT/~'S93/Or -6 2 ~ 2 9 9 7 1 -~6-trated in Fig. 3 of the drawings. Since fatigue cracking occurs primarily in the continuous medium of the bone cement~ reinforcement of this medium only realizes much of the potential benefit of the invention. In this manner, less changes in current bone cement manufacturing pro cesses are required.
In carrying out this alternate embodiment of the invention, sized fibers and sized radiopaque powders are dry blended, but with unreinforced PMMA powder. The blend i~ then mixed with room temperature precursor MMA (liquid) monomer to yield a bone cement with the coupled radiopac~
ifier and rDinforcing fibers in the continuous medium o~ly.
An alternative process for sizing of the fibers includes rotation of the reaction vessel to insure expo-ure of the fibers to the sizing agent throughout the sizing step. Similarly, the fibers may be agitated by a variety of means including, but not limited to, mechani-al, electromagn~tic or rheologic processss such as shaking, tumbling,: or free fall in a column, electromag~
netic levitation or electrostatic self-repulsion, and the creatio~ of ~ortices in the flowing (gaseous) coupling gen~.
Instead of milling or grinding the bulk rein-~orced polymer during powder preparation, the powderparticles may be prepared by combining fiber incorporation with bead pol~merization.
~: :

'~ , SUBSTITUTE~ SH~ET

Claims

Claims:

1. An orthopaedic composition, comprising:
an amount of a physiologically acceptable poly-meric matrix material; and a quantity of fibers disbursed in said matrix for enhancing functional qualities of the composition, said fibers having a layer of a sizing material thereover which is chemi-cally joined to the surface of the fibers, said sizing material on the fibers also being chemically joined with the matrix material, said fibers being present in said composition in an effective amount for reinforcing said matrix and having an average length of from about 1 µm to about 2 cm, said fibers having a stiffness defined as the product of the tensile elastic modulus of the fibers and the area moment of inertia of the fibers, said stiffness being from about 1.0 x 10-13 to 150 x 10-13 Nm2.

2. An orthopaedic composition as set forth in claim 1, wherein said sizing material is directly chemi-cally joined to said fibers.

3. An orthopaedic composition as set forth in claim 1, wherein said sizing material is a coupling agent different from said matrix.

4. An orthopaedic composition as set forth in claim 1, wherein said fibers comprise polymeric reinforc-ing fibers formed of a relatively high strength polymer of intermediate stiffness.

5. An orthopaedic composition as set forth in claim 1, said composition being in the form of a particu-WO 93/16661 ?93/00056 late powder adapted for placement in a continuous medium to form a bone cement.

WO 93/16661 PCT/US93/???56

6. An orthopaedic composition as set forth in claim 5, the particles of said powder having an average size of from about 5 to 100 µm.

7. An orthopaedic composition as set forth in claim 5, said fibers being in the form of polymeric fibers.

8. An orthopaedic composition as set forth in claim 7, said fibers being selected from the group con-sisting of polyaramids, polyesters, polyalkenes and polyamides.

9. An orthopaedic composition as set forth in claim 7, said fibers having a diameter of from about 1µm to 100µm.

10. An orthopaedic composition as set forth in claim 9, wherein at least certain of said fibers have a diameter of from about 2-15µm.

11. An orthopaedic composition as set forth in claim 7, said fibers having a length of up to about the diameter of said particle.

12. An orthopaedic composition as set forth in claim 7, said fibers having a stiffness defined as the product of the tensile elastic modulus of the fibers and the area moment of inertia of the fibers from about 1.0 x 10-13 to 150 x 10-13Nm2.

13 . An orthopaedic composition as set forth in claim 12, wherein said stiffness is from about 10 x 10-13 to 75 x 10-13Nm2.

14. An orthopaedic composition as set forth in claim 7, wherein said fibers have a room temperature fatigue strength of at least about 7 MPa at 106 cycles.

15, An orthopaedic composition as set forth in claim 14, said fatigue strength being at least 30 MPa at 106 cycles.

16. An orthopaedic composition as set forth in claim 7, said fibers being present in said powder at a level of from about 6 to 70 volume percent.

17. An orthopaedic composition as set forth in claim 16, said level being about 50 volume percent.

18. An orthopaedic composition as set forth in claim 5, wherein said matrix is a substituted or unsubsti-tuted acrylate.

19. An orthopaedic composition as set forth in claim 18, said matrix being polymethylmethacrylate.

20. An orthopaedic composition as set forth in claim 19, said polymethylmethacrylate having a viscosity average molecular weight of not less than about 1 x 105 g./mole.

21. An orthopaedic composition as set forth in claim 5, wherein said sizing material is selected from the group consisting of ethyl silane, methylmethacrylate, ethylmethacrylate, ethylene, propylene and methane.

22. An orthopaedic composition as set forth in claim 21, wherein said sizing material is an acrylate.

23. An orthopaedic composition as set forth in claim 21, wherein said sizing material is methylmeth-acrylate.

24. An orthopaedic composition as set forth in claim 5, including a radiopaque agent, said agent having said sizing material thereover.

25. An orthopaedic composition as set forth in claim 5, wherein said sizing material has been chemically joined to the fibers by a technique selected from the group consisting of glow discharge induced reaction, ultraviolet induced reaction, free-radical induced reac-tion and catalytic reaction.

26. An orthopaedic composition as set forth in claim 25, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out at a frequency of up to about 100 MHz at a power level of at least about 20 W.

27. An orthopaedic composition as set forth in claim 26, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out at a frequency between about 5-15 MHz.

28. An orthopaedic composition as set forth in claim 25, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out for a time period equivalent to 30 minutes exposure for each 0.05 kg of fibers having a density of about 1g/cm3 and an average diameter of about 10 µm.

29. An orthopaedic composition as set forth in claim 1, said composition being in the form of a continu-ous medium adapted for mixing with reinforced particles to form a bone cement.

30. An orthopaedic composition as set forth in claim 29, said fibers being in the form of polymeric fibers.

31. An orthopaedic composition as set forth in claim 30, said fibers being selected from the group con-sisting of polyaramids, polyesters, polyalkenes and polyamides.

32. An orthopaedic composition as set forth in claim 30, said fibers having a diameter of from about 1µm to 100µm.

33. An orthopaedic composition as set forth in claim 32, wherein at least certain of said fibers have a diameter of from about 2-15µm.

34. An orthopaedic composition as set forth in claim 29, said fibers having a length of up to about 5 mm.

35. An orthopaedic composition as set forth in claim 29, said fibers having a stiffness defined as the product of the tensile elastic modulus of the fibers and the area moment of inertia of the fibers, from about 1.0 x 10-13 to 150 x 10-13Mm2.

36. An orthopaedic: composition as set forth in claim 35, wherein said stiffness is from about 10 x 10-13 to 75 x 10-13Nm2.

WO 93/16661 PCT/US93/???56

37. An orthopaedic composition as set forth in claim 29, wherein said fibers have a room temperature fatigue strength of at least about 7 MPa at 106 cycles.

38. An orthopaedic composition as set forth in claim 37, said fatigue strength being at least 30 MPa at 106 cycles.

39. An orthopaedic composition as set forth in claim 29, said fibers being present in said medium at a level of from about 6-20 volume percent.

40. An orthopaedic composition as set forth in claim 29, wherein said matrix is a substituted or unsub-stituted acrylate.

41. An orthopaedic composition as set forth in claim 40, said matrix being polymethylmethacrylate.

42. An orthopaedic composition as set for h in claim 41, said polymethylmethacrylate having a viscosity average molecular weight of not less than about 1 x 105 g./mole.

43. An orthopaedic composition as set forth in claim 29, wherein said sizing material is selected from the group consisting of ethyl silane, methylmethacrylate, ethylmethacrylate, ethylene, propylene and methane.

44. An orthopaedic composition as set forth in claim 43, wherein said sizing material is an acrylate.

45. An orthopaedic composition as set forth in claim 43, wherein said sizing material is polymethylmeth-acrylate.

46. An orthopaedic composition as set forth in claim 29, including a radiopaque agent, said agent having said sizing material thereover.

47. An orthopaedic composition as set forth in claim 29, wherein said sizing material has been chemically joined to the fibers by a technique selected from the group consisting of glow discharge induced reaction, ultraviolet induced reaction, free-radical induced reac-tion and catalytic reaction.

48. An orthopaedic composition as set forth in claim 47, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out at a frequency of up to about 100 MHz at a power level of at least about 20 W.

49. An orthopaedic composition as set forth in claim 47, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out at a frequency between about 5-15 MHz.

50. An orthopaedic composition as set forth in claim 47, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out for a time period equivalent to 30 minutes exposure for each 0.05 kg of fibers having a density of about 1g/cm3 and an average diameter of about 10 µm.

51. An orthopaedic composition as set forth in claim 1, said composition being in the form of a coating for application to an orthopaedic appliance.

52. An orthopaedic composition as set forth in claim 51, said fibers being in the form of polymeric fibers.

53. An orthopaedic composition as set forth in claim 52, said fibers being selected from the group con-sisting of polyaramids, polyesters, polyalkenes and polyamides.

54. An orthopaedic composition as set forth in claim 52, said fibers having a diameter of from about 1µm to 100µm.

55. An orthopaedic composition as set forth in claim 54, wherein at least certain of said fibers have a diameter of from about 2-15µm.

56. An orthopaedic composition as set forth in claim 51, said fibers having a stiffness defined as the product of the tensile elastic modulus of the fibers and the area moment of inertia of the fibers, from about 1.0 x 10-13 to 150 x 10-13Nm2.

57. An orthopaedic composition as set forth in claim 56, wherein said stiffness is from about 10 x 10-13 to 75 x 10-13Nm2.

58. An orthopaedic composition as set forth in claim 51, wherein said fibers have a room temperature fatigue strength of at least about 7 MPa at 106 cycles.

59. An orthopaedic composition as set forth in claim 58, said fatigue strength being at least 30 MPa at 106 cycles.

60. An orthopaedic composition as set forth in claim 51, said fibers being present at a level of from about 6 to 70 volume percent.

61. An orthopaedic composition as set forth in claim 60, said level being about 50 volume percent.

62. An orthopaedic composition as set forth in claim 51, wherein said matrix is a substituted or unsub-stituted acrylate.

63. An orthopaedic composition as set forth in claim 62, said matrix being polymethylmethacrylate.

64. An orthopaedic composition as set forth in claim 63, said polymethylmethacrylate having a viscosity average molecular weight of not less than about 1 x 105 g./mole.

65. An orthopaedic composition as set forth in claim 51, wherein said sizing material is selected from the group consisting of ethyl silane, methylmethacrylate, ethylmethacrylate, ethylene, propylene and methane.

66. An orthopaedic composition as set forth in claim 65, wherein said sizing material is an acrylate.

67. An orthopaedic composition as set forth in claim 66, wherein said sizing material is polymethylmeth-acrylate.

68. An orthopaedic composition as set forth in claim 51, including a radiopaque agent, said agent having said sizing material thereover.

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69. An orthopaedic composition as set forth in claim 51, wherein said sizing material has been chemically joined to the fibers by a technique selected from the group consisting of glow discharge induced reaction, ultraviolet induced reaction, free-radical induced reac-tion and catalytic reaction.

70. An orthopaedic composition as set forth in claim 69, wherein flow discharge reaction of the sizing material while in contact with said fibers is carried out at a frequency of up to about 100 MHz at a power level of at least about 20 W.

71. An orthopaedic composition as set forth in claim 70, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out at a frequency between about 5-15 MHz.

72. An orthopaedic composition as set forth in claim 70, wherein glow discharge reaction of the sizing material while in contact with said fibers is carried out for a time period equivalent to 30 minutes exposure for each 0.05 kg of fibers having a density of about 1g/cm3 and an average diameter of about 10 µm.

73. A bone cement comprising:
a continuous medium comprising a physiologically acceptable polymeric material; and a particulate powder dispersed in said continuous medium, the particles making up said powder including a physiologically acceptable polymeric matrix and reinforcing fibers extending through and at least partially out of the particles, said polymeric material of the continuous medium being chemically joined with said fibers.

74. The bone cement of claim 73, said powder comprising from about 55-80% by weight of the bone cement.

75. The bone cement of claim 73, said continu-ous medium comprising a substituted or unsubstituted acrylate.

76. The bone cement of claim 75, said continu-ous medium comprising polymethylmethacrylate.

77. The bone cement of claim 73, said continu-ous medium including therein fibers distinct from the fibers present in said particles.

78. The bone cement of claim 73, said continu-ous medium including therein an amount of sized radiopaque agent.

79. The bone cement of claim 73, said fibers being selected from the group consisting of polyaramids, polyesters, polyalkenes and polyamides.

80. The bone cement of claim 73, said fibers having a layer of sizing material thereover chemically joined to the surface thereof, said sizing material on the fibers also being chemically joined with said matrix material.

81. The bone cement of claim 80, said continu-ous medium also being chemically joined to the sizing material on said fibers.

82. A system for permanently installing an orthopaedic appliance, said system comprising:
a coating adapted for application on the surface of said appliance, said coating including a poly-meric continuous phase having therein and ex-tending outwardly from the surface thereof a plurality of fibers, said fibers having a layer of sizing material thereover which is chemically joined to the surface of the fibers and also chemically joined with said continuous phase;
and bone cement adapted for contacting and adhering to a bone surface, and for contacting said coating, said bone cement including a polymeric: continu-ous medium chemically joined with the portions of said fibers extending outwardly from the surface of said coating.

83. A coated orthopaedic appliance, comprising:
a rigid orthopaedic appliance presenting an outer surface; and a coating applied over said outer surface and chemi-cally joined with said surface.

84. The appliance of claim 83, there being a sizing agent applied to said outer surface and chemically joined with both said outer surface and said coating.

85. A method of preparing an orthopaedic composition comprising the steps of:
chemically bonding a layer of a sizing material onto the outer surfaces of a quantity of fibers; and polymerizing a monomeric material in the presence of said sized fibers for chemically joining the sized fibers to the resultant polymerized mate-rial in order to enhance the properties of the orthopaedic composition.

86. A method of preparing an orthopaedic composition as set forth in claim 85, wherein said step of chemically bonding a sizing material to the fibers com-prises using a technique selected from the group consist-ing of glow discharge induced reaction, ultraviolet induced reaction, free-radical induced reaction, and catalytic reaction.

87. A method of preparing an orthopaedic composition as set forth in claim 86, wherein glow dis-charge polymerization is employed to couple a sizing layer onto the surface of the fibers, said glow discharge polymerization being effected by exposing the surfaces of the fiber and the sizing material to an electromagnetic field at a frequency of 1 to 100 MHz at a power of at least 20 W per square centimeter of fiber surface area.

88. A method of preparing an orthopaedic composition as set forth in claim 87, wherein said compo-sition is in the form of a bulk solid, and further includ-ing the steps of comminuting said bulk solid to form a particulate powder.

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89. A method of preparing an orthopaedic implant comprising the steps of:
providing a rigid orthopaedic implant presenting an outer surface; and applying to said outer surface a coating comprising a physiologically acceptable polymeric continu-ous phase having a quantity of polymeric rein-forcing fibers therein which extend outwardly from said coating, there being a layer of sizing material over said fibers and chemically joined with said fibers and continuous phase.

90. The method as set forth in claim 89, including the step of etching the outer surface of said coating material to remove from about 0.1-1 mm of the matrix material in order to expose the outer ends of said fibers.

91. The method as set forth in claim 90, said etching step comprising the steps of contacting said outer surface of said coating with an effective solvent for said continuous phase.

92. An orthopaedic composition, consisting essentially of:
an amount of a physiologically acceptable poly-meric matrix material, said material se-lected from the group consisting of substi-tuted acrylates and unsubstituted acrylate-s; and a quantity of fibers disbursed in said matrix for enhancing functional qualities of the composition, said fibers having a layer of a sizing material thereover which is chemi-cally joined to the surface of the fibers, said sizing material on the fibers also being chemically joined with the matrix material, said fibers being present in said composition in an effective amount for reinforcing said matrix and having an average length of from about 1 µm to about 2 cm, said fibers having a stiffness defined as the product of the tensile elastic modulus of the fibers and the area moment of inertia of the fibers, said stiffness being from about 1.0 x 10-13 to 150 x 10-13 Nm2.