AU617159B2

AU617159B2 - A bone implant

Info

Publication number: AU617159B2
Application number: AU31627/89A
Authority: AU
Inventors: Roy D. Crowningshield; Thirumalai N.C. Devanathan; Jack E. Parr; Howard C. Price; Abner K. Wang
Original assignee: Bristol Myers Squibb Co
Current assignee: Bristol Myers Squibb Co
Priority date: 1988-03-22
Filing date: 1989-03-22
Publication date: 1991-11-21
Anticipated expiration: 2009-03-22
Also published as: BE1002983A5; IT1228684B; JPH01317435A; GB2216425B; GB8906098D0; DE3909545C2; AU3162789A; NL8900692A; FR2628966A1; JP2823585B2; GB2216425A; DE3909545A1; CA1332098C; IT8919842A0; FR2628966B1

Description

fe: i L '1u AUSTRALIA Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

617159 Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art:

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APPLICANT'S REFERENCE: ZM-0125 Name(s) of Applicant(s): r-i-stol-Myers- ompany- ris(o (Wsh ,Address(es) of Applicant(s): 345 Park Avenue, New York, New York, UNITED STATES OF AMERICA.

Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Ma-k Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA COAna 'I O M Complete Specification for the invention entitled: A BONE IMPLANT Our Ref 126899 POF Code: 1490/1490 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 6003q/1 1 1_ 1_ M 0125 A BONE IMPLANT The present invention relates to a bone implant which is used in a surgical proceeding to repair or reconstruct skeletal deformities. These bone implants have been utilized by orthopaedic surgeons in hip and knee arthroplasty to reconstruct articulating joints, as well as in trauma situations to secure fractured bones together.

Various metals have been propose.d to manufacture bone 'o implants. Titanium and cobalt chrome, for example, are in wide spread use because of their biocompatibility with bone tissue *o.0 and their strength characteristics for carrying loads imparted o to the skeletal structure following implantation. With a metal bone implant, U.S. Patents 3,605,123 and 3,900,550 further provide a porous metallic surface to enhance fixation of the *1r implant with a resected bone at the intramedullary canal.

These metals are stronger than bone; however, bone is somewhat o flexible, and the stiff metals do not exactly match the flexibility of bone. As a result, numerous recent articles and ."o0 c patents are proposing the use of composites or nonmetals for '0o: the construction of bone implants in order c. provide the implant with a modulus substantially the same- E bone.

In United States Patent 4,662,887 a polyetheretherketone commonly referred to as PEEK is disclosed for use as an orthopaedic device. The PEEK polymer is biocompatible and sufficiently flexible In fiial form to approximate the anatomic elasticity of bone. In Hochman United States Patent 3,893,196, a composite hip implant is provided with a graphite fiber core, an outer layer of graphite fiber circumscribing the core and a plastic skin enclosing all of the fiber and providing a porous

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-2plastic surface to enable the bone to knit thereto. In further support of Hochman is Patent 4,164,794, wherein a porous composite material is provided on the surface of a hip prosthesis to enhance fixation to bone.

Comparing the metal implant with the composite implant, advantages and disadvantages are apparent. With the metal implant, the strength characteristics of metals results in a stiff implant which may stress shield portions of the bone. To date, no composite implant has established the intimate bone association believed to be necessary for adherence to bone for long term fixation in spite ,f the numerous attempts to provide a porous composite surface for the composite implant. Further it is believed that polymer oo 0:0 surfaces may be insufficiently durable to transfer load and o posses inadequate abrasion resistance for long term ~fixation.

p94090 0 0 00 o The present invention teaches an orthopaedic implant which incorporates the advantages of metal and composite materials. Rather than relying upon a total composite or a total metal implant, the invention provides a composite core which closely approximates the flexibility of bone and o a porous metallic surface secured to the composite core so that bone growth and/or cement will readily penetrate and o adhere to the porous metallic surface for long term fixation of the orthopaedic implant.

It is an advantage of the present invention that the composite/metal implant approximates the flexibility of bone and provides a porous metallic surface which is readily compatible with bone to provide unrestricted ingrowth of bone into the porous surface and such porous metallic surface is

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sufficiently strong and durable to provide for long term fixation. Moreover, the porous metallic surface is provided by a metallic fiber metal pad which resists abrasion and remains integrally secured to the composite core during implantation as well as after implantation.

In the drawings, Figure 1 is a side view of a femoral component following implantation. Figure 2 is a cross sectional view taken along line 2-2 of Figure 1. Figure 3 is a 'cross sectional view taken along line 3-3 of Figure'1. Figure I' 4 is a cross sectional view of the porous fiber metal pad separate from the composite stem, and Figure 5 is a view S similar to Figure 3 showing an alternative embodiment of the invention.

ooo* .The femoral component 10 is surgically implanted into the intramedullary canal 12 of the femur 14. The intramedullary canal 12 is exposed by resection of the anatomic femoral head o (not shown). A head 16 is coupled to a neck 18 of the femoral component. The head 16 is spherical in shape to provide for articulation within a socket 20 of an acetabulum 22.

The femoral component 10 includes a core 24 comprising a plurality of longitudinally extending fibers, an intermediate layer 26 comprising a braided sheath of fibers, a skin 28 enclosing the core 24 and intermediate layer 26, and a pair of porous fiber metal pads 30 and 31 secured to- the skin 28. In the drawings the intermediate layer 26 is shown as a larger fibercross section than the core 24 for illustration purposes only. The core 24 and intermediate layer 26 are constructed from the same fibers.

-4- The core 24, intermediate layer 26 and skin 28 extend from a distal end 33 to a proximal end 32 forming the neck 18. The porous fiber metal pads 30 and 31 are preferably disposed adjacent the neck 18 and on both sides, anteriorly and posteriorly, of the femoral component.

The plurality of fibers forming the core 24 and the braided sheath of fibers forming the intermediate layer 26 are made of APC-2 as sold by FIBERITE, and Imperial Chemical Industry affiliate, see FIBERITEP Data Sheet 3a propriety data of aromatic polymer composite, APC-2/Hercules Magnamite- AS4 Carbon Fibre. This material includes continuous carbon fibre with PEEK impregnated into 000 1 the continuous carbon fibre.

S 00 0 00 0000 The skin 28 is made of polyetheretherketone or PEEK o as taught by United States Patent, 4,662,887. This material is available from Imperial Chemical Industries per the specification for VictrexO 450G polyetheretherketone (PEEK) natural color granular molding resin.

0 The fiber metal pads 30 and 31 are disclosed in United States Patent 3,906,550 as short titanium wires which are kinked in a sinusoidal pattern with a specific amplitude to period ratio of .24. Numerous short wires are sintered together to form a unitary porous pad for fixation to the skin 28.

0 0 In order to manufacture the femoral component 0 0 the longitudinal fibers for the core 24 are bundled together and pulled through braiders for braiding a sheath of layer 26 over the core. With the sheath or layer covering the core 24, a suitable length is cut and disposed in a mold so that the skin 28 can be injection molded over

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the sheath 26 and core 24. The PEEK material for the skin 28 is heated in the injection molding step and readily attaches to the impregnated PEEK in the carbon fibers of the sheath 26 and the core 24. After the skin is cooled, a fiber metal pad as shown in Figure 4 is heated to a temperature sufficient to permit the skin to penetrate the heated pad. It is believed that a temperature of about 600*F suffices for penetration. A heated fiber metal pad is then forced into each side of the stem to penetrate via melting into the skin 28 a predetermined distance.

Preferably, one-half of the thickness of the fiber metal pad is penetrated into the skin as seen in comparing Figures 3 and 4. When the fiber metal pad cools, the Bpenetrated portion of the fiber metal pad is trapped within O: or secured to the skin 28 while an outer portion of the fiber metal pad remains porous or open for intimate contact ~with bone and the resulting bony ingrowth that follows in view of the affinity for bone to associate with titanium wire.

no- porous, pre-Perak/lf In the alternative embodiment of Figure 5, a(meta l barrier 40 separates the fiber metal pads 30 into an inner fiber metal portion 42 and an outer fiber metal portion 44. The barrier 40 separates that portion of the pad intended for impregnation into the skin from that portion of the fiber metal pad intended for bony ingrowth.

Although the aforegoing description proceeds with reference to PEEK and titanium fiber metal pad, it is contemplated that other composite cores with or without fiber reinforcement can be utilized with other types of metallic porous surfaces, e.g. beads, to generate a hybrid composite/metal bone implant that includes a modulus

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li substantially the equivalent of bone and a porous metallic surface to encourage bone ingrowth. Prosthetic knee components can also be made by the composite/metal bone implant of the present invention. In addition, the composite bone implant with the porous metallic surface of the present invention, is also readily adapted for use in a cemented hip arthroplasty where PMMA bone cement is used to secure the implant to bone.

The material for the skin 28 is referred to hereinabove as S polyetheretherketone or PEEK; however,' su'ch material is a-lso o TO referred to as polyaryletherketone. As an alternative material, it is believed that polyetherketone (PEK) or polyetherketoneketone (PEKK) is suitable for forming the skin Sand as a matrix for the' carbon fibers of the core and braid.

The polyetherketone (PEK) is available from Imperial Chemical Industries and the polyetherketoneketone is available from S" DuPont as PEKK polymer. As such this material is also included I in the invention claimed.

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Claims

01-A?42: The claims defining the invention are as follows: hip s4em compos;te. 1. A bone implant comprising a nonmetallic core and a porous metallic component fixedly secured to the nonmetallic core. coMp6Si-e.
2. A bone implant of claim 1 in which the nometallic core includes polyetheretherketone and the porous metallic component includes a fiber metal pad.
3. The bone implant of claim 1 in which the metallic porous surface component includes a substantially nonporous coaMPos i- 4 barrier embedded therein and the nonmetallic core extends into the metallic porous surface component up to but not at a* Spast the nonporous barrier. Z
4. The bone implant of any one of claims 1 to 3 in which the nonmetallic core comprises a first set of fibers oriented in a longitudinal direction from one end to an opposite end for the bone implant, a second set of fibers forming a a. braided sheath covering the first set of fibers, and a o e* polymer layer surrounding the first and second sets of fibers. A bone implant for a hip prosthesis comprising a first set of composite fibers extending longitudinally from one end to an opposite end for the implant, a second set of composite fibers forming a braided sheath over the first set of fibers, a polymer skin enclosing the first and second sets of fibers, and a porous metallic pad fixedly secured to the polymer skin and adapted for intimate contact with the hip bone.
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6. The bone implant of claim 5 in which the first set of fibers, the second set of fibers and the polymer skin include polyetheretherketone as ,a material component of each.
7. The bone implant of either one of claims 5 or 6 in which the first set of fibers and the second set of fibers are designed to sustain a substantial portion of the load transmitted to the bone implant, and the polymer skin is designed to transmit loads from the bone to the first and second set of fibers, and the porous metallic pad is designed to encourage bone ingrowth therein to fixedly 000oo o secure the bone implant to the hip bone. 8 0 so 0o o
8. The bone implant of any one of claims 5 to 7 in which the o "oo 9 first set of fibers comprises a plurality of long fibers 0oo, made from carbon impregnated with polyetheretherketone, .o the second set of fibers comprises a plurality of long fibers made from carbon impregnated with polyetheretherketone, and the polymer skin is made from 0 0 polyetheretherketone for ready assimilation with the first 22 0 and second sets of fibers.
9. The bone implant of any one of claims 5 to 8 in which the porous metallic pad penetrates into an outer portion of the polymer skin such that an inner portion of the polymer skin separates the porous metallic pad from the second set of composite fibers.
A method for constructing a bone implant comprising the steps of: j -9- providing a nonmetallic composite core of predetermined configuration for orientation adjacent the bone; providing a metallic porous pad; heating the metallic porous pad to a temperature sufficient to permit penetration of the core into the metallic porous pad; advancing the heated metallic porous pad into engagement with the nonmetallic composite core to melt a portion of the latter and permit ^penetration of a portion of both the core and pad into each other; and cooling the heated metallic porous pad to the same temperature as the nonmetallic composite core such that the penetrated portion of the metallic porous pad fixedly secures the latter to the nonmetallic composite core.
11. The method of claim 10 in which the heating and advancing steps take place in the absence of oxygen.
12. A bone implant for a hip prosthesis comprising a corposiit. nonmetallicA core forming a predetermined shape adapted to fit into a femoral canal of the hip and a metallic porous surface fixedly secured to the ndnmetallic core for intimate contact with the femoral canal.
13. The bone implant of claim 12 in which the porous metallic surface is formed from a fiber metal pad. WDP 1 2N /it" JI +o 0 2
14. The bone implant of claim 13 in which the fiber metal pad defines an inner portion embedded into the nonmetallic core and an outer portion with open pores for bone ingrowth.
The bone implant of any one of claims 12 to 14 in which the nonmetallic core includes a plurality of fibers some of which extend in a longitudinal direction and a skin encloses the plurality of fibers, and the metallic porous surface is fixedly secured to the skin. '0I
16. The bone implant of any one of claims 12 to 15 in which the metallic porous surface comprises a metallic Sporous element with a first portion of the element embedded in the skin and a second portion of the element forming open pores.
17. The bone implant of any one of claims 12 to 16 in which the nonmetallic core comprises polyetherketoneketone. S
18. A bone implant substantially as hereinbefore particularly described with reference to any one of Figures 1 to DATED: 22 March 1989 2O PHILLIPS ORMONDE FITZPATRICK Attorneys For: -BR-lS-TOL-MY=EmR'-S-e@©M-Pft Y-¥ BnrlSit -0'k1e/s SCibb Couqfo '^L7^ to 6 Nc'