CA2075848A1

CA2075848A1 - Modular implant and method of assembly

Info

Publication number: CA2075848A1
Application number: CA002075848A
Authority: CA
Inventors: Roy Y. Hori; William H. Harris
Original assignee: Individual
Current assignee: Bristol Myers Squibb Co
Priority date: 1991-09-03
Filing date: 1992-08-12
Publication date: 1993-03-04
Also published as: GB9217846D0; AU2037692A; DE4228710A1; JPH0767898A; GB2259253A; FR2680689A1

Abstract

ABSTRACT OF THE DISCLOSURE

A modular implant system for assembly by a surgeon comprises at least two implant components and a plastic layer to be positioned between the components, the plastic film being able to adhere to the components when activated by heating.

Description

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BACKGROUND OF THE INVENTION

The present invention relates to the attachment of modular orthopaedic implant components to one another and, more specifically, to the use of plastic materials to isolate and adhere these components.

In applying orthopaedic implants to the human body, especially hip and knee implants, a surgeon often encounters a less than optimal fit of the implant to a bone. To accommodate the variations in patients and surgical situations that lead to poor fit, many designers have developed modular implant systems.
Modular implant systems allow opt:ional, pre-operative or intra-operative assembly of components by a surgeon as needed to fit a specific patient.

Previous modular implants have employed a variety of mechanical fixation means as illustrated in U.S. 4,482,606 and U.S.
4,995,883 directed to hip implants and U.S. 4,~50,298 and U.S.
4,936,847 directed to knee implants. These mechanical connecting means can be problematic in that they allow small relative motion between components and between the connecting members. This motion in turn generates wear debris, compromises the implant fixation to the bone, and concentrates stress on the components and connecting members. All of these results of component relative motion have been implicated in failure of implant procedures.

It is also known in the field of modular joint implants to use polymethylmethacrylate "bone" cement to attach components. The cement is applied in liquid form, the components assembled, and the cement allowed to cure. The cement, in this case, simply fills the - ; 2~738~8 space between the components and forms a mechanical interlock so far as interlocking surfaces are provided. There is substantially no adhesion of the cement to the implant surface. This form of connection is characterized by low overall fixation strength as well as potential separation between the cement and component resulting in relative motion and debris. In addition, liquid cement is messy and awkward to work with for this purpose in that it must be mixed and then used within a specified working time, it tends to run onto articular and bone interface surfaces from which it must be removed and it gives off noxious fumes.

SUMMARY OF THE INVENTION

The invention of this disclosure addresses the deficiencies of the above-mentioned attachment means by providing a solid, heat activated, adhesive to join modular implant components. The present invention isolates components to prevent debris generation between components and adheres tightly to the components surfaces to prevent motion and debris generation between the components and the adhesive. In addition the secure bond distributes stress evenly between the components. It does this while being clean and convenient to use both pre-operatively and intra-operatively.

BRIEF DESCRIPTION OF THE DRAWINGS

The before mentioned features and advantages of the present invention are apparent from the following detailed description and the drawings wherein:

FIG. 1 is an exploded perspective view of a tibial knee embodiment of the invention.

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FIG. 2 is a perspec-tive view of a tibial augmentation component.
FIG. 3 is an exploded side view of a ~emoral knee embodiment of the invention.
FIG. 4 is an exploded perspective view of a femoral hip embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention as shown in FIG. 1 comprises a modular orthopaedic implant with a tibial base component 1, a tibial augment component 3, ancl a thin plastic wafer or film 2 for adhesively joining and preventing relative motion between components l and 3. The film 2 is a thermoplastic with a lower melting point than the components 1 and 3. It also exhibits good adhesive bonding characteristics with the components l and 3.
Experiments have shown members of the polyaryletherketone (PAEK) family of thermoplastic polymers to develop strong adhesive bonds with commonly used implant metals such as cobalt-chromium-molybdenum alloy (Co~Cr-Mo~ and titanium-vanadium-aluminum alloy (Ti-6Al-4V). Speci~ically, a PAEK sold by BASF under the tradename Ultrapek~ KR4177 was tested to determine its bonding strength with Co Cr-Mo and Ti-6Al-4V. Pairs of cylindrical rod samples with .G
square inch faces were adhered together with Ultrapek KR~177 fully engaging the faces. The polymer was placed between the faces and the assembly heated in a furnace at 770 F for 45 minutes. The 2~ samples were then cooled to room temperature and subjected to tensile testing to determine the stress required to separate the sample pairs. The testing showed that for Co-Cr-Mo samples that were cleaned, glass bead blasted and passivated prior to bonding;
the separation stress was equal to the ultimate tensile strength of the PA~X of 17 KSI. For similarly treated Ti-6Al-4V samples the separation stress was 7 KSI. The lower strength bond was - ~73~
determined to be due to the build-up of an oxide layer on the samples during heating in the furnace. When the experiment was repeated with Ti-6Al 4V samples that were titanium nitride coated, the stress increased to lO KSI. In addition, when the samples were heated by induction for 4 minutes rather than in the furnace, the stress increased to 13 XSI.

The preferred embodiment of the present invention comprises the tibial base component 1 and a tibial augment component 5 (FIG. 2) with a thin layer of PAEK 4 pre-bonded to it. After a surgeon has selected the proper components for use with a specific patient, he assembles the chosen components and positions them with a bonding fixture such as a clamp as is well Xnown in the art. He then applies heat to the assembly such as in a furnace or by induction heating. The assembly is allowed to cool and the custom assembled implant is implanted.

While the foregoing has described a pre~erred embodiment of the present invention, variations in design, materials and method are possible to attach any modular implant component. For example, FIG. 3 shows a ~emoral knee component 6 with a variety of augmentation components. An anterior augmentation component 7, a distal augmentation component 8, and a stem extension component 9 can all be attached to the ~emoral component 6 via bonding with a thermoplastic polymer as described above. FIG. 4 shows a femoral hip stem component 10 with a lateral augmentation component ll, an anterior/posterior augmentation 12, a distal stem augmentation 13, and a femoral head 14 all of which can be assembled according to the present invention in order to securely at~tach them and prevent relative motion and debris generation between components.

As noted previo~lsly the thermoplastic layer may be supplied pre-bonded to one of the components of a mating pair or the layer may be supplied as a separate wafer shaped to conform to the ~ 2 ~ 7 ~
corresponding components. The present invention is also useful in combination with a primary mechanical fixation means, such as screws, dovetail interlocks, snap fits, etc. For example, in FIG.
1, the thermoplastic adhesive layer 18 prevents micromotion and debris generation between system components such as ~he tibial base plate 1 r an augmentation block 16 and an attachment screw 17. In addition, materials other than metals may be joined in the disclosed manner so long as the thermoplastic layer has a lower melting point than the components to be joined and exhibits good adhesive bonding characteristics with the components. The tibial base component 1 can be joined to a polymer tibial articular surface 20 with a thermoplastic bonding layer 21. It is also within the scope of this invention to use an operating room autoclave to heat the components provided that the thermoplastic has a sufficiently low melting point to be within the range of autoclave temperatures. Finally, various surface modifications such as grooving, roughening or porous coating may be employed to compliment the adhesion of the thermoplastic to the component.

It will be understood by those s~illed in the art that the aforementioned emkodiments and modifications and numerous others may be made without departing from the spirit and scope of the invention defined by the appended claims.

Claims

1. A modular implant system for assembly during surgery comprising at least two implant components to be connected together and a solid plastic film to be positioned between the components, the plastic film adhering to the components when activated.

2. The modular implant system of claim 1 wherein the plastic film is composed of a thermoplastic resin which is activated by heating when in contact with the components.

3. The modular implant system of claim 2 wherein the thermoplastic resin has a lower melting temperature than the implant components.

4. The modular implant system of claim 2 wherein the thermoplastic resin is from the polyaryetherketone family.

5. The modular implant system of claim 4 wherein the components are composed of a metal alloy which has been blasted with abrasive media.

6. The modular implant system of claim 1 wherein the plastic film is supplied pre-bonded to one of the implant components.

7. The modular implant system of claim 1 further comprising mechanical fixation means for connecting the components.

8. The modular implant system of claim 7 wherein the mechanical fixation means comprises a screw threadably engageable with one of the components.

9. A method of bonding modular implant components during surgery comprising the steps of:
selecting the components to be joined, positioning the components with a solid plastic layer disposed therebetween to form an assembly, applying heat to the assembly to effect bonding between the plastic layer and each of the components.

10. The method of claim 9 wherein the step of applying heat is accomplished by placing the assembly in a furnace.

11. The method of claim 9 wherein the step of applying heat is accomplished by inductively heating the assembly.

12. The method of claim 9 wherein the step of applying heat is accomplished by placing the assembly in an operating room autoclave.