Patent Application
20060149387
The present disclosure relates generally to implantable orthopaedic bearings and methods of making the same.
Implantable orthopaedic bearings, such as glenoid bearings, are typically made with polyethylene. One type of polyethylene commonly used in the fabrication of such bearings is Ultra-High Molecular Weight Polyethylene (UHMWPE). Certain characteristics of UHMWPE may be enhanced by exposing it to radiation such as gamma radiation. In particular, exposing UHMWPE to predetermined doses of radiation crosslinks the UHMWPE thereby increasing its wear resistance. Techniques for crosslinking, quenching, or otherwise preparing UHMWPE are described in numerous issued U.S. patents, examples of which include U.S. Pat. No. 5,728,748 (and its counterparts) issued to Sun, et al, U.S. Pat. No. 5,879,400 issued to Merrill et al, U.S. Pat. No. 6,017,975 issued to Saum, et al, U.S. Pat. No. 6,242,507 issued to Saum et al, U.S. Pat. No. 6,316,158 issued to Saum et al, U.S. Pat. No. 6,228,900 issued to Shen et al, U.S. Pat. No. 6,245,276 issued to McNulty et al, and U.S. Pat. No. 6,281,264 issued to Salovey et al. The disclosure of each of these U.S. patents is hereby incorporated by reference.
According to one aspect of the disclosure, an orthopaedic bearing includes a metallic component having a polymer composite secured thereto. The polymer composite may include a non-crosslinked layer of polymer and a crosslinked layer of polymer. The non-crosslinked layer of polymer may be positioned between the metallic component and a crosslinked layer of polymer.
The crosslinked layer of polymer may have an articulating surface defined therein.
The crosslinked layer of polymer may include gamma irradiated polymer.
Both layers of polymer may include polyethylene. The polyethylene may be UHMWPE.
The metallic component may include a solid metal body with a porous coating disposed thereon.
The metallic component may include a porous metal body.
In lieu of a non-crosslinked layer of polymer, a layer of polymer which has been crosslinked to a lesser degree than the crosslinked layer may be used.
According to another aspect of the disclosure, a method of making an orthopaedic bearing includes securing a polymer composite to a metallic component. The polymer composite may be molded to the metallic component. The polymer composite may be compression molded to the metallic component.
The polymer composite may include a non-crosslinked layer of polymer and a crosslinked layer of polymer. The non-crosslinked layer of polymer may be positioned between the metallic component and a crosslinked layer of polymer.
An articulating surface may be molded into the crosslinked layer of polymer.
The crosslinked layer of polymer may include gamma irradiated polymer.
Both layers of polymer may include polyethylene. The polyethylene may be UHMWPE.
Both layers of polymer and the metallic component may be molded in a single molding process. The layers of polymer may first be molded to one another, and thereafter molded to the metallic component in a subsequent molding process. The non-crosslinked layer of polymer may first be molded to the metallic component, with the crosslinked layer of polymer being molded to the non-crosslinked layer of polymer in a subsequent molding process.
A polymer preform may be used as the starting material for one or both of the crosslinked layer of polymer and the non-crosslinked layer of polymer.
A polymer powder may be used as the starting material for one or both of the crosslinked layer of polymer and the non-crosslinked layer of polymer.
The metallic component may include a solid metal body with a porous coating disposed thereon.
The metallic component may include a porous metal body.
In lieu of a non-crosslinked layer of polymer, a layer of polymer which has been crosslinked to a lesser degree than the crosslinked layer may be used.
The above and other features of the present disclosure will become apparent from the following description and the attached drawings.
The detailed description particularly refers to the accompanying figures in which:
The present disclosure relates to implantable orthopaedic bearings and methods of making the same. Such bearings may be utilized in a number of joint replacement or repair procedures such as surgical procedures associated with the shoulders, hips, knees, ankles, knuckles, or any other joint. As such, although the following description illustrates one exemplary type of bearing (i.e., a glenoid bearing), it should be appreciated that the invention is not limited to glenoid bearings and may find applicability in the design of any type of orthopaedic bearing.
Referring now to
The polymer composite 14 has a number of polymer layers 24, 26. The polymer layer 24 of the composite 14 is constructed with a material which possesses mechanical properties favorable for use in the construction of the articulating surface 18 (e.g., enhanced wear and oxidation resistance). The polymer layer 26, on the other hand, is constructed of a material which possesses mechanical properties favorable for use in securing the polymer layer 24 to the metallic component 16. It should be appreciated that, as used herein, the term “layer” is not intended to be limited to a “thickness” of material positioned proximate to another similarly dimensioned “thickness” of material, but rather is intended to include numerous structures, configurations, and constructions of material. For example, the term “layer” may include a portion, region, or other structure of material which is positioned proximate to another portion, region, or structure of differing material.
As used herein, the term “polymer” is intended to mean any medical grade polymeric material which may be implanted into a patient. A specific example of such a polymer is medical grade polyethylene. The term “polyethylene”, as defined herein, includes polyethylene, such as a polyethylene homopolymer, high density polyethylene, high molecular weight polyethylene, high density high molecular weight polyethylene, ultrahigh molecular weight polyethylene, or any other type of polyethylene utilized in the construction of a prosthetic implant. A more specific example of such a polymer is medical grade UHMWPE. The term “polymer” is also intended to include both homopolymers and copolymers. The term “polymer” also includes oriented materials, such as the materials disclosed in copending U.S. patent application Ser. No. 09/961,842 entitled “Oriented, Cross-Linked UHMWPE Molding for Orthopaedic Applications”, which was filed on Sep. 24, 2001 by King et al., which is hereby incorporated by reference, and which is owned by the same assignee as the present application.
The term “polymer” is also intended to include high temperature engineering polymers. Such polymers include members of the polyaryletherketone family and the polyimide family. Specific members of the polyaryletherketone family include polyetherketoneetherketoneketone, polyetheretherketone, and polyetherketone.
In one exemplary embodiment, a polymer composite 14 is utilized in which the polymer layer 24 is made with a crosslinked polymer, whereas the polymer layer 26 is made with a non-crosslinked polymer. In a more specific exemplary embodiment, the polymer utilized in the construction of both polymer layers 24, 26 of the polymer composite 14 is polyethylene. One particularly useful polyethylene for use in the construction of the polymer layers 24, 26 is UHMWPE.
As described above, a polymer may be crosslinked by, for example, exposure to radiation such as gamma radiation. As such, the polymer layer 24 (i.e., the crosslinked polymer layer) of the polymer composite 14 of this exemplary embodiment may be fabricated by exposing the polymer layer 24 to gamma radiation. Such exposure may be in the exemplary range of 10-150 KGy. The polymer layer 26 (i.e., the non-crosslinked polymer layer) of the polymer composite 14 of this exemplary embodiment is not exposed to such gamma radiation. In a more specific exemplary embodiment, the polymer layer 24 (and hence the articulating surface 18 formed therein) is constructed of a crosslinked polyethylene such as crosslinked UHMWPE, whereas the polymer layer 26 is constructed of a non-crosslinked polyethylene such as a non-crosslinked UHMWPE.
In another exemplary embodiment, a polymer composite 14 is utilized in which the polymer layer 24 is made from a polymer which has been crosslinked to a first degree, whereas the polymer layer 26 is constructed from a polymer which has been crosslinked to a second degree. Specifically, the polymer layer 26 is made with a polymer which has been crosslinked to a lesser degree than the polymer utilized to make the polymer layer 24. One way to vary the degree in which a polymer is crosslinked is to vary the dose of radiation to which it is exposed. In a general sense, the greater the dose of radiation to which the polymer is exposed, the greater the degree in which the polymer is crosslinked. As such, in regard to the polymer composite 14 of this exemplary embodiment, the polymer layer 24 is exposed to a first dose of gamma radiation, whereas the polymer layer 26 is exposed to a second, different dose of gamma radiation. In a more specific exemplary embodiment, the dose of gamma radiation to which the polymer layer 26 is exposed is less than the dose of radiation to which the polymer layer 24 is exposed.
Hence, in a specific implementation of the polymer composite 14 of this exemplary embodiment, the first polymer layer 24 may be made from a polyethylene such as UHMWPE which has been exposed to a first dose of gamma radiation. The second layer 26, on the other hand, may be made with a polyethylene such as UHMWPE which has been exposed to a second, different dose of gamma radiation. It should be appreciated that the dose of gamma radiation to which the polyethylene of the polymer layer 26 is exposed is less than the dose of radiation to which the polyethylene of the polymer layer 24 is exposed. It should be appreciated that the polymer layer 26 of this exemplary polymer composite 14, although crosslinked to some degree, still possesses many favorable mechanical characteristics to facilitate securing the more highly crosslinked polymer layer 24 to the metallic component 16.
As alluded to above, the material from which the polymer layer 26 is made may include polymers other than polyethylene. For example, the polymer layer 26 may be made with poly methyl methacrylate (PMMA). Along a similar line, although crosslinked polymers are believed at present to provide superior wear resistance and oxidation resistance for the articulating surface in orthopaedic implants, new materials may be developed in the future with improved properties. Accordingly, the present invention is not limited to any particular material, and may encompass newly developed materials, unless a particular material is expressly set forth in the claims.
Referring in particular now to
The components of the one-piece glenoid component 12 (i.e., the metallic component 16, the polymer layer 24, and the polymer layer 26) may be assembled by use of a number of different techniques. One exemplary manner for doing so is by use of compression molding techniques. For example, the metallic component 16, the material from which the polymer layer 24 is to be made, and the material from which the polymer layer 26 is to be made may be placed in a mold with one another. Thereafter, the components are compression molded to one another under process parameters which cause the material from which the polymer layer 26 is made to be molten and fused to the material from which the polymer layer 24 is made thereby creating the polymer composite 14. At the same time, the material from which the polymer layer 26 is made is mechanically secured to the metallic component 16 by the compression molding process. As described above, the molten polymer layer 26 interdigitates with the porous coating 30 of the metallic component 16 when molded thereto. It should also be appreciated that the mold may be configured to not only fuse the components to one another, but also form the articulating surface 18 into the polymer composite 14.
Other methods of compression molding the one-piece glenoid bearing 12 are also contemplated. For example, in lieu of contemporaneously molding the components of the one-piece glenoid component 12 (i.e., the metallic component 16, the polymer layer 24, and the polymer layer 26) to one another in a single molding process, multiple molding processes may be employed. For instance, the polymer composite 14 may be formed in a first molding process by compression molding the material from which the polymer layer 24 is to be made and the material from which the polymer layer 26 is to be made to one another. Thereafter, the polymer composite 14 and the metallic component 16 may be molded to one another in a separate mold process.
In another multi-step molding process, the material from which the polymer layer 26 is to be made may be molded to the metallic component 16 in a first molding process. Thereafter, in a second molding process, the material from which the polymer layer 24 is to be made is molded onto the polymer layer 26.
The starting composite materials (e.g., polymers such as polyethylene) for use in the molding process may be provided in a number of different forms. For example, each of the starting materials may be provided as a preform. What is meant herein by the term “preform” is an article that has been consolidated, such as by ram extrusion or compression molding of polymer resin particles, into rods, sheets, blocks, slabs, or the like. The term “preform” also includes a preform “puck” which may be prepared by intermediate machining of a commercially available preform. Polymer preforms such as polyethylene preforms may be provided in a number of different pre-treated or preconditioned variations. For example, crosslinked or non-crosslinked (e.g., irradiated or non-irradiated) preforms may be utilized. Such preforms may be treated to eliminate (e.g., re-melting or quenching) or stabilize (e.g., the addition of vitamin E as an antioxidant) any free radicals present therein. Alternatively, the preforms may not be treated in such a manner.
The starting composite materials (e.g., polymers and copolymers) may also be provided as powders. What is meant herein by the term “powder” is resin particles. Similarly to as described above in regard to preforms, powders may be provided in a number of different pre-treated or preconditioned variations. For example, crosslinked or non-crosslinked (e.g., irradiated or non-irradiated) powders may be utilized.
It should be appreciated that the starting composite materials (e.g., the preforms or powders) may be “pre-irradiated”, “pre-treated to eliminate or stabilize free radicals”, or otherwise preconditioned prior to use thereof. In particular, it may be desirable for a manufacturer of prosthetic bearings to purchase material (e.g. polyethylene) which has been irradiated (or otherwise crosslinked), pre-treated to eliminate or stabilize free radicals, or otherwise preconditioned by a commercial supplier or other manufacturer of the material. Such “out-sourcing” of preconditioning processes is contemplated for use in the processes described herein.
In regard to fabrication of a bearing 12 having a polymer composite 14 in which the polymer layer 24 is made of crosslinked polymer and the other polymer layer 26 is made of non-crosslinked polymer, a preform of polymer which is non-crosslinked (i.e., non-irradiated) may be positioned in a mold between a preform of crosslinked polymer (i.e., pre-irradiated) and the metallic component 16. Thereafter, the metallic components and the two preforms are compression molded under process parameters which cause the non-crosslinked preform of polymer to be (i) molten and fused to the preform of crosslinked polymer, and (ii) molten and mechanically secured to the metallic component 16. It should also be appreciated that during such a molding process, the articulating surface 18 is formed in the resultant polymer composite 14. Moreover, during such a molding process, the polymer associated with the layer 26 is interdigitated with the porous coating 30 of the metallic component 16. In an exemplary implementation of this process, a preform of a crosslinked polyethylene such as crosslinked UHMWPE is compression molded to a preform of a non-crosslinked polyethylene such as non-crosslinked UHMWPE, which is, in turn, molded to the metallic component 16. As alluded to above, such a fabrication process may be performed in a number of different molding steps. For example, the two preforms may first be molded to one another, with the resultant polymer composite then being molded to the metallic component 16 in a subsequent molding process. Alternatively, the non-crosslinked polymer preform may first be molded to the metallic component 16, with the crosslinked polymer preform being molded to the non-crosslinked layer in a subsequent molding process.
Such a polymer composite 14 (i.e., the polymer layer 24 made of crosslinked polymer and the polymer layer 26 made of non-crosslinked polymer) may also be fabricated by the use of polymer powders. For example, polymer powder which is non-crosslinked (i.e., non-irradiated) may be placed in a mold between a preform of crosslinked polymer (i.e., pre-irradiated) and the metallic component 16. Thereafter, the components are compression molded under process parameters which cause the non-crosslinked polymer powder to be (i) molten and fused to the preform of crosslinked polymer, and (ii) molten and mechanically secured to the metallic component 16. It should also be appreciated that during such a molding process, the articulating surface 18 is formed in the resultant polymer composite 14. Moreover, during such a molding process, the polymer associated with the layer 26 is interdigitated with the porous coating 30 of the metallic component 16. In an exemplary implementation of this process, the crosslinked preform may be provided as a crosslinked polyethylene preform such as a crosslinked UHMWPE preform, whereas the non-crosslinked powder may be provided as a non-crosslinked polyethylene powder such as a non-crosslinked UHMWPE powder. Similarly to as described above in regard to use of two preforms, the fabrication process may be performed in a number of different molding steps. For example, the crosslinked preform and the non-crosslinked powder may first be molded to one another, with the resultant polymer composite then being molded to the metallic component 16 in a subsequent molding process. Alternatively, the non-crosslinked polymer powder may first be molded to the metallic component 16, with the crosslinked polymer preform being molded to the non-crosslinked layer in a subsequent molding process.
In regard to fabrication of a bearing 12 having of a polymer composite 14 in which the polymer layer 24 is made of a polymer which has been crosslinked to a first degree and the other polymer layer 26 is made of a polymer which has been crosslinked to a second, lesser degree, a preform of polymer which is crosslinked to the second (lesser) degree may be positioned in a mold between a preform of the polymer which has been crosslinked to the first (greater) degree and the metallic component 16. Thereafter, the metallic components and the two preforms are compression molded under process parameters which cause the lesser crosslinked preform of polymer to be (i) molten and fused to the preform of greater crosslinked polymer, and (ii) molten and mechanically secured to the metallic component 16. It should also be appreciated that during such a molding process, the articulating surface 18 is formed in the resultant polymer composite 14. Moreover, during such a molding process, the polymer associated with the layer 26 is interdigitated with the porous coating 30 of the metallic component 16. In an exemplary implementation of this process, a preform of polyethylene such as UHMWPE which is crosslinked to a first degree is compression molded to a preform of polyethylene such as UHMWPE which is crosslinked to a second, lesser degree, which is, in turn, molded to the metallic component 16. In a similar manner to as described above, this fabrication process may also be performed in a number of different molding steps. For example, the two preforms may first be molded to one another, with the resultant polymer composite then being molded to the metallic component 16 in a subsequent molding process. Alternatively, the lesser crosslinked polymer preform may first be molded to the metallic component 16, with the greater crosslinked polymer preform being molded to the lesser crosslinked layer in a subsequent molding process.
Such a polymer composite 14 (i.e., a polymer layer 24 constructed of a polymer which has been crosslinked to a first degree and a polymer layer 26 constructed of a polymer which has been crosslinked to a second, lesser degree) may also be fabricated by the use of polymer powders. For example, polymer powder which is crosslinked to the second (lesser) degree may be placed in a mold between a preform of polymer crosslinked to the first (greater) degree and the metallic component 16. Thereafter, the components are compression molded under process parameters which cause the lesser crosslinked polymer powder to be (i) molten and fused to the preform of greater crosslinked polymer, and (ii) molten and mechanically secured to the metallic component 16. It should also be appreciated that during such a molding process, the articulating surface 18 is formed in the resultant polymer composite 14. Moreover, during such a molding process, the polymer associated with the layer 26 is interdigitated with the porous coating 30 of the metallic component 16. In an exemplary implementation of this process, a powder of polyethylene such as UHMWPE which is crosslinked to a first degree is compression molded to a preform of polyethylene such as UHMWPE which is crosslinked to a second, lesser degree. Similarly to as described above in regard to use of two preforms, the fabrication process may be performed in a number of different molding steps. For example, the greater crosslinked preform and the lesser crosslinked powder may first be molded to one another, with the resultant polymer composite then being molded to the metallic component 16 in a subsequent molding process. Alternatively, the lesser crosslinked polymer powder may first be molded to the metallic component 16, with the greater crosslinked polymer preform being molded to the lesser crosslinked layer in a subsequent molding process.
It should also be appreciated that although the composites 14 have herein been described as having two layers, other composite configurations are also contemplated. For example, the polymer composite 14 may be configured to include several alternating layers of materials similar to the materials used in regard to the two-layer composites described above. For instance, the polymer composite 14 may be configured to include several (i.e., more than two) layers of alternating crosslinked and non-crosslinked UHMWPE. It should also be appreciated that more than two different material types may also be used in the construction of the composite. For example, a third material type may be used as an adhesion promoter between two layers (or between a layer and the underlying (e.g., metallic) component).
Moreover, it may be desirable to use vacuum molding for some materials. For example, vacuum molding may be preferred where one or more of the layers include a non-quenched material.
Other methods of securing the two polymer layers can be used for some applications. For example, instead of melt-fusion, mechanical interlocks can be used in some applications. With the choice of appropriate materials and processes, mechanical interlocks between polymer layers may provide an interface with adequate mechanical and dynamic properties. For an application relying upon mechanical interlocks, it is believed that mechanical interlocking with adequate interfacial strength can be achieved by providing a layer of polymer 26 having a porous structure of a high-temperature engineering polymer, such as one from the polyaryletherketone family or the polyimide family, and by control of process parameters. In such an application, a crosslinked UHMWPE layer may be used for the polymer layer 24 for the articulating surface. The crosslinked UHMWPE layer 24, in the form of a powder or preform, may be compression molded to the layer 26 of porous high temperature engineering polymer under a temperature that will melt at least a portion of the UHMWPE layer, so that UHMWPE melts into and fills some of the pores of the high temperature engineering material; when this UHMWPE material solidifies, the two polymer layers will be mechanically bonded together. The compression molding can be done at a temperature high enough to melt the UHMWPE layer but below the melting point of the polymer layer of polymer 26. The high temperature may be localized at the interface of the layers 24, 26. The porous structure may have a solid section.
The polymer layer 26 of porous high temperature engineering polymer may comprise an engineering polymer such as polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone or polyimide. These materials are biocompatible and are able to withstand the processing temperature for UHMWPE without significant deformation. Preforms can be readily fabricated from these raw materials using conventional processing techniques. Although it is expected that these polymer materials will be useful as one of the polymer layers when relying upon a mechanical interlock, the present invention is not limited to these materials unless the claims expressly call for them. The present invention may also encompass newly developed polymers, unless a particular polymer is expressly set forth in the claims.
In addition, although the mechanical interlock that secures the two polymer layers together can be formed by compression molding the two polymer layers together, methods such as hot isostatic pressing may be used to secure the two layers of polymer 24, 26 together with a mechanical interlock. In addition, as new polymer materials are developed, new methods of securing the polymer layers together may also be developed. Accordingly, the present invention is not limited to any particular method of securing the polymer layers together, and may encompass newly developed materials and securing means, unless a particular material or process is expressly set forth in the claims.
Referring now to
Prior to molding the polymer layer 26 to the porous metallic component 36, a sacrificial layer of polymer (not shown) may be molded to the backside 40 of the metallic component 36. The molding process may be controlled to allow the sacrificial layer of polymer to penetrate a predetermined distance into the metallic component 36. As such, when the polymer of the polymer layer 26 is molded to the front side 42 of the metallic component 36 the polymer of the polymer layer 26 is prevented from penetrating the entire thickness of the metallic component 36 by the sacrificial layer of polymer.
Once the polymer layer 26 has been molded to the metallic component 36 (with or without the polymer layer 24), the glenoid bearing 12 (or partially fabricated bearing 12) the sacrificial layer of polymer is removed by water extraction. This removes the sacrificial layer of polymer without disturbing the polymer layer 26 (and the polymer layer 24 if present) thereby exposing the porous backside 40 of the metallic component 36 (including the depth into its porous body 38 previously occupied by the sacrificial layer of polymer). Such exposed portions of the porous body promote bony ingrowth or cement adhesion into the glenoid bearing 12 when its implanted in a manner similar to as described above in regard to the porous coating 30 of the bearing 12 of
It should be appreciated that any desirable type of material may be used as the sacrificial layer of polymer. One type of such material is a meltable, high molecular weight hydrophilic polymer. A specific example of one such polymer is polyethylene oxide.
While the disclosure is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and has herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.
There are a plurality of advantages of the present disclosure arising from the various features of the apparatus and methods described herein. It will be noted that alternative embodiments of the apparatus and methods of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of an apparatus and method that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present disclosure.
For example, although it has been described herein to crosslink materials via irradiation, it should be appreciated that such materials may be crosslinked by any suitable technique. In addition, although the crosslinked polymer or more highly crosslinked polymer is typically be used for the articulating surface of the composite with non-crosslinked or less crosslinked polymer being used to facilitate securing the crosslinked polymer or more highly crosslinked polymer to the metallic component, there may be instances where it is desirable for the crosslinked polymer or more highly crosslinked polymer layer to be used to secure the non-crosslinked or less crosslinked polymer to the metallic bearing, with the latter layer being used for the articulating surface.
Moreover, in lieu of the of a metallic component, a ceramic component may be used in the fabrication of the orthopaedic bearing 10. In such a case, a porous ceramic component or porous coated ceramic component is used in lieu of the metallic component 16, with the bearing 10 being fabricated otherwise as described herein.
Cross reference is made to copending U.S. patent applications Ser. No. ______ entitled “Orthopaedic Bearing and Method of Making the Same” (Attorney Docket No. 265280-76607, DEP-5269DIV1) and Ser. No. ______ entitled “Orthopaedic Bearing and Method of Making the Same” (Attorney Docket No. 265280-76608, DEP-5269DIV2), both of which are assigned to the same assignee as the present application, are filed concurrently herewith, and are hereby incorporated by reference.
