METAL-REINFORCED POLYMER FEMORAL COMPONENT OF AN ORTHOPAEDIC KNEE PROSTHESIS AND ASSOCIATED METHOD OF MAKING THE SAME

An orthopaedic knee prosthesis includes a femoral component having a metal base with a polymer articular layer molded thereto. A method for making a metal-reinforced femoral component of an orthopaedic knee prosthesis is also disclosed.

TECHNICAL FIELD

The present disclosure relates generally to an implantable orthopaedic knee prosthesis, and more particularly to an implantable femoral component of an orthopaedic knee prosthesis.

BACKGROUND

During the lifetime of a patient, it may be necessary to perform a joint replacement procedure on the patient as a result of, for example, disease or trauma. As a result, joint arthroplasty has become a well-known surgical procedure by which the diseased and/or damaged natural joint is replaced by a prosthetic joint. For example, in a total knee arthroplasty surgical procedure, a patient's natural knee joint is partially or totally replaced by a prosthetic knee knee prosthesis. A typical knee prosthesis includes a tibial tray, a femoral component, and a polymer insert or bearing positioned between the tibial tray and the femoral component. In such a case, the femoral component is secured to a surgically-prepared distal end of the patient's femur, whereas the tibial tray is secured to a surgically-prepared proximal end of the patient's tibia. The polymer bearing is coupled to the tibial tray and thus provides a bearing surface upon which the femoral component articulates during extension and flexion of the knee.

A conventional femoral component is embodied as a monolithic metallic component constructed with an implant-grade biocompatible metal. Examples of such metals include cobalt, including cobalt alloys such as a cobalt chrome alloy, titanium, including titanium alloys such as a Ti6Al4V alloy, and stainless steel.

SUMMARY

According to an aspect of the disclosure, an orthopaedic knee prosthesis includes a femoral component. The femoral component includes a metal base that has an inferior base surface that is curved in the sagittal plane. The inferior base surface has a plurality of elongated ribs extending inferiorly therefrom. The metal base also has a superior base surface that includes a posterior fixation surface that extends generally in the superior/inferior direction, a distal fixation surface that extends generally in the anterior/posterior direction, a posterior-chamfer fixation surface that extends superiorly and posteriorly from the distal fixation surface in the direction toward the posterior fixation surface, an anterior fixation surface that extends generally in the superior/inferior direction, and an anterior-chamfer fixation surface that extends superiorly and anteriorly from the distal fixation surface in the direction toward the anterior fixation surface. The femoral component also includes a polymer articular layer molded to the inferior base surface of the metal base and into a plurality of elongated grooves defined by the plurality of ribs. The polymer articular layer has an articulation surface that is curved in the sagittal plane and configured to articulate with a bearing surface of a tibial component.

In an embodiment, a porous-metal coating is disposed on the superior base surface of the metal base.

The porous-metal coating may be disposed on the entirety of each of the posterior fixation surface, the distal fixation surface, the posterior-chamfer fixation surface, the anterior fixation surface, and the anterior-chamfer fixation surface of the superior base surface of the metal base.

In an embodiment, the metal base includes a number of lugs extending superiorly from the distal fixation surface, and the porous-metal coating is disposed on the lugs.

An inferior end of each of the plurality of ribs may have an undercut formed therein. The inferior ends of the plurality of ribs defining the undercuts may include rounded surfaces.

In an embodiment, the plurality of ribs extend in the sagittal plane. In another embodiment, the plurality of ribs extend in the coronal plane.

In an embodiment, the plurality of ribs are completely embedded in the polymer articular layer.

In an embodiment, a number of the plurality of ribs are hollow.

The polymer articular layer of the femoral component may be constructed with polyaryletherketone (PAEK). In other embodiments, the polymer articular layer of the femoral component is constructed with other biocompatible polymers, copolymers, and/or polymer blends.

In another aspect, an orthopaedic knee prosthesis system includes a tibial component configured to be implanted on a proximal end of a patient's tibia and a femoral component configured to be implanted on a distal end of a patient's femur. The tibial component includes a concave bearing surface. The femoral component includes a metal base that has an inferior base surface that is curved in the sagittal plane. A plurality of elongated ribs extend inferiorly from the inferior base surface. The metal base also includes a superior base surface having a number of bone fixation surfaces. A number of lugs extend superiorly from one of the number of bone fixation surfaces. The femoral component also includes a porous-metal coating disposed on the superior base surface of the metal base and the lugs. A polymer articular layer is molded to the inferior base surface of the metal base and into a plurality of elongated grooves defined by the plurality of ribs. The polymer articular layer has an articulation surface that is curved in the sagittal plane and configured to articulate with the bearing surface of the tibial component.

In an embodiment, the superior base surface includes a posterior fixation surface that extends generally in the superior/inferior direction, a distal fixation surface that extends generally in the anterior/posterior direction, a posterior-chamfer fixation surface that extends superiorly and posteriorly from the distal fixation surface in the direction toward the posterior fixation surface, an anterior fixation surface that extends generally in the superior/inferior direction, and an anterior-chamfer fixation surface that extends superiorly and anteriorly from the distal fixation surface in the direction toward the anterior fixation surface.

The porous-metal coating may be disposed on the entirety of each of the posterior fixation surface, the distal fixation surface, the posterior-chamfer fixation surface, the anterior fixation surface, and the anterior-chamfer fixation surface of the superior base surface of the metal base.

An inferior end of each of the plurality of ribs may have an undercut formed therein. The inferior ends of the plurality of ribs defining the undercuts may include rounded surfaces.

In an embodiment, the plurality of ribs extend in the sagittal plane. In another embodiment, the plurality of ribs extend in the coronal plane.

In an embodiment, the plurality of ribs are completely embedded in the polymer articular layer.

In an embodiment, a number of the plurality of ribs are hollow.

The polymer articular layer of the femoral component may be constructed with polyaryletherketone (PAEK). In other embodiments, the polymer articular layer of the femoral component is constructed with other biocompatible polymers, copolymers, and/or polymer blends.

According to another aspect, a method of making a femoral component of an orthopaedic knee prosthesis includes disposing a porous-metal coating onto a metal base. The metal base has a superior base surface that includes a number of bone fixation surfaces and a number of lugs. A polymer articular layer is molded onto an inferior base surface of the metal base that is curved in the sagittal plane such that a plurality of elongated ribs extending inferiorly from the inferior base surface are embedded in the polymer articular layer, and an outer surface of the polymer articular layer forms an articulation surface that is curved in the sagittal plane and configured to articulate with a bearing surface of a tibial component.

The porous-metal coating may be disposed onto the superior base surface and the number of lugs of the metal base by 3D-printing the porous-metal coating and the metal base as a monolithic metal component.

In an embodiment, an inferior end of each of the plurality of ribs has an undercut formed therein, and the polymer articular layer is molded onto the inferior base surface of the metal base such that polymer articular layer is molded to the undercuts of each of the plurality of ribs.

DETAILED DESCRIPTION

Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout the specification in reference to the orthopaedic implants or prostheses and surgical instruments described herein as well as in reference to the patient's natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the written description and claims is intended to be consistent with their well-understood meanings unless noted otherwise.

Referring toFIGS.1and2, there is shown an orthopaedic knee prosthesis10that includes a metal-reinforced polymer femoral component12, a tibial bearing14, and a tibial tray16. The femoral component12is configured to articulate with the tibial bearing14, which is configured to be coupled to the tibial tray16. In the illustrative embodiment ofFIG.1, the tibial bearing14is embodied as a rotating or mobile tibial bearing and it is, therefore, rotatable relative to the tibial tray16. However, in other embodiments, the tibial bearing14may be embodied as a fixed tibial bearing (not shown), which is restricted from rotating relative to the tibial tray16.

The tibial tray16is configured to be secured to a surgically-prepared proximal end of a patient's tibia (not shown). The tibial tray16includes a platform18having a superior surface20and an opposite inferior surface22. The tibial tray16also includes a stem24extending downwardly from the inferior surface22of the platform18. A bore26is defined in the superior surface20of the platform18and extends inferiorly into the stem24. The bore26is configured to receive a complimentary stem36of the tibial bearing14as discussed in more detail below.

The inferior surface22of the platform18and the stem24define a bone-engaging surface28of the tibial tray16. As can be seen inFIG.1, the bone-engaging surface28has a porous-metal coating32disposed thereon. It should be appreciated that the porous-metal coating32could be a separately-applied coating such as Porocoat®, Gription®, or Affixium® Porous Coatings which are commercially available from DePuy Synthes of Warsaw, Indiana. Alternatively, the porous-metal coating32is disposed on the metallic body34of the tibial tray16by virtue of being additively manufactured contemporaneously with the tray's metallic body34so as to create a common, monolithic component of the two metal structures.

As discussed above, the tibial bearing14is configured to be coupled with the tibial tray16. The tibial bearing14includes a platform30having an upper bearing surface and a bottom bearing surface. In the illustrative embodiment in which the tibial bearing14is embodied as a rotating or mobile tibial bearing, the bearing14includes a stem36extending downwardly from the bottom surface of the platform30. When the tibial bearing14is coupled to the tibial tray16, the stem36is received in the bore26of the tibial tray16. In use, the tibial bearing14is configured to rotate about an axis defined by the stem36relative to the tibial tray16. In embodiments in which the tibial bearing14is embodied as a fixed tibial bearing, the bearing14may or may not include the stem36and/or may include other devices or features to secure the tibial bearing14to the tibial tray16in a non-rotating configuration. The upper bearing surface of the tibial bearing14includes a medial bearing surface42and a lateral bearing surface44. The medial and lateral bearing surfaces42,44are configured to receive or otherwise contact corresponding medial and lateral condyles52,54of the femoral component12. As such, each of the bearing surfaces42,44has a concave contour.

Referring toFIG.2, the femoral component12is configured to be coupled to a surgically-prepared surface of the distal end of a patient's femur (not shown). The femoral component12illustrated inFIGS.1and2is a posterior cruciate-retaining knee prosthesis and the tibial bearing14is embodied as a posterior cruciate-retaining tibial bearing14. However, in other embodiments, the orthopaedic knee prosthesis10may be embodied as a posterior cruciate-sacrificing knee prosthesis (not shown).

As mentioned above, the femoral component12includes a pair of medial and lateral condyles52,54. The condyles52,54are spaced apart to define an intracondylar notch56therebetween. In use, the condyles52,54replace the natural condyles of the patient's femur. Each condyle52,54of the femoral component12includes an outer articular surface50, which is convexly curved in the sagittal plane and configured to articulate on the respective bearing surfaces42,44of the tibial bearing14.

Opposite to the articular surface50, the femoral component12includes a bone-engaging surface62. The bone-engaging surface62contacts the surgically-prepared distal femur of the patient. The bone-engaging surface62includes multiple surfaces that mate with planar surfaces surgically cut into the patient's distal femur. For example, as shown inFIG.2, a pair of posterior fixation surfaces64are opposite the posterior surfaces of the condyles52,54, with one of the posterior fixation surfaces64being the medial fixation surface, the other the lateral fixation surface. As can be seen inFIGS.1and2, the posterior fixation surfaces64extend generally in the superior/inferior direction. A pair of distal fixation surfaces66(one being medially positioned, the other the laterally positioned) is opposite the distal surfaces of the condyles52,54and extend generally in the anterior/posterior direction. A pair of posterior-chamfer fixation surfaces68(one being medially positioned, the other the laterally positioned) is opposite the posterior-chamfer surfaces of the condyles52,54. The medial and lateral posterior-chamfer fixation surfaces68extend superiorly and posteriorly from their respective medial and lateral distal fixation surfaces66in the direction toward their respective posterior fixation surfaces64. The medial and lateral anterior-chamfer fixation surfaces70are opposite the anterior-chamfer surfaces of the condyles52,54, respectively, and extend superiorly and anteriorly away from their respective distal fixation surfaces66in the direction toward an anterior fixation surface72. The anterior fixation surface72is opposite the anterior condyle surface and, like the posterior fixation surfaces64, extends generally in the superior/inferior direction.

The bone-engaging surface62of the femoral component12may also include the outer surfaces of a pair of lugs74extending superiorly from the distal fixation surfaces66. The lugs74are configured to be received into holes formed in the surgically-prepared distal femur of the patient during installation of the femoral component12.

The femoral component12described herein is embodied as a metal-reinforced polymer component. As such, the femoral component12includes a polymer articular layer82molded onto a metal base84so as to create a one-piece (i.e., non-modular) final product. The articular surface50of the femoral component12is formed in the polymer articular layer82of the femoral component12thus defining a polymeric articular surface that is configured to articulate on the bearing surfaces42,44of the tibial bearing14.

The polymer articular layer82of the femoral component12is embodied as a monolithic polymer body constructed with a material that allows for smooth articulation between the femoral component12and the tibial bearing14(which is generally constructed with a biocompatible polymer such as polyethylene, including ultrahigh molecular weight polyethylene (UHMWPE)). A polymer or a blend of polymers is preferably used to construct the polymer articular layer82. As used herein, the term “polymer” is intended to mean any polymeric material which may be implanted into a patient. Specific examples of polymers that may be used in the construction of the femoral component12are the polyaryletherketone (PAEK) family, the polysulfone family, the polyimide family, and the polyacetal family. The term “polyaryletherketone,” as defined herein, includes polyetheretherketone (PEEK), polyetherketone, and polyetherketoneetherketoneketone or any other type of polyaryletherketone used in the construction of a prosthetic implant, including PEEK blends such as PEEK-polyetherimide and PEEK-polyphenylsulfone blends.

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.

Referring now toFIGS.4-7, the metal base84is shown in more detail. As can be seen best inFIG.4(and in the cross section ofFIG.2), the metal base84of the femoral component12includes a superior base surface86that includes the component's bone-engaging surface62and an opposite inferior base surface88onto which the polymer articular layer82is molded. As can be seen inFIGS.2-4, the posterior fixation surfaces64, the distal fixation surfaces66, the posterior-chamfer fixation surfaces68, the anterior-chamfer fixation surfaces70, and the anterior fixation surface72are formed in the superior base surface86.

As can be seen inFIGS.2and4, the inferior base surface88is curved in the sagittal plane and extends generally parallel to the femoral component's articular surface50. A plurality of elongated ribs90extend inferiorly from the inferior base surface88. Like the inferior base surface88, the elongated ribs90extend in the sagittal plane. An inferior end92of each of the plurality of ribs90has an undercut94formed therein. Specifically, the inferior ends92of each of the ribs90is wider than the opposite ends of the ribs90(i.e., the ends of the ribs90that are secured to the inferior base surface88). As can be seen inFIG.7, the ribs90extend from their inferior ends92along a convex surface96that transitions to a concave surface98prior transitioning to the inferior base surface88thereby creating the undercuts94. It should be appreciated that although the undercuts94are shown as blended-radius undercuts40(i.e., the surfaces defining the undercuts are rounded), other configurations are also contemplated including, for example, undercuts that that are more squared off in design (e.g., the ribs90define orthogonal transitions instead of rounded transitions).

As can be seen inFIG.7, the surfaces of the ribs90defining the undercuts94create a combined surface that faces away from the inferior base surface88of the metal base84to which the polymer articular layer82is molded. In such a way, the undercuts94resist pull-off of the polymer articular layer82from the metal base84.

It should be appreciated that although the ribs90are herein described as extending in the sagittal plane, other configurations of the ribs90may also be used to fit the needs of a given design of the femoral component12. For example, the ribs90may be arranged to extend in the coronal plane. As a further example, the ribs90may be arranged to extend in both the sagittal and the coronal plane.

It should also be appreciated that the number and geometry (e.g., length, width, cross-sectional shape, etc.) of the ribs90may be altered to fit the needs of a given design of the femoral component12and/or to impart desired properties into a given design of the femoral component12. For example, the stiffness of the metal base84may be controlled as a function of the number of ribs90and the cross-sectional shape of the ribs90. Furthermore, the ribs90may be configured as hollow structures (by the use of 3D printing, for example). Doing so creates an outer rib geometry that is useful in molding the polymer articular layer82to the metal base84, while also allowing the overall stiffness of the femoral component12to be controlled by altering the wall thickness of the hollow ribs. In such an embodiment, the wall thickness could be uniform throughout the cross section of the ribs90or thicker in some regions (e.g., the inferior ends92of the ribs90) and thinner in other areas based on the structural stiffness desired in a given design of the femoral component12.

The femoral component12is embodied as a cementless component—that is, the femoral component12is designed to be installed on the surgically-prepared distal end of a patient's femur without the use of bone cement. As such, the bone-engaging surface62of the femoral component has the porous-metal coating32disposed thereon. Similarly to the tibial tray16, the porous-metal coating32disposed on the femoral component12may be a separately-applied coating (e.g., Porocoat®, Gription®, or Affixium® Porous Coatings). However, in the illustrative embodiment described herein, the porous-metal coating32is disposed on the metal base84by virtue of being additively manufactured contemporaneously with the metal base84so as to create a common, monolithic component of the two metal structures. For example, Affixium® Porous Coating may be additively manufactured contemporaneously with the metal base so as to create a common, monolithic component.

In one example, the porous-metal coating32may be made of a porous material80as described in U.S. patent application Ser. No. 16/365,557, which was filed Mar. 26, 2019 and is assigned to the same assignee as the present disclosure, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. Additive manufacturing processes can include, by way of example, powder bed fusion printing, such as melting and sintering, cold spray 3D printing, wire feed 3D printing, fused deposition 3D printing, extrusion 3D printing, liquid metal 3D printing, stereolithography 3D printing, binder jetting 3D printing, material jetting 3D printing, and the like.

In one example, referring toFIG.7, the porous material80of the porous-metal coating32can be defined by a porous three-dimensional structure that can includes a plurality of connected unit cells. Each unit cell can define a unit cell structure that includes a plurality of lattice struts that define an outer geometric structure and a plurality of internal struts that define a plurality of internal geometric structures that are disposed within the outer geometric structure. In one example, the outer geometric structure may be a rhombic dodecahedron, and the inner geometric structures may be a rhombic trigonal trapezohedron. It should be appreciated that such geometric structures may vary to fit the needs of a given design. Further, it should be appreciated that the unit cells that make up the porous-metal coating32may also have any suitable alternative geometry to fit the needs of a given design.

The porous material80is formed from a metal powder. Illustratively, the metal powders may include, but are not limited to, titanium, titanium alloys, stainless steel, cobalt chrome alloys, tantalum, or niobium powders. The porous-metal coating32has a porosity suitable to facilitate bony ingrowth into the femoral component12when the superior base surface86and the lugs74of the metal base84are implanted into the surgically-prepared posterior surface of the patient's patella.

In the illustrative embodiment described herein, the porous-metal coating32is additively manufactured directly onto the superior base surface86and the lugs74of the metal base84. In such an embodiment, the two structures—i.e., the metal base84and the porous-metal coating32—may be manufactured contemporaneously during a common additive manufacturing process. For example, the two structures may be manufactured contemporaneously in a single 3D printing operation that yields a common, monolithic metallic component including both structures. Alternatively, the porous-metal coating32could be manufactured as a separate component that is secured to the metal base84.

The polymer articular layer82may be assembled to the metal base84by use of a number of different techniques. One exemplary manner for doing so is by use of compression molding techniques. For example, the metal base84and the material from which the polymer articular layer82is to be made (e.g., PEEK) 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 articular layer82is made (e.g., PEEK) to be molten and mechanically secured to the metal base84by the compression molding process. As described above, the molten polymer articular layer82interdigitates with the ribs90of the metal base84when molded thereto (i.e., the molten polymer articular layer82is injected into the grooves102defined by the ribs90). It should also be appreciated that the mold may be configured to not only mold the components to one another, but also form the articular surface50of the femoral component12into the polymer articular layer82. Another illustrative, and equally effective, method of assembling the polymer articular layer82to the metal base84is by the use of injection molding.

The starting materials (e.g., polymers such as PEEK) 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 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 materials (e.g., polymers, copolymers, and/or blended polymers) may also be provided as powders or pellets. What is meant herein by the terms “powder” and “pellets” are resin particles. Similarly to as described above in regard to preforms, powders and/or pellets 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 and/or pellets may be utilized. Moreover, in the case of blended polymers, the powder and/or pellets may be provided as pre-blended resin particles or blended in situ in a hopper associated with the molding machine to produce the desired blend composition for use in the molding process.

As described herein, the metal-reinforced femoral component12has certain enhanced properties. For example, use of the ribbed metal base84increases the overall stiffness of the component and creates a uniform wall thickness for accurate injection molding of the polymer articular layer82.

In some designs of the femoral component12, an alternative to use of the metal base84includes sprayed coatings. For example, a titanium plasma spray (TPS) coating may be applied to a previously-molded polymer femoral component to provide a metal layer on the backside of the component. Another alternative approach is the use of a two-shot molding process. In such a case, the polymer articular layer82is formed in a first shot with a porous coating then being applied to the backside of the articular layer82via a porogen-filled second shot.