Patent Description:
Implants can be used to replace deteriorated or otherwise damaged cartilage within a joint. Such devices can be used to treat osteoarthritis, rheumatoid arthritis, other inflammatory diseases, generalized joint pain, and joint damages. <CIT> discloses an implant system for repairing the cartilage of a knee joint. The implant system includes a femur implant and a tibia implant. The femur implant includes an anchor and a flexible material pad that may be in a hydrogel material. The anchor includes a plurality of layers including a bone attachment layer having a porous structure which is in contact with or implanted into bone and promotes bony ingrowth and/or ongrowth of bone into the pores of the structure. The anchor may additionally include securing tabs that have apertures. The securing tabs are positioned over bony structure and bone screws are inserted through the apertures to attach the anchor to the femur.

An object of the invention is an implant as defined in claim <NUM>. Another object of the invention is an implant as defined in claim <NUM>. Disclosed herein is an implant for replacing a portion of an articulation surface of a joint, the implant comprising: a main portion configured for inserting into a joint, wherein the main portion comprises: a porous material portion having a first bone-engaging surface; and a hydrogel portion that is bonded to the porous material portion and forming an articulation surface opposite from the first bone-engaging surface; and a bone plate portion configured for securing the implant to a bone that forms the joint;wherein the main portion has a leading end and a trailing end, wherein the leading end is configured for being inserted into the joint, and wherein the bone plate portion extends from the trailing end;wherein the porous material portion has an extension piece that extends from the first bone-engaging surface and forms a second bone-engaging surface that is also formed of the porous material and extends from the first bone-engaging surface in a direction opposite from the articulation surface at an angle with respect to the first bone-engaging surface, whereby a space is formed between the porous material portion and the extension piece at the trailing end;wherein the bone plate portion comprises a solid metal portion that fills the space and also forms all exterior surfaces of the bone plate portion except for the second bone-engaging surface; and wherein the bone plate portion has at least one screw hole for receiving a bone screw.

Further disclosed herein but not forming part of the present invention is an implant for replacing a portion of an articulation surface of a joint. The implant comprises: a main portion configured for inserting into a joint, wherein the main portion comprises:.

Another implant for replacing a portion of an articulation surface of a joint is disclosed herein. The implant comprises: a main portion configured for inserting into a joint and comprising a leading end, a trailing end, an articulation surface and a bone-contacting surface extending between the leading end and the trailing end, wherein the leading end is configured for being inserted into the joint, wherein the main portion further comprises:.

The novel implants disclosed herein provide hydrogel implants having hybrid structures that allow repair of articular cartilage surfaces in various joint spaces that were not easily repaired and provide robust and durable repaired surfaces utilizing the benefits of utilizing hydrogel material for articulation surfaces.

The various embodiments of the inventive hydrogel implant of the present disclosure will be described in more detail in conjunction with the following drawing figures. The structures in the drawing figures are illustrated schematically and are not intended to show actual dimensions.

This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as "horizontal," "vertical," "up," "down," "top" and "bottom" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including "inwardly" versus "outwardly," "longitudinal" versus "lateral" and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as "connected" and "interconnected," refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. When only a single machine is illustrated, the term "machine" shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. The term "operatively connected" is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses, if used, are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures.

According to an embodiment illustrated in <FIG>, an implant <NUM> for replacing a portion of an articulation surface of a joint is disclosed. As shown in <FIG>, the implant comprises a main portion <NUM> configured for inserting into a joint and a bone plate portion <NUM> extending from the main portion <NUM> at an angle and configured for securing the implant <NUM> to a bone that forms the joint. As shown in the exploded view of <FIG>, the main portion <NUM> comprises a porous material portion <NUM> having a first bone-engaging surface <NUM>, and a hydrogel portion <NUM> that is bonded to the porous material portion <NUM>.

Referring to <FIG> and <FIG>, the hydrogel portion <NUM> forms an articulation surface <NUM> located opposite from the first bone-engaging surface <NUM>. In other words the articulation surface <NUM> and the first bone-engaging surface <NUM> face away from each other. The bone plate portion <NUM> comprises a solid metal portion <NUM> that forms all exterior surfaces of the bone plate portion <NUM> except for the second bone-engaging surface <NUM>. The second bone-engaging surface <NUM> of the bone plate portion <NUM> is formed of the same porous material as the porous material portion <NUM> and is preferably integrally formed with the porous material portion <NUM> as a unitary structure for ease of manufacturing and producing a more compact structure.

The bone plate portion <NUM> comprises at least one screw hole <NUM> for receiving a bone screw that is used to secure the implant <NUM> to a bone. There can be more than one screw holes provided in the bone plate portion <NUM> for implanting into a joint repair site that may require more than one bone screw to secure the implant.

The main portion <NUM> of the implant <NUM> has a leading end <NUM> and a trailing end <NUM>, where the leading end is configured for being inserted into the joint. Here, the terms "leading" and "trailing" references generally the implant's orientation in its implanted position in a joint space and also the orientation as the implant is being inserted into the joint space.

The bone plate portion <NUM> is integrally formed with the porous material portion <NUM> and extends from the trailing end, forming a second bone-engaging surface <NUM>. Because the extension piece <NUM> is formed of the same porous material as the porous material portion <NUM>, the second bone-engaging surface <NUM> also promotes the cancellous bone's growth into the second bone-engaging surface <NUM> and enhance the implant's stability in the repair site.

As shown by the dashed lines in the side view of the implant <NUM> in <FIG>, the porous material portion <NUM> has an extension piece <NUM> that extends from the first bone-engaging surface <NUM> in a direction opposite from the articulation surface <NUM> at an angle θ with respect to the first bone-engaging surface <NUM>. The angle θ between the first and second bone-engaging surfaces <NUM>, <NUM> is selected to enable secure attachment of the implant to the bone. In some embodiments, that angle can be substantially <NUM>°. This means that the angle can be <NUM>° ± <NUM>°. In some embodiments, the angle is an obtuse angle. In some embodiments, the obtuse angle is ≥ <NUM>° and ≤ <NUM>°. In some embodiments, the obtuse angle is ≥ <NUM>° and ≤ <NUM>°.

The extension piece <NUM> is provided to form the second bone-engaging surface <NUM>. The porous material portion <NUM> and the extension piece <NUM> together provide a skeletal base structure on which the hydrogel portion <NUM> is applied and bonded thereto. This skeletal structure is shown in <FIG>. The solid metal portion <NUM> fills the space <NUM> between the extension piece <NUM> and the porous material portion <NUM>. In some embodiments, the solid metal portion <NUM> can be integrally formed with the porous material portion <NUM> and the extension piece <NUM>. <FIG> show the porous material structures <NUM>, <NUM> and the solid metal portion <NUM> together.

In <FIG>, because only porous material structures <NUM> and <NUM> are shown, without the solid metal portion <NUM>, the hole 150A in the extension piece <NUM> is larger than the bone screw hole <NUM> which is the final dimension screw hole that is formed by the solid metal portion <NUM> that overlays on the extension piece <NUM>.

In a preferred embodiment, the porous material structures <NUM>, <NUM> and the solid metal portion <NUM> are formed as a unitary structure. For example, the porous material structures and the solid metal portion <NUM> can be <NUM>-D printed and sintered to form a unitary structure.

In some embodiments, the bone plate portion <NUM> and the porous material portions <NUM> and are formed of surgical grade metal. In a preferred embodiment, the surgical grade metal used is titanium. In more preferred embodiment, the solid metal portion <NUM> is formed of titanium metal and the porous material portion <NUM> and the extension piece <NUM> are made of porous titanium metal foam.

The hydrogel portion <NUM> is bonded to the porous material portion by having some hydrogel material infiltrate into pores of the porous material portion. In preferred embodiments where the porous material is porous titanium metal foam, the hydrogel material infiltrate into pores of the porous titanium metal foam.

The porous material may comprise an oxide material. The porous material can comprise at least one of surgical grade materials such as aluminum, alumina, zirconia, titanium, titania, stainless steel, PEEK, and steatite that are approved for implantation in humans. The porous material can have a porosity between <NUM> ppi and <NUM> ppi. Pores of the porous material can have a dimension between <NUM> and <NUM>. The porous material can be ceramic, metal, or plastic. In some embodiments, the porous material comprises porous ceramic material (e.g., oxide-ceramic), metal (e.g., titanium (e.g., titanium mesh, printed titanium), stainless steel (e.g., stainless steel wool), plastic (e.g., polyaryl ether ketone (PAEK) (e.g., polyether ether ketone (PEEK)), other biocompatible materials, combinations thereof, etc.) In some preferred embodiments, the porous material is porous metal foam material that has open-celled three-dimensional scaffold structure for bone and tissue growth.

In more preferred embodiments, the porous metal foam material is porous titanium foam. An example of such porous titanium foam material is Wright Medical Technology's BIOFOAM® Cancellous Titanium™ technology. The titanium matrix of BIOFOAM® Cancellous Titanium™ technology has fully interconnected porosity of up to <NUM>% providing an ideal environment for optimum bone ingrowth and incorporation. The titanium matrix of BIOFOAM® Cancellous Titanium™ technology has: compressive strength that is between that of cortical and cancellous bone, thus minimizing deformation under dynamic loading conditions; compressive modulus that is close to that of cancellous bone, allowing the natural transfer of dynamic loads away from the implant to the surrounding bone; and high surface coefficient of friction that provides initial stability in the interface between the implant and the bone, minimizing micro motion and creating a stable environment for rapid ingrowth and fixation. Examples of alternative materials for the porous metal foam is titanium dioxide foam and porous tantalum foam.

Referring to <FIG>, when the implant <NUM> is implanted in a patient to repair or replace a portion of an articulation surface (e.g., articular cartilage) in a joint, the damaged articulation surface and the adjacent bone region would be prepared to receive the implant <NUM>. The prepared site would have resected bone surfaces B1 and B2 corresponding to the first bone-engaging surface <NUM> and the second bone-engaging surface <NUM> of the implant <NUM>. All or much of the resected bone surfaces B1 and B2 would generally be comprised of cancellous bone and because the first and second bone-engaging surfaces <NUM>, <NUM> are formed of porous metal foam material that has a mesh-like structure with many pores mimicking the cancellous bone structure, the cancellous bone grows into the porous metal foam structure and further enhances the securement of the implant <NUM> in the repair site.

The hydrogel portion <NUM> can be formed by applying the hydrogel material in a liquid form on the porous material structure <NUM> in a mold and then allowing the hydrogel material to cross-link by conducting the appropriate processes that are appropriate for the particular type of hydrogel material that is selected for a given application for the implant.

In some embodiments of the implant <NUM>, the bond between the hydrogel portion and the porous material portion is enhanced by having some hydrogel material infiltrating into the pores in a portion of the porous material along the surface that comes in contact with the hydrogel material. Thus, in a region in the porous material structure <NUM> along the hydrogel portion <NUM>, both the hydrogel material and the porous material co-exist while in the remainder of the porous material structure <NUM> toward the bone-engaging surface <NUM>, only the porous material exists without any hydrogel material. That allows the bone-engaging surface <NUM> to present pores that enable cancellous bone ingrowth.

The hydrogel material referred to herein refers to a three-dimensional solid resulting from cross-linked hydrophilic polymer chains formed of polyvinyl alcohol (PVA). The hydrogel material can comprise one or more other materials in addition to PVA, such as, for example, other hydrogels, other polymeric materials, additives, and/or the like. In some embodiments, the PVA content of the hydrogel in the implants disclosed herein can be about <NUM>% by weight. The PVA content of the hydrogel can range from about <NUM>% by weight to about <NUM>% by weight, as appropriate for particular application.

The hydrogel can comprise water, saline, other liquids, combinations thereof, and/or the like. In some embodiments, saline may be preferred over water, because, under certain circumstances, saline can help maintain osmotic balance with surrounding anatomical tissues following implantation. The exact composition of the hydrogel component in an implant can be selected for optimal performance in a particular application to achieve the desired or required strength, load bearing capacity, compressibility, flexibility, longevity, durability, resilience, coefficient of friction, and/or other properties and characteristics.

In some embodiments, such hydrogel portions of the implants can be formulated for drug delivery and/or is seeded with growth factors and/or cells. In such embodiments, the hydrogel component can comprise one or more of the following: chondrocytes, growth factors, bone morphogenetic proteins, collagen, hyaluronic acid, nucleic acids, and stem cells. Such factors and/or any other materials included in the implants can help facilitate and/or promote long-term fixation of the implants at the joint site.

<FIG> shows a top view illustration of the hydrogel implant <NUM>. <FIG> is a cross-section view illustration of the hydrogel implant <NUM> taken through the section line M-M shown in <FIG> is a detailed view of the region N identified in the sectional view of <FIG>.

Referring to <FIG>, an implant 100A for replacing a portion of an articulation surface of a joint is disclosed, which does not form part of the present invention. As shown in <FIG>, the implant comprises a main portion 110A configured for inserting into a joint and a bone plate portion 120A extending from the main portion 110A at an angle and configured for securing the implant 100A to a bone that forms the joint. As shown in the exploded view of <FIG>, the implant 100A comprises four different components that are bonded together in the following order: a first porous material portion 117A, a solid metal portion 116A, a second porous material portion 115A, and a hydrogel poriton 112A.

Referring to <FIG> and <FIG>, which is a side view of the implant 100A, the first porous material portion 117A has a first bone-engaging surface 130A, and a second bone-engaging surface 140A. The top portion 121A of the first porous material portion 117A form the second bone-engaging surface 140A and the remaining portion of the first porous material portion 117A form the first bone-engaging surface 130A. On the side opposite of the two bone-engaging surfaces 130A, 140A, the solid metal portion 116A is bonded to the first porous material portion 117A.

The solid metal portion 116A comprises a top portion 122A, which together with the top portion 121A of the first porous material portion 117A form the bone plate portion 120A of the implant 100A. Similar to the implant <NUM> described above, the bone plate portion 120A of the implant 100A also comprises at least one screw hole for receiving a bone screw that is used to secure the implant 100A to a bone. In the illustrated example shown, two screw holes 150A and 151A are provided in the bone plate portion 120A for implanting into a joint repair site that may require more than one bone screw to secure the implant. The top pportion 121A of the first porous material portion 117A comprises holes 150A' and 151A' that correspond to the two screw holes 150A and 151A.

The top portion 122A of the solid metal portion 116A forms the exterior surface of the bone plate portion 120A while the second bone-engaging surface 140A is formed by the first porous material portion 117A.

The second porous material portion 115A is positioned between and bonded to both the solid metal portion 116A and the hydrogel portion 112A. The hydrogel portion 112A forms an articulation surface 114A located opposite from the first bone-engaging surface 130A. In other words, the articulation surface 114A and the first bone-engaging surface 130A face away from each other.

The main portion 110A of the implant 100A has a leading end 111A and a trailing end 113A, where the leading end 111A is configured for being inserted into the joint. Here, the terms "leading" and "trailing" references generally the implant's orientation in its implanted position in a joint space and also the orientation as the implant is being inserted into the joint space.

Both the first and second porous material portions 117A and 115A are preferably made of the same porous material. The first porous material portion 117A which forms the first and second bone-engaging surfaces, 130A and 140A, respectively, promotes the cancellous bone's growth into the bone-engaging surfaces 130A, 140A and enhance the implant's stability in the repair site.

As shown in <FIG>, the first bone-engaging surface 130A is substantially parallel to the articulation surafce 114A of the hydrogel portion 112A. The second bone-engaging surface 140A of the bone plane portion 120A and the first bone-engaging surface 130A form an angle θ with respect to the first bone-engaging surface <NUM>. The angle θ between the first and second bone-engaging surfaces 130A, 140A is selected to enable secure attachment of the implant to the bone. In some examples, that angle can be substantially <NUM>°. This means that the angle can be <NUM>° ± <NUM>°. In some examples the angle is an obtuse angle. In some examples, the obtuse angle is ≥ <NUM>° and ≤ <NUM>°. In some examples, the obtuse angle is ≥ <NUM>° and ≤ <NUM>°.

The first porous material portion 117A, the solid metal portion 116A, and the second porous material portion 115A together provide a skeletal base structure on which the hydrogel portion 112A is applied and bonded thereto. In some embodiments, the solid metal portion 116A can be integrally formed with the first and second porous material portions 117A and 115A as a unitary structure. For example, the porous material structures and the solid metal portion 116A can be <NUM>-D printed and sintered to form a unitary structure.

As in the implant embodiment <NUM>, the solid metal portion 116A and the porous material portions 117A, 115A can be formed of surgical grade metal such as titanium and/or titanium alloys.

The hydrogel portion 112A is bonded to the second porous material portion 115A by having some hydrogel material infiltrate into pores of the porous material portion. In preferred embodiments where the porous material is porous titanium metal foam, the hydrogel material infiltrate into pores of the porous titanium metal foam. The porous material may comprise of the materials described above in connection with the implant <NUM>.

When implanted in a patient, the implant 100A's arrangement will be similar to the exaple for implant <NUM> shown in <FIG>.

The hydrogel portion 112A can be formed by applying the hydrogel material in a liquid form on the porous material structure 115A in a mold and then allowing the hydrogel material to cross-link by conducting the appropriate processes that are appropriate for the particular type of hydrogel material that is selected for a given application for the implant.

In some embodiments of the implant, the bond between the hydrogel portion and the porous material portion is enhanced by having some hydrogel material infiltrating into the pores in a portion of the porous material along the surface that comes in contact with the hydrogel material. Thus, in a region in the porous material structure 115A along the hydrogel portion 112A, both the hydrogel material and the porous material co-exist while in the remainder of the porous material structure 115A toward the bone-engaging surface 130A, only the porous material exists without any hydrogel material. That allows the bone-engaging surface 130A to present pores that enable cancellous bone ingrowth.

<FIG> is a top view illustration of the hydrogel implant 100A. <FIG> is a cross-section view illustration of the hydrogel implant 100A taken through the section line AF-AF shown in <FIG> is a detailed view of the region AG identified in the sectional view of <FIG>.

Referring to <FIG>, an implant <NUM> for replacing a portion of an articulation surface of a joint is disclosed, which does not form part of the present invention. The implant <NUM> comprises a main portion <NUM> configured for inserting into a joint. The main portion <NUM> can comprise a hydrogel portion <NUM> forming a bone-contacting surface <NUM> and an articulation surface <NUM> opposite from the bone-contacting surface <NUM>. The main portion <NUM> has a leading end <NUM> and a trailing end <NUM>, wherein the leading end is configured for being inserted into the joint. A bone plate portion <NUM> configured for securing the implant <NUM> to a bone that forms the joint. The bone plate portion <NUM> comprises a first part <NUM> having a perforated structure that is embedded in the hydrogel portion <NUM>; and a second part <NUM> that is not embedded in the hydrogel portion and extending from the trailing end <NUM> in a direction opposite from the articulation surface <NUM> at an angle ≤ <NUM>° but ≥ <NUM>° with respect to the bone-contacting surface <NUM>. The second part <NUM> has at least one screw hole <NUM> for receiving a bone screw (not shown). The second part <NUM> can have generally circular configuration around the screw hole <NUM> as shown in <FIG>, but the shape of the second part <NUM> can be designed to have any appropriate shape to fit into the structure (e.g. contour) of the bones around the particular joint space into which the implant <NUM> will be implanted.

In some examples of the implant <NUM>, the second part <NUM> extends from the trailing end <NUM> at an angle that is ≤ <NUM>° and ≥ <NUM>°. In some examples of the implant <NUM>, the second part <NUM> extends from the trailing end <NUM> at an angle that is substantially <NUM>° (i.e., <NUM> ±<NUM>°). In some examples of the implant <NUM>, the first part <NUM> of the bone plate portion <NUM> is embedded in the hydrogel portion <NUM> and located closer to the bone-contacting surface <NUM> than the articulation surface <NUM>. In some examples of the implant <NUM>, the bone-contacting surface <NUM> is a flat surface. When the bone-contacting surface <NUM> is a flat surface, the first part <NUM> of the bone plate portion <NUM> has substantially flat configuration as shown in <FIG> to correspond to the flat contour of the bone-contacting surface <NUM>.

The implant <NUM> can be formed by molding the hydrogel material around the first part <NUM> of the bone plate portion <NUM> using injection molding or open cavity molding processes known to those in the art. As shown in <FIG> and <FIG>, the first part <NUM> of the bone plate portion <NUM>, the part that gets embedded in the hydrogel portion <NUM>, can be perforated with holes <NUM> to better enable the hydrogel material to intimately surround and envelope the first part <NUM> during the molding process so that the resulting implant <NUM> has the optimal structural integrity.

The bone plate portion <NUM> is made of a surgical grade metal, such as stainless steel, cobalt based superalloys, titanium, titanium alloys, etc. In some examples, the surgical grade metal is titanium.

Referring to <FIG>, an implant <NUM> not forming part of the present invention is disclosed. The implant <NUM> is similar to the implant <NUM> just described with one of the differences being the provision of a protruding part <NUM> on the bone-contacting surface <NUM>.

The implant <NUM> for replacing a portion of an articulation surface of a joint comprises a main portion <NUM> configured for inserting into a joint. The main portion <NUM> comprises a hydrogel portion <NUM> forming a bone-contacting surface <NUM> and an articulation surface <NUM> opposite from the bone-contacting surface <NUM>. The bone-contacting surface <NUM> comprises the protruding part <NUM> that provides additional structural stability at the interface between the bone and the bone-contacting surface <NUM> when the implant <NUM> is implanted in position in a joint space. Preferably, the bone surface that is receiving the implant <NUM> would be prepared to have a contour that is complementary to the contour of the bone-contacting surface <NUM> that includes the protruding part <NUM>.

Similar to the implant <NUM>, the main portion <NUM> of the implant <NUM> comprises a leading end <NUM> and a trailing end <NUM>, where the leading end <NUM> is configured for being inserted into the joint. The implant <NUM> further comprises a bone plate portion <NUM> configured for securing the implant <NUM> to a bone that forms the joint. The bone plate portion <NUM> comprises a first part <NUM> having a perforated structure that is embedded in the protruding part <NUM> of the hydrogel portion <NUM>, and a second part <NUM> that is not embedded in the protruding part of the hydrogel portion. The second part <NUM> extends from the trailing end <NUM> in a direction opposite from the articulation surface <NUM> at an angle ≤ <NUM>° but ≥ <NUM>° with respect to the base flat portion of the bone-contacting surface <NUM> (i.e., the part of the bone-contacting surface <NUM> excluding the protruding part <NUM>. The second part has at least one screw hole <NUM> for receiving a bone screw (not shown). Similar to the implant <NUM>, the second part <NUM> can have generally circular configuration around the screw hole <NUM> as shown in <FIG>, but the shape of the second part <NUM> can be designed to have any appropriate shape to fit into the structure (e.g. contour) of the bones around the particular joint space into which the implant <NUM> will be implanted.

In some examples of the implant <NUM>, the second part <NUM> extends from the trailing end <NUM> at an angle that is ≤ <NUM>° and ≥ <NUM>°. In some examples of the implant <NUM>, the second part <NUM> extends from the trailing end <NUM> at an angle that is substantially <NUM>° (i.e., <NUM> ±<NUM>°). In some examples, the first part <NUM> of the bone plate portion is embedded in the hydrogel portion and located closer to the bone-contacting surface <NUM> than the articulation surface <NUM>. Preferably, the first part <NUM> of the bone plate portion <NUM> has a contour that substantially matches the contour of the protruding part <NUM> of the hydrogel portion <NUM>.

In some examples, the protruding part <NUM> of the bone-contacting surface <NUM> has a half-cylinder contour and the first part <NUM> of the bone plate portion has a complementary curved contour. In some examples of the implant <NUM>, the bone plate portion <NUM> is made of a surgical grade metal, such as stainless steel, cobalt based superalloys, titanium, titanium alloys, etc. In some examples, the surgical grade metal is titanium.

Referring to <FIG>, an example of a molding process for forming the implants <NUM> and <NUM> is disclosed. A mold <NUM> having a plurality of mold cavities <NUM> is provided. Each of the mold cavity <NUM> is configured with the outline shape of either the implant <NUM> or the implant <NUM>. A bone plate portion <NUM> or <NUM> is first placed in each of the mold cavity <NUM>. Then, a nozzle <NUM> for dispensing the hydrogel material is positioned into the mold cavity <NUM> as shown in <FIG>. Next, the hydrogel material, represented by the arrow <NUM>, is dispensed into each of the mold cavity <NUM>. Next, with each of the mold cavities <NUM> holding a bone plate portion <NUM> and filled with the hydrogel material, an appropriate post processing is carried out for cross-linking the hydrogel material to form the finished implant product <NUM>. This process is equally applicable to the implant <NUM>. The specifics of this post processing would be determined by the particular hydrogel material being used but would be well known to those in the art for the particular formulation of hydrogel.

Referring to <FIG>, another embodiment of an implant <NUM> for replacing a portion of an articulation surface of a joint is disclosed. The implant <NUM> comprises a main portion <NUM> configured for inserting into a joint and a bone plate <NUM> configured for securing the implant <NUM> to a bone that forms a joint.

Referring to <FIG>, the main portion <NUM> comprises a leading end <NUM>, a trailing end <NUM>, an articulation surface <NUM> and a bone-contacting surface <NUM> extending between the leading end and the trailing end. The leading end <NUM> is configured for being inserted into the joint. The main portion <NUM> further comprises a porous material portion <NUM> and a hydrogel portion <NUM> forming the articulation surface <NUM> and the bone-contacting surface <NUM> opposite from the articulation surface <NUM>. The porous material portion <NUM> is bonded to the hydrogel portion <NUM> and the porous material portion <NUM> extends partially from the trailing end <NUM> towards the leading end <NUM> and forms a portion of the bone-contacting surface <NUM>.

Referring to <FIG> and the cross-sectional view in <FIG>, the porous material portion <NUM> comprises a tapered hole <NUM> at the trailing end <NUM>.

Referring to the cross-sectional views of <FIG>, in some embodiments, the bone plate <NUM> is formed of a solid metal and comprises a tapered stem <NUM> that is configured to be inserted into the tapered hole <NUM> in the porous material portion <NUM>. The tapered stem <NUM> and the tapered hole <NUM> cooperate to urge the bone-contacting surface <NUM> of the implant <NUM> toward the bone when the implant <NUM> is inserted into the joint. Referring to <FIG>, <FIG>, the bone plate <NUM> comprises at least one screw hole <NUM> for receiving a bone screw S.

The porous material for the porous material portion <NUM> can be the same material as the porous material portion <NUM> of the implant <NUM> discussed above.

In some embodiments, the hydrogel portion <NUM> is bonded to the porous material portion <NUM> by having some hydrogel material infiltrating into pores in a portion of the porous material portion. The main portion <NUM> comprising the hydrogel portion <NUM> and the porous material portion <NUM> can be formed by an appropriate process such as an injection molding or open cavity molding process as described above in connection with the implant embodiment <NUM>.

<FIG> are illustrated with the bone of a joint in which the implant <NUM> is secured. A portion of the bone immediately surrounding the implant <NUM> is illustrated conceptually as a box-like volume Bone for illustration purposes. <FIG> show how the tapered stem <NUM> of the bone plate <NUM> and the tapered hole <NUM> of the porous material portion <NUM> engage each other and cooperate to urge the bone-contacting surface <NUM> of the implant <NUM> toward the bone when the implant <NUM> is inserted into the joint. <FIG> shows the implant <NUM> positioned in place in the Bone. The bone-contacting surfaces <NUM> are contacting the prepared bone surface B3. The tapered stem <NUM> of the bone plate <NUM> is partially inserted into the mating tapered hole <NUM> in the porous material portion <NUM> and a bone screw S is placed through the screw hole <NUM> in the bone plate <NUM> and starting to engage the pre-drilled hole in the Bone. <FIG> shows the implant <NUM> where the bone screw S is fully screwed into the Bone and has secured the bone plate <NUM> to the Bone. With the bone plate <NUM> in its fully-seated position, the tapered stem <NUM> is fully inserted into the tapered hole <NUM>. The tapered surface of the tapered stem <NUM> pushes against the sidewall of the tapered hole <NUM> as the tapered stem <NUM> reaches its fully-seated position and securely holds the main portion <NUM> of the implant <NUM> in place.

In <FIG> and <FIG>, two examples of the implant <NUM> are shown implanted in joint spaces between a metatarsal bone and a cuneiform bone. In <FIG>, a third implant <NUM> is shown implanted in a subtalar joint space between the talus and the calcaneus.

Claim 1:
An implant (<NUM>) for replacing a portion of an articulation surface of a joint, the implant comprising:
a main portion (<NUM>) configured for inserting into a joint, wherein the main portion comprises:
a porous material portion (<NUM>) having a first bone-engaging surface (<NUM>); and
a hydrogel portion (<NUM>) that is bonded to the porous material portion and forming an articulation surface (<NUM>) opposite from the first bone-engaging surface; and
a bone plate portion (<NUM>) configured for securing the implant to a bone that forms the joint;
wherein the main portion (<NUM>) has a leading end (<NUM>) and a trailing end (<NUM>), wherein the leading end is configured for being inserted into the joint, and wherein the bone plate portion extends from the trailing end;
wherein the bone plate portion (<NUM>) comprises a solid metal portion (<NUM>) that forms all exterior surfaces of the bone plate portion except for the second bone-engaging surface (<NUM>); and
wherein the bone plate portion (<NUM>) has at least one screw hole (<NUM>) for receiving a bone screw (S);
characterized in that the porous material portion (<NUM>) has an extension piece (<NUM>) that extends from the first bone-engaging surface (<NUM>) and forms a second bone-engaging surface (<NUM>) that is also formed of the porous material and extends from the first bone-engaging surface (<NUM>) in a direction opposite from the articulation surface (<NUM>) at an angle (Θ) with respect to the first bone-engaging surface, whereby a space (<NUM>) is formed between the porous material portion (<NUM>) and the extension piece (<NUM>) at the trailing end (<NUM>);
and in that the solid metal portion (<NUM>) fills the space (<NUM>).