Orthopaedic implant

Abstract

The implant component 1 comprises a base portion 11 with a first side configured to interface with a bone of a patient and a second side A configured to interface with a plastic component. The implant

Description

This invention relates generally, but not exclusively, to an implant component for an orthopaedic implant. Orthopaedic implants often have plastic components attached to other, usually metal, components. For example, tibial implants for knee arthroplasty often have a plastic articulating joint component attached to a metal tibial tray; acetabular cups for hip arthroplasty often have a plastic liner within and attached to a metal cup; and femoral implants for hip arthroplasty often have a plastic femoral head attached to a metal femoral stem. In these cases, the plastic component is usually attached to the metal component using fasteners or adhesives. Problematically, this can lead to loosening or disconnection of the plastic component from the metal component due to issues such as loosening of the fasteners or failure of some or all of the adhesive. This can lead to the patient needing to undergo revision surgery. Metal component of implants have many forms, some of which are implants with porous structures. Such implants may have advantages in that the porous structure deforms more than a fully solid implant would, and so a porous implant may better replicate strain in native bone, thereby providing less stress shielding in the bone and allowing for bone ingrowth into the porous structure. However, the issue with loosening of the plastic component can be exacerbated in such implants, because of greater strain in the porous structure leading to greater strain of the metal component, which might lead to greater movement of the plastic component relative to the metal component, which, in turn, might lead to loosening of the plastic component, for example due to loosening of the fasteners. It would therefore be advantageous to address at least some of these limitations. Accordingly, a first aspect of the invention provides an implant component for, e.g., for use in, an orthopaedic implant, the implant component comprising: a base portion with a first side configured to interface with a bone of a patient and a second side configured to interface with a plastic component; and a plurality of protrusions extending from and distributed across the second side of the base portion, the protrusions being spaced apart from one another to define a network of passages therebetween. The network of passages may be configured to receive plastic material of the plastic component during moulding of the plastic component to the implant component. Another aspect of the invention provides an implant component for, e.g., for use in, an orthopaedic implant, the implant component comprising: a base portion with a first side configured to interface with a bone of a patient and a second side configured to interface with a plastic component; and a plurality of protrusions extending from and distributed across the second side of the base portion, the protrusions being spaced apart from one another to define a network of passages therebetween; wherein the network of passages is configured to receive plastic material of the plastic component during moulding of the plastic component to the implant component. The plastic component may become interdigitated with the protrusions when moulded to the implant component. Advantageously, this may provide more robust connection between the implant component and the plastic component due to an increased surface area of contact between the plastic component and the metal component. This may also be advantageous in that the contact surface between the plastic component and the implant component may have many different planes, or directions, and so cyclic deformation of the implant component may be less likely to continuously work loose a large contact surface. The protrusions may otherwise be referred to as pins. The protrusions may be distributed across the entirety of the second side of the base portion. Some or all of the protrusions may be arranged in rows and / or columns. The network of passages may have a repeating pattern in a first direction. The network of passages may have a repeating pattern in a second direction which is different, e.g., perpendicular, to the first pattern. Advantageously, a regular pattern may allow for more consistent overmoulding, as the width of the passages can be determined based upon the parameter of the flow of plastic into the passages during moulding. Each protrusion may have a first end, which is furthest from the base portion. A gap between the first ends of any two adjacent protrusions may be less than four times, three times, or two times a width, or less than four times, three times, or two times a maximum width, of the first ends of the respective protrusions. A gap between the first ends of any two adjacent protrusions may be less than a width, or less than a maximum width, of the first ends of the respective protrusions. The gap between the first ends of any two adjacent protrusions may be more than 10%, 25%, 50%, or 75% of a width, or more than 10%, 25%, 50%, or 75% of a maximum width, of the first ends of the respective protrusions. The gap between the first ends of any two adjacent protrusions may be more than a width, or more than a maximum width, of the first ends of the respective protrusions. All of the protrusions may have the same width, or maximum width. Any part of the network of passages may have a width which is less than four times, three times, or two times a width, or less than four times, three times, or two times a maximum width, of the first ends of the protrusions. Any part of the network of passages may have a width which is less than a width, or less than a maximum width, of the first ends of the protrusions. Any part of the network of passages may have a width which is greater than 10%, 25%, 50%, or 75% of a width, or more than 10%, 25%, 50%, or 75% of a maximum width, of the first ends of the protrusions. Any part of the network of passages may have a width which is greater than a width, or greater than a maximum width, of the first ends of the protrusions..The first end of each protrusion may have a width, or a maximum width, which is less than 1.5 mm, for example between 0.25 and 1.25 mm, for example between 0.5 mm and 1 mm. Each protrusion may have a height, normal to a part of the base portion from which it extends, which is less than 3 mm, for example between 0.1 and 2.5 mm, for example between 0.2 mm and 2 mm. Any number of the protrusions, or a centreline of any number of the protrusions, may extend from the base portion at an oblique angle. That is, any number of the protrusions, or a centreline of any number of the protrusions, may be slanted or tilted relative to a part of the base portion from which the respective protrusion extends. Any number of the protrusions may be axially symmetric in shape. The line of axial symmetry of any number of the protrusions may intersect the second side of the base portion at an oblique angle. Advantageously, an overhanging shape may be created by the protrusion, which defines an undercut. Plastic material of the plastic component may engage this undercut which might lead to a more robust interface between the implant component and the plastic component, to provide better longevity to the orthopaedic implant by rendering loosening or failure less likely. Any number of the protrusions may comprise an overhanging portion which overhangs the second side of the base portion. The overhanging portion of each protrusion may provide or define, an undercut between the second side of the base portion and the overhanging portion. Advantageously, the plastic component may be even more robustly fixed to the second side of the implant component due to engagement with the undercut. Any number of the protrusions, or centrelines of any number of the protrusions, may be parallel with one another. The base portion may comprise a porous structure. The porous structure may provide at least a part of the first side of the base portion. The second side of the base portion may comprise a barrier layer disposed on the porous structure. A base of at least some of the protrusions may be attached to the barrier layer. The barrier layer may be configured to prevent or reduce penetration of plastic material into the porous structure during moulding of the plastic component to the implant component. Advantageously, the amount of plastic material used may be well controlled, and cavitation during moulding of the plastic component may be reduced, as pressure within the plastic component moulding can be established and resisted by the barrier layer. The barrier layer may be substantially non-porous. The barrier layer may have a lower porosity, for example an order of magnitude lower porosity, than the porous structure. Alternatively, the porous structure may provide at least a part of the second side of the base portion. The base portion may comprise a barrier layer proximal the second side. The barrier layer may be configured to limit penetration of plastic material into the porous structure during moulding of the plastic to the implant component. Advantageously, the amount of plastic material used may be well controlled, and cavitation during moulding of the plastic component may be reduced, as pressure within the plastic component moulding can be established and resisted by the barrier layer. A base of some or all of the protrusions may be attached to the porous structure. The barrier layer may be substantially non-porous. The barrier layer may have a lower porosity, for example an order of magnitude lower porosity, than the porous structure. The base portion may comprise a substantially non-porous rim extending around a perimeter of the porous structure. The substantially non-porous rim may provide at least a part of the second side of the base portion. Any number of the plurality of protrusions may extend from the substantially non-porous rim. The non-porous rim may be divided into at least two portions, wherein a first portion of the at least two portions is thicker than a second portion of the at least two portions. It will be appreciated that thickness is in a direction along, or parallel to, the bone-interfacing side. In other words, the non-porous rim may be divided into at least two portions, wherein a first portion of the at least two portions has a greater thickness than a second portion of the at least two portions, the thickness being in a direction extending away from the porous structure at any position around a perimeter of the porous structure. The thicker first portion may be stiffer and so lead to less deformation of the base portion relative to the plastic component, further increasing the longevity of the orthopaedic implant. For example, an area with a particularly high load may have an increased thickness, to reduce the amount of deformation relative to the plastic component. The first portion of the non-porous rim may be located between the second portion and a third portion of the at least two portions of the non-porous rim. The first portion may have a greater thickness than the third portion. The thickness of the second portion and the third portion may be the same. An inner edge of each of the first, second and third portion, which is connected to the porous structure, may be shaped to follow a corresponding outer shape of the non-porous rim. The non-porous rim may comprise a first intermediate portion between, and adjacent both of, the first and second portions. The non-porous rim may comprise a second intermediate portion between, and adjacent both of, the second and third portions. The thickness of the first intermediate portion may vary with position between the first and second portions. The thickness of the second intermediate portion may vary with position between the second and third portions. At least a part of the thickness of the first intermediate portion may vary linearly with position between the first and second portions. At least a part of the thickness of the second intermediate portion may vary linearly with position between the second and third portions. Intersections between the first intermediate portion and each of the first and second portions may be rounded, for example filleted. Intersections between the second intermediate portion and each of the second and third portions may be rounded, for example filleted. Advantageously, this may provide smoother, or more gradual, deformation of the non-porous rim, and so might further reduce the likelihood of loosening or failure of the interface between the implant component and the plastic component The substantially non-porous rim may have one or more areas of increased height. The one or more areas of increased height of the substantially non-porous rim may be devoid of protrusions. The porous structure may be a lattice structure. The lattice structure may comprise a plurality of struts connected together at nodes. Each strut may have a direction component in each of 3 directions, e.g., in each of 3 Cartesian directions. The porous structure may have an elastic modulus, e.g., a bulk elastic modulus, of between 0.1 and 5 GPa. The porous structure may have a porosity of between 5 and 30 %. The lattice structure of the may have a strut density of between 2 and 7 struts per mm3. Each strut may have a thickness, or diameter, of between 100 and 400 microns. The implant component may comprise a bone-insertion feature configured to be inserted into a corresponding slot or a cavity in a bone of a patient, for example for fixation, and / or alignment, of the implant component with the bone. The bone-insertion feature may be a keel or a peg. The bone-insertion feature may extend from the first side of the body portion. The bone-insertion feature may extend from an insertion feature portion of the non-porous rim, in a direction away from the first side of the body portion. Advantageously, the implant component may be stronger because the bone-insertion feature extends from the substantially non-porous rim, instead of from the porous structure. This may lead to less deformation of the body portion in this region, which may, in turn, reduce the relative deformation of the plastic component and the implant component. The height of the non-porous rim may be greater at a location of an edge, or end, of the bone-insertion feature than away from the edge, or end, of the bone-insertion feature. The height may be greater at respective locations of multiple edges, or ends, of the boneinsertion feature than away from the edges, or ends, of the bone-insertion feature. This may reduce the effects of stress concentrations at the edge or edges of the bone-insertion feature and so may, in turn, reduce the relative deformation of the plastic component and the implant component. The bone-insertion feature may comprise an insertion feature central portion provided by a porous structure, for example a lattice structure. The bone-insertion feature may comprise a substantially non-porous insertion feature peripheral rim extending at least partially around a periphery of the insertion feature central portion. This may advantageously provide the ability for bone in-growth into the central portion while providing strength and stiffness for the bone-insertion feature to be inserted into bone, for example with a tight fit. The porous structure may be a lattice structure. The lattice structure may comprise a plurality of struts connected together at nodes. Each strut may have a direction component in each of 3 directions, e.g., in each of 3 Cartesian directions. The porous structure may have an elastic modulus, e.g., a bulk elastic modulus, of between 0.1 and 5 GPa. The porous structure may have a porosity of between 5 and 30 %. The lattice structure of the may have a strut density of between 2 and 7 struts per mm3. Each strut may have a thickness, or diameter, of between 100 and 400 microns. The bone-insertion feature may be a keel which is elongated in shape, with a length direction parallel to the body portion. The keel may comprise one or more reinforcing region. Each of the one or more reinforcing region may divide regions of the insertion feature central portion. That is, the insertion feature central portion may be divided by one or more reinforcing regions. Each reinforcing region may be substantially non-porous. Each reinforcing region may have a greater elastic modulus than the porous structure of the insertion feature central portion. Each reinforcing region may extend in any one of the following directions: between an inferior part of the insertion feature peripheral rim and the body portion or a superior part of the insertion feature peripheral rim; between the inferior part of the insertion feature peripheral rim and a posterior part of the insertion feature peripheral rim; between the inferior part of the insertion feature peripheral rim and an anterior part of the insertion feature peripheral rim; between the posterior part of the insertion feature peripheral rim and the plate portion or the superior part of the insertion feature peripheral rim; between the anterior part of the insertion feature peripheral rim and the plate portion or the superior part of the insertion feature peripheral rim; between the posterior part of the insertion feature peripheral rim and the anterior part of the insertion feature peripheral rim Advantageously, the keel may be stiffer and stronger, and so better withstand a force of being inserted into a keel slot. Furthermore, the keel may be stiffer and so offer greater stiffness to the body portion, thereby reducing deformation of the body portion relative to the plastic component. Each protrusion may have a first end, which is furthest from the base portion, and an intermediate part which is between the connection to the second side of the base portion and the first end, or between a base of the protrusion and the first end. A width, or a maximum width, of the first end may be greater than a width, or a maximum width, of the intermediate part. Any of the one or more protrusions may be axially symmetric in shape. Any of the one or more protrusions may have a triangular plane shape swept around the line of axial symmetry. An undercut may be provided between the first end and the base, or between a first end and the connection to the second side of the base portion, of each respective protrusion. Advantageously, the plastic component may be even more robustly fixed to the second side of the body portion, as plastic material may engage with the undercut during moulding. Any of the one of or more of the protrusions may have a cross-sectional shape which is one of: rectangular, e.g., with rounded corners; square, e.g., with rounded corners; circular; elliptical; polygonal, e.g., pentagonal, hexagonal; or octagonal. It will be understood that the cross-sectional shape is in a plane normal to a centreline of the respective protrusion. Any number of the protrusions may have a first end, which is furthest from the base portion, and a base connected to the second side of the base portion, wherein the base is a fillet or a chamfer. The base of any number of the protrusions may have a width, or a maximum width, which is greater than a width, or a maximum width, of the respective first end. Advantageously, this may reduce stress concentrations at a position where the respective protrusions are attached to the second side of the base portion. The bases of the protrusions may be connected to one another. The bases of the protrusions may be connected to one another to provide the or a barrier layer. A height of the protrusions may vary with position on the second side of the base portion. The protrusions at a central area of the base portion may be shorter than protrusions at a peripheral area of the base portion. The height may be defined as a distance to a first end of the respective protrusion, normal to the second side of the base portion at the location of the respective protrusions. Advantageously, the protrusions may have a smaller height in areas of higher expected wear of the plastic component, such that the plastic component has better longevity. The protrusions in areas with less expected wear may have a greater height, to provide more robust fixation of the plastic component to component. The implant component may be a unitary structure. The implant component may be metallic. The implant component may be made from titanium alloy, for example Ti64. The implant component may be manufactured using additive manufacturing, for example laser sintering. The implant component may comprise, or consist of, fused metal particles. In embodiments the implant component is a tibial component for, e.g., for use in, an orthopaedic implant for knee arthroplasty. The base portion of the implant component may be a plate portion of the tibial component, the first side of the base portion may be an inferior side of the plate portion, and the second side of the base portion may be a superior side of the plate portion which is configured to interface with a plastic articulating joint component. That is, the protrusions may extend from and be distributed across the superior side of the plate portion, the protrusions being spaced apart from one another to define a network of passages. The articulating joint component may be for articulating engagement or contact with an articulation surface of a femoral component or of a femur. The tibial component may be for partial knee arthroplasty. The bone-insertion feature may be a or the keel of the tibial component. A further aspect of the invention provides an orthopaedic implant comprising the aforementioned component, and a plastic component attached to the second side of the implant component, wherein plastic material of the plastic component is located in the network of passages. The plastic component may be interdigitated with the protrusions. The plastic component may be made from polyethylene. A further aspect of the invention provides a method of manufacturing any one of the aforementioned implant components, the method comprising: providing metal powder; and selectively heating areas of the metal powder to fuse the metal powder together into a unitary metallic component which is the implant component. A further aspect of the invention provides computer readable instructions which, when executed by a computer, cause an additive manufacturing machine to perform the aforementioned method of manufacturing the implant component. A further aspect of the invention provides a method of manufacturing an orthopaedic implant, the method comprising: providing any one of the aforementioned implant components; overmoulding a plastic component onto the second side of the implant component such that plastic material of the plastic component is moulded into the network of passages of the implant component. Providing any one of the aforementioned implant components may comprise manufacturing the implant component using the aforementioned method of manufacturing an implant component. According to a further aspect of the invention, there is provided a method of performing orthopaedic surgery, or a method of performing orthopaedic surgery on a cadaveric specimen, the method comprising: preparing a bone for receiving any one of the aforementioned implant components; and attaching the implant component to the prepared bone such that the first side of the implant component interfaces with bone material. It will be appreciated that anatomical directions used throughout, refer to anatomical directions when the implant component is in-situ in the intended position and orientation in a patient. That is, posterior, anterior, superior, inferior, lateral and medial have their usual meanings, and refer to when the implant component is in-situ in the intended position and orientation in a patient. Another aspect of the invention provides a computer program element comprising and / or describing and / or defining a three-dimensional design, e.g. of the implant component described above or an embodiment thereof. The three-dimensional design may be for use with a simulation means or an additive or subtractive manufacturing means, system or device. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. For the avoidance of doubt, the terms “may”, “and / or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a first view of a tibial implant component according to a first aspect; Figure 2 is a second view of the tibial implant component of Figure 1; Figure 3 is third view of the tibial implant component of Figure 1; Figure 4 is a bottom view of the tibial implant component of Figure 1; Figure 5 is a first detail view of protrusions of the tibial implant component of Figure 1; Figure 6 is a second detail view of protrusions of the tibial implant component of Figure 1; Figure 7 is a section view of the tibial implant component of Figure 1; Figure 8 is a section view of an orthopaedic implant which includes the tibial implant component of Figure 1; Figure 9 is a detailed section view of protrusions of an implant component according to a second aspect; Figure 10 is a detailed section view of protrusions of an implant component according to a third aspect; and Figure 11 is an image of a lattice structure in the tibial implant components. Referring now to Figures 1 to 4, there is shown an implant component for an orthopaedic implant, which in this case is a tibial component 1 for use in an orthopaedic implant for partial knee arthroplasty. It will be appreciated that anatomical directions used to describe the tibial component 1, and used to describe subsequent embodiments of the invention, relate to anatomical directions when the component is correctly installed in a patient. More specifically, lateral, medial, posterior, anterior, superior and inferior all have their usual anatomical meanings, and relate to the respective direction when the component is located in the patient. The tibial component 1 has a base portion 11 with a first side B configured to interface with a bone of a patient and a second side A configured to interface with a plastic component, which in this case is an articulating joint component P (shown in Figure 8). A plurality of protrusions 12 extend from and are distributed across the second side A of the base portion 11. The protrusions 12 are spaced apart from one another to define a network of passages 13 (as best shown in Figures 5 and 6) therebetween. In this example, the protrusions 12 are distributed across the entirety of the second side A, but it will be appreciated that the protrusions 12 may be distributed across any amount of the second side A and the second side A may have areas devoid of protrusions. As best shown in Figure 4, in this example the base portion has a non-porous rim 111 extending around a perimeter of a porous structure 112. The non-porous rim 111 provides a part of the first side B of the base portion 11 and provides a part of the second side A of the base portion 11. Some of the protrusions 121 extend from the second side A of the non-porous rim 111. The non-porous rim 111 has a side portion 111a, which is a lateral or medial portion, in use. The side portion 111a is located between an anterior portion 111b and a posterior portion 111c. The side portion 111a has a greater thickness TD than the anterior portion 111b and a greater thickness TD than the posterior portion 111c. In this example, each of the side, anterior and posterior portions 111a-c has substantially uniform, or constant, thickness TD. In this example the non-porous rim 111 has a first intermediate portion 111 d located between, and adjacent both of, the anterior portion 111b and the side portion 111a. The non-porous rim 111 has a second intermediate portion 111e located between, and adjacent both of, the posterior portion 111c and the side portion 111a. The thickness TD of the first intermediate portion 111d varies with position between the side portion 111a and the anterior portion 111b, and the thickness TD of the second intermediate portion 111 e varies with position between the side portion 111a and the posterior portion 111c. As shown by the dashed arrowhead lines, the thickness TD is defined along or parallel to the second side. This may also be referred to as along or parallel to a plane of the body portion 11, in this example. The thickness TD may also be defined as extending away from the central portion at any position around a perimeter of the central portion. That is, the thickness TD is in a direction which is normal to the perimeter of the central portion at each location on the perimeter. It will be appreciated that, using this definition, the direction normal to the perimeter refers to the direction normal to the perimeter on a macro scale, and does not account for surface details of the porous structure. In this example the tibial component 1 has a bone-insertion feature, in the form of a keel 3. The keel 3 is configured to be inserted into a corresponding keel slot in a bone of a patient during partial knee arthroplasty. The keel 3 extends from the first side B of the body portion 11. The keel 3 extends from an insertion feature portion, which is a keel portion, of the substantially non-porous rim 111, in a direction away from the first side B of the body portion 11. In this example the keel 3 has a keel central portion 31 which is provided by a porous structure, which in this case is a lattice structure. The keel 3 has a substantially non-porous keel peripheral rim 32 extending around a periphery of the keel central portion 31. The solid keel peripheral rim 32 may provide strength to the keel 3 for when the keel 3 is inserted into the keel slot, may provide additional stiffness to the plate portion 11, and may provide smoother edges than the lattice structure, which causes less abrasion to surrounding bone material. In this example the keel 3 has three reinforcing regions 34a, 34b, 34c. Each reinforcing region 34a, 34b, 34c divides regions of the porous structure of the keel central portion 31. That is, the keel central portion 31 is divided by the reinforcing regions 34a, 34b, 34c. Each reinforcing region 34a, 34b, 34c is substantially non-porous. One of the reinforcing regions 34a extends between an inferior part of the keel peripheral rim 32 and a posterior part of the keel peripheral rim 32. The other two reinforcing regions 34b, 34c are spaced apart and extend between an inferior part of the keel peripheral rim 32 and a superior part of the keel peripheral rim 32. It will be appreciated, however, that the number and configurations of the reinforcing regions may be present, for example to offer different amounts of stiffness or strength, or because the keel has a different shape. Reinforcing regions may instead extend between the inferior part of the keel peripheral rim 32 and the superior part of the keel peripheral rim 32, between the inferior part of the keel peripheral rim 32 and an anterior part of the keel peripheral rim 32, between the posterior part of the keel peripheral rim 32 and the superior part of the keel peripheral rim 32, between the anterior part of the keel peripheral rim 32 and the superior part of the keel peripheral rim 32, or between the posterior part of the keel peripheral rim 32 and the anterior part of the keel peripheral rim 32. In this example, the substantially non-porous rim 111 of the body portion 11 has three areas 113a, 113b, 113c of increased height HD. Each area 113a, 113b, 113c of increased height of the substantially non-porous rim 111 is devoid of protrusions. A first area 113a of increased height is provided on the side portion 111a of the tibial component 1. This area 113a of increased height provides greater bending stiffness to the body portion 11. The second and third areas 113b, 113c of increased height are provided at respective anterior and posterior ends of the keel 3, to reduce the effects of stress concentrations caused by the edges of the keel 3. It will be appreciated that height HD is defined in a direction perpendicular to the second side A, which may also be referred to as perpendicular to the plane of the body portion 11. With reference to Figures 5 and 6, the protrusions 12 of this example are now described in more detail. In this example, the protrusions 12 are arranged in rows and columns. In this way, the network of passages 13 has a repeating, or regular, pattern in a first and second direction. Each protrusion 12 has a first end 121, which is furthest from the base portion 11. In this example, a gap between the first ends 121 of any two adjacent protrusions 12 is less than two times a maximum width of the first ends 121 of the respective protrusions 12 and more than the maximum width of the first ends 121 of the respective protrusions 12. All of the protrusions 12 may have the same maximum width. The first end 121 of each protrusion 12 has a maximum width of between 0.5 mm and 1 mm. Each protrusion has a height, normal to a part of the base portion 11 from which it extends, which is between 0.2 mm and 2 mm. Each protrusions 12, and in this case a centreline of each protrusion 12, extends from the base portion 11 at an oblique angle a, as indicated by a dashed line in Figure 5. That is, each protrusion 12, and the centreline thereof, is slanted or tilted relative to a part of the base portion 11 from which it extends. The protrusions 12 are all parallel with one another. In this way, each protrusions 12 has an overhanging portion which overhangs the second side B of the base portion 11. The overhanging portion provides an undercut between the second side B of the base portion 11 and the overhanging portion. When plastic material enters the network of passages 13 during moulding of the articulating joint component P, plastic material engages the undercuts to provide a more robust connection between the articulating joint component P and the tibial component 1. In this example, each protrusion 12 has an octagonal cross-sectional shape. However, it will be appreciated that any polygonal cross-sectional shape may be provided, e.g., pentagonal, or hexagonal. Indeed, alternative cross-sectional shapes may be provided, such as rectangular, e.g., with rounded corners; square, e.g., with rounded corners; circular; or elliptical. It will be understood that the cross-sectional shape is in a plane normal to the centreline of the respective protrusion. It will also be appreciated that the protrusions may be axially symmetric in shape. Each protrusion has a base 122 connected to the second side B of the base portion 11 of the tibial component 1. In this example, the base 122 is a chamfer. It will be appreciated that the base 1222 of each protrusion 12 may, instead, be a fillet. The base 122 of each protrusion 12 has a maximum width which is greater than the maximum width of the first end 121 of the respective protrusion. Thereby, effects of stress concentrations, where the respective protrusions are attached to the second side of the base portion, are reduced. Referring now to Figure 7, an enlarged view of a section through the base portion 11, along a passage of the network of passages 13, is shown. The second side A of the base portion 11 has a barrier layer 14 disposed on the porous structure 112 of the base portion 11. The barrier layer 14 in this example is substantially non-porous. The bases 122 of the protrusions 12 which extend from the base portion 11 in the region of the porous structure 112 are attached to the barrier layer 14. The barrier layer 14 is configured to prevent penetration of plastic material into the porous structure 122 during moulding of the plastic component P to the tibial component 1. The presence of the barrier layer 14 means that an amount of plastic material used may be well controlled, and cavitation during moulding of the plastic component P to the tibial component 1 can be reduced, as pressure within the plastic component P moulding can be established and resisted by the barrier layer 14. It will be appreciated that in other embodiments the barrier layer might have some porosity, but much less porosity than the porous structure 112, thereby reducing penetration of plastic material into the porous structure during moulding of the plastic component P to the tibial component. Referring now to Figure 8, a cross-section of an orthopaedic implant 10 is shown, which has the tibial component 1 and the articulating joint component P moulded to the second side A of the tibial component 1. Plastic material of the articulating joint component P is located in the network of passages 13 such that the articulating joint component P is interdigitated with the protrusions 12. The articulating joint component 12 is shown as being transparent in Figure 8, for illustration purposes only. Referring now to Figure 9 there is shown a cross-section of protrusions 12’ used in an implant component according to another embodiment of the invention. Features of the protrusions 12’ of this embodiment, which are similar to those in the previous embodiment, have the same reference numerals with a succeeding prime (‘). The protrusions 12’ of this embodiment have an intermediate part 123’ which is between the base 122’ and the first end 12T. A width, or a maximum width, of the first end 121’ is greater than a width, or a maximum width, of the intermediate part 123’. In this way, the protrusions 12’ have an overhanging portion which overhangs the second side A’ of the base portion 1T. The overhanging portion provides an undercut between the second side A’ of the base portion 11’ and the overhanging portion. When the plastic component P’ is moulded onto the second side A’ of the body portion 1T, plastic material will engage with the undercut to provide a more robust connection between the implant component T and the plastic component P’. In this example, a centreline of each protrusion 12’ is perpendicular to the part of the base portion 11’ from which it extends. In this example, the cross-sectional shape of each protrusion 12’ may be any of rectangular, e.g., with rounded corners; square, e.g., with rounded corners; circular; elliptical; polygonal, e.g., pentagonal, hexagonal; or octagonal. The protrusion 12’ may be axially symmetric such that they have a triangular plane shape swept around the line of axial symmetry. The base 122’ of each protrusion 12’ of this example does not have a fillet or chamfer, but a fillet or chamfer could be provided, as is provided on the protrusions 12 of the previous embodiment. In another embodiment, similar to that shown in Figure 8, the protrusions have the same shape as those described with reference to Figure 8, but a centreline of the protrusions is at an oblique angle to the part of the base portion 11’ from which it extends. Thereby, an even deeper undercut may be provided. Referring now to Figure 10, there is shown a cross-section of protrusions 12” used in an implant component 1” according to another embodiment of the invention. Features of the protrusions 12” of this embodiment, which are similar to those in the first embodiment, have the same reference numerals with a succeeding double-prime (“). The protrusions 12” of this example differ from the protrusions 12 of the first embodiment, and the protrusions 12’ of the embodiment illustrated in Figure 8, in that there is no overhanging portion and so no undercut defined by the protrusions 12”. In this example, a centreline of each protrusion 12” is perpendicular to the part of the base portion 11” from which it extends. In this example, the cross-sectional shape of each protrusion 12” may be any of rectangular, e.g., with rounded corners; square, e.g., with rounded corners; circular; elliptical; polygonal, e.g., pentagonal, hexagonal; or octagonal. The base 122” of each protrusion 12” of this example does not have a fillet or chamfer, but a fillet or chamfer could be provided, as is provided on the protrusions 12 of the first embodiment. In another embodiment, the porous structure of the base portion provides a part of the second side of the base portion. The base portion has a barrier layer proximal the second side, such that the barrier layer is present below a surface (on a macro scale, and not surfaces of the solid parts of the porous structure) of the porous structure. The barrier layer may be configured to limit penetration of plastic material into the porous structure during moulding of the plastic to the implant component. The barrier layer may be non-porous, or may have some porosity which is much less than the porosity of the porous structure. In another embodiment, the height of the protrusions varies with position on the second side of the base portion. The protrusions at a central area of the base portion, relative to the plane of the base portion, are shorter than protrusions at a peripheral area of the base portion. The height is defined as a distance to a first end of the respective protrusion, normal to the second side of the base portion at the location of the respective protrusions. The protrusions may have a smaller height in areas of higher expected wear of the plastic component, such that the plastic component has better longevity. The protrusions in areas with less expected wear may have a greater height, to provide more robust overall fixation of the plastic component to implant component. In all of the described embodiments, the implant component, or more specifically the tibial component, has porous structures which are lattice structures, a detailed image of which is shown in Figure 11. That is, the porous structures in the base portion and in the boneinsertion feature are lattice structures. The lattice structures are formed of a plurality of struts S connected together at nodes N. Each strut S has, or at least the majority of the struts S have, a direction component in each of 3 directions, e.g., in each of 3 Cartesian directions. The lattice structures have an elastic modulus, e.g., a bulk elastic modulus, of between 0.1 and 5 GPa. The lattice structures have a porosity of between 5 and 30 %. The lattice structures have a strut density of between 2 and 7 struts per mm3. Each strut S has a thickness, or diameter, of between 100 and 400 microns. In all of the described embodiments, the implant component, or more specifically the tibial component, is a unitary, metallic structure. The implant component is made up of metal particles fused together. The implant component of the embodiments is made from titanium alloy, for example Ti64. The implant component is manufactured using additive manufacturing, for example laser sintering. In this manufacturing process, areas of metal powder are selectively heated to fuse the metal powder together into a unitary metallic component which is the implant component. The method is controlled by computer readable instructions which, when executed by a computer, cause an additive manufacturing machine to perform the method of manufacturing the implant component. In a separate manufacturing step, an orthopaedic implant is produced by overmoulding the plastic component to the second side of the implant component, such that plastic material of the plastic component is received into the network of passages, such that the plastic component is interdigitated with the protrusions. The orthopaedic implant is subsequently used in orthopaedic surgery, for example knee arthroplasty. For example, a surgeon may prepare a bone for receiving the implant component and attach the implant component to the prepared bone such that the first side of the implant component interfaces with bone material. Whilst the examples provided herein relate to tibial components for knee arthroplasty, the invention is applicable to any orthopaedic implant which has an implant component and a plastic component, where the plastic component is attached to the implant component. In one embodiment the implant component is an acetabular cup for use in an orthopaedic implant for hip arthroplasty. The acetabular cup is metallic, unitary, and formed of a porous, or preferably a lattice, structure, which is received in a pelvis of a patient, is the body portion of the implant component, and an outer surface of the cup-shaped part provides the first side of the base portion, which is configured to interface with bone material. An inside surface of the cup-shaped part provides the second side of the base portion. Similar to in any of the tibial components described earlier, a plurality of protrusions are distributed across the second side. However, in this case the second side is curved unlike the second side of the tibial components. Plastic material of a plastic liner component of the orthopaedic implant is received in the network of passages defined between the protrusions, during overmoulding of the plastic liner component to the acetabular cup. The acetabular cup is produced using the same technique as the tibial component, that is using additive manufacturing. In another example the implant component is a femoral component for use in an orthopaedic implant for hip arthroplasty. The femoral component has a porous structure, preferably a lattice structure. An outer surface of a femoral stem of the femoral component provides the first side of a base portion, which is configured to interface with bone material. An outer surface of a superior end of the femoral component provides the second side of the base portion. The femoral stem and the superior end of the femoral component together provide the base portion. Similar to in any of the tibial components described earlier, a plurality of protrusions are distributed across the second side of the femoral component. Plastic material of a plastic ball of the orthopaedic implant is received in the network of passages defined between the protrusions, during overmoulding of the plastic ball to the femoral component. The femoral component is produced using the same technique as the tibial component, that is using additive manufacturing. The plastic ball is configured to be received in a liner of an orthopaedic implant located in the pelvis. Another example is a patellar component for use in an orthopaedic implant for knee arthroplasty. The patellar component has a bone-interfacing side configured to interface with a patellar, and a second side configured to interface with a plastic articulating joint component. Such a patellar component may have a peripheral rim surrounding a porous, or lattice structure, a side of the peripheral rim and porous structure providing the boneinterfacing side. A first portion of the peripheral rim has a greater thickness than a second portion, thereby reducing strain in the patellar beneath the first portion. A height dimension of the peripheral rim may vary around the perimeter of the peripheral rim, as in the tibial component described earlier. Similar to in any of the tibial components described earlier, a plurality of protrusions are distributed across the second side of the patellar component. Plastic material of a plastic articulating joint component of the orthopaedic implant is received in the network of passages defined between the protrusions, during overmoulding of the plastic articulating joint to the patellar component. Areas of increased height of the peripheral rim may be devoid of protrusions. The patellar component has a bone-insertion feature for insertion into the bone of the patient. The bone-insertion feature may be partly made of porous, or preferably lattice, structure, and may have a solid peripheral rim extending around the porous structure. The porous structure of the bone-insertion feature may also be divided by reinforcing regions which are solid. The patellar component is produced using the same technique as the tibial components, that is using additive manufacturing. Another example is a scapula or humeral component for use in an orthopaedic implant for shoulder arthroplasty. The scapula or humeral component has a bone-interfacing side configured to interface with a scapula or humerus, and a second side configured to interface with an articulating joint component. Such a scapula or humerus component has a peripheral rim surrounding a porous, or lattice structure, a side of the peripheral rim and porous structure providing the bone-interfacing side. A first portion of the peripheral rim has a greater thickness than a second portion, thereby reducing strain in the scapula beneath the first portion. A height dimension of the peripheral rim may vary around the perimeter of the peripheral rim, as in the tibial component described earlier. Similar to in any of the tibial components described earlier, a plurality of protrusions are distributed across the second side of the scapula or humeral component. Plastic material of a plastic articulating joint component of the orthopaedic implant is received in the network of passages defined between the protrusions, during overmoulding of the plastic articulating joint to the scapula or humeral component. Areas of increased height of the peripheral rim may be devoid of protrusions. The scapula or humeral component has a bone-insertion feature for insertion into the bone of the patient. The bone-insertion feature may be partly made of porous, or preferably lattice, structure, and may have a solid peripheral rim extending around the porous structure. The porous structure of the bone-insertion feature may also be divided by reinforcing regions which are solid. The scapula or humeral component is produced using the same technique as the tibial components, that is using additive manufacturing. 5 It will be appreciated that other features described with reference to the tibial components are applicable to the acetabular cup, the femoral component, the patellar component and the scapula or humeral component. Furthermore, whilst the various components described herein have porous structures, it will 10 be appreciated that the protrusions may be provided on components which are solid components, that is, without porous structures. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and / or those shown in the appended drawings provide clear is advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

1. An implant component for an orthopaedic implant, the implant component comprising: a base portion with a first side configured to interface with a bone of a patient and a second side configured to interface with a plastic component; and a plurality of protrusions extending from and distributed across the second side of the base portion, the protrusions being spaced apart from one another to define a network of passages therebetween;wherein the network of passages is configured to receive plastic material of the plastic component during moulding of the plastic component to the implant component.

2. An implant component according to claim 1, wherein each protrusion has a first end, which is furthest from the base portion, and a gap between the first ends of any two adjacent protrusions is less than two times a width, or less than two times a maximum width, of the first ends of the respective protrusions.

3. An implant component according to claim 1 or claim 2, wherein each protrusion has a or the first end, which is furthest from the base portion, and a or the gap between the first ends of any two adjacent protrusions is more than half of a width, or more than half of a maximum width, of the first ends of the respective protrusions.

4. An implant component according to any preceding claim, wherein each protrusion has a or the first end, which is furthest from the base portion, wherein the first end of each protrusion has a width, or a maximum width, of between 0.5 mm and 1 mm.

5. An implant component according to any preceding claim, wherein each protrusion has a height, normal to a part of the base portion from which it extends, which is between 0.2 mm and 2 mm.

6. An implant component according to any preceding claim, wherein any number of the protrusions, or a centreline of any number of the protrusions, extends from the base portion at an oblique angle.

7. An implant component according to any preceding claim, wherein each protrusion comprises an overhanging portion which overhangs the second side of the baseportion to provide an undercut between the second side of the base portion and the overhanging portion.

8. An implant component according to any preceding claim, wherein any number of the protrusions, or centrelines of any number of the protrusions, are parallel with one another.

9. An implant component according to any preceding claim, wherein the base portion comprises a porous structure, the porous structure providing at least a part of the first side of the base portion.

10. An implant component according to claim 9, wherein the second side of the base portion comprises a barrier layer disposed on the porous structure, wherein a base of at least some of the protrusions is attached to the barrier layer, and the barrier layer is configured to prevent or reduce penetration of plastic material into the porous structure during moulding of the plastic component to the implant component.

11. An implant component according to claim 9 or claim 10, wherein the base portion comprises a substantially non-porous rim extending around a perimeter of the porous structure, the substantially non-porous rim providing at least a part of the second side of the base portion, wherein any number of the plurality of protrusions extend from the substantially non-porous rim.

12. An implant component according to claim 11, wherein the substantially non-porous rim has one or more areas of increased height, the one or more areas of increased height being devoid of protrusions.

13. An implant component according to any of claims 9 to 12, wherein the porous structure is a lattice structure, comprising a plurality of struts connected together at nodes.

14. An implant component according to any preceding claim, wherein each protrusion has a or the first end, which is furthest from the base portion, and an intermediate part which is between the connection to the second side of the base portion and thefirst end, wherein a width, or a maximum width, of the first end is greater than a width, or a maximum width, of the intermediate part.

15. An implant component according to any preceding claim, wherein any of the one of or more of the protrusions has a cross-sectional shape which is one of:rectangular, e.g., with rounded corners;circular;elliptical;polygonal, e.g., pentagonal, hexagonal or octagonal.

16. An implant component according to any preceding claim, wherein each protrusion has a or the first end, which is furthest from the base portion, and a base connected to the second side of the base portion, wherein the base is a fillet or a chamfer.

17. An implant component according to any preceding claim, wherein a height of the protrusions varies with position on the second side of the base portion.

18. An implant component according to claim 17, wherein the protrusions at a central area of the base portion are shorter than protrusions at a peripheral area of the base portion.

19. An implant component according to any preceding claim, wherein the implant component is a unitary structure and is metallic.

20. An implant component according to any preceding claim, wherein the implant component is a tibial component for an orthopaedic implant for knee arthroplasty, wherein the base portion of the implant component is a plate portion of the tibial component, the first side of the base portion is an inferior side of the plate portion, and the second side of the base portion is a superior side of the plate portion which is configured to interface with a plastic articulating joint component.

21. An orthopaedic implant comprising an implant component according to any preceding claim, and a plastic component attached to the second side of the implant component, wherein plastic material of the plastic component is located in the network of passages.

22. A method of manufacturing an implant component according to any of claim 1 to 20, the method comprising:providing metal powder; and5 selectively heating areas of the metal powder to fuse the metal powdertogether into a unitary metallic component which is the implant component.

23. Computer readable instructions which, when executed by a computer, cause an additive manufacturing machine to perform the method of claim 22.1024. A method of manufacturing an orthopaedic implant, the method comprising: providing an implant component according to any of claims 1 to 20; overmoulding a plastic component onto the second side of the implant component such that plastic material of the plastic component is moulded is into the network of passages of the implant component.

25. A method according to claim 24, wherein providing the implant component according to any of claims 1 to 20 comprises manufacturing the implant component using a method of manufacture of an implant component according to claim 22.

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