GB2614335A

GB2614335A - Improvements in or relating to implant apparatus

Info

Publication number: GB2614335A
Application number: GB2200033.5A
Authority: GB
Inventors: Jonas Ambrose Cullum Charles; Nicholas Collins Simon
Original assignee: MatOrtho Ltd
Current assignee: MatOrtho Ltd
Priority date: 2022-01-04
Filing date: 2022-01-04
Publication date: 2023-07-05
Also published as: GB202200033D0; WO2023131781A1

Abstract

Arthroplasty implant apparatus 10 comprises an implant body 14 having a bearing surface (44 Fig. 2), and an implant stem 12 having first and second body elements 20a, 20b and a hinge element 20c. The implant further includes an implant fixation-agent-access aperture 16 for enabling the injection and/or egress therethrough of a fixation agent to allow escape of air, fluids, or fixation agent to prevent pockets forming in the agent as the implant is settled into the bone. The stem may have an adhesion/bone growth promoting coating and be tapered and stepped 30 to help with e.g., Morse fixation. The hinge element may comprise sets, e.g., pairs, of linking portions 32a defining a hinge axis 40 and gaps 36a,b, between the stem portions and a spacer and allows adjustment of the stem. A channel (18 Fig. 3) may be provided in the stem surface stem to allow fluids, e.g., air, blood to escape on fixation agent injection or as a result of displacement during implantation. The implant may be part of an implant kit comprising an implant (210, Fig. 6), a stem (212) and an implant stem adapter (250).

Description

Improvements in or relating to Implant Apparatus The present invention relates to an implant apparatus having a greater stability due to reducing or eliminating air pockets in the fixation agent during implantation of an implant in a bone cavity. The present invention also relates to an adaptor for the stem of an 5 implant. The present invention also relates to a kit comprising the adaptor and an implant.

Arthroplasty designates the replacement of a joint with an artificial joint. When the whole natural joint is replaced for the first time, this is referred to as primary total arthroplasty. However, the artificial joint can fail for a number of reasons and may need to be replaced by a new implant during revision arthroplasty. Both primary and revision arthroplasty aim to restore the joint's function as best as possible.

However, due to the unknown state of the soft tissues and native bone stock, revision surgery is typically more complex than primary surgery. In order to cater for the unknowns intraoperatively, revision arthroplasty systems tend to offer a variety of interchangeable and adjustable bearing and fixation options, such as distal and posterior augments, a stem offset, or translation of a stem within an implantable cone or sleeve.

Furthermore, a fragile or damaged bone may not be able to accommodate the forces of the primary or revision implant without any additional structural support. A solution is to implant a cone or sleeve into the bone within which the stem of the implant is received.

Thus, arthroplasty is or is often modular, usually involving an array of bearings and 20 fixations which can be used individually or in combination, as required. This modularity means that surgery is lengthy and complicated. Additionally, an extensive inventory needs to be stocked which is both expensive and space consuming.

The interface between the cone or sleeve and the implant is via a fixation agent such as bone cement. The fixation agent is typically injected into the bone cavity during implantation of the artificial joint. Upon drying, the fixation agent solidifies, thereby immobilising the implant in the desired position and orientation. An issue with the procedure is that pockets of air are trapped during insertion of the fixation agent. The air pockets weaken the engagement of the fixation agent with the implant and/or the bone, thereby reducing the stability of the implant.

The present invention seeks to provide a solution to these problems.

According to a first aspect of the invention, there is provided an implant apparatus for arthroplasty, the implant apparatus comprising: an implant body having a bearing surface, an implant stem having a hinge element thereon, and an implant fixation-agentaccess aperture for enabling the injection and/or egress therethrough of a fixation agent for an implant.

The fixation-agent-access aperture enables a fixation agent to be injected therethrough into the implant and/or bone cavity during or after insertion of the implant, rather than necessarily before. The positioning of the implant apparatus may be facilitated in the absence of the fixation agent.

Conversely, the fixation agent may be inserted prior to the implant. Upon inserting the implant into the bone cavity filled with fixation agent, air and surplus fixation agent displaced by the implant are able to egress via the fixation agent aperture. As air pockets are eliminated between the implant and the bone, the stability of the implant apparatus is increased.

Preferably, the implant stem may define at least one central cavity such that the stem is at least partly hollow. The implant may be lighter than a corresponding implant having a solid stem Beneficially, the fixation-agent-access aperture may be in the implant body at or adjacent a central position of the bearing surface such that the fixation-agent-access aperture may overlie, overlap, and/or be in, preferably fluid, communication with the or a said central cavity for enabling injection and/or egress of the fixation agent through the aperture into or from the central cavity. The user can inject fixation agent directly into the hollow implant. Alternatively or additionally, any excess fixation agent displaced by the implant which has entered the implant stem is able to exit through the aperture in the implant body.

Preferably, the fixation-agent-access aperture may have a dimension which may correspond to a dimension of the or a said central cavity. The aperture does not create a bottleneck, irrespective of the direction of flow of the fixation agent.

Optionally, the stem may include the or a further said fixation-agent-access aperture 30 which may extend from the or a said central cavity to an outer surface of the stem. In addition to or instead of the aperture in the implant body, a through-bore may be provided in the stem to permit fixation agent therethrough. Furthermore, once the fixation agent has solidified in the central cavity, in the aperture in the stem and around the implant, the solid fixation agent further helps to immobilise the implant.

Additionally or alternatively, the implant body may include the or a further said fixation-5 agent-access aperture, the or the further fixation-agent-access aperture being spaced-apart from a central position of the bearing surface for enabling ingress and/or egress of fixation agent therethrough into a gap between the bone and the stem when the stem is received in a bone cavity. Instead of or in addition to the one or more above-mentioned apertures, an aperture may be provided in a peripheral portion of the implant body. This 10 may be beneficial to enable ingress and/or egress of fluid, such as air, blood or fixation agent, to and/or from the bone cavity around the implant stem. The fixation agent can be inserted after positioning of the implant. Furthermore, if the implant is solid or non-hollow, the peripheral aperture may be the only aperture for ingress and/or egress of fixation agent into and/or from the bone cavity.

Preferably, the apparatus may further comprise a plug receivable in the or a said fixationagent-access aperture. Once the plug is received in the or a said fixation-agent-access aperture of the implant body, the plug enables the bearing surface to be continuous or more continuous, thereby reducing the risk of structural failure of the implant.

Furthermore, the stem may further include at least one elongate channel extending at least in part along a proximal-distal axis of the implant apparatus. Beneficially, the elongate channel may be a recess in a surface of the stem such that the channel may be at least partly an open channel. Optionally, the recess may be provided on an outer surface of the stem. Alternatively or additionally, the or a further recess may be provided on an inner surface of the stem. An open channel may be easier to manufacture and/or inspect for impurities and foreign contaminants prior to implantation of the implant. One or more channels can be provided on the inner and/or outer surfaces of the stem. A same channel may even start on one of the inner and outer surfaces of the stem, extend through the wall of the stem and terminate on the other of the inner and outer surfaces. The channel may optionally meet or join a fixation-agent-access aperture in the implant body.

According to a second aspect of the invention, there is provided an implant stem adaptor for an implant having an implant body from which extends a stem, the implant stem adaptor comprising: an adaptor body having: a first body element, and a second body element which is engaged via a hinge element with the first-body element and at least one of the first body element and the second body element having an engagement portion for engaging the stem. An implant can be lengthened by providing an adaptor body. Additionally, as the adaptor body has a hinge, the angular orientation of the implant body may be adjusted.

Optionally, the other of the first body element and the second body element may comprise a second engagement portion for engaging with a second stem of the implant. The implant may have two or more stems, each connectable with one of the ends of the adaptor such that the adaptor is in an intermediate position to the two stems. The second stem may be selectable, for enabling customisability of the stem. The adaptor may be reversibly usable or non-reversibly usable.

Preferably, the first body element may be coaxial with the second body element. The adaptor does not provide any offsetting, although non-coaxial may be an option.

Beneficially, the adaptor body may taper inwardly in a direction from the second body element to the first body element or vice-versa. The adaptor body may narrow with increasing distance from the bearing surface. This may facilitate the insertion into the bone and/or enable more natural bone to be retained. Non-tapering, such as constant thickness, may be an option, however. If the adaptor body is non-reversibly usable, the adaptor body may only taper in one direction, which is preferably from the second body element and/or stem associated with the implant body to the first body element.

Advantageously, the first engagement portion may have a complementary shape and size to engage with a corresponding, third engagement portion of the first said stem, preferably via interference fit, and/or the second engagement portion may have a complementary shape and size to engage with a corresponding, fourth engagement portion of the first stem, preferably via interference fit. One or both ends of the adaptor may have an engagement portion. The engagement may be by interference fit. Interference fit is a simple engagement which requires no additional engagement features such as interlocking portions or screw threads. The additional engagement features may be difficult to assemble during surgery. Additional engagement features may increase the risk of structural failure of the implant. An interference fit engagement may also have the additional advantage of providing lateral stability of the adaptor relative to the first and/or second stem.

Optionally, at least one of: the first engagement portion and the second engagement portion may be conical or frustoconical for providing a Morse taper engagement with the third engagement portion and the fourth engagement portion respectively. Cones or truncated cones taper to a point or narrow end. The tip of the cone or the narrow end of the truncated cone may facilitate the engagement of the first and/or second engagement portion with the third and/or fourth engagement portion. Non-tapering interference fit engagement may be envisioned, however.

Additionally or alternatively, at least one of: the first engagement portion, the second engagement portion, the third engagement portion, and the fourth engagement portion may have a polygonal transverse cross-section. The polygonal transverse cross-section may prevent or inhibit undesirable rotation of the adaptor relative to the first stem and/or the second stem. For example, the engagement portions may be pyramidal or frustopyramidal.

Furthermore, the implant stem adaptor may further comprise a stabilisation element. The 15 stabilisation element may prevent or inhibit accidental rotation of the implant relative to the bone.

Beneficially, the stabilisation element may have a bridge portion and a main stabilisation body connected to the adaptor body by the bridge portion, the main stabilisation body being spaced-apart from the adaptor body by the bridge portion. The main stability body being spaced apart from the adaptor body provides a gap to accommodate the adaptor body and/or the first said stem therein if the adaptor body is bent at the hinge element.

Additionally or alternatively, the stabilisation element may include an indexing element for enabling a user to rotate the adaptor body easily and precisely to a specific position. Furthermore, the indexing element may include at least one of: a protrusion and a receiving recess, crenulation, and a ratchet. The indexing element enables or increases the ease of selecting a preferred angular position of the adaptor relative to the stem. The indexing element may simultaneously prevent or inhibit movement away from the selected relative position, thereby increasing the stability of the implant.

According to a third aspect of the invention, there is provided an implant kit comprising 30 an implant stem adaptor, preferably in accordance with the second aspect of the invention, and an implant having at least an implant body from which extends a stem.

Optionally, the kit may further comprise a second stem. The kit includes the adaptor and the implant which has at least one and preferably two stems usable with the adaptor.

According to a fourth aspect of the invention, there is provided an implant apparatus for arthroplasty, the implant apparatus comprising: an implant body having a bearing surface, an implant stem having a hinge element thereon, and at least one elongate channel extending at least in part along a proximal-distal axis of the implant apparatus. The elongate channel may facilitate the movement of fluid therealong, such as air, blood, and/or fixation agent. This reduces or prevents the formation of fluid pockets in the bone cavity.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a side representation of a first embodiment of an implant apparatus in accordance with the first aspect of the invention; Figure 2 is a perspective top representation of the implant apparatus of Figure 1; Figure 3 illustrates a perspective representation of a stem of the implant apparatus of Figure 1, in which an implant body has been omitted for clarity; Figure 4 shows a perspective back representation of a second embodiment of an implant apparatus in accordance with the first aspect of the invention; Figure 5 is a close-up perspective front view of the implant apparatus of Figure 4; Figure 6 shows a perspective representation of a first embodiment of an implant kit in accordance with the third aspect of the invention, the implant kit having an implant stem adaptor in accordance with the second aspect of the invention and an implant, with a second stem being omitted for clarity; Figure 7 is a longitudinal cut-away representation of the implant kit of Figure 6, additionally showing the second stem; Figure 8 illustrates a perspective representation of a second embodiment of an implant kit in accordance with the third aspect of the invention, the implant kit having an implant stem adaptor in accordance with the second aspect of the invention and an implant, with a second stem being omitted for clarity; Figure 9 is a longitudinal cut-away representation of the implant kit of Figure 8; Figure 10 shows a perspective representation of a third embodiment of an implant 5 kit in accordance with the third aspect of the invention, the implant kit having an implant stem adaptor in accordance with the second aspect of the invention and an implant, with a second stem being omitted for clarity; Figure 11 is a longitudinal cut-away representation of the implant kit of Figure 10; Figure 12 shows a perspective representation of a fourth embodiment of an 10 implant kit in accordance with the third aspect of the invention, the implant kit having an implant stem adaptor in accordance with the second aspect of the invention and an implant, with a second stem being omitted for clarity; Figure 13 is a longitudinal cut-away representation of the implant kit of Figure 12, and Figure 14 illustrates a cut-away representation of a fifth embodiment of an implant kit in accordance with the third aspect of the invention, the implant kit having an implant stem adaptor in accordance with the second aspect of the invention and an implant, with a second stem being omitted for clarity.

Referring to Figure 1, there is shown an artificial joint or implant apparatus indicated generally at 10. The implant apparatus 10 may also be referred to as an implant or implant device. The implant apparatus 10 may be used in partial or total arthroplasty. The arthroplasty may be primary arthroplasty or revision arthroplasty. More specifically, the replaced joint shown in Figures 1 to 3 is a knee. The artificial joint in the present embodiment comprises only a tibial component, but it could easily be envisioned that the implant apparatus may further comprise a femoral component and/or a meniscal component.

The implant apparatus 10 or any part thereof may comprise plastics, ceramics, metal, glass, or any combination thereof. Preferably, the implant 10 or part thereof is formed of one or more metals, such as titanium, cobalt, or chromium, or an alloy, although any 30 suitable material may be considered.

The implant apparatus 10 includes a stem 12, an implant body 14, an aperture 16, a plug, and a channel 18, but any of the above may be omitted and/or a plurality of any of the above may be provided. The aperture 16 is visible in Figure 2 whilst the channel 18 is visible in Figure 3.

The stem or implant stem 12 is in-use receivable within the medullary canal of the bone. The stem 12 also in-use supports, engages, holds, or receives part of the implant body 14. Preferably, the stem 12 is integrally formed with the implant body 14, but connected or connectable may be options. In other words, the stem 12 and the implant body 14 form a one-piece or monobloc structure.

The stem 12 comprises a first body element 20a, a second body element 20b and a hinge element 20c, but any of the above may be omitted and/or a plurality of any of the above may be provided. The stem 12 or parts thereof may be formed by extrusion and/or moulding.

The first body element 20a is the part of the stem 12 which is inserted first into the bone.

The first body element 20a may be referred to as a first portion, or a sleeve. The first body element 20a is preferably received in or positioned within at least the epiphysis, but metaphyseal or even diaphyseal fixation may be considered, if required. The first body element 20a preferably extends in-use at least in part along a longitudinal axis or proximal-distal axis 22. The proximal-distal axis 22 of the implant 10 and/or of the first body element 20a is preferably coaxial with and/or parallel with a proximal-distal axis of the bone. The proximal-distal axis 22 is illustrated as a dashed line in Figure 1. The first body element 20a extends to terminate at a tip, an end or end region 24. Preferably, the first body element 20a is integrally formed with the hinge element or hinge 20c, and more preferably as a one-piece. The first body element 20a is preferably hollow, but non-hollow may be an option.

The second body element 20b is the part of the stem 12 which is inserted second into the bone. The second body element 20b may be referred to as a second portion, a cone, or a sleeve. The second body element 20b is engageable or engaged via the hinge element 20c with the first body element 20a. Preferably, the second body element 20b is integrally formed with the hinge element 20c and/or the first body element 20a. At least one of and preferably both: the first body element 20a and the second body element 20b define together at least one central cavity 26. Optionally, one or more internal partitions may provide a plurality of central cavities. The stem 12 is thus preferably at least partly hollow. Non-hollow or part hollow may be options in alternative embodiments. The, each or at least one central cavity 26 may optionally receive fixation agent. The, each or at least one central cavity 26 may even be left empty, for weight considerations.

The second body element 20b is or is substantially a trapezium in cross-section in the coronal plane and/or at or adjacent the connection with the implant body 14, although any non-trapezium cross-section may be envisioned. In other words, the second body element 20b preferably tapers towards the hinge element 20c along the proximal-distal axis 22. Furthermore, in lateral or transverse cross-section, an inner face and an outer face of the second body element 20b may be the same, or substantially the same as each other, or they may differ from each other. The second body element 20b and/or one or both of the inner and outer face of the second body element 20b may be in transverse cross-section any of: circular, non-circular, an ellipse, an oval, an ovoid, a flattened oval, a flattened ellipse, and square or a rectangle with at least one and up to four rounded edges and/or rounded corners, fabiform, reniform, cardioid, an hourglass-shape, a figure of eight, an ellipse having one or more waisted sections, or any other desirable cross-sectional shape. The cross-section of the second body element 20b may even change along the proximal-distal axis 22.

The second body element 20b is also preferably truncated or chamfered, optionally along an oblique plane, but non-truncated or non-chamfered may be options. The plane preferably is angled relative to the coronal plane, and more preferably is non-perpendicular and non-parallel thereto. The oblique plane is also angled relative to the transverse plane, and more preferably is non-perpendicular and non-parallel thereto. In other words, the oblique plane preferably forms an acute angle with one or both of the coronal plane and the transverse plane. The chamfer may in-use prevent or inhibit any undesirable rotation of the implant body 14 around its longitudinal axis due to an increased contact area. It may easily be envisioned that the oblique plane may be angled relative to the sagittal plane. The oblique plane may be non-perpendicular and/or nonparallel to the sagittal plane but perpendicular or parallel may be options.

As the average width or diameter of the stem 12 or at least one of: the first body element 20a, the second body element 20b, and the hinge element 20c preferably decreases monotonically with increasing distance from the implant body 14, the stem 12 or part thereof can be generally considered to have at least a single taper, and more preferably to have a double taper or substantially double taper towards the tip or end region 24. In other words, the stem 12 or any part thereof may be considered to be generally shaped as any of: a cone, a cone which may flare, a trumpet, and a frustrum of a cone. The stem 12 or any part thereof may be symmetrical in the sagittal plane and/or the coronal plane but it could be envisioned that the first body element may be symmetrical in only one of the above planes, symmetrical in another plane altogether or even may have no symmetry.

An inner surface 28a of the stem 12 or at least one of: the first body element 20a, the second body element 20b, and the hinge element 20c may be smooth or substantially smooth, although non-smooth, textured, or coated may be options. The inner surface 28 10 may have a, preferably continuous, side wall and a base end.

An outer surface 28b of the stem 12 or at least one of: the first body element 20a, the second body element 20b, and the hinge element 20c may have one or more steps or stepped portions 30. These steps 30 help with fixation, for instance via Morse fixation. Furthermore, the outer surface 28b or part thereof may be smooth or, preferably, non-smooth. The outer surface 28b is preferably coated at least in part with a suitable material to encourage bone growth, but this is optional. The outer surface 28b may additionally be at least in part porous and/or, preferably, may have a porous coating, but this is optional. In other words, the implant apparatus 10 or part thereof may optionally be coated, partially or fully, with a cementless coating or a coating enabling a fixation agent to be omitted. The coating may be on the inner surface 28a and/or on the outer surface 28b. The porous coating may be plasma-sprayed and/or electrochemically deposited onto the relevant part of the receiver. The porous portion or porous coating and/or the receiver may be formed by Additive Manufacturing. The porous portion or coating may be formed from a solid billet which may be machined into the desired shape and/or texture. The porous and non-porous parts may be formed of the same material and/or of different materials. If the implant apparatus 10 comprises a coating, a fixation agent may be used or may be omitted entirely. In a further embodiment, a fixation agent may be insertable into a cavity of an implant apparatus whilst a fixation agent may be omitted between the bone and an outer surface of the implant apparatus provided with such a coating.

In lateral or transverse cross-section, any or any combination of: the first body element 20a, the second body element 20b, the hinge element 20c, the inner surface 28a of any of the above, the outer surface 28b of any of the above, and the or a said central cavity 26 may be circular in lateral or transverse cross-section, although non-circular alternatives may be envisioned. Alternative cross-sections include elliptical, ovoid, lachrymiform, curved, non-curved, part curved, linear, polygonal, such as a square, trapezoid, rectangular, hexagonal, octagonal, a polygon having one or more chamfered and/or rounded corners, whether regular, irregular, truncated or chamfered, a polygon having one or more curved edges, any other suitable cross-section, or any combination thereof The cross-sectional shape may even change along the proximal-distal axis 22 or longitudinal axis of the stem 12 or any part thereof Any of: the first body element 20a, the second body element 20b, and the hinge element 20c may comprise, in lateral cross-section, a major dimension and a minor dimension. As at least one of: the first body element 20a, the second body element 20b, and hinge element 20c are preferably circular in lateral cross-section, the major dimension is the same as the minor dimension, and both correspond to a diameter.

The hinge element 20c enables the second body element 20b to be re-orientable, angularly adjustable, bendable or bent relative to the first body element 20a. The stem 12 may even be formed in a bent orientation from the onset, or be bent secondarily. The hinge element 20c comprises at least one linking portion 32a. Preferably as shown, the hinge element 20c comprises two pairs of linking portions 32a, referred to as a first pair and a second pair for clarity, but it could be envisioned that either pair may be omitted or that more pairs may be provided. The hinge element 20c also comprises a spacer segment 32b but this feature may be omitted, or more than one spacer segment may be provided.

Each linking portion, link, connector, or hinge section 32a functions as a hinge or hinge section. As such, each linking portion 32a may be said to be bendable or deformable.

More specifically, each linking portion 32a may be a live hinge, a living hinge or a hinge which is integrally formed as a one piece in the present embodiment. At least one linking portion 32a, and preferably the first pair connects or joins the first body element 20a and the spacer segment 32b. Alternatively or preferably additionally, at least one linking portion 32a, and preferably the second pair connects or joins the second body element 20b with the spacer segment 32b. In other words, the components of the stem 12 are connected in the following order: the first body element 20a, the first pair of linking portions 32a, the spacer segment 32b, the second pair of linking portions 32a, and second body element 20b. Each linking portion 32a and/or each pair of linking portions 32a may be connectable, connected, or here, integrally formed with the spacer segment 32b and/or one of the first body element 20a and the second body element 20b. In the present embodiment, all the above components are preferably integrally formed with each other as a one piece for ease of manufacture and/or strength, but this feature may 5 be omitted.

As shown, each linking portion 32a comprises at least one strip or pillar. Each linking portion 32a has four linking surfaces: an outward-facing surface 34a, an inward-facing surface 34b and two lateral surfaces 34c. Each linking portion 32a has a rectangular or square in lateral cross-section, but may alternatively non-square or non-rectangular. For example, each linking portion 32a may be curved, non-curved, part-curved, circular, non-circular, oval, or polygonal, such as hexagonal or octagonal, whether regular, irregular, truncated, or chamfered in lateral, latitudinal or transverse cross-section, and/or may have fewer or more linking surfaces. The outward-facing surface 34a faces or abuts against the bone whilst the inward-facing surface 34b faces inwards, i.e. towards the central cavity 26. Preferably the stem 12 comprises a material which is simultaneously strong and/or rigid, whilst being pliable, bendable or deforrnable at the linking portion 32a without any risk of structural failure or with a reduced likelihood of structural failure.

At least one linking portion 32a, and more preferably the first pair of linking portions 32a spaces apart the first body element 20a from the spacer segment 32b along the longitudinal direction or proximal-distal axis 22 to provide a gap therebetween, referred to as a first gap 36a, for clarity. The first pair of linking portions 32a optionally delimitates the first gap 36a into two first sub-gaps or first hollows. The first body element 20a has at least one first rim or rim surface 38a. The first rim 38a faces the spacer segment 32b and/or the second body element 20b. Preferably, the first rim 38a defines at least in part the first gap 36a. Preferably, the spacer segment 32b has a similar spacer rim which faces the first rim 38a.

Similarly, at least one linking portion 32a, and more preferably the second pair spaces apart the second body element 20b from the spacer segment 32b to provide a gap therebetween, referred to for clarity as a second gap 36b. The second gap 36b may be divided into two second sub-gaps or second hollows by the second pair of linking portions 32a. The second body element 20b has at least one second rim or rim surface 38b. The second rim 38b faces the spacer segment 32b and/or the first body element 20a. Preferably, the second rim 38b defines at least in part the second gap 36b. Preferably, the spacer segment 32b has a similar spacer rim which faces the second rim 38b. Any of the rims may be any of: planar, non-planar, or part-planar.

Each linking portion 32a of a pair is preferably positioned on either side of the central cavity 26. Each linking portion 32a and/or each pair of linking portions 32a has or defines an axis of bending or rotation, referred to as a hinge axis 40. For clarity, the hinge axes 40 defined by the first pair and the second pair may be referred to as the first hinge axis and the second hinge axis respectively. The first hinge axis is illustrated as dotted lines in Figure 1.

The or each hinge axis 40 may extend across or span a major or minor dimension of the central cavity 26. As the first body element 20a and/or the second body element 20b preferably has a circular cross-section, at least at or adjacent to the hinge element 20c, the or each hinge axis 40 preferably extends diametrically across or spans the diameter of the central cavity 26. In other words, the or each hinge axis 40 is along, on or parallel to a diameter of the first body element 20a and/or the second body element 20b.

A said hinge axis 40 may extend in the coronal plane, preferably in a medial-lateral direction for enabling angular adjustment of the second body element 20b relative to the first body element 20a in the anterior-posterior plane or sagittal plane. Alternatively or additionally, a said hinge axis 40 may extend in the sagittal plane, preferably in an anterior-posterior direction for enabling angular adjustment of the second body element 20b relative to the first body element 20a in the medial-lateral plane or coronal plane. In this latter case, by mechanical necessity, the spacer segment 32b, if provided, is also rotated in the corona! plane. It may be envisioned that either or both axes may extend in any other suitable plane.

The second hinge axis 40 is preferably non-parallel with the first hinge axis 40 to enable 25 angular re-orientation in two distinct planes. More preferably, the second hinge axis 40 is perpendicular with the first hinge axis 40.

The spacer segment or element 32b connects, at least indirectly, the first body element 20a and the second body element 20b. The spacer segment 32b is preferably positioned therebetween and spaces the first and second body elements apart along the longitudinal or proximal-distal axis 22 of the stem 12. The spacer segment 32b preferably also tapers outwardly or flares, preferably like a trumpet, outwardly along the proximal-distal axis 22 in a direction from the tip 24 to the implant body 14, but non-flaring may be an option. For example, the spacer segment may alternatively have a constant extent in transverse cross-section.

The hinge element 20c preferably further comprises at least one recessed portion 42 and preferably eight recessed portions 42. The recessed portions 42 are recessed along 5 a longitudinal direction of the stem 12. The linking portions 32a extend from and connect to the recessed portions 42. The advantage of the linking portion 32a connecting with the recessed portions 42 is that the linking portion 32a may be more elongate, or at least more elongate than the height of the relevant gap. An elongate linking portion 32a may provide a better distribution of the forces, such as the stress forces acting on the linking 10 portion 32a, and consequently a better distribution of the bending. In turn, a better distribution of forces may result in a lower risk of structural failure.

Alternatively or, preferably, additionally to recessing along the longitudinal direction, the, each or at least one said recessed portion 42 may also be recessed in a radial direction or transverse cross-section, as most clearly shown in Figure 3, relative to the outer 15 and/or inner surfaces of the stem 12.

The implant 10 further comprises an aperture 16 and a said channel 18, but any of the above features may be omitted and/or a plurality of any of the above features may be provided.

The fixation-agent-access aperture 16 may also referred to as a through-bore. The aperture 16 may have any shape. By way of examples only, the aperture 16 may be a slot, a circle, or an oval. The aperture 16 permits movement of fluid therethrough. Preferably, the fluid is fixation agent used for fixing an implant, at least when the fixation agent is in a malleable or fluid form. The aperture 16 may thus also be referred to as a fixation-agent-access aperture 16. However, it may easily be envisioned that the aperture may be permit movement of a non-fixation agent therethrough.

The fixation agent or fixing agent may be cured, curable or non-curable. The fixation agent preferably solidifies as it dries or ages. The fixation agent may be any of: polymethyl methacrylate (PMMA), calcium phosphate cement (CPC), Glass polyalkenoate (ionomer) cement (GPC), or any other fixing agent. The fixation agent may also be referred to as bone cement.

The fixation-agent-access aperture 16 may be provided anywhere on the implant 10. More preferably, the or at least one fixation-agent-access aperture 16 is provided on the stem 12 but may additionally or alternatively be provided on the implant body 14. The, each or at least one said fixation-agent-access aperture 16 preferably extends from the or a said central cavity 26 to an outer surface of the stem 12. The aperture 16 may thus be a conduit fluidly connecting the or a said central cavity to a space between the bone and the implant.

More preferably, the or at least one fixation-agent-access aperture 16 is provided in the first body element 20a, but any number of apertures could be provided on the second body element and/or in the spacer element. Even more preferably, the fixation-agentaccess aperture 16 is provided at or adjacent the end region 24 but spaced-apart therefrom may be an option.

The or each gap 36a,36b of the hinge element 20c may also enable fixation agent ingress and/or egress therethrough. For clarity however, the or each gap 36a,36b of the hinge element 20c is considered to be a distinct feature from the fixation-agent-access aperture 16. Thus, a hollow implant 10 may optionally have simultaneously at least one gap 36a,36b at the hinge element 20c and at least on fixation-agent-access aperture 16.

The, preferably elongate, channel 18 in-use, enables or facilitates fluid, such as air and/or blood, to escape upon fixation agent injection into the bone cavity and/or upon the displacement of the fixation agent by the stem 12 during implantation of the implant 10. Additionally or alternatively, the channel 18 may facilitate injection of fixation agent into the bone cavity and/or into the stem 12. The channel 18 is or includes preferably a recess or groove in a surface of the stem 12. In other words, the channel 18 is or is at least partly an open channel but a closed or partially closed channel may be an option.

The channel 18 is shown in Figure 3. The, preferably elongate, recess extends at least in part along the longitudinal axis or proximal-distal axis 22 of the apparatus 10. The channel 18 in the shown embodiment extends along the second body element 20b and the hinge element 20c but could easily be omitted from either feature. Alternatively or additionally, the channel 18 may optionally extend at least in part along the first body element. The channel 18 is provided on the outer surface of the stem 12. Additionally or alternatively, the or a further channel 18 may be provided on the inner surface 28a of the stem 12. There may be a plurality of channels.

Preferably, if a channel is provided along at least two of: the second body element, the hinge element, and the first body element, the channels of the respective parts are preferably in alignment or in substantial alignment, but non-alignment may be an option. Furthermore, the channel or channels preferably extend along the proximal-distal axis 22 without extending rotationally or circumferentially around the stem. However, this alternative may be envisioned. In other words, a channel may form a spiral or helix around the stem, by way of example.

The implant body 14 is also integrally formed with, connected or connectable to the stem 12. The implant body 14 therefore also has a stem-connecting surface, also referred to as a stem-engaging surface or stem-joining surface, not shown. The dimensions and/or shape of the stem 12 mean that further stabilising and/or support elements, such as flanges, struts, a keel, or support structures are unnecessary and thus omitted but could easily be provided in an alternative embodiment. The illustrated implant body 14 is a tibial component. As such, the implant body 14 includes a tibial plateau. The implant body 14 in-use provides an articular surface or at least a support therefor. In other words, the implant body 14 has a bearing surface 44 and a lip 46, but either feature may be omitted and/or a plurality of either feature may be provided.

The implant body 14 is preferably devoid of a stem. As such the implant body 14 is preferably stemless. However, it could be envisioned that the implant may comprise a stem. Such a stem may be referred to as a secondary stem, and the above-mentioned stem 12 may be referred to as a primary stem 12 for clarity. The secondary stem may be receivable within the or a said central cavity. The secondary stem may alternatively be receivable around the primary stem.

The bearing surface 44 is preferably integrally formed with the tibial plateau here, but non-integrally formed may be an option. The bearing surface 44, also referred to as a joint-facing surface, provides the surface which, directly or indirectly, articulates with or is engageable with the bone or a further artificial joint component. A liner and/or a meniscal component may be received on the bearing surface 44 for example. The bone or further artificial joint component would be here the femur or a femoral component, respectively in this case, due to the shown embodiment being a tibial component. However, any other joint may be envisioned. The bearing surface 44 is here preferably planar or substantially planar, but non-planar or part planar may be options.

The bearing surface 44 also comprises a central point or position. The central position may be a centre of gravity of the implant body 14 and/or of the bearing surface 44. Preferably, the central position is considered to be the intersection between the bearing surface 44 and the proximal-distal axis 22 of the implant 10 or at least the longitudinal axis of at least one of the first body element 20a and the second body element 20b.

However, it could easily be envisioned that the central position may be otherwise defined. For example, the central position may be a mid-point of a dimension of the bearing surface 44 and/or the implant body 14. The dimension may be a minor dimension or a major dimension. The dimension may be a length or width. More preferably, the dimension may be a minimum length, average length, median length, or a maximum length, but any alternative length may be envisioned.

The lip or flange 46, best shown in Figure 2, may be provided around a periphery of the bearing surface 44. The lip 46 may help retain a liner and/or meniscal component on the bearing surface 44.

Preferably, the implant body 14 comprises a said implant fixation-agent-access aperture 16, but the aperture in the implant body may be omitted or a plurality of apertures in the implant body may be provided. The aperture 16 is preferably in addition to the implant fixation-agent-access aperture or apertures of the stem 12, but the implant fixationagent-access aperture or apertures of the stem may be omitted. The implant fixation-agent-access aperture 16 in the implant body 14 is preferably similar in function to the or a said implant fixation-agent-access aperture 16 of the stem 12. The aperture 16 in-use enables the ingress and/or egress therethrough of a fixation agent for an implant 10. The fixation-agent-access aperture 16 in the implant body 14 preferably is at or adjacent a central position of the bearing surface 44. In other words, the aperture 16 preferably includes the central position of the bearing surface 44. Thus, the fixation-agent-access aperture 16 preferably overlies or overlaps with the central cavity 26 for enabling injection and/or egress of the fixation agent through the aperture 16 into the central cavity 26. The fixation-agent-access aperture 16 has a dimension which corresponds to a dimension of the central cavity 26, but this feature may be omitted. In other words, a transverse cross-sectional area and shape of the aperture 16 preferably corresponds to the transverse cross-sectional area and shape of the or at least one said central cavity 26. Furthermore, the aperture 16 is preferably aligned with the or at least one said central cavity 26. Matching or substantially matching dimensions and an exact overlap reduces or eliminates the risk of the aperture 16 becoming a bottleneck, for example, during ingress or egress of fixation agent. A bottleneck could other cause an increase in pressure, which may result in undesirable movement of the implant 10 and/or an increased risk of structural failure of the implant.

Optionally, a plurality of fixation-agent-access apertures 16, whether of the stem 12 and/or of the implant body 14, may fluidly connect to the or a same said central cavity. Additionally or alternatively, the or each fixation-agent-access aperture 16 may connect to exactly one central cavity 26.

Preferably, the apparatus 10 may further comprise a plug or plug-element, but this may be omitted. The plug, not shown, may be configured to obstruct the or a said aperture 16. In other words, the plug may be receivable in the or a said fixation-agent-access aperture 16. This may be important to provide a continuous or substantially continuous bearing surface. Any sharp edges in the bearing are undesirable as potentially inhibiting or preventing the functioning of the artificial joint and/or resulting in damage and potentially structural failure. The plug is preferably complementarily shaped with the aperture. The plug may be formed of a compressible material and/or of a non-compressible material. If a plug is omitted, a bearing liner may be sufficient to provide the continuous surface.

In-use, in preparation for arthroplasty, in this case for a tibia, a surgeon obtains at least 20 one implant apparatus 10. If not integrally formed or connected, the surgeon may need to assemble the implant body 14 and the stern 12 during or prior to implantation.

During surgery, the surgeon prepares the relevant bone, here the tibia, to receive the implant. In the case of primary surgery, this may involve calculating the alignment data and cutting the natural joint off. In the case of revision surgery, the surgeon may need to remove the existing implant, assess and calculate the alignment data. The alignment data may be obtained by any or any combination of techniques, methods, or tools. The techniques, methods or tools may include X-Rays, CT scans, M RI, XROMM, or any other suitable technique or combination thereof. The alignment data may additionally or alternatively be obtained intraoperatively.

The native anatomy of the patient determines the orientation and the positions along the anterior-posterior and medial-lateral directions of the first body element 20a. Adjustment along the distal-proximal direction of the first body element 20a is possible at this stage.

The tibial cut is positioned and oriented using extramedullary instruments. Relevant angles, such as the relative flexion and varus/valgus angles between the tibial cut and the prepared receiving cavity for receiving the first body element 20a are recorded.

After obtaining alignment data, a trial reduction checking any of, and preferably all of the 5 range of motion (ROM), the balancing and assessment of the soft tissues is undertaken. Any adjustments to the angles are recorded.

The final implant 10 is then prepared. The stem 12 is bent, preferably prior to insertion into the bone. This is preferably done in-theatre and/or during surgery. However, the bending may be done outside of the theatre and/or prior to surgery. The reorientation may even be done during manufacture and/or in the factory. This involves re-orienting the second body element 20b relative to the first body element 20a via the hinge element 20c, preferably using dedicated instrumentation.

Fixation agent, such as bone cement, is preferably inserted into the bone cavity prior to the insertion of the implant 10. The stem 12 is then inserted or introduced into the bone cavity. At least half of the volume of the bone cavity, and more preferably all the bone cavity is filled with fixation agent, but less than half the volume may be filled with fixation agent. Care is taken to avoid any air pockets being introduced or trapped in the bone cavity.

The stem 12 is inserted into the bone cavity. As the stem 12 is inserted, the stem 12 20 displaces a volume of fixation agent.

In the case of a non-hollow stem, the displaced fixation agent is forced out around the stem 12 and surplus fixation agent exits the bone cavity. The surplus may exit the bone cavity by flowing around the implant body 14.

In the case of a hollow stem 12 having at least one fixation-agent-access aperture 16 in 25 the stem 12, all or at least a portion of the displaced fixation agent flow from the bone cavity into the at least one fixation-agent-access aperture 16 and into the or at least one central cavity 26.

Optionally, all or at least a portion of the displaced fixation agent in the or a said central cavity 26 may then flow through the gap or gaps 36 of the hinge element 20c back into 30 the bone cavity, however this may be omitted, for instance, if a central cavity connects directly with a fixation agent access aperture in the implant body without fluidly connecting to the hinge element gap or gaps, if any are even provided.

If the implant body 14 has at least one fixation-agent-access aperture 16, the fixation agent may flow out through the at least one fixation-agent-access aperture 16 instead or in addition to flowing around the implant body 14. Flow through the aperture 16 instead of around the implant body 14 may be desirable, for example by being easier to remove any excess and/or to clean.

The surgeon may push the implant 10 until the implant body 14 is fully received in its final position. The implant body 14 may cap or substantially cap the bone cavity. To 10 ensure a secure engagement between the stem 12 and the surrounding bone, the stem 12 may be impacted or hit further into the bone.

Although preferably here the fixation agent is inserted first into the bone cavity and forced out by the insertion of the implant, this could easily be omitted. The implant may be inserted prior to the injection of fixation agent. Once the implant is in position, the fixation agent may be injected into the, each or at least one fixation-agent-access aperture, for example in the implant body. The injected fixation agent may flow into the bone gap, optionally via at least one of: the or at least one central cavity, a said gap of the hinge element, and at least one said fixation-agent-access aperture in the stem.

Channels 18 on the inner and/or outer surface of the implant 10 may help fluid, such as 20 fixation agent, air, or blood, move through the bone cavity and/or through the central cavity 26. This may reduce or eliminate the presence of pockets of air.

The fixation agent solidifies, helping to immobilise the implant 10. The fixation agent, once solidified, also prevents or inhibits any further rotational movement about the hinge element 20c.

Referring now to Figures 4 and 5, there is shown a second embodiment of an implant apparatus 110. The second embodiment of the implant apparatus 110 is similar to the first embodiment of the apparatus 10, having similar implant body 114, stem 112, first body element 120a, second body element 120b, hinge element 120c, at least one implant fixation-agent-access aperture 116 in the implant body 114, at least one and preferably four implant fixation-agent-access apertures 116 in the stem 112, at least one central cavity, a plug, although any of the above may be omitted and/or a plurality of any of the above may be provided. For brevity, detailed description of the common features is omitted. The same caveats as in the first embodiment may also apply to the second embodiment. Features of the second embodiment of the implant apparatus 110 which are similar to the features of the first embodiment 10 have similar reference numerals with the prefix "1" added.

The second embodiment of the implant apparatus 110 is preferably a femoral component or part thereof. The bearing surface is preferably non-planar. The aperture 116 of the implant body 114 may optionally be provided in a recessed portion of the implant body 114. In the shown embodiment, the aperture 116 of the implant body 114 is preferably located between the artificial condyles, but this may be optional.

The uses of the second embodiment of the implant apparatus 110 are the same as those of the first embodiment of the implant apparatus 10, with the difference that the femur is the receiving bone, rather than the tibia.

Referring now to Figures 6 and 7, there is shown an implant kit 248. The implant kit 248 comprises an implant 210, a stem 212, a second stem 212b, and an implant stem adaptor 250, although either feature may be omitted and/or a plurality of any of the above may be provided. The second stem 212b is shown in Figure 7. If two or more stems are provided as in the shown embodiment, stem 212 may be referred to as a first stem 212a for clarity. For clarity, the implant 210 of the first embodiment of the implant kit 248 may be referred to as a third embodiment of an implant, to distinguish from the above-described first and second embodiments of an implant.

The implant 210 has at least an implant body 214 from which extends the stem 212, although either feature may be omitted and/or a plurality of any of the above may be provided.

The third embodiment of an implant 210 may be similar or the same as the first or second embodiments of the implant, having similar implant body 214. Detailed description of the common features and caveats is omitted for brevity. Features of the third embodiment of the implant apparatus 210 which are similar to the features of the first embodiment have similar reference numerals with the prefix "2" added.

Preferably the third embodiment of the implant 210 does not include at least one implant fixation-agent-access aperture in the implant body, at least one implant fixation-agent-access apertures in the adaptor, at least one central cavity in implant body, a plug, and/or a coating enabling the omission of a fixation agent for encouraging bone growth, although any of the above or combination thererof may be provided in a modified embodiment.

Furthermore, the, each or at least one of the stems of the kit 248 does not have a first body element, second body element, hinge element, at least one aperture in the stem, at least one central cavity in the stem, at least one channel, a coating enabling the omission of a fixation agent for encouraging bone growth, although any of the above may be provided in a modified embodiment for at least one said stem.

The implant body 214 may be formed as a monobloc or one-piece but a non-monobloc structure may be an option. For example, the implant body 214 may be formed by connecting, optionally separably, two or more implant body sub-parts.

Preferably, the first stem 212a is integrally formed with the implant body 214 but non-integrally formed may be an option. The first stem 212a has a first stem body. The second 15 stem 212b is preferably non-integrally formed with the implant body 214. The second stem 212b has a second stem body.

Furthermore, the implant 210 may additionally comprise at least one stabilisation element 252. The stabilisation element may also be referred to as a portion or stabiliser. Here, the stabiliser 252 includes two wings, fins, brackets or flanges 254. Together the 20 stabiliser 252 and the first stem 212a form a keel.

The implant stem adaptor 250 in-use enables an implant 210 to be adapted. In particular the length of the stem may be adjusted by connecting one or more adaptors 250 to the first stem 212a. Additionally or alternatively, the implant stem adaptor 250 may enable the orientation of the implant 210 to be adjusted or adjustable. The implant stem adaptor 250 has an adaptor body 256 and at least one, and preferably two engagement portions 258.

The adaptor body 256 has a first body element 220a, a second body element 220b and a hinge element 220c, but any of the above features may be omitted and/or a plurality of any of the above may be provided. The first body element 220a may also be referred to as a first adaptor-body element or part. The second body element 220b may be referred to as second adaptor-body element or part. The adaptor body 256 is similar to the stem of the apparatus 10 of the first embodiment. Detailed description of the common features and of the caveats is omitted for brevity. The adaptor 250 preferably does not any aperture nor any channel, but it may easily be envisioned that at least one of either or both may be provided in an alternative embodiment.

The first body element 220a is preferably inserted first into a bone cavity, whilst the second body element 220b is inserted second. The second body element 220b is engaged via the hinge element 220c with the first-body element 220a. Preferably, the first body element 220a is coaxial with the second body element 220b but non-coaxial may be an option, for example to provide an offset.

As shown in Figure 7, the adaptor body 256 preferably tapers inwardly in a direction from the second body element 220b and/or implant body 214 to the first body element 220a. The opposite may easily be envisioned. Any alternative shape or geometry in transverse and/or longitudinal cross-section may be an option. For example, the adaptor body may be cylindrical along at least part of the longitudinal extent of the adaptor.

In the embodiment of Figures 6 and 7, the adaptor body 256 or at least part thereof is hollow. The first and/or second body elements 220a,220b may define at least in part one or more central cavities 226, similarly to the first embodiment of the implant 10.

At least one of or preferably each of the first body element 220a and the second body element 220b has a said engagement portion 258. The first stem 212a and/or the second 20 stem 212b, and preferably both the first stem 212a and the second stem 212b also each comprise an engagement part or portion 258, best shown in Figure 7.

For clarity, the engagement portion 258 in, on, at or adjacent to the second body element 220b may be referred to as a first engagement portion 258a. The engagement portion 258 in, on, at or adjacent to the first body element 220a may be referred to as a second engagement portion 258b. The engagement portion 258 of the first stem 212a may be referred to as a third engagement portion 258c. The engagement portion 258 of the second stem 212b may be referred to as a fourth engagement portion 258d.

The engagement portions enable engagement with corresponding engagement portions of the first stem 212a and/or second stem 212b. The implant stem adaptor 250 is non-30 reversibly usable in the shown embodiment. Thus, the second body element 220b is preferably only engageable with the first stem 212a or at least the engagement portion 258c thereof Similarly, the first body element 220a is preferably only engageable with the second stem 212b or at least the engagement portion 258d thereof.

Thus, the first engagement portion 258a has a complementary shape and size to engage with the corresponding, third engagement portion 258c. The second engagement portion 5 258b has a complementary shape and size to engage with the corresponding, fourth engagement portion 258d.

In the shown embodiment, the engagement of each pair of engagement portions is preferably via interference fit. More preferably, at least one of: the first engagement portion, the second engagement portion, the third engagement portion, and the fourth engagement portion is conical or frustoconical. In the shown embodiment, the second and third engagement portions 258b,258c are frustoconical. The first and fourth engagement portions 258a,258d have corresponding conical or frustoconical recesses. The engagement of the corresponding pairs of engagement portions provides a Morse taper engagement.

The hinge element 220c of the adaptor 250 is the same or similar to the first embodiment of the implant 10, having similar at least one linking portion 232a, spacer segment 232b, one or more bending axes, one or more gaps 236. Detailed description of the common features and caveats is omitted for brevity. The hinge element 220c is preferably hollow such that a pair of linking portions defines a hinge axis.

In-use, a surgeon obtains a kit. Before or during surgery, the alignment data is obtained and may be adjusted if an implant trial is undertaken. The or at least one adaptor is connected to the first stem. This involves engaging the first and third engagement portions. In the shown embodiments, the engagement is via Morse tapers.

Before or after engagement of the first and third engagement portions 258a,258c, the first body element 220a and the second body element 220b are reoriented relative to each other by bending the linking portion or portions 232a along at least one hinge axis. The adaptor 250 may also be rotated relative to the first stem 212a to enable the hinge axis or axes and/or any stabilisation element or elements 252 to be in a desired relative position relative to the implant body 214.

Optionally, the second stem 212b and/or a further implant stem adaptor may be engaged with the first body element 220a of the adaptor 250. The assembled kit is inserted into the bone cavity. If fixation agent is used, the fixation agent may be inserted before, during or after insertion of the kit into the bone cavity.

Figures 8 and 9 illustrate a second embodiment of a kit 348. The second embodiment of the kit 348 is similar to the first embodiment of the kit 248. Detailed description of the 5 common features and caveats is omitted for brevity. In the second embodiment of the kit 348, the first stem 312 is shorter than the first stem 212a of the first embodiment of the kit 248 and may optionally be omitted entirely. The stabiliser 352 extending from the first stem 312 may be omitted. Instead in the shown embodiment, a stabilisation element or portion 352 may be provided on the adaptor 350 but this feature may be omitted. The 10 stabilisation element 352 has a stem, spacer or bridge portion 360 and a main stabilisation body 362 The main stabilisation body 362 is connectable or connected to the adaptor body 256 by the bridge portion 360. The bridge portion 360 spaces the main stabilisation body 362 apart from the adaptor body 256 to provide a gap 364 therebetween. There are preferably two stabilisation elements 352 here, but any number, including none, one, or at least two may be envisioned. The shape and arrangement of the stabilisation elements 352 in the shown embodiment may act or act substantially as a keel.

Figures 10 and 11 illustrate a third embodiment of a kit 448. The third embodiment of the kit 448 is similar to the first embodiment of the kit 248. Detailed description of the 20 common features and caveats is omitted for brevity. The adaptor 450 is preferably solid or non-hollow, although part hollow may be an option.

Figures 12 and 13 illustrate a fourth embodiment of a kit 548. The fourth embodiment of the kit 548 is similar to the second embodiment of the kit 348. Detailed description of the common features and caveats is omitted for brevity. The adaptor 550 is preferably solid 25 or non-hollow.

The uses of the second, third and fourth embodiments are the same or similar to the first embodiment of the kit. Detailed description of the common features and of the caveats is omitted for brevity.

Figure 14 illustrates a fifth embodiment of a kit 648. The fifth embodiment of the kit 648 30 is similar to the second embodiment of the kit 348. Detailed description of the common features and caveats is omitted for brevity. The implant body 614 is preferably a femoral component, rather than a tibial component. The femoral component may optionally comprise two assembleable sub-parts 666. Instead of a Morse taper engagement, the engagement with at least one of: the first stem 612a and, if provided, the second stem is via a non-Morse taper arrangement. Any of the engagement portions, and more preferably, the first and third engagement portions 658a,658c are abuttable against each other as shown. Any of the engagement portions, and more preferably, the first and/or third engagement portions 658a,658c further comprise a screw thread 668, but this may be omitted, or a plurality of screw threads may be provided. Optionally, at least one of the engagement portions may include a flange or lip. The flange may extend at least in part axially or parallel with the proximal-distal axis of the adaptor and/or of the or a said stem. The flange may enable an interference fit other than Morse tapers. The flange may prevent or inhibit lateral movement of the engagement portions relative to each other, and thereby increase the lateral stability of the engagement.

The, each or at least one screw thread 668 may be external or, preferably, is internal on at least one engagement portion and more preferably on the first and third engagement portions 658a,658c but this is optional. The kit 648 optionally further comprises at least one screw 670 which engages with the internal screw thread 668. A head of the screw is preferably receivable in a cavity in the implant body 614, but may be receivable in the adaptor body 656 instead. If the implant body and/or the adaptor comprises an aperture, similar to the above-described fixation-agent-access aperture, the screw 670 may be inserted therethrough. Alternatively or additionally, if the implant body 614 is formed by connecting two sub-parts 666 together, the screw 670 may be inserted prior to the subparts being connected.

The uses of the fifth embodiment of a kit 648 are similar to those of the first to fourth 25 embodiments of the kit. Detailed description of the common steps is omitted for brevity.

To assemble the adaptor 650, if the implant body 614 and/or the adaptor 650 comprises an aperture, similar to the above-described fixation-agent-access aperture, the screw 670 may be inserted therethrough. Alternatively or additionally, if the implant body 614 is formed by connecting two sub-parts 666 together, the screw 670 may be inserted prior to the sub-parts 670 being connected. The screw 670 may even be inserted via the adaptor body. The adaptor body 656 may beneficially enable this by being hollow.

Although the adaptor is preferably non-reversible, in a modified embodiment, the implant stem adaptor may be reversibly usable. In such an embodiment, the first body element may be selectably engageable with either stem. Similarly, the second body element may be selectably engageable with either the first or the second stem.

In the above-described embodiments of the implant stem adaptor, at least one of: the first engagement portion, the second engagement portion, the third engagement portion, and the fourth engagement portion has a circular transverse cross-section. However, any engagement portion or any combination thereof may have a non-circular transverse cross-section. For example, the transverse cross-section may be polygonal, by way of example. A non-circular transverse cross-section may prevent or inhibit accidental rotation of one engagement portion relative to the other engagement portion.

In addition to or instead of the above-described embodiments of the stabilisation element, the stabilisation element may include an indexing element, portion or indexing for enabling a user to easily and precisely rotate the adaptor body to a specific position.

The indexing element may include at least one of a protrusion and a receiving recess, crenulation, and a ratchet. Crenulation may comprise any or any combination of: saw 15 teeth, square teeth, rounded teeth, or any other desirable shape of teeth, by way of example.

Although the above embodiments disclose knee joint and/or hip joint replacements or replacements of an existing tibial and/or femoral implant for the knee and hip, the joint replacement may be adapted for a shoulder, an elbow, an ankle, a finger, a toe, or any 20 other desirable joint.

In the above embodiments, the primary or revision arthroplasty may be partial or total.

In a modified embodiment, the second body element of the implant apparatus stem may be omitted. The hinge element may connect or be integrally formed with the implant body directly.

In any of the above embodiments, any or any combination of: the implant or part thereof, the first body element of the stem, the second body element of the stem, the first body element of the adaptor, the second body element of the adaptor, the hinge element of the stem, the hinge element of the adaptor, the first stem, and the second stem may further be coated with plasma-sprayed and/or electrochemically deposited materials such Hydroxyapatite and/or Titanium. These deposited materials may increase the friction fit to the bone and/or encourage bone growth, therein, thereagainst or therearound, between the bone and implant receiver and/or implant. The coating may also have antibacterial properties by inclusions of silver, copper, or other known substances. Similarly, in any of the above embodiments, any of: the implant or part thereof, a said stem, and the adaptor may be manufactured by 3D printing or Additive Manufacturing methods (AM) which involves building the parts from typically digital files rather than removing material from bar or forgings using conventional cutting machinery. Such AM methods allow increased flexibility to incorporate complex shapes/forms, and this allow a porous type of bone enhancing surface into the necessary bone contact areas.

Whilst in all the above embodiments, the hinge element only has one spacer segment, a plurality of spacer segments may be a desirable option. Two spacer segments may be connected to each other by one or more linking portions and/or by non-bendable connections. Multiple spacer segments or elements provide a greater range of angular adjustments and/or angular adjustments in a greater number of planes.

Whilst in the present embodiments, the surfaces of the linking portions are square or rectangular in side view and preferably along their entire length or width when viewed at a right angle, alternative cross-sections may be considered. For instance, any of the linking portion surfaces may be non-square or non-rectangular. More specifically, any of the linking portion surfaces or part thereof may be curved, non-curved, concave, planar, linear, polygonal whether regular, irregular, truncated or chamfered in longitudinal and/or lateral cross-section. Alternatively or additionally, any linking portion surface may have an indented section along their width or longitudinal extent. Said indent or indented portion may be considered to be or be substantially in longitudinal and/or lateral cross-section curved, non-curved, part-curved, concave, convex, linear, polygonal such as triangular, whether regular, irregular, truncated, chamfered, tapering inwards to the narrowest point, a trapezium, a trapezoid, a square, a rectangle, a pentagon, hexagon, octagon, or any other desirable cross-sectional shape which may enable bending.

Whilst a preferred shape may have been specified for any of the above features, any alternative shape in any of longitudinal, lateral and/or transverse cross-section may be envisioned. The shape may be curved, non-curved, part-curved, concave, convex, a circle, an ellipse, linear, polygonal, whether regular, irregular, truncated, chamfered, tapering inwards to the narrowest point, a trapezium, a trapezoid, a square, a rectangle, a pentagon, hexagon, octagon, or any abstract shape.

VVhilst the engagement portions of the adaptor preferably connect via Morse tapers to the first and/or second stems, any alternative to Morse tapers may be envisioned. The engagement portions may be connected to the first step and/or second stem by being at least one of: non-Morse taper interference fit, boltable, screwable, connectable via an adhesive, cementable, abuttable, constrainable by the shape and/or form of interlocking features, and any other suitable means of connection. An external screw-thread on one of the engagement portions may be engageable with a complementary screw thread on the corresponding engagement portion. The interlocking features may, for example include a flange or flanges. The flange or flanges may provide a C-shape or U-shape.

The C-or U-shape may provide support against lateral displacement. Further examples of interlocking features may include a bayonet engagement, and a slidable engagement of male and female parts.

Any of the above-mentioned embodiments may have one or more grip-enhancing portions or elements. A grip-enhancing portion may include any of: a protrusion, a projection, a fin, a groove, a recess, a dimple, a ring, a notch, a concave portion, a convex portion, or any other suitable grip-enhancing portion. This improves the engagement between two elements, such as between the stem and the bone, or the fixation agent and the implant.

If any hinged component of the stem and/or the adaptor body comprises ceramics, each 20 linking portion may need to comprise a non-ceramics material to enable bending thereat.

The spacer segment may be omitted entirely such that the stem and/or adaptor may have only one linking portion or pair of linking portions, connecting the first and second body elements directly.

The, each or at least one linking portion may not necessarily be a live hinge. A said linking portion may be insertable, connectable, or connected to any of: the spacer segment, the first body element of the stem, the second body element of the stem, the first body element of the adaptor, the second body element of the adaptor. The connection may be via complementary engagement portions. The engagement portions may be complementary male and female features. A linking portion may be integrally formed at one end and connectable at the other. Further alternatives may be envisioned, for instance, a ball-bearing or ball-bearing system. The ball bearing may be centrally positioned relative to a said stem. The hinge element may be lockable.

In the preferred embodiments, the hinge axes preferably extend along a major or minor directions of the adaptor body and/or apparatus. However, a hinge axis may be offset from a major or minor dimension in an alternative embodiment of the adaptor body and/or the implant apparatus. A hinge axis may not even span the central cavity. A single linking portion may even be provided on a side of the or a said central cavity. The hinge axis of the single linking portion may be or be substantially tangential to the central cavity.

If the stem of the apparatus and/or the adaptor body is non-hollow, at least at the hinge element, each linking portion may not comprise an inward-facing surface. Instead, each linking portion may comprise at least two outward-facing surfaces. Each linking portion may span all or a majority of a transverse direction of the stem and/or adaptor body, but less than a majority of a dimension may be an option. Each linking portion may be formed by extrusion or moulding. Furthermore, only one linking portion may suffice to define a hinge axis, although nothing excludes a plurality of linking portions from defining the hinge axis.

Whilst preferably the transverse cross-sectional area and shape of the aperture of the implant body matches that of the or a said central cavity and the aperture and the or a said cavity are directly in alignment, it may, however, be possible that the transverse cross-sectional area and/or shape of the aperture may be greater or smaller than the corresponding area and/or shape of the or a said central cavity. A smaller aperture may, for example result in proportionally a greater area of the bearing surface being formed of solid material, thereby providing better support. The transverse cross-sectional area and/or shape of the aperture may be the same as that of the or a said central cavity, but the aperture may not be directly aligned with the or a said central cavity such that there is only partial overlap.

In a further alternative embodiment, if the central cavity is offset relative to the central position of the bearing surface, the fixation-agent-access aperture may be equally offset from the central position, so as to overlie or overlap with the central cavity.

Additionally or alternatively to a central position, at least one aperture may be provided at or adjacent a peripheral position. In other words, the or a further said fixation-agent-access aperture may be spaced-apart from the central position of the bearing surface. This peripheral position may enable the aperture to overlap or overlie a gap provided between the bone and the stem. Thus, the peripheral position may enable ingress and/or egress of the fixation agent therethrough into the gap. This may be particularly beneficial if the stem is non-hollow. It may be envisioned in a further embodiment that no fixationagent-access aperture may be provided on the implant body. It may be envisioned that no fixation-agent-access aperture may be provided on the stem.

Whilst a preferred shape may have been specified for any of the above-described any 5 alternative shape may be envisioned in any of lateral or cross-section, longitudinal cross-section, in side view, in plan view. The shape may be any or any combination of: curved, part curved, non-curved, linear, part linear, non-linear, a broken line, any polygon, whether regular or irregular, having one or more chamfered and/or rounded corners, a triangle, a quadrilateral, such as a square, a rectangle, a trapezium, a trapezoid, a 10 pentagon, a hexagon, a heptagon, an octagon, or any other polygon, a cross, an ellipse, a circle, part circular, an oval, or any abstract shape.

It is therefore possible to provide an implant for arthroplasty which reduces or eliminates the presence of pockets in fixation agent by virtue of having an implant fixation-agentaccess aperture for enabling the injection and/or egress therethrough of a fixation agent 15 for an implant.

It is also possible to provide an adaptor for a stem of an implant which enables the stem to be elongated and/or the position of the implant body to be adjusted by virtue of the adaptor having a hinge element.

It is further possible to provide a kit comprising an implant stem adaptor and an implant.

There is also provided an implant apparatus for arthroplasty having at least one elongate channel extending at least in part along a proximal-distal axis of the implant apparatus which provides a path for fluid such as air or blood to escape as the bone cavity is filled with fixation agent, and/or which helps channel the fixation agent deeper into the bone cavity.

The words 'comprises/comprising' and the words 'having/including' when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in 30 the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from 5 the scope of the invention as defined herein.

Claims

Claims 1 2. 4. 5An implant apparatus for arthroplasty, the implant apparatus comprising: an implant body having a bearing surface, an implant stem having a hinge element thereon, and an implant fixation-agent-access aperture for enabling the injection and/or egress therethrough of a fixation agent for an implant.
An apparatus as claimed in claim 1, wherein the implant stem defines at least one central cavity such that the stem is at least partly hollow.
An apparatus as claimed in claim 2, wherein the fixation-agent-access aperture in the implant body at or adjacent the or a said central position of the bearing surface such that the fixation-agent-access aperture overlies or overlaps with the or a said central cavity for enabling injection and/or egress of the fixation agent through the aperture into or from the central cavity.
An apparatus as claimed in claim 3, wherein the fixation-agent-access aperture has a dimension which corresponds to a dimension of the central cavity.
An apparatus as claimed in any one of claims 2 to 4, wherein the stem includes the or a further said fixation-agent-access aperture which extends from the or a said central cavity to an outer surface of the stem.
An apparatus as claimed in any one of the preceding claims, wherein the implant body includes the or a further said fixation-agent-access aperture, the or the further fixation-agent-access aperture being spaced-apart from a central position of the bearing surface for enabling ingress and/or egress of fixation agent therethrough into a gap between the bone and the stem when the stem is received in a bone cavity.
7. An apparatus as claimed in any one of the preceding claims, further comprising a plug receivable in the or a said fixation-agent-access aperture.
8 An apparatus as claimed in any one of the preceding claims, wherein the stem further includes at least one elongate channel extending at least in part along a proximal-distal axis of the implant apparatus.
9. An apparatus as claimed in claim 8, wherein the elongate channel is a recess in a surface of the stem such that the channel is at least partly an open channel.
10. An apparatus as claimed in claim 9, wherein the recess is provided on an outer surface of the stem.
11. An apparatus as claimed in claim 9 or claim 10, wherein the or a further recess is provided on an inner surface of the stem.
12. An implant stem adaptor for an implant having an implant body from which extends a stem, the implant stem adaptor comprising: an adaptor body having: a first body element, and a second body element which is engaged via a hinge element with the first-body element and at least one of the first body element and the second body element having an engagement portion for engaging the stem.
13. An implant stem adaptor as claimed in claim 12, wherein the other of the first body element and the second body element comprises a second engagement portion for engaging with a second stem of the implant.
14. An implant stem adaptor as claimed in claim 13, wherein the first body element is coaxial with the second body element.
15. An implant stem adaptor as claimed in claim 14, wherein the adaptor body tapers inwardly in a direction from the second body element to the first body element or vice-versa.
16. An implant stem adaptor as claimed in any one of claims 12 to 15, wherein the first engagement portion has a complementary shape and size to engage with a corresponding, third engagement portion of the first said stem via interference fit and/or the second engagement portion has a complementary shape and size to engage with a corresponding, fourth engagement portion of the first stem via interference fit.
17. An implant stem adaptor as claimed in claim 16, wherein at least one of: the first engagement portion and the second engagement portion is conical or frustoconical for providing a Morse taper engagement with the third engagement portion and the fourth engagement portion respectively.
18. An implant stem adaptor as claimed in claim 16 or claim 17, wherein at least one of: the first engagement portion, the second engagement portion, the third engagement portion, and the fourth engagement portion has a polygonal transverse cross-section.
19. An implant stem adaptor as claimed in any one of the claims 12 to 18, wherein the implant stem adaptor further comprises a stabilisation element.
20. An implant stem adaptor as claimed in claim 19, wherein the stabilisation element has a bridge portion and a main stabilisation body connected to the adaptor body by the bridge portion, the main stabilisation body being spaced-apart from the adaptor body by the bridge portion.
21. An implant stem adaptor as claimed in claim 19 or claim 20, wherein the stabilisation element includes an indexing element for enabling a user to easily and precisely rotate the adaptor body to a specific position.
22. An implant stem adaptor as claimed in claim 21, wherein the indexing element includes at least one of: a protrusion and a receiving recess, crenulation, and a ratchet.
23. An implant kit comprising an implant stem adaptor as claimed in any one of claims 12 to 22, and an implant having at least an implant body from which extends a stem.
24. An implant kit as claimed in claim 23, further comprising a second stem.An implant apparatus for arthroplasty, the implant apparatus comprising: an implant body having a bearing surface, an implant stem having a hinge element thereon, and at least one elongate channel extending at least in part along a proximal-distal axis of the implant apparatus.