GB2571349A

GB2571349A - An implant for resurfacing bone

Info

Publication number: GB2571349A
Application number: GB1803167.4A
Authority: GB
Inventors: Mohanlal Meswania Jayantilal; Fitzpatrick Noel
Original assignee: Fitzbionics Ltd
Current assignee: Fitzbionics Ltd
Priority date: 2018-02-27
Filing date: 2018-02-27
Publication date: 2019-08-28
Also published as: WO2019166793A1; GB201803167D0

Abstract

Implants 20,40 for resurfacing articulating bones at an implant site in a joint of a human or animal subject, such as an humeroulnar joint, comprise a back portion 41,21 configured to be housed within a recess 70,80 formed in a bone and a front, bearing surface portion 42,22 configured to project outwardly from the recess when implanted, for contacting the other of the implants. A side edge 43,23 forms a ramped, angular shoulder between side walls and the front surface to negate precise positioning and facilitate articulation. The implant is designed to replace a damaged region of cartilage and with extra thickness to jack the joint apart to relieve pressure on the surrounding cartilage and allow it to regenerate.

Description

Field of the Invention

The invention relates to an implant for resurfacing bone at an implant site in a joint of a human or animal subject. In particular the implant may be used as a component for a unicompartmental implant assembly for resurfacing part of an elbow joint, however it may relate to resurfacing of other joints.

Background to the Invention

Osteoarthritis can occur in elbow joints from failure of the cartilage in the joint, leading to bone-on-bone contact and the onset of pain. Frequently, osteoarthritis first manifests itself in the medial compartment of the elbow, at the humeroulnar joint.

Total elbow replacement implants are available which replace both medial and lateral compartments of the joint with a single implant assembly. There is increasing interest in partial joint replacements instead of total joint replacements. Partial elbow replacement involves replacement of the articular surfaces in only one compartment, leaving intact the other joint surfaces and some/all of the ligaments. Such joint replacement implants are known as unicompartmental or unicondylar joint replacement implants. Partial joint replacement can act prophylactically, reducing the rate of development of the disease in the other compartments. With the improvements in surgical techniques and instruments, unicompartmental joint replacement arthroplasty has many advantages over total joint replacement such as a smaller incision, less soft tissue injury, preservation of bone stock, preservation of normal joint kinematics, less morbidity because of minimal postoperative blood loss, lower infection rate, and shortened recovery etc.

Elbow dysplasia is the most common cause of forelimb lameness in young, large and giant breed dogs. Collectively, elbow dysplasia and elbow osteoarthritis are the commonest causes of forelimb lameness in dogs of any age. Small dogs can also be affected by elbow dysplasia. The clinical impact of elbow osteoarthritis is unpredictable and, regardless of treatment, arthritis will progress to some extent for all affected joints. In some dogs, lameness can be mild and intermittent, whilst in others, lameness can cause severe and permanent disability. Where persistent cartilage erosion occurs, it is generally in the inner (medial) part of the elbow. An improved implant for joint resurfacing in canines would be advantageous.

Summary of the Invention

According to a first aspect of the invention there is provided an implant for resurfacing bone at an implant site in a joint of a human or animal subject, the implant being configured to be installed in a recess that has been formed in the subject’s bone at the implant site by removal of bone between a planned resection cut surface and a corresponding resected articular surface, the implant having a back portion configured to be housed within the recess and a front portion configured to project outwardly from the recess when implanted, the front portion of the implant having an outer surface, at least part of the outer surface of the front portion forming a bearing surface that projects outwardly from the recess when implanted.

The implant of the invention is designed to replace a damaged region of tissue in the joint and is designed with extra thickness to jack the joint apart sufficiently to relieve excessive pressure on the surrounding cartilage which with time can regenerate to normal thickness. When implanted, at least part of the front portion of the implant will bulge away from the remaining tissue around the recess at the implant site.

Preferably the outer surface of the front portion of the implant comprises an inner portion having a shape that substantially matches or approximates to at least part of the resected articular surface at the implant site and a boundary portion surrounding at least a part of the inner portion, the implant having a side edge, the boundary portion forming a ramped surface projecting outwardly from the side edge of the implant to the inner portion of the bearing surface.

The implant has a back surface for engaging the planned resection cut surface, the thickness of the implant between the back surface and the bearing surface being predetermined such that the inner portion of the bearing surface forms a raised platform that is spaced away from the subject’s resected articular surface that was present before the recess was formed. The ramped surface of the boundary portion provides a contoured lead on / lead off which helps the other opposing articular surface of the joint glide between the subject’s tissue around the recess and the raised inner portion of the bearing surface of the implant.

Preferably the boundary portion comprises a first portion extending outwardly from the side edge of the implant and a second portion extending from the first portion to the inner portion of the bearing surface, the first and second portions of the boundary portion having differently shaped outer surfaces.

Preferably the first portion of the boundary portion has a substantially planar outer surface and the second portion has a curved outer surface in a plane substantially orthogonal to a tangent line to the implant’s side edge.

In certain embodiments the inner portion of the bearing surface is convexly curved in at least one plane. The inner portion of the bearing surface may be convexly curved in two planes.

In other embodiments the inner portion of the bearing surface is concavely curved in at least one plane.

The implant may be an elbow implant for resurfacing part of an elbow joint. The implant may be configured to resurface at least part of the ulna in a subject’s elbow joint. In other embodiments the implant may be configured to resurface at least part of the humerus in a subject’s elbow joint.

In certain embodiments the implant has a peg extending from its back portion.

The implant may further comprise a fixation portion comprising at least one through hole for receiving a bone screw.

Preferably least part of the back portion of the implant is formed of three-dimensional porous metallic mesh.

In some embodiments the implant comprises a bearing component and a supporting component secured together in use, the bearing surface being on the bearing component, the bearing component being formed of polymeric material and the supporting component being formed of metal.

According to a further aspect of the invention there is provided a method of manufacturing an implant for resurfacing a bone at an implant site in a joint of a human or animal subject, the implant being configured to be installed in a recess that has been formed in the subject’s bone at the implant site by removal of bone between a planned resection cut surface and a corresponding resected articular surface, the method comprising forming an implant having a back portion configured to be housed within the recess and a front portion configured to project outwardly from the recess when implanted, the front portion of the implant having an outer surface, at least part of the outer surface of the front portion forming a bearing surface, the implant having a back surface for engaging the planned resection cut surface, the thickness between the back surface and the bearing surface being selected such that the bearing surface projects outwardly from the recess when implanted.

According to a further aspect of the invention there is provided a method of resurfacing bone at an implant site in a joint of a human or animal subject, the method comprising providing an implant according to any aspect of the invention as described above, forming a recess in the subject’s bone at the implant site by removal of bone between a planned resection cut surface and a corresponding resected articular surface and seating the implant in the recess such that the bearing surface projects outwardly from the recess when implanted.

The term “bearing surface” as used herein in relation to the implant refers to a surface designed to bear against another part of the joint, whether that be another prosthetic joint surface, a natural articular surface or both.

The term subject as used herein can be a human or animal subject.

Brief Description of the Drawings

A preferred embodiment of the present invention will now be more particularly described by way of example only with reference to the accompanying drawings, wherein:

Figure 1 shows a front view of a humeral implant of the invention implanted in a humerus;

Figure 2 shows a front view of an ulnar implant of the invention implanted in an ulna;

Figure 3 shows a perspective view of the humeral implant of Figure 1 before implantation and showing two bone screws exploded from the implant;

Figure 4 shows a side view of humeral implant of Figure 3;

Figure 5 shows a front perspective view of the humeral implant of Figure 3;

Figure 6 shows a perspective view of the ulna implant of Figure 2;

Figure 7 shows a close-up view of part of the main body of the humeral implant of Figure 3;

Figure 8 shows a side view of the humeral implant of Figure 3 implanted in a humerus, with the bone shown as partially translucent;

Figure 9 shows a perspective view of the ulnar implant of Figure 2 implanted in an ulna with the bone shown as partially translucent;

Figure 10 shows a diagrammatic cross-sectional view of the humeral implant of Figure 1 through a plane orthogonal to the back surface of the implant;

Figure 11 shows a diagrammatic cross-sectional view of the ulnar implant of Figure 2 through a plane orthogonal to the back surface of the implant;

Figure 12 shows a diagrammatic close-up view of the humeral implant of Figure 10 at the boundary between the implant and the tissue surrounding the implant recess; a close-up view of the ulnar implant at the boundary between the implant and the tissue surrounding the implant recess would look very similar;

Figure 13 shows a close-up view of the ulnar implant of Figure 2.

Description of the Preferred Embodiments

The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only.

Referring to Figures 1 to 13, an implant assembly for partial resurfacing at the humeroulnar joint in the elbow comprising an ulna implant according to the invention and a humeral implant according to the invention is shown. The particular implant assembly shown in the figures is for implantation in the medial compartment of the elbow, i.e. the humeroulnar joint, however it will be understood that a modified assembly according to the invention could be employed for implantation at the humeroradial joint on the lateral side (or at another joint besides the elbow).

Referring to Figures 1 and 2, the particular implant assembly comprises an ulnar component 20 for engaging the subject’s ulna 11 and a humeral component 40 for engaging the subject’s humerus 12. The ulnar component 20 and humeral component 40 are configured to articulate with one another when implanted. The ulnar and humeral components 20,40 are for location at the medial articular surfaces of the ulna and humerus in the region of peak load during a walking cycle.

Referring to Figure 4, the humeral component 40 has a back surface 51 and a front surface 52 opposing the back surface, which includes a bearing surface 57 for articulating with the front surface 22 of the ulnar component 20 when installed. Referring to Figure 3, the bearing surface 57 is convexly curved in first and second orthogonal planes, for articulating with a concavely curved ulnar surface.

Referring to Figure 8, the humeral component 40 is configured to be installed in a recess 70 that has been formed in the subject’s humerus 12. Referring to Figure 10, a diagrammatic side view of the humeral component 40 implanted in the humerus 12 is shown. The recess 70 has a resection cut surface 71 that the back surface 51 of the implant rests on when implanted and a resected articular surface 72, shown in dotted lines in Figure 10, corresponding to the articular surface of bone at the implant site before the bone was removed to form recess 70. The humeral component 40 has a back portion 41 configured to be received within the recess 70 when implanted and a front portion 42 configured to project beyond the resected articular surface 72 when implanted. At the boundary between the back portion 41 and the front portion 42, the humeral component 40 has a side edge 43 surrounding around at least part of the implant. The side edge 43 forms an angular shoulder between side walls of the implant and the front surface 52. The recess is shaped and sized to receive the back portion 41 of the humeral component 40. In this embodiment, the humeral component 40 has a rounded parallelogram shaped body and the recess 70 will be similarly shaped.

Referring to Figure 12, a further diagrammatic close-up view of the humeral component 40 received in recess 70 is shown (although shown for the humeral component, this diagram applies equally for the ulnar component also). The recess 70 has an opening 73 around which is a top edge 74. The front surface 52 of the humeral component 40 comprises an inner portion 53 having a shape that substantially matches or approximates to at least part of the resected articular surface 72. Surrounding at least part of the inner portion 53 of the front surface 52 is a boundary portion 54 forming a ramped surface projecting outwardly from the side edge 43 of the humeral component to meet the inner portion 53. As can be seen from Figures 4 and 5, the inner portion 53 is a parallelogram shape and the boundary portion 54 is present on three sides of the inner portion 53. The side edge 43 of the humeral component 40 aligns with the top edge 74 of the recess 70 when implanted. In practice, the alignment of the side edge 43 of the implant with the top edge 74 of the recess need not be exact and may be only a rough alignment.

Referring to Figure 12, the boundary portion 54 comprises a first portion 55 which extends from the side edge 43 of the humeral component and a second portion 56 configured to extend between the first portion 55 and the inner portion 53, the first and second portions having differently shaped outer surfaces. In cross-section along a plane substantially orthogonal with a tangent line taken from the humeral component’s side edge, the first portion 55 has a substantially planar outer surface and the second portion 56 has a convexly curved outer surface as shown in Figure 12. Together the first portion 55 and second portion 56 form a ramped surface that extends from the side edge 43 to the inner portion 53. In the cross-sectional view shown in Figure 12, the first portion 55 has an incline with substantially constant gradient and the second portion 56 is convexly curved. Referring to Figure 12, the second portion 56 is preferably shorter than the first portion 55, the first portion 55 providing the ramp and the second portion 56 transitioning to the inner portion 53.

The thickness of the implant between its back surface 51 and its front surface 52 is predetermined and the depth of the recess 70 between its planned resection cut surface 71 and resected articular surface 72 predetermined such that the inner portion 53 of the front surface forms a raised platform above the subject’s resected articular surface 72 that was present before the bone was removed to form the recess. The implant of the invention is designed to replace a damaged region of the cartilage in the joint and is designed with extra thickness to jack the joint apart sufficiently to relieve excessive pressure on the surrounding cartilage which with time can regenerate to normal thickness. The sloped surface of the boundary portion 54 forms a lead on I lead off ramp surface between the subject’s tissue around the recess 70 and the raised inner portion 53 of the implant so that the other articulating part of the joint can easily glide over the boundary between the subject’s tissue and the implant. The contoured slope to the raised inner portion 53 provided by the boundary portion 54 means that the alignment of the side edge 43 of the implant with the top edge 74 of the recess does not need to be exact as the radiused slope of the boundary portion 54 will assist the opposing articular surface when articulating over the boundary between the implant and the subject’s native tissue around the recess. The boundary portion 54 is contoured so that the straight sloped first portion 55 blends into the curved second portion 56. Positioning of a straight slope adjacent a convexly curved slope allows a smooth transition from the lower native tissue to the raised inner portion 53 of the implant.

Referring to Figure 12, a layer of cartilage 13 is on top of the humeral bone 12. The view of the humeral component 40 shown in Figure 12 shows the implant after cartilage 13 has had an opportunity to grow up to the implant after preparation of the recess 70 and implantation of the humeral component 40 in the recess. The thickness of the humeral component 40 is sized such that the cartilage layer 13 will extends partway up the boundary portion 54, but will not extend as far as the apex of the second portion 56. Therefore the inner portion 53 of the front surface forms a raised platform above the cartilage surrounding the recess 70.

The humeral component 40 has various features to aid with fixation to the humerus 12. The features aiding with fixation are optional and other implants may have only one or some of the features or may have alternative features to aid with fixation to the bone. Referring to Figure 3, the humeral component 40 has a peg 63 extending from the back surface 51, the peg being configured to be received in a peg recess 75 beneath the main recess 70 for receiving the implant body. The peg 63 is substantially cylindrical in shape and has longitudinal flutes 64 on its outer surface. At least part of the back portion 41 of the humeral component 40 is made of three-dimensional porous metallic mesh 44. The humeral component 40 may be formed as one integral metallic unit comprising the solid front portion 42, the mesh back portion 41 and the solid peg 63. The humeral component 40 may be made using Additive Layer Manufacturing (ALM) techniques, such as laser sintering. Preferably the humeral component 40 is made of cobalt chromium alloy. The thickness of the humeral component 40 from its back surface 51 to its side edge 43 is around 2 mm or so.

Referring to Figure 3, adjacent the bearing surface 57 is a fixation portion 60 comprising first and second through holes 61,62, each for receiving a bone screw 14 (bone screws are shown in Figure 3, but not shown in the other views of the humeral component). In the particular embodiment shown in the figures, the fixation portion 60 has first and second through holes 61,62, but it may have an alternative number of through holes. Each bone screw 14 has a head portion 14a and a shank portion 14b. The shank portion 14b of each bone screw is externally threaded to secure into bone. The head portion 14a of each bone screw is also externally threaded. The external threading of the head portion 14a of each bone screw corresponds with internal threading of the corresponding through holes 61,62 that the bone screw is received in such that each bone screw 14 can be rigidly fixed relative to the humeral component 40 when installed. In alternative embodiments, the bone screws may not be threadedly fastenable to the humeral component. The longitudinal axis of each through hole 61,62 is inclined at a predetermined angle relative to the humeral component 40 such that when installed, each screw 14 extends at a predetermined angle relative to the humeral component 40. The humeral component 40 can be provided with different spacings between the first and second through holes 61, 62 and provided with throughholes 61, 62 that have different inclines relative to the fixation portion 60 of the component, so as to suit different bone geometry.

The ulnar component 20 of the implant assembly shown in Figures 2, 6, 9, 11 and 13 is another embodiment of an implant according to the invention and will now be further described. Referring to Figure 6, the ulnar component 20 has a back surface 31 and a front surface 32 opposing the back surface, which includes a bearing surface for articulating with the front surface 52 of the humeral component 40 when installed. The bearing surface of the ulnar component 20 is concavely curved, for articulating with a convexly curved humeral surface.

Referring to Figure 11, the ulnar component 20 is configured to be installed in a recess 80 that has been formed in the subject’s ulna 11. The recess 80 has as resection cut surface 81 that the back surface 31 of the implant overlies when implanted and a resected articular surface 82, shown in dotted lines in Figure 11, corresponding to the articular surface of bone at the implant site before the bone is removed. The ulnar component 20 has a back portion 21 configured to be received within the recess 80 when implanted and a front portion 22 configured to project beyond the resected articular surface 82 when implanted.

At the boundary between the back portion 21 and the front portion 22, the ulnar component has a side edge 23 around the perimeter of the implant.

Referring to Figures 2 and 6, the front surface 32 of the ulnar component 30 is a rounded shape formed from two overlapping circles or ovals. The back portion 21 is similarly shaped in cross-section parallel with the back surface 31.

Referring to Figure 13, like the humeral component shown in close-up view in Figure 12, the front surface 32 of the ulnar component 20 comprises an inner portion 33 having a shape that substantially matches or approximates to at least part of the resected articular surface 82. As can be seen from Figure 11, the inner portion 33 is concavely curved. Surrounding at least part of the inner portion 33 is a boundary portion 34 forming a ramped surface projecting outwardly from the side edge 23 of the ulnar component to meet the inner portion 33. The boundary portion 34 fully encircles the inner portion 33. As can be seen from Figure 11, the concave curvature of the inner portion 33 dips away from the boundary between the boundary portion 34 and the inner portion 33, however the outer surface of the inner portion 33 is still raised away from the subject’s resected articular surface 82. The ulnar component is sized such that the side edge 23 of the ulnar component 20 aligns with the top edge 84 of the recess 80 when implanted. In practice, the alignment of the side edge 23 of the implant with the top edge 84 of the recess need not be exact and may be only a rough alignment. The recess 80 is shaped and sized to receive the back portion 31 of the ulnar component 30. In this embodiment, the ulnar component 30 has a shape formed from two overlapping circles or ovals and the recess 80 will be similarly shaped.

Referring to Figure 13, like the humeral component 40, the boundary portion 34 of the ulnar component 20 comprises a first portion 35 which extends from the side edge 23 of the ulnar component and a second portion 36 configured to extend between the first portion 35 and the inner portion 33, the first and second portions having differently shaped outer surfaces. Referring to Figure 11, in cross-section along a plane substantially orthogonal with a tangent line taken from the ulnar component’s side edge, the first portion 35 has a substantially planar outer surface and the second portion 36 has a curved outer surface. Together the first portion 35 and second portion 36 form a ramped surface that extends from the top edge 84 of the recess (when implanted) to the inner portion 33. The boundary portion 34 is contoured so that the straight sloped first portion 35 blends into the curved second portion 36. The thickness of the implant between its back surface 31 and its front surface 32 is predetermined with reference to the depth of the recess 80 between its planned resection cut surface 81 and resected articular surface 82 such that the inner portion 33 of the bearing surface forms a raised platform above the subject’s resected articular surface 82 that was present before the bone was removed to form the recess. As for the humeral component, the surface of the raised inner portion 33 above the anatomical articular surface jacks the joint apart to relieve pressure on the surrounding cartilage so that it can regenerate. The sloped surface of the boundary portion 34 forms a lead on I lead off ramp surface between the subject’s tissue around the recess 80 and the raised inner portion 33 of the implant so that the other articulating part of the joint can easily glide over the boundary between the subject’s tissue and the implant.

To aid with fixation of the ulnar component 20 to bone, at least part of the back portion 21 of the ulnar component 20 is made of three-dimensional porous metallic mesh 24. Referring to Figure 6, the back portion 21 of the ulnar component has a metallic mesh section 24 having a thickness of around 2.5 mm, above which is a polymeric section 25, preferably made of polyether ether ketone (PEEK) which has a similar thickness and includes the front portion 22 of the implant. The metallic mesh section 24 and the PEEK 25 section are preferably manufactured separately and secured together before the ulnar component 20 is implanted. The metallic mesh section 24 may be made by additive layer manufacturing and may be manufactured with a recess for receiving a keel (not visible in the figures) protruding from the back of the PEEK section 25. The PEEK section 25 and metallic mesh section 24 can then be secured together using a pin (not shown) that passes through throughhole 26 in the metallic mesh section. The metallic mesh section is preferably made of titanium alloy.

In order to install either the ulnar or humeral component 20,40, firstly a recess for receiving the implant is prepared. Suitable tools and guides may be provided to assist with preparing the bone before implantation. The depth of the recess and thickness of the implant from its back surface to its front surface are selected such that the front surface of the implant projects from the recess above the resected articular surface that was present before the bone was resected. The implant is placed into the prepared recess in the bone and if any additional fixation means are employed (such as bone screws for the humeral component), these are installed.

The humeral component 40 and the ulnar component 20 described herein may be employed independently of one another to resurface humeral and ulnar surfaces respectively, or they may be used together as an implant assembly comprising two implant components.

The humeral component may have a polymeric bearing surface (such as PEEK) supported by a metal base (like the ulnar component) and vice versa the ulnar component may be made wholly of metal.

The present invention has been illustrated in relation to implants for partial resurfacing of the humeroulnar joint in the elbow, however implants according to the invention may be manufactured for partial resurfacing at other joints, such as the knee.

Claims

1. An implant for resurfacing bone at an implant site in a joint of a human or animal subject, the implant being configured to be installed in a recess that has been formed in the subject’s bone at the implant site by removal of bone between a planned resection cut surface and a corresponding resected articular surface, the implant having a back portion configured to be housed within the recess and a front portion configured to project outwardly from the recess when implanted, the front portion of the implant having an outer surface, at least part of the outer surface of the front portion forming a bearing surface that projects outwardly from the recess when implanted.

2. An implant according to claim 1, wherein the outer surface of the front portion of the implant comprises an inner portion having a shape that substantially matches or approximates to at least part of the resected articular surface at the implant site and a boundary portion surrounding at least a part of the inner portion, the implant having a side edge, the boundary portion forming a ramped surface projecting outwardly from the side edge of the implant to the inner portion of the bearing surface.

3. An implant according to claim 2, wherein the boundary portion comprises a first portion extending outwardly from the side edge of the implant and a second portion extending from the first portion to the inner portion of the bearing surface, the first and second portions of the boundary portion having differently shaped outer surfaces.

4. An implant according to claim 3, wherein the first portion of the boundary portion has a substantially planar outer surface and the second portion has a curved outer surface in a plane substantially orthogonal to a tangent line to the implant’s side edge.

5. An implant according to any of claims 2 to 4, wherein the inner portion of the bearing surface is convexly curved in at least one plane.

6. An implant according to claim 5, wherein the inner portion of the bearing surface is convexly curved in two planes.

7. An implant according to any of claims 2 to 4, wherein the inner portion of the bearing surface is concavely curved in at least one plane.

8. An implant according to any preceding claim, wherein the implant is an elbow implant for resurfacing part of an elbow joint.

9. An implant according to claim 8, wherein the implant is configured to resurface at least part of the ulna in a subject’s elbow joint.

10. An implant according to any of claims 1 to 8, wherein the implant is configured to resurface at least part of the humerus in a subject’s elbow joint.

11. An implant according to any preceding claim, wherein the implant has a peg extending from its back portion.

12. An implant according to any preceding claim, wherein the implant further comprises a fixation portion comprising at least one through hole for receiving a bone screw.

13. An implant according to any preceding claim, wherein at least part of the back portion of the implant is formed of three-dimensional porous metallic mesh.

14. An implant according to any preceding claim, wherein the implant comprises a bearing component and a supporting component secured together in use, the bearing surface being on the bearing component, the bearing component being formed of polymeric material and the supporting component being formed of metal.

15. A method of manufacturing an implant for resurfacing a bone at an implant site in a joint of a human or animal subject, the implant being configured to be installed in a recess that has been formed in the subject’s bone at the implant site by removal of bone between a planned resection cut surface and a corresponding resected articular surface, the method comprising forming an implant having a back portion configured to be housed within the recess and a front portion configured to project outwardly from the recess when implanted, the front portion of the implant having an outer surface, at least part of the outer surface of the front portion forming a bearing surface, the implant having a back surface for engaging the planned resection cut surface, the thickness between the back surface and the bearing surface being selected such that the bearing surface projects outwardly from the recess when implanted.

16. A method of manufacturing an implant according to any of claims 1 to 14, the method comprising forming an implant having a back portion configured to be housed within the recess and a front portion configured to project outwardly from the recess when implanted, the front portion of the implant having an outer surface, at least part of the outer surface of the front portion forming a bearing surface that projects outwardly from recess when implanted.

17. A method of resurfacing bone at an implant site in a joint of a human or animal subject, the method comprising providing an implant according to any of claims 1 to 14, forming a recess in the subject’s bone at the implant site by removal of bone between a planned resection cut surface and a corresponding resected articular surface and seating the implant in the recess such that the bearing surface projects outwardly from the recess when implanted.

18. An implant substantially as hereinbefore described with reference to any suitable combination of the accompanying drawings.

19. A method of manufacturing an implant as hereinbefore described with reference to any suitable combination of the accompanying drawings.

20. A method of resurfacing bone as hereinbefore described with reference to any suitable combination of the accompanying drawings.

Intellectual

Property

Office

Application No: GB1803167.4

Claims searched: 1-16

Examiner: Robert Crowshaw