A prosthetic implant

Abstract

The invention relates to a polymeric prosthetic implant (2) for attaching to a bone. The implant comprises a first surface (4) and a second surface (10). The second surface is arranged for attachment to a bone, and has a textured surface finish. At least one protrusion (14) is located on said textured surface. The or each protrusion has a flash (38) thereon.

Description

[0001] A Prosthetic Implant

[0002] The present invention relates to prosthetic implants for attaching to a bone, methods of manufacturing prosthetic implants for attaching to a bone, and moulds for use in methods of manufacturing a prosthetic implant. Particularly, but not exclusively, the invention relates to orthopaedic knee implants, for example, femoral implants.

[0003] Background

[0004] Prosthetic implants are typically used to replace damaged or diseased bone. A common type of prosthesis is a knee replacement, which is used to replace the load-bearing surfaces of a knee joint. This is usually done to relieve pain and / or disability resulting from trauma or disease, for example osteoarthritis. Other types of prosthetics include other joint replacements, for example hips and vertebral discs.

[0005] Typically, prosthetic implants are made from metals such as cobalt chrome. However, more recently, there has been a focus on the use of polymeric materials which are lightweight and do not suffer the problems associated with metal counterparts, for example, “Stress Shielding”. An example of a polymeric knee implant made from polyetheretherketone (PEEK) is described in US2009 / 0164023 (Devine).

[0006] Polymeric prosthetic implants may be secured to bone by a cementless fixation, for example, incorporating hydroxyapatite into the material composition to promote bone ingrowth through a porous lattice or, alternatively, may be fixed by a cemented fixation method with the use of suitable adhesive cement. However, the success of a cemented polymer prosthesis is dependent on the strength of the bond both between the cement and the implant surface, and the cement and the bone.

[0007] It is known to apply a textured surface finish to polymeric prosthetic implants using laser cutting and / or chemical treatment such as acid etching, to promote an increase in adhesion between the bone and bone cement. However, such processes are time consuming, can produce errors in the patterned surface, and often lead to failure in adhesion between the implant and cement.

[0008] It is an aim of the subject-matter of the present disclosure to improve on the prior art.

[0009] According to an aspect of the present disclosure, there is provided a polymeric prosthetic implant for attaching to a bone, comprising: a first surface and a second surface the second surface being arranged for attachment to a bone, the second surface having a textured surface finish, wherein at least one protrusion is located on said textured surface, the or each protrusion having a flash thereon.

[0010] Preferably, the flash is located on a first side and / or a second side of the at least one protrusion. Preferably, at least a part of the flash is located adjacent the base of the protrusion. Preferably, the flash is obtainable by electrical discharge machining (EDM) of a corresponding mould tool used to mould the implant. Preferably, the flash is provided in a random pattern arrangement on the or each protrusion. Preferably, the flash is provided on at least 10% of the overall surface area of the or each protrusion, more preferably, at least 20% of said protrusion, preferably less than 100% of the overall surface area of the or each protrusion. Preferably, the flash comprises a plurality of edges, preferably the edges project away from the first and / or second side of the protrusion. Preferably, the flash is formed at less than 90 degrees to the longitudinal axis of the protrusion, preferably less than 60 degrees.

[0011] Advantageously, the flash provides for an increase in bonding strength between the polymeric implant and the bone cement. This is due to the cement embedding in pockets formed under the flash, for example, under the edges. In turn, the prosthetic implant may be more securely attached to a bone, which may increase the lifetime of the prosthetic implant and success of a prosthetic surgery. Due to the flash or “spark” effect pattern, the polymer to cement bond is stronger than the cement itself. In so doing, the polymeric implant to cement interface is at least as strong as that of a cemented metal implant of the same design.

[0012] The use of EDM or spark erosion is a process that the skilled person in the field of medical polymeric implantables would avoid using due to the resultant jagged, rough, unpredictable surface that is produced. Creation of such a surface is counterintuitive in a field that typically demands certainty of an implantable surface.

[0013] Additionally, applying surface texture to the mould surfaces improves efficiency compared to applying the surface texture to each individual implant.

[0014] Said implant is preferably an injection moulded prosthesis. Said prosthesis is preferably made substantially entirely by injection moulding. Said prosthesis preferably comprises a polymeric material, for example a thermoplastic polymeric material. At least 50wt%, suitably at least 70wt%, preferably at least 80wt%, more preferably 90wt%, especially at least 95wt%, for example at least 99wt%. of said prosthesis is made from thermoplastic polymeric material, for example from a first polymer as herein described. Preferably, the prosthesis is a knee prosthesis, preferably a femoral component. Said femoral component is preferably a solid body. It is preferably monolithic. It is preferably made in one piece by injection moulding.

[0015] Said first polymer is preferably a polyaryletherketone. A preferred polyaryletherketone has a repeat unit of formula (I) where t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2.

[0016] Said polyaryletherketone suitably includes at least 90, 95 or 99 mol % of repeat unit of formula I. Said polyaryletherketone suitably includes at least 90, 95 or 99wt% of repeat units of formula I.

[0017] Said polyaryletherketone preferably consists essentially of a repeat unit of formula I. Preferred polymeric materials comprise (especially consist essentially of) a said repeat unit wherein t1 =1 , v1=0 and w1 =0; t1 =0, v1=0 and w1 =0; t1 =0, w1 =1 , v1=2; or t1 =0, v1=1 and w1 =0. More preferred comprise (especially consist essentially of) a said repeat unit wherein t1 =1 , v1=0 and w1=0; or t1 =0, v1 =0 and w1 =0. The most preferred comprises (especially consists essentially of) a said repeat unit wherein t1 =1 , v1 =0 and w1=0.

[0018] In preferred embodiments, said first polymer is selected from polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone and polyetherketoneketone. In a more preferred embodiment, said first polymer is selected from polyetherketone and polyetheretherketone. In an especially preferred embodiment, said first polymer material is polyetheretherketone.

[0019] Said polyaryletherketone may have a Notched Izod Impact Strength (specimen 80mm x 10mm x 4mm with a cut 0.25mm notch (Type A), tested at23°C, in accordance with ISO180) of at least 4KJm-2, preferably at least 5KJm-2, more preferably at least 6KJm-2. Said Notched Izod Impact Strength, measured as aforesaid, may be less than 10KJm-2, suitably less than 8KJm-2.. The Notched Izod Impact Strength, measured as aforesaid, may be at least 3KJnrr2, suitably at least 4KJrrr2, preferably at least 5KJrrr2. Said impact strength may be less than 50 KJm-2, suitably less than 30KJm-2.

[0020] Said polyaryletherketone suitably has a melt viscosity (MV) of at least 0.06 kNsm-2, preferably has a MV of at least 0.09 kNsm-2, more preferably at least 0.12 kNsm-2, especially at least 0.15 kNsm-2. Advantageously, the MV may be at least 0.35 kNsm-2and especially at least 0.40 kNsm-2An MV of 0.45 kNsm-2has been found to be particularly advantageous in the manufacture of accurate, strong frameworks.

[0021] Unless otherwise stated herein, MV is measured using a Bohlin Instruments RH2000 capillary rheometer according to ISO 11443 operating at 340°C and a shear rate of 1000s-1using a 0.5mm (capillary diameter) x 8.0mm (capillary length) die with entry angle 180°C. Granules are loaded into the barrel and left to pre-heat for 10 minutes. The viscosity is measured once steady state conditions are reached and maintained, nominally 5 minutes after the start of the test. Said polyaryletherketone may have a MV of less than 1 .00 kNsm-2, preferably less than 0.5 kNsm-2. Said polyaryletherketone may have a MV in the range 0.09 to 0.5 kNsm-2, preferably in the range 0.14 to 0.5 kNsm-2, more preferably in the range 0.4 to 0.5 kNsm-2.

[0022] Preferably, the or each protrusion comprises ridges with grooves preferably extending between adjacent ridges. Preferably, the ridges are parallel to one another, and preferably substantially parallel to a longitudinal axis of the protrusion.

[0023] In an embodiment, the textured surface finish may have an average texture depth of between 50 to 200 micrometres, preferably between 100 and 180 micrometres, most preferably, between 111 micrometres to 150 micrometres.

[0024] In an embodiment, the surface texture finish may have an average texture depth of between 118 micrometres and 145 micrometres.

[0025] Such a textures surface depth may provide for optimum increases in adhesion between the prosthetic implant and a bone. Advantageously, this means that the prosthetic implant may withstand large loads over a longer lifetime.

[0026] In an embodiment, the polymeric composition may be a reinforced polymeric composition comprising one or more fillers selected from a group consisting of: fibres, particles, and platelets. For example, a filler may comprise a hydroxyapatite. The filler may comprise a radiopaque material such as barium sulphate.

[0027] Such polymeric compositions may have improved mechanical properties and / or bonding characteristics and / or biological acceptability for the prosthetic implant.

[0028] According to an aspect, there is provided a method of manufacturing a polymeric prosthetic implant for attaching to a bone, the method comprising: providing a mould, the mould including a second surface part and a first surface part combining to form a cavity, the second surface part for shaping a second surface of the prosthetic implant and the first surface part for shaping a first surface of the prosthetic implant, the second surface part comprising a plurality of upstanding members obtained by electrical discharge machining, and for shaping corresponding protrusions of the second surface; injecting a polymeric material into the cavity; and separating the second surface part and the first surface part to release the prosthetic implant, producing a flash on the second surface of said implant.

[0029] When the second surface part and first surface part are separated, the texturing of the second surface part causes the flash to occur on the protrusions on the implant. The flash increases the strength of the bone cement to polymer bond because bone cement is able to flow into and occupies the pockets or regions under the flash.

[0030] Advantageously, the use of electrical discharge machining on the mould tool surface part, results in a corresponding textured surface on the prosthetic implant which provides for an improved adhesion at the implant and cement interface. Such adhesion is comparable to that between bone cement and a metal implant.

[0031] Furthermore, electrical discharge machining promotes consistency in manufacture of implant as the surface finish is more reproducible than for example, acid etching.

[0032] In an embodiment, texturing the second surface part using electrical discharge machining may comprise texturing the second surface part to a surface finish to an average texture depth greater than or equal to 50 micrometres, and less than or equal to 200 micrometres. The average depth is the Z-difference measured by OGP scanning.

[0033] In an embodiment, texturing the second surface part using electrical discharge machining comprises texturing the second surface part to a surface finish to an average texture depth greater than or equal to 100 and less than 180 micrometres, for example, greater than 118 micrometres and less than or equal to 150 micrometres.

[0034] If the average texture depth is less than 110 micrometres, flash is unlikely to occur, or at least will not occur to a level that will improve adhesion to the bone cement.

[0035] If the average texture depth is greater than 150 micrometres, the implant may get stuck in the mould which may damage a surface of the implant.

[0036] In an embodiment, the polymeric material is selected from polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone and polyetherketoneketone. In a more preferred embodiment, the polymeric material is selected from polyetherketone and polyetheretherketone. In an especially preferred embodiment, said polymeric material is polyetheretherketone.

[0037] According to an aspect of the present disclosure, there is provided a prosthetic implant of the aspect defined above, manufactured using the method of the aspect defined above.

[0038] According to an aspect of the present disclosure, there is provided a mould for use in a method of manufacturing a polymeric prosthetic implant for attaching to a bone, the mould comprising: a second surface part and a first surface part configured to combine to form a cavity, the second surface part for shaping a second surface of the prosthetic implant and the first surface part for shaping a first surface of the prosthetic implant, wherein the second surface part comprises a plurality upstanding members obtained by electrical discharge machining.

[0039] In an embodiment, the second surface of the mould may be textured with a surface finish with an average texture depth greater than or equal to 111 micrometres, and less than or equal to 200 micrometres. Preferably, the or each upstanding member has an average depth of between 50 and 200 micrometres, more preferably between 100 and 150 micrometres.

[0040] Brief Description of the Drawings

[0041] Examples of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a schematic drawing of a femoral component of a knee replacement assembly, according to an embodiment of the invention;

[0042] Figure 2 shows a schematic cross sectional side view of a femoral component according to an embodiment of the invention;

[0043] Figure 3 is a 3-Dimensional digital scan of a surface of a prosthetic implant according to the invention;

[0044] Figure 4 shows a schematic cross sectional side view of protrusions according to the invention;

[0045] Figure 5a to 5d show a schematic of a method of manufacturing a textured surface of a prosthetic implant according to the invention;

[0046] Figure 6a shows a laser scan of a polymeric surface produced from a laser cut and acid etched mould tool;

[0047] Figure 6b shows a laser scan of a polymeric surface polymeric surface produced from an electrical discharge machined mould tool according to the present invention;

[0048] Figure 7 shows a simple schematic of a testing arrangement according to the invention;

[0049] Figure 8 shows a schematic mould tool for manufacturing a prosthetic implant.

[0050] Detailed Description

[0051] Figure 1 shows a femoral component 2 of a prosthetic knee implant. The component 2 includes a curved outer surface 4 having a first condyle 6 and a second condyle 8. The first and second condyles 6, 8 define an articulation surface of the femoral component and are arranged to contact an articulation surface of a tibial component (not shown). The component is a one-piece, monolithic injection moulded part.

[0052] An internal face or second surface 10 of femoral component 2 includes cement pockets 12 and protrusions 14. Conical stems 18 may be provided on the second surface 10 as shown in Figure 2. The stems 18 extend inwardly away from the second surface 10 and are arranged to engage corresponding sockets formed in a patient's femur. Figure 2 shows the protrusions 14 in further detail. The protrusions 14 are located around the second surface 10, in a generally parallel arrangement to each other. The protrusions 14 stand upright from the second surface 10 and are spaced apart so as to form a series of ridges 32 and channels or grooves 34. The grooves 34 extend between adjacent ridges 32. The ridges 32 and grooves 34 may be mutually parallel. In examples, the protrusions 14 may have a different shape, for example longitudinal, hexagonal, curved or circular protrusions.

[0053] The grooves 34 provide a channel for bone cement to flow into and in so doing facilitates retention of the bone cement; this aids securement of the femoral component onto a femur of a patient being provided with a prosthetic knee.

[0054] Flash 38 is located on each protrusion 14 as shown most clearly in Figure 3 and 4. The flash 38 is provided along each side wall 36 of a protrusion 14, extending towards an upper surface 37 of the protrusion 14. A substantial part of the flash 38 is located towards the base of said protrusion 14. The flash 38 is jagged, providing a rough, uneven surface with many sharp regions.

[0055] The flash 38 is formed during an injection moulding process using a mould tool having a surface texture created by EDM as will be described in detail below.

[0056] Electric Discharge Machining (EDM) is known to be used to texture metal surfaces exploiting electrical energy to etch the metal surface. A high potential is induced between the tool and the surface to generate a spark. Whenever sparking takes place between two electrodes, a small amount of material is removed. Multiple sparks are used to machine the material generating a textured finish. The amount of material eroded by every spark and the resulting surface finish both depend on the spark energy, duration, and frequency. The volume of material removed per discharge is typically in the range of 10"6-10"4mm3. Typical MRR for the process is between 2 and 400 mm3 / min, depending on geometrical and machining parameters. In general, higher currents lead to larger craters, thus higher MRR but coarser surface finish.

[0057] Figures 5 are schematics to show how a mould tool 40 surface pattern is created on a mould tool surface 42. In Figure 5a, a series of recurring current discharges between the surface 42 and a source electrode creating sparking 44 at the point of least electrical resistance. The localized heat generated by the sparking removes material from the surface 42 as shown in Figure 5b, providing an irregularly textured surface 48 with a surface texture depth as required. During injection moulding as shown in Figure 5c, molten polymer (shown as dotted lines) flows into the mould 40 and into the textured sparked surface 48. Specifically, the polymer fills the peaks and troughs of the sparked surface 48, such that the pattern is imprinted to create a textured surface finish on the implant surface (Figure 5d). As the implant 2 is ejected from the mould tool 40, the ejection process causes the PEEK, that has flowed into the peaks and troughs of the textured mould tool, to deform. This deformation creates tiny areas of flash, which are undercuts in the moulded textured surface as shown in Figure 3.

[0058] Advantageously, by applying the surface texture to the mould 40, rather than individual moulded prosthetic implants 2, the resulting implant will include flash 38 which improves a strength of a bond between the polymer and the bone cement. The textured surface finish is irregular having a high number of peaks and troughs formed across the surface. Such an irregular surface finish means that the bone cement can penetrate into the second surface 10 of the prosthetic 2, thereby improving adhesion.

[0059] The textured surface finish has an average texture depth of between 110 micrometres to 150 micrometres. Such average texture depths relate to VDI 39 to 42. VDI (or VDI 3400) is a standard scale for surface finishes set by the Verein Deutscher Ingenieure, Society of German Engineers.

[0060] Figure 6a shows a laser scan of the surface texture on a PEEK surface produced by the conventional process of laser cutting and acid etching of a mould tool. Figure 6b shows a laser scan of the surface texture on a PEEK surface produced by EDM of a mould tool. The scans show that the EDM or spark texture has more high and low points along the same scan length, also the transition between the peaks and troughs are much sharper than the smoother scans of the laser and acid texturing process.

[0061] The surface texture of the VDI 39 corresponds to an average measured surface depth range of between 111 and 128pm. A surface texture finish of VDI 42 corresponds to an average measured surface depth range of between 140 pm and 150 pm. Advantageously, such surface texture depths optimise adhesion with bone cement such that the prosthetic implant 2 may be strongly and reliably attached to a prepared bone. Further, such surface texture depths comprise flash 38 on the protrusions 14, formed as part of the moulding process. This further enhances adhesion between the prosthetic implant 2 and a prepared bone. Whilst the average texture depth may be between 111 micrometres and 150 micrometres, empirical results demonstrate that an average texture depth of between 118 micrometres and 145 micrometres provides optimal results.

[0062] Referring to Figure 8, a mould 200 for use in a method of manufacturing a prosthetic implant is schematically shown. The mould 200 may be formed, at least in part, of a metal. The mould 200 comprises a first surface part 210 and a second surface part 220. Together, the first surface part 210 and the second surface part 220 form a cavity 230. The mould 200 may be suitable for injection moulding of a prosthetic implant. In use, a polymeric material is injected into the cavity 230 to form the prosthetic implant.

[0063] The first surface part 210 is shaped to shape the first surface 110 of a prosthetic implant. In examples, the first surface part 210 has a substantially smooth surface texture. In examples, the first surface part 210 may be arranged to shape a replacement condyle of a prosthetic implant which may be a femoral component. In examples, the first surface part 210 may be arranged to shape an outer, or load-bearing, surface of a joint, for example as part of a joint replacement assembly.

[0064] The second surface part 220 is shaped to shape the second side 120 of a prosthetic implant 100. In examples, the second surface part 220 is arranged to shape a second surface 120 for attachment of the prosthetic implant 100 to a prepared distal femur, as part of a femoral component. In examples, the second surface part 220 may be arranged to shape a surface for attachment to a prepared bone or joint surface.

[0065] In examples, the second surface part 220 has a plurality of upstanding members 222. The upstanding members 222 are shaped to form corresponding protrusions 14 on the second surface 10 of a prosthetic implant that is formed from the mould 200. In examples, the upstanding members 222 form both ridges 132 and grooves 134 on a corresponding prosthetic implant. In examples, the upstanding members 222 may be longitudinal, hexagonal, curved or circular protrusion moulds 222 to provide correspondingly shaped protrusions 14. The upstanding members 222 may be provided on distinct parts of the second surface part 220. In examples, the upstanding members 222 may be provided on substantially all of the second surface part 220.

[0066] At least part of the second surface part 220 of the mould 200 is textured. The second surface part of the mould is textured with a surface finish that has an average textured depth between 118 and 150 micrometres. In examples, the average texture depth of the second surface part 220 may be greater than or equal to 111 micrometres, or more preferable 150 micrometres. This corresponds to a surface texture of VDI 39 or greater. Such a texture depth on the second surface part 220 will impart a corresponding average texture depth on a second surface 120 of a prosthetic implant that is moulded using the mould 200. Such a surface texture depth provides for flash 38 to be formed on the protrusions 14 of the implant. Advantageously, this surface texture depth and the flash 38 provides for improved adhesion with bone cement to increase the reliability and durability of the interface between the prosthetic implant and a prepared bone.

[0067] In examples, the average texture depth of the second surface part 220 may be less than or equal to 200 micrometres, or more preferable less than 150 micrometres. This corresponds to a surface texture of 42 VDI or lower. Such an average texture depth on the second part 220 provides for optimised roughness and provides flash 38 on the protrusions which increases the adhesion between the prosthesis and bone cement. Having an average texture depth of less than or equal to 150 micrometres means that release of the moulded prosthetic implant from the mould 200 is simple and the prosthetic implant may not be damaged during release.

[0068] Texture depth is measured using OGP laser scanning to measure the depth of the surface. The depth is derived according to the following method: a flat section of the texture is first scanned; the lowest and highest data points are measured to determine the depth height in the Z direction.

[0069] Experimental

[0070] The impact of different textured surface finishes on adhesion between bone cement and the PEEK interface was tested. PEEK-OPTIMA™ material by Invibio Limited was used throughout the study.

[0071] The texturing was applied by a first method (A) A chemically applied texturing, supplied by Gravutex Eschmann International Ltd, and a second method (B) An Electric Discharge Machining (EDM) eroded texturing supplied by Complexa HPE Ltd.

[0072] Both textured samples were compared with non-textured samples (the control) to gauge the impact each texture has on the fixation performance. Since there is no known standardised method for measuring this mode of failure, a new methodology was created and used for the comparative test. The results cannot demonstrate efficacy of any specific device and should only be used to enable a comparison of the cemented interface shear resistance of multiple textures.

[0073] ASTM F1044-05 for the shear testing of metallic coatings allows a lap shear method to be used on a plate sample to evaluate an interfacial strength between two materials as shown in Figure 7.

[0074] Method

[0075] PEEK-OPTIMA™ coupons (60 x25 x6 mm) with 25 x 25 mm designed interface area, were prepared. The coupons were mounted in polyethylene mould cavities designed to accept the specific coupon design. Secondary mould cavities were then placed on top of the first to overlap the interface area. Palacos R™ cement from Heraeus Medical GmbH was prepared using vacuum mixing at room temperature and in a temperature and humidity controlled environment. Secondary mould cavities were filled with cement and the mould compressed using steel plates. The moulds were clamped applying an even load across the face of the tool. The cement was allowed to polymerise for a minimum of 24 hours at room temperature before removing the samples. Samples were mounted in a mechanical testing rig and a tensile load applied at a constant rate of displacement of 2 mm / min until the point of failure (defined as the point at which load drops significantly and / or the displacement is above the size of a single feature on the cement interface.

[0076] The following textures were applied to the PEEK coupons and 5 of each variant were initially bonded to cement coupons and subjected to static shear testing, to test the adhesion strength:

[0077] Samples A: A laser-cut followed by a chemical acid etch to apply a texture to the fixation design supplied by Gravutex Eschmann International Ltd.

[0078] Samples B: An EDM process to apply the texture to the fixation design at a roughness of VDI 42 as supplied by Complexa HPE Ltd.

[0079] Samples C: Control samples having no texture applied to the fixation design.

[0080] The results from the initial shear testing indicate which texturing method achieved the highest adhesion strength between the bone cement and the moulded PEEK femoral component. Table 1 details the results of the initial Lap Shear mechanical testing of cemented coupons (sample set 5).

[0081] Table 1

[0082] The results showed that the spark eroded (EDM) textured samples achieved a 60% increase in fixation compared to the laser etched samples. The spark samples achieved fixation stronger than the bone cement itself, resulting in the cement fracturing in half before being able to de-bond from the fixation interface.

[0083] A range of VDI surface finishes / ranging from VDI33 to VDI39 - Light to heavy were also tested. Both the VDI 39 and VDI 42 textures performed well on the mechanical tests, with the strength of the fixation interface surpassing the actual strength of the bone cement. Both textures achieved an average force of approx. 2500N.

[0084] Advantageously, the results demonstrate that the spark-eroded (EDM) texturing offers a superior performance in bone cement fixation over the current laser and acid etch texturing process. The attachment between the PEEK surface and the bone cement surpasses the strength of the cement itself.

[0085] Although a few example embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. All the features disclosed in this specification, including any accompanying claims, abstract and drawings, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification, including any accompanying claims, abstract and drawings, may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0086] The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification, including any accompanying claims, abstract and drawings, or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

Claims1 . A polymeric prosthetic implant for attaching to a bone, comprising: a first surface and a second surface the second surface being arranged for attachment to a bone, the second surface having a textured surface finish, wherein at least one protrusion is located on said textured surface, the or each protrusion having a flash thereon.

2. A polymeric prosthetic implant as claimed in claim 1 , wherein the flash is located on a first side and / or a second side of the at least one protrusion.

3. A polymeric prosthetic implant as claimed in claim 1 or 2, wherein at least a part of the flash is located adjacent the base of the protrusion.

4. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein the flash is obtainable by electrical discharge machining (EDM) of a corresponding mould tool used to mould the implant.

5. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein the flash is provided in a random pattern arrangement on the or each protrusion.

6. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein the flash comprises a plurality of edges and the edges project away from the first and / or second side of the protrusion.

7. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein said implant is an injection moulded prosthesis.

8. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein said prosthetic implant is made from a thermoplastic polymeric material.

9. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein the thermoplastic polymeric material is polyetheretherketone (PEEK).

10. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein the textured surface finish has an average texture depth of between 50 to 200 micrometres.

11. A polymeric prosthetic implant as claimed in claim 10, wherein the textured surface finish has an average texture depth of between 111 micrometres to 150 micrometres.

12. A method of manufacturing a polymeric prosthetic implant for attaching to a bone, the method comprising: providing a mould, the mould including a second surface part and a first surface part combining to form a cavity, the second surface part for shaping a second surface of the prosthetic implant and the first surface part for shaping a first surface of the prosthetic implant, the second surface part comprising a plurality of upstanding members obtained by electrical discharge machining, and for shaping corresponding protrusions of the second surface; injecting a polymeric material into the cavity; and separating the second surface part and the first surface part to release the prosthetic implant producing a flash on the second surface of said implant.

13. A method as claimed in claim 12, wherein the second surface part comprises a surface finish texturing having an average texture depth greater than or equal to 50 micrometres, and less than or equal to 200 micrometres.

14. A mould for use in a method of manufacturing a polymeric prosthetic implant for attaching to a bone, the mould comprising: a second surface part and a first surface part configured to combine to form a cavity, the second surface part for shaping a second surface of the prosthetic implant and the first surface part for shaping a first surface of the prosthetic implant, wherein the second surface part comprises a plurality upstanding members obtained by electrical discharge machining.

15. A polymeric prosthetic implant as claimed in any one of the preceding claims, wherein the prosthesis is a knee prosthesis, preferably a femoral component.

16. A prosthetic implant of any of Claims 1 to 11 manufactured using the method of any of Claims 12 or 13.

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