MEDICAL IMPLANT

Abstract

The invention relates to an orthopaedic implant comprising a surface arranged to contact bone in a human or animal body. The surface of said implant comprises a polymeric material which includes a repeat unit of general formula

##STR00001##

The polymeric material is polyetheretherketone, and said surface is a plasma treated surface.

Claims

1. An orthopaedic implant comprising a surface arranged to contact bone in a human or animal body, wherein said surface of said implant comprises a polymeric material which includes a repeat unit of general formula ##STR00003## wherein said polymeric material is polyetheretherketone, and wherein said surface is a plasma treated surface.

2. An implant according to claim 1 wherein the level of crystallinity of said polymeric material is greater than 25%.

3. An implant according to claim 1, wherein said orthopaedic implant has a first surface area which represents the entire surface area of the implant, wherein less than 100% of the first surface area is plasma treated as aforesaid.

4. An implant according to claim 3, wherein at least 40% of said first surface area is plasma treated.

5. An implant according to claim 1, wherein a back side of the implant which contacts cement in use, is treated.

6. An implant according to claim 1, wherein said surface arranged to contact bone has an Ra in at least one region thereof of at least 5 m.

7. An implant according to claim 6, wherein said Ra extends across at least 50% of the area of said surface.

8. An implant according to claim 1, wherein said implant comprises a femoral stem for a hip arthroplasty or a knee component for a knee arthroplasty.

9. An implant according to claim 1, wherein said implant is arranged to cooperate with a second orthopaedic member thereby to define an assembly for use in arthroplasty.

10. An implant according to claim 1, wherein said orthopaedic implant includes at least 50 wt % of said polymeric material.

11. An arrangement comprising: (i) an orthopaedic implant as described in claim 1, (ii) a second orthopaedic member arranged to be assembled with the orthopaedic implant to define an orthopaedic assembly.

12. An arrangement according to claim 11, wherein said second orthopaedic member comprises a polymeric material.

13. An arrangement according to claim 11, wherein the arrangement comprises a cement or one or more precursors arranged to form such a cement, for securing the orthopaedic implant in position.

14. An arrangement according to claim 13, wherein the cement, or at least one precursor of the cement, is acrylic-based.

15. An arrangement according to claim 14, wherein a precursor of said cement is arranged to define a polyacrylate cement.

16. An assembly comprising: (i) an orthopaedic implant as described in claim 1; (ii) a second orthopaedic member assembled with the orthopaedic implant to define an orthopaedic assembly.

17. An assembly according to claim 15, wherein the orthopaedic implant is associated with a cement which is acrylic-based.

18. An assembly according to claim 17, wherein said cement is a polyacrylate cement.

19. An assembly according to claim 17, wherein said cement contacts said plasma treated surface of said orthopaedic implant.

20. An assembly according to claim 16 wherein, in the assembly, the only surface of said orthopaedic implant which said cement contacts is a surface of said orthopaedic implant which is a plasma treated surface.

21. A method of preparing for surgery, the method comprising: (a) selecting an orthopaedic implant according to claim 1; (b) selecting a cement for securing the implant to bone or selecting one or more precursors arranged to define a cement.

22. A method according to claim 21, wherein the method comprises a step (c) which comprises selecting a second orthopaedic member which is arranged to cooperate with said orthopaedic implant referred to in (a) to define an assembly for use in arthroplasty.

23. A method of securing an orthopaedic implant to a bone of a human or animal body, the method comprising: (A) selecting an orthopaedic implant according to claim 1; (B) cementing the implant to a bone of the human or animal body.

24. A combination comprising: (I) an orthopaedic implant as described in claim 1; (II) an acrylic-based cement; said combination being for use arthroplasty.

Description

[0057] Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0058] FIG. 1 is a perspective view of part of an apparatus used to prepare samples for assessment; and

[0059] FIG. 2 is a representation of a lap-joint.

[0060] The following material is referred to hereinafter:

[0061] PEEK-OPTIMA (Trade Mark)refers to grade LTI polyetheretherketone (PEEK) having a melt viscosity of 0.45 KNsm.sup.2 obtained from Invibio Ltd. UK.

[0062] Various samples comprising PEEK-OPTIMA were made, with different roughnesses and surface treatments and were tested to assess how adhesion between PEEK and PMMA could be improved. Example 1 describes a general method of preparing a substrate; example 2 describes how substrates may be plasma treated; examples 3 to 20 describe specific samples; examples 21 and 22 describe how samples may be prepared and tested.

Example 1General Method for Preparing PEEK-OPTIMA Substrates

[0063] PEEK-OPTIMA substrates in the form of plates having dimensions 6 mm25 mm60 mm were prepared by injection moulding PEEK using standard conditions. In some cases, smooth PEEK-OPTIMA substrates were prepared; in other cases the PEEK-OPTIMA substrates were post-treated (e.g. by grit-blasting) to increase surface roughness (Ra).

Example 2Plasma Treated of PEEK-OPTIMA Substrate

[0064] Substrates were plasma treated using a commercially available Nano series plasma surface machine by Diener Electronics (Germany) having the following features: [0065] Chambercylindrical with 24 litres capacity. [0066] Plasma generator power used: 100%. [0067] Plasma generator type: Radio frequency signal of 40 kHz. [0068] Gas used: Oxygen 99% pure. [0069] Admission of oxygen time: 5 minutes. [0070] Plasma treatment time: 30 minutes.

Example 3Samples Prepared

[0071] Using the procedures described in Examples 1 and 2, a range of samples were made for testing as described in Table 1 below. Note that all plates made consist of PEEK-OPTIMA unless otherwise stated.

[0072] The Ra surface roughness value of samples was measured using a TALYSURF (Trade Mark) contact surface profilometer, with a standard diamond stylus, following ISO4288-1996 in each case, six measurements were taken across each sample in the direction of the tensile force to be applied during shear testing.

TABLE-US-00001 TABLE 1 Surface Example Roughness No. Description of Example (Ra) in m 4 Plasma treated as described in Example 2. 0.5 5 Post treated and plasma treated as described 100* in Example 2. 6 Post treated and plasma treated as described 200* in Example 2. 7 Post treated as Example 5 (but without 100* plasma treatment). 8 Post treated as Example 6 (but without 200* plasma treatment). 9 Grit blasted to specified roughness. 6 10 Grit blasted to specified roughness. 3 11 Grit blasted to specified roughness. 6 12 Post treated having the specified roughness. 70* 13 Post treated having the specified roughness. 20 14 Post treated having the specified roughness. 40 15 Post treated having the specified roughness. 17 16 Post treated having the specified roughness. 15 17 Post treated having the specified roughness. 20 18 Post treated having the specified roughness. 70* 19 Post treated having the specified roughness. 300* A fine pitched rib. 20 Post treated having the specified roughness. 10* A stepped plaque. *micro surface roughnss Ra-1 m.

Example 21Preparation of Cemented Samples for Testing

[0073] A cementing mould assembly 20, shown in FIG. 1, includes a mould part 22, which includes five rectangular openings 24 in which samples 2, shown in FIG. 2, are prepared. To prepare samples for testing, the assembly 20 is set up with 25 mm25 mm areas 28 of each sample exposed. Cement was mixed in accordance with the manufacturer's instructions. Then, using a powder-free gloved hand, cement was finger packed into each mould, ensuring each mould was fully filled. Then a polyethylene spacer sheet was positioned to cover the samples, a lid applied and G-clamps applied. The cement was accordingly cured under pressure in accordance with the manufacturer's instructions. After the appropriate time, the mould was disassembled and samples pressed out by hand. Samples were stored and conditioned for three days prior to testing as described in Example 22.

Example 22Testing of Interfacial Strength of Samples

[0074] Testing was performed on an Instron 5569 electromechanical test machine with a 50 kN load cell. The sample was positioned vertically in the jaws using 6 mm thickness aluminium alignment plates so that the load axis was coincident with the lap interface of the test sample, with an equal area of either end of the sample supported in the grips. Samples were then loaded at a rate of 2 mm/min to failure.

[0075] Shear interface strength was calculated from the following equation.

[00001]$\mathrm{Shear}.Math..Math.\mathrm{strength}.Math..Math.\left(\mathrm{MPa}\right)=\frac{\mathrm{failure}.Math..Math.\mathrm{load}.Math..Math.\left(N\right)}{\mathrm{Lap}.Math..Math.\mathrm{joint}.Math..Math.\mathrm{area}.Math..Math.\left({\mathrm{mm}}^2\right)}$

[0076] Statistical analysis was then performed with IBM SPSS Statistics 20. Analysis of variance (ANOVA) tests with 5% significance criteria were chosen to allow multiple comparisons of mean strength between all independent sample groups tested (assuming normal distribution). Test results are provided in Table 2.

TABLE-US-00002 TABLE 2 Average shear Example No. strength, MPa 4 0.37 5 3.16 6 2.39 7 1.24 8 1.12 9 1.53 10 0.62 11 1.31 12 0.77 13 0.91 14 1.18 15 0.52 16 0.51 17 1.35 18 0.94 19 2.07 20 0.52

[0077] Note that attempts were made to test untreated and untextured PEEK-OPTIMA samples (i.e. like Example 4 but without the plasma treatment) but the bond strength between the PEEK-OPTIMA and the cement was so low that the samples could not be removed from the mould so no relevant quantitative result could be obtained.

[0078] The results in Table 2 show, unpredictably, that the plasma treatment can be used to significantly increase the strength of the bond between PMMA and PEEK-OPTIMA. The bond is, in many cases, stronger than for samples which have post treated surface features (resulting in significant Ra) and significant mechanical interlock with the PMMA.

[0079] The invention is not restricted to the details of the foregoing embodiment(s). 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.