Orthopedic Paek-On-Polymer Bearings

Abstract

An orthopedic prosthetic joint comprising a joint couple having a first bearing surface made of a poly aryl ether ketone (PAEK) and a second joint component having a second bearing made of a polymer that is softer than the PAEK such as UHMWPE the first and second bearing surfaces in sliding engagement with one another.

Claims

1. An orthopedic prosthetic hip joint comprising: a joint couple having a first joint component capable of being mounted on a femur of a hip, the first joint component having a first bearing surface made of a poly aryl ether ketone (PAEK), and a second joint component capable of being mounted on a acetabulum, the second joint component having a second bearing surface made of a polymer, the first and second bearing surfaces in sliding engagement directly with one another, wherein the first bearing surface made of the PAEK is composed of a substantially pure non-fiber reinforced polyetheretherketone (PEEK) and the second bearing surface made of the polymer is composed of ultra high molecular weight polyethylene (UHMWPE), and wherein the first bearing surface has a higher shore D hardness than the second bearing surface.

2. The orthopedic prosthetic joint as set forth in claim 1, wherein the second bearing surface comprises UHMWPE which is crosslinked.

3. The orthopedic prosthetic joint as set forth in claim 1, wherein the first joint component is a stand-alone component.

4. The orthopedic prosthetic joint as set forth in claim 1, wherein the PEEK bearing comprises a layer of pure PEEK coated, molded or grafted onto a solid or porous polymer substrate.

5. The orthopedic prosthetic joint as set forth in claim 1, wherein the PEEK bearing comprises a layer of pure PEEK coated, molded or grafted onto a solid or porous metallic substrate.

6. The orthopedic prosthetic joint as set forth in claim 1, wherein the PEEK bearing comprises a layer of pure PEEK coated, molded or grafted onto a solid or porous ceramic substrate.

7. The orthopedic prosthetic joint as set forth in claim 1, wherein the first bearing surface or the second bearing surface is configured to contact a bone and comprises a porous PAEK layer for bone ingrowth.

8. The orthopedic prosthetic joint as set forth in claim 1, wherein the second bearing comprises a crosslinked polyethylene.

9. An orthopedic prosthetic hip joint comprising: a first bearing surface consisting of a substantially pure non-fiber reinforced PEEK, the first bearing surface capable of being mounted on a femur of a hip; and a second bearing surface capable of being mounted on an acetabulum, in direct sliding contact with the first bearing surface, the second bearing surface consisting of ultra high molecular weight polyethylene (UHMWPE).

10. The orthopedic prosthetic joint as set forth in claim 9, wherein the UHMWPE is cross-linked at least three times by irradiation, heating after irradiation and cooling after each heating.

11. The orthopedic prosthetic joint as set forth in claim 9, wherein the PEEK bearing comprises a layer of pure PEEK coated, molded or grafted onto a solid or porous polymer composite substrate.

12. The orthopedic prosthetic joint as set forth in claim 9, wherein the PEEK bearing comprises a layer of pure PEEK coated, molded or grafted onto a solid or porous metallic substrate.

13. The orthopedic prosthetic joint as set forth in claim 9, wherein the PEEK bearing comprises a layer of pure PEEK coated, molded or grafted onto a solid or porous ceramic or ceramic composite substrate.

14. The orthopedic prosthetic joint as set forth in claim 9, wherein the first bearing surface or the second bearing surface is configured to contact a bone and has a porous PEEK layer for bone ingrowth.

15. The orthopedic prosthetic joint as set forth in claim 9, wherein the polyethylene has been crosslinked by irradiation.

16. The orthopedic prosthetic joint as set forth in claim 1, wherein the second bearing surface comprises polyethylene which is non-crosslinked.

17. An orthopedic prosthetic hip joint comprising: a joint couple having a first joint component capable of being mounted on a femur of a hip, the first joint component having a first bearing surface, the first bearing surface made of a poly aryl ether ketone (PAEK) and a second joint component capable of being mounted on an acetabulum, the second joint component having a second bearing surface, the second bearing surface made of a polymer, the first and second bearing surfaces in sliding engagement directly with one another, wherein the first bearing surface made of the PAEK is composed of a substantially pure non-fiber reinforced polyetheretherketone (PEEK) and the second bearing surface made of the polymer is composed of ultra high molecular weight polyethylene (UHMWPE), wherein the first bearing surface has a higher shore D hardness than the second bearing surface.

18. An orthopedic prosthetic hip joint comprising: a first bearing surface consisting of a substantially pure non-fiber reinforced PEEK, the first bearing surface capable of being mounted on a femur of a hip; and a second bearing surface capable of being mounted on an acetabulum, in direct sliding contact with the first bearing surface, the second bearing surface consisting of ultra high molecular weight polyethylene (UHMWPE).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a graph showing the wear of a Cobalt Chrome alloy and a non-reinforced PEEK 32 mm femoral head on a cup of X3? UHMWPE which have been crosslinked three times for 1.25 million cycles.

[0021] FIG. 2 is a graph showing test results similar to those in FIG. 1 but the femoral heads having been scratched.

[0022] FIG. 3 is a photograph of the UHMWPE cup of FIG. 1 prior to wear testing.

[0023] FIG. 4 is a photograph of the UHMWPE cup used against the CoCr head of FIG. 1 after wear testing.

[0024] FIG. 5 is a photograph of UHMWPE cup used against the un-reinforced PEEK head of FIG. 1.

[0025] FIG. 6 shows photographs of unscratched PEEK head before and after testing.

[0026] FIG. 7 shows photographs of a scratched PEEK head before and after testing.

[0027] FIG. 8 is a comparison of CoCr and PEEK heads against N.sub.2Vac cross-linked

[0028] UHMWPE.

[0029] FIG. 9 is a comparison of a ceramic Alumina, 25% ZnO.sub.2 Delta head against X3? UHMWPE for a 28 mm head.

[0030] FIGS. 10 and 11 are photographs of the UHMWPE bearing before and after wear testing with PEEK and CoCr heads respectively.

[0031] FIG. 12 are photographs of the CoCr, Delta and PEEK heads after testing.

[0032] FIG. 13 shows wear rates of scratched (using diamond indentor) CoCr, Delta and PEEK heads against X3? UHMWPE cups.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a hip simulator wear results with as-polished femoral heads. This figure shows that X3? UHMWPE cup in a CoCr-on-UHMWPE couple has a positive volumetric wear rate about 2.41 mm.sup.3/million cycles (Mc), while the X3? UHMWPE cup in the PEEK-on-X3? UHMWPE couple with a polished PEEK head is only 0.38 mm.sup.3/million cycles (Mc). The average wear rate of X3? UHMWPE cup in the PEEK-on-X3? against the as-polished PEEK femoral head is about 84% less than that against the as-polished CoCr femoral head. This difference in wear rate is statistically significant (Student's t-test, P=0.025). The wear rate of the PEEK head was not measurable using the gravimetric technique.

[0034] FIG. 2 shows hip simulator wear results with intentionally scratched femoral heads. The average wear rate of the highly crosslinked polyethylene cup against the scratched

[0035] PEEK head is about 1.82 mm.sup.3/million cycles (Mc) while the average wear rate of X3? UHMWPE cup against the scratched CoCr head is about 16.67 mm.sup.3/million cycles (Mc). This represents an 89% lower wear rate for the highly crosslinked polyethylene cup against the scratched PEEK head than that against the scratched CoCr head. This difference in the wear rate is statistically significant (Student's t-test, P=0.0002). In fact, the average wear rate of the highly crosslinked polyethylene cup against the scratched PEEK head is statistically insignificantly different from that against as-polished PEEK head (Student's t-test, P=0.20), which indicates that the PEEK-on-highly crosslinked polyethylene bearing couple is insensitive or immune to scratching of the PEEK head. In contrast, scratching of the CoCr head caused an almost 7 fold increase in the wear rate of the highly crosslinked polyethylene cup (Student's t-test, P=0.0009).

[0036] FIG. 3 shows white light microscopy of a typical X3?M UHMWPE cup prior to wear testing (unworn cup). Before the hip simulator wear test, machining marks are clearly seen. Surface peak height is about 5160 nm, valley depth about ?4758 nm and average roughness about 998 nm (Ra).

[0037] FIG. 4 shows white light microscopy of the worn surface of a X3? UHMWPE cup in the CoCr-on-UHMWPE couple with a polished CoCr head after 1.25 million cycles hip simulator wear testing. The machining marks are gone. Surface peak is 950 nm high, valley 1207 nm deep, and average roughness Ra=80 nm.

[0038] FIG. 5 is a white light microscopy of the worn surface of a X3? UHMWPE cup in the PEEK-on-UHMWPE couple with a polished PEEK head after 1.25 million cycles hip simulator wear testing. Machining marks are still visible. Surface peak is 1872 nm high, valley 2715 nm deep, and an average roughness Ra=335 nm.

[0039] FIG. 6 shows a photograph of an as-polished PEEK head before and after wear testing. No wear scar or roughening was found.

[0040] FIG. 7 shows a photograph of the intentionally scratched PEEK head before and after wear testing. All scratching marks are still clearly visible on the head after 1.25 million cycles of testing.

EXAMPLE 1

[0041] A 1.5 diameter pure PEEK extruded rod was purchased from McMaster with the brand name Quadrant Ketron?1000 (Reading, PA), and machined into 32 mm diameter femoral heads. The 32 mm PEEK heads were polished to an average surface roughness of Ra=20 nm. Three 32 mm PEEK heads were tested against three 32 mm sequentially crosslinked UHMWPE cups in a hip simulator under maximum load of 2450 N at 1.0 HZ in 50% diluted Alpha Calf serum lubricant. Three 32 mm CoCr heads against three 32 mm X3? UHMWPE cups were conducted in the same wear test as a control.

[0042] Wear results of the sequentially crosslinked polyethylene cup (X3) (about shore D 70) against as-polished CoCr (Vicher 450) and PEEK heads (about shore D 85) at 1.75 million cycles on the hip simulator are shown in FIG. 1. The X3? UHMWPE cup in a PEEK-on-UHMWPE wear couple had an average wear rate of about 0.38 mm.sup.3/million cycles (Mc), while the cup in CoCr-on-UHMWPE wear couple had an average wear rate of about 2.41 mm.sup.3/million cycles (Mc), which represents an 84% lower wear rate for the PEEK-on-UHMWPE couple. This difference is statistically significant (Student's t-test, P=0.025).

EXAMPLE 2

[0043] Everything was the same as in Example 1, except 32 mm PEEK heads were intentionally scratched and then wear tested against 32 mm X3? UHMWPE cups. White light microscopy showed that peak-to-valley height of the scratches was about 25 micron (m), which is much higher than the 3.5 micron for a CoCr head scratched in the same way. The wear results indicated that the scratched 32 mm PEEK heads articulating against 32 mm sX3? UHMWPE cups had an average wear rate of 1.82 mm.sup.3/Mc (FIG. 2). By comparison, the non-scratched CoCr-on-X3? UHMWPE pair showed a higher wear rate (2.41 mm.sup.3/Mc, see FIG. 1). A more direct comparison was to use scratched CoCr heads against X3? UHMWPE cups, which had an average wear rate of about 16.67 mm.sup.3/Mc, according to R. Lee, A. Essner, A. Wang, W. L Jaffe available online 2 Apr. 2009 Scratch and Wear Performance Of Prosthetic Femoral Head Components Against Crosslinked UHMWPE Sockets (Wear, 2009). This means that scratching the PEEK bearing surface does not significantly affect the wear of X3? UHMWPE part. This may be due to: [0044] 1. lower contact stress [0045] 2. self-polishing between PEEK and polyethylene, reducing harmful effect of scratching as often seen with metal surfaces

EXAMPLE 3

[0046] 3. less rigid and less sharp scratches on the PEEK head

[0047] Everything was the same as Example 1, except 40 mm PEEK heads were rotated against 44 mm X3? UHMWPE cups, which is a size mismatch done to simulate a non-conforming joint such as a knee joint. This mismatched PEEK-on-X3? UHMWPE pair did not have a measurable wear rate (gravimetric weight gain more than weight loss). In comparison, the wear rate of the perfectly matched 32 mm X3? UHMWPE cup against 32 mm CoCr head was measurable (2.41 mm.sup.3/Mc as shown in FIG. 1).

EXAMPLE 4

[0048] Everything was the same as in Example 1, except 32 mm PEEK heads were rotated against 32 mm X.sup.3? UHMWPE cups that were grafted by MPC (2-methacryloyloxyethyl phosphsrylcholine, a biocompatible phospholipid, as described by Toru Moro, et al in Nature Materials, published online: 24 Oct. 2004, p. 829-836). This pair showed no measurable wear.

EXAMPLE 5

[0049] PEEK-N2\Vac: 4.0 million cycle wear study on 28 mm PEEK components on UHMWPE irradiated at 3 MRad in nitrogen with less than 1% oxygen (N.sub.2\Vac), N2\Vac D size cups found a wear rate of 16.6 mm.sup.3/mc was measured (SD 1.8; n=7). For comparison, study (HIP231) tested 28 mm CoCr heads on N2\Vac cups for a wear rate of 30.0 mm.sup.3/mc at 3.0 million cycles (SD 0.022; n=2) This corresponds to a statistically significant reduction in wear of 45% as shown in FIG. 8 (p<0.05).

EXAMPLE 6

PEEK-X3

[0050] 5.0 million cycle wear study (HIP284) on 32 mm PEEK components on X3? UHMWPE D size cups, a wear rate of ?2.75 mm.sup.3/mc was measured (SD 1.86; n=3) as shown in FIG. 9. The wear rate of CoCr, Delta and PEEK/x3, Delta/X3 were taken from a previous study for 28 mm heads. Despite dynamically loaded and temperature compensated soaking controls, the X3? UHMWPE cup tested against a PEEK head did not show weight loss. For comparison, previously published wear rates for Delta ceramic on X3? UHMWPE cup (28 mm; n=3) are also shown in the chart (0.55 mm.sup.3/mc SD 0.58). Machining marks were also still visible at 3.5 million cycles on the X3? UHMWPE cups when tested against the PEEK head (FIG. 10) while machining marks were invisible at 0.75 mc when tested against CoCr heads (FIG. 11).

[0051] Machining marks as shown in FIG. 10 were still visible at 3.5 million cycles. As shown in FIG. 11 marks are no longer visible at 0.75 million cycle with CoCr heads due to the higher wear rate.

[0052] In this same study, three PEEK heads were scratched utilizing the previously established diamond indenter method (30N, spiral pattern). These heads showed significant damage of approximately 40 ?m PV (compared to 7.11 ?m for CoCr and 0.3 ?m for Delta) as shown in FIG. 12. These heads were then utilized for wear testing for 4.5 million cycles against X3? cups. Wear rates were ?3.1 mm.sup.3/mc after 4.5 million cycles (SD 1.827; n=3) for PEEK/X3 couples. At the same cycle count, this is not statistically different from the unscratched PEEK/X3? bearing (p=0.353). In comparison, scratched 28 mm CoCr components exhibited 19.6 mm.sup.3/mc wear rate (SD 0.5;n=2) and scratched 28 mm Delta components exhibited 0.58 mm3/mc wear rate (SD 0.43; n=2 in a previously published study as shown in FIG. 13.

[0053] CoCr and Delta data were taken from a previous study published as Lee, R. et al., Scratch and wear performance of prosthetic femoral head components against crosslinked UHMWPE sockets, Wear 267, pages 1915-1921, 2009.

[0054] Additionally, three 40 mm PEEK heads were tested against 44 mm F size X3inserts. This study was used to determine wear rates in a higher stress non conforming bearing situation. At 1.0 million cycles, wear rates for this bearing were 0.60 mm3/mc (SD 503).

[0055] PEEK head wear has not yet been quantitatively measured. Utilizing a PEEK head on N2\Vac cups shows a significant 45% reduction in wear. Wear rates were negative for PEEK heads on X3? cups. Wear rates were unchanged when the PEEK head was severely abraded. Wear rates remained near zero (but positive) when testing a non-conforming (40 mm PEEK head on 44 mm X3? cup) geometry. PEEK head wear will be assessed after testing is completed.

[0056] Pure PEEK on UHMWPE all polymer bearing system (soft on soft) has shown unexpected results such as lower wear rates than CoCr on UHMWPE, regardless whether the PEEK femoral head is scratched or not.

[0057] Other companies which supply PAEK are BASF, UltraPAEK, PEKEKK; Dupont, Ureton PEKK, Declar; OPM, Oxford Performance Materials, Inc. PEKK; Hoechst Celanese (Hostatec)PEEKK 5 and ICI (Vitrex), PEK and PEEK. Medical grade PEEK suppliers are ICI, Invibo, Solvay and Evonik.

[0058] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.