Improved prosthetic implants

Abstract

There is described an arthroplasty kit comprising a first joint prosthesis component (30) having a portion which is coated with pyrolytic carbon and a second joint prosthesis component (70) comprising a polyethylene portion.

Description

[0001] IMPROVED PROSTHETIC IMPLANTS

[0002] Field of the invention

[0003] The present invention in concerned with improved prosthetic implants, particularly with improved arthroplasty kits and methods of arthroplasty using same.

[0004] Background to the invention

[0005] Arthroplasty is a surgery to restore the function of a joint. The modern era of shoulder replacement (shoulder arthroplasty) began with the first generation of anatomical shoulder replacements pioneered by Charles Neer in 1953. The two main bones of the shoulder are the humerus (the bone of the upper arm) and the scapula (the shoulder blade). The scapula defines a number of anatomical features including the glenoid which is a shallow, concave, pear-shaped cavity located on the lateral aspect of the scapula (i.e. the outer side of the scapula, away from the midline of the body). Within the shoulder joint (the glenohumeral joint), the surface of the glenoid is covered by articulate cartilage which provides a low-friction surface, allowing smooth movement between the bones in the joint. Initial implants were used to treat fractures and were essentially a hemiarthroplasty, i.e. a replacement of the humerus humeral head with a metal monoblock anatomic component having a stem extending into the intramedullary space of the humerus. Subsequently, a total shoulder replacement was designed, again using a monoblock stemmed humeral component combined with a cemented polyethylene resurfacing of the glenoid.

[0006] There have been numerous refinements of both surgical technique and HDP (HDPE; high density polyethylene) over the last 60 years. Using the correct indication, implant survival rates of 87% at 15 years have been reported (Torchia ME, Cofield RH, Settergren CR. Total shoulder arthroplasty with the Neer prosthesis: long-term results. J Shoulder Elbow Surg. 1997 Nov-Dec;6(6):495-505. doi: PMID: 9437598; Trail IA, Nuttall D. The results of shoulder arthroplasty in patients with rheumatoid arthritis. J Bone Joint Surg Br. 2002 Nov;84(8):1121-5. doi: 10.1302 / 0301-620x.84b8.12695. PMID: 12463655.

[0007] Reverse shoulder arthroplasty (RSA) has also been developed (Grammont PM, Baulot E. Delta shoulder prosthesis for rotator cuff rupture. Orthopedics. 1993 Jan;16(l):65-8. doi: 10,3928 / 0147 -7447- 19930101-11. PMID: 8421661; Favard L, Levigne C, Nerot C, Gerber C, De Wilde L, Mole D. Reverse prostheses in arthropathies with cuff tear: are survivorship and function maintained over time? Clin Orthop Relat Res. 2011 Sep;469(9):2469-75. doi: 10.1007 / sll999-011-1833-y. PMID: 21384212; and is a surgical procedure in which the normal anatomy of the shoulder joint is reversed - a metal ball is attached to the glenoid and a plastic socket is attached to the humerus. This design change alters the biomechanics of the shoulder joint, allowing different muscles to take on the work of damaged or weakened muscles.

[0008] A number of factors affect polyethylene wear in anatomic shoulder replacement, including positioning and alignment of the polyethylene resurfacing of the glenoid, and the position of the humeral head. Terrier A et al. (Comparison of polyethylene wear in anatomical and reversed shoulder prostheses. J Bone Joint Surg Br. 2009 Jul;91(7):977-82. doi: 10.1302 / 0301-620X.91B7.21999. PMID: 19567857) used in vivo recorded data to simulate activities of daily living and determined that after one year of use, the volumetric polyethylene wear (against a cobalt-chromium (CoCr) alloy humeral head) was 8.4 mmA3 for the anatomical prosthesis and 44.6 mmA3 for the reversed version. They also noted that the wear was abrasive particularly in the reverse designs. Thus, there was highly significant wear, particularly for the reverse prostheses, limiting the lifespan of the implant with an inevitable impact on patients.

[0009] As stated in Schwartsmann CR et al. (NEW BEARING SURFACES IN TOTAL HIP REPLACEMENT. Rev Bras Ortop. 2015 Dec 6;47(2):154-9. doi: i iO16 / S2255;4971115j30079- . PMID: 27042514; PMCID: PMC479937?), "Although polyethylene failure may occur because of external fracturing or wear, the most common type of polyethylene failure is internal wear at the metal-plastic interface." and "The biggest advantage of using metal-to-metal surfaces in total hip arthroplasty is the reduction in wear. A conventional polyethylene acetabulum has an average wear rate of 0.1 mm to 0.2 mm per year. Metal- to-metal joints have wear rates that may be 40 to 100 times lower".

[0010] Pyrolytic carbon (Ratner, Buddy D. (2004). Pyrolytic carbon. In Biomaterials science: an introduction to materials in medicine. Academic Press, p. 171-180. ISBN 0-12-582463-7), also referred to as pyrocarbon, PyC and PYC, is a high-strength, low-friction, and biocompatible form of graphite.

[0011] Shoulder hemiarthroplasty using a humerus head coated in pyrolytic carbon is known (Park CN, Zhang GX, Chang J, Zeng SL, Meyer LE, Hurley ET, Hatzidakis AM, Anakwenze O, Klifto CS. Pyrocarbon hemiarthroplasty of the shoulder: a systematic review and meta-analysis of clinical results. J Shoulder Elbow Surg. 2023 Jun;32(6):1323-1332. doi: 10.1016 / i.jse.2022.12.005. Epub 2023 Jan 4. PMID:

[0012] Ramirez-Martinez, I. et al. (2020. Journal of the Mechanical Behavior of Biomedical Materials 103, 103553; PMID: 31790849) is an in vitro shoulder simulator study of the wear behaviour of polyethylene glenoid inserts against pyrocarbon humeral heads (i.e. a conventional anatomical arthroplasty arrangement). It concludes that (a) wear rates were similar to well-proven CoCr humeral heads on UHMWPE (ultra-high molecular weight polyethylene) shoulder arthroplasties, and (b) there is little clinical cost-benefit in the use of a pyrocarbon on UHMWPE shoulder implant. Thus, Ramirez-Martinez teaches against arthroplasty using a pyrocarbon (PyC) coated component against a polyethylene (particularly an ultra-high molecular weight polyethylene) component.

[0013] Summary of the Invention

[0014] The present inventor has now found that despite the teachings in the Ramirez-Martinez paper, wear of polyethylene (UHMWPE) against pyrocarbon is significantly reduced as compared to wear of the same polyethylene against CoCr. Thus, arthroplasty using polyethylene and pyrolytic carbon components (i.e. opposed polyethylene and pyrolytic carbon surfaces) shows a significant improvement as compared to the same arthroplasty using polyethylene and CoCr components (i.e. opposed polyethylene and CoCr surfaces).

[0015] Thus, for example, shoulder arthroplasty using a humeral component comprising a cup-shaped polyethylene insert and a glenoid component comprising a glenosphere having a head portion coated with pyrolytic carbon (PyC) results in significantly improved (reduced) wear (at the pyrolytic carbonpolyethylene interface) and thus improved (extended) implant lifespan as compared to the CoCr- polyethylene equivalent. This is a significant improvement and mitigates issues encountered to date with existing reverse shoulder arthroplasty techniques.

[0016] This determination that a joint arthroplasty kit comprising a polyethylene component which in-use articulates against a pyrocarbon-coated component results in improved (reduced) wear is applicable to both anatomical and reverse arthroplasty kits.

[0017] Thus, according to a first aspect of the present invention there is provided an arthroplasty kit comprising:

[0018] (i) a first joint prosthesis component for in-use attachment to a first bone of a joint, the first joint prosthesis component having a portion which is coated with pyrolytic carbon, and

[0019] (ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, the second joint prosthesis component comprising a polyethylene portion. The first joint prosthesis component can also be referred to as being the "first joint component", e.g. as a first joint component for in-use attachment to a first bone of a joint, the first joint component having a portion which is coated with pyrolytic carbon. The second joint prosthesis component can also be referred to as being the "second joint component", e.g. a second joint component for in-use attachment to a second bone of the joint, the second joint component comprising a polyethylene portion.

[0020] In certain embodiments, the portion of the first joint prosthesis component which is coated with pyrolytic carbon and the polyethylene portion of the second joint prosthesis component in-use define articular surfaces of the joint. The portion of the first joint prosthesis component which is coated with pyrolytic carbon and the second joint prosthesis component comprising a polyethylene portion may in-use define articular surfaces of the joint. In particular, they can in-use define opposing articular surfaces. Thus, they can be said to in-use articulate against one another. Thus, they can be said to be configured to in-use articulate against one another. Thus, they can be described as being configured to define articulating surfaces / opposing articular surfaces. Similarly, they can be described as being arranged or dimensioned to define articulating surfaces / opposing articular surfaces.

[0021] In certain embodiments, the portion of the first joint prosthesis component which is coated with pyrolytic carbon is a head portion.

[0022] In certain embodiments, the second joint prosthesis component is a polyethylene joint resurfacing component. In certain embodiments, the second joint prosthesis component is a polyethylene joint socket resurfacing component.

[0023] The polyethylene may be selected from the group consisting of high-density polyethylene, ultra-high molecular weight polyethylene, cross-linked ultra-high molecular weight polyethylene, highly crosslinked ultra-high molecular weight polyethylene, and vitamin E incorporated highly crosslinked ultra-high molecular weight polyethylene. Preferably, the polyethylene is ultra-high molecular weight polyethylene.

[0024] In certain embodiments, the polyethylene is a high-density polyethylene joint socket resurfacing component. In certain embodiments, it is an ultra-high molecular weight polyethylene (UHMWPE) (Kurtz, S.M. (2015) UHMWPE Biomaterials Handbook: Ultra High Molecular Weight Polyethylene in Total Joint Replacement and Medical Devices. 3rd Edition, Elsevier, Amsterdam, ISBN: 9780323354011; ISO 5834-2:2019 Implants for surgery Ultra-high-molecular-weight polyethylene). In certain embodiments, it is a cross-linked ultra-high molecular weight polyethylene (XLPE). XLPE can be an UHMWPE that has been irradiated with at least 50 kGy of gamma (or beta) or electron beam radiation. Other suitable polyethylenes include highly crosslinked (HXLPE) (highly cross-linked UHMWPE), and vitamin E incorporated HXLPE (VEPE).

[0025] In certain embodiments, the polyethylene is cross-linked. For example, in certain embodiments it is a cross-linked high molecular weight polyethylene. Polyethylene cross-linking can be performed by a number of techniques, for example irradiation cross-linking (PE-Xc). Other cross-linking techniques include peroxide cross-linking (PE-Xa), silane cross-linking (PE-Xb), and azo cross-linking (PE-Xd).

[0026] In certain embodiments, the first joint prosthesis component portion which is coated with pyrolytic carbon is a head portion comprising cobalt-chrome alloy.

[0027] In certain embodiments, the first joint prosthesis component has a head portion which is coated with pyrolytic carbon. In certain embodiments, the second joint prosthesis component is a polyethylene joint socket resurfacing component. In certain embodiments, the first joint prosthesis component has a head portion which is coated with pyrolytic carbon and the second joint prosthesis component is a polyethylene joint socket resurfacing component.

[0028] In certain embodiments, the arthroplasty kit is a reverse shoulder arthroplasty kit. Preferably, the arthroplasty kit is a reverse shoulder arthroplasty kit. In certain embodiments, the first joint prosthesis component portion which is coated with pyrolytic carbon is a glenosphere, preferably a head portion of a glenosphere. In certain embodiments, the first joint prosthesis component comprises a metaglene and a glenosphere. In certain embodiments, the second joint prosthesis component comprises a polyethylene insert. In certain embodiments, the polyethylene insert is a polyethylene insert for a humeral stem (this can be referred to as being a humeral component). As detailed in the experiments section below, results obtained show significantly improved (reduced) wear with the pyrocarbon- UHMWPE components as compared to the CoCr-UHMWPE components, and thus improved (extended) implant lifespan.

[0029] The arthroplasty kit may be a reverse shoulder arthroplasty kit comprising:

[0030] (i) a first joint prosthesis component for in-use attachment to a first bone of a joint, the first joint prosthesis component having a portion which is coated with pyrolytic carbon, and (ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, the second joint prosthesis component comprising a polyethylene portion, wherein the first joint prosthesis component comprises a glenosphere, and wherein the portion of the first joint prosthesis component which is coated with pyrolytic carbon is a head portion of the glenosphere.

[0031] The joint may be the shoulder joint. The joint may be the glenohumeral joint. The first bone of the joint may be the scapula. The second bone of the joint may be the humerus. The first joint prosthesis component may comprise a metaglene and a glenosphere. The first joint prosthesis component may be a glenoid component. The second joint prosthesis component may be a humeral component. The polyethylene portion may be a polyethylene insert. The second joint prosthesis component may comprise a polyethylene insert. The second joint prosthesis component may comprise an ultra-high molecular weight polyethylene insert.

[0032] The arthroplasty kit may be a reverse shoulder arthroplasty kit comprising:

[0033] (i) a first joint prosthesis component for in-use attachment to a first bone of a joint, wherein the first joint prosthesis component is a glenoid component comprising a glenosphere having a head portion which is coated with pyrolytic carbon, and

[0034] (ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, wherein the second joint prosthesis component is a humeral component comprising a polyethylene insert.

[0035] The glenoid component may comprise a metaglene and a glenosphere. The polyethylene insert may be a polyethylene insert for a humeral stem. The polyethylene insert may be a humeral cup. The humeral cup may be fabricated from ultra-high molecular weight polyethylene. The humeral component may comprise a humeral stem, a metal plate and a humeral cup. The humeral component may comprise a humeral stem, a metal plate and a humeral cup fabricated from ultra-high molecular weight polyethylene.

[0036] In certain embodiments, the polyethylene insert is cup-shaped. The polyethylene insert may be a cupshaped polyethylene insert. The polyethylene insert may be a humeral cup. The polyethylene insert is preferably an ultra-high molecular weight polyethylene insert.

[0037] In certain embodiments, the arthroplasty kit is other than (i.e. is not / excludes) an anatomical shoulder arthroplasty kit. The arthroplasty kit is preferably a reverse shoulder arthroplasty kit. In certain embodiments, the arthroplasty kit is an anatomical shoulder arthroplasty kit. Thus, in certain embodiments, the first joint prosthesis component portion coated with pyrolytic carbon comprises a humeral head coated with pyrolytic carbon. In certain embodiments, the second joint prosthesis component is a polyethylene glenoid resurfacing component. In certain embodiments, the arthroplasty kit comprises a humeral head coated with pyrolytic carbon and a polyethylene glenoid resurfacing component.

[0038] Thus, the arthroplasty kit can be for use in a method of shoulder arthroplasty.

[0039] The first joint prosthesis component having a portion which is coated with pyrolytic carbon is coated with pyrolytic carbon on the surface which will in-use interface with (i.e. abut) the second joint prosthesis component.

[0040] In certain embodiments, the arthroplasty kit is an elbow arthroplasty kit. In certain embodiments, it is a total elbow arthroplasty (TEA) kit. In certain embodiments, the first joint prosthesis component is a humeral component, and the second joint prosthesis component is an ulnar component. In other embodiments, the first joint prosthesis component is an ulnar component, and the second joint prosthesis component is a humeral component.

[0041] In certain embodiments, the arthroplasty kit is a wrist arthroplasty kit. In certain embodiments, the first joint prosthesis component is a radius component (i.e. for insertion into the radius, i.e. the radius of the forearm), and the second joint prosthesis component is a carpal component. In other embodiments, the first joint prosthesis component is a carpal component, and the second joint prosthesis component is a radius component (i.e. for insertion into the radius, i.e. the radius of the forearm).

[0042] In certain embodiments, the arthroplasty kit is a hand arthroplasty kit. In certain embodiments, it is a total joint replacement arthroplasty kit. In certain embodiments, it is a metacarpophalangeal (MCP) arthroplasty kit, carpometacarpal (CMC) arthroplasty kit, or proximal interphalangeal (PIP) arthroplasty kit.

[0043] In certain embodiments, the first joint prosthesis component has a surface (i.e. defines a surface) that is adapted to (e.g. is configured to / is dimensioned to) in-use interface with the second joint prosthesis component. In certain embodiments, the first joint prosthesis component further comprises (i.e. defines) a boneengagement surface that is configured (e.g. is dimensioned) to in-use engage with the first bone.

[0044] In certain embodiments, the second joint prosthesis component comprises (i.e. defines) a bone engagement surface that is configured (e.g. is adapted to / is dimensioned) to in-use engage with the second bone.

[0045] Thus, the first and second joint prosthesis components can be described as being configured to / adapted to / dimensioned to articulate with one another.

[0046] In certain embodiments, the joint is a ball-and-socket type joint.

[0047] The first joint prosthesis component can include any stem (e.g., short stem, long stem, intermediate stem, etc.), intramedullary rod, keel, sleeve, adapter, augment, etc., that has any size, shape, feature, morphology, etc., that is described or contemplated herein, as well as any a stem (short stems, long stems, etc.), intramedullary rod, keel, sleeve, adapter, augment, etc., that has any size, shape, feature, morphology, etc., that is not described or contemplated herein.

[0048] In a reverse shoulder arthroplasty kit, the second joint prosthesis component may be a humeral component comprising a humeral stem. The humeral stem may be any stem (e.g., short stem, long stem, intermediate stem, etc.), intramedullary rod, keel, sleeve, adapter, augment, etc., that has any size, shape, feature, morphology, etc., that is described or contemplated herein, as well as any a stem (short stems, long stems, etc.), intramedullary rod, keel, sleeve, adapter, augment, etc., that has any size, shape, feature, morphology, etc., that is not described or contemplated herein.

[0049] The term "joint prosthesis component bone-engagement surface" (and its analogs) encompasses any prosthesis that comprises at least one bone-engagement surface (or at least one bone cement engagement surface, or at least one bone augment material engagement surface, etc.), or that is coupled to or supports (either directly or indirectly) another component of the prosthesis that comprises the at least one bone-engagement surface (or the at least one bone cement engagement surface, or the at least one bone augment material engagement surface, etc.) that is implantable within, adjacent, or near a bone of a patient or an animal. Also provided according to a second aspect of the present invention is a method of arthroplasty using an arthroplasty kit according to the first aspect of the present invention, wherein the method comprises:

[0050] (A) securing the first joint prosthesis component to a first bone of the joint; and

[0051] (B) securing the second joint prosthesis component to a second bone of the joint.

[0052] In certain embodiments, the first joint prosthesis component defines a bone-engagement surface which is secured with the first bone. In certain embodiments, the bone-engagement surface of the first joint prosthesis component is secured with a resected surface of the first bone. In certain embodiments, the first bone is resected prior to the step of securing the bone-engagement surface of the joint prosthesis with the resected surface of the first bone.

[0053] In certain embodiments, the second joint prosthesis component defines a bone engagement surface which is engaged with the second bone.

[0054] In certain embodiments, the method is a method of shoulder arthroplasty or reverse shoulder arthroplasty. Preferably, the method is a method of reverse shoulder arthroplasty. The method may be a method of reverse shoulder arthroplasty using a reverse shoulder arthroplasty kit according to the first aspect of the invention. In other embodiments, it is a method of wrist arthroplasty. In other embodiments, it is a method of elbow arthroplasty. In certain embodiments, the method is a method of hand arthroplasty. In certain embodiments, it is a method of metacarpophalangeal (MCP) joint arthroplasty, carpometacarpal (CMC) joint arthroplasty, or proximal interphalangeal (PIP) joint arthroplasty.

[0055] In certain embodiments, it is a method of total joint replacement.

[0056] The bone engagement surface of the joint prosthesis can be secured with the resected surface of the first bone by conventional means, e.g. use of bone cement. Bone cements include acrylic bone cement, e.g. as per the standard ASTM-F451 (American Society for Testing and Materials, Pennsylvania, USA; www.astm.org). Cements include, but are not limited to, polymethylmethacrylate (Webb JC, Spencer RF. The role of polymethylmethacrylate bone cement in modern orthopaedic surgery. J Bone Joint Surg Br. 2007 Jul;89(7):851-7. doi: PMID: 17673574). Other bone cements and securing agents / fixation agents will be readily apparent to one of ordinary skill in the art. The method of arthroplasty of the present invention can also be performed using an anatomical shoulder arthroplasty kit. Thus, in certain embodiments of the method, the first joint prosthesis component portion coated with pyrolytic carbon comprises a humeral head coated with pyrolytic carbon. In certain embodiments of the method, the second joint prosthesis component is a polyethylene glenoid resurfacing component. In certain embodiments of the method, the arthroplasty kit comprises a humeral head coated with pyrolytic carbon and a polyethylene glenoid resurfacing component. Unless the context dictates otherwise, the optional aspects of the arthroplasty kit of the present invention can apply mutatis mutandis to the anatomical shoulder arthroplasty kit used in the method of arthroplasty.

[0057] Thus, the method can also be described as a method of arthroplasty using an anatomical shoulder arthroplasty kit, the anatomical shoulder arthroplasty kit comprising:

[0058] (i) a first joint prosthesis component for in-use attachment to a first bone of a joint, the first joint prosthesis component having a portion which is coated with pyrolytic carbon, and

[0059] (ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, the second joint prosthesis component comprising a polyethylene portion, wherein the joint prosthesis is a humeral head coated with pyrolytic carbon and wherein the second joint prosthesis component is a glenoid resurfacing component, wherein the method comprises:

[0060] (A) securing the first joint prosthesis component to a first bone of the joint; and

[0061] (B) securing the second joint prosthesis component to a second bone of the joint.

[0062] In certain embodiments, the first joint prosthesis component defines a bone-engagement surface which is secured with the first bone. In certain embodiments, the bone-engagement surface of the first joint prosthesis component is secured with a resected surface of the first bone. In certain embodiments, the first bone is resected prior to the step of securing the bone-engagement surface of the joint prosthesis with the resected surface of the first bone.

[0063] In certain embodiments, the second joint prosthesis component defines a bone engagement surface which is engaged with the second bone.

[0064] The method of arthroplasty may be performed using a reverse shoulder arthroplasty kit. Thus, the first joint prosthesis component may comprise a glenosphere having a head portion coated with pyrolytic carbon. The second joint prosthesis component may comprise a polyethylene insert. Unless the context dictates otherwise, the optional aspects of the arthroplasty kit of the first aspect of the present invention can apply mutatis mutandis to the arthroplasty kit used in the method of arthroplasty.

[0065] Thus, the method can also be described as a method of arthroplasty using a reverse shoulder arthroplasty kit, the reverse shoulder arthroplasty kit comprising:

[0066] (i) a first joint prosthesis component for in-use attachment to a first bone of a joint, the first joint prosthesis component having a portion which is coated with pyrolytic carbon, and

[0067] (ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, the second joint prosthesis component comprising a polyethylene portion, wherein the first joint prosthesis component comprises a glenosphere, and wherein the portion of the first joint prosthesis component which is coated with pyrolytic carbon is a head portion of the glenosphere, wherein the method comprises:

[0068] (A) securing the first joint prosthesis component to a first bone of the joint; and

[0069] (B) securing the second joint prosthesis component to a second bone of the joint.

[0070] The second joint prosthesis component may comprise a polyethylene insert for a humeral stem.

[0071] The invention will be further apparent from the following description and drawings which show by way of example only forms of the present invention.

[0072] Drawings

[0073] Figure 1 shows average wear factor (mmA3 / Nm) of the UHMWPE pins which articulated against the pyrocarbon discs and the CoCr discs (** p < 0.01);

[0074] Figure 2 shows average phospholipid concentration from the pyrocarbon discs and the CoCr discs (* p < 0.05);

[0075] Figure 3 shows average area of transferred UHMWPE on the surface of pyrocarbon (PyC) discs and CoCr discs (*** p < 0.001);

[0076] Figures 4A-4D are inverted photos (A,B) and inverted confocal images (C,D) of CoCr (A,C) and pyrocarbon (B,D) surfaces respectively obtained after 5 million cycles of wear testing;

[0077] Figure 5A shows the number of UHMWPE particles per microlitre of lubricant for pyrocarbon and CoCr (*** p < 0.001); Figure 5B shows the average area of UHMWPE particles for pyrocarbon and CoCr (*** p < 0.001);

[0078] Figure 6A shows an inverted visualisation of UHMWPE wear particles in CoCr and lubricant prepared in agarose gel after the last 500,000 cycles of wear testing;

[0079] Figure 6B shows an inverted visualisation of UHMWPE wear particles in pyrocarbon lubricant prepared in agarose gel after the last 500,000 cycles of wear testing; and

[0080] Figure 7 shows a reverse shoulder arthroplasty kit.

[0081] Specific Embodiments

[0082] A fully and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification. Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention.

[0083] It will be apparent to those of ordinary skill in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention. For instance, features described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.

[0084] Other objects, features, and aspects of the present invention are disclosed in the remainder of the specification. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

[0085] Repeat use of reference symbols in the present specification and drawings is intended to represent the same or analogous features or elements.

[0086] Experiments

[0087] Summary

[0088] In order to investigate the wear of pyrocarbon against an ultra-high molecular weight polyethylene (UHMWPE), a 50-station, clinically validated wear screening machine was used. Half the stations tested UHMWPE pins against pyrocarbon discs, and half the stations tested UHMWPE pins against cobalt chromium (CoCr) discs. The test rig ran at 1Hz, the nominal contact stress was 2.07MPa, and testing ran to 5 million cycles. A biomimetic lubricant was used, and was replaced every 500,000 cycles.

[0089] After 5 million cycles of wear testing, average wear factors of 1.62 x 10A-6 mmA3 / Nm and 2.15 x 10A- 6 mmA3 / Nm were calculated for the UHMWPE test pins of the pyrocarbon group and CoCr group, respectively. The difference between the wear factors was statistically different, p < 0.01. Therefore, it has been shown that the use of a pyrocarbon counterface results in a statistically significant reduction in wear of UHMWPE compared to a CoCr counterface.

[0090] Materials and Methods

[0091] A 50-station Circularly Translating Pin-on-Disc (Super-CTPOD) wear screening machine was used for the wear tests (Saikko V. Proc Inst Meeh Eng H. 2005 Sep;219(5):309-18. doi: 10.1243 / 095441105X34301. PMID: 16225147). The Super-CTPOD has been shown to provide clinically relevant wear rates when testing UHMWPE (Harsha AP et al. Proc Inst Meeh Eng H. 2013 May;227(5):600-8. doi: 10.1177 / 0954411913479528. PMID: 23637270.; Saikko, supra).

[0092] The Super-CTPOD and its working principles are described in Kandemir G et al. (J Meeh Behav Biomed Mater. 2020 Dec;112:104067. doi: 10.1016 / j.jmbbm.2020.104067. PMID: 32905920)

[0093] UHMWPE (International Standards Organisation. (2019). ISO 5834-2:2019 Implants for surgery Ultra- high-molecular-weight polyethylene Part 2: Moulded forms) pins of nominal size 9mm diameter and 12mm long were used as test samples. At the articulation, the diameter was reduced to 6.6mm. The load applied was 70.7N, which therefore corresponded to a nominal contact stress of 2.07MPa. This value was selected to fit within the range given by the ASTM standard associated with wear testing of biopolymers, ASTM F732-17 (American Society for Testing and Materials, 2017). The Super-CTPOD operated at 1Hz, and the wear track consisted of an ellipse of 12 x 10mm, giving a sliding distance per cycle of 34.6mm. Testing ran to 5 million cycles. Additional UHMWPE pin samples also acted as 'controls' to account for lubricant uptake. Twenty-five pins were articulated against CoCr discs, of nominal 25mm diameter. A further 24 pins were articulated against similar CoCr discs, but which had a 2mm thick by 23mm diameter pyrocarbon disc glued to the surface. In this way, two articulations, one UHMWPE rubbing against CoCr, the other UHMWPE rubbing against pyrocarbon, were created. Prior to wear testing, the surface roughness of all pins and discs were measured using a Zygo NewView 5000 (Zygo Corporation, CT, non-contacting profilometer (Kandemir G et al. 2020, supra). Prior to testing and at the end of testing, pins were weighed using a Kern ABT 220-5DM balance with a resolution of 10 pg (Kern & Sohn GmbH; www. ; Kandemir G et al. 2020, supra). This was different to a typical wear test, where weighting intervals are around every 500,000 cycles (Kandemir G et al. 2020, supra). Instead, as pyrocarbon seems to favour the adsorption of phospholipids and thus contributes to its boundary lubricating properties (Impergre A et al. Biotribology, 33-34, 2023, 100237, doi: 10.1016 / j.biotri.2023.100237), so the decision was made not to clean and weigh the test pins on a regular basis. Instead, the lubricant was removed at every 500,000 cycles and then stored in a refrigerator at 4 DegC; each test chamber was then refilled with fresh lubricant. It was decided not to weigh the discs before and after testing as the effects of the glue in terms of variable fluid uptake were considered too problematic. Moreover, the focus was on the wear of the polyethylene. However, measurements of surface roughness of the discs were undertaken at the start of testing and following a phospholipid-based assessment of the surfaces.

[0094] From the gravimetric changes, a wear factor (k, units mmA3 / Nm) was calculated for the UHMWPE pins which articulated against the pyrocarbon discs and those which articulated against the CoCr discs. The equation used was: k = V / LD where V is the volume of material lost (mm3), L is the load (N), and D is the sliding distance (m). The volume of material lost was determined from the mass loss and taking the density of UHMWPE as 0.00093 g / mmA3. The 5 million cycles total test duration was equivalent to 173,500 m. Statistical tests were undertaken on the wear and roughness data, using a t-test with a 95% confidence interval and 0.05 significance.

[0095] The lubricant used for the wear testing was intended to reproduce the structure and chemical composition of healthy synovial fluid. Further details and the manufacturing method are detailed in Sava MM et al. (Comput Methods Biomech Biomed Engin. 2013;16 Suppl 1:216-8. doi: 10.1080 / 10255842.2013.815866. PMID: 23923915).

[0096] After 5 million cycles of wear testing, all of the test discs were assessed. First, the discs were placed in 6-well plates, immersed in PBS and slowly agitated on a Thermo Scientific Digital Rockers (thermofisher.com; catalog number: 88882001) type device to remove any trace of lubricant not attached to the surface. Afterwards the quantity of phospholipids adsorbed onto the surfaces of the pyrocarbon discs, and the CoCr discs, was assessed. For this, the rubbing surface of the discs was immersed twice in 5 ml of ethanol to remove adsorbed phospholipids. To have better sensitivity for the detection of small quantities of phospholipids, the washing solutions of three samples of the same disc material were pooled. Thus, eight pyrocarbon and eight CoCr lipid-enriched ethanol solutions were obtained. The 16 lipid-enriched ethanol solutions were evaporated under a flow of dry nitrogen at room temperature and then redissolved in 1ml chloroform (solution 1) and quantification was done according to the Stewart method (Stewart JC. Colorimetric determination of phospholipids with ammonium ferrothiocyanate. Anal Biochem. 1980 May l;104(l):10-4. doi: 10.1016 / 0003- 2697(80)90269-9. PMID: 6892980). Briefly a ferrothiocyanate solution consisting of a mixture of ferric chloride hexahydrate 0.1 M and ammonium thiocyanate 0.4 M was prepared in distilled water (solution 2). One mL of solution 2 was added to 1 mL of solution 1 and the mixture was stirred for 30 seconds to promote the formation of the complex between the phosphate group of the phospholipids and the metal ions present in the ferrothiocyanate solution. The mixture was centrifuged for 10 minutes at 300 x g s at room temperature. Two phases were obtained and the chloroformic phase, containing the phospholipid-ferrothiocyanate complex, was recovered and the absorbance was measured at 488 nm using a Shimadzu UV-2550PC UV-Vis Spectrophotometer (Shimadzu Corporation; www.shimadzu.com).

[0097] Secondly, confocal fluorescence imaging was used to quantify the amount of UHMWPE attached to the pyrocarbon and CoCr disks, as well as the wear particles present in the lubricant. Disc surfaces were visualized after lipid extraction using a Zeiss Axio microscope (Zeiss Group; www BSjxoni) with confocal head, type LSM700, and visualizations were performed with 555nm lasers and the LD EC Epiplan-Neofluar 50x / 0.55 DIC M27 objective (df=9.1mm) following the protocol of Impergre A et al. (Biotribology, Volume 18, 2019, 100091. doi: 10.1016 / j. biotri.2019.100091). To analyze the entire surface of the CoCr and pyrocarbon disks, it was necessary to take 16x10 images for each sample with the x50 objective and x0.5 digital zoom (Zeiss ZEN software).

[0098] Lubricant from the last 500,000 cycles of the wear test was combined into an agarose gel (4% Thermo Scientific TopVision Low Melting Point Agarose gel (Thermo Fisher; www.thermofisher.com)) in a 1:5 (vokvol) ratio. Agarose and lubricant were stirred on a magnetic rotary shaker for 2 min at 70 DegC, then 1 mm-thick, 100 mm-diameter cylinders were cast at room temperature. Five confocal images were taken on each cylinder using the 555nm laser and x50 objective.

[0099] All confocal microscopy images were analyzed using ImageJ software (j agej.net; github.com / imagej / lmageJ; Schneider, C. A. et al. Nature Methods, 9(7), 671-675. doi:10.1038 / nmeth.2089) with the Threshold option followed by the Analyse Particles option. Statistical analysis was carried out on all pyrocarbon and CoCr samples using Excel software and the T.TEST statistical test.

[0100] Results At the end of the wear test, the UHMWPE pins which articulated against the pyrocarbon discs had a wear factor of 1.62 x 10A-6 mmA3 / Nm; the UHMWPE pins which articulated against the CoCr discs had a wear factor of 2.15 x 10A-6 mmA3 / Nm (figure 1). This was a statistically significant difference (p < 0.01). In particular, the UHMWPE pins rubbing against pyrocarbon discs had a statistically significant reduced wear, compare with the UHMWPE pins rubbing against CoCr discs.

[0101] The initial average roughness of the pyrocarbon discs was 0.015 pm Sa (standard deviation 0.002 pm Sa). The initial average roughness of the CoCr discs was 0.011 pm Sa (standard deviation 0.004 pm Sa). This was statistically different (p<0.0001). At the end of the 5 million cycle wear test of both the pyrocarbon and CoCr discs, the average roughness of the pyrocarbon discs showed a statistically significant smaller increase in roughness as compared to the CoCr discs. Specifically, at the end of the 5 million cycle wear test, the average roughness of the pyrocarbon discs was 0.066 pm Sa (standard deviation 0.017 pm Sa), and the average roughness of the CoCr discs was 0.294 pm Sa (standard deviation 0.117 pm Sa). These were statistically different (p<0.001).

[0102] The initial average roughness of the UHMWPE pins which articulated against the pyrocarbon discs was 0.257 pm Sa (standard deviation 0.040 pm Sa). The initial average roughness of the UHMWPE pins which articulated against the CoCr discs was 0.259 pm Sa (standard deviation 0.025 pm Sa). At the end of the 5 million cycle wear test of UHMWPE pins, the average roughness of the UHMWPE pins which articulated against the pyrocarbon discs showed a statistically significant improvement as compared to that of the UHMWPE pins which articulated against the CoCr discs.

[0103] Unloaded control pins, 2 for each group, were used to account for the lubricant uptake. The average weight change of the control pins in the 'pyrocarbon' group was 0.37mg ± 0.15mg; that in the 'CoCr1group was 0.38mg ± 0.16mg. These were not statistically different. These values were considered in the weight loss calculations. For completeness, the average weight loss of the pyrocarbon test pins was 14.8mg (range 9.4 - 27.1mg); that for the CoCr pins was 20.7mg (range 9.8 - 39.5mg).

[0104] Measurements of the concentration of phospholipids on the two bearing surfaces showed that there were more phospholipids on the pyrocarbon discs than the CoCr discs (figure 2).

[0105] Far less UHMWPE was attached to the pyrocarbon discs than to the UHMWPE discs. This is shown in terms of the average area of transferred UHMWPE on the surface of pyrocarbon discs compared with CoCr discs (figure 3). Visual images of the wear tracks from a CoCr disc compared to a wear track on a pyrocarbon disc is shown in Figure 4 A and B respectively. The comparative reconstruction of a CoCr surface versus a pyrocarbon surface is shown in Figure 4 C and D respectively. Overall, the CoCr surface shows greater UHMWPE transfer than the pyrocarbon surface.

[0106] As can be seen from Figures 5A and 5B, far fewer UHMWPE particles were found in the lubricant which had UHMWPE pins rubbing against pyrocarbon than in lubricant which had UHMWPE pins rubbing against CoCr (Figure 5).

[0107] Figures 6A and 6B are typical images of UHMWPE particles from CoCr and pyrocarbon lubricants. On these images, many more particles were observed in the CoCr lubricant (Figure 6A) compared with the pyrocarbon lubricant (Figure 6B).

[0108] Conclusions

[0109] After 5 million cycles of wear testing, average wear factors of 1.62 x 10A-6 mmA3 / Nm and 2.15 x 10A- 6 mmA3 / Nm were calculated for the UHMWPE test pins of the pyrocarbon group and CoCr group, respectively. The difference between the wear factors was statistically different, p < 0.01. Therefore, it has been shown that the use of a pyrocarbon counterface results in a statistically significant reduction in wear of UHMWPE compared to a CoCr counterface.

[0110] The average initial roughness of the pyrocarbon discs was 0.015pm Sa, and that of the CoCr discs was 0.011pm Sa (p<0.001). Therefore, the pyrocarbon discs were initially rougher than the CoCr discs. After 5 million cycles of wear testing, the average roughness of the pyrocarbon discs was 0.066 pm Sa, and that of the CoCr discs was 0.294 pm Sa (p<0.001). Both materials had increased in roughness from the average initial values of 0.015pm and 0.011pm Sa respectively. However, the increase in roughness of the CoCr discs was far greater than that of the pyrocarbon discs.

[0111] Figures 3 and 4 (C and D) showed that there is less adhesive wear of UHMWPE when articulated against a pyrocarbon counterface, than when articulated against a CoCr counterface. Therefore, pyrocarbon is associated with less adhesive wear of UHMWPE than CoCr.

[0112] Analysis of the discs at the end of testing showed greater adherence of phospholipids on pyrocarbon discs than CoCr discs. It was also observed that far less UHMWPE was attached to the pyrocarbon discs than to the CoCr discs. Therefore, this evidence also suggests that pyrocarbon surfaces are associated with reduced adhesive wear of UHMWPE compared with CoCr surfaces. Without wishing to be bound by theory, this may be due to increased adsorption of phospholipids on the pyrocarbon surface, which reduces adhesive wear of UHMWPE. On the CoCr surface, higher roughness and a greater quantity of UHMWPE was observed, which can be linked to greater adhesive wear of UHMWPE. The higher roughness of the CoCr surface is likely to accelerate the wear of UHMWPE compared to the pyrocarbon surface.

[0113] Arthroplasty Kits

[0114] In one embodiment, a reverse shoulder arthroplasty kit comprises a humeral component comprising a cup-shaped polyethylene insert and a glenoid component comprising a glenosphere having a head portion coated with pyrolytic carbon.

[0115] In one embodiment, an anatomical shoulder arthroplasty kit comprises a humeral head coated with pyrolytic carbon and a polyethylene glenoid resurfacing component.

[0116] In one embodiment, a reverse shoulder arthroplasty kit comprises a humeral component comprising a cup-shaped portion coated with pyrolytic carbon, and a glenoid component comprising a glenosphere having a polyethylene portion. In one embodiment, an anatomical shoulder arthroplasty kit comprises a humeral head comprising a polyethylene portion, and a glenoid component having a portion coated with pyrolytic carbon.

[0117] In one embodiment, an elbow arthroplasty kit comprises a humeral component having a head coated with pyrolytic carbon, and a polyethylene ulnar component (i.e. an ulnar component comprising a polyethylene portion).

[0118] In one embodiment, an elbow arthroplasty kit comprises a humeral component having a head comprising a polyethylene portion, and an ulnar component having a portion coated with pyrolytic carbon.

[0119] In one embodiment, a wrist arthroplasty kit comprises a radius component (i.e. for insertion into the radius, i.e. the radius of the forearm) having a portion which is coated with pyrocarbon, and a carpal component which comprises a polyethylene portion.

[0120] In one embodiment, a wrist arthroplasty kit comprises a carpal component having a portion which is coated with pyrocarbon, and a radius component (i.e. for insertion into the radius, i.e. the radius of the forearm) which comprises a polyethylene portion. Surgical method

[0121] In a surgical method of reverse shoulder arthroplasty, a conventional reverse shoulder arthroplasty method is followed, albeit using a joint prosthesis having a portion coated in pyrolytic carbon, and a second joint prosthesis component.

[0122] Referring to Figure 7, the first joint prosthesis component is a glenoid component (10), the glenoid component (10) comprising:

[0123] (a) metaglene (20) (a metal baseplate) that presents a central plug (20A) and a defines plurality of holes (not shown) into which can be inserted compression screws; and

[0124] (b) glenosphere (30) (a metallic ball).

[0125] Glenosphere (30) has a domed portion (30A) which is coated in pyrolytic carbon.

[0126] The metaglene (20) is secured to the patient glenoid (the socket portion of the shoulder blade) with compression screws, and serves as the foundation / baseplate for the glenosphere (30).

[0127] The glenosphere (30) is then impacted and screwed onto the metaglene (20) such that it is secured in place, completing the glenoid component (10).

[0128] Thus, the metaglene (20) and glenosphere (30) can together be described as defining a glenoid component (10).

[0129] The second joint prosthesis component is a humeral component (40), the humeral component (40) comprising:

[0130] (a) humeral insert (50);

[0131] (b) metal plate (60); and

[0132] (c) humeral cup (70).

[0133] The patient's humerus is resected and humeral stem (50) is inserted into the resected humerus. Metal plate (60) is then joined to / secured to humeral stem (50). Humeral cup (70) is fabricated from UHMWPE, and is impacted onto (secured with) metal plate (60) to complete the second joint prosthesis component. Humeral cup (70) thus defines a surface against which glenosphere (30) (specifically, the pyrolytic carbon-coated domed portion (30A) of glenosphere (30)) can articulate / which articulate against glenosphere (30) (specifically, the pyrolytic carbon-coated domed portion (30A) of glenosphere (30)).

[0134] In-use, humeral cup (70) articulates against / articulates with / opposes the pyrolytic carbon-coated glenosphere (30) (i.e. the pyrolytic carbon-coated portion of the glenosphere (30)).

[0135] Anatomical shoulder arthroplasty, wrist arthroplasty, hand arthroplasty, and elbow arthroplasty are similarly performed with arthroplasty kits of the present invention.

[0136] Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the invention contained herein is not limited to this precise embodiment and that changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and / or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.

[0137] Reference signs

[0138] 10 - glenoid component

[0139] 20 - metaglene

[0140] 20A - central plug (of metaglene 20)

[0141] 30 - glenosphere

[0142] 30A - domed portion (of glenosphere 30)

[0143] 40 - humeral component

[0144] 50 - humeral stem

[0145] 60 - metal plate

[0146] 70 - humeral cup

Claims

CLAIMS1. An arthroplasty kit comprising:(i) a first joint prosthesis component for in-use attachment to a first bone of a joint, the first joint prosthesis component having a portion which is coated with pyrolytic carbon, and(ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, the second joint prosthesis component comprising a polyethylene portion.

2. An arthroplasty kit according to claim 1, wherein the portion of the joint prosthesis which is coated with pyrolytic carbon and the second joint prosthesis component in-use define articular surfaces of the joint.

3. An arthroplasty kit according to claim 1 or claim 2, wherein the portion of the first joint prosthesis component which is coated with pyrolytic carbon is a head portion.

4. An arthroplasty kit according to any preceding claim, wherein the second joint prosthesis component is a polyethylene joint resurfacing component.

5. An arthroplasty kit according to claim 4, wherein the second joint prosthesis component is a polyethylene joint socket resurfacing component.

6. An arthroplasty kit according to any preceding claim, wherein the second joint prosthesis component comprises polyethylene selected from the group consisting of high density polyethylene, ultra-high molecular weight polyethylene, cross-linked ultra-high molecular weight polyethylene, highly crosslinked ultra-high molecular weight polyethylene, and vitamin E incorporated highly crosslinked ultra-high molecular weight polyethylene.

7. An arthroplasty kit according to claim 6, wherein the polyethylene is ultra-high molecular weight polyethylene.

8. An arthroplasty kit according to any of claims 1-7, wherein the arthroplasty kit is a reverse shoulder arthroplasty kit.

9. An arthroplasty kit according to claim 8, wherein the first joint prosthesis component comprises a glenosphere, and wherein the portion of the first joint prosthesis component which is coated with pyrolytic carbon is a head portion of the glenosphere.

10. An arthroplasty kit according to claim 9, wherein the first joint prosthesis component comprises a metaglene and a glenosphere.

11. An arthroplasty kit according to any of claims 8-10, wherein the second joint prosthesis component comprises a polyethylene insert.

12. An arthroplasty kit according to claim 11, wherein the polyethylene insert is a polyethylene insert for a humeral stem.

13. An arthroplasty kit according to any of claims 1-7, wherein it is an elbow arthroplasty kit, a wrist arthroplasty kit, or a hand arthroplasty kit.

14. A method of arthroplasty using an arthroplasty kit according to any preceding claim, wherein the method comprises:(A) securing the first joint prosthesis component to a first bone of the joint; and(B) securing the second joint prosthesis component to a second bone of the joint.

15. A method according to claim 14, wherein the first joint prosthesis component defines a boneengagement surface which is secured with the first bone.

16. A method according to claim 15, wherein the bone-engagement surface of the first joint prosthesis component is secured with a resected surface of the first bone.

17. A method according to claim 16, wherein the first bone is resected prior to the step of securing the bone-engagement surface of the joint prosthesis with the resected surface of the first bone.

18. A method according to any of claims 14-17, wherein the second joint prosthesis component defines a bone engagement surface which is engaged with the second bone.

19. A method according to any of claims 14-17, wherein it is a method of shoulder arthroplasty.

20. A method according to any of claims 14-17, wherein it is a method of reverse shoulder arthroplasty.

21. A method according to any of claims 14-17, wherein it is a method of elbow arthroplasty, wrist arthroplasty, or hand arthroplasty.

22. A method of arthroplasty using an anatomical shoulder arthroplasty kit, the anatomical shoulder arthroplasty kit comprising:(i) a first joint prosthesis component for in-use attachment to a first bone of a joint, the first joint prosthesis component having a portion which is coated with pyrolytic carbon, and(ii) a second joint prosthesis component for in-use attachment to a second bone of the joint, the second joint prosthesis component comprising a polyethylene portion, wherein the first joint prosthesis component is a humeral head coated with pyrolytic carbon and wherein the second joint prosthesis component is a glenoid resurfacing component, wherein the method comprises:(A) securing the first joint prosthesis component to a first bone of the joint; and(B) securing the second joint prosthesis component to a second bone of the joint.

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