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1.
Bone Joint Res ; 6(2): 113-122, 2017 Feb.
Article in English | MEDLINE | ID: mdl-28246095

ABSTRACT

OBJECTIVES: The high revision rates of the DePuy Articular Surface Replacement (ASR) and the DePuy ASR XL (the total hip arthroplasty (THA) version) have led to questions over the viability of metal-on-metal (MoM) hip joints. Some designs of MoM hip joint do, however, have reasonable mid-term performance when implanted in appropriate patients. Investigations into the reasons for implant failure are important to offer help with the choice of implants and direction for future implant designs. One way to assess the performance of explanted hip prostheses is to measure the wear (in terms of material loss) on the joint surfaces. METHODS: In this study, a coordinate measuring machine (CMM) was used to measure the wear on five failed cementless Biomet Magnum/ReCap/ Taperloc large head MoM THAs, along with one Biomet ReCap resurfacing joint. Surface roughness measurements were also taken. The reason for revision of these implants was pain and/or adverse reaction to metal debris (ARMD) and/or elevated blood metal ion levels. RESULTS: The mean wear rate of the articulating surfaces of the heads and acetabular components of all six joints tested was found to be 6.1 mm3/year (4.1 to 7.6). The mean wear rate of the femoral head tapers of the five THAs was 0.054 mm3/year (0.021 to 0.128) with a mean maximum wear depth of 5.7 µm (4.3 to 8.5). CONCLUSION: Although the taper wear was relatively low, the wear from the articulating surfaces was sufficient to provide concern and was potentially large enough to have been the cause of failure of these joints. The authors believe that patients implanted with the ReCap system, whether the resurfacing prosthesis or the THA, should be closely monitored.Cite this article: S. C. Scholes, B. J. Hunt, V. M. Richardson, D. J. Langton, E. Smith, T. J. Joyce. Explant analysis of the Biomet Magnum/ReCap metal-on-metal hip joint. Bone Joint Res 2017;6:113-122. DOI: 10.1302/2046-3758.62.BJR-2016-0130.R2.

2.
J Biomech ; 48(12): 3072-9, 2015 Sep 18.
Article in English | MEDLINE | ID: mdl-26278181

ABSTRACT

Reverse shoulder arthroplasty is an increasingly common surgical intervention. However there are concerns and known limitations in relation to such joint replacement, while novel designs of reverse shoulder prostheses continue to appear on the market. Many claim to offer improvements over older designs but such assertions are difficult to validate when there is no consensus as to how such implants should be tested in vitro or even if such testing is necessary. In order to permit appropriate in vitro testing of reverse shoulder prostheses a unique, multi-station test rig was designed which was capable of applying motion in three axes to test prostheses. The shoulder simulator can apply up to 110° of motion in the flexion-extension and abduction-adduction axes and up to 90° in the internal-external rotation axis. Dynamic loading of up to 1500 N can be provided. The simulator is computer controlled so that the motions and loading associated with particular activities of daily living can be applied. A 4.5 million cycle wear test of commercially available reverse shoulder prostheses was undertaken using a 'mug to mouth' activity of daily living. Gravimetric analysis was used to characterise wear. After 4.5 million cycles of 'mug to mouth', the average wear rate of the test components was 14.3mm(3)/million cycles. Polyethylene test components showed a reduction in roughness and the median wear particle diameter was 167 nm. A three axis shoulder simulator has been designed and used to successfully test multiple samples of a commercially available reverse shoulder prosthesis.


Subject(s)
Materials Testing , Mechanical Phenomena , Prosthesis Design , Shoulder Joint/surgery , Activities of Daily Living , Arthroplasty, Replacement , Polyethylene , Range of Motion, Articular , Shoulder Joint/physiology
3.
Proc Inst Mech Eng H ; 223(1): 1-12, 2009 Jan.
Article in English | MEDLINE | ID: mdl-19239063

ABSTRACT

Artificial joints have been much improved since their introduction but they still have a limited lifetime. In an attempt to increase their life by improving the lubrication acting within these prostheses, compliant layered polyurethane (PU) joints have been devised. These joints mimic the natural synovial joint more closely by promoting fluid film lubrication. In this study, tests were performed on compliant layer joints to determine their ability to function under a range of conditions. Both static and dynamic compression tests were undertaken on compliant artificial hip joints of two different radial clearances. Friction tests were also performed before and after static loading. In addition to this, knee wear tests were conducted to determine the suitability of a compliant layer in these applications. In the knee tests, variations in experimental testing conditions were investigated using both active and passive rotation and severe malalignment of the tibial inserts. The static compression tests together with the friction studies suggest that a small radial clearance is likely to result in 'grabbing' contact between the head and cup. The larger radial clearance (0.33 microm) did not exhibit these problems. The importance of the design of the compliant layer joints was highlighted with delamination occurring on the lateral bearings during the knee wear studies. The bearings with a layer 2 mm thick performed better than the bearings with a layer 3 mm thick. Tests conducted on flat PU bearings resulted in no delamination; therefore, it was concluded that the layer separation was caused by design issues rather than by material issues. It was found that, with careful material choice, consideration of design, and effective manufacturing techniques, the compliant layer joint functioned well and demonstrated durability of the union between the hard and soft layers. These results give encouragement for the suitability of these joints for clinical use.


Subject(s)
Elastomers/chemistry , Equipment Failure Analysis/instrumentation , Joint Prosthesis , Materials Testing/instrumentation , Polyurethanes/chemistry , Prosthesis Design/instrumentation , Adhesiveness , Elasticity , Equipment Failure Analysis/methods , Friction , Lubrication , Surface Properties
4.
Proc Inst Mech Eng H ; 223(1): 13-25, 2009 Jan.
Article in English | MEDLINE | ID: mdl-19239064

ABSTRACT

The introduction of unicondylar knee prostheses has allowed the preservation of the non-diseased compartment of the knee while replacing the diseased or damaged compartment. In an attempt to reduce the likelihood of aseptic loosening, new material combinations have been investigated within the laboratory. Tribological tests (friction, lubrication, and wear) were performed on metal-on-carbon-fibre-reinforced (CFR) poly (ether-ether-ketone) (PEEK) (pitch-based) mobile unicondylar knee prostheses up to 5 x 10(6) cycles. Both a loaded soak control and an unloaded soak control (both medial and lateral components) were used to compensate for weight change due to lubricant absorption. For this material combination the loaded soak control gave slightly lower wear for both the medial and the lateral components than did the unloaded soak control. The medial components gave higher steady state wear than the lateral components (1.70 mm3 per 10(6) cycles compared with 1.02 mm3 per 10(6) cycles with the loaded soak control). The results show that the CFR PEEK unicondylar knee joints performed well in these wear tests. They gave lower volumetric wear rates than conventional metal-on-ultra-high-molecular-weight polyethylene prostheses have given in the past when tested under similar conditions. The friction tests showed that, at physiological viscosities, these joints operated in the boundary-mixed-lubrication regime. The low wear produced by these joints seems to be a function of the material combination and not of the lubrication regime.


Subject(s)
Biocompatible Materials/chemistry , Carbon/chemistry , Equipment Failure Analysis , Ketones/chemistry , Knee Prosthesis , Polyethylene Glycols/chemistry , Benzophenones , Carbon Fiber , Friction , Lubrication , Materials Testing , Polymers , Prosthesis Design
5.
J Mater Sci Mater Med ; 20(1): 163-70, 2009 Jan.
Article in English | MEDLINE | ID: mdl-18704647

ABSTRACT

It is well known that a reduction in the volume of wear produced by articulating surfaces in artificial joints is likely to result in a lower incidence of failure due to wear particle induced osteolysis. Therefore, new materials have been introduced in an effort to produce bearing surfaces with lower, more biologically acceptable wear. Polyetheretherketone (PEEK-OPTIMA) has been successfully used in a number of implant applications due to its combination of mechanical strength and biocompatibility. Pin-on-plate wear tests were performed on various combinations of PEEK-OPTIMA and carbon fibre reinforced PEEK-OPTIMA (CFR-PEEK) against various CoCrMo alloys to assess the potential of this material combination for use in orthopaedic implants. The PEEK/low carbon CoCrMo produced the highest wear. CFR-PEEK against high carbon or low carbon CoCrMo provided low wear factors. Pin-on-plate tests performed on ultra-high molecular weight polyethylene (UHMWPE) against CoCrMo (using comparable test conditions) have shown similar or higher wear than that found for CFR-PEEK/CoCrMo. This study gives confidence in the likelihood of this material combination performing well in orthopaedic applications.


Subject(s)
Biocompatible Materials , Joint Prosthesis , Ketones , Polyethylene Glycols , Prosthesis Failure , Vitallium , Benzophenones , Biomechanical Phenomena , Bone Nails , Bone Plates , Carbon , Carbon Fiber , Humans , In Vitro Techniques , Materials Testing , Polymers , Stress, Mechanical , Surface Properties
6.
Proc Inst Mech Eng H ; 222(6): 853-64, 2008 Aug.
Article in English | MEDLINE | ID: mdl-18935802

ABSTRACT

The premise that elastomeric materials could be used as one or more of the articulating components in both hip and knee prostheses was postulated first by Unsworth and co-workers. It was thought that such materials might have the capacity to mimic natural joint behaviour more closely than the more rigid bearing surfaces commonly in use. A more natural joint function in artificial joints should promote better tribology, with full fluid-film lubrication being the goal. Early tests showed that this objective could potentially be achieved with a judicious choice of materials and carefully controlled manufacturing techniques. This paper (Part 1 of a two-part series) describes and explains the techniques used to verify the material selection as well as to determine the most appropriate manufacturing procedure to obtain a strong and robust interface between the support and bearing material of the prosthesis. Two polycarbonate urethane (PU) materials with different hardness values (Corethane 80A and Corethane 75D) gave sufficient interfacial strength when moulded under optimum conditions. Corethane 80A was used as the soft bearing material while Corethane 75D provided the rigid backing component. Peel tests revealed strong interface bonds, varying with processing conditions between 350 and 862 N. Fourier transform infrared spectroscopy and micro-thermal analysis showed that a fusion bond over 30 microm thick formed at the interface. The results of the range of tests and analyses, which have been used in this study, have provided sufficient evidence to validate the process used to manufacture these components.


Subject(s)
Elastomers/chemistry , Joint Prosthesis , Polyurethanes/chemistry , Prosthesis Design/methods , Adhesiveness , Elasticity , Equipment Failure Analysis , Friction , Lubrication , Materials Testing , Surface Properties
7.
Proc Inst Mech Eng H ; 222(3): 273-83, 2008 Apr.
Article in English | MEDLINE | ID: mdl-18491697

ABSTRACT

New material combinations have been introduced as the bearing surfaces of hip prostheses in an attempt to prolong their life by overcoming the problems of failure due to wear-particle-induced osteolysis. This will hopefully reduce the need for revision surgery. The study detailed here used a hip simulator to assess the volumetric wear rates of large-diameter carbon-fibre-reinforced pitch-based poly(ether-ether-ketone) (CFR-PEEK) acetabular cups articulating against alumina femoral heads. The joints were tested for 25 x 10(6) cycles. Friction tests were also performed on these joints to determine the lubrication regime under which they operate. The average volumetric wear rate of the CFR-PEEK acetabular component of 54 mm diameter was 1.16 mm(3)/10(6) cycles, compared with 38.6 mm(3)/10(6) cycles for an ultra-high-molecular-weight polyethylene acetabular component of 28 mm diameter worn against a ceramic head. This extremely low wear rate was sustained over 25 x 10(6) cycles (the equivalent of up to approximately 25 years in vivo). The frictional studies showed that the joints worked under the mixed-boundary lubrication regime. The low wear produced by these joints showed that this novel joint couple offers low wear rates and therefore may be an alternative material choice for the reduction of osteolysis.


Subject(s)
Acetabulum/pathology , Aluminum Oxide/chemistry , Femur Head/pathology , Hip Prosthesis , Ketones/chemistry , Polyethylene Glycols/chemistry , Aluminum Oxide/therapeutic use , Benzophenones , Biocompatible Materials/chemistry , Biocompatible Materials/therapeutic use , Carbon/therapeutic use , Carbon Fiber , Ceramics/chemistry , Ceramics/therapeutic use , Friction , Hip Prosthesis/adverse effects , Humans , Ketones/therapeutic use , Lubrication , Materials Testing , Models, Structural , Osteolysis/etiology , Osteolysis/prevention & control , Polyethylene Glycols/therapeutic use , Polyethylenes/chemistry , Polyethylenes/therapeutic use , Polymers , Prosthesis Failure , Surface Properties
8.
Proc Inst Mech Eng H ; 222(8): 1197-208, 2008 Nov.
Article in English | MEDLINE | ID: mdl-19143414

ABSTRACT

Total joint replacements (TJRs) have a limited lifetime, but the introduction of devices that exhibit good lubricating properties with low friction and low wear could well extend this. A novel tibial bearing design, using polyurethane (PU) as a compliant layer, to mimic the natural joint, has been developed. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the effects of material modulus and surface roughness, together with bearing design parameters such as bearing thickness and conformity, on lubrication. Corethane 80A was the preferred material and was chosen as the compliant layer for subsequent testing. A low surface roughness resulted in lower asperity contact as the asperities were depressed by the pressurized entraining fluid and full-fluid-film lubrication was approached. The three different tibial bearing conformities (low, medium, and high) did not appear to influence the mode of lubrication and all these bearings performed with extremely low friction. Similarly, the bearing thickness effects on lubrication at the levels tested (2 mm, 3 mm, and 4 mm) were minimal, although the effects of layer thickness on interface shear stress could be expected to be significant. This study describes a series of friction tests that have been used to select the most appropriate material and to optimize the design parameters to establish optimum conditions for these compliant layer joints.


Subject(s)
Computer-Aided Design , Equipment Failure Analysis , Knee Prosthesis , Prosthesis Design , Biomimetics/instrumentation , Biomimetics/methods , Elastic Modulus , Equipment Design , Friction , Lubrication , Stress, Mechanical
9.
Proc Inst Mech Eng H ; 221(3): 281-9, 2007 Apr.
Article in English | MEDLINE | ID: mdl-17539583

ABSTRACT

In an attempt to prolong the lives of rubbing implantable devices, several 'new' materials have been examined to determine their suitability as joint couplings. Tests were performed on a multidirectional pin-on-plate machine to determine the wear of both pitch and PAN (polyacrylonitrile)-based carbon fibre reinforced-polyetheretherketone (CFR-PEEK-OPTIMA) pins articulating against both BioLox Delta and BioLox Forte plates (ceramic materials). Both reciprocation and rotational motion were applied to the samples. The tests were conducted using 24.5 per cent bovine serum as the lubricant (protein concentration 15 g/l). Although all four material combinations gave similar low wear with no statistically significant difference (p > 0.25), the lowest average total wear of these pin-on-plate tests was provided by CFR-PEEK-OPTIMA pitch pins versus BioLox Forte plates. This was much lower than the wear produced by conventional joint materials (metal-on-polyethylene) and metal-on-metal combinations when tested on the pin-on-plate machine. This therefore indicates optimism that these PEEK-OPTIMA-based material combinations may perform well in joint applications.


Subject(s)
Acrylic Resins/chemistry , Biocompatible Materials/chemistry , Carbon/chemistry , Ceramics/chemistry , Joint Prosthesis , Ketones/chemistry , Materials Testing/methods , Polyethylene Glycols/chemistry , Benzophenones , Carbon Fiber , Equipment Failure Analysis , Friction , Lubrication , Materials Testing/instrumentation , Polymers , Prosthesis Design
10.
Proc Inst Mech Eng H ; 221(1): 11-20, 2007 Jan.
Article in English | MEDLINE | ID: mdl-17315764

ABSTRACT

Total hip replacements offer relief to a great many patients every year around the world. With an expected service life of around 25 years on most devices, and with younger and younger patients undergoing this surgery, it is of great importance to understand the mechanisms of their function. Tribological testing of both conventional and hard bearing joint combinations have been conducted in many centres throughout the world, and, after being initially abandoned owing to premature failures, hard bearing combinations have been revisited as viable options for joint replacements. Improved design, manufacturing procedures, and material compositions have led to improved performance over first-generation designs in both metal-on-metal and ceramic-on-ceramic hip prostheses. This paper offers a review of the work conducted in an attempt to highlight the most important factors affecting joint performance and tribology of hard bearing combinations. The tribological performance of these joints is superior to that of conventional metal- or ceramic-on-polymer designs.


Subject(s)
Biocompatible Materials/chemistry , Ceramics/chemistry , Equipment Failure Analysis , Hip Prosthesis , Metals/chemistry , Models, Chemical , Computer Simulation , Friction , Lubrication , Stress, Mechanical , Surface Properties
11.
Phys Med Biol ; 52(1): 197-212, 2007 Jan 07.
Article in English | MEDLINE | ID: mdl-17183136

ABSTRACT

Many materials are used as artificial joint bearing surfaces; these include conventional stainless steel or CoCrMo-on-ultra-high molecular weight polyethylene (UHMWPE), CoCrMo on itself and alumina-on-alumina. However, these joints have a limited lifespan resulting in failure of the prosthesis and the need for revision surgery. A number of materials have been introduced recently in an attempt to overcome these problems. Polycarbonate urethane (PU) is a compliant material that can be used as an artificial joint bearing surface which has been developed to mimic the natural synovial joint more accurately by promoting fluid film lubrication. Tribological tests were performed on CoCrMo-on-PU unicondylar knee prostheses to assess their performance in vitro. The wear produced by these components was considerably lower than that found for conventional joints. They also exhibited low friction and operated close to full-fluid film lubrication with viscosities of lubricant similar to those found in patients with arthritis. These tests gave encouraging results for the tribological performance of this material couple for use as an alternative bearing combination.


Subject(s)
Joint Prosthesis , Knee Prosthesis , Polycarboxylate Cement/chemistry , Polymers/chemistry , Polyurethanes/chemistry , Biocompatible Materials , Computer Simulation , Equipment Design , Femur/pathology , Friction , Humans , Materials Testing , Microscopy, Electron, Scanning , Polycarboxylate Cement/pharmacology , Prosthesis Design , Prosthesis Failure , Stainless Steel , Surface Properties
12.
Proc Inst Mech Eng H ; 220(6): 687-93, 2006 Aug.
Article in English | MEDLINE | ID: mdl-16961188

ABSTRACT

The tribological testing of artificial hip and knee joints in the laboratory has been ongoing for several decades. This work has been carried out in an attempt to simulate the loading and motion conditions applied in vivo and, therefore, the potential for the success of the joint. However, several different lubricants have been used in these tests. The work documented in this paper compares results obtained using different lubricants and makes suggestions for future work. Hip joints and knee joints of different material combinations were tested in a friction simulator to determine their friction and lubrication properties. Both carboxymethyl cellulose (CMC) fluids and bovine serum (with CMC fluids added) were used as the lubricants. These were prepared to various viscosities to produce the Stribeck plots. Human synovial fluid, of just one viscosity, was used as the lubricant with some of the joints to give a true comparison with physiological lubricants. The results showed that, in most cases, the lubricant had a significant effect on the friction developed between the joint surfaces. This is thought to be due to the proteins that are present within the bovine serum adsorbing to the bearing surfaces, creating 'solid-like' films which rub together, protecting the surfaces from solid-to-solid contact. This would be beneficial in terms of wear but can either increase or decrease the friction between the contacting surfaces. It is important to simulate the conditions in vivo as closely as possible when testing these joints to try to obtain a better comparison between the joints and to simulate more accurately the way that these joints will operate in the body. In an attempt to simulate synovial fluid, bovine serum seems to be the most popular lubricant used at present. It would be beneficial, however, to develop a new synthetic lubricant that more closely matches synovial fluid. This would allow us to predict more accurately how these joints would operate long-term in vivo.


Subject(s)
Body Fluids/chemistry , Equipment Failure Analysis , Hip Prosthesis , Knee Prosthesis , Proteins/chemistry , Synovial Fluid/chemistry , Friction , Humans , Lubrication , Prosthesis Design
13.
Proc Inst Mech Eng H ; 220(5): 583-96, 2006 Jul.
Article in English | MEDLINE | ID: mdl-16898216

ABSTRACT

Total joint replacements (TJRs) have a limited lifetime, but the introduction of components that exhibit good lubricating properties with low friction and low wear could extend the life of TJRs. A novel acetabular cup design using polyurethane (PU) as a compliant layer (to mimic the natural joint) has been developed. This study describes a series of friction tests that have been used to select the most appropriate material, optimize the design parameters, and fine-tune the manufacturing processes of these joints. To determine accurately the mode of lubrication under which these joints operate, a synthetic lubricant was used in all these tests. Friction tests were carried out to assess the lubrication of four PU bearing materials. Corethane 80A was the preferred material and was subjected to subsequent testing. Friction tests conducted on acetabular cups, manufactured using Corethane 80A articulating against standard, commercially available femoral heads, demonstrated friction factors approaching those for full-fluid-film lubrication with only approximately 1 per cent asperity contact. As the joint produces these low friction factors within less than half a walking cycle after prolonged periods of loading, start-up friction was not considered to be a critical factor. Cups performed well across the full range of femoral head sizes, but a number of samples manufactured with reduced radial clearances performed with higher than expected friction. This was caused by the femoral head being gripped around the equator by the low clearance cup. To avoid this, the cup design was modified by increasing the flare at the rim. In addition to this the radial clearance was increased. As the material is incompressible, a radial clearance of 0.08 mm was too small for a cup diameter of 32 mm. A clearance of between 0.10 and 0.25 mm produced a performance approaching full-fluid-film lubrication. This series of tests acted as a step towards the optimization of the design of these joints, which has now led to an in vivo ovine model.


Subject(s)
Acetabulum/physiology , Acetabulum/surgery , Biomimetic Materials , Biomimetics/instrumentation , Hip Prosthesis , Synovial Fluid/physiology , Biocompatible Materials/chemistry , Biomimetics/methods , Computer Simulation , Computer-Aided Design , Elasticity , Equipment Failure Analysis , Friction , Hip Joint/physiology , Hip Joint/surgery , Humans , Lubrication , Materials Testing , Models, Biological , Prosthesis Design , Stress, Mechanical , Torque
14.
Proc Inst Mech Eng H ; 220(2): 183-94, 2006 Feb.
Article in English | MEDLINE | ID: mdl-16669386

ABSTRACT

Total hip surgery is an effective way of alleviating the pain and discomfort caused by diseased or damaged joints. However, in the majority of cases, these joints have a finite life. The main reason for failure is osteolysis (bone resorption). It is well documented that an important cause of osteolysis, and therefore the subsequent loosening and failure of conventional metal- or ceramic-on-ultra-high molecular weight polyethylene joints, is the body's immunological response to the polyethylene wear particles. To avoid this, interest has been renewed in metal-on-metal joints. The intention of this paper is to review the studies that have taken place within different laboratories to determine the tribological performance of new-generation metal-on-metal total hip replacements. These types of joint offer a potential solution to enhance the longevity of prosthetic hip systems; however, problems may arise owing to the effects of metal ion release, which are, as yet, not fully understood.


Subject(s)
Biocompatible Materials/analysis , Biocompatible Materials/chemistry , Hip Prosthesis , Metallurgy/methods , Metals/analysis , Metals/chemistry , Models, Chemical , Computer Simulation , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , Friction , Lubrication , Materials Testing , Prosthesis Failure , Surface Properties
15.
Proc Inst Mech Eng H ; 220(2): 269-77, 2006 Feb.
Article in English | MEDLINE | ID: mdl-16669393

ABSTRACT

It is well documented that hard bearing combinations show a running-in phenomenon in vitro and there is also some evidence of this from retrieval studies. In order to investigate this phenomenon, five Birmingham hip resurfacing devices were tested in a hip wear simulator. One of these (joint 1) was also tested in a friction simulator before, during, and after the wear test and surface analysis was conducted throughout portions of the testing. The wear showed the classical running in with the wear rate falling from 1.84 mm3 per 10(6) cycles for the first 10(6) cycles of testing to 0.24 mm3 per 10(6) cycles over the final 2 x 10(6) cycles of testing. The friction tests suggested boundary lubrication initially, but at 1 x 10(6) cycles a mixed lubrication regime was evident. By 2 x 10(6) cycles the classical Stribeck curve had formed, indicating a considerable contribution from the fluid film at higher viscosities. This continued to be evident at both 3 x 10(6) and 5 x 10(6) cycles. The surface study complements these findings.


Subject(s)
Biocompatible Materials/analysis , Biocompatible Materials/chemistry , Hip Prosthesis , Metals/analysis , Metals/chemistry , Prosthesis Failure , Equipment Design , Equipment Failure Analysis/instrumentation , Equipment Failure Analysis/methods , Friction , Lubrication , Materials Testing , Particle Size , Prosthesis Design , Surface Properties
16.
Proc Inst Mech Eng H ; 219(2): 79-87, 2005.
Article in English | MEDLINE | ID: mdl-15819479

ABSTRACT

Currently, an artificial hip joint can be expected to last, on average, in excess of 15 years with failure due, in the majority of cases, to late aseptic loosening of the acetabular component. A realistic alternative to the problem of wear in conventional joints is the introduction of bearing surfaces that exhibit low wear and operate in the full fluid-film lubrication regime. Contact analyses and friction tests were performed on compliant layer joints (metal-on-polyurethane) and the design of a prototype ovine arthroplasty model was investigated. When optimized, these components have been shown to achieve full fluid-film lubrication.


Subject(s)
Computer-Aided Design , Equipment Failure Analysis/methods , Hip Joint/physiopathology , Hip Joint/surgery , Hip Prosthesis , Models, Biological , Prosthesis Design/methods , Animals , Cattle , Coated Materials, Biocompatible/analysis , Coated Materials, Biocompatible/chemistry , Computer Simulation , Elasticity , Friction , Humans , Lubrication , Stress, Mechanical
17.
Phys Med Biol ; 49(15): 3413-25, 2004 Aug 07.
Article in English | MEDLINE | ID: mdl-15379022

ABSTRACT

Compliant layer knee joints have been considered for use in an attempt to increase the serviceable life of artificial joints. If designed correctly, these joints should operate within the full-fluid film lubrication regime. However, adverse tribological conditions, such as the presence of bone and bone cement particles, may breach the fluid film and cause surface wear. The frictional behaviour of both polyurethane (PU) and conventional polyethylene (PE) tibial components against a metallic femoral component was therefore assessed when bone cement particles were introduced into the lubricant. The bone cement particles caused a large increase in the frictional torque of both the PE and PU bearings; however, the friction produced by the PU bearings was still considerably lower than that produced by the PE bearings. The volume of bone cement particles between each of the bearings and the resultant frictional torque both decreased over time. This occurred more quickly with the PE bearings but greater damage was caused to the surface of the PE bearings than the PU components.


Subject(s)
Bone Cements/chemistry , Equipment Failure Analysis/methods , Knee Prosthesis , Materials Testing/methods , Polyethylene/chemistry , Polyurethanes/chemistry , Biocompatible Materials/chemistry , Friction , Humans , Lubrication , Particle Size , Surface Properties , Torque
18.
Proc Inst Mech Eng H ; 217(2): 99-104, 2003.
Article in English | MEDLINE | ID: mdl-12666776

ABSTRACT

Tests were performed on six large Kinemax Plus knee bearings (snap-fit design) to evaluate the amount of movement between 10- and 15-mm-thick tibial inserts and the tibial base plates. The knee bearings were tested up to 1 x 10(6) cycles on the Durham six-station knee wear simulator which subjected the bearings to similar motion and loading profiles that would be experienced by the natural knee during walking. Although passive internal/external (I/E) rotation was allowed, no active I/E rotation was applied. The movement of the tibial inserts was measured with dial gauges (accuracy +/-0.01 mm) before and after the bearings were tested on the simulator, when unloaded, and throughout the tests while the bearings were being dynamically loaded in the simulator. Movement occurred between the tibial insert and the tibial base plate after initial assembly due to the snap-fit mechanism used to locate the tibial insert within the tibial base plate. However this decreased appreciably when the bearings were loaded in the simulator. The amount of movement did not change with time when the bearings were continuously loaded in the simulator. However, after each test the amount of movement of the tibial inserts, when unloaded, was only 65 per cent (anterior-posterior) and 46 per cent (medial-lateral) of the values before the test. This was thought to be due to creep of the ultra-high molecular weight polyethylene (UHMWPE) inserts. The movement between the tibial insert and tibial base plate in situ is likely to be much less than that observed by a surgeon at the time of assembly due to loading of the knee bearing in the body. However, the amount of movement when the tibial inserts are loaded may still be great enough to produce a second interface where wear of the tibial insert may take place.


Subject(s)
Equipment Failure Analysis/methods , Knee Joint/physiopathology , Materials Testing/methods , Weight-Bearing , Coated Materials, Biocompatible , Equipment Failure Analysis/instrumentation , Humans , Knee Joint/surgery , Knee Prosthesis , Lubrication , Materials Testing/instrumentation , Movement , Polyethylenes , Prosthesis Design , Range of Motion, Articular , Sensitivity and Specificity , Surface Properties , Tibia/physiopathology , Walking/physiology
19.
J Mater Sci Mater Med ; 12(4): 299-303, 2001 Apr.
Article in English | MEDLINE | ID: mdl-15348290

ABSTRACT

An important cause of osteolysis and subsequent loosening of replacement hip joints is the body's biological response to polyethylene wear debris. Interest has thus been renewed in hard bearing surfaces such as metal-on-metal implants. Tests were performed on a pin-on-plate machine to determine the effects of pin rotation on the wear of two different compositions of cobalt chrome molybdenum (CoCrMo) against itself (high carbon and low carbon). With reciprocating motion only, the low carbon material gave an order of magnitude higher wear than the high carbon material. The overall wear (that for both the pin and the plate) was significantly reduced with added rotation for the low carbon material but remained approximately the same for the high carbon material. However, the wear of the low carbon material was not reduced below that of the high carbon material which remained the best material in terms of wear.

20.
Proc Inst Mech Eng H ; 215(6): 523-30, 2001.
Article in English | MEDLINE | ID: mdl-11848384

ABSTRACT

New generation metal-on-metal prostheses have been introduced to try and overcome the problem of osteolysis often attributed to the wear particles of the polyethylene component of conventional metal-on-ultra-high molecular weight polyethylene (UHMWPE) joints. The wear rates of four metal-on-metal joints (two different clearances) were assessed along with that of a conventional metal-on-UHMWPE joint. Friction measurements of the metal-on-metal joints were taken before and after the wear test and compared. Two distinct wear phases were discernible for all the metal-on-metal joints: an initial wear phase up to 0.5 x 10(6) cycles and then a lower steady state wear phase. The steady state wear rate of the 22 microm radial clearance metal-on-metal joint was lower than that for the 40 microm radial clearance joint, although this difference was not found to be significant (p > 0.15). The wear rates for all the joints tested were consistent with other simulator studies. The friction factors produced by each joint were found to decrease significantly after wear testing (p < 0.05).


Subject(s)
Friction , Hip Prosthesis , Materials Testing , Metals , Biocompatible Materials , Equipment Failure Analysis , Humans , Lubrication , Osteolysis/etiology , Osteolysis/prevention & control , Polyethylenes , Prosthesis Failure , Stress, Mechanical , United Kingdom , Vitallium
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