Acetabular Cup Wear Research Articles

A Mixed Elasto-Hydrodynamic Lubrication Model for Wear Calculation in Artificial Hip Joints

The aim of this paper was to propose a novel in silico mixed elasto-hydrodynamic lubrication model with the purpose of wear prediction in Total Hip Replacements (THRs). The model considers the progressive wear contribution in the calculation of the meatus filled by the non-Newtonian synovial fluid. The results were referred to the gait cycle kinematics, calculated by using musculoskeletal multibody software, while the loading was assumed by literature in vivo measurements. The simulations allow evaluating the fluid and the contact pressure fields and the acetabular cup wear over the time. The results were obtained considering a Ultra High Molecular Weight PolyEthylene, UHMWPE, cup and were compared with results from the literature, showing a good agreement in terms of total volume wear of the cup.

Wear Failure Analysis of UHMWPE Acetabular Cups in THR

The UHMWPE acetabular cups are the most popular joints for joint prostheses after Charnley introduced UHMWPE for the acetabular component in 1962. It has been demonstrated that polyethylene wear remains the main source of particles in the THR and therefore requires particular attention. The paper presents a series of theoretical and practical aspects regarding the wear of acetabular cups (made of UHMWPE) from the total hip prosthesis component. At the same time, the other tribological phenomena that occur in these MoP (metal on polyethylene) combinations are treated, such as lubrication and friction. Total Hip Replacement & Hip Resurfacing A hip replacement involves replacing the hip joint with a mechanical bearing system which is comprised of a femoral component and an acetabular component. During a hip replacement the acetabulum is reamed and the acetabular component is fitted into the cavity and the femoral component can either be placed over a reamed femoral head, in a procedure referred to as hip resurfacing, or positioned inside the femoral shaft during a total hip replacement [1]. Fig. 1. Total Hip Replacement (a) and Hip Resurfacing Replacement (b) [2].

Effects of femoral head diameter on the predicted acetabular cup wear volume of CP-Ti and UHMWPE hip implants

Numerical investigation is a method capable to study the expensive and long-time duration wear problems in biotribology. The technique has been used to predict the wear of hip implants specially those made from metal on polymer biomaterials. This research studied the effect of commercially pure titanium (CP-Ti) femoral head diameter on the wear volume of ultra-high molecular weight polyethylene (UHMWPE) acetabular cup. Diameter variations are 22 mm, 28 mm and 32 mm. Hip implant models were created and the numerical approximations conducted with the finite element method. Wear calculations used a nonlinear load and contact area mathematical model. A Python script was developed to proceed the calculations. Accurate wear predictions can be obtained with the use of fine elements those maximum contact loads are closer to the physiological load. Verification with experimental data on the 32 mm femoral head model shows a good agreement with error rates below 1%.

Wear Prediction of UHMWPE Acetabular Cup against CP Titanium Femoral Head in a Hip Joint Simulator

Ultra high molecular weight polyethylene (UHMWPE) is a biomaterial used for the human hip joint prosthesis bearings for decades. The main disadvantage is the wear resistant. The products should be in service in the lifetime of the patients. Tribological assessments by experiments and computations should be made to solve that problem. The aim of this research is to predict the UHMWPE acetabular cup wear volume sliding against commercially pure titanium (cp Ti) femoral head in a hip simulator. The cp Ti has the highest biocompatibility compared with other femoral head metals such as cobalt chrome, titanium alloy and 316L stainless steel. Computation processes use the Abaqus contact mechanics algorithm followed by a custom made Python script for the data extractions and Archard wear model calculations. Models were an assembly of the UHMWPE acetabular cup and 32 mm cp Ti femoral head in a biaxial rocking motion hip simulator. Sliding between the models was a 60 cycles per minute rotation. Calculations conducted for one million cycles cumulative polymer wear volume in five steps of 200,000 cycles. The geometries of the models were updated in every step. Experimental pin on disc tests conducted to obtain the wear factor and coefficient of friction. Those data support the input of computations. Wear volume verification use the experimental data from Röstlund. Results show a numerical error at 31.42 percents.

Correction of radiographic measurements of acetabular cup wear for variations in pelvis orientation.

Radiographic measurement of two-dimensional acetabular cup wear is usually carried out on a series of follow-up radiographs of the patient’s pelvis. Since the orientation of the pelvis might not be consistent at every X-ray examination, the resulting change in view of the wear plane introduces error into the linear wear measurement. This effect is amplified on some designs of cup in which the centre of the socket is several millimetres below the centre of the cup or circular wire marker. This study describes the formulation of a mathematical method to correct radiographic wear measurements for changes in pelvis orientation. A mathematical simulation of changes in cup orientation and wear vectors caused by pelvic tilt was used to confirm that the formulae corrected the wear exactly if the radiographic plane of the reference radiograph was parallel to the true plane of wear. An error analysis showed that even when the true wear plane was not parallel to the reference radiographic plane, the formulae could still provide a useful correction. A published correction formula was found to be ineffective.

Study of Sensor Deflection in Hip Simulator : Numerical and Experimental Method

A lot of Hip Joint Simulator have been made nowadays, most of them use different structure and method. This research reports a pin-on-ring tribometer design that is used to became hip joint simulator based on the movement of the salat (salat gait). Modified femoral head and acetabular cup holder are performed, to design a reciprocating motion for simulation of artificial hip movement. An interesting finding from this study is a new linked-bar mechanism that leads to the ability to move femoral head against the acetabular cup and measure wear volume of an THR patients during normal salat gait. The designed motion angle is 121.5° in the flexion direction and 15.5° in the direction of abduction. Linked bar for sensor dial indicator have enough adjustment, but there is still a movement that is not rigid upon running hip joint process simulator. This research concentrates on the bar is already linked in accordance or not when compared with the data in the simulate on a computer. Estimation error and deviations that occur between numerical and experimental is going forward to improve hip joint simulator Undip to be more precise and relevant research to use THR Undip.

Evaluation of a new methodology to simulate damage and wear of polyethylene hip replacements subjected to edge loading in hip simulator testing

Wear and fatigue of polyethylene acetabular cups have been reported to play a role in the failure of total hip replacements. Hip simulator testing under a wide range of clinically relevant loading conditions is important. Edge loading of hip replacements can occur following impingement under extreme activities and can also occur during normal gait, where there is an offset deficiency and/or joint laxity. This study evaluated a hip simulator method that assessed wear and damage in polyethylene acetabular liners that were subjected to edge loading. The liners tested to evaluate the method were a currently manufactured crosslinked polyethylene acetabular liner and an aged conventional polyethylene acetabular liner. The acetabular liners were tested for 5million standard walking cycles and following this 5million walking cycles with edge loading. Edge loading conditions represented a separation of the centers of rotation of the femoral head and the acetabular liner during the swing phase, leading to loading of the liner rim on heel strike. Rim damage and cracking was observed in the aged conventional polyethylene liner. Steady-state wear rates assessed gravimetrically were lower under edge loading compared to standard loading. This study supports previous clinical findings that edge loading may cause rim cracking in liners, where component positioning is suboptimal or where material degradation is present. The simulation method developed has the potential to be used in the future to test the effect of aging and different levels of severity of edge loading on a range of cross-linked polyethylene materials. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1456-1462, 2018.

Severe Polyethylene Wear Requiring Revision Total Hip Arthroplasty in Three Dogs.

To describe the occurrence of severe polyethylene wear of the acetabular component in 3 dogs that ultimately led to implant failure, and to report the outcome of revision of total hip arthroplasty (THA) in these cases. Case report Dogs (n=3). Three dogs with hip dysplasia underwent routine THA before 2 years of age. All dogs became acutely lame 4-5 years after THA. Radiographs revealed acetabular cup wear in all cases, shell fragmentation in 2 cases, and additional stem failure in 1 case. All dogs underwent successful revision surgery, during which severe polyethylene wear and metallosis was observed. Revision surgery provided an excellent clinical outcome in all dogs from 10 months to 4 years post revision. Polyethylene wear and implant failure may be a significant long-term complication of THA not previously recognized, which may be especially true when placed at an early age in a large breed, active dog, or in a dog with significant morbidity associated with other limbs. A successful revision was achieved in all 3 dogs. Additional investigation is warranted to document the risk factors associated with severe polyethylene wear in canine THA.

A finite element method approach to compare the wear of acetabular cups in polyethylene according to their lateral tilt in relation to the coronal plane

In this work, the finite element method was used to model and simulate the hip joint prosthetic tribosystem. We use an adaptation of the Archard equation to determine the abrasive wear of acetabular cups in UHMWPE as a function of their lateral tilts in relation to the coronal plane. Numerical simulations performed with acetabular cups at tilt angles of 30°, 45°, and 60° presented respectively linear wear of 0.19mm, 0.17mm, and 0.26mm per year, and volumetric wear of 30.85mm3, 30.97mm3, and 47.41mm3, for the same period. The results of the study suggest that acetabular cups assembled at 45° present lower linear wear rates, whereas a significant increase in the volumetric wear rate is obtained for sets positioned at tilts above 45°. This conclusion is corroborated by comparison with clinical results presented in the literature.

Quantifying the wear of acetabular cups using coordinate metrology

Abstract In an ageing population where individuals demand a pain free and active existence, hip arthroplasty has become one of the most important operations of later life, with developments increasing the longevity of this prosthesis. Accurate assessment of wear is an important way to assess how well hip prostheses perform over time. This paper describes a new protocol to accurately locate and map the wear of acetabular cups. 16 metal-on-metal acetabular cups were tested in a hip simulator for up to 6 million cycles at a range of angles of inclination in order to create a large range of wear volumes. Unworn and worn regions of acetabular cups were digitised in two separate scans using a CMM. The two scans were superimposed in order to allow calculation of maximum depth, wear volume loss and rim damage. Values obtained from the CMM protocol (CMM) were compared to the wear volume determined gravimetrically (G); a strong correlation (CMM = 0.992G−0.504) was established. The CMM protocol established was shown to be a methodology more powerful than many existing geometric protocols which could be used to assess explants and implants tested in vitro.

Validation of a 3D CT method for measurement of linear wear of acetabular cups

Background We evaluated the accuracy and repeatability of a 3D method for polyethylene acetabular cup wear measurements using computed tomography (CT). We propose that the method be used for clinical in vivo assessment of wear in acetabular cups.Material and methods Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner.Results The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17°.Interpretation This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy.

Wear Behaviour and Wear Debris Characterization of UHMWPE on Alumina Ceramic, Stainless Steel, CoCrMo and Ti6Al4V Hip Prostheses in a Hip Joint Simulator

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total hip replacement for the last three decades. Despite the advancements in prosthesis design, the wear of UHMWPE remains a serious clinical problem; the release of wear debris may induce osteolysis and implant loosening. Understanding of wear behavior and wear debris morphology of the polyethylene is essential to improve the reliability of hip joint implants. The investigation in this paper carried out wear simulation tests of UHMWPE on Al2O3, 316L stainless steel, CoCrMo alloy and Ti6Al4V alloy, respectively. The lubrication of plasma solution and bovine serum solution was presented in wear tests. The effect of motion and loading on the wear behavior and wear debris morphology, and the influence of femoral head material and assembly style were studied in order to obtain a better understanding of the morphology of ultra-high molecular weight polyethylene wear particles. It is shown that the wear of UHMWPE acetabular cups against metal femoral heads was significantly higher than that against ceramic heads. The presence of protein in lubricant increases the wear of UHMWPE acetabular cups on Al2O3 heads. The wear rates of UHMWPE in multi-directional motion are approximately 2.5 times of those in uni-directional motion. The size distribution range of the UHMWPE debris particles for all head materials varies from submicron particles up to several hundreds micron. The size distribution range of wear debris particles is not directly related to wear resistance of UHMWPE, but significantly influenced by wear mechanisms. The UHMWPE debris particles produced in hip wear simulation tests are classified as round debris, flake-like debris and stick debris, which are closely related to the primary mechanisms of abrasive wear, adhesive wear and fatigue wear.

ATR-FTIR as a thickness measurement technique for hydrated polymer-on-polymer coatings.

Hydrated polymer coatings on polymer substrates are common for many biomedical applications, such as tissue engineering constructs, contact lenses, and catheters. The thickness of the coatings can affect the mechanical behavior of the systems and the cellular response, but measuring the coating thickness can be quite challenging using conventional methods. We propose a new method, that is, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the relative thickness, combined with atomic force microscopy to calibrate the ATR-FTIR measurements. This technique was successfully employed to determine the hydrated thickness of a series of crosslinked tetraglyme coatings on ultrahigh molecular weight polyethylene substrates intended to reduce wear of acetabular cups in total hip replacements. The hydrated coatings ranged from 30 to 200 nm thick and were accurately measured despite the relatively high root-mean-square (RMS) roughness of the substrates, 20-35 nm (peak-to-peak roughness 55-100 nm). The calibrated ATR-FTIR technique is a promising new method for measuring the thickness of many other polymer-on-polymer and hydrated coatings.

Comparison of wear of ultra-high molecular weight polyethylene acetabular cups against surface-engineered femoral heads

Alumina ceramic heads have been previously shown to reduce polyethylene wear in comparison to cobalt chrome (CoCr) heads in artificial hip joints. However, there are concerns about the brittle nature of ceramics. It is therefore of interest to investigate ceramic-like coatings on metallic heads. The aim of this study was to compare the friction and wear of ultra-high molecular weight polyethylene (UHMWPE) against alumina ceramic, CoCr, and surface-engineered ceramic-like coatings in a friction simulator and a hip joint simulator. All femoral heads tested were 28 mm diameter and included: Biolox Forte alumina, CoCr, arc evaporative physical vapour deposition (AEPVD) chromium nitride (CrN) coated CoCr, plasma-assisted chemical vapour deposition (PACVD) amorphous diamond-like carbon (aDLC) coated CoCr, sputter CrN coated CoCr, reactive gas controlled arc (RGCA) AEPVD titanium nitride (TiN) coated CoCr, and Graphit-iC coated CoCr. These were articulated against UHMWPE acetabular cups in a friction simulator and a hip joint simulator. Alumina and CoCr gave the lowest wear volumes whereas the sputter coated CrN gave the highest. Alumina also had the lowest friction factor. There was an association between surface parameters and wear. This study indicates that surface topography of surface-engineered femoral heads is more important than friction and wettability in controlling UHMWPE wear.

Effect of head surface roughness and sterilization on wear of UHMWPE acetabular cups

The impact of femoral head surface roughness on wear of gamma-irradiation sterilized (3 MRad in nitrogen, crosslinked) and nonsterilized (not crosslinked) UHMWPE acetabular cups has been evaluated. Gravimetric wear testing was performed in a hip joint simulator for 2 x 10(6) cycles. CoCrMo heads were used with different surface roughness (R(a) = 15 nm and R(a) = 400 nm). The surface roughness after wear test was unchanged for the roughened heads, whereas the initially smooth heads showed a few scratches. The roughened heads increased the wear of the acetabular cups 2-fold. The gamma-irradiated cups tested against rough heads underwent the highest wear. The absorption of water was highest for the gamma-irradiated cups (0.0204% compared to 0.0031% after 85 days). Raman spectroscopy showed small but significant crystallinity changes in the wear zone, where the gamma-irradiated cups with the most extensive abrasion increased in crystallinity, whereas the nonsterilized cups underwent a crystallinity decrease.

Activity levels and polyethylene wear of patients 10 years post hip replacement

Background Wear of the acetabular cup and implant loosening in total hip arthroplasty are thought to be affected by individual patient activity levels. Methods Activity levels of 100 patients with unilateral primary hip replacements were measured using a digital pedometer 10-years post-operatively. Findings Activity rates of hip replacement patients 10 years post surgery were found to fall with increasing age strata, with the age group 70–74 years showing significantly reduced activity rates compared to the 55–64 years age group and the age group greater than 80 years showing significantly reduced activity rates compared to both the 55–64 years age group and the 65–69 years age group. However, a clear correlation between age and activity was not found. Acetabular cup wear showed no relationship with patient activity levels. Interpretation Progressive reduction in activity levels with more elderly hip replacement patients may inform long term planning of hip arthroplasty and implant choice.

A new approach for assessment of wear in metal-backed acetabular cups using computed tomography: A phantom study with retrievals

Background and purpose Polyethylene wear is an important cause of aseptic loosening in hip arthroplasty. Detection of significant wear usually happens late on, since available diagnostic techniques are either not sensitive enough or too complicated and expensive for routine use. This study evaluates a new approach for measurement of linear wear of metal-backed acetabular cups using CT as the intended clinically feasible method.Material and methods 8 retrieved uncemented metal-backed acetabular cups were scanned twice ex vivo using CT. The linear penetration depth of the femoral head into the cup was measured in the CT volumes using dedicated software. Landmark points were placed on the CT images of cup and head, and also on a reference plane in order to calculate the wear vector magnitude and angle to one of the axes. A coordinate-measuring machine was used to test the accuracy of the proposed CT method. For this purpose, the head diameters were also measured by both methods.Results Accuracy of the CT method for linear wear measurements was 0.6 mm and wear vector angle was 27°. No systematic difference was found between CT scans.Interpretation This study on explanted acetabular cups shows that CT is capable of reliable measurement of linear wear in acetabular cups at a clinically relevant level of accuracy. It was also possible to use the method for assessment of direction of wear.

Effect of contact pressure on wear and friction of ultra-high molecular weight polyethylene in multidirectional sliding

Computational wear models need input data from valid tribological tests. For the wear model of a total hip prosthesis, the contact pressure dependence of wear and friction of ultra-high molecular weight polyethylene (UHMWPE) against polished CoCr in diluted calf serum lubricant was studied, and useful input data produced. Two test devices were designed and built: a heavy load circularly translating pin-on-disc (HL-CTPOD) wear test device and an HL-CTPOD friction measurement device. Both can be used with a wide range of loads. The wear surface diameter of the test pin was kept constant at 9 mm, whereas the load was varied so that the nominal contact pressure ranged from 0.1 to 20 MPa. The wear factor decreased with increasing contact pressure, whereas the coefficient of friction first increased with increasing contact pressure with low pressure values and then decreased. Up to the pressure of 2.0 MPa, the wear mechanisms and wear factors were in good agreement with clinical findings. In the critical range of 2.0-3.5 MPa, the wear mechanisms and wear factors started to differ from clinical ones, and the decrease of the wear factor steepened. The discrepancy became more and more evident as the pressure was gradually increased beyond 3.5 MPa. It appears that the pressure value of 2.0 MPa should not be exceeded in pin-on-disc wear tests that are to reproduce the clinical wear of UHMWPE acetabular cups.

In-vivo wear of hip surface replacements—a comparison of retrievals and simulator results

The wear of ultra-high molecular weight polyethylene (UHMWPE) has become a major focus regarding the long-term clinical performance of total joint replacements. Clinical retrieval analysis has revealed the existence of two distinct wear mechanisms that are operational in both total hip and total knee replacements. While the majority of the wear debris produced from the acetabular component is less than a micron in size and often particulate or fibrous in shape, much larger thin flakelike wear debris is produced from the tibial component. Two theoretical wear models that are based on the scale of intimate asperity interactions are proposed to account for the observed differences in hip and knee wear. Cyclic plastic strain accumulation is identified as the common cause for wear debris generation in both hip and knee replacements. In the case of acetabular cup wear, the scale of plastic deformation is limited to the sites of intimate micro-asperity contacts and the wear rate is defined by a critical strain criterion. In the case of tibial component wear, however, plastic deformation spreads into the subsurface to the site of macro-asperity contacts, and material can be removed by subsurface cracking and delamination. In both cases, the wear rate is strongly affected by the ultimate tensile strength and breaking elongation of the UHMWPE material.

Application of a stereometric structural analysis for an evaluation of surface and for a forecast of the wear of endoprothesis acetabular cups

To improve the resistance to wear and permanent deformation of polyethylene operating in a polymer/metal friction couple, initial plastic deformation of the polyethylene and its electron irradiation was applied. This contributed to a change of the polymer structure, visible already while machining when the sample surfaces were being prepared for a tribological test. The study shows that the interactions that shape the structure of polyethylene, at the same time cause adequate changes to the stereometric structure of its surface. The parameters of surface microgeometry characterize the future tribological behavior of polyethylene during its operation in a friction couple. It has been shown that an analysis of stereometric parameters may constitute the first projection of polymer wear resistance.