Investigation of the short-term in vivo performance of metal-on-carbon fibre reinforced poly ether ether ketone Motec wrists: an explant analysis.

Total wrist arthroplasty (TWA) aims to restore pain-free motion to diseased joints. One such TWA, the Motec, has demonstrated good results with acceptable complication rates. It has recently been suggested that the metal-on-carbon fibre reinforced poly ether ether ketone (Mo-CFR-PEEK) version of the Motec TWA be implanted instead of the metal-on-metal version. An explant analysis was undertaken on seven Motec Mo-CFR-PEEK TWAs, revised for a variety of reasons, after a mean time of 2 years in vivo. Compared to a new Motec implant, five of the explanted metal heads and three of the CFR-PEEK cups became smoother in vivo, suggesting self-polishing and negative skewness, indicating some material loss in vivo. Two explanted cups showed indentation marks on their rims and one of these was from component impingement with embedded metallic debris. In the short-term, the articulating surfaces of Motec Mo-CFR-PEEK TWAs did not show major damage.Level of evidence: IV.

The impact of femoral head size on the wear evolution at contacting surfaces of total hip prostheses: A finite element analysis.

Total Hip Arthroplasty has been a revolutionary technique in restoring mobility to patients with damaged hip joints. The introduction of modular components of the hip prosthesis allowed for bespoke solutions based on the requirements of the patient. The femoral stem is designed with a conical trunnion to allow for assembly of different femoral head sizes based on surgical requirements. The femoral head diameters for a metal-on-polyethylene hip prosthesis have typically ranged between 22 mm and 36 mm and are typically manufactured using Cobalt-Chromium alloy. A smaller femoral head diameter is associated with lower wear of the polyethylene, however, there is a higher risk of dislocation. In this study, a finite element model of a standard commercial hip arthroplasty prosthesis was modelled with femoral head diameters ranging from 22 mm to 36 mm to investigate the wear evolution and material loss at both contacting surfaces (acetabular cup and femoral stem trunnion). The finite element model, coupled with a validated in-house wear algorithm modelled a human walking for 10 million steps. The results have shown that as the femoral head size increased, the amount of wear on all contacting surfaces increased. As the femoral head diameter increased from 22 mm to 36 mm, the highly cross-linked polyethylene (XLPE) volumetric wear increased by 61% from 98.6 mm3 to 159.5 mm3 while the femoral head taper surface volumetric wear increased by 21% from 4.18 mm3 to 4.95 mm3. This study has provided an insight into the amount of increased wear as the femoral head size increased which can highlight the life span of these prostheses in the human body.

Long-term results and explant analysis of the ReMotion total wrist arthroplasty.

The ReMotion wrist replacement has good short- to medium-term survival with an acceptable complication profile as we previously reported in a cohort of patients with rheumatoid arthritis. We now report the long-term results of the same cohort and details of explant analysis of revisions undertaken for aseptic loosening. A total of 16 wrists were reviewed. Seven prostheses remain in situ with no obvious signs of wear or radiological loosening at a mean follow-up of 15.5 years. Three wrists had been revised: one for infection and two for aseptic loosening. Five patients (six wrists) died 2-9 years after operation from unrelated causes. Explant analysis demonstrated relatively minor wear compared with the published results of the Universal-2 prosthesis. We hypothesize that this may be explained by differences in polyethylene sterilization and prosthetic design. The ReMotion wrist replacement has favourable long-term results in patients with rheumatoid arthritis with a 16-year survival rate of 78%-86%.Level of evidence: IV.

Multi-functional bioactive silver- and copper-doped diamond-like carbon coatings for medical implants.

Diamond-like carbon (DLC) coatings doped with bioactive elements of silver (Ag) and copper (Cu) have been receiving increasing attention in the last decade, particularly in the last 5 years, due to their potential to offer a combination of enhanced antimicrobial and mechanical performance. These multi-functional bioactive DLC coatings offer great potential to impart the next generation of load-bearing medical implants with improved wear resistance and strong potency against microbial infections. This review begins with an overview of the status and issues with current total joint implant materials and the state-of-the art in DLC coatings and their application to medical implants. A detailed discussion of recent advances in wear resistant bioactive DLC coatings is then presented with a focus on doping the DLC matrix with controlled quantities of Ag and Cu elements. It is shown that both Ag and Cu doping can impart strong antimicrobial potency against a range of Gram-positive and Gram-negative bacteria, but this is always accompanied so far by a reduction in mechanical performance of the DLC coating matrix. The article concludes with discussion of potential synthesis methods to accurately control bioactive element doping without jeopardising mechanical properties and gives an outlook to the potential long-term impact of developing a superior multifunctional bioactive DLC coating on implant device performance and patient health and wellbeing. STATEMENT OF SIGNIFICANCE: Multi-functional diamond-like carbon (DLC) coatings doped with bioactive elements of silver (Ag) and copper (Cu) offer great potential to impart the next generation of load-bearing medical implants with improved wear resistance and strong potency against microbial infections. This article provides a critical review of the state-of-the-art in Ag and Cu doped DLC coatings, beginning with an overview of the current applications of DLC coatings in implant technology followed by a detailed discussion of Ag/Cu doped DLC coatings with particular focus on the relationship between their mechanical and antimicrobial performance. Finally, it ends with a discussion on the potential long-term impact of developing a truly multifunctional ultra-hard wearing bioactive DLC coating to extend the lifetime of total joint implants.

How does bicycling affect the longevity of Total Hip Arthroplasty? A finite element wear analysis.

As the number of young and active individuals undergoing Total Hip Arthroplasty (THA) are increasing yearly, there is a need for hip prostheses to have increased longevity. Current investigations into the longevity of these prostheses only include walking as the patient's activity as there is limited data on the amount and intensity of other activity performed by the patient. To further understand the evolution of wear and increase the longevity of these implants, the impact of different activities on the hip prosthesis needs to be investigated. In this study, a finite element model and wear algorithm was developed to simulate both walking and bicycling over a 5-year period. The XLPE acetabular cup volumetric wear rate was found to be 33 mm3/yr while the femoral head taper wear rates were between 0.01 - 0.39 mm3/yr. The results showed that by adding bicycling of up to 80 km per week with normal walking activity, the XLPE mean volumetric wear rate increased by 67% and the metallic mean volumetric wear rate by 11%. However, the patient may gain further health benefits from this additional activity. Assistive electric bikes may also be used to further reduce the loads on the hip joint, allowing for lower amounts of wear.

Explant analysis of a Discocerv cervical disc: A case study for a ceramic-on-ceramic cervical disc.

Explant analyses are key to better understanding the effectiveness of medical implants in replacing natural joints. For the first time, an explanted Discocerv cervical disc was examined. The implant utilised the articulation of a caudal zirconia cup (inferior component) and a cephalic alumina head (superior component). The articulating surface of the superior alumina head had an average surface roughness of 0.016 ± 0.003 µm (Sa) and the articulating surface of the inferior zirconia cup had an average surface roughness of 0.015 ± 0.002 µm (Sa). Both articulating surfaces had negative skewness, indicating the removal of local peaks. The difference between the average surface roughness of the components was not significant (p-value: 0.741). Dark grey marks were observed on both of the articulating surfaces, which were found to be adhered titanium debris that was generated due to component impingement. This titanium debris may explain the small amount of metallosis that was reported at explantation. Some transfer of zirconium to the alumina articulating surface was also seen.

Erratum: Author Correction: The influence of HLA genotype on the development of metal hypersensitivity following joint replacement.

[This corrects the article DOI: 10.1038/s43856-022-00137-0.].

The influence of HLA genotype on the development of metal hypersensitivity following joint replacement.

Background: Over five million joint replacements are performed across the world each year. Cobalt chrome (CoCr) components are used in most of these procedures. Some patients develop delayed-type hypersensitivity (DTH) responses to CoCr implants, resulting in tissue damage and revision surgery. DTH is unpredictable and genetic links have yet to be definitively established. Methods: At a single site, we carried out an initial investigation to identify HLA alleles associated with development of DTH following metal-on-metal hip arthroplasty. We then recruited patients from other centres to train and validate an algorithm incorporating patient age, gender, HLA genotype, and blood metal concentrations to predict the development of DTH. Accuracy of the modelling was assessed using performance metrics including time-dependent receiver operator curves. Results: Using next-generation sequencing, here we determine the HLA genotypes of 606 patients. 176 of these patients had experienced failure of their prostheses; the remaining 430 remain asymptomatic at a mean follow up of twelve years. We demonstrate that the development of DTH is associated with patient age, gender, the magnitude of metal exposure, and the presence of certain HLA class II alleles. We show that the predictive algorithm developed from this investigation performs to an accuracy suitable for clinical use, with weighted mean survival probability errors of 1.8% and 3.1% for pre-operative and post-operative models respectively. Conclusions: The development of DTH following joint replacement appears to be determined by the interaction between implant wear and a patient's genotype. The algorithm described in this paper may improve implant selection and help direct patient surveillance following surgery. Further consideration should be given towards understanding patient-specific responses to different biomaterials.

Tibial tray debonding from the cement mantle is associated with deformation of the backside of polyethylene tibial inserts.

AIMS: The aim of this study was to investigate whether wear and backside deformation of polyethylene (PE) tibial inserts may influence the cement cover of tibial trays of explanted total knee arthroplasties (TKAs). METHODS: At our retrieval centre, we measured changes in the wear and deformation of PE inserts using coordinate measuring machines and light microscopy. The amount of cement cover on the backside of tibial trays was quantified as a percentage of the total surface. The study involved data from the explanted fixed-bearing components of four widely used contemporary designs of TKA (Attune, NexGen, Press Fit Condylar (PFC), and Triathlon), revised for any indication, and we compared them with components that used previous generations of PE. Regression modelling was used to identify variables related to the amount of cement cover on the retrieved trays. RESULTS: A total of 114 explanted fixed-bearing TKAs were examined. This included 76 used with contemporary PE inserts which were compared with 15 used with older generation PEs. The Attune and NexGen (central locking) trays were found to have significantly less cement cover than Triathlon and PFC trays (peripheral locking group) (p = 0.001). The median planicity values of the PE inserts used with central locking trays were significantly greater than of those with peripheral locking inserts (205 vs 85 microns; p < 0.001). Attune and NexGen inserts had a characteristic pattern of backside deformation, with the outer edges of the PE deviating inferiorly, leaving the PE margins as the primary areas of articulation. CONCLUSION: Explanted TKAs with central locking mechanisms were significantly more likely to debond from the cement mantle. The PE inserts of these designs showed characteristic patterns of deformation, which appeared to relate to the manufacturing process and may be exacerbated in vivo. This pattern of deformation was associated with PE wear occurring at the outer edges of the articulation, potentially increasing the frictional torque generated at this interface. Cite this article: Bone Joint J 2021;103-B(12):1791-1801.

Retrieval analysis of an explanted Mobi-C cervical disc replacement: A case study.

Ex vivo analysis of artificial discs is essential to better understand their ability to replace degenerated intervertebral discs. The Mobi-C differs from some other contemporary disc designs in that it has a mobile polyethylene insert that is sandwiched between superior and inferior cobalt chromium endplates. While some studies claim the Mobi-C to have restored normal cervical spinal biomechanics, others have noted high levels of migration. Our objective was to contribute to this debate by, for the first time, analysing an explanted Mobi-C cervical disc which was removed due to worsening myelopathy at the nano and macro scales. Intraoperatively, the insert was found to have excessively migrated and it compressed the spinal cord. Roughness was measured as 0.016 ± 0.006 µm (Sa) and 0.055 ± 0.020 µm (Sa) for the superior and inferior plates, and 1.210 ± 0.154 µm (Sa) and 0.446 ± 0.083 µm (Sa) for the superior and inferior surfaces of the insert. Compared to unworn surfaces, the roughness increased for the superior and inferior plates and decreased for both surfaces of the insert. However, the only statistically significant change occurred on the articulating surface of the inferior plate (p = 0.04). At the nanoscale, valleys dominated the articulating surfaces. The superior plate had a burnished appearance whereas the inferior plate appeared matt. Impingement was observed on the endplates. The insert was severely damaged, burnished and had scratches. Additionally, subsurface whitening and internal cracking were observed on the insert.

Metallosis is commonly associated with magnetically controlled growing rods; results from an independent multicentre explant database.

PURPOSE: Determine the incidence of metallosis around MAGEC rods. METHODS: A multicentre explant database was searched to identify cases with complete intraoperative findings at rod removal. Surgeons removing rods detailed the presence or absence of tissue metallosis associated with rods. More recently surgeons measured the 'length' of tissue metallosis. Prior to rod disassembly, the majority underwent testing with an external remote controller (ERC). The impact of clinical and explant variables on metallosis was assessed. RESULTS: Sixty-six cases were identified. Mean age at insertion was 8.1 ± 2.3 years with mean duration of implantation 37.6 ± 15.1 months. Tissue metallosis was noted at revision surgery in 52/66 cases (79%). Metallosis was noted more commonly when rods were removed during fusion surgery than rod removal/exchange (97% vs. 58% (p = < 0.01)). The mass at insertion was greater in cases with metallosis (25.9 ± 7.8 kg vs. 21.1 ± 6.2 kg, p = 0.04). Length of tissue metallosis was reported for 45 rods, median 9 cm (range 1-25). Metallosis was noted in 43/59 (73%) rods that produced no force and 22/30 (73%) rods that produced some force on ERC activation (p = 0.96). Wear debris was found within the actuator in all rods, and all but 3 rods had damaged O-rings. CONCLUSION: MAGEC rods are associated with tissue metallosis in the majority of cases. It is seen with functional rods as well as failed rods and appears related to wear debris within the actuator and high rates of O-ring failure. Until the implications of metal debris in children are known, we urge caution with the use of this implant.

How does lubricant viscosity affect the wear behaviour of VitE-XLPE articulated against CoCr?

Using a 50-station pin-on-disc (SuperCTPOD) machine, the influence of lubricant viscosity on the wear of vitamin E blended crosslinked polyethylene was investigated. Five different test lubricants were prepared by mixing different concentrations of carboxymethyl cellulose powder with deionised water. The viscosity range of the lubricants was 0.002-0.155 Pa, a range that represents the viscosities of diseased and healthy synovial fluids. Five groups of pins (10 pins in each group) were articulated against cobalt chromium discs. Wear was measured in terms of weight loss from each pin and disc for every group. Every 500,000 cycles the experiment was stopped to take gravimetric measurements along with roughness measurements of the articulating surfaces. The test discs did not show a significant change in weight after 2.5 million cycles of testing (p > 0.05). For the pins, the group tested with the lowest viscosity (0.002 Pa) produced the highest wear rate, namely 0.931 mg/million cycles, and the wear rates of the other groups were 0.074, 0.027, 0.034 and 0.021 mg/million cycles respectively. The wear rates calculated for the five groups were all lower than the wear rates recorded for ultrahigh molecular weight polyethylene and not significantly different to crosslinked polyethylene. In addition, apart from group 1 pins (tested with the lowest lubricant viscosity (0.002 Pa)), the machining marks on the other pins were still present after 2.5 million cycles of testing, indicating low wear.

Explant analysis of a Maestro™ wrist prosthesis and calculation of its lubrication regime.

Explant analysis can provide key insights to understanding failures of artificial joints and thus how they might be improved for the ultimate benefit of patients. There are no previous reports of explant analysis of an artificial wrist joint. In this study, an explanted metal-on-polymer Maestro wrist was analysed both in macro and nanoscales to estimate its biotribological performance. The articulation was formed between a cobalt chromium carpal head and an ultrahigh molecular weight polyethylene bearing. The surface roughness values of its articulating surfaces and the backside of the articulation were measured. On average, the articulating surface roughness values were calculated as 0.06 ± 0.02 µm and 1.29 ± 0.63 µm for the cobalt chromium carpal head and ultrahigh molecular weight polyethylene bearing, respectively. Both surfaces had negative skewness, indicating a preponderance of valleys. On the articulating surface of the carpal head, light scratches were observed, and no impingement was observed throughout the component. The polymeric surface had a polished appearance. It had unidirectional scratches at the centre of the articulation, pits of different sizes on its articulating surface, and matt white subsurface regions. The backside of the UHMWPE bearing and the convex surface of the radial body that it was sitting on, were found to have average surface roughness values of 4.23 ± 0.69 µm and 5.57 ± 1.05 µm, respectively. The difference in the means was not significant (p > 0.05). Taking the articulating surface roughness values, the lubrication regime that the explanted Maestro wrist operated under in vivo was estimated for varying physiological conditions, i.e. varying loads, entraining velocities and lubricant viscosities. In every case considered, the explant was found to operate under boundary lubrication.

Analysis of the surface topography of retrieved metal-on-polyethylene reverse shoulder prostheses.

Despite the encouraging short- and medium-term clinical results and increased usage of reverse shoulder replacements, a higher revision rate is documented compared with other major joint arthroplasties. Adverse reaction to polyethylene wear debris is still an important factor which may influence the long-term survival of reverse shoulder arthroplasty. To date, only a small number of retrieval studies of reverse shoulder arthroplasty have reported the different damage modes on polyethylene components, but none have quantified the ex vivo surface roughness on both articulating surfaces. The main purpose of this study was to assess, for the first time, the surface roughness of 13 retrieved metal-on-polyethylene reverse shoulder replacements using a white light profilometre with nanometre resolution. Although no significant relationship was observed between the surface roughness values and patient variables, it was noted that half of the polyethylene components still showed their original machining marks, indicating little change in vivo and that the metallic humeral components in the reversed design configuration showed low values of surface roughness after their time in vivo.

The NuVasive MAGEC Rod Urgent Field Safety Notice Concerning Locking Pin Fracture: How Does Data From an Independent Explant Center Compare?

STUDY DESIGN: Analysis of explanted MAGnetic Expansion Control (MAGEC) growing rods. OBJECTIVE: The aim of this study was to quantify the rate of locking pin breakage in explanted MAGEC rods and compare with the manufacturer's data. SUMMARY OF BACKGROUND DATA: On June 25, 2019, NuVasive released an Urgent Field Safety Notice stating that MAGEC rods manufactured before March 26, 2015 had a higher than expected locking pin breakage rate of 5%. For rods made on or after that date, no pin breakages had occurred. METHODS: From our independent explant database of 139 explanted MAGEC rods supplied from 10 UK spinal centers (Belfast, Bristol, Birmingham, Edinburgh, Exeter, Leeds, Newcastle, Nottingham, Oxford, and Sheffield) and one Danish center (Aarhus), we divided the rods into those manufactured before March 26, 2015, and those manufactured on or after that date. MAGEC rods were cut open to fully assess internal components including locking pins. From each of the two cohorts, 10 locking pins were selected at random and their diameters were measured using a micrometer. RESULTS: One hundred and five explanted MAGEC rods were made before March 26, 2015 and could be disassembled to allow the locking pin to be examined. Fifty-nine percent (62/105) of these locking pins had fractured. For the MAGEC rods manufactured on or after March 26, 2015, 21% (6/29) were found to have fractured locking pins. Locking pins in MAGEC rods made on or after March 26, 2015 were of a stronger material and a larger diameter. CONCLUSION: Fifty-nine percent of the locking pins in MAGEC rods manufactured before March 26, 2015 had fractured, far greater than the 5% stated in the Urgent Field Safety Notice. Locking pin fracture still occurred in MAGEC rods manufactured on or after that date, in 21% of cases. This contrasted with the 0% reported by the manufacturer. LEVEL OF EVIDENCE: 4.

Hip simulator testing of the taper-trunnion junction and bearing surfaces of contemporary metal-on-cross-linked-polyethylene hip prostheses.

Adverse reaction to metal debris released from the taper-trunnion junction of modular metal-on-polyethylene (MoP) total hip replacements (THRs) is an issue of contemporary concern. Therefore, a hip simulator was used to investigate material loss, if any, at both the articulating and taper-trunnion surfaces of five 32-mm metal-on-cross-linked-polyethylene THRs for 5 million cycles (Mc) with a sixth joint serving as a dynamically loaded soak control. Commercially available cobalt-chromium-molybdenum femoral heads articulating against cross-linked polyethylene (XLPE) acetabular liners were mounted on 12/14 titanium (Ti6Al4V) trunnions. Weight loss (mg) was measured gravimetrically and converted into volume loss (mm3 ) for heads, liners, and trunnions at regular intervals. Additionally, posttest volumetric wear measurements of the femoral tapers were obtained using a coordinate measuring machine (CMM). The surface roughness (Sa) of femoral tapers was measured posttest. After 5 Mc, the mean volumetric wear rate for XLPE liners was 2.74 ± 0.74 mm3 /Mc. The CMM measurements confirmed material loss from the femoral taper with the mean volumetric wear rate of 0.045 ± 0.024 mm3 /Mc. The Sa on the worn area of the femoral taper showed a significant increase (p < 0.001) compared with the unworn area. No other long-term hip simulator tests have investigated wear from the taper-trunnion junction of contemporary MoP THRs. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:156-166, 2020.

Spinal Lengthening With Magnetically Controlled Growing Rods: Data From the Largest Series of Explanted Devices.

STUDY DESIGN: Laboratory analysis of explanted MAGnetic Expansion Control (MAGEC) rods. OBJECTIVE: The aim of this study was to identify the in vivo lengthening of MAGEC rods. SUMMARY OF BACKGROUND DATA: Little data is available regarding the lengthening achieved by MAGEC rods. METHODS: Cases were identified from the largest series of independently analyzed explanted MAGEC rods. The in vivo growth of rods was determined by the distance between the first "growth mark" and the actuator. The instrumented spinal lengthening was calculated for each construct. Constructs were considered functional if all rods could lengthen with external remote controller activation and no rods were "telescoping". RESULTS: Fifty-five MAGEC constructs (99 rods) from 53 patients treated at 10 centers were included. The mean age at insertion was 8.5 years with rods implanted a mean of 35 months. Sixty rods were suitable for analysis with mean lengthening 21.7 mm, 8.9 mm/year. Of these 60 rods, three were maximally distracted. Mean instrumented spinal lengthening for 38 suitable cases was 22.1 mm, 8.4 mm/year. This was positively correlated with the duration of implantation (r = 0.34, P = 0.04) but negatively with patient age at insertion (r = -0.35, P = 0.03). The rate of instrumented spinal lengthening was negatively correlated with duration of implantation (r = -0.47, P = 0.004). Of 55 constructs, 34 were nonfunctional at time of removal with nine functional and 12 indeterminate. Functional constructs had been implanted significantly less time (20.0 vs. 39.7 months, P < 0.001) and lengthened less than those nonfunctional (12.3 mm vs. 23.3 mm, P = 0.04). CONCLUSION: This multicenter explant study represents the largest cohort managed with MAGEC rods reported. Rods are very rarely removed having fully lengthened with mean instrumented spinal growth of 22 mm over the implant's life. This may be explained by a high rate of lengthening mechanism failure in received rods after around 3 years in vivo. Our findings question the effectiveness of the MAGEC system and mandate urgent comparative clinical studies. LEVEL OF EVIDENCE: 4.

Wear behaviour of polyethylene glenoid inserts against PyroCarbon humeral heads in shoulder arthroplasties.

The generation of polyethylene wear debris, and the subsequent tissue reaction to such debris is considered to be a limitation in the long-term survival of shoulder arthroplasties. The purpose of this study was to investigate, for the first time, the wear of a novel PyroCarbon-on-Polyethylene (PyCoP) shoulder arthroplasty system. A 5 million cycle wear test was performed on PyroCarbon humeral heads, which were articulated against commercially available polyethylene glenoid insert components to form an anatomic total shoulder arthroplasty (aTSA). A "Repeat-motion-load" physiological combined cycle was applied using the unique Newcastle Shoulder Wear Simulator. Wear was assessed gravimetrically, and the change of the surface roughness was measured with a non-contacting profilometer. The mean wear rate of the ultra-high molecular weight polyethylene (UHMWPE) components was 19.3 ± 9.5 mm3/million cycles after 5 million cycles of testing. The roughness value, Sa, of the UHMWPE glenoid inserts, reduced, changing from 296 ± 28 nm Sa to 32 ± 8 nm Sa. In contrast, the mean roughness of the PyroCarbon humeral heads remained in the same range (21 ± 2 nm Sa to 20 ± 10 nm Sa). There was no reduction in weight (no measurable wear) of the PyroCarbon humeral heads over the duration of testing. This study is the first to describe the wear performance of UHMWPE glenoid inserts against PyroCarbon humeral heads. No significant difference in the wear of UHMWPE was found in comparison with published studies.

Wear behaviour of CFR PEEK articulated against CoCr under varying contact stresses: Low wear of CFR PEEK negated by wear of the CoCr counterface.

Total hip replacement with metal-on-polymer hip prostheses is the most common treatment for late-stage osteoarthritis. However, the wear debris generated from the polymer acetabular liner remains a problem. Alternative materials with claimed superior wear properties have been proposed to overcome this problem. In this study, the wear behaviour of carbon fibre reinforced polyether ether ketone (CFR PEEK) was investigated under different contact stresses that are observed in the natural hip joint. A 50-station pin-on-disc machine (SuperCTPOD) was used to investigate the wear behaviour of 50 CFR PEEK pins articulated against cobalt chromium (CoCr) discs under five different contact stresses, namely 1.11, 1.38, 1.61, 2.00 and 5.30 MPa. The results showed that the wear rates of the pins did not differ significantly between groups under different contact stresses. In addition, CFR PEEK produced lower wear rates than ultrahigh molecular weight polyethylene and cross-linked polyethylene. However, the weight of the CoCr discs was found to decrease significantly at the end of the wear test, which was indicative of metallic wear. The findings of this study indicated that, despite having relatively low wear rates, CFR PEEK is not a good alternative to be utilised against orthopaedic metals.

The effect of combined loading cycles on the wear of reverse shoulder joint replacements.

Wear of polyethylene is a current limitation in the long-term survival of reverse shoulder arthroplasties (RSAs). The purpose of this study was to investigate, for the first time, the influence of a combination of clinically relevant activities of daily living (ADLs) as patterns of motion and loading on the wear of ultra-high molecular-weight polyethylene (UHMWPE) in RSA. This physiological combined cycle, termed "repeated-motion-load", was applied on four new samples of a commercially available reverse shoulder prosthesis for five million cycles using the unique Newcastle Shoulder Wear Simulator. This resulted in a mean wear rate of 12.0 ±â€¯3.9 mm3/million cycles for the UHMWPE components in combination with metallic glenospheres, while the average articulating UHMWPE surface roughness reduced from 692 ±â€¯132 nm Sa to 42 ±â€¯29 nm Sa.