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).

Introduction. The causes for revision of primary total hip arthroplasty (THA) are various and quite well known. The developing use of dual-mobility THA (DM-THA) seems a relevant option to decrease the risk of instability. Due to lack of long-term follow-up, this innovative retentive concept is suspected to increase the risk of polyethylene (PE) wear. The aim of the study was to analyse the causes for DM-THA revision and assess whether or not its occurrence is different from that of fixed-standard (FS) THA, particularly for aseptic loosening or wear and/or osteolysis. Materials and methods. The SoFCOT group conducted an observational prospective multicentre study from 1 January. 2010 to 31 December 2011. Inclusion criteria comprised an exhaustive collection of 2044 first-revision THAs with 251 DM-THAs and 1793 FS-THAs. After excluding complications linked to patient factors (infection and periprosthetic fractures), we performed a matched case–control study (matching ratio 1:1) comparing two groups of 133 THAs. Results. Revisions for aseptic loosening or osteolysis/wear were as frequent in DM-THA (58.7 %) as in FS-THA (57.1 %) (p 0.32); 7.5 % of DM-THAwere revised for dislocation versus 19.5 % of FS-THA (p 0.007). Discussion. Revision for osteolysis/wear and aseptic loosening were as frequent in DM-THA as in FS-THA; revision for dislocation was less frequent in DM-THA. This confirms the efficiency of the DM concept regarding the risk of dislocation. Causes for revision were different between groups, and revisions for dislocation were less frequent in DM-THA. Only prospective comparative studies could provide reliable information that may support broader use of the DM concept

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated with a mean follow-up of 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant level over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR after twenty years

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) system after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated. The mean follow-up was 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant rate over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR and does not stop after twenty years

Total Hip Arthroplasty (THA) is a well-established, cost-effective treatment for improving function and alleviating pain in patients who have disabling hip disease with excellent long-term results. Based on the excellent results, there is an ongoing trend for THA to be performed in younger and more active patients, having higher physical demands on their new total joints. Polyethylene (PE) wear and its biological consequences are one of the main causes of implant failure in THA. Macrophages phagocytise PE wear particles and this will result in osteolysis and loss of periprosthetic bone. The risk of these complications can be estimated in relation to the amount of volumetric wear based on two assumptions: that the number of PE particles dispersed in the peri-prosthetic tissues is controlled by the amount of PE wear; and that the development of osteolysis and the resulting aseptic loosening is triggered by these PE particles. Based on these assumptions, a model was developed to estimate the osteolysis-free life of a THA, depending on the Linear Wear Rate (LWR) and femoral head size of the PE bearing. A review of the literature was conducted to provide an estimate of the radiologic osteolysis threshold based on the volumetric wear of the PE bearing. This review demonstrates that this radiologic osteolysis threshold is approximated 670 mm3 for conventional PE. The osteolysis-free life of the THA was estimated by simply dividing this threshold volume by the annual Volumetric Wear Rate (VWR) of the bearing. The annual VWR is basically controlled by two parameters: (1) annual LWR and (2) head size, and was calculated by using published formulae. For 28 mm heads, following osteolysis-free life was determined in function of the annual LWR. LWR: 10 µm/y => 116.6 years / LWR: 25 µm/y => 46.6 years / LWR: 50 µm/y => 23.3 years / LWR: 100 µm/y => 11.6 years. For 40 mm heads, following osteolysis-free life was determined in function of the annual LWR. LWR: 10 µm/y => 57.1 years / LWR: 25 µm/y => 22.9 years / LWR: 50 µm/y => 11.4 years / LWR: 100 µm/y => 5.7 years. The osteolysis-free life determined by this model is in good agreement with the clinical results of PE bearings having a 28 mm head size and demonstrates that extreme low LWRs are mandatory to assure a descent osteolysis-free life for THA (PE bearings) using large heads, such as 40 mm. For such head sizes, small variations of the LWR may have large impacts on the osteolysis-free life of the THA

Introduction. Polyethylene (PE) wear is clearly linked to total hip arthroplasty (THA) failure, leading to osteolysis and decreasing survivorship rates. Dual mobility cups (DMC) are widely used to prevent or treat THA instability. However some studies have pointed PE wear risk as a “dual wear” risk. Hip wear simulation is usually used to understand factors influencing wear and to differentiate design, PE types and materials performances. To date, few works have been published studying dual mobility insert wear. Objectives. Our objective was to evaluate wear of DMC with comparison with a fixed single articulating hip design and to measure wear under same conditions (loading cycle, temperature, sterilization, material and surface roughness). Methods. The test bench includes one station for a control sample and one for dynamic test. Those are driven independently one from the other. Two electrical actuators applied the forces and two forces sensors putted on the fixing plate of the acetabular part gave the corresponding values. On the dynamic station, the angular movements are generated by an electric motor. Sleeves are installed on the bowls containing the testing liquid and on the supports of acetabular parts, in order to get a tight volume that excludes contaminant particles. Wear is measured by a gravimetric method. The simulator is stopped and implants have been removed from the simulators in order to achieve weighting and observations at 0.5, 1, 2, 3, 4 and 5 millions cycles. At the end, the sample PE insert and the control one are removed from their cup in the aim to measure the mass loss. Results. Under same conditions the gravimetric wear and the linear penetration of the head are perfectly comparable between a conventional and a dual mobility cup. Conclusion. In vitro, DMC wear is equal or less important than a standard single fixed cup and volumetric wear is lower than published data. Wear of the two joints of a DMC is not increased thanks to the recruitment phenomenon and the freedom induced by the concept

Introduction. Pelvic posterior tilt change (PPTC) after THA is caused by release of joint contracture and degenerative lumbar kyphosis. PPTC increases cup anteversion and inclination and results in a risk of prosthesis impingement (PI) and edge loading (EL). There was reportedly no component orientation of fixed bearing which can avoid PI and EL against 20°PPTC. However, dual mobility bearing (DM) has been reported to have a large oscillation angle and potential to withstand EL without increasing polyethylene (PE) wear against high cup inclination such as 60∼65°. Objective. The purpose of this study was to investigate the optimal orientation of DM-THA for avoiding PI and EL against postoperative 20°PPTC. Methods. Our study was performed with computer tomography -based three-dimensional simulation software (ZedHip. LEXI co. Japan). The CT data of hip was derived from asian typical woman with normal hips. Used prosthesises were 50mm cup and 42mm outer head of modular dual mobility system and Accolade II 127°(stryker). Femoral coordinate system was retrocondylar plane with z-axis from trochanteric fossa to intercondylar notch. Cup orientation was described as anatomical definition. The safe zone was calculated by the required hip range of motion which was defined as 130°flexion, 40°extension, 30°external rotation, and 50°internal rotation with 90°flexion and the maximum inclination of DM cup which was 60°in consideration of withstanding EL. Cup orientations withstanding 20°PPTC were defined as the primary cup orientation which changes consistently within the safe zone with the match of 20°PPTC. And among them cup orientation with lowest inclination was defined as the optimal cup orientation. result. The optimal orientations could be identified only within stem anteversion from 15°to 40°. The relationship between the optimal cup orientation and stem anteversion could be automatically identified. The correlation between stem anteversion and cup anteversion was linearly distributed and could be expressed as an approximated line of the formula that (stem anteversion)+(cup anteversion)=36.8. And likewise the relationship between stem anteversion and cup inclination was curved-linerly distributed and could be expressed as an approximated curved line of the formula that (cup inclination)=0.04(stem anteversion). 2. 2.18(stem anteversion)+74.8. Cup orientation calculated by the Widmer's combined anteversion theory is easily deviated from the safe zone by PPTC. The optimal cup orientation calculated in this study could be set more inclination and retroversion than it calculated by the Widmer's theory in contribution of large oscillation angle and admissibility of high inclination cup setting of DM. Therefore it could be possible to withstand 20°PPTC. Conclusion. Performing THA with considering postoperative PPTC is necessary for good long term outcome without dislocation and PE wear. The solution for 20°PPTC after THA is to apply dual mobility bearing and the formula of combined orientation theory calculated in this study

Introduction. In Total Hip Arthroplasty (THA), polyethylene wear reduction is key to implant longevity. Oxidized Zirconium (OxZi) unites properties of a ceramic bearing surface and metal head, producing less wear in comparison to standard Cobalt-Chromium (CoCr) when articulating with Cross-linked polyethylene (XLPE) in vitro. This study investigates in vivo polyethylene (PE) wear, outcomes and complications for these two bearing couples in patients at 5 year follow-up. Methods. 400 patients undergoing THA across four institutions were prospectively randomised into three groups. Group I received a cobalt-chrome (CoCr) femoral head/ cross-linked polyethylene (XLPE) liner; Group II received an OxZi femoral head/ ultrahigh molecular weight polyethylene (UHMWPE) liner; Group III received an OxZi femoral head/XLPE liner. All bearing heads were 32 mm. Linear wear rate was calculated with Martell computer software. Functional outcome and complications were recorded. Results. At median follow-up of 3.7 years, implant survivorship was 98% across all groups with no difference in SF-36, WOMAC, pain score or complications (p > 0.05). After the first 12 months of creep, rate of linear wear over 3 years was 0.07 mm for Group I, 0.16 mm for Group II, and 0.03 mm/year for Group III. A significant difference was detected when using UHMWPE (p = 0.012) but not when using XLPE (P = 0.75). Conclusion. At midterm follow-up, an XLPE acetabular liner is more important in reducing wear than the femoral head bearing. There is a trend towards lower wear when coupling OxZi rather than CoCr with XLPE; further long-term analysis is recommended to observe this pattern

We have developed and tested the accuracy of a completely automated method for polyethylene (PE) wear measurement of digitised antero-posterior and lateral radiographs. New computer algorithms have been developed to measure PE wear on digitised hip radiographs. The only user input required is the file name of the x-ray. Validation was performed by simulation of PE wear in an acrylic phantom. Radiographs were analysed with the new software and results were compared to know penetration of the femoral head. Accuracy using 10 antero posterior and lateral phantom radiographs was within ±0.08mm (95% CI) of the real femoral head penetration. There was no inter or intra-observer error (identical results with all measurements). Perhaps most importantly, this system gave accurate results in 94% of 600 clinical radiographs of variable quality. Only 74% of this same group of radiographs were considered of sufficient quality to allow reliable manual measurement. This new method of PE wear measurements eliminated inter and intra-observer error, allowing comparison of wear results between different institutions. Accuracy is improved, but still limited by resolution of the scanned image

Background: The role of polyethylene (PE) wear in relation to synovitis and elevated hydrostatic pressure in the loosening process after THA has gained increased attention. The aim of our study was to investigate the correlation between prosthetic head size, PE wear and sonographic capsular distention, reflecting the degree of intracapsular synovitis/synovia/hydrostatic pressure. Patients and methods: In 2005 we analyzed 60 randomly selected and unrevised OA patients 10 years after surgery with 32 or 28mm femoral heads. We evaluated radiographic signs of loosening, linear and volumetric PE wear. Sonographic examination was performed to measure the “capsular distance”, i.e. the capsular distension, defined as the distance between the metallic echo from the anterior surface of the prosthetic femoral neck, and the echo from the anterior surface of the anterior capsule. Results: The linear wear was 0.2 mm per year and 0.1 mm per year in the 32 mm and 28 mm head size group respectively (p< 0.001), the volumetric wear was 139 mm3/year and 48 mm3/year (p< 0.001), and the capsular distention was 17 mm and 13 mm respectively (p< 0.001). There was also a significant positive correlation between PE volumetric wear and capsular distension (r=0.63, p< 0.001). Interpretation: We conclude that 32 mm femoral heads were associated with almost three times higher volumetric wear as compared to 28 mm heads, and increased “capsular distension”, reflecting increased synovitis/synovia/hydrostatic pressure in prosthetic hip

In total hip arthroplasty (THA), aseptic loosening induced by polyethylene (PE) wear debris is the most important cause that limits the longevity of implants. Abrasive wear generated through the mechanism such that micrometer-roughened regions and small asperities on the metallic femoral heads surface locally plow through the PE cup surface. Abrasive wear results in the PE material being removed from the track traced by the asperity during the motion of the metallic femoral heads surface. For the purpose of reducing wear, alumina ceramics was introduced in Europe and Japan in 1970s. The clinical results of ceramic-on-PE bearings regarding the wear resistance have been superior to that of the metal-on-PE bearings. Compared with Co–Cr–Mo alloys, alumina ceramics is advantageous for precision machining because of its higher hardness, enable to form spherical and smooth surface. The fracture resistance of the alumina ceramics itself is related to grain size; the grain size reduction leads to the improvement of its resistance. In this study, we evaluated the roundness and the roughness of retrieved two distinct alumina ceramics having different grain size, and Co–Cr–Mo alloy heads. Fourteen retrieved alumina ceramic femoral heads; ten heads with a diameter of 28 mm made of small grain size alumina (SG-alumina; mean grain size is 3.4 μm) with clinical use for 16–28 years and four heads with a diameter of 26 mm made of extra-small grain size alumina (XSG-alumina; mean grain size is 1.3 μm) with clinical use for 14–19 years, were examined. Six retrieved Co–Cr–Mo alloy femoral heads with a diameter of from 22 to 32 mm with average clinical use for 12–28 years were examined. SG-alumina and XSG-alumina heads showed significantly lower roundness compared with Co–Cr–Mo alloy heads, due to higher precision machining [Fig. 1]. The surface roughness for the contact area of the heads increased in order of XSG-alumina, SG-alumina and Co–Cr–Mo alloy. The surface roughness of the non-contact area for all kinds of heads was lower than that for the contact area [Fig. 2]. Surface profiles of the SG-alumina and XSG-alumina showed the reentrant surface while Co–Cr–Mo alloy heads showed the protrusion surface. The roundness and roughness of the Co–Cr–Mo alloy or ceramic surface and the presence or absence of hard third-body particles correlate to the amount of abrasive PE wear. When the third-body was entrapped during the clinical use, a reentrant surface might be formed on the ceramic while protrusion surface formed on the Co–Cr–Mo alloy. The differences in clinical results may be due in part to the influence of third-body particles. The ceramic becomes more resistant than Co–Cr–Mo alloy against the scratching by the entrapped abrasive contaminants because of its harder surface. From the good clinical results of more than 20 years using SG-alumina, the greater long term clinical results using XSG-alumina will be expected

Over the past decade, there has been an increase in the number of total knee arthropalsty (TKA). Demand of TKA for the young patients who often have high physical demands is also increasing. However, the revision rate in such young patients is much higher due to polyethylene (PE) wear and instability (Julin J, Acta Orthop 2010). Therefore, next generation total knee prostheses are expected to decrease PE wear and to provide stability. Although in vitro study such as wear simulator test provides important information about PE wear, we have often encountered the discrepancy between the in vitro results and in vivo results. Thus we have performed in vivo PE wear particle analysis, and showed that in vivo PE wear was affected by the design of articulating surface and the materials of femoral component and PE insert (Minoda Y, JBJS Am 2009). Medial pivot design, ceramic femoral component, and highly cross-linked PE decreased in vivo PE wear particle generation. Patients who underwent bilateral staged TKAs were more likely to prefer medial pivot prosthesis or ACL-PCL retaining prosthesis than the other types of prostheses, because they feels “more stable overall” (Pritchett JW, J Arthroplasty 2011). In vivo fluoroscopic 3D analysis showed that medical pivot and bi-cruciate substituting designs restored physiological knee motion and provided higher reproducibility (Mueller J. Komistek RD, Trans ORS 2009, Iwakiri K, Trans ORS 2007). The excellent mid-term clinical results of those newly introduced total knee prosthesis, such as alumina medial pivot TKA (Iida T, ORS 2008), medial pivot TKA (Mannan K, JBJS Br 2009, Kakachalions T, Knee 2009), ACL-PCL retaining TKA (Clouter JM, JBJS Am 1999), and highly cross-linked PE (Hodrick JT, CORR 2008), have been reported. From the point of view of in vivo PE wear, in vivo stability, and the mid-term clinical results, we suspect that medial pivot prosthesis is one of the prostheses which meet the demand in future especially for young active patients

Background: The Delta Inverse Shoulder Arthroplasty, has gained considerable popularity in France and Europe for Rotator Cuff (RC) deficient patients. However complications related to surgical difficulties with insertion, mechanical loosening, and polyethylene (PE) wear are now being reported. The increasing numbers of complications are alarming. Methods: A computerised analysis of the kinematics associated with inverse shoulder replacements has been developed. Different glenoid dome sizes and humeral cup dimensions have been tested. This has highlighted the deficiencies associated with the design of the inverse shoulder prostheses currently available on the market. Modifications of the prosthesis geometry and the inclusion of a mobile bearing have also been subjected to computer analysis and have demonstrated improved kinematics and a reduction in the risk of bone/prosthesis contact. A medium term follow-up of 9 patients with a mobile bearing Inverse shoulder design has been carried out. Compression tests have been carried out on the PE bearing to identify the risk of plastic deformity of the PE. Results: The results of the computerised analysis and the clinical results from the first 9 patients will be reported. One patient suffered an operative complication with failure of reduction of the prosthesis which was rectified at an immediate re-operation. The early clinical results are similar to the good results obtained with the Delta prosthesis. However polyethylene bearing failure has occurred in one case, highlighting the importance of optimising the geometry of the inverse shoulder. Both Radio-Stereometric Analyses (RSA) and prospective randomised studies comparing this Inverse prosthesis with either a Cuff Tear Arthropathy (CTA) hemiarthroplasty designes (when Gleno-Humeral(GH) OA is present) or with cuff reconstruction using augmentation (when no GH OA is present) have been designed and will be discussed

To prevent aseptic loosening resulting from osteolysis induced by polyethylene (PE) wear particles in THA, it is necessary to develop a high wear-resistance bearing material. We have investigated the bearing surface mimicking the articular cartilage; grafting a biocompatible polymer, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), onto the PE surface. High wear-resistance of PMPC-grafted surface has been revealed in the hip simulator wear test of 20 million cycles. Additionaly, in THA, oxidation degradation induced by residual free radicals resulting from gamma-ray irradiation for cross-linking or sterilization is also regarded as serious issue. Recently, gas plasma (GP) sterilization has been used as a less residual radical sterilization method. In this study, we ask a question: the GP sterilization would affect to PMPC surface and/or PE substrate? Hence, we investigated surface chemical, wear, mechanical, physical and oxidation properties of GP sterilized PMPC-grafted highly cross-linked PE (CLPE). GP-sterilized CLPE and PMPC-grafted CLPE (CLPE (GP) and PMPC-CLPE (GP), respectively; GUR 1020 resin, 75 kGy irradiation), and 25 kGy-gamma-sterilized PMPC-grafted CLPE (PMPC-CLPE (g); GUR 1020 resin, 50 kGy irradiation) were evaluated. Surface property of PMPC layer was evaluated by X-ray photoelectron spectroscopy (XPS), fourier-transform infrared (FT-IR) spectroscopy, fluorescence microscope and cross-sectional transmission electron microscope (TEM) observations. Wettability and lubrication of the PMPC-CLPE surface were evaluated by static water contact angle measurement and ball-on-plate friction test, respectively. Wear properties of the acetabular cups were examined by using hip simulator in the combination with Co-Cr-Mo femoral heads. To evaluate the GP sterilization effect to the CLPE substrate, tensile test, izod impact test, small punch test, gel content, residual radical concentration and oxidation degradation were conducted. Oxidation degradation was evaluated as oxidation index by using a FT-IR spectroscopy. By the XPS and FT-IR measurements, phosphorus peak and P-O peak attributed to grafted PMPC were observed, respectively. Uniform PMPC layer (100–200 nm thick) was observed on both surfaces of PMPC-CLPE (g) and PMPC-CLPE (GP) [Fig. 1]. Water contact angle of CLPE (GP) was almost 100 degree, while those for PMPC-CLPE (g) and PMPC-CLPE (GP) decreased dramatically to almost 10 degree. Dynamic coefficient of friction of PMPC-CLPE (g) and PMPC-CLPE (GP) was lower than that for CLPE (GP). In the hip simulator wear test, PMPC-CLPE (g) and PMPC-CLPE (GP) cups showed significantly lower amount of wear than that of CLPE (GP) [Fig. 2]. The number of the wear particles was extremely less in PMPC-CLPE (g) and PMPC-CLPE (GP), though the size was not different of all cases. Water thin film might be formed at the grafted PMPC layer, which acted as significantly efficient lubricant. There was no difference in the mechanical and physical properties among three groups. Oxidation index for PMPC-CLPE (GP) after acceleration of aging was lower than that of PMPC-CLPE (g). The GP sterilization might affect only to the PMPC-grafted surface, whereas gamma irradiation affects also to the PE substrate. From these results, the PMPC-CLPE (GP) is expected to be one of the great bearing materials having not only high-wear resistance but also high-oxidation resistance, which could give further longevity of implantation

Knee wear simulator studies are performed to evaluate wear behavior of implants. Simulation of the human gait cycle is often carried out continuously, without considering resting periods as they are part of patient’s daily live. In addition to dynamic activities like walking, daily activities also consist of static periods like standing, sitting or lying. During the day dynamic activities alternate continuously with static periods and most of the day is spent in passive periods, where no joint motion occurs. Such resting periods have not yet been considered in prosthetic knee wear tests. Implementing resting periods may cause an increase in friction and thus increased wear of the implant. The aim of the current study was to determine if the implementation of resting periods would increase polyethylene (PE) wear in total knee replacement (TKR). Two wear studies were conducted using a force controlled AMTI knee simulator on a conventional bicondylar TKR. For the first study, simulation was carried out continuously according to ISO 14243-1. For the second test, four active gait cycles according to ISO 14243-1 were followed by one resting period cycle. In both tests 5x10E6 active load cycles at a frequency of 1 Hz (resulting in additional 1.25x10E6 pause cycles for the second test) were applied. Wear was measured gravimetrically and wear scars were documented photographically. The mean wear rates measured 2.85 ± 0.27 mg/10E6 cycles for the ISO test without considering resting periods and 2.27 ± 0.23 mg/10E6 cycles for the test with resting periods implemented. There was no significant difference (p=0.22) in wear rate between both tests. The inserts showed similar wear scars in both tests and no relevant differences in dimension and localization on the surface. Therefore the wear behavior after the two tests was similar. Since wear is one of the most limiting factors for implant longevity, proper preclinical wear studies are essential. Based on the results of this experimental wear study, a continuous simulation without additional resting periods seems to be valid in wear simulation of TKR

Polyethylene (PE) wear affects survivorship in the long term while dislocation remains a significant factor in the short term. Increasing head size can reduce impingement and dislocation. However, this increases wear rates and reduces the net thickness of the liner. Several reports have demonstrated significant reduction in wear in cross-linked PE. This study reports wear rates in crosslinked PE liners with increased head size. Four groups of PE liners were tested against cobalt-chrome heads in a hip wear simulator: highly crosslinked liners with head size 28mm (28XPE) and 32mm (32XPE), and minimally crosslinked liners with head size 28mm (28PE) and 32mm (32PE). Additional liners were used as load-soak controls to monitor weight gain due to fluid absorption. Gravimetric analysis was performed every 500,000 cycles for a total of 5,000,000 cycles. 28PE and 32PE liners had mean wear rates of 12.5(±1.0) and 17.45 (±2.6) mg/million cycles. Both highly crosslinked PE liners (28XPE and 32XPE) had significant less wear rates that regular polyethylene 1.49 (±0.72) and 2.55 (±0.19) mg/million cycles respectively. Increasing head size resulted in increased wear, which is consistent with previous reports. Highly crosslinked PE significantly reduced wear rates in both head sizes. Although there was a small increase in wear in the 32XPE group compared to the 28XPE group, wear was significantly less than both 32PE and 28PE groups. These encouraging results suggest that a dual benefit (reduced wear and reduced dislocation rate) might be achieved using 32XPE liners. Further studies that evaluate fatigue damage, crack propagation and impingement are necessary

Introduction: Mobile bearing total knee arthroplasty (TKA) has been developed to theoretically provide a better, more physiological function of the knee and produce less polyethylene (PE) wear. The theoretical superiority of mobile bearing TKA’s over fixed bearing devices has not yet been proven in clinical studies. The objective of the present study was to analyze in vivo the knee joint kinematics in the sagittal plane in a patient population that had received either a fixed or a mobile TKA in a prospective, randomized, patient- and observer-blinded, clinical study. Methods: 31 patients were evaluated by means of fluoroscopy during unloaded flexion and extension against gravity, as well as during step-up and step-down with full weight bearing. In these 31 patients, 22 fixed bearing TKAs, 16 mobile-bearing TKAs and 19 natural knee joints were included. All patients had been operated in a prospective, randomized, patient- and observer-blinded, clinical study, and had received either fixed or a mobile bearing, cruciate retaining Genesis II TKA for primary osteoarthritis. Fluoroscopic radiographs were evaluated by measuring the „patella tendon angle” as a measure of antero-posterior translation as well as the “kinematic index” as a measure of reproducibility. Results: During unloaded movement, fluoroscopic analysis did not show a significant difference between both types of prosthesis designs and the natural knee. In the weight-bearing movement, both types of TKA designs did not show the typically arched but a more linear patellar tendon angle curve, with a greater angle in extension and in flexion than the natural knees. This means that the femur glides anteriorly under load near extension and does not show the natural roll-back in flexion. In the mobile-bearing group, inter-individual deviations from the mean during weight-bearing movements were significantly less than in the fixed-bearing group. Conclusions: In the present study, no functional advantage of mobile bearing TKA over fixed bearing devices could be found. Both TKA designs showed the typical kinematics of an anterior instability. Long-term follow-ups are necessary to elucidate the possible influence of lower PE wear on the incidence of aseptic loosenings

Because we encountered a high failure rate of the acetabular component of the uncemented, hydroxy-apatite coated, Omnifit total hip prosthesis (Osteonics corporation, Allendale, NJ, USA), we conducted a retrospective study of 418 consecutive total hip arthroplasties with a mean follow up of 60 months. The results of 418 hydroxy-apatite coated, uncemented Omnifit total hip arthroplasties, conducted between 1989 and 1996 were evaluated. Two different acetabulum cups were used: 145 screwcups with one central screwhole, and 273 press fit (PF) cups with several screwholes. The internal geometry of these cups and the fixation of the polyethylene insert in the metal cups were identical. In 339 arthroplasties a 32-mm femur-head was used, in 79 a 28-mm head. Patients’ records and x-rays were evaluated for clinical findings, polyethylene (PE) wear, acetabular and femoral osteolysis and findings during revision surgery. Revision surgery was performed in 73 patients, mainly because of symptomatic acetabular osteolysis (79%). Mean PE wear was 0.16 mm/year (0.19 mm in PF cups, 0.11 mm in screwcups). Acetabular osteolysis was found to be present in178 hips (70 screwcups and 108 PF cups). In both cupdesigns the osteolysis was mainly found around the screwholes of the metal cups. During revision surgery these osteolytic defects were a lot larger than suggested by x-ray imaging. In 22.6% of the hips osteolysis was also present in the proximal femur. Kaplan-Meier survival analysis showed, after 6 year follow up, a better survival for of the screwcup (96%, confidence interval 93–99%) than the PF cup (66%, 95%CI 56–77%). We hypothesized that this specific combination of metal cup and polyethylene insert -possibly due to an insufficient fitting- is responsible for the migration of polythylene wear particles through the screwholes in the metal cup, causing acetabular osteolysis and neces-satating revision surgery. For this reason we abandonned the use of this type of uncemented acetabular component

Background:. The number of young patients undergoing total knee arthroplasty is rapidly increasing. Long-term follow-up of modern type implants is needed to provide a benchmark of implant longevity for these patients. Methods:. Between January 1995 and October 1997, 245 consecutive total knee arthroplasties were performed in 217 patients by a single surgeon. In 156 knees, the Genesis I implant was used, and in 89 knees the Genesis II implant was used. Mean age at surgery was 69.3 years for the Genesis I cohort and 66 years for the Genesis II (p = 0.016). At 15 to 17 years, cumulative survivorship was calculated using Kaplan-Meier statistics whilst outcomes were rated with the ‘Knee society score’ and with the ‘Knee Injury and Osteoarthritis Outcome Score’. Radiological assessment included coronal alignment measured on full leg standing X-rays, and analysis of radiolucent lines and polyethylene thickness on AP, Lateral and Axial X-rays, positioned under fluoroscopic control. Results:. At 15 to 17 years, 79 patients had died (56 with Genesis I) and 27 were lost to follow-up. Eleven TKA had been revised including 10 Genesis I for infection (1), recurrent dislocation (1), loosening (1), patellar maltracking (2) or polyethylene (PE) wear (5) and 1 Genesis II for PE wear. 139 knees in 129 patients were in situ. Overall, the cumulative survivorship with endpoint revision for any reason was 92.4% at 15.7 years (95%CI: 91.0–93.8). In the Genesis I cohort, cumulative survivorship was 90.1% at 15.1 years (95%CI: 88.0–92.2). In the Genesis II cohort, cumulative survivorship was 98.1% at 14.9 years (95%CI: 97.9–98.3). The difference in survivorship was not statistically significant (log rank 3.136; p = 0.077), but the odds ratio for failure was 7.6 for the Genesis I compared to Genesis II. Logistic regression further identified gamma-air sterilization of PE as a significant predictor of failure, with an odds ratio of 13.4 compared to ETO sterilization. There was no difference in survivorship between patients younger or older than 55 years at surgery or between genders. Patients who underwent a revision had a significantly higher BMI (p = 0.027). There was no statistically significant difference in clinical outcome, radiographic radiolucencies or PE thickness changes between the surviving Genesis I and II cohorts. Conclusions:. At 15 years, the overall 92.4% survivorship of the Genesis I TKA is good with excellent 98.1% survivorship for the Genesis II with the adapted femoral trochlear design. The results confirm the risk of PE wear when gamma-air sterilisation is used. Excellent longer-term outcome is obtained with a contemporary TKA implant using non cross-linked polyethylene

Measurement of polyethylene (PE) wear in total hip joint replacement (THJR) is performed by measuring change in the position of the femoral head on post-operative radiographs. Early methods used manual measurement with calipers and concentric circles, while more recent techniques involve the use of computer assisted technology. RSA, while mainly used for measuring component migration, can also be used for measurement of PE wear. The aim of this paper is to describe two new methods for measuring PE wear;. A completely automated measurement (which eliminates user error and is 100% reproducible). A method currently under development which uses artificial intelligence to match CAD models to radiographs, enabling measurement of both PE wear and prosthesis migration. For the Automated Measurement Technique (AMT), software has been developed which locates the centre of the acetabular cup and femoral head on both the anteroposterior and lateral radiographs. No user input is required. Accuracy is ± 0.16 mm. Clinically, it has been used in a double-blinded randomized controlled trial (RCT) comparing conventional with cross-linked PE. For the Model Matching Technique (MMT), two pieces of software are combined, Ray-Tracing technology (used in the generation of animated movies), and the Genetic Algorithm (a branch of Artificial Intelligence). CAD models of an acetabular cup and femoral head are matched to post-operative films to position them in 3D space. Change in position of these models over time represents PE wear. CAD models of the patients’ pelvis and femur (built from CT scans) can be similarly used to measure femoral and acetabular component migration. The AMT was used to measure the PE wear of 116 patients enrolled in a prospective RCT comparing conventional and cross-linked PE. At a follow-up of two to four years, cross-linked PE showed statistic ally significant lower PE wear than the conventional material. A cadaver pelvis and femur has been used to analyse accuracy of the MMT for measurement of component migration. Preliminary results show an accuracy of ± 0.22mm for component migration. The accuracy of PE wear measurement appears to be significantly less than this. The development of new bearing surfaces to reduce wear in THJR requires new techniques of in-vivo wear measurement. These two new techniques should give important information on the performance of new bearings, and possibly allow measurement of clinical component migration without the need for bead implantation