Aims. Highly cross-linked polyethylene (HXLPE) greatly reduces wear in total hip arthroplasty, compared to conventional polyethylene (CPE). Cross-linking is commonly achieved by irradiation. This study aimed to compare the degree of cross-linking and in vitro wear rates across a cohort of retrieved and unused polyethylene cups/liners from various brands. Methods. Polyethylene acetabular cups/liners were collected at one centre from 1 April 2021 to 30 April 2022. The trans-vinylene index (TVI) and oxidation index (OI) were determined by Fourier-transform infrared spectrometry. Wear was measured using a pin-on-disk test. Results. A total of 47 specimens from ten brands were included. The TVI was independent of time in vivo. A linear correlation (R. 2. = 0.995) was observed between the old and current TVI standards, except for vitamin E-containing polyethylene. The absorbed irradiation dose calculated from the TVI corresponded to product specifications for all but two products. For one electron beam-irradiated HXLPE, a mean dose of 241% (SD 18%) of specifications was determined. For another, gamma-irradiated HXLPE, a mean 41% (SD 13%) of specifications was determined. Lower wear was observed for higher TVI. Conclusion. The TVI is a reliable measure of the absorbed irradiation dose and does not alter over time in vivo. The products of various brands differ by manufacturing details and consequently cross-linking characteristics. Absorption and penetration of electron radiation and gamma radiation differ, potentially leading to higher degrees of cross-linking for electron radiation. There is a non-linear, inverse correlation between TVI and in vitro wear. The wear resistance of the HXLPE with low TVI was reduced and more comparable to CPE. Cite this article: Bone Joint Res 2024;13(11):682–693

Aims. Isolated acetabular liner exchange with a highly crosslinked polyethylene (HXLPE) component is an option to address polyethylene wear and osteolysis following total hip arthroplasty (THA) in the presence of a well-fixed acetabular shell. The liner can be fixed either with the original locking mechanism or by being cemented within the acetabular component. Whether the method used for fixation of the HXLPE liner has any bearing on the long-term outcomes is still unclear. Methods. Data were retrieved for all patients who underwent isolated acetabular component liner exchange surgery with a HXLPE component in our institute between August 2000 and January 2015. Patients were classified according to the fixation method used (original locking mechanism (n = 36) or cemented (n = 50)). Survival and revision rates were compared. A total of 86 revisions were performed and the mean duration of follow-up was 13 years. Results. A total of 20 patients (23.3%) had complications, with dislocation alone being the most common (8.1%; 7/86). Ten patients (11.6%) required re-revision surgery. Cementing the HXLPE liner (8.0%; 4/50) had a higher incidence of re-revision due to acetabular component liner-related complications than using the original locking mechanism (0%; 0/36; p = 0.082). Fixation using the original locking mechanism was associated with re-revision due to acetabular component loosening (8.3%; 3/36), compared to cementing (0%; 0/50; p = 0.038). Overall estimated mean survival was 19.2 years. There was no significant difference in the re-revision rate between the original locking mechanism (11.1%; 4/36) and cementing (12.0%; 6/50; p = 0.899). Using Kaplan-Meier survival analysis, the revision-free survival of HXLPE fixed with the original locking mechanism and cementing was 94.1% and 93.2%, respectively, at ten years, and 84.7% and 81.3%, respectively, at 20 years (p = 0.840). Conclusion. The re-revision rate and the revision-free survival following acetabular component liner exchange revision surgery using the HXLPE liner were not influenced by the fixation technique used. Both techniques were associated with good survival at a mean follow-up of 13 years. Careful patient selection is necessary for isolated acetabular component liner exchange revision surgery in order to achieve the best outcomes. Cite this article: Bone Joint J 2024;106-B(5 Supple B):59–65

Dislocation is one of the most common and disturbing complications after total hip arthroplasty (THA). This is a challenging situation, especially in patients with a high risk of dislocation. Constrict acetabular liner is among the different types of technics for preventing instability. Describe the radiological and clinical results of patients submitted to a primary or revision THA using a constrict acetabular liner. 52 patients with high risk for dislocation were operated between 2006 and 2015 with a constrict acetabular liner. They were evaluated clinically and radiographically after 3 months, 6 months and 1 year after surgery and them annually. The Merle D'Aubigné Postel Method was used to access the clinical outcomes and anteroposterior pelvic and hip profile radiography was performed to access any evidence of loosening of the acetabular cup. 33 (63%) patients were female, the average age were 80 (52 – 94) years old. 29 (75%) cases were primary THA and 13 (25%) revision surgery. The mean follow up was 49(19 – 126) months. 31 (59%) patients died during the study, 5 deaths (9.6%) occurred in the first 3 months after surgery. There were 4 unsatisfactory results: 2 (3.8%) dislocations (secondary to high energy trauma) and 2 (3.8%) early aseptic loosening that required revision surgery. The median preoperative global score of Merle D'Aubigné Postel was 16.7% and the postoperative was 88.9%. The population that presented the least improvement in the clinical outcome (< 50% of improvement) were patients with previous surgery on the same hip (p<0.0001) and revisions surgeries due to instability (p=0.005). When comparing the mortality rate with the percent of clinical improvement after surgery, there was no statistic difference. Constricted acetabular liner is a good option for treatment in selected cases, with a low rate of complications and a good implant survival with a short follow up

There are several clinical scenarios to consider cementing an acetabular liner into a secure cementless shell including cases of: 1) inadequate capturing mechanism, 2) damaged locking mechanisms, 3) unavailability of the mating polyethylene liner, 4) instability following debridement for wear, 5) instability at the time of femoral side revision, and 6) recurrent dislocation. The last two situations are common scenarios for cementing a constrained liner into a secure shell. Technique includes: 1) scoring the shell in cases with no screw holes or polished inner shells, 2) scoring the acetabular liner in a “spider web” pattern, 3) pressurising cement into the shell, and 4) inserting a liner that allows 2mm of cement mantle. Results of Cementing Constrained Liner Into Secure Cementless Shell: Callaghan et al. JBJS 2004 (31 hips, 2–10 year follow up, 2 of 31 failed, Technical considerations - Do not cement proud, Do not cement into a malpositioned shell); Haft et al. J Arthroplasty 2002 (17 hips, Minimum 1 year follow up, 1 of 17 failed, Technical considerations - Do not cement proud). Results of Cementing Non-Constrained Liners Into Secure Cementless Shell: Beaule et al. JBJS 2004 (32 hips, Mean 5.1 year avg follow up, 4 components revised for loosening); Callaghan et al. CORR 2012 (31 hips, Mean 5.3 year follow up, No revisions)

There are several clinical scenarios to consider cementing an acetabular liner into a secure cementless shell including cases of: 1) inadequate capturing mechanism, 2) damaged locking mechanisms, 3) unavailability of the mating polyethylene liner, 4) instability following debridement for wear, 5) instability at the time of femoral side revision, and 6) recurrent dislocation. The last two situations are common scenarios for cementing a constrained liner into a secure shell. Technique includes: 1) scoring the shell in cases with no screw holes or polished inner shells, 2) scoring the acetabular liner in a “spider web” pattern, 3) pressurising cement into the shell, and 4) inserting a liner that allows 2 millimeters of cement mantle. Results of Cementing Constrained Liner Into Secure Cementless Shell . A. Callaghan et al. JBJS 2004. i. 31 hips. ii. 2-10 year follow-up. iii. 2 of 31 failed. iv. Technical considerations. 1. Do not cement proud. 2. Do not cement into a malpositioned shell. B. Haft et al. J Arthroplasty 2002. i. 17 hips. ii. Minimum 1 year follow-up. iii. 1 of 17 failed. iv. Technical considerations. 1. Do not cement proud. Results of Cementing Non-Constrained Liners Into Secure Cementless Shell . A. Beaule et al. JBJS 2004. i. 32 hips. ii. mean 5.1 year avg f/u. iii. 4 components revised for loosening. B. Callaghan et al. CORR 2012, in press. i. 31 hips. ii. mean 5.3 year f/u. iii. no revisions

The protective effect of lipped polyethylene uncemented acetabular liners against revision THA for instability has been reported. However, the effect of lip size has not been explored, nor has the effect on revision THA for loosening. We aimed to determine if uncemented acetabular liner geometry, and lip size, influences the risk of revision THA for instability or loosening. 202511 primary THAs with uncemented polyethylene acetabular components were identified from the NJR dataset (2003 – 2017). The effect of acetabular liner geometry and lip size on the risk of revision THA for instability or loosening was investigated using binomial regression and competing risks survival analyses (competing risks were revision for other causes or death) adjusting for age, gender, ASA grade, diagnosis, side, institution type, surgeon grade, surgical approach, head size and polyethylene crosslinking. The distribution of acetabular liners was: neutral – 39.4%, offset neutral – 0.9%, 10-degree – 34.5%, 15-degree – 21.6%, 20-degree – 0.8%, offset reorientating – 2.82%. There were 690 (0.34%) revision THAs for instability and 604 (0.3%) for loosening. Significant subhazard risk ratios were found in revision THA for instability with 10-degree (0.63), 15-degree (0.48) and offset reorientating (1.6) liners, compared to neutral liners. There was no association found between liner geometry and risk of revision THA for loosening. This Registry based study confirms a significantly lower risk of revision THA for instability when a lipped liner is used, compared to neutral liners, and a higher risk with the use of offset reorientating liners. Furthermore, 15degree liners seem to have a lower risk than 10degree liners. We did not find an association between acetabular liner geometry and revision THA for loosening. 10- and 15-degree lipped polyethylene liners seem to offer a lower revision risk over neutral liners, at least at medium term followup. Further studies are required to confirm if this benefit continues into the long-term

HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. No significant difference in in vivo or ex vivo was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (r=.520, p = .011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims. Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time

Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. Results. No significant difference in in vivo or ex vivo was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (Δ=.520, p=.011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p<.0005, η. 2. = 0.322). Post hoc analysis revealed hardness was significantly lower in the retrieved remelted group compared to both the single annealed (p=.001) and sequentially annealed (p<.0005) cohorts. Hardness was significantly higher in the retrieved remelted liners compared to controls (p=.007), with no different in either annealed cohort (figure 1). Detectable subsurface oxidation (OI > 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims (figure 2). Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Conclusion. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time. For any tables or figures, please contact the authors directly

Aims. The primary outcome was investigating differences in wear, as measured by femoral head penetration, between cross-linked vitamin E-diffused polyethylene (vE-PE) and cross-linked polyethylene (XLPE) acetabular component liners and between 32 and 36 mm head sizes at the ten-year follow-up. Secondary outcomes included acetabular component migration and patient-reported outcome measures (PROMs) such as the EuroQol five-dimension questionnaire, 36-Item Short-Form Health Survey, Harris Hip Score, and University of California, Los Angeles Activity Scale (UCLA). Methods. A single-blinded, multi-arm, 2 × 2 factorial randomized controlled trial was undertaken. Patients were recruited between May 2009 and April 2011. Radiostereometric analyses (RSAs) were performed from baseline to ten years. Of the 220 eligible patients, 116 underwent randomization, and 82 remained at the ten-year follow-up. Eligible patients were randomized into one of four interventions: vE-PE acetabular liner with either 32 or 36 mm femoral head, and XLPE acetabular liner with either 32 or 36 mm femoral head. Parameters were otherwise identical except for acetabular liner material and femoral head size. Results. A total of 116 patients participated, of whom 77 were male. The median ages of the vE-PE 32 mm and 36 mm groups were 65 (interquartile range (IQR) 57 to 67) and 63 years (IQR 56 to 66), respectively, and of the XLPE 32 mm and 36 mm groups were 64 (IQR 58 to 66) and 61 years (IQR 54 to 66), respectively. Mean total head penetration was significantly lower into vE-PE acetabular liner groups than into XLPE acetabular liner groups (-0.219 mm (95% confidence interval -0.348 to -0.090); p = 0.001). There were no differences in wear according to head size, acetabular component migration, or PROMs, except for UCLA. There were no cases of aseptic loosening or failures requiring revision at long-term follow-up. Conclusion. Significantly lower wear was observed in vE-PE acetabular liners than in XLPE acetabular liners. No difference in wear was observed between different head size or PROMs except for the UCLA at ten years. Cite this article: Bone Joint J 2023;105-B(10):1052–1059

Introduction. Retrieval investigations have shown that cracking or rim failure of polyethylene hip liners may occur at the superior aspect of the liner, in the area that engages the locking ring of the shell. 1. Failure could occur due to acetabular liner/stem impingement and/or improper cup position. Other contributing factors may include high body mass index, patient activity and design characteristics such as polyethylene material properties, thin liner rim geometry and cup rim design. Currently no standard multi-axis simulator methodology exists for high angle rim fatigue testing, although tests have been developed using static uniaxial load frames. 2. The purpose of this study was to develop a technique to create a clinically relevant rim crack/fracture event on a 4-axis hip simulator, and to understand the contribution of component design and loading and motion parameters. Method. A method for creating rim fracture in vitro was developed to evaluate implant design features and polyethylene liner materials. Liners were secured into acetabular shells, fixtured in resin mounted at a 55° (in vitro; 65° in vivo) inclination to ensure high load/stress was at the area of interest. Ranges of kinematic and maximum applied load profiles were investigated (parameters summarized in Table 1). Testing was conducted on an AMTI 12-station hip simulator for 0.25–1.0 million cycles or until fracture (lubrication maintained with lithium grease). At completion, liners were cleaned and examined for crack propagation/fracture. Inspection of the impingement site on the opposite rim was also analyzed. Additional assessments included liner disassociation/rock out, deformation of characteristics such as anti-rotation devices and microscopic inspection of high-stress regions. Results/Discussion. This study summarizes testing on hip wear simulators to create rim cracking/fracture in vitro. Results indicate that cup/stem angles must be controlled to ensure contact areas are reproducible, and therefore on a multi-station machine (i.e. AMTI), only one test station can/should be run at a time to ensure repeatability. Component design characteristics, such as head size and liner material had a marked effect on the results. It is noted that the kinematics, load and cycle count must be adjusted per the component design to create rim fracture in the high-risk region. Finite element analysis modeling may help identify the high-stress region(s) prior to simulator testing. Deformation of the rim opposite the fracture region (rim/taper impingement) was observed due to the high angle of inclination combined with the abduction/adduction angles. Conclusion. Rim fractures similar in location and morphology to those seen in retrieval studies can be created using a multi-axis hip simulator in vitro. It is noted, however, that the factors presented in this study must be considered and controlled to assure a repeatable method, as the differences in component design investigated and simulator inputs were seen significantly affect the outcome. This study was limited and did not attempt to reproduce rim damage seen in all implant retrievals (e.g. lateralized liners, high offset implants, etc.). These design inputs are being investigated and will be reported upon in the future. For any figures or tables, please contact the authors directly

Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and Methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by microindentation hardness testing using a Micromet II Vickers microhardness tester following ASTM standards. A subset of 16 explants with ex vivo time under one year along with five control liners were assessed for oxidation by FTIR, crystallinity by Raman spectroscopy, and evidence of microcracking by SEM. Results. No significant difference in in vivo or ex vivo time was found between thermal stabilization groups in either set of explants studied. In the mechanically tested explants, there was no significant correlation between in vivo time and Vickers hardness in any thermal stabilization group. A significant correlation was found between ex vivo time and hardness in remelted liners (r=.520, p=.011), but not in either annealed cohort. ANCOVA with ex vivo time as a covariate found a significant difference in hardness between the thermal free radical stabilization groups (p<.0005, η. 2. = 0.322). Post hoc analysis revealed hardness was significantly lower in the retrieved remelted group compared to both the single annealed (p=.001) and sequentially annealed (p<.0005) cohorts. Hardness was significantly higher in the retrieved remelted liners compared to controls (p=.007), with no different in either annealed cohort. Detectable subsurface oxidation (OI > 0.1) was found in retrieved remelted (25%), single annealed (100%) and sequentially annealed (75%) liner rims. Crystallinity was increased in the subsurface region relative to control liners for both annealed, but not remelted, liner rims. Hardness was increased in oxidized rims for both annealed cohorts but not in the remelted cohort. Microcracking was only found along the surface of one unoxidized remelted liner rim. Conclusion. Mechanical properties were reduced at baseline and worsened after in vivo time for remelted HXLPE liner rims. Rim oxidation was detected in all groups. Oxidation was associated with increased crystallinity and hardness in annealed cohorts, but not remelted liners. Increased crystallinity and oxidation do not appear to be directly causing the worsened mechanical behavior of remelted HXLPE liner rims after extended in vivo time. For any figures or tables, please contact authors directly

Introduction. Periprosthetic osteolysis is considered the main problem limiting the longevity and clinical success of artificial hip joints. Aiming at the reduction of the wear particles and the elimination of periprosthetic osteolysis, we have recently developed a novel articular cartilage-inspired technology for surface modification (Aquala® technology) with poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) grafting (100–150 nm in thickness) for an acetabular liner in an artificial hip joint. Our previous study on the mechanical and biological effects of PMPC revealed that the grafting decreased the production of wear particles and the bone resorptive responses. However, as well as wear-resistance, oxidation is an important indicator of the clinical performance of acetabular liners. The incorporation of the antioxidant vitamin E has been proposed recently as an alternative to post melting treatment after gamma-ray irradiation to avoid oxidation. The purpose of this study is to investigate the effects of substrate materials, vitamin E-blended cross-linked polyethylene (CLPE), on the oxidative stability and wear resistance of the PMPC-grafted CLPE liner for artificial hip joints. Materials & Methods. Vitamin E-blended (0.1 mass%) PE sheet stock was irradiated with a high dose of gamma-rays (100–150 kGy) and annealed for cross-linking (HD–CLPE+E). PMPC grafting onto the HD–CLPE+E liners was performed by a photoinduced polymerization technique. Then, the PMPC-grafted HD-CLPE+E was sterilized by gamma-ray with a dose of 25 kGy. A CLPE with 50 kGy gamma-ray irradiation and 25 kGy gamma-ray sterilization was used as control. Surface properties and oxidative properties of the liners were examined. The wear test was performed using a 12-station hip joint simulator according to the ISO 14242-3. A 26-mm Co-Cr-Mo alloy femoral head component was used for the tests. Results. After PMPC grafting, the peaks ascribed to the MPC unit were clearly observed in both Fourier-transform infrared and X-ray photoelectron spectroscopy spectra. Furthermore, PMPC-grafted CLPE and HD-CLPE+E surface became wettable drastically. Oxidation-induction time of PMPC-grafted HD-CLPE+E was significantly longer compared with non-additive CLPE. After 5.0 million cycles of the simulator test, PMPC-grafted HD–CLPE+E were found to show extremely low and stable wear. Substantially fewer wear particles isolated from lubricants were found for both PMPC-grafted liners than for untreated CLPE liners. Discussion. In this study, we confirmed that the PMPC-grafted layer was successfully fabricated on the HD-CLPE+E surface, and the PMPC-grafted HD-CLPE+E brought high oxidation and wear-resistances. When the surface is modified by PMPC grafting, the PMPC-grafted layer leads to a significant reduction in the sliding friction between the surfaces which are grafted because water thin films formed can act as extremely efficient lubricants. Based on clinical trials and other related evidence, the Japanese government (Ministry of Health, Labour and Welfare) approved the clinical use of PMPC-grafted CLPE without vitamin E acetabular liners in April 2011. Furthermore, and in spite of high-dose gamma-ray irradiation for cross-linking, the substrate modified by vitamin E-blending maintains high oxidation-resistance. Indeed vitamin E is an extremely efficient radical scavenger. Conclusion. In conclusion, the PMPC-grafted HD–CLPE+E provides not only high wear resistance but also high oxidation stability, i.e., life-long durability

Previous studies suggested that the shallow Ultra High Molecular Weight Polyethylene (UHMWPE) acetabular socket liner or the liner with no head centre inset can significantly increase the risk of hip joint dislocation. Independent to the traditional neck impingement models, the purpose of this study was to investigate an additional dislocation force pushing the femoral head out of UHMWPE acetabular liner bearing under direct hip joint loading and the factors including the head centre inset affecting the magnitude of this force. The 3 D Finite Element Analysis (FEA) models were constructed by (30) 10 mm thick UHMWPE liners with six inner bearing diameters ranging from 22 mm to 44 mm and five head centre insets in each bearing size from 0 mm to 2 mm. A load of 2 446 N was applied through the corresponding CoCr femoral head to the rim of the liner. The DF was recorded as a function of head centre inset and head diameter. The results were verified by the physical tests of two 28 mm head bearing liners with 0 and 1.5 mm head centre insets respectively. The results showed that the highest DF was 1 269N in 0 mm head centre inset and 22 mm head. The lowest DF was 171 N in 2 mm head centre inset and 44 mm head. The DF decreased as the head centre inset and head size increased. When head centre inset increased from 0 mm to 1 mm, the DF was reduced more than 50%. Two experimental data points were consistent with the trend of DF curve found in the FEA. We concluded that the new intrinsic dislocating force DF can be induced by the rim directed joint loading force alone and can reach as high as 51% of the femoral loading force. This can be the addition to the dislocating moment generated by the neck impingement. A head inset above 1mm can effectively reduce DF to less than 25% of the joint force. Furthermore, the larger head diameter generates less DF. The DF is likely caused by the wedge effect between the deformed polyethylene bearing and the femoral head. The inset allows the femoral head to be separated from the spherical bearing surface, thus reducing the wedge effect. Our observation of the stabilizing effect trend of the head centre inset was consistent with reported clinical data. However, the increased height of the capture wall also reduces the range of motion. It is therefore necessary to minimize the inset height with the maximum benefit of the stabilize effect. This study suggested the larger femoral head has the advantage of reducing the DF and the stabilizing effect is more effective when combining with the inset wall. The result of this study should provide the guidance to improve acetabular poly liner design for better joint stability

Hip instability is one of the most common complications after total hip arthroplasty (THA). Among the possible techniques to treat and prevent hip dislocation, the use of constrained liners is a well-established option. However, there is concern regarding the longevity of these devices due to higher mechanical stress caused by limited hip motion. The primary aim of this paper is to analyze the failure rate of a specific constrained liner in a series of consecutive cases.

This study is a retrospective consecutive case series of THA and revision hip arthroplasty (RHA), in which a constrained polyethylene insert was used to treat or prevent hip instability. Patients were divided in 3 different groups (THA for hip fracture, THA for osteoarthrosis, and RHA). Survival analysis was performed for failure, defined as at least one episode of hip dislocation or radiographical signs of acetabular loosening. Logistical regression was used to investigate risk factors for failure.

A total of 103 patients were included in the study. Fourteen patients (13,6%) were THA for osteoarthrosis, 60 (58,3%) were THA for hip fracture, and 29(28,2%) were RHA. The median follow-up was 28 months (ranging 12 − 173 months). Failure occurred in 4 cases (3,9%) comprehending 2 dislocations (1,9%) and 2 early acetabular loosening (1,9%). Amongst the groups, there were no cases of failures in the THA due to osteoarthrosis, in the THA for hip fracture there were 3 cases (5%) and in the RHA one case (3,4%). Failure-free survival was not statistically different between groups. There were no risk factors statistically related to failure.

The use of constrained acetabular insert to prevent or treat instability achieved an adequate survival time with a low rate of complications. Further studies are necessary to corroborate our findings.

The Trident acetabular system is the second most common cementless cup implanted in the UK. Recent studies have shown that malseating of the liner can be as high as 16.4%. We felt this was very high and were prompted to review our series and early clinical outcomes.

We reviewed 118 hips in 110 patients, implanted between from 2005-2007. We reviewed initial post operative X-rays using the technique described by Howcroft to identify malseating. The posterior approach was used in all cases. All cups were Trident PSL and all 85 Patients had OA, 10 RA, 8 AVN, 5 DDH, 3 OA post trauma, 2 Perthes, 2 Psoriatic Arthritis, 3 other. We only identified 3 malseated cups in 118 hips. 2 were in patients with OA secondary to trauma and 1 in primary OA. The rate of malseating for trainees operating was 5 % and only 1% when consultants were operating. There were no adverse events in these patients. No-one required revision. Oxford Hip Score (OHS) improved from 47 pre-op to 20 post op. This was compared to 47 and 22 in the correctly seated group (115 cases). Surprisingly the subgroup with the poorest OHS at 1 year had surgery for DDH, with a mean OHS of 31. The reasons for this are unclear.

Contrary to other studies our malseating rate is very low. We do not feel that malseating is a problem with Trident if adequate exposure is obtained. In those patients with sclerotic bone, we suggest over reaming the rim of the acetabulum by 1mm to avoid excess deformation of the shell which may lead to difficulty with seating the liner. We suggest trainees are supervised closely when using Trident.

Isolated liner and head exchange procedure has been an established treatment method for polyethylene wear and osteolysis when the acetabular component remains well-fixed. In this study, its mid-term results were evaluated retrospectively in 34 hips.

Among the consecutive patients operated upon from September 1995, 2 patients (3 hips) were excluded because of inadequate follow-up and the results of remaining 34 hips of 34 patients were evaluated. They were 20 men and 14 women with a mean age of 49 years at the time of index surgery. Conventional polyethylene liner was used in 26 cases and highly cross-linked polyethylene liner was used in 8 cases. In 3 cases, liner was cemented in the metal shell because compatible liner could not be used. After a minimum follow-up of 5 years (range, 5∼20.2), re-revision surgery was necessary in 10 cases (29.4%); 8 for wear and osteolysis, 2 for acetabular loosening. In all re-revision cases, conventional polyethylene was used. There was no failure in the cases in which highly cross-linked polyethylene was used. There was no case complicated with dislocation.

The results of this study suggest more promising results with the use of highly cross-linked polyethylene in isolated liner exchange.

Polyethylene liners of modular acetabular components wear and sometimes need to be replaced, despite the metal shell being well fixed. Replacing the liner is a relatively simple procedure, but very little is known of the outcome of liner revision. We prospectively followed up 1126 Harris-Gallante 1 metal backed, uncemented cups for between 9 and 19 years. 38 (3.4%) liners out of 1126 acetabular components wore and required revision. These revisions were then followed up for a mean of 4.8 years. The rate of dislocation was 28.9%. Nine of the dislocations were single dislocations and 2 were recurrent.

The overall re-revision rate was 3 out of 38 total hip replacements (7.9%) at a mean follow up of 4.8 years. This gives a 92.1% survivorship at just under 5 years. In isolated liner revision we had a complication rate of 23%. In liner revision combined with stem revision we had a complication rate of 48%. Possible reasons for high dislocation rates are discussed.

Leaving the well fixed acetabular shell in-situ leads to an increased risk of instability. However, this needs to be balanced against the otherwise low complication rate for liner revision. Patients should be consented accordingly

Previous studies suggested the lack of capture wall of acetabular Ultra High Molecular Weight Polyethylene (UHMWPE) liner can significantly increase the risk of hip joint dislocation. To date, the dislocation studies have been focused on the femoral neck impingement models. The purpose of this study was to identify a new Dislocating Force (DF) generated by rim directed joint force alone and investigate the factors to affect the magnitudes of the DF. The 3 D Finite Element Analysis (FEA) models were constructed by (30) 10 mm thick UHMWPE liners with six inner bearing diameters ranging from 22 mm to 44 mm and five capture wall heights in each bearing size from 0 mm to 2 mm. A load of 2 446 N was applied through the corresponding CoCr femoral head to the rim of the liner. The DF was recorded as a function of capture wall height and head diameter. The results were verified by the physical tests of two 28 mm head bearing liners with 0 and 1.5 mm capture wall heights respectively.

The results showed that the highest DF was 1 269N in 0 mm capture wall and 22 mm head. The lowest DF was 171 N in 2 mm capture wall and 44 mm head. The DF decreased as the capture wall and head size increased. When capture wall increased from 0 mm to 1 mm, the DF was reduced more than 50%. Two experimental data points were consistent with the trend of DF curve found in the FEA.

We concluded that the new intrinsic dislocating force DF can be induced by the rim directed joint loading force alone and can reach as high as 51% of the femoral loading force. A capture wall height above 1mm can effectively reduce DF to less than 25% of the joint force. In addition, the larger head diameter also resulted in less DF generation.

Polyethylene contact stresses have been shown to correlate with wear in total hip arthroplasty (THA). Several liner designs have been introduced in an attempt to increase stability or reduce impingement and increase range of motion. This study analyzed the effect of liner design on range of motion (ROM) and PE contact stresses in a finite element model (FEM).

FEMs of four liner designs were generated: Generic was modelled as a simple hemisphere, Chamfer had a wide chamfer on the inner edge of the liner to increase ROM, Highwall had an extended lip to increase stability, and Anteverted created a 20° anteversion with lat-eralisation of the centre of rotation. With the liners in varying positions of abduction and anteversion, physiologic loads were applied through the femoral head. Hip ROM was measured by rotating the head and neck in different directions until prosthetic impingement.

Significant differences in ROM were seen relative to the Generic liner. Chamfer increased ROM by mean 16%. Highwall reduced ROM by mean 12%. Anteverted increased flexion by 17% but decreased extension, abduction, and external rotation. Contact stresses were also significantly affected by liner design and acetabular orientation. Overall for the same acetabular position, contact stresses were higher for Chamfer and lower for Highwall and Anteverted.

These results underline the complex interaction between cup design, hip stability, range of motion and contact stresses. Design features that increase stability tend to reduce contact stresses and ROM, while those features that increase ROM, tend to increase contact stresses. This data can help the surgeon match liner design to specific patient requirements.

Introduction. Femoral neck impingement occurs clinically in total hip replacements (THR) when the acetabular liner articulates against the neck of a femoral stem prosthesis. This may occur in vivo due to factors such as prostheses design, patient anatomical variation, and/or surgical malpositioning, and may be linked to joint instability, unexplained pain, and dislocation. The Standard Test Method for Impingement of Acetabular Prostheses, ASTM F2582 −14, may be used to evaluate acetabular component fatigue and deformation under repeated impingement conditions. It is worth noting that while femoral neck impingement is a clinical observation, relative motions and loading conditions used in ASTM F2582-14 do not replicate in vivo mechanisms. As written, ASTM F2582-14 covers failure mechanism assessment for acetabular liners of multiple designs, materials, and sizes. This study investigates differences observed in the implied and executed kinematics described in ASTM F2582-14 using a Prosim electromechanical hip simulator (Simulation Solutions, Stockport, Greater Manchester) and an AMTI hydraulic 12-station hip simulator (AMTI, Watertown, MA). Method. Neck impingement testing per ASTM F2582-14 was carried out on four groups of artificially aged acetabular liners (per ASTM F2003-15) made from GUR 1020 UHMWPE which was re-melted and cross-linked at 7.5 Mrad. Group A (n=3) and B (n=3) consisted of 28mm diameter femoral heads articulating on 28mm ID × 44mm OD acetabular liners. Group C (n=3) and D (n=3) consisted of 40mm diameter femoral heads articulating on lipped 40mm ID × 56mm OD 10° face changing acetabular liners. All acetabular liners were tested in production equivalent shell-fixtures mounted at 0° initial inclination angle. Femoral stems were potted in resin to fit respective simulator test fixtures. Testing was conducted in bovine serum diluted to 18mg/mL protein content supplemented with sodium azide and EDTA. Groups A and C were tested on a Prosim; Groups B and D were tested on an AMTI. Physical examination and coordination measurement machine (CMM) analyses were conducted on all liners pre-test and at 0.2 million cycle intervals to monitor possible failure mechanisms. Testing was conducted for 1.0 million cycles or until failure. An Abaqus/Explicit model was created to investigate relative motions and contact areas resulting from initial impingement kinematics for each test group. Results. Effects of kinematic differences in the execution of ASTM F2582-14 were observed in the four groups based on simulator type (Figure 1) and liner design. The Abaqus/Explicit FEA model revealed notable differences in relative motions and contact points (Figure 2) between specimen components i.e. acetabular liner, femoral head, and femoral stem throughout range of motion. Acetabular liner angular change within shell-fixtures, rim deformation, crack propagation, and metal-on-metal contact between acetabular shell-fixtures and femoral stems were observed as potential failure mechanisms (Figure 3) throughout testing. These mechanisms varied in severity by group due to differing contact stresses and simulator constraints. Significance. Investigating failure mechanisms caused by altered kinematics of in-vitro neck impingement testing, due to influences of simulator type and acetabular liner design, may aid understanding of failure mechanisms involved when assessing complaints/retrievals and influence future prosthetic designs. For any figures or tables, please contact the authors directly