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

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. 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

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.

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

Introduction. Dual mobility (DM) total hip arthroplasty (THA) prostheses are designed to increase stability. In the setting of primary and revision THA, DM THA are used most frequently for dysplasia and instability diagnoses, respectively. As the use of DM THA continues to increase, with 8,031 cases logged in the American Joint Replacement Registry from 2012–2018, characterizing in vivo damage and clinical failure modes are important to report. Methods. Under IRB-approved implant retrieval protocol, 43 DM THA systems from 41 patients were included. Each DM THA component was macroscopically examined for standard damage modes. Clinically-relevant data, including patient demographics and surgical elements, were collected from medical records. Fretting and corrosion damage grading is planned, according to the Goldberg et al. classification system. Results. In this 43-retrieved implant series, there were 23 female and 17 male patients (n=1, unknown), with an average body mass index of 29 (range, 19–49), and average ages at index and revision of 63 years (range, 34–80) and 64 years (range, 38–88), respectively. The average duration of implantation was 12.9 months (range, 0.1–72.0). Reasons for revision included infection (n=11, 26%), mechanical complication (n=10, 23%), intraprosthetic dislocation (n=6, 14%), periprosthetic fracture (n=5, 12%), pain (n=4, 9%), acetabular-associated loosening (n=3, 7%), unknown (n=3, 7%), hematoma (n=2, 5%), leg length discrepancy (n=1, 2%), and inflammatory reaction (n=1, 2%); some cases included multiple reasons for revision. On articular surfaces, scratching was the most commonly observed damage mode on all components, with more than 40% of acetabular cup and femoral heads showing scratching damage (Figure 1A). Abrasion, burnishing, and pitting damage were also observed in more than 10% of acetabular cup and acetabular liner components; further, approximately 20% of polyethylene acetabular liners exhibited edge deformation damage. On backside surfaces, polyethylene acetabular liners showed the greatest damage, with more than 60% of components exhibiting abrasion, scratching, or pitting damage (Figure 1B). Conclusion. This series showed various reasons for revision as well as in vivo damage of retrieved DM systems following short-to-midterm implantation. Damage was observed on both articular and backside surfaces of the five components of DM THA. Modularity of DM THA prostheses may amplify rates of in vivo damage. Future studies are needed to confirm these results and clinical significance. For any figures or tables, please contact the authors directly

Introduction. Modular acetabular liners offer surgeons the flexibility of using various bearing materials and sizes to accommodate the patient's needs. The need for a robust locking mechanism to ensure the long term successful performance of the implant is critical due to the hardship a revision surgery would have on the patient. The traditional method to evaluate torque resistance by using epoxy to affix a roughed femoral head to the acetabular liner has been acceptable to this point. However, efforts to design an acetabular liner that is resistant to high torque failures have shown this method to be inadequate to evaluate the performance of the lock detail, as failures only occur between the femoral head and the liner. Therefore a test method that would ensure failure of the lock detail was needed. Materials and Methods. In the current study the performance of prototype vs. production acetabular liners and shells were evaluated. Aluminum test shells were provided and a combination of production acetabular liners and prototype liners were provided by the Prototype Department at MicroPort Orthopedics. The traditional method was followed. A custom holding fixture was attached to the load cell plate of the test machine, and a roughed femoral head was attached to the actuator. The appropriate shell and liner combination was selected and assembled using three firm hammer blows with a two pound surgical hammer. Once assembled, the test construct was affixed to the holding fixture mounted to the test machine. Devcon 5 minute epoxy was mixed per the instruction and approximately 10 cc was placed into the cup of the liner. The femoral head was then brought into place using load control until contact was made. After the epoxy had cured torque was applied via the femoral head at a rate of 0.417° per second until failure of the epoxy or the lock detail was observed. In every trial the epoxy failed before the lock detail. A new method was devised. A paddle fixture was fabricated and attached to the actuator of the test frame (See Figure 1). The interior of the cups were modified to receive the paddle fixture. The test was repeated using the new fixation method and failure of the lock detail was achieved. Results and Discussion. Table 1 and Figure 2 below shows the results of the torque testing for the group using the epoxy and the group using the mechanical lock fixturing. The development of higher torque resistant polyethylene liners shows a need to develop a fixation method that will ensure the proper evaluation of the lock detail. For figures/tables, please contact authors directly.

Introduction. Total hip replacement with metal-on-polymer (MoP) hip prostheses is a successful treatment for late-stage osteoarthritis. However, the wear debris generated from the polymer acetabular liners remains a problem as it can be associated with osteolysis and aseptic loosening of the implant. This has led to the investigation of more wear resistant polymers in orthopaedics. Cross-linked polyethylene (XLPE) is now the gold-standard acetabular liner material. However, we asked if carbon fibre reinforced polyether ether ketone (CFR-PEEK) might be a lower wear material. In addition, we sought to understand the influence of contact stress on the wear of both XLPE and CFR-PEEK as this has not previously been reported. Materials and Methods. A 50-station circularly translating pin-on-disc (SuperCTPOD) machine was used to wear test both XLPE and CFR-PEEK pins against cobalt chromium (CoCr) discs to investigate the influence of contact stress on their wear rates. Fifty XLPE and 50 CFR-PEEK pins were articulated against CoCr discs. The pins, 9 mm in outer diameter and 12 mm in height, were drilled with different diameter holes to generate different sized annuli and thus, different contact areas. The pins were tested at 1.10, 1.38, 1.61, 2.00 and 5.30 MPa, which are typical contact stresses observed in the natural hip joint. An additional pin for every test group was used as a control to track the lubricant uptake. The discs were polished to 0.015 μm Sa prior to testing. The test stations contained 16 ml of diluted newborn calf serum (protein concentration: 22 g/L). Wear was measured gravimetrically with a balance (resolution: 10 μm) every 500,000 cycles. A standardised cleaning and weighing protocol was followed. Results and Discussion. The wear rates for the XLPE pins were calculated as 1.05, 0.90, 0.77, 0.48 and 0.28 mg/million cycles for the different pin stress groups respectively. The wear rates decreased with increasing contact stress, which was similar to what was observed for ultra-high molecular weight polyethylene (UHMWPE). The change in weight of the discs was insignificant (p-value:0.85). For the CFR-PEEK pin groups, the wear rates were calculated as 0.56, 0.65, 0.61, 0.58 and 0.65 mg/million cycles respectively. The difference between the wear rates was insignificant (p-value: 0.92). However, the weight of the discs decreased significantly (p-value: 0.00). At 1.11 MPa and taking data for UHMWPE tested in the same way, comparison of the three polymers showed that CFR-PEEK produced the lowest wear against CoCr. Although the wear rates for CFR-PEEK were found to be the lowest, the decrease in weight of the CoCr discs articulated against CFR-PEEK was indicative of metallic wear. Conclusion. CFR-PEEK should not be used against orthopaedic metals. XLPE articulating against CoCr was found to be the optimum combination, producing low wear without causing weight change from the counterface, under varying contact stresses

Component malposition in total hip arthroplasty (THA) contributes to wear, dislocation, and leg length discrepancy (LLD). Robotic assisted total hip arthroplasty (rTHA) utilises computer-assisted haptically guided bone preparation and implant insertion to improve accuracy. The goal of this study is to compare accuracy and clinical outcome with manual THA (mTHA) and rTHA at minimum 1 year follow-up interval. Consecutive primary THA performed by one fellowship trained surgeon included: the first 100 mTHAs in his clinical practice (Group1- year 2000), the last 100 mTHAs before rTHA use (Group2- year 2010), and the first 100 rTHA (Group3- year 2011). All THAs utilised cementless implants, cross-linked polyethylene, and a posterior approach. Comparisons included age, sex, diagnosis, implant head size, blood loss (EBL), operative time, LLD, early dislocation and infection. Acetabular abduction (AAB), anteversion (AAV), and LLD were measured using validated software (Martell Hip Analysis Suite). The Lewinnek safe zone defined accuracy (AAB- 30°-50°, AAV- 5°-25°). Statistical analysis included ANOVA, Chi squared, and Fisher tests. Power analysis demonstrated adequate sample sizes. No differences were noted regarding group demographics. Average operative times varied: Group 1, 2, and 3- (160, 129, and 143 minutes, respectively). No deep infections occurred in any group. LLD greater than 1.5 cm varied: Groups 1, 2, and 3 (9%, 1%, 1%, respectively). Dislocation rates varied: Groups 1, 2, and 3- (5%, 3%, and 0%, respectively). EBL was less with rTHA than mTHA (Groups 1, 2, 3: 533cc, 437cc, 357cc, respectively). Average implant head size increased comparing Groups 1, 2, and 3 (31mm, 34.6mm, and 35.2mm, respectively). AAB accuracy varied: Groups 1, 2, and 3 (66%, 91%, and 98%, respectively). AAB greater than 55 degrees varied: Groups 1, 2, and 3 (15%, 1%, and 0%, respectively). There was a 3% fractured acetabular liner rate in Group 1, all cases occurred with AAB > 55 degrees, and AAB greater than 55 degrees correlated with increased acetabular liner fracture rate (20% vs. 0%, P < 0.05). No cases of fractured acetabular liners occurred in Group 2 or 3. rTHA improved AAV accuracy compared with mTHA (Group 2- 48%, Group 3- 75%; p<0.0001). Improved acetabular component accuracy with rTHA correlated with lower dislocation rates compared with mTHA (p<0.001). Total hip arthroplasty performed with traditional manual techniques has demonstrated excellent clinical outcomes in the majority of patients with many THA designs if components are placed accurately. Limitations in mTHA remain that alter results if accurate component placement is not achieved. In our study, clinical experience over 10 years improved AAB accuracy with mTHA, but AAV remained problematic. rTHA improved AAB and AAV accuracy compared with mTHA and demonstrated reduced early dislocation rates, improved rate of LLD, and reduced acetabular liner fracture risk compared with mTHA (p<0.05). Average rTHA operative times were 14 minutes longer than mTHA (Group 2), but this was not associated with increased EBL or infection rates. Further study is needed to evaluate whether the short term clinical and radiographic advantages noted with rTHA compared with mTHA will be maintained at longer follow up intervals

Introduction:. First generation highly crosslinked polyethylenes (HXPLEs) have proven successful in lowering both penetration and osteolysis rates. However, 1. st. generation annealing and remelting thermal stabilization have been associated with in vivo oxidation or reduced mechanical properties. Thus, 2. nd. generation HXLPEs were developed to improve oxidative stability while still maintaining material properties. Little is known about the in vivo clinical failure modes of these 2. nd. generation HLXPEs. The purpose of this study was to assess the revision reasons, wear, oxidative stability, and mechanical behavior of retrieved sequentially annealed Vitamin E diffused HXLPE in THA and TKA. Methods:. 251 2. nd. Generation HXLPE hip and knee components were consecutively retrieved during revision surgeries and continuously analyzed in a prospective, IRB approved, multicenter study. 123 acetabular liners (Implanted 1.2y; Range 0–5.0y) and 117 tibial inserts (Implanted 1.6y; Range 0–5.8y) were highly crosslinked and annealed in 3 sequential steps (X3). Five acetabular liners (Implanted 0.6y; Range 0–2.0y) and six tibial inserts (Implanted 1.3y; Range 0.5–1.8y) were diffused with Vitamin E (E1). Patient information was collected from medical records (Table 1). Linear penetration of liners was measured using a calibrated digital micrometer (accuracy: 0.001 mm). Surface damage of tibial components was assessed using the Hood method. Thin sections were taken from the acetabular liners (along the superior/inferior axis) and the tibial components (along the medial condyle and central spine) for oxidation analysis and analyzed according to ASTM 2102. Mechanical behavior was assessed via the small punch test (ASTM 2183). Results:. The liners and tibial components fabricated from both HXLPEs were revised predominantly for loosening, instability, and infection (Figure 1). The average penetration rate for the Sequentially Annealed group was low (PR = 0.045 mm/yr). Pitting, scratching and burnishing were the predominant damage mechanisms of the tibial inserts within both material groups, with no evidence of delamination. Oxidation indices were low (Mean OI≤0.3) and similar between liners and inserts of the Sequentially Annealed components at the bearing and backside surface (Figure 2, p ≥ 0.15). Oxidation was positively correlated with implantation time at the bearing surface of the Sequentially Annealed groups (Rho > 0.29, p < 0.005). The Ultimate Load of the Sequentially Annealed acetabular liners was statistically higher than the tibial components (p < 0.001), however the mean difference was minimal (∼6N). Discussion:. This study evaluated the properties of 2. nd. generation HXLPEs used in THA and TKA. Sequentially Annealed liners had penetration rates comparable with 1. st. generation HXLPEs. While oxidation was low for both sequentially annealed and Vitamin E HXLPEs, we were able to detect regional variations in the oxidative in the sequentially annealed cohort. Longer-term retrievals are necessary to fully assess the oxidative stability of Vitamin E diffused HXLPE used in TKA and THA

Introduction. Subluxation and dislocation are frequently cited reasons for THA revision. For patients who cannot accommodate a larger femoral head, an offset liner may enhance stability. However, this change in biomechanics may impact the mechanical performance of the bearing surface. To our knowledge, no studies have compared wear rates of offset and neutral liners. Herein we radiographically compare the in-vivo wear performance of 0mm and 4mm offset acetabular liners. Methods. Two cohorts of 40 individuals (0mm, 4mm offset highly crosslinked acetabular liners, respectively) were selected from a single surgeon's consecutive caseload. All patients received the same THA system via the posterior approach. AP radiographs were taken at 6-week (‘pre’) and 5-year (‘post’) postoperative appointments. Patients with poor radiograph quality were excluded (n. 0mm. =5, n. 4mm. =4). Linear and volumetric wear were quantified according to Patent US5610966A. Briefly, images were processed in computer aided design (CAD) software. Differences in vector length between the center of the femoral head and the acetabular cup (pre- and post-vector, Figure 1) allow for calculation of linear wear and wear rate. The angle (β) between the linear wear vector and the cup inclination line was quantified (Figure 1). Patients with negative β were excluded from volumetric analyses (n. 0mm. =11, n. 4mm. =7). Volumetric wear was accordingly calculated accounting for wear vector direction. The results from three randomly selected patients were compared to results achieved using the “Hip Analysis Suite” software package (UChicagoTech). Results. Linear wear rate (Figure 2A) for 0mm offsets was significantly lower than the 4mm offsets (0.011±0.091 vs. 0.080±0.122mm/yr, p=0.008). Volumetric wear rate (Figure 2B) for 0mm offsets was significantly lower than the 4mm offsets (30.37±20.45 versus 61.58±42.14mm. 3. /year, p=0.001). Demographic differences existed between the two cohorts (age, gender, femoral head size, and acetabular cup size). However, there were no significant correlations found between linear/volumetric wear rate and any demographic including age, gender, BMI, femoral head size, or acetabular cup size. Validation showed no significant differences between the CAD method used herein and the gold standard method (0.083±0.014 versus 0.093±0.041mm/year, p=0.71). Discussion. This study is the first to show that 0mm offset liners have significantly lower linear and volumetric wear rates than do 4mm offset liners. Despite this difference, no revisions have been required in either cohort. The linear wear rates computed in this study are below literature-reported clinically relevant values for wear-induced-osteolysis (∼0.10mm/year). As such, the clinical impact of this wear rate difference is unknown. The higher wear rate in the offset group may owe to the altered biomechanics of the construct. By lateralizing the femoral head through an offset liner, the femur is lateralized with respect to the patient's center of mass (COM) (Figure 3). To maintain stability, the patient must pull the COM over the femoral head by increasing force from the hip abductors. This increased force is transmitted through the polyethylene acetabular liner. Thus, increased wear may result from the forces required to maintain balance in gait. Further work is needed to determine whether these higher wear rates will have clinical sequelae

Introduction. Modular acetabular liners are fixed in metal shells by a taper locking mechanism. Male tapers of the liner and female tapers of the metal shell have different taper angles resulting in an angular gap. Depending on the specific manufacturing tolerances varying angular gaps may result and, thus, different contact mechanics may be generated that could alter the stresses within the acetabular liner. Therefore, the aim of the current study was to experimentally determine stresses in a ceramic liner depending on different angular gaps under in vivo like loading conditions. Materials and Methods. Two ceramic liners were instrumented at the outer contour with five strain gauge (SG) rosettes each (Fig.1). First, metal shells were axially seated in an asymmetric press-fit model with 0.5 mm under-reaming, then liners were assembled with a 2 kN axial load. SG5 was placed at the flat area of the liner, the other four were placed circumferentially in 90 degrees offset on the rear side. SG2 and SG4 were mounted opposite to each other in press-fit direction while SG1 and SG3 were placed in the non-supported direction. Three inclination angles (0°, 30°, 45°) were tested under in vivo relevant loads of 4.5 and 11 kN. Four positive angular gaps (A1=0.162°±0.007°, A2=0.084°±0.002°, A3=0.054°±0.004°, A4=0.012°±0.005°) and one negative angular gap (A5=−0.069°±0.006°) were examined. For all tests a mid-tolerance clearance between liner and ball head of 70 µm was chosen. Strain data were converted to stresses and compared using a paired 2-sided Wilcoxon Signed Rank Test at an α-level of 0.05. Results. Generally, similar stress distributions under the two loads were found (Fig.2, Fig.3). Stresses for SG1 increased with increasing inclination angle while stresses for the other strain gauges decreased. Highest stresses were found for 0° inclination in press-fit direction (SG2, SG4) and at the bottom of the liner (SG5). Almost no effect of the different angular gaps on the stresses was found for SG5 while for SG1, SG2, SG3 and SG4 significantly lower stresses with decreasing angular gap were found. Discussion. This study showed that the in vivo stress state of acetabular liners strongly depends on acetabular component orientation. Higher stresses for larger angular gaps are attributed to the contact zone of the liner with respect to the metal shell resulting in larger lever arms and, thus, leading to higher bending moments acting on the liner. The contact zone shifts downward with decreasing angular gap. Due to the dimension of strain gauges the strain measurements are limited to a defined region and, thus, no complete strain map of the whole component could be determined. Nevertheless, current results are very useful to calibrate numerical studies concerning ceramic components of a total hip arthroplasty

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) pressurizing 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. Thirty-one hips at 2–10 year follow-up. Two of 31 failed. Technical considerations: do not cement proud and do not cement into a malpositioned shell; Haft et al. J Arthroplasty 2002. Seventeen hips with minimum 1 year follow-up. One of 17 failed. Technical considerations: do not cement proud. Results of Cementing Non-Constrained Liners Into Secure Cementless Shell: Beaule et al. JBJS 2004. Thirty-two hips at mean 5.1 year avg f/u. Four components revised for loosening; Callaghan et al. CORR 2012. Thirty-one hips at mean 5.3 year f/u. No revisions

Introduction. The development of new bearing surfaces for total joint replacement is constantly evolving. Oxidized zirconium (Oxinium) has been introduced for use in total hip arthroplasty (THA) and total knee arthroplasty (TKA). One of the most common causes of failure of THA is aseptic loosening secondary to polyethylene wear debris. The aetiology of wear is multifactorial and includes adhesive, abrasive, third-body and fatigue wear mechanisms. Oxidized zirconium is a relatively new material that features an oxidized ceramic surface chemically bonded to a hard metallic substrate. This material possesses the reduced polyethylene wear characteristics of a ceramic, without the increased risk of implant fracture While short-term results of oxidized zirconium in THA have been reported, there have been no reports on retrieved highly cross linked PE articulating with Oxinium headsObjectives:. Objectives. The purpose of this study was to compare matched pairs of retrieved highly cross-linked polyethylene (XLPE) acetabular liners with OxZr and CoCr articulation. The liners were examined for evidence of wear damage, including articular surface damage, impingement, screw-hole creep, and rim cracks. Materials and Methods. Four retrieved highly cross-linked polyethylene (XLPE) acetabular liners with 32mm OxZr femoral heads were identified and matched to four retrieved highly cross-linked polyethylene (XLPE) acetabular liners with 32mm CoCr femoral heads by duration of implantation, patient age, and body mass index. Visual damage grading of the articular surface was performed by two independent graders by direct visualization and by light stereomicroscopy. The articular surfaces were subjectively graded for abrasion, burnishing, cracking, delamination, pitting, plastic deformation, third body debris, and scratching using a 0 to 3 scale as described by Hood et al. Liners were divided into quadrants with the elevated rim, when present, to the left and the quadrants labeled in a clockwise fashion beginning in the upper left hand corner. When an elevated rim was not present, liners were divided into quadrants based on the ocation of the etchings. Each quadrant was scored separately. Results. The retrieved components showed predominantly abrasion and burnishing primarily in zones 1 and 2 representing the supero-anterior and supero- posterior regions in the liner. The mean damage score for the Oxinium group was 17.3 vs 23.3 in the CoCr group. The mean time in vivo for the oxinium group was 7.1 yrs vs 4.5 yrs for the CoCr group. Interestingly, the damage scores in zones 3 and 4 were very similar in both groups representing the infero post and anterior portions on the liner. Conclusion. The development of new bearing surfaces for total joint replacement is constantly evolving and will continue to do so as polyethylene wear and osteolysis continue to be a major problem in the long-term survival of total hip arthoplasties. CoCr roughens significantly more in situ compared with OxZr components. Despite the small number of retrieved implants in our study, OxZr demonstrated lower damage on XLPE liners when compared to the CoCr group. Longer-term studies will be necessary to establish the overall clinical fatigue performance of highly crosslinked liners with newer bearing surfaces such as OxZr

A well-fixed uncemented acetabular component is most commonly removed for chronic infection, malposition with recurrent dislocation, and osteolysis. However, other cups may have to be removed for a broken locking mechanism, a bad “track record”, and for metal-on-metal articulation problems. Modern uncemented acetabular components are hemispheres which have 3-dimensional ingrowth patterns. Coatings include titanium or cobalt-chromium alloy beads, mesh, and now the so-called “enhanced coatings”, such as tantalum trabecular metal, various highly porous titanium metals, and 3-D printed metal coatings. These usually pose a problem for safe removal without fracture of the pelvis or creation of notable bone deficiency. Preoperative planning is essential for safe and efficient removal of these well-fixed components. Strongly consider getting the operative report, component “stickers”, and contacting the implant manufacturer for information. There should a preoperative check list of the equipment and trial implants needed, including various screwdrivers, trial liners, and a chisel system. The first step in component removal is excellent 360-degree exposure of the acetabular rim, and this can be accomplished by several approaches. Then, the acetabular polyethylene liner is removed; a liner that is cemented into a porous shell can be “reamed out” using a specific device. Following this, any central or peripheral screws are removed; broken or stripped screw heads add an additional challenge. A trial acetabular liner is placed, and an acetabular curved chisel system is used. There are two manufacturers of this type of system. Both require the known outer acetabular diameter and the inner diameter of the trial liner. With the curved chisel system and patience, well-fixed components can be safely removed, and the size of the next acetabular component to be implanted is usually 4mm larger than the one removed. There are special inserts for removal of monobloc metal shells. Remember that removal of these well-fixed components is more difficult in patients compared to models, and is just the first step of a successful acetabular revision

Patients with longstanding hip fusion are predisposed to symptomatic degenerative changes of the lumbar spine, ipsilateral knee and contralateral hip. In such patients, conversion of hip arthrodesis to hip replacement can provide relief of such symptoms. However, this is a technically demanding procedure associated with higher complication and failure rates than routine total hip replacement. The aim of this study was to determine the early functional results and complications in patients undergoing hip fusion conversion to total hip replacement, performed or supervised by a single surgeon, using a standardised approach and uncemented implants. We hypothesised that a satisfactory functional improvement can be achieved in following conversion of hip fusion to hip replacement. Eighteen hip fusions were converted to total hip replacements. A constrained acetabular liner was used in 3 hips. Mean follow up was 5 years (2 to 15 years). Two (11%) hips failed, requiring revision surgery and two patients (11%) had injury to the peroneal nerve. Heterotopic ossification developed in 7 (39%) hips, in one case resulting in joint ankylosis. No hips dislocated. Conversion of hip fusion to hip replacement carries an increased risk of heterotopic ossification and neurological injury. We advise prophylaxis against heterotopic ossification. When there is concern about hip stability we suggest that the use of a constrained acetabular liner is considered. Despite the potential for complications, this procedure had a high success rate and was effective in restoring hip function

Revision of fractured ceramic-on-ceramic total hip replacements with a cobalt-chromium (CoCr) alloy-on-polyethylene articulation can facilitate metallosis and require further expensive revision surgery [1–3]. In the present study, a fifty-two year old male patient suffered from fatal cardiomyopathy after undergoing revision total hip arthroplasty. The patient had received a polyethylene-ceramic acetabular liner and a ceramic femoral head as his primary total hip replacement. The polyethylene-ceramic sandwich acetabular liner fractured in vivo after 58 months and the patient underwent his first revision surgery where he received a Vitamin E stabilized acetabular Polyethylene (PE) liner and a CoCr alloy femoral head with documented synovectomy at that time. After 15 months, the patient was admitted to hospital in cardiogenic shock, with retrieval of the bearing components. Before the second revision surgery, peak serum cobalt levels measured 6,521 μg/L, 78-times greater than serum cobalt levels of 83μg/L associated with cobalt poisoning [4]. Serum titanium levels found in the patient measured 17.5 μg/L) normal, healthy range 0–1.4 μg/L). The retrieved CoCr alloy femoral head had lost a total of 28.3g (24% or an estimated amount of 102 × 10. −9. wear particles (∼2 μm diameter) [1]) within 16 months of in vivo service. Despite initiating a cobalt chelating therapy, the patients' cardiac left ventricular ejection fraction remained reduced at 6%. This was followed by multi-organ failure, and ultimately the patient passed away shortly after being taken off life support. Embedded ceramic particles were found on the backside and articular surfaces of the Vitamin E-stabilized PE acetabular liner. Evidence of fretting wear on the titanium (Ti) alloy acetabular shell was present, possibly explaining the increased serum Ti levels. Scanning electron microscopy and energy dispersive X-ray analyses confirmed Ti alloy transfer on the embedded ceramic particles on the backside PE liner surface and CoCr alloy transfer on the embedded ceramic particles on the articular PE liner surface. A fractured ceramic-on-ceramic total hip replacement should not be revised to a CoCr alloy-on-polyethylene articulation irrespective of concurrent synovectomy [5] as it can cause severe, third-body wear to the CoCr alloy femoral head that can lead to metallosis with fatal, systemic consequences