Abstract. Objectives. Currently, total hip replacement surgery is an effective treatment for osteoarthritis, where the damaged hip joint is replaced with an artificial joint. Stress shielding is a mechanical phenomenon that refers to the reduction of bone density as a result of altered stresses acting on the host bone. Due to solid metallic nature and high stiffness of the current orthopaedic prostheses, surrounding bones undergo too much bone resorption secondary to stress shielding. With the use of 3D printing technology such as selective laser melting (SLM), it is now possible to produce porous graded microstructure hip stems to mimics the surrounding bone tissue properties. Method. In this study we have compared the physical and mechanical properties of two triply periodic minimal surface (TPMS) lattice structure namely gyroid and diamond TPMS. Based on initial investigations, it was decided to design, and 3D print the gyroid and diamond scaffolds having pore size of 800 and 1100 um respectively. Scaffold of each type of structure were manufactured and were tested mechanically in compression (n=8), tension (n=5) and bending (n=1). Results. Upon FEA validation of the scaffold in Abaqus, the desired scaffold for hip implant application was evaluated to have a young's modules of 12.15 GPa, yield strength of 242 MPa and porosity of 55%. Topology and lattice optimization were performed using nTopology to design an optimised graded porous hip implant based on stress shielding reduction. It was understood that the designed optimised hip implant can reduce the stress shielding effect by more than 65% when compared to the conventional generic implant. Conclusions. The designed hip implant presented in this work shows clinical promise in reducing bone loss while having enhanced osseointegration with the surrounding cortical bones. Hence, this will help reduce the risk of periprosthetic fracture and the probability of revision surgery

Background

Many factors contribute to the occurrence of edge-loading conditions in hip replacement; soft tissue tension, surgical position, patient biomechanical variations and type of activities, hip design, etc. The aim of this study was to determine the effect of different levels of rotational and translational surgical positioning of hip replacement bearings on the occurrence and severity of edge-loading and the resultant wear rates.

We revised seven alumina-blasted cementless hip prostheses (Ti-alloy stems, cp Ti threaded sockets) with low- or high-carbon Co-alloy bearings at a mean of 20.1 months after implantation because of pain and loosening. Histological examination of the retrieved periprosthetic tissues from two cases in which the implant was stable and three in which the socket was loose showed macrophages with basophilic granules containing metal and alumina wear particles and lymph-cell infiltrates. In one of the two cases of stem loosening the thickened neocapsule also contained definite lymphatic follicles and gross lymphocyte/plasma-cell infiltrates. Spectrometric determination of the concentration of elements in periprosthetic tissues from six cases was compared with that of joint capsules from five control patients undergoing primary hip surgery. In the revisions the mean concentration of implant-relevant elements was 693.85 μg/g dry tissue. In addition to Cr (15.2%), Co (4.3%), and Ti (10.3%), Al was predominant (68.1%) and all concentrations were significantly higher (p < 0.001) than those in the control tissues. The annual rates of linear wear were calculated for six implants. The mean value was 11.1 μm (heads 6.25 μm, inserts 4.82 μm). SEM/EDXA showed numerous fine scratches and deep furrows containing alumina particles in loosened sockets, and stems showed contamination with adhering or impacted alumina particles of between 2 and 50 μm in size.

In severe cases of total knee & hip arthroplasty, where off-the-shelf implants are not suitable (i.e., in cases with extended bone defects or periprosthetic fractures), 3D-printed custom-made knee & hip revision implants out of titanium or cobalt-chromium alloy represent one of the few remaining clinical treatment options. Design verification and validation of such custom-made implants is very challenging. Therefore, a methodology was developed to support surgeons and engineers in their decision on whether a developed design is suitable for the specific case. A novel method for the pre-clinical testing of 3D-printed custom-made knee implants has been established, which relies on the biomechanical test and finite element analysis (FEA) of a comparable clinically established reference implant. The method comprises different steps, such as identification of the main potential failure mechanism, reproduction of the biomechanical test of the reference implant via FEA, identification of the maximum value of the corresponding FEA quantity of interest at the required load level, definition of this value as the acceptance criterion for the FEA of the custom-made implant, reproduction of the biomechanical test with the custom-made implant via FEA, decision making for realization or re-design based on the acceptance criterion is fulfilled or not. Exemplary cases of custom-made knee & hip implants were evaluated with this new methodology. The FEA acceptance criterion derived from the reference implants was fulfilled in both custom-made implants and subsequent biomechanical tests verified the FEA results. The suggested method allows a quantitative evaluation of the biomechanical properties of custom-made knee & hip implant without performing physical bench testing. This represents an important contribution to achieve a sustainable patient treatment in complex revision total knee & hip arthroplasty with custom-made 3D printed implants in a safe and timely manner

In 2020 almost 90% of femoral heads for total hip implants in Germany were made of ceramic. Nevertheless, the cellular interactions and abrasion mechanisms in vivo have not been fully understood until now. Metal transfer from the head-neck taper connection, occurring as smear or large-area deposit, negatively influences the surface quality of the articulating bearing. In order to prevent metal transfer, damage patterns of 40 Biolox delta ceramic retrievals with CoC and CoPE bearings were analysed. A classification of damage type and severity for each component (n=40) was done according to an established scoring system. To investigate the physical properties, the surface quality was measured using confocal microscopy, quantitative analysis of phase composition were performed by Raman spectroscopy and qualitative analysis of metal traces was done by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). The periprosthetic tissue was analysed for abrasion particles with SEM and EDX. Both bearing types show different damage patterns. Dotted/ drizzled metal smears were identified in 82 % of CoC (n=16) and 96 % of CoPE (n=24) bearings. Most traces on the ceramic heads were identified in the proximal area while they were observed predominantly in the distal area for the ceramic inlays. The identified marks are similar to those of metallic bearings. Metallic smears lead to an increase of up to 30 % in the monoclinic crystalline phase of the ceramic. The roughness increases by up to six times to Ra=48 nm. Ceramic and metallic wear particles from the articulating surfaces or head neck taper junctions were found in the periprosthetic tissue. Damage patterns on CoC hip implants seem to be similar to those of metallic implants. More detailed analysis of CoC implants are needed to understand the described damage patterns and provide advice for prevention

Total joint replacement (TJR) was one of the most revolutionary breakthroughs in joint surgery. The majority studies had shown that most implants could last about 25 years, anyway, there is still variation in the longevity of implants. In US, for all the hip revisions from 2012 to 2017 in the United States, 12.0% of the patients were diagnosed as aseptic loosening. Variable studies have showed that any factor that could cause a systemic or partial bone loss, might be the risk of periprosthetic osteolysis and aseptic loosening. Breast cancer is the most frequent malignancy in women, more than 2.1 million women were newly diagnosed with breast cancer, 626,679 women with breast cancer died in 2018. It's been reported that the mean incidence of THA was 0.29% for medicare population with breast cancer in USA, of which the incidence was 3.46% in Norwegian. However, the effects of breast cancer chemotherapy and hormonotherapy, such as aromatase inhibitors (AI), significantly increased the risk of osteoporosis, and had been proved to become a great threat to hip implants survival. In this case, a 46-year-old female undertook chemotherapy and hormonotherapy of breast cancer 3 years after her primary THA, was diagnosed with aseptic loosening of the hip prosthesis. Her treatment was summarized and analyzed. Breast cancer chemotherapy and hormonotherapy might be a threat to the stability of THA prosthesis. More attention should be paid when a THA paitent occurred with breast cancer. More studies about the effect of breast cancer treatments on skeleton are required

Abstract. Objectives. Dual mobility (DM) hip implants whereby the polyethylene liner is “free-floating” are being used increasingly clinically. The motion of the liner is not well understood and this may provide insight into failure mechanisms; however, there are no published methods on tracking liner motion while testing under clinically relevant conditions. The aim was to develop and evaluate a bespoke inertial tracking system for DM implants that could operate submerged in lubricant without line-of-sight and provide 3D orientation information. Methods. Trackers (n=5) adhered to DM liners were evaluated using a robotic arm and a six-degree of freedom anatomical hip simulator. Before each set of testing the onboard sensor suites were calibrated to account for steady-state and non-linearity errors. The trackers were subjected to ranges of motion from ±5° to ±25° and cycle frequencies from 0.35Hz to 1.25Hz and the outputs used to find the absolute error at the peak angle for each principle axis. In total each tracker was evaluated for ten unique motion profiles with each sequence lasting 60 cycles. Results. Across all test conditions the angular error was consistently less than 1.1 ± 1.8° (mean ± SD) per principle axis with no relationship found between range of motion or cycle frequency and measurement error. Rotations about the trackers X and Y axes produced more repeatable results with a maximum spread of 5.5°, where as rotations about Z spread by up to 10.1°. Conclusions. The results of this study show that a system for monitoring DM liner motion without line of sight is possible, going forward this will be used to determine the effects of different loading and kinematic conditions on liner motions in a hip simulator

Objectives. Recently, high failure rates of metal-on-metal (MOM) hip implants have raised concerns of cobalt toxicity. Adverse reactions occur to cobalt nanoparticles (CoNPs) and cobalt ions (Co. 2+. ) during wear of MOM hip implants, but the toxic mechanism is not clear. Methods. To evaluate the protective effect of zinc ions (Zn. 2+. ), Balb/3T3 mouse fibroblast cells were pretreated with 50 μM Zn. 2+. for four hours. The cells were then exposed to different concentrations of CoNPs and Co. 2+. for four hours, 24 hours and 48 hours. The cell viabilities, reactive oxygen species (ROS) levels, and inflammatory cytokines were measured. Results. CoNPs and Co. 2+. can induce the increase of ROS and inflammatory cytokines, such as tumour necrosis factor α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6). However, Zn pretreatment can significantly prevent cytotoxicity induced by CoNPs and Co. 2+. , decrease ROS production, and decrease levels of inflammatory cytokines in Balb/3T3 mouse fibroblast cells. Conclusion. These results suggest that Zn pretreatment can provide protection against inflammation and cytotoxicity induced by CoNPs and Co. 2+. in Balb/3T3 cells. Cite this article: Y. Liu, H. Zhu, H. Hong, W. Wang, F. Liu. Can zinc protect cells from the cytotoxic effects of cobalt ions and nanoparticles derived from metal-on-metal joint arthroplasties? Bone Joint Res 2017;6:649–655. DOI: 10.1302/2046-3758.612.BJR-2016-0137.R2

Modular hip prostheses were introduced to optimize the intra-surgical adaptation of the implant design to the native anatomy und biomechanics of the hip. The downside of a modular implant design with an additional modular interface is the potential susceptibility to fretting, crevice corrosion and wear. For testing hip implants with proximal femoral modularity according to ISO & ASTM, sodium chloride solutions are frequently used to determine the fatigue strength and durability of the stem-neck connection. The present study illustrate that the expansion of standard requirements of biomechanical testing is necessary to simulate metal ion release as well as fretting and crevice corrosion by using alternative test fluids. To assess the primary stability of tibial plateaus in vitro, different approaches had been undergone: cement penetration depth analysis, static tension or compression loading until interface failure. However, these test conditions do not reflect the in vivo physiologic loading modes, where the tibial plateau is predominantly subjected to combined compression and shear forces. The objectives were to evaluate the impact of the tibial keel & stem length on the primary stability of a posterior-stabilised tibial plateau under dynamic compression-shear loading conditions in human tibiae

It is well documented that implant loosening rate in sickle cell disease patients is higher than that seen in patients with hip arthroplasty from other indications. The Hypoxic inducible factor(HIF) - is activated in the microcellular hypoxic environment and this through a cascade of other enzymatic reactions promotes the activity of other factors and further help enhance angiogenesis and osteogenesis. The aim of this study was to investigate and propose a potential model for investigating osseointegration in a hypoxic microcellular environment using osteoblasts(MG63). Human MG63 osteoblastic cells were cultured under normoxia and hypoxic conditions (20%; and 1% oxygen saturation) for 72 hours under two different condition- with and without cobalt chloride. The samples cultured under normoxic condtions without cobalt chloride acted as control. Using qualitative polymerase chain reaction-(qPCR) - HIF expression was assessed under the above conditions in relation to the control. The results showed there was significant expression of the HIF 1 alpha protein under hypoxic condition with cobalt chloride in comparison with the control samples- all at 72hours incubation. Mann-Whitney U test was used to deduce level of significance of fold change.(p=0.002; <0.05). This was deemed as being a significant difference in the level of expression of HIF compared to the control. The results show that the hypoxic inducible factor can be expressed using the above tested. experimental invitro-model with significant results which can be a foundation for further research into improving hip implant prosthesis design to help enhance osseo-integration in sickle cell disease patient with AVN

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

Introduction. A deep squat (DS) is a challenging motion at the level of the hip joint generating substantial reaction forces (HJRF). During DS, the hip flexion angle approximates the functional range of hip motion. In some hip morphologies this femoroacetabular conflict has been shown to occur as early as 80° of hip flexion. So far in-vivo HJRF measurements have been limited to instrumented hip implants in a limited number of older patients performing incomplete squats (< 50° hip flexion and < 80° knee flexion). Clearly, young adults have a different kinetical profile with hip and knee flexion ranges going well over 100 degrees. Since hip loading data on this subgroup of the population is lacking and performing invasive measurements would be unfeasible, this study aimed to report a personalised numerical model solution based on inverse dynamics to calculate realistic in silico HJRF values during DS. M&M. Fifty athletic males (18–25 years old) were prospectively recruited for motion and morphological analysis. DS motion capture (MoCap) acquisitions and MRI scans of the lower extremities with gait lab marker positions were obtained. The AnyBody Modelling System (v6.1.1) was used to implement a novel personalisation workflow of the AnyMoCap template model. Bone geometries, semi-automatically segmented from MRI, and corresponding markers were incorporated into the template human model by an automated nonlinear morphing. Furthermore, a state-of-the-art TLEM 2.0 dataset, included in the Anybody Managed Model Repository (v2.0), was used in the template model. The subject-specific MoCap trials were processed to compute squat motion by resolving an overdeterminate kinematics problem. Inverse dynamics analyses were carried out to compute muscle and joint reaction forces in the entire body. Resulting hip joint loads were validated with measured in-vivo data from Knee bend trials in the OrthoLoad library. Additionally, anterior pelvic tilt, hip and knee joint angles were computed. Results. A preliminary set of results (20 out of 50 subjects) was analysed. The average HJRF was 3.42 times bodyweight at the peak of DS (95% confidence interval: 2.99 – 3.85%BW). Maximal hip and knee flexion angles were 113° (109.7°–116.8°) and 116° (109.4 – 123.0°) respectively. The anterior pelvic tilt demonstrated a biphasic profile with peak value of 33° (28.1° – 38.4°). Discussion. A non-invasive and highly personalised alternative for determining hip loading was presented. Consistently higher HJR forces during DS in young adults were demonstrated as opposed to the Orthoload dataset. Similarly, knee and hip flexion angles were much higher, which could support the increase in HJRF. We can conclude that DS hip kinetics in young adults clearly differ from the typical total hip arthroplasty population

The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or edge loading related, have not been eliminated. Early dislocations are becoming very rare and most of them probably occur in “outlier” patients with atypical pelvic/hip kinematics. Because singular problems usually need singular treatments, those patients need a more specific personalised planning of the treatment rather than a basic systematic application of Lewinnek recommendations. We aim in this review to define the potential impacts that the spine-hip relations (SHRs) have on hip arthroplasty. We highlight how recent improvements in hip implants technology and knowledge about SHRs can substantially modify the planning of a THR, and make the « Lewinnek recommendations » not relevant anymore. We propose a new classification of the SHRs with specific treatment recommendations for hip arthroplasty whose goal is to help at establishing a personalized planning of a THR. This new classification gives a rationale to optimize the short and long-term patient's outcomes by improving stability and reducing edge loading. We believe this new concept could be beneficial for clinical and research purposes

Background. Metal-on-metal (MoM) hip arthroplasty has been associated with adverse reactions including pseudotumours, and osteolysis. Tissues surrounding failed MoM hip implants are often infiltrated by inflammatory cells such as monocytes and neutrophils. The mechanisms by which these cells are recruited to the tissues remain unclear. Cobalt from MoM implants activates Toll-like receptor 4 (TLR4), an immune cell surface receptor usually responsible for recognition of bacteria and prevention of sepsis. Activation by bacteria leads to secretion of pro-inflammatory cytokines which guide other immune cells to the site of inflammation. The effect of cobalt on this response is unknown and therefore this study aims to determine the effect of cobalt-mediated TLR4 activation on the migration of inflammatory cells. Methods. A human macrophage cell line (MonoMac 6) was stimulated with a physiologically-relevant range of cobalt ions for 24h with or without pre-treatment with a TLR4 antagonist. Conditioned media was collected and used in a trans-well migration assay to determine its effect on migration of primary monocytes and neutrophils isolated from whole human blood. Migrated cells were stained with haematoxylin and counted at ×40 magnification. Results. Conditioned media from cobalt-treated macrophages caused elevated monocyte and neutrophil migration across all concentrations. Pre-treatment of MonoMac 6 cells with a TLR4 antagonist significantly decreased the response. This suggests that the cytokine profile produced in response to cobalt-mediated TLR4 activation is pro-migratory for immune cells. Conclusions. Cobalt activation of TLR4 leads to secretion of inflammatory cytokines that attract monocytes and neutrophils. This work highlights a potential mechanism by which cobalt ions from failed MoM joints could be involved in inflammatory cell recruitment to the surrounding tissues. The TLR4 signalling pathway represents an exciting area for further investigation as a therapeutic target in the prevention of adverse reactions to cobalt ions. Disclosure. This work is funded by DePuy Synthes Ltd and the Newcastle NIHR Biomedical Research Centre

Background. Fretting at modular junctions is thought to be a ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to increased contact stresses and micromotions at the taper interface. We adopted a finite element approach to model the head-taper junction, to analyse the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants, to demonstrate the importance of a good assembly during surgery. Methods. Models of the Bimetric taper and adaptor were created, with elastic-plastic material properties based on material tests with the actual implant alloy. FE contact conditions were validated against push-on and pull-off experiments. The models were loaded according to ISO 7206-4 and −6, after being assembled at 2-4-15kN, both axially and at a 30° angle. Average micromotions and contact pressures were analysed, and a wear score was calculated based on the contact pressures and micromotions. Results. The average contact pressure decreased when a higher assembly force was used, with loads being distributed over a larger contact area, but increased when tested at a 30° angle. Average micromotions reduced with a higher assembly load, except when assembled at a 30° angle. The wear score decreased with increasing assembly force, when applied perpendicularly, while when assembled at a 30° angle, the wear score did not reduce with assembly force. Conclusions. The location and patterns of micromotions were consistent with retrieved tapers and those generated in in-vitro test models. Increased impaction loads reduced the average amount of micromotion and fretting. We intend to apply more complex loading regimes in future analyses, enabling to study phenomena such as edge loading and frictional torque. Level of evidence. IIb - Experimental study. Disclosure. This study was financially supported by Biomet UK Healthcare Ltd

Increased failure rates due to metallic wear particle-associated adverse local tissue reactions (ALTR) is a significant clinical problem in resurfacing and total hip arthroplasty. Histological analysis and particle characterization are important elements for understanding the biological mechanisms of the reaction and different histological subtypes may have unique needs for longitudinal clinical follow-up and complication rates after revision arthroplasty. Consecutive patients (N=285 cases) presenting with ALTR from three major hip implant classes, metal-on-metal resurfacing and total hip arthroplasty (THA) and non-metal-on-metal THA with dual modular neck were identified from our prospective Osteolysis Tissue Database and Repository and 53 cases were selected for wear particle nano-analysis. Conventional histology: Tissue samples taken from multiple regions around the hip with extensive sampling performed at macroscopic examination were examined by light microscopy. Particle analysis: Tissue samples selected after frozen section evaluation for cellularity and particle content were examined by scanning electron microscopy (SEM), backscatter scanning electron microscopy (BSEM), BSEM-energy-dispersive X-ray spectroscopy (EDS) element mapping examination, transmission electron microscopy (TEM), TEM-EDS element mapping, and X-ray diffraction spectrometry (XRD) examination. ALTR encompasses three main histological patterns: 1) macrophage predominant, 2) mixed lymphocytic and macrophagic, and 3) predominant sarcoid-like granulomas. Duration of implantation and composition of periprosthetic cellular infiltrates was significantly different among the three implant types examined. Distinct differences in the size, shape, and element composition of the metallic particulate material were detected in each implant class, with correlation of the severity of the adverse reaction with element complexity of the particles. ALTR encompasses a diverse range of histological patterns, which are reflective of both the implant configuration independent of manufacturer and clinical features such as duration of implantation. Distinct differences in the metallic particulate material can contribute to explain the histological features of the ALTR and variability of performance of the implants. ALTR exhibits different histological patterns and is dependent on the characteristics of the wear particulate material of each implant class and host immunological reaction

Although cemented fixation provides excellent results in primary total hip replacement (THR), particularly in patients older than 75 years, uncemented implants are most commonly used nowadays. We compare the rate of complications, clinical and radiological results of three different designs over 75-years-old patients. 433 hips implanted in patients over 75 years old were identified from our Local Joint Registry. Group A consisted of 139 tapered cemented hips, group B of 140 tapered grit-blasted uncemented hips and group C of 154 tapered porous-coated uncemented hips. A 28 mm femoral head size on polyethylene was used in all cases. The mean age was greater in group A and the physical activity level according to Devane was lower in this group (p<0.001 for both variables). Primary osteoarthritis was the most frequent diagnoses in all groups. The radiological acetabular shape was similar according to Dorr, however, an osteopenic-cylindrical femur was most frequently observed in group A (p<0.001). The pre- and post-operative clinical results were evaluated according to the Merle-D'Aubigne and Postel scale. Radiological cup position was assessed, including hip rotation centre distance according to Ranawat and cup anteversion according to Widmer. We also evaluated the lever arm and height of the greater trochanter distances and the stem position. Kaplan-Meier analysis was done for revision for any cause and loosening. The hip rotation centre distance was greater and the height of the greater trochanter was lower in group B (p=0.003, p<0.001, respectively). The lever arm distance was lower in group C (p<0.001). A varus stem position was more frequently observed in group B (p<0.001). There were no intra- or post-operative fractures in group A, although there were five intra-operative fractures in the other groups plus two post-operative fractures in group B and four in group C. The rate of dislocation was similar among groups and was the most frequent cause for revision surgery (8 hips for the whole series). The mean post-operative clinical score improved in all groups. The overall survival rate for revision for any cause at 120 months was 88.4% (95% CI 78.8–98), being 97.8% (95% CI 95.2–100) for group A, 81.8% (95% CI 64.8–98.8) for group B and 95.3% (95% CI 91.1–99.6) for group C (log Rank: 0.416). Five hips were revised for loosening. The overall survival rate for loosening at 120 months was 91.9% (95% CI 81.7–100), being 99.2%(95% CI 97.6–100) for group A, 85.5 (95% CI 69.9 −100) for group B and 100% for group C (Log Rank 0.093). Despite a more osteopenic bone in the cemented group, the rate of peri-prosthetic fractures was higher after uncemented THR in patients older than 75 years. Although the overall outcome is good with both types of fixation, the post-operative reconstruction of the hip, which might be more reliable after cemented fixation, may affect the rate of complications in this population

Aims

Second-generation metal-on-metal (MoM) articulations in total hip arthroplasty (THA) were introduced in order to reduce wear-related complications. The current study reports on the serum cobalt levels and the clinical outcome at a minimum of 20 years following THA with a MoM (Metasul) or a ceramic-on-polyethylene (CoP) bearing.

Introduction. Total hip prostheses which use a ceramic head within a metal liner are a relatively recent introduction. As such, survivorship rates from independent centres alongside explant analysis are rare. The early experience with this novel ceramic-on-metal (CoM) bearing couple is reported. Methods and Materials. All CoM hips implanted between 2008 and 2009 at a single hospital by a single surgeon were reviewed. Radiographs were analysed using EBRA software to determine acetabular cup inclination and anteversion angles. Blood metal ion concentrations were measured using inductively coupled plasma mass spectroscopy (ICPMS). Explants were measured for bearing surface and taper wear using a high precision co-ordinate measuring machine. The roughness of the articulating surfaces was measured with a non-contact profilometer. Results. In 54 patients 56 CoM hips were implanted. Mean (range) age was 64 years (34-87). There were 41 females and 15 males. Patients were followed-up for a mean of 1.5 years. Three hips were revised at mean of 1.2 years (2 female, 1 male) with a further 3 listed for revision under 1.5 years giving an overall failure rate of 10.7%. All these patients reported with pain. X-rays of failed devices showed a characteristic pattern of femoral stem loosening. Serum cobalt and chromium were less than 2 micrograms/L. Explant analysis of the three revised hips showed wear at the liner rim in each case. In two of these cases the wear extended completely around the circumference. The wear volumes were 4.1, 2.0 and 2.3mm3 respectively. The ceramic heads were unworn but some transfer of metal could be seen visually. There was no significant wear or deformation at the taper junctions. Typical ceramic head roughness values were 3nm Ra and so most of the surface area of the heads remained in a pristine condition. Discussion. The very high early failure rate using COM is concerning. Explant analysis suggests equatorial contacts with propagation of high frictional forces distally. These forces may have caused early loosening of the femoral stems. Orthopaedic surgeons need to be aware of this new mechanism of failure which is associated with low metal ions