Biological reactions to wear debris in total joint replacement

Large acetabular defects can be managed with cementless revision components

BACKGROUND

Optimal techniques for acetabular revision in the setting of major pelvic osteolysis have not been established. Bilobed components, structural grafts, and reinforcement cages have demonstrated 10-24% midterm failure rates. While cementless hemispherical components have been utilized to treat large acetabular defects, most reports have not focused specifically on patients with extensive deficiencies.

QUESTIONS/PURPOSES

We report midterm clinical scores, component revisions, and complications following focal bone grafting and cementless acetabular revision in cases with major periacetabular osteolysis.

METHODS

We identified 30 patients (32 hips) who underwent cementless acetabular revision to treat massive acetabular bone loss at an average followup of 53 months. We excluded three patients lost to followup and two patients who died prior to minimum 24 month followup. Harris Hip Scores were assessed before and after surgery. Postoperative radiographs were evaluated for graft incorporation and component migration. Component revision and component migration are reported as failures.

RESULTS

Mean Harris Hip Score improved from 52.5 (range, 17.7-90.7) to 87.3 (range, 25.3-100) points. Three hips (9%) were revised for aseptic loosening. Three components (10.7%) demonstrated radiographic migration, but were not revised. Complete graft incorporation was seen in 17 cases (68%). There were five major complications (14%).

CONCLUSIONS

Cementless acetabular fixation and bone grafting result in clinical scores and survivorship comparable to other options at midterm followup, with potential for biological fixation.

LEVEL OF EVIDENCE

Level IV, clinical research study. See the Guidelines for Authors for a complete description of levels of evidence.

Histological and Ultrastructural Reaction to Different Materials for Orthopaedic Application

Prosthetic joints loosening in absence of infection is the most common reason for revision surgery and is known as aseptic loosening. A significant role in the pathogenesis of implant failure undoubtedly played by the generation of wear debris, mainly from the load bearing joint surfaces, and the cellular reaction through the formation of tissue membrane around implants. This article analyzes histologic, immunohistochemical ad ultrastructural aspects of periprosthetic tissue membrane collected at time of surgical revision, paying attention on cell host response to different materials: metals, polyethylene and ceramics. Dimension of particles seems to be crucial in the activation of different cell population to wear debris.

An Original Method for the Evaluation of in Vivo Controlled Release of the Ceramic Materials

In recent years, the use of ceramic materials in orthopaedics and dentistry is becoming increasingly popular. However, it is important to know their biological and mechanical properties to optimize their use. The aim of this study is to describe a specific method to assess in vivo the effects of chronic release of ceramic materials implanted, in relation also to the type of material, pellets or powders. This was achieved by implanting ceramic powders and pellets, formed by low cohesion grains, in the patellar tendon of 48 New Zealand adult rabbits (24 with powders and 24 with pellets). The motion of the joint allowed easily and progressively the release of grains, detached from surface of the pellets and released to the joint space. Animals were sacrificed at different intervals (1, 3, 6, 12 months). Retrieved knee joints underwent X-Ray, histological and ultrastructural analysis.

Distinct immunohistomorphologic changes in periprosthetic hip tissues from historical and highly crosslinked UHMWPE implant retrievals

Assessment of immune response to implant wear debris in periprosthetic tissue following total hip arthroplasty suggests that multiple factors are involved in the loss implant function. The current study investigated wear debris and the associated immunohistomorphologic changes in tissues from nine patients with historical (gamma air-sterilized) and nine highly crosslinked UHMWPE implant components. Paraffin embedded tissue sections were evaluated for the presence of histiocytes, giant cells, fibrocartilage/bone, and necrosis. To determine the incidence, degree and co-localization of immunohistomorphologic changes and wear, overlapping full-field tissue arrays were collected in brightfield and polarized light. The historical cohort tissues predominantly showed histiocytes associated with significant accumulations of small wear (0.5-2 microm), and giant cells associated with large wear (> or =2 microm). Frequently, focal regions of necrosis were observed in association with wear debris. For the highly crosslinked cohort, inflammation and associated wear debris were limited, but in tissues from patients revised after implantation times of >2 years a response was observed. Whereas significant amounts of fibrocartilage/bone were observed in patients at earlier implantation times. In both cohorts, tissue responses were more extensive in the retroacetabular or proximal femoral regions. The current findings suggest that wear debris-induced inflammation may be a major contributor to the loss of implant function for both the historical and highly crosslinked cohorts, but it is not the primary cause of early implant loosening. This study highlights the importance of using a more quantitative and standardized assessment of immunohistomorphologic responses in periprosthetic tissues, and emphasizes differences in specific anatomical regions of individual patient tissues.

Initial increased wear debris of XLPE-Al₂O₃ bearing in total hip arthroplasties

INTRODUCTION

Aseptic implant loosening caused by wear debris is a common reason for early implant failure after total hip replacement (THR).

MATERIALS AND METHODS

We prospectively studied 96 patients (110 hips), 48 men and 48 women (mean age 46.8 years, mean body mass index 26.1) who had undergone cementless THR (titanium stem, press-fit cup, Al(2)O(3) ball, XLPE liner) at a mean of 17.4 months (SD 13.4).

RESULTS

The semi-computerized evaluation of wear rate showed wear of 0.25 mm (SD 0.3) corresponding to a volume of 97.6 mm(3) (SD 121.1) during the first year. It was remarkable that the annual rate of wear was significantly lower in the second year: 0.14 mm (SD 0.1), 60.0 mm(3) (SD 78.7). The implant survival rate was 100%. However, two patients underwent revision surgery.

INTERPRETATION

Good, early functionality can be achieved by a cementless THR including a modular stem and a XLPE-Al(2)O(3) bearing system. The rate of wear debris for XLPE-Al(3)O(2) was much higher than expected within the first year after THR. However, after the initial running-in period a significant decrease of wear was documented, suggesting a biphasic abrasion [0.38 mm (SD 0.2) within the first year vs. 0.14 mm (SD 0.1)] after the running-in-period 1 year following surgery.

Crosslinked polyethylene in knee arthroplasty: a simulator study evaluating the positive influence on the tribocontact area in the fixed-bearing knee

BACKGROUND

Crosslinked polyethylene (XPE) was developed to reduce the wear rate in hip as well as knee arthroplasty. The crosslinking process reduces the mechanical properties of ultra-high-molecular-weight polyethylene (UHMWPE), particularly its fatigue strength. UHMWPE fatigue occurs more frequently in the knee than in the hip joint due to its changing tribocontact areas (TCAs) combined with high weight bearing. This is why XPE is still controversially discussed for use in total knee arthroplasty. Therefore, the potential advantage of using XPE in the knee was analysed in a simulator study with a focus on potential fatigue wear mechanisms.

METHODS

Three different kinds of XPE and one conventional UHMWPE were tested over 5 million cycles in fixed-bearing knee designs. The TCAs were examined by replicas, and their extent was measured. The wear mechanism was analysed by scanning electron microscopy.

RESULTS

The extent of the TCAs was less than 5% for all XPEs, whereas 35% for the conventional UHMWPE. Fatigue wear mechanisms were not observed.

CONCLUSION

The measured small extent of the TCAs as a predictor of a low wear rate without any fatigue wear mechanism shows a possible advantage for the use of XPE even in knee arthroplasty.

In vivo tissue responses to thermal-responsive shape memory polymer nanocomposites

To explore the safe use of thermal-responsive shape memory polymers (SMPs) as minimally invasive tissue scaffolds, we recently developed a class of biodegradable POSS-SMP nanocomposites exhibiting stable temporary shape fixing and facile shape recovery within a narrow window of physiological temperatures. The materials were covalently crosslinked from star-branched building blocks consisting a bioinert polyhedral oligomeric silsesquioxane (POSS) core and 8 degradable poly(D,L-lactide) (PLA) arms. Here we examine the degradation profiles and immunogenicity of POSS-SMPs as a function of the PLA arm lengths using a rat subcutaneous implantation model. We show that POSS-SMPs elicited a mild foreign body type immune response upon implantation. The degradation rates of POSS-SMPs, both in vitro and in vivo, inversely correlated with the length of the PLA chains within the crosslinked amorphous network. Upon in vivo degradation of POSS-SMPs, a second acute inflammatory response was elicited locally, and the inflammation was able to resolve over time without medical interventions. One year after the implantation of POSS-SMPs, no pathologic abnormalities were detected from the vital/scavenger organs examined. These minimally immunogenic and biodegradable SMPs are promising candidates for scaffold-assisted tissue repair where both facile surgical delivery and controlled degradation of the scaffold are desired for achieving optimal short-term and long-term clinical outcomes.

Biotribology of alternative bearing materials for unicompartmental knee arthroplasty

The objective of our wear simulator study was to evaluate the suitability of two different carbon fibre-reinforced poly-ether-ether-ketone (CFR-PEEK) materials for fixed bearing unicompartmental knee articulations with low congruency. In vitro wear simulation was performed according to ISO 14243-1:2002 (E) with the clinically introduced Univation F fixed bearing unicompartmental knee design (Aesculap AG, Tuttlingen, Germany) made of UHMWPE/CoCr29Mo6 in a direct comparison to experimental gliding surfaces made of CFR-PEEK pitch and CFR-PEEK PAN. Gliding surfaces of each bearing material (n=6+2) were gamma-irradiated, artificially aged and tested for 5 million cycles with a customized four-station knee wear simulator (EndoLab, Thansau, Germany). Volumetric wear assessment, optical surface characterization and an estimation of particle size and morphology were performed. The volumetric wear rate of the reference PE1-6 was 8.6 +/- 2.17 mm(3) per million cycles, compared to 5.1+/-2.29 mm(3) per million cycles for PITCH1-6 and 5.2 +/- 6.92 mm(3) per million cycles for PAN1-6; these differences were not statistically significant. From our observations, we conclude that CFR-PEEK PAN is obviously unsuitable as a bearing material for fixed bearing knee articulations with low congruency, and CFR-PEEK pitch also cannot be recommended as it remains doubtful wether it reduces wear compared to polyethylene. In the fixed bearing unicompartmental knee arthroplasty examined, application threshold conditions for the biotribiological behaviour of CFR-PEEK bearing materials have been established. Further in vitro wear simulations are necessary to establish knee design criteria in order to take advantage of the biotribiological properties of CFR-PEEK pitch for its beneficial use to patients.

Designing Fail-Safe Biomaterials against Wear for Artificial Total Hip Replacement

This review paper presents a fail-safe approach in designing biomaterials against wear for application in an artificial total hip replacement in view of the recent advances in orthopedic bioengineering materials. It has been established that substantially different alloys should be used for minimizing wear in bearing surfaces. Frictional forces at these rubbing counter-faces must be minimized to prevent loosening of the femoral stem and acetabular socket assembly from their positions secured by the fixation agent. A comparative analysis of various wear-resistant biomaterials resulted in the lowest production of wear particles in a total hip where a ceramic socket articulates against the ceramic ball: it produces only 0.004 cubic millimeters of ceramic wear particles. Surface modification, through the application of coatings, offers the potential to reduce the wear rate without compromising the bulk mechanical behavior of the implant material. These hard coatings were found to include diamond-like carbon, amorphous diamond, and titanium nitride.

Wear testing of a DJOA finger prosthesis in vitro

Although the market for replacement of diseased metacarpophalangeal (MCP) joints is dominated by single-piece silicone prostheses, several two-piece designs have been implanted. One such is the Digital Joint Operative Arthroplasty (DJOA) which consists of a part-spherical stainless steel metacarpal component which articulates within a matching concave phalangeal component made of ultra high molecular weight polyethylene (UHMWPE). A DJOA MCP prosthesis was tested using a clinically-validated finger simulator while a second DJOA prosthesis acted as a statically-loaded soak-control. Testing ran to 7.1 million cycles of flexion-extension. It was found that the UHMWPE components, both test and control, gained in weight by a similar amount. Therefore apparently there was no wear of the test components. However, the initial and final surface finish values of the test stainless steel metacarpal head were relatively high. Calculations based on this roughness data, plus recent dynamically-loaded soak data, may explain the apparent lack of wear.

A New Formulation for the Prediction of Polyethylene Wear in Artificial Hip Joints

Artificial joints employing ultra-high molecular weight polyethylene (UHMWPE) are widely used to treat joint diseases and trauma. Wear of the polymer bearing surface largely limits the use of these joints in younger and more active patients. Previous studies have shown the wear factor used in Archard's law for the conventional polyethylene to be highly dependent on contact pressure and this has produced variability in experimental data and has constrained the reliability and applicability of previous computational predictions. A new wear law is proposed, based on wear volume being dependent on, and proportional to, the product of the sliding distance and contact area. The dimensionless proportional constant, wear coefficient, which was independent of contact pressure, was determined from a multi-directional pin on plate study. This was used in computational predictions of the wear of the conventional UHMWPE hip joints. The wear of the polyethylene cup was independently experimentally determined in physiological full hip joint simulator studies. The predicted wear rate from the new computational model was generally increased, with an improved agreement with the experimental measurement compared with the previous computational model. It was shown that wear in the UHMWPE hip joints increased as head size and contact area increased. This resulted in a much larger increase in the wear rate as the head size increased, compared with the previous computational model, and is consistent with clinical observations. This new understanding of the wear mechanism in artificial joints using the UHMWPE bearing surfaces, and the improved ability to predict wear independently and to address previously described discrepancies offer new opportunities to optimize design parameters.

Functional Coatings or Films for Hard-Tissue Applications

Metallic biomaterials like stainless steel, Co-based alloy, Ti and its alloys are widely used as artificial hip joints, bone plates and dental implants due to their excellent mechanical properties and endurance. However, there are some surface-originated problems associated with the metallic implants: corrosion and wear in biological environments resulting in ions release and formation of wear debris; poor implant fixation resulting from lack of osteoconductivity and osteoinductivity; implant-associated infections due to the bacterial adhesion and colonization at the implantation site. For overcoming these surface-originated problems, a variety of surface modification techniques have been used on metallic implants, including chemical treatments, physical methods and biological methods. This review surveys coatings that serve to provide properties of anti-corrosion and anti-wear, biocompatibility and bioactivity, and antibacterial activity.

Efficacy of periprosthetic erythromycin delivery for wear debris-induced inflammation and osteolysis

OBJECTIVES

We have reported that oral erythromycin (EM) inhibits periprosthetic tissue inflammation in a group of patients with aseptic loosening. The purpose of this study was to assess the efficacy of local, periprosthetic EM delivery in a rat model.

METHODS

Uncoated Ti pins were press-fit into the right tibia of fourteen Sprague-Dawley rats following an intramedullar injection of UHMWPE (ultra high molecular weight polyethylene) particles. Revision surgeries were performed 2 months after the primary surgery. EM was applied to the Peri-Apatite™ (PA) layer of the titanium (Ti) pins. The previously implanted Ti pins were withdrawn and replaced with Ti pins coated either with (n = 7) or without (n = 7) EM. The rats were killed 1 month after "revision surgery". The EM efficacy was evaluated by (MicroCT) μCT and histology.

RESULTS

μCT analysis showed that bone volume percentage (BV/TV) was significantly higher in the EM-treated group compared to the untreated group (p < 0.05). Histological analysis showed that EM treatment inhibits UHMWPE particle-induced periprosthetic tissue inflammation compared to the untreated group.

CONCLUSION

This study demonstrated that periprosthetic EM delivery reduced periprosthetic inflammation and improved the quality of surrounding bone.

Bone mineral density of the femoral neck in resurfacing hip arthroplasty

BACKGROUND AND PURPOSE

Resurfacing total hip arthroplasty (RTHA) may preserve the femoral neck bone stock postoperatively. Bone mineral density (BMD) may be affected by the hip position, which might bias longitudinal studies. We investigated the dependency of BMD precision on type of ROI and hip position.

METHOD

We DXA-scanned the femoral neck of 15 resurfacing patients twice with the hip in 3 different rotations: 15 degrees internal, neutral, and 15 degrees external. For each position, BMD was analyzed with 3 surface area models. One model measured BMD in the total femoral neck, the second model divided the neck in two, and the third model had 6 divisions.

RESULTS

When all hip positions were pooled, average coefficients of variation (CVs) of 3.1%, 3.6%, and 4.6% were found in the 1-, 2-, and 6-region models, respectively. The externally rotated hip position was less reproducible. When rotating in increments of 15 degrees or 30 degrees , the average CVs rose to 7.2%, 7.3%, and 12% in the 3 models. Rotation affected the precision most in the model that divided the neck in 6 subregions, predominantly in the lateral and distal regions. For larger-region models, some rotation could be allowed without compromising the precision.

INTERPRETATION

If hip rotation is strictly controlled, DXA can reliably provide detailed topographical information about the BMD changes around an RTHA. As rotation strongly affects the precision of the BMD measurements in small regions, we suggest that a less detailed model should be used for analysis in studies where the leg position has not been firmly controlled.

Characterization and tribology of PEG-like coatings on UHMWPE for total hip replacements

A crosslinked hydrogel coating similar to poly(ethylene glycol) (PEG) was covalently bonded to the surface of ultrahigh molecular weight polyethylene (UHMWPE) to improve the lubricity and wear resistance of the UHWMPE for use in total joint replacements. The chemistry, hydrophilicity, and protein adsorption resistance of the coatings were determined, and the wear behavior of the PEG-like coating was examined by two methods: pin-on-disk tribometry to evaluate macroscale behavior, and atomic force microscopy (AFM) to simulate asperity wear. As expected, the coating was found to be highly PEG-like, with approximately 83% ether content by x-ray photoelectron spectroscopy and more hydrophilic and resistant to protein adsorption than uncoated UHMWPE. Pin-on-disk testing showed that the PEG-like coating could survive 3 MPa of contact pressure, comparable to that experienced by total hip replacements. AFM nanoscratching experiments uncovered three damage mechanisms for the coatings: adhesion/microfracture, pure adhesion, and delamination. The latter two mechanisms appear to correlate well with wear patterns induced by pin-on-disk testing and evaluated by attenuated total reflection Fourier transform infrared spectroscopy mapping. Understanding the mechanisms by which the PEG-like coatings wear is critical for improving the behavior of subsequent generations of wear-resistant hydrogel coatings.

Microscale wear behavior and crosslinking of PEG-like coatings for total hip replacements

The predominant cause of late-state failure of total hip replacements is wear-mediated osteolysis caused by wear particles that originate from the ultrahigh molecular weight polyethylene (UHMWPE) acetabular cup surface. One strategy for reducing wear particle formation from UHMWPE is to modify the surface with a hydrophilic coating to increase lubrication from synovial fluid. This study focuses on the wear behavior of hydrophilic coatings similar to poly(ethylene glycol) (PEG). The coatings were produced by plasma-polymerizing tetraglyme on UHMWPE in a chamber heated to 40 degrees C or 50 degrees C. Both temperatures yielded coatings with PEG-like chemistry and increased hydrophilicity relative to uncoated UHMWPE; however, the 40 degrees C coatings were significantly more resistant to damage induced by atomic force microscopy nanoscratching. The 40 degrees C coatings exhibited only one damage mode (delamination) and often showed no signs of damage after repeated scratching. In contrast, the 50 degrees C coatings exhibited three damage modes (roughening, thinning, and delamination), and always showed visible signs of damage after no more than two scratches. The greater wear resistance of the 40 degrees C coatings could not be explained by coating chemistry or hydrophilicity, but it corresponded to an approximately 26-32% greater degree of crosslinking relative to the 50 degrees C surfaces, suggesting that crosslinking should be a significant design consideration for hydrophilic coatings used for total hip replacements and other wear-dependent applications.

2009 Knee Society Presidential Guest Lecture: Polyethylene wear in total knees

Knee arthroplasties in young and active patients place a substantial increase in the lifetime tribological demand and potential for wear-induced osteolysis. Polyethylene materials have advanced in recent years, reducing the potential for oxidative degradation and delamination failure. It is timely to consider tribological design variables and their potential to reduce surface wear and the long-term risk of osteolysis. The influence of reduced cross shear in rotating platform mobile-bearing knee designs and reduced surface wear area in low conforming fixed-bearing knees has been investigated. A reduction in cross shear substantially reduced wear in both multidirectional pin-on-plate studies and in rotating platform mobile-bearing designs in knee simulator studies. A reduction in bearing surface contact area substantially reduced surface wear in multidirectional pin-on-plate simulations and in low conforming fixed-bearing knee designs in knee simulator studies. This offers potential for a paradigm shift in knee design predicated by enhanced mechanical properties of new polymer materials. We describe two distinct low-wearing tribological design solutions: (1) a rotating platform design solution with reduced cross shear provides reduced wear with conformity and intrinsic stability; and (2) a low conformity fixed bearing with reduced surface area, provides reduced wear, but has less intrinsic stability and requires good soft tissue function.

Micro-Structural Alterations in MoM Hip Implants

Since the introduction of CoCrMo alloy metal-on-metal hip replacements have shown a great clinical performance. Metal-on-metal couplings produce a much lower wear rate and volume than e.g. metal-on-polyethylene. However, the particle size is significantly smaller within a nm-range. To evaluate the formation of nano-size wear particles in metal-on-metal hip replacements it is essential to understand the micro-structural changes in the sub-surface region of the CoCrMo alloy. For this study a MoM hip implant was analyzed by means of TEM. The results revealed that the good wear performance of this CoCrMo alloy is linked to a strain induced fcc  hcp phase transformation and in-situ re-crystallization under high shear stresses. The result is a nano-crystalline surface zone of ~200 to 400 nm thickness which undergoes an ongoing process of mechanical intermixing with componants of the interfacial fluid. The incorporation of organic carbon from proteins in between the nano-crystals could be visualised by EFTEM and EDS. This mechanically mixed nc-zone must be the origin of the wear particle detachment. An earlier study by Catelas et. al confirms the hypothesis of the location of wear particle detachment by analyzing the shape and chemical composition of emitted wear particles which exhibits the same size and shape of crystals observed in the nc-zone of the implant analyzed in this study.

Metal wear particles: What we know, what we do not know, and why

The importance of wear particle characterization for orthopaedic implants has long been established in the hip and knee arthroplasty literature. With the increasing use of motion preservation implants in the spine, the characterization of wear debris, particularly metallic nature, is gaining importance. An accurate morphological analysis of wear particles provides for both a complete characterization of the biocompatibility of the implant material and its wear products, and an in-depth understanding of the wear mechanisms, ion release, and associated corrosive activity related to the wear particles. In this paper, we present an overview of the most commonly-used published protocols for the isolation and characterization of metal wear particles, and highlight the limitations and uncertainties inherent to metal particle analysis.

Multi-body simulation of a canine hind limb: model development, experimental validation and calculation of ground reaction forces

BACKGROUND

Among other causes the long-term result of hip prostheses in dogs is determined by aseptic loosening. A prevention of prosthesis complications can be achieved by an optimization of the tribological system which finally results in improved implant duration. In this context a computerized model for the calculation of hip joint loadings during different motions would be of benefit. In a first step in the development of such an inverse dynamic multi-body simulation (MBS-) model we here present the setup of a canine hind limb model applicable for the calculation of ground reaction forces.

METHODS

The anatomical geometries of the MBS-model have been established using computer tomography- (CT-) and magnetic resonance imaging- (MRI-) data. The CT-data were collected from the pelvis, femora, tibiae and pads of a mixed-breed adult dog. Geometric information about 22 muscles of the pelvic extremity of 4 mixed-breed adult dogs was determined using MRI. Kinematic and kinetic data obtained by motion analysis of a clinically healthy dog during a gait cycle (1 m/s) on an instrumented treadmill were used to drive the model in the multi-body simulation.

RESULTS AND DISCUSSION

As a result the vertical ground reaction forces (z-direction) calculated by the MBS-system show a maximum deviation of 1.75%BW for the left and 4.65%BW for the right hind limb from the treadmill measurements. The calculated peak ground reaction forces in z- and y-direction were found to be comparable to the treadmill measurements, whereas the curve characteristics of the forces in y-direction were not in complete alignment.

CONCLUSION

In conclusion, it could be demonstrated that the developed MBS-model is suitable for simulating ground reaction forces of dogs during walking. In forthcoming investigations the model will be developed further for the calculation of forces and moments acting on the hip joint during different movements, which can be of help in context with the in silico development and testing of hip prostheses.

ATR-FTIR as a thickness measurement technique for hydrated polymer-on-polymer coatings

Hydrated polymer coatings on polymer substrates are common for many biomedical applications, such as tissue engineering constructs, contact lenses, and catheters. The thickness of the coatings can affect the mechanical behavior of the systems and the cellular response, but measuring the coating thickness can be quite challenging using conventional methods. We propose a new method, that is, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the relative thickness, combined with atomic force microscopy to calibrate the ATR-FTIR measurements. This technique was successfully employed to determine the hydrated thickness of a series of crosslinked tetraglyme coatings on ultrahigh molecular weight polyethylene substrates intended to reduce wear of acetabular cups in total hip replacements. The hydrated coatings ranged from 30 to 200 nm thick and were accurately measured despite the relatively high root-mean-square (RMS) roughness of the substrates, 20-35 nm (peak-to-peak roughness 55-100 nm). The calibrated ATR-FTIR technique is a promising new method for measuring the thickness of many other polymer-on-polymer and hydrated coatings.

A meta-analysis of design- and manufacturing-related parameters influencing the wear behavior of metal-on-metal hip joint replacements

This article aims to clarify the influence of design- and manufacturing-related parameters on wear of metal-on-metal (MoM) joint bearings. A database search for publications on wear simulator studies of MoM bearings was performed. The results of published studies were normalized; groups with individual parameters were defined and analyzed statistically. Fifty-six investigations studying a total of 200 implants were included in the analysis. Clearance, head size, carbon content, and manufacturing method were analyzed as parameters influencing MoM wear. This meta-analysis revealed a strong influence of clearance on running-in wear for implants of 36-mm diameter and an increase in steady-state wear of heat treated components.

Influence of design and bearing material on polyethylene wear particle generation in total knee replacement

Periprosthetic osteolysis is one of the main reasons for revision of arthroplasty. The osteolytic reaction is influenced by the dose, size and shape of the wear particles. For arthroplasty, a low number and biologically less active particles are required. This is the first study which analyzes the impact of different knee designs, combined with crosslinked polyethylenes (sequentially irradiated and annealed as well as remelted techniques), on the amount, size and shape of particles. Overall, six material combinations, four of them with crosslinked polyethylene (XPE) and two of them with ultra-high molecular weight polyethylene (UHMWPE) inserts, including fixed and mobile bearings, were tested in a knee joint simulator. After isolation nearly 100,000 particles were analyzed in size, shape and number by scanning electron microscopy and image analysis. For all the designs, the wear was predominantly smooth and granular with few fibrillar particles. The Scorpio design with the X3 insert, the Natural Knee II design with the Durasul insert and the LCS design, also combined with a crosslinked polyethylene insert, generated statistically significant (P<0.05) lower particle numbers. The particle size was independent of the radiation dose. The wear generated by the LCS knee design (XPE and UHMWPE) had a higher percentage fraction of particles >1microm in size (equivalent circle diameter). The NexGen design, tested with the Prolong insert, showed a high number of particles in the biologically active size range compared with the other crosslinked designs, which could be a predictor for higher biological reactivity.

Monoclonal antibody interactions with micro- and nanoparticles: adsorption, aggregation, and accelerated stress studies

Therapeutic proteins are exposed to various wetted surfaces that could shed subvisible particles. In this work we measured the adsorption of a monoclonal antibody (mAb) to various microparticles, characterized the adsorbed mAb secondary structure, and determined the reversibility of adsorption. We also developed and used a front-face fluorescence quenching method to determine that the mAb tertiary structure was near-native when adsorbed to glass, cellulose, and silica. Initial adsorption to each of the materials tested was rapid. During incubation studies, exposure to the air-water interface was a significant cause of aggregation but acted independently of the effects of microparticles. Incubations with glass, cellulose, stainless steel, or Fe(2)O(3) microparticles gave very different results. Cellulose preferentially adsorbed aggregates from solution. Glass and Fe(2)O(3) adsorbed the mAb but did not cause aggregation. Adsorption to stainless steel microparticles was irreversible, and caused appearance of soluble aggregates upon incubation. The secondary structure of mAb adsorbed to glass and cellulose was near-native. We suggest that the protocol described in this work could be a useful preformulation stress screening tool to determine the sensitivity of a therapeutic protein to exposure to common surfaces encountered during processing and storage.

Tribological and surface analysis of 38mm alumina–as-cast Co–Cr–Mo total hip arthroplasties

There is currently much discussion over the use of ceramic femoral components against metal acetabular cups, for use in total hip arthroplasty. The current study investigates six hot isostatically pressed alumina femoral heads of 38 mm diameter articulating against six as-cast Co—Cr—Mo metallic acetabular cups. Standard walking-cycle simulator wear testing was carried out to 5×106 cycles using the Durham Mark II hip wear simulator, and wear was determined gravimetrically. In addition, surface topography, using a non-contacting profilometer, an atomic force microscope, and an optical microscope, was monitored throughout the wear test. The wear of the ceramic heads was found to be undetectable using the current gravimetric method; however, a change in the surface topography was seen, as grain removal on the pole was observed through atomic force microscopy analysis. A biphasic wear pattern was found for the metallic cups, with low wear rates of 1.04 ± 0.293 mm3/106 cycles (mean, ±95 per cent confidence interval) and 0.0209 ± 0.004 mm3/106 cycles (mean, ±95 per cent confidence interval) for running-in and steady state wear phases respectively. Frictional measurement revealed that the joints were tending towards full fluid-film lubrication in parts of the walking cycle. The results show that the combination of hot isostatically pressed alumina and as-cast Co—Cr—Mo is a promising alternative for total hip arthroplasties.

Response of human osteoblasts exposed to wear particles generated at the interface of total hip stems and bone cement

Aseptic loosening of total hip replacement is mainly caused by wear particles. Abrasive wear occurs at articulating surfaces or as a consequence of micro-motions at the interface between femoral stem and bone cement. Direct impact of wear particles on osteolysis, the remodeling of the bone stock and a directly affected function of osteoblasts was described. The present study examined the response of human osteoblasts exposed to different wear particles, which were generated in a test device providing oscillating micro-motions at the interface between femoral stem and standard bone cement. Characterization of released particles was performed by quantifying the size distribution and the metal content of the wear debris. Human osteoblasts were incubated with particles obtained from hip stems with different material compositions (Ti-6Al-7Nb and Co-28Cr-6Mo) and rough and smooth surface finishings combined with standard bone cement (Palacos(R) R) containing zirconium oxide particles. Commercially pure titanium particles (cp-Ti) and particulate zirconium oxide (ZrO(2)) were used for comparative analyses. The results revealed significant (p < 0.05) reduction of the cell viability after exposure to higher concentration of metallic particles, particularly from Co-based alloys. In contrast, ZrO(2) alone showed significantly less adverse effects on the cells. When increasing metallic particle concentrations massive inhibition was also observed in the release of cytokines including interleukine-6 (IL-6) and interleukine-8 (IL-8), but the expression of Procollagen I and the cell viability showed the highest reduction after exposure to Co-based alloy particles from rough stems.

Cross-linked compared with historical polyethylene in THA: an 8-year clinical study

Wear particle-induced osteolysis is a major cause of aseptic loosening in THA. Increasing wear resistance of polyethylene (PE) occurs by increasing the cross-link density and early reports document low wear rates with such implants. To confirm longer-term reductions in wear we compared cross-linked polyethylene (irradiation in nitrogen, annealing) with historical polyethylene (irradiation in air) in a prospective, randomized clinical study involving 48 patients who underwent THAs with a minimum followup of 7 years (mean, 8 years; range, 7-9 years). The insert material was the only variable. The Harris hip score, radiographic signs of osteolysis, and polyethylene wear were recorded annually. Twenty-three historical and 17 moderately cross-linked polyethylene inserts were analyzed (five patients died, three were lost to followup). At 8 years, the wear rate was lower for cross-linked polyethylene (0.088 +/- 0.03 mm/year) than for the historical polyethylene (0.142 +/- 0.07 mm/year). This reduction (38%) did not diminish with time (33% at 5 years). Acetabular cyst formation was less frequent (39% versus 12%), affected fewer DeLee and Charnley zones (17% versus 4%), and was less severe for the cross-linked polyethylene. The only revision was for an aseptically loose cup in the historical polyethylene group. Moderately cross-linked polyethylene maintained its wear advantage with time and produced less osteolysis, showing no signs of aging at mid-term followup.

LEVEL OF EVIDENCE

Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Effect of oral erythromycin therapy in patients with aseptic loosening of joint prostheses

There is currently no cure for aseptic loosening (AL) of total joint replacement (TJR) except surgical revision. The purpose of this study was to determine whether oral EM could improve the periprosthetic tissue profiles and reduce serum cytokine production in AL patients who are candidates for surgical revision. We recruited 32 AL patients. AL patients were treated with either EM (600 mg/day, n=18) or placebo (n=14) daily, started one month before surgery and ending on the day of surgery. Blood samples were obtained before EM treatment and during surgery. Periprosthetic tissues and joint fluids were collected during surgery. Our results demonstrate that oral EM reduces the inflammation of periprosthetic tissues, as manifested by the reduction of the numbers of infiltrating cells, CD68+ macrophages, RANKL+ cells, and TRAP+ cells. Remarkable decreases of TNFalpha (9.6-fold), IL-1beta (21.2-fold), and RANKL (76-fold) gene transcripts were observed in periprosthetic tissues of patients treated with oral EM. Serum levels of both TNFalpha and (to a lesser extent) IL-1beta were significantly reduced following EM treatment (p<0.05). Our results suggest that EM represents a biological cure or prevention for those patients who might need repeated revision surgeries and/or show the early signs of progressive osteolysis after TJR.

Fixed and mobile bearing total knee arthroplasty--influence on wear generation, corresponding wear areas, knee kinematics and particle composition

BACKGROUND

Several studies in literature are dealing with a direct comparison between fixed and mobile bearing knee replacements, but to our knowledge there is no published data comparing the wear behaviour of the two design principles based on the same femur and superior gliding surface geometry. The objective of our study was to investigate a fixed and mobile bearing knee design with identical femoral articulation in regard to wear, tibio-femoral kinematics and particle size distribution.

METHODS

In vitro wear simulation according to ISO 14243-1 has been performed with the Columbus knee system (Aesculap, Tuttlingen) in the configurations fixed and mobile bearing for five million cycles on a customized four station knee wear simulator. The tests were running under force control and the tibio-femoral kinematics were assessed. A particle analysis has been undergone after each inspection interval when the lubricant was replaced.

FINDINGS

Due to the additional wear in the tibial articulation of the mobile bearing design the mean gravimetric wear rates are not statistically different between the two groups. Apart of that there is a substantial reduction in the amount of wear per area unit for the mobile versus the fixed bearing gliding surfaces. Both groups show comparable tibio-femoral kinematics and a similar wear debris morphology.

INTERPRETATION

Our investigation of a fixed and mobile bearing knee design with identical femoral articulation demonstrates that there are no significant differences in wear rate, resulting kinematics and polyethylene particle release. Therefore it can be recommended that surgeons decision for one or the other design principle should be based on the individual patient profile.

Effects of titanium(iv) ions on human monocyte-derived dendritic cells

Orthopaedic metal implants composed of titanium are routinely used in bone fracture repair and for joint replacement therapies. A considerable fraction of implant recipients are unable to benefit due to implant failure resulting from aseptic loosening, while others may experience cutaneous sensitivity to titanium after implantation. An adaptive immune reactivity towards titanium ions, originating from the biocorrosion of the implants, could play a role. As an initiator of the adaptive immune response, dendritic cells (DC) were studied for uptake and characteristics after titanium exposure. Energy filtered transmission electron microscopy showed uptake of titanium(iv) (Ti(iv)) ions by DCs in vitro and co-localisation with phosphorus-rich cell structures of the DC membranes (phospholipids), cytoplasm (ribosomes and phosphorylated proteins) and the nucleus (DNA). DC maturation and function were investigated by measuring cell surface marker expression by flow cytometry. After exposure, DCs showed a decrease in MHC class II (HLA-DR), co-stimulatory molecules (CD40, CD80 & CD86) and chemokine receptors (CCR) 6 and CCR7 but an increase in CCR4 after Ti(iv) treatment. However, Ti(iv) treated DCs had an increased stimulatory capacity towards allogenic lymphocytes. A Ti(iv) concentration dependant increase of IL-12p70 was observed amidst decrease of the other measured cytokines (TGF-β1 and TGF-β2). Hence, Ti(iv) alters DC properties, resulting in an enhanced T lymphocyte reactivity and deviation towards a Th1 type immune response. This effect may be responsible for the inflammatory side effects of titanium implants seen in patients.

Fabrication and testing of silicon nitride bearings in total hip arthroplasty: winner of the 2007 "HAP" PAUL Award

Total hip arthroplasty (THA) bearings were fabricated from silicon nitride (Si(3)N(4)) powder. Mechanical testing showed that Si(3)N(4) had improved fracture toughness and fracture strength over modern alumina (Al(2)O(3)) ceramic. When tested with Si(3)N(4) cups in a hip simulator, both cobalt-chromium (CoCr) and Si(3)N(4) femoral heads produced low wear rates that were comparable to Al(2)O(3)-Al(2)O(3) bearings in THA. This study offers experimental support for a novel metal-ceramic THA bearing couple that combines the reliability of CoCr femoral heads with the wear advantages of ceramic surfaces.

Comparison of wear of ultra-high molecular weight polyethylene acetabular cups against surface-engineered femoral heads

Alumina ceramic heads have been previously shown to reduce polyethylene wear in comparison to cobalt chrome (CoCr) heads in artificial hip joints. However, there are concerns about the brittle nature of ceramics. It is therefore of interest to investigate ceramic-like coatings on metallic heads. The aim of this study was to compare the friction and wear of ultra-high molecular weight polyethylene (UHMWPE) against alumina ceramic, CoCr, and surface-engineered ceramic-like coatings in a friction simulator and a hip joint simulator. All femoral heads tested were 28 mm diameter and included: Biolox Forte alumina, CoCr, arc evaporative physical vapour deposition (AEPVD) chromium nitride (CrN) coated CoCr, plasma-assisted chemical vapour deposition (PACVD) amorphous diamond-like carbon (aDLC) coated CoCr, sputter CrN coated CoCr, reactive gas controlled arc (RGCA) AEPVD titanium nitride (TiN) coated CoCr, and Graphit-iC coated CoCr. These were articulated against UHMWPE acetabular cups in a friction simulator and a hip joint simulator. Alumina and CoCr gave the lowest wear volumes whereas the sputter coated CrN gave the highest. Alumina also had the lowest friction factor. There was an association between surface parameters and wear. This study indicates that surface topography of surface-engineered femoral heads is more important than friction and wettability in controlling UHMWPE wear.

The influence of tibial tray design on the wear of fixed-bearing total knee replacements

Debris-induced osteolysis due to surface wear is a potential long-term problem in total knee replacements (TKRs). Wear between the tibial tray and ultra-high molecular weight polyethylene insert is thought to contribute to the wear. This study investigated the influence of tibial tray design on the wear of fixed-bearing TKRs. Specifically, this study investigated the influence of the material's surface finish and design characteristics of the locking mechanism of the tibial tray on the wear in fixed-bearing knees for both cruciate-retaining (CR) and posterior-stabilized designs. A new fixed-bearing tibial tray design using Co—Cr and with an improved locking mechanism significantly reduced polyethylene wear from 22.8 ± 6.0 mm3 per 106 cycles to 15.9 ± 2.9 mm3 per 106 cycles compared with a previous titanium alloy tray with a CR design. The wear rates were similar to those of a fixed-bearing insert clamped into a tibial tray, suggesting that the decrease in wear was due to a reduction in backside wear. There was no significant difference between the wear rates of a cruciate-retaining design and a posterior-stabilized design under the two kinematic conditions tested.

Biotribological evaluation of artificial disc arthroplasty devices: influence of loading and kinematic patterns during in vitro wear simulation

Wear simulation is an essential pre-clinical method to predict the mid- and long-term clinical wear behavior of newly introduced devices for total disc arthroplasty. The main requirement of a suitable method for spinal wear simulation has to be the ability to distinguish between design concepts and allow for a direct comparison of predicate devices. The objective of our study was to investigate the influence of loading and kinematic patterns based on two different protocols for spinal wear simulation (ISO/FDIS 18192-1 (2006) and ASTM F2423-05). In vitro wear simulation was performed with six activ L lumbar artificial disc devices (Aesculap Tuttlingen, Germany). The applied kinematic pattern of movement was multidirectional for ISO (elliptic track) and unidirectional with a curvilinear shape for ASTM. Testing was done for 10 million cycles in the ISO loading mode and afterwards with the same specimens for 5 million cycles according to the ASTM protocol with a customized six-station servohydraulic spinal wear simulator (EndoLab Thansau, Germany). Gravimetrical and geometrical wear assessment, a slide track analysis correlated to an optical surface characterization, and an estimation of particle size and morphology were performed. The gravimetric wear rate for the first 10 million cycles was ISO(initial) = 2.7 +/- 0.3 mg/million cycles. During the ASTM test period (10-15 million cycles) a gravimetric wear rate of 0.14 +/- 0.06 mg/million cycles was estimated. The wear rates between the ISO and ASTM driven simulations differ substantially (approximately 20-fold) and statistical analysis demonstrates a significant difference (p < 0.001) between the test groups. The main explanation of divergency between ISO and ASTM driven wear simulations is the multidirectional pattern of movement described in the ISO document resulting in a cross-shear stress on the polyethylene material. Due to previous retrieval observations, it seems to be very unlikely that a lumbar artificial disc is loaded with a linear wear path.Testing according to ASTM F2423-05 with pure unidirectional motion does not reflect the kinematics of TDA patients' daily activities. Based on our findings it seems to be more reliable to predict the clinical wear behavior of an artificial disc replacement using the ISO/FDIS 18192-1 method.

Alteration of the amount and morphology of wear particles by the addition of loading profile transitions during artificial hip wear testing

Current validation tests of total hip arthroplasty endo-prostheses capture only a single activity performed by patients: continuous walking. A more representative test that includes transitions from a static loaded position to dynamic motion would simulate common motions by patients in which they change from standing to walking. The introduction of such transitions into a traditional test protocol could provide insight into actual wear behaviours and more realistic wear particle properties such as size and shape. First, the introduction of transitions will increase the measured wear rate. Second, the amount of wear will be positively correlated to the number of transitions per day. Finally, the size and shape of polyethylene particle produced via testing with transitions will differ from those of a conventional continuous walking test. Three identical sets of four cobalt chromium femoral heads and sterilized acetabular cups sterilized in ethylene oxide were tested in 30 per cent bovine serum under three conditions: continuous walking (0 transitions/day), 10 transitions/day, and 100 transitions/day. A day was defined as 2500 steps. The static and peak dynamic loads were 260 N and 1.9 kN respectively. A testing duration of 106 cycles was completed for each of the three tests. The wear rate was found to be inversely related to the number of transitions. Particle analysis showed that the particle size decreased as the number of transitions increased. Particles from the 100 transitions/day test were more fibular and produced more particles of the size known to promote an immune reactive response. Contrary to our hypothesis, as the number of transitions performed by patients increased, the wear rate and accumulated wear decreased. In addition, as the number of transitions increased, a larger percentage of wear particles were in the submicron size range. Consequently, despite a decrease in wear due to the presence of loading profile transitions, there is a potentially greater risk of osteolysis owing to the increased production of immunoreactive particles.

Design Modifications and Optimization of a Commercially Available Knee Simulator

To determine the wear behavior of knee endoprostheses, implants are tested in knee simulators before being introduced to the market. Implants may undergo mechanical failure and wear debris is generated. The magnitude and morphology of this debris are determined to gain information about its biological reactivity. In this study, we describe the modifications made to the AMTI multistation knee simulator. The simulator is not capable to ensure a medially biased load distribution as required per ISO 14243, and therefore the usage of the simulator is limited. Thus, simulator modifications were made to implement a wear test as outlined in ISO 14243, and to improve both user-friendliness of operation and cost of simulation. In particular, this involved modifying the implant holders and controlling implant kinematics during the simulation. For component design, a 3D computer-aided design software was used. After the manufacturing of all components had been completed, the redesigned system was put into operation. In a final wear test, functionality and conformance with the ISO standard were tested for the modified simulator. After implementation of design modifications, it is possible to run wear tests with a medially biased load distribution according to ISO 14243.

Macrophages detoxify the genotoxic and cytotoxic effects of surgical cobalt chrome alloy particles but not quartz particles on human cells in vitro

Particles of surgical cobalt chrome alloy are cytotoxic and genotoxic to human fibroblasts in vitro. In vivo orthopaedic patients are exposed to cobalt chrome particles as a result of wear of a joint replacement. Many of the wear debris particles that are produced are phagocytosed by macrophages that accumulate at the site of the worn implant and are disseminated to local and distant lymph nodes the liver and the spleen. In this study we have tested whether this process of phagocytosis could have altered the cytotoxic and genotoxic properties of the cobalt chrome particles. Quartz particles have been investigated as a control. Micron-sized particles of cobalt chrome alloy were internalised by either white cells of peripheral blood or by THP-1 monocytes for 1 week and 1 day, respectively. The particles were then extracted and presented at different doses to fibroblasts for 1 day. There was a reduction of the cytotoxicity and genotoxicity of the cobalt chrome particles after phagocytosis by white cells or THP-1 cells. Cobalt chrome particles that were internalised by fibroblasts also showed a reduction of their cytotoxicity but not their genotoxicity. In contrast the cytotoxicity and genotoxicity of quartz particles was increased after internalisation by THP-1 cells. The surface morphology of the cobalt chrome particles but not the quartz particles was changed after phagocytosis by THP-1 cells. This study suggests that the genotoxic and cytotoxic properties of particles that fall within the size range for phagocytosis may be highly complex in vivo and depend on the combination of material type and previous phagocytosis. These results may have relevance for particle exposure from orthopaedic implants and from environmental or industrial pollution.

Femoral stem wear in cemented total hip replacement

The great success of cemented total hip replacement to treat patients with end-stage osteoarthritis and osteonecrosis has been well documented. However, its long-term survivorship has been compromised by progressive development of aseptic loosening, and few hip prostheses could survive beyond 25 years. Aseptic loosening is mainly attributed to bone resorption which is activated by an in-vivo macrophage response to particulate debris generated by wear of the hip prosthesis. Theoretically, wear can occur not only at the articulating head—cup interface but also at other load-bearing surfaces, such as the stem—cement interface. Recently, great progress has been made in reducing wear at the head—cup interface through the introduction of new materials and improved manufacture; consequently femoral stem wear is considered to be playing an increasingly significant role in the overall wear of cemented total hip replacement. In this review article, the clinical incidences of femoral stem wear are comprehensively introduced, and its significance is highlighted as a source of generation of wear debris and corrosion products. Additionally, the relationship between femoral stem surface finish and femoral stem wear is discussed and the primary attempts to reproduce femoral stem wear through in-vitro wear testing are summarized. Furthermore, the initiation and propagation processes of femoral stem wear are also proposed and a better understanding of the issue is considered to be essential to reduce femoral stem wear and to improve the functionality of cemented total hip replacement.

Macrophage depletion diminishes implant-wear-induced inflammatory osteolysis in a mouse model

The purpose of this study was to determine whether macrophage depletion using clodronate liposomes diminishes wear-debris-induced inflammatory osteolysis in a murine osteolysis model. Ultra high molecular weight polyethylene (UHMWPE) particles were introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. Macrophages were depleted by the intraperitoneal injection of clodronate liposome (2 mg) 2 days before bone implantation and re-injection every 3 days (1 mg) until the sacrifice of the mice. Mice without clodronate liposome therapy or treated with empty liposome as well as mice injected with saline alone were included in this study as controls. Pouch tissues were collected 14 days after bone implantation for molecular and histology analysis. Our findings indicated that (1) macrophage depletion in clodronate-liposome-treated mice was achieved, as illustrated by F4/80 immunostaining in both pouch and spleen tissues; (2) clodronate-liposome treatment significantly reduced UHMWPE-induced tissue inflammation, with diminished pouch membrane thickness, reduced inflammatory cellular infiltration, and lowered interleukin 1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) expression; (3) clodronate-liposome treatment markedly reduced the number of TRAP(+) cells in pouch tissues and protected against bone collagen depletion. In conclusion, this study demonstrates that macrophage depletion using clodronate-liposome reduces UHMWPE particle-induced inflammatory osteolysis. This observation supports the hypothesis that macrophages contribute to the severity of UHMWPE particles induced inflammatory osteolysis, and suggest that macrophage depletion represents a viable therapeutic approach to the prevention and treatment of patients with aseptic loosening.

Reduction of wear volume from ultrahigh molecular weight polyethylene knee components by the addition of vitamin E

Wear performance and debris-size distribution of vitamin E (DL-alpha tocopherol, VE)-added ultrahigh molecular weight polyethylene (UHMWPE) was evaluated using a knee-simulator test. VE was mixed with GUR 1050 UHMWPE powder at 0.3 wt%, and the tibial components of the knee joint were made by direct compression molding. The VE-added UHMWPE showed consistently lower wear volume throughout the test.