Michel P. Laurent

Tribolayer formation in a metal-on-metal (MoM) hip joint: an electrochemical investigation.

The demand for total hip replacement (THR) surgery is increasing in the younger population due to faster rehabilitation and more complete restoration of function. Up to 2009, metal-on-metal (MoM) hip joint bearings were a popular choice due to their design flexibility, post-operative stability and relatively low wear rates. The main wear mechanisms that occur along the bearing surface of MoM joints are tribochemical reactions that deposit a mixture of wear debris, metal ions and organic matrix of decomposed proteins known as a tribolayer. No in-depth electrochemical studies have been reported on the structure and characteristics of this tribolayer or about the parameters involved in its formation. In this study, we conducted an electrochemical investigation of different surfaces (bulk-like: control, nano-crystalline: new implant and tribolayer surface: retrieved implant) made out of two commonly used hip CoCrMo alloys (high-carbon and low-carbon). As per ASTM standard, cyclic polarization tests and electrochemical impedance spectroscopy tests were conducted. The results obtained from electrochemical parameters for different surfaces clearly indicated a reduction in corrosion for the tribolayer surface (Icorr: 0.76μA/cm(2)). Further, polarization resistance (Rp:2.39±0.60MΩ/cm(2)) and capacitance (Cdl:15.20±0.75μF/cm(2)) indicated variation in corrosion kinetics for the tribolayer surface, that attributed to its structure and stability in a simulated body environment.

Surface topography of viable articular cartilage measured with scanning white light interferometry

OBJECTIVE By means of scanning white light interferometry, develop a noncontact, nondestructive technique capable of measuring surface topography of viable cartilage. METHODS Using full thickness cylindrical cartilage explants obtained from bovine calf knees, experiments were performed to produce a surface preparation protocol that yields highly repeatable topographical measurements while maintaining cartilage viability. To further validate the technique, a series of human talar cartilage samples, displaying varying degrees of cartilage degeneration, was then subjected to interferometric measurements and compared to their histology. RESULTS A key aspect of the technique of surface topographic measurement by interferometry was the development of an optimal surface preparation process. The technique was successfully validated against standard 2-D profilometry. The intrinsic variability of the technique is less than 2%, which is much less than the average point-to-point variability of 17% observed across a cartilage specimen. The technique was hence sufficiently sensitive to readily detect differences in roughness between surfaces of healthy cartilage in different locations on the bovine knee. Thus, the average roughness of the medial explants exceeded that of the lateral explants by 0.35 microm Ra (P=0.003) and the roughness of the trochlear explants exceeded that of the condylar explants by 0.55 microm Ra (P<0.0001). Also, applying this technique to diseased human talar cartilage samples, a statistically significant increase in the average surface roughness value per unit increase in histological degeneration score was observed (> or =0.2 microm Ra, P< or =0.041), making surface roughness obtained via interferometry a useful parameter for evaluating cartilage health nondestructively. CONCLUSIONS The aim of developing a protocol based on white light interferometry to measure the surface topography of viable articular cartilage was achieved. This interferometric technique opens the door to monitoring the surface topography of live cartilage, as is desirable for ex vivo tests on cartilage explants.

Analysis of Retrieved Acetabular Components of Three Polyethylene Types

The polyethylene used in total hip arthroplasty has gone through many changes over the past several decades, including consolidation processes, resin types, method of sterilization, packaging, and the extent of crosslinking. To isolate the in vivo performance of material changes from implant system design changes, we assessed the postretrieval surface wear and damage of components made from three different polyethylene types used in a single implant system. The polyethylene types investigated are representative of the sequentially available bearing materials that have dominated use in total hip arthroplasty over the last several decades. Forty-six components with implantation durations of 12 to 96 months were assessed for surface wear and damage and for socket wear and creep volume change. Acetabular components made from highly crosslinked polyethylene had a 50% lower total damage score than components made from polyethylene that was either gamma-sterilized in air or in nitrogen. The wear and creep socket volume change was 80% and 90% lower for the highly crosslinked components compared with the gamma-sterilized in air and nitrogen groups, respectively. These data of direct component measurement are consistent with earlier predictions that recent changes in polyethylene material processing can lead to clinically improved bearing performance.Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Surface Damage Versus Tibial Polyethylene Insert Conformity: A Retrieval Study

BackgroundSurface damage of the tibial polyethylene insert in TKA is thought to diminish with increasing conformity, based on computed lower contact stresses. Added constraint from higher conformity may, however, result in greater forces in vivo.Questions/purposesWe therefore determined whether increased conformity was associated with increased surface pitting, delamination, creep, and polishing in a group of retrieved tibial inserts.MethodsWe compared 38 inserts with a dished articular surface (conforming group) with 31 inserts that were unconstrained and nonconforming in the sagittal plane (less conforming group). The two groups had identical polyethylene composition and processing history. The articulating surfaces were scored for pitting, delamination, deformation/creep, and polishing. Evidence of edge loading and the presence of embedded bone cement were also recorded.ResultsThe conforming inserts were associated with higher delamination and pitting scores but lower polishing scores, even after adjusting for the effects of sex, age, insert thickness, and implantation duration. Long implantation duration and male sex were also associated with increased delamination, pitting, and polishing, whereas long shelf life was associated only with increased delamination. The conforming group also had approximately a fourfold greater prevalence of edge loading and approximately a threefold greater prevalence of embedded bone cement. The latter was associated with higher scores and proportions of delamination and pitting.ConclusionsThese findings suggest more conformity may increase surface fatigue damage in TKA. Higher constraint-induced stresses during secondary motions and more possibility for edge loading and bone cement capture on a dished surface may account for these results.Clinical RelevanceThe selection of materials with high fatigue resistance may be particularly important for high-conformity/constraint tibial inserts. In addition, awareness of the benefits and trade-offs with conformity may allow better matching of TKA design to patient.

Tribochemical Reactions in Metal-on-Metal Hip Joints Influence Wear and Corrosion

Recent findings indicate the presence of tribochemically generated layers on metal-on-metal (MoM) bearing surfaces. These tribolayers are films of a few-hundred-nanometer thickness and are constituted of carbonaceous material mixed with metal and oxide particles. The purpose of the study was to characterize these tribofilms mechanically and electrochemically. Using a nanoindenter, the local mechanical properties of the tribolayer were measured. On average a hardness of 1.0 GPa was determined, which was softer than the underlying metal. The influence of tribomaterial on the electrochemistry of the cobalt–chromium–molybdenum alloy (CoCrMo) was investigated. Bovine calf serum mixture was used as the electrolyte. Highand low-carbon CoCrMo-samples with and without tribolayer were compared using potentiodynamic testing. This corrosive investigation was followed by tribocorrosive tests using a custom made apparatus, where a ceramic ball Manuscript received May 23, 2012; accepted for publication September 5, 2012; published online April 10, 2013. Dept. of Orthopedic Surgery, Rush Univ. Medical Center, Orthopedic Building, 1611 W. Harrison St., Suite 204, Chicago, IL 60612, United States of America (Corresponding author), e-mail: markus_a_wimmer@rush.edu Dept. of Orthopedic Surgery, Rush Univ. Medical Center, Chicago, IL 60612, United States of America. Dept. of Materials Science and Engineering, Northwestern Univ., Evanston, IL 60201, United States of America. Materials Science and Engineering, Univ. of Duisburg-Essen, 47057 Duisburg, Germany. Copyright VC 2013 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Metal-On-Metal Total Hip Replacement Devices STP 1560, 2013 Available online at www.astm.org DOI:10.1520/STP156020120050 oscillated against a flat CoCrMo surface. Potential and coefficient of friction were monitored throughout this 100 K cycle test. Electrochemical impedance spectroscopy tests before and after testing were conducted. Weight loss was determined using planimetric analysis. It was found that the tribolayered surface had better corrosion resistance than the corresponding tribolayer-free (polished) surface. The tribolayered surface also exhibited a more noble potential during tribocorrosive testing and demonstrated less wear. Highcarbon was the superior alloy compared with low carbon for all surface conditions; however, the differences seemed to equalize in the presence of a tribofilm. There were also differences in tribofilm generation, possibly related to the microstructure of the two alloys.

In Vivo Wear of a Squeaky Alumina-on-Alumina Hip Prosthesis

Alumina-on-alumina bearings for total hip replacement have been in use for over three decades and are associated with good long-term clinical performance1,2. However, recently there have been anecdotal reports of audible noise, usually characterized as squeaking, in ceramic-on-ceramic joints, which have been publicized even in the media3. The reported prevalence of squeaking and noise in these bearings has varied from 10% (as reported by Varnum et al.7, Keurentjes et al.8, and Jarrett et al.9). The etiology of hip squeaking remains unclear and is undoubtedly a multifactorial phenomenon that may involve component femoral neck-cup impingement, microseparation, and subluxation10. Although limited in number, case reports on squeaky ceramic hip bearings appear to reflect this varied etiology. Thus, squeaking was seen in connection with the use of a mismatched zirconia head and alumina cup wear couple11, femoral neck-socket impingement12,13, and acetabular cup abduction and retroversion coupled with leg-length discrepancy14. There is an ongoing debate about whether squeaking of ceramic hips is a cause for concern15 or not16. Regardless of its prevalence, squeaking of ceramic-on-ceramic joints warrants investigation as it may signal abnormal wear of the bearing surfaces, which, in view of the brittle nature of ceramics, may progressively increase in severity. In the present case study, we had the opportunity to examine an alumina-on-alumina hip that was explanted because of severe persistent squeaking with all activities. The purpose of the present study was to determine if the severe noise was accompanied by substantial joint wear. We hypothesized that the squeaking was associated with degradation of the bearing surfaces. We …

Establishing a live cartilage-on-cartilage interface for tribological testing

Mechano-biochemical wear encompasses the tribological interplay between biological and mechanical mechanisms responsible for cartilage wear and degradation. The aim of this study was to develop and start validating a novel tribological testing system, which better resembles the natural joint environment through incorporating a live cartilage-on-cartilage articulating interface, joint specific kinematics, and the application of controlled mechanical stimuli for the measurement of biological responses in order to study the mechano-biochemical wear of cartilage. The study entailed two parts. In Part 1, the novel testing rig was used to compare two bearing systems: (a) cartilage articulating against cartilage (CoC) and (b) metal articulating against cartilage (MoC). The clinically relevant MoC, which is also a common tribological interface for evaluating cartilage wear, should produce more wear to agree with clinical observations. In Part II, the novel testing system was used to determine how wear is affected by tissue viability in live and dead CoC articulations. For both parts, bovine cartilage explants were harvested and tribologically tested for three consecutive days. Wear was defined as release of glycosaminoglycans into the media and as evaluation of the tissue structure. For Part I, we found that the live CoC articulation did not cause damage to the cartilage, to the extent of being comparable to the free swelling controls, whereas the MoC articulation caused decreased cell viability, extracellular matrix disruption, and increased wear when compared to CoC, and consistent with clinical data. These results provided confidence that this novel testing system will be adequate to screen new biomaterials for articulation against cartilage, such as in hemiarthroplasty. For Part II, the live and dead cartilage articulation yielded similar wear as determined by the release of proteoglycans and aggrecan fragments, suggesting that keeping the cartilage alive may not be essential for short term wear tests. However, the biosynthesis of glycosaminoglycans was significantly higher due to live CoC articulation than due to the corresponding live free swelling controls, indicating that articulation stimulated cell activity. Moving forward, the cell response to mechanical stimuli and the underlying mechano-biochemical wear mechanisms need to be further studied for a complete picture of tissue degradation.

How Does Wear Rate Compare in Well-functioning Total Hip and Knee Replacements? A Postmortem Polyethylene Liner Study.

BackgroundThe longevity of total hip (THR) and knee replacements (TKR) that used historical bearing materials of gamma-in-air sterilized UHMWPE was affected more by osteolysis in THRs than in TKRs, although osteolysis remains a concern in TKRs. Therefore, the study of polyethylene wear is still of interest for the knee, particularly because few studies have investigated volumetric material loss in tibial knee inserts. For this study, a unique collection of autopsy-retrieved TKR and THR components that were well-functioning at the time of retrieval was used to compare volumetric wear differences between hip and knee polyethylene components made from identical material.Questions/purposesThe following questions were addressed: (1) How much did the hip liners wear and what wear patterns did they exhibit? (2) How much did the knee inserts wear and what wear patterns did they exhibit? (3) What is the ratio between TKR and THR wear after controlling for implantation time and patient age?MethodsWe compared 23 THR components (Harris-Galante [HG] and HG II) and 20 TKR components (Miller-Galante [MG II]) that were retrieved postmortem. The components were made from the same polyethylene formulation and with similar manufacturing and sterilization (gamma-in-air) processes. Twenty-one patients (12 males, nine females) had THRs and 16 (four males, 12 females) had TKRs. Patients who had TKRs had an older (p = 0.001) average age than patients who had THRs (age, 75 years; SD, 10, versus 66 years; SD, 12, respectively). Only well-functioning components were included in this study. Therefore, implants retrieved postmortem from physically active patients and implanted for at least 2 years were considered. In addition, only normally wearing TKR components were considered, ie, those with fatigue wear (delamination) were excluded. The wear volume of each component was measured using metrology. For the tibial inserts an autonomous mathematic reconstruction method was used for quantification.ResultsThe acetabular liners of the THR group had a wear rate of 38 mm3 per year (95% CI, 29–47 mm3/year). Excluding patients with low-activity, the wear rate was 47 mm3 per year (95% CI, 37–56 mm3/year). The wear rate of normally wearing tibial inserts was 17 mm3 per year (95% CI, −6 to 40 mm3/year). After controlling for the relevant confounding variable of age, we found a TKR/THR wear rate ratio of 0.5 (95% CI, 0.29–0.77) at 70 years of age with a slightly increasing difference with increasing age.ConclusionsExcluding delamination, TKRs exhibited lower articular wear rates than THRs for historical polyethylene in these two unique cohorts of postmortem retrievals.Clinical RelevanceThe lower TKR wear rate is in line with the lower incidence of osteolysis in TKRs compared with THRs.

Effect of europium(II) stearate on the mechanical properties and the oxidation resistance of UHMWPE

The objective of this pilot study is to investigate the effect of europium(II) stearate additive on the mechanical properties and oxidation resistance of an ultra-high molecular weight polyethylene (UHMWPE), which has been used as an articulating surface in prosthetic devices for many years. It is hypothesized in this study that combining the UHMWPE with lanthanide stearates could enhance oxidation resistance, leading to better preservation of the materials mechanical integrity. Compression molded UHMWPE was doped at 0, 375 and 750 ppm of europium(II) stearate, γ-irradiated to 35 kGy in a nitrogen atmosphere, and accelerated aged in accordance with the ASTM standard F2003-02. Non-irradiated and nonaged samples were used as controls. Miniature samples were comparatively tested for mechanical properties using the small punch test. Oxidation indices (OIs) were obtained through the FTIR spectroscopy on thin film sections of all irradiated samples. The UHMWPE doped with the europium(II) stearate had the same small punch test curve shape as the conventional UHMWPE control; the ultimate displacement remained unchanged (approximately 4.33±0.02 mm), while the ultimate load and work-to-failure exhibited only small changes (<7.5% and <5.0%, respectively). The doped material was more resistant to oxidation than the control material, retaining 83% of its as-irradiated work-to-failure after irradiation and accelerated aging, versus only 53% for the control. Accelerated aging changed the average oxidation index of the control group from 0.07 to 0.40; whereas the average oxidation indices changed from 0.03 to 0.15 and from 0.05 to 0.13 for the 375 ppm and the 750 ppm doped condition, respectively.

Protein State Affects Wear of UHMWPE

It is well established that the lubricant properties play a key role in the wear of UHMWPE in prosthetic knees [1] and hips [2, 3]. The total protein concentration, the albumin – globulin ratio, the lubricant volume turnover rate, and the protein precipitation rate, all have ben found to affect the polyethylene wear rate [3]. A factor that has not yet been studied, but may be of clinical relevance, is the effect of the state of protein on the wear and friction of prosthetic joints. Protein cleavage is expected in the presence of an inflammatory response [4] and through wear processes at the articular interface. Such cleavage may have a significant effect on the lubrication regime and the wear mechanism of the prosthetic joint. An understanding of this effect is therefore required to further elucidate UHMWPE wear mechanisms, to increase the reliability and validity of wear tests for the preclinical evaluation of prosthetic joints, and to clinically assess patient effects.Copyright