Increased Total Knee Arthroplasty Ultra-High Molecular Weight Polyethylene Wear Using a Clinically Relevant Hyaluronic Acid Simulator Lubricant

Synthesis of a Lubricant to Mimic the Biorheological Behavior of Osteoarthritic and Revision Synovial Fluid

The rheological properties of synovial fluid (SF) are essential for the friction behavior and wear performance of total joint replacements. Standardized in vitro wear tests for endoprosthesis recommend diluted calf serum, which exhibits substantial different rheological properties compared to SF. Therefore, the in vitro test conditions do not mimic the in vivo conditions. SF samples from osteoarthritis knee patients and patients undergoing knee endoprosthesis revision surgery were compared biochemically and rheologically. The flow properties of SF samples were compared to synthetic fluid constituents, such as bovine serum albumin (BSA) and hyaluronic acid (HA). Interestingly, HA was identified as a significant contributor to shear-thinning. Using the acquired data and mathematical modelling, the flow behavior of human SF was modelled reliably by an adapted adjustment of biorelevant fluid components. Friction tests in a hard/soft bearing (ceramic/UHMWPE) demonstrated that, in contrast to serum, the synthetic model fluids generate a more realistic friction condition. The developed model for an SF mimicking lubricant is recommended for in vitro wear tests of endoprostheses. Furthermore, the results highlight that simulator tests should be performed with a modified lubricant considering an addition of HA for clinically relevant lubrication conditions.

Corrosion resistance of the nickel-free high-nitrogen steel FeCrMnMoN0.9 under simulated inflammatory conditions

Nickel-free, high-nitrogen austenitic steels (AHNS) have been introduced for biomedical applications, with encouraging results in terms of mechanical and corrosion properties. Here, we tested the corrosion resistance of a nickel-free high nitrogen steel (FeCrMnMoN0.9) in bovine serum solutions containing 0 or 3 g/L hyaluronic acid (HA), and 0, 3, or 30 mM hydrogen peroxide (H₂ O₂ ) simulating no, moderate, or strong inflammatory conditions, respectively. Nondestructive electrochemical measurements (open circuit potential [OCP], linear polarization resistance "R_P ", and electrochemical impedance spectroscopy) were run in triplicate over 10 hr. The presence of HA had no significant effect either on the stabilized OCP values, or on the corrosion resistance of FeCrMnMoN0.9. Increasing H₂ O₂ concentrations shifted the OCP to more electropositive values; the corrosion resistance decreased only at a 30 mM H₂ O₂ . Final R_P values at 0, 3, and 30 mM H₂ O₂ resulted in 1598 ± 276, 1746 ± 308, and 439 ± 47 kΩ cm² , respectively. These values were 4-14 times higher, than the R_P values measured on LC-CoCrMo in our previous study, conducted under identical conditions. While these findings are encouraging, future studies need to focus on tribocorrosive properties of the AHNS to evaluate its applicability in joint replacement.

Effects of bovine serum albumin and hyaluronic acid on the electrochemical response of a CoCrMo alloy to cathodic and anodic excursions

The problem of wear and corrosion of CoCrMo-implant surfaces in the human body following total joint replacement has been commonly investigated with tribocorrosion tests, using different lubricants meant to simulate the pseudo-synovial fluid. While results considering the synovial fluid components separately have highlighted their individual influence on the tribological performance of CoCrMo-alloy, an understanding about the influence of the synovial fluid components under the electrochemical point of view is missing. This work aims to investigate the effect of bovine serum albumin (BSA) and hyaluronic acid (HA) on electrochemical potential variations of CoCrMo alloys tested in a model synovial fluid. To simulate the environment inside the synovial capsule, the tests were performed inside a CO₂ incubator at 37°C. Open circuit potential, electrochemical impedance spectroscopy, cathodic and anodic potentiodynamic measurements were performed with different electrolytes, prepared with cell culture medium (RMPI-1640), BSA and HA. The final CoCrMo-surface was analyzed by SEM/EDS and infrared spectroscopy. The influence of HA on the corrosion of the CoCrMo-alloy depended on the presence of BSA proteins adsorbed on the CoCrMo-surface: EIS and anodic polarization results showed a corrosive action of HA in the absence of adsorbed proteins. In the presence of both BSA and HA, organometallic precipitates were found on the CoCrMo surface following reverse anodic polarization, which remind of corrosion products found in-vivo. These results indicate that HA affects the interaction of CoCrMo implant alloys with protein-containing model synovial fluids, and suggest that HA needs to be considered in tribocorrosion studies for more clinically relevant outcomes.

The effect of hyaluronic acid on the corrosion of an orthopedic CoCrMo-alloy in simulated inflammatory conditions

During joint inflammation, various reactive oxygen species (ROS) are present in the surrounding tissue and joint fluid. In the laboratory, hydrogen peroxide (H₂O₂) is typically used to simulate inflammatory conditions, and media containing proteins and hyaluronic acid (HA) are employed to simulate joint synovial fluid. Electrochemical interactions between H₂O₂ and HA in the presence of a CoCrMo surface are expected, since HA molecules contain redox-active moieties. We hypothesized that any redox reactions of these moieties with ROS will mitigate the oxidizing effect of H₂O₂ on the CoCrMo surface, limiting the corrosion rate of the metal. Non-destructive electrochemical measurements (open circuit potential, linear polarization resistance and electrochemical impedance spectroscopy) were used to investigate the corrosion response of CoCrMo in synovial model fluid containing physiologically relevant concentrations of albumin proteins and hyaluronic acid, with and without H₂O₂. Two different molarities of H₂O₂, 3 mM and 30 mM, were tested. While both molarities are within physiological limits, 3mM is well within the range HA could mitigate, whereas 30 mM is not. Contrary to our hypothesis, HA did not alleviate corrosion in 3 mM H₂O₂ and even caused a corrosion increase in the case of 30 mM H₂O₂. The decrease in corrosion resistance of the alloy may be attributed to the complexation of degenerated HA molecular chains with chromium ions released from the metallic surface, which are necessary to build a protective oxide film. This finding has clinical implications, suggesting that HA accelerates corrosion of CoCrMo implants in the presence of strong inflammation.

A comparison between electromechanical and pneumatic-controlled knee simulators for the investigation of wear of total knee replacements

More robust preclinical experimental wear simulation methods are required in order to simulate a wider range of activities, observed in different patient populations such as younger more active patients, as well as to fully meet and be capable of going well beyond the existing requirements of the relevant international standards. A new six-station electromechanically driven simulator (Simulation Solutions, UK) with five fully independently controlled axes of articulation for each station, capable of replicating deep knee bending as well as other adverse conditions, which can be operated in either force or displacement control with improved input kinematic following, has been developed to meet these requirements. This study investigated the wear of a fixed-bearing total knee replacement using this electromechanically driven fully independent knee simulator and compared it to previous data from a predominantly pneumatically controlled simulator in which each station was not fully independently controlled. In addition, the kinematic performance and the repeatability of the simulators have been investigated and compared to the international standard requirements. The wear rates from the electromechanical and pneumatic knee simulators were not significantly different, with wear rates of 2.6 ± 0.9 and 2.7 ± 0.9 mm³/million cycles (MC; mean ± 95% confidence interval, p = 0.99) and 5.4 ± 1.4 and 6.7 ± 1.5 mm³/MC (mean ± 95 confidence interval, p = 0.54) from the electromechanical and pneumatic simulators under intermediate levels (maximum 5 mm) and high levels (maximum 10 mm) of anterior-posterior displacements, respectively. However, the output kinematic profiles of the control system, which drive the motion of the simulator, followed the input kinematic profiles more closely on the electromechanical simulator than the pneumatic simulator. In addition, the electromechanical simulator was capable of following kinematic and loading input cycles within the tolerances of the international standard requirements (ISO 14243-3). The new-generation electromechanical knee simulator with fully independent control has the potential to be used for a much wider range of kinematic conditions, including high-flexion and other severe conditions, due to its improved capability and performance in comparison to the previously used pneumatic-controlled simulators.

Role of hyaluronic acid and phospholipid in the lubrication of a cobalt-chromium head for total hip arthroplasty

The tribological performance of total hip arthroplasty has an important influence on its success rate. This study examined the concentration-dependent role of hyaluronic acid (HA) and phospholipid (dipalmitoylphosphatidylcholine, DPPC) in the boundary lubricating ability of retrieved cobalt-chromium femoral heads. The microscale frictional coefficients (μ) were measured by atomic force microscopy using a rectangular silicon cantilever integrated with sharp silicon tips. In the case of HA lubricant, the frictional coefficients decreased significantly at concentrations of 2.0 (0.16 ± 0.03) and 3.5 mg/ml (0.11 ± 0.01) while increased at 5.0 mg/ml (0.15 ± 0.01), compared to that with phosphate buffer saline (0.25 ± 0.03). The concentration-dependent lubrication behavior of DPPC was most effective when DPPC was in the physiological concentration range, showing μ = 0.16 ± 0.01 in polypropylene glycol, and 0.05 ± 0.01, 0.02 ± 0.01, and 0.03 ± 0.01 at a DPPC concentration of 0.05, 0.2, and 3.0 mg/ml, respectively. Results obtained show significant differences between the DPPC concentration groups. Conclusively, the microscale frictional response of the retrieved CoCr femoral head has a significant dependence on the concentrations of HA and DPPC. Moreover, observed optimal concentration of HA and DPPC for effective lubrication is similar to that observed in normal human synovial fluid. Therefore, a retrieval of the synovia may be considered during total hip replacement surgeries in an effort for reduction of friction between head and liner of total hip replacement implants.

Wear testing of crosslinked polyethylene: wear rate variability and microbial contamination

The wear performance of two types of crosslinked polyethylene (Marathon™ and XLK™, DePuy Synthes Inc., Warsaw, IN) was evaluated in a pin-on-disc wear tester, a hip wear simulator, and a knee wear simulator. Sodium azide was used as the microbial inhibitor in the calf serum-based lubricant. In the pin-on-disc wear tester, the Marathon wear rate of 5.33±0.54mm(3)/Mc was significantly lower (p=0.002) than the wear rate of 6.43±0.60mm(3)/Mc for XLK. Inversely, the Marathon wear rate of 15.07±1.03mm(3)/Mc from the hip wear simulator was 2.2-times greater than the XLK wear rate of 6.71±1.03mm(3)/Mc from the knee wear simulator. Differences in implant design, conformity, GUR type, and kinematic test conditions were suggested to account for the difference between the wear rates generated in the different types of wear testing apparati. In all wear tests, sodium azide was ineffective at inhibiting microbial growth in the lubricant. Eight different organisms were identified in the lubricant samples from the wear tests, which suggested the necessity of using an alternative, more effective microbial inhibitor. Careful sample preparation and thorough cleaning has shown to improve the consistency of the wear results. The wear rates generated in the hip and knee wear simulators closely reflected the wear behaviour of Marathon and XLK reported in published data that were tested under similar conditions.

Biochemical analyses of human osteoarthritic and periprosthetic synovial fluid

Biochemical analyses were performed on osteoarthritic and periprosthetic synovial fluid in order to propose changes to lubricant specifications currently outlined in orthopaedic wear testing standards. Osteoarthritic and periprosthetic synovial fluid samples were obtained from the hip and knee joints of 40 patients. The samples in each group were analysed and compared in order to identify differences between the protein concentration, constituent fractions, osmolality, thermal stability and the hyaluronic acid concentration and molecular weight distribution of osteoarthritic and periprosthetic synovial fluid. The average total protein concentration was approximately 30 g/L, which was much higher than the 20 g/L currently specified in the knee wear testing standard; however, the 30 g/L protein concentration matched the recently revised standard for hip simulator wear testing. No significant difference was found between the protein concentration, osmolality, thermal stability, and hyaluronic acid concentration of osteoarthritic and periprosthetic synovial fluid. The clinical data provided should be used to better define the composition of a more clinically relevant lubricant for orthopaedic wear testing.

Development of a synovial fluid analogue with bio-relevant rheology for wear testing of orthopaedic implants

The rheological properties of synovial fluid (SF) are crucial to the performance of joint prostheses. During the development of joint prostheses, wear tests are performed, which simulate joint movements in diluted solutions (usually between 25 and 33% v/v) of bovine serum which has very different rheological properties compared with native SF, where rheology is maintained by hyaluronan. Consequently, there is a need to develop a more suitable artificial SF. In this study, we used rheological techniques to understand SF flow properties which provided an insight into the mechanical behaviour required of a practical SF analogue. Steady-shear viscosity measurements were performed to reveal changes as a function of shear rate. To analyse the viscoelastic properties small deformation oscillatory measurements of storage modulus (G') loss modulus (G″) and complex viscosity (η(⁎)) were made. The rheological properties of the SF where compared with those of the polysaccharides sodium alginate, gellan gum and mixtures of both polymers. Initial results revealed classic shear thinning behaviour for the SF with a small Newtonian plateau at low shear rates with a gradual reduction in viscosity with increasing shear rate. Viscoelasticity measurements also showed that at low frequencies of oscillation there was a viscous response with G″ greater than G' and at higher frequencies there was an elastic response. Rheological properties were found to be similar to that of a 50:50 mix of 2% w/v high molecular weight alginate and 0.75% w/v gellan gum. Importantly, the lubricating behaviour of the serum differed significantly from the biopolymer blend over a full range of sliding velocities. The biopolymer blend was shown to lubricate the opposing surfaces more effectively. This difference was attributed to the more rapid alignment of the polysaccharide during shear when compared with the bovine albumin (the most abundant protein in serum), which typically exhibits a globular structure and has a tendency for self-association. These results suggest that polysaccharide solutions with bio-relevant rheology maybe be suitable as lubricants for in vitro orthopaedic prosthetic wear tests.

In vitro tests of substitute lubricants for wear testing orthopaedic biomaterials

Bovine serum is the lubricant recommended by several international standards for the wear testing of orthopaedic biomaterials; however, there are issues over its use due to batch variation, degradation, cost and safety. For these reasons, alternative lubricants were investigated. A 50-station Super-CTPOD (circularly translating pin-on-disc) wear test rig was used, which applied multidirectional motion to ultra-high-molecular-weight polyethylene test pins rubbing against cobalt chromium discs. Thirteen possible alternative lubricants were tested. The use of soy protein as a lubricant gave statistically higher wear, while soya oil, olive oil, Channel Island milk, whole milk, whey, wheatgerm oil, 11 mg/mL egg white, albumin/globulin mix and albumin/globulin/chondroitin sulphate mix all gave statistically lower wear than bovine serum. The lubricants giving the closest wear results to bovine serum were 20 and 40 mg/mL egg white solutions. A light absorbance assay found that these egg white solutions suffered from a high degradation rate that increased with increasing protein content. While egg white solutions offer the best alternative lubricant to bovine serum due to the wear volumes produced, cost-effectiveness and safety of handling, protein degradation will still occur, leading to the need for regular lubricant replacement. Of the lubricants tested in this study, none were found to be superior to bovine serum.

Calf serum constituent fractions influence polyethylene wear and microbial growth in knee simulator testing

Calf serum lubricants consisting of various polypeptide constituent fractions are routinely used in knee wear simulators as part of the standardized test protocol. Three calf sera (bovine, new-born and alpha) were diluted as per the recommendation of ISO 14243-3 and used in displacement-controlled knee wear simulators to investigate their effects on polyethylene wear. Biochemical analyses included measuring total polypeptide degradation, electrophoretic profiles and low-molecular weight polypeptide concentrations to elucidate their involvement in the wear process. The effects of the various calf sera constituent fractions on microbial growth were also explored. The polyethylene wear rates and the results from the biochemical analyses for the three calf serum lubricants were all found to be statistically significantly different from each other. The lubricant derived from the alpha-calf serum was closest in constituent fractions to human synovial fluid. It also showed the lowest polyethylene wear rate (14.38 ± 0.85 mm3/million cycles) and the lowest amount of polypeptide degradation (7.77 ± 3.87%). Furthermore, the alpha-calf serum lubricant was associated with the least amount of change in the electrophoretic profile, the least change in low-molecular weight polypeptide concentration, and the lowest microbial growth in the presence of sodium azide (a microbial inhibitor conventionally used in implant wear testing). Replacing sodium azide with a broad spectrum antibiotic-antimycotic eradicated the microbial growth. Some speculation was entertained regarding the effect of alpha-calf serum on colloid-mediated boundary lubrication. Based on the results, it was recommended that ISO 14243-3 be modified to include guidelines on calf serum constituent fractions that would favour using alpha-calf serum in order to improve the fidelity of the simulation in knee implant wear testing.

Challenges associated with using bovine serum in wear testing orthopaedic biopolymers

For appropriate in vitro wear testing of prostheses and their biomaterials, the choice of lubricant is critical. Bovine serum is the lubricant recommended by several international standards for wear testing artificial joints and their biomaterials because the wear rate and wear mechanisms closely match clinical results of polyethylene bearings. The main problem with the use of bovine serum as a lubricant is protein degradation and precipitation formation, effects that are recognized as having a direct impact on wear processes. Hence, some researchers have questioned the validity of using bovine serum in simulator testing. This paper reviews the various lubricants used in laboratory wear studies and also the properties of the synovial fluid that the lubricant is trying to replicate. It is clear from the literature survey that the composition of bovine-serum-based lubricants does not match that of synovial fluid. In view of this conclusion, it is suggested that there is a need to develop an alternative lubricant that can replace bovine serum.

The effects of applying adhesion prevention gel on the range of motion and pain after TKA

A mixed solution of sodium hyaluronate and sodium carboxymethylcellulose (HA/CMC) has been shown to be effective for decreasing postoperative adhesions in various kinds of surgeries. We evaluated the clinical efficacy and safety of HA/CMC gel on the early postoperative range of motion and pain relief after total knee arthroplasty (TKA). Thirty one patients who underwent bilateral TKA as a single-stage procedure for primary osteoarthritis were included in the study. At the completion of surgery, among both knees, the HA/CMC gel was applied to one knee (the HA/CMC group) and HA/CMC gel was not applied to the other knee (the control group). The primary outcome measure was the early assessment of range of motion and the secondary outcome measures were the VAS pain scores and the number of complications in each group. Periarticular application of HA/CMC gel was safe without causing any wound problems or infection. However, local application of HA/CMC gel neither increased the range of motion nor reduced the pain during the early postoperative period of TKA.

Biochemical comparisons of osteoarthritic human synovial fluid with calf sera used in knee simulator wear testing

Osteoarthritic human synovial fluid was obtained from the knees of 20 patients and was compared with four different calf sera solutions frequently used as lubricants in knee simulator wear testing. Assuming that the fluid after arthroplasty was the same as the fluid in patients with osteoarthritis, the total protein concentration, protein constituent fractions, osmolality, trace element concentrations, and the thermal stability obtained via differential scanning calorimetry were determined. Human synovial fluid, with an average total protein concentration of 34 g/L, was significantly different from all undiluted calf sera. However, alpha-calf serum and iron-supplemented alpha-calf serum were closest in protein constituent fractions (albumin, alpha-1-globulin, alpha-2-globulin, ss-globulin, and gamma-globulin) to human synovial fluid. Diluting calf sera with low-ion distilled water to a total protein concentration of 17 g/L (as recommended by ISO 14243) produced non-clinically relevant total protein concentration and osmolality levels. Performing the same dilution of iron-supplemented alpha-calf serum with phosphate-buffered saline solution and 1.5 g/L hyaluronic acid produced an artificial lubricant with both a clinically relevant level of osmolality and clinically relevant thermal stability as seen in human synovial fluid from patients with osteoarthritis. The present study suggested that alpha-calf serum, phosphate-buffered saline solution and hyaluronic acid were essential constituents of an artificial lubricant to mimic the major biochemical properties of human synovial fluid for simulator wear testing of total knee replacements.

Characterization of protein degradation in serum-based lubricants during simulation wear testing of metal-on-metal hip prostheses

A size exclusion high performance liquid chromatography (SEC-HPLC) method has been developed which is capable of separation and quantitation of bovine serum albumin (BSA) and bovine serum globulin (BSG) components of serum-based lubricant (SBL) solutions. This allowed characterization of the stability profiles of these proteins when acting as lubricants during hip wear simulation, and identification of wear-specific mechanisms of degradation. Using cobalt-chromium metal-on-metal (MOM) hip joints, it was observed that BSA remained stable for up to 3 days (215K cycles) of wear testing after which the protein degraded in a fairly linear fashion. BSG on the other hand, began to degrade immediately and in a linear fashion with a rate constant of 5% per day. Loss of both proteins occurred via the formation of high molecular weight aggregates which precipitated out of solution. No fragmentation of the polypeptide backbone of either protein was observed. Data obtained suggest that protein degradation was not due to microbial contamination, denaturation at the air-water interface, or frictional heating of articulating joint surfaces in these studies. We conclude that the primary source of protein degradation during MOM simulation testing occurs via high shear rates experienced by SBL solutions at articulating surfaces, possibly coupled with metal-protein interactions occurring as new and reactive metal surfaces are generated during wear testing. The development of this analytical methodology will allow new studies to clarify the role of SBL solutions in wear simulation studies and the interactions and lubricating properties of serum proteins with prosthetic surfaces other than MOM.