Observations at the articular surface of hip prostheses: an analytical electron microscopy study on wear and corrosion

Periarticular metal hypersensitivity complications of hip bearings containing cobalt-chromium

Hip joints with bearings composed of cobalt-chromium alloy (metal-on-metal bearings) have been one of the most widely used implants in joint replacement arthroplasty. Unfortunately, these implants can contribute to a complication called aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL), a type IV metal hypersensitivity response around the joint. Consistent with such bearings, increased metal debris can be found in the surrounding fluids and in remote tissues and organs, due to wear and corrosion. It is hypothesized that metal ions released from the prosthesis (including Co2+) can potentially form haptens with proteins such as serum albumin in synovial fluid that in turn elicit ALVAL. Generally, elevated cobalt and chromium levels in synovial fluids may indicate implant failure. However, such measurements cannot be used as a reliable tool to predict the onset of ALVAL. To detect ALVAL, some diagnostic tests, questionnaires and imaging techniques have been used clinically with some success, but a standardized approach is lacking. At present, guidelines for implant usage and patient management are ambiguous and inconsistent across health care authorities. To reduce and better manage the development of ALVAL, further research into the precise molecular mechanism(s) by which ALVAL develops is urgently needed. Identification of diagnostic and prognostic biomarkers for ALVAL is required, as are more standardized guidelines for surgery and patient management.

EFORT recommendations for off-label use, mix & match and mismatch in hip and knee arthroplasty

Off-label use is frequently practiced in primary and revision arthroplasty, as there may be indications for the application of implants for purposes outside the one the manufacturers intended.

Under certain circumstances, patients may benefit from selective application of mix & match. This can refer to primary hip arthroplasty (if evidence suggests that the combination of devices from different manufacturers has superior results) and revision hip or knee arthroplasty (when the exchange of one component only is necessary and the invasiveness of surgery can be reduced).

Within the EFORT ‘Implant and Patient Safety Initiative’, evidence- and consensus-based recommendations have been developed for the safe application of off-label use and mix & match in primary as well as revision hip and knee arthroplasty.

Prior to the application of a medical device for hip or knee arthroplasty off-label and within a mix & match situation, surgeons should balance the risks and benefits to the patient, obtain informed consent, and document the decision process appropriately.

Nevertheless, it is crucial for surgeons to only combine implants that are compatible. Mismatch of components, where their sizes or connections do not fit, may have catastrophic effects and is a surgical mistake.

Surgeons must be fully aware of the features of the components that they use in off-label indications or during mix & match applications, must be appropriately trained and must audit their results.

Considering the frequent practice of off-label and mix & match as well as the potential medico-legal issues, further research is necessary to obtain more data about the appropriate indications and outcomes for those procedures.

Cite this article: EFORT Open Rev 2021;6:982-1005. DOI: 10.1302/2058-5241.6.210080

Microstructural evolution and corrosion behavior of a laser surface modified cast Co-Cr-Mo-C alloy

A Co-Cr-Mo-C biomedical alloy was processed by investment casting, and its surface was modified using pulsed laser melting. The modified surface underwent rapid solidification, and the exhibited microstructure as well as its corrosion properties were investigated. It was found that the laser surface modified (LSM) Co-Cr-Mo-C alloy possesses enhanced corrosion resistance when compared with the same alloy in the as-cast condition. Microstructural determinations indicated that the LSM Co-Cr-Mo-C alloy exhibited a lack significant solute segregation and a predominantly cellular morphology as a result of the development of a cellular solid-liquid front. The cellular morphology was characterized by a fine distribution of nano-scale M₂₃ C₆ carbides at the intercellular regions. Moreover, the austenite (γ) to athermal ε-martensite transformation was totally suppressed in the cellular solidified regions. In contrast, the as-cast alloy develops a coarse dendritic microstructure with coarse carbides in the interdendritic regions. Solute segregation is also present, as well as athermal ε-martensite (13 pct). It was found that the corrosion resistance of the LSM alloy in the Ringer solution exhibits improved corrosion potential and a reduced corrosion current density (-281 mV and 0.032 μA/cm² , respectively),when compared with the same alloy in the investment as-cast condition (-356 mV and 0.150 μA/cm² ).

Microstructural effects on the wear behavior of a biomedical as-cast Co-27Cr-5Mo-0.25C alloy exposed to pulsed laser melting

In this work, the effect of pulsed laser melting on the exhibited microstructure and properties of a cast Co-27Cr-5Mo-0.25C alloy was investigated. In particular, properties such as surface hardness and wear behavior of the laser modified microstructure were determined as a function of the implemented laser melting parameters. It was found that laser melting promotes significant grain refinement while preventing the precipitation of coarse carbide phases. Apparently, a refined dendritic grain structure develops which is surrounded by a fine carbide distribution in the interdendritic regions. Moreover, the high-temperature face centered cubic (FCC) phase remains untransformed at room temperature. Hardness measurements and wear testing using a Pin-On-Disk tribological machine indicate that the modified laser surfaces exhibit both, high wear resistance and high microhardness when compared with the untreated as-cast Co-27Cr-5Mo-0.25C alloy. In particular, it was found that the laser modified surfaces exhibit improved wear and friction properties comparable to the ones found in Co-Cr-Mo alloys with a predominantly hexagonal closest packed (HCP) matrix. However, surface defects associated with the laser process can be detrimental for the improved wear performance and they should be considered in identifying the proper laser parameters in alloy melting.

Effects of soluble cobalt and cobalt incorporated into calcium phosphate layers on osteoclast differentiation and activation

Metal ions originating from mechanical debris and corrosive wear of prosthetic implant alloys accumulate in peri-implant soft tissues, bone mineral, and body fluids. Eventually, metal ions such as cobalt (II) (Co(2+)), which is a major component of cobalt-chromium-based implant alloys and a known activator of osteolysis, are incorporated into the mineral phase of bone. We hypothesize that the accumulation of Co(2+) in the mineral could directly activate osteolysis by targeting osteoclasts. To test this hypothesis, we coated tissue culture plastic with a thin layer of calcium phosphate (CaP) containing added traces of Co(2+), thereby mimicking the bone mineral accumulation of Co(2+). Murine bone marrow osteoclasts formed in the presence of M-CSF and RANKL were cultured on these surfaces to examine the effects of Co(2+) on osteoclast formation and resorptive activity. Treatment conditions with Co(2+) involved incorporation into the CaP layer, adsorption to the mineral surface, or addition to culture media. Micromolar concentrations of Co(2+) delivered to developing osteoclast precursors by all 3 routes increased both osteoclast differentiation and resorptive function. Compared to CaP layers without Co(2+), we observed a maximal 75% increase in osteoclast numbers and a 2.3- to 2.7-fold increase in mineral resorption from the tissue culture wells containing 0.1 microM Co(2+) and 0.1-10 microM Co(2+), respectively. These concentrations are well within the range found in peri-implant tissues in vivo. This direct effect of Co(2+) on osteoclasts appears to act independently of the particulate phagocytosis/inflammation-mediated pathways, thus enhancing osteolysis and aseptic implant loosening.

Wear of an experimental metal-on-metal artificial disc for the lumbar spine

STUDY DESIGN

In vitro wear simulation.

OBJECTIVE

To determine the type and amount of wear produced by experimental metal-on-metal artificial discs for the lumbar spine. To minimize the amount of wear by changing the carbon content, clearance, and presence of a keel and notch.

SUMMARY OF BACKGROUND DATA

In contrast to the extensive number of hip joint replacement simulator studies examining the effects of individual design variables on wear, existing artificial lumbar disc wear publications have measured wear using only the final version of each product. That is, the effects of individual variables such as material, diameter, or clearance on wear of artificial discs are not known, even though the importance of such variables has been established in artificial hip wear studies.

METHODS

Experimental metal-on-metal artificial discs for the lumbar spine were tested in a 3-station, biaxial spine wear simulator designed and constructed by the investigators. Two versions of the implants were manufactured with differences in carbon content, clearance, and the presence of a keel. Additionally, implants were tested with or without a surgical notch.

RESULTS

The wear rates of the experimental metal-on-metal lumbar discs in the current study ranged from 6.2 to 15.8 mm3/million cycles. However, changing the carbon content of the ball from low to high, decreasing the initial clearance, and eliminating the anteroposterior keel reduced the wear rate from 12.4 to 7.6 mm3/million cycles. Furthermore, removing the surgical notch reduced the wear rate from 7.6 to 6.2 mm3/million cycles. The surface damage was generally consistent with low lubrication and varying degrees of abrasive and fatigue wear, with impingement of nonbearing surfaces observed at 1.5 million cycles for the longer-term test.

CONCLUSION

Although the implants tested in the current study were experimental, the results suggest that metal-on-metal lumbar discs have the potential to produce wear of this magnitude and mechanism in vivo. Therefore, careful consideration of individual design variables, including those considered in the current study, is necessary to avoid production of excessive wear in artificial lumbar discs.

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

In this study, osteoarthritic and periprosthetic synovial fluid samples were rheologically and biochemically compared to develop a hyaluronic acid (HA) supplemented bovine serum (BS) lubricant that mimicked the properties of human joint synovial fluid. The effect of this BS + HA lubricant (50 per cent bovine calf serum + 1.5 g/l HA) on the wear rate of ultra-high molecular weight polyethylene (UHMWPE) during a total knee replacement wear test was then investigated. In conjunction with biochemical similarities, the rheological analysis showed that the BS + HA lubricant viscosity was not statistically different to aspirated total knee arthroplasty (TKA) revision joint fluid viscosity over a range of physiologic shear rates. Gravimetric results at 5 million wear testing cycles showed that the BS + HA lubricant produced an average of 6.88 times more UHMWPE wear than 50 per cent bovine serum lubricant alone. The BS + HA lubricated CoCr femoral component surfaces revealed pitting and surface roughening that was not observed using standard bovine serum only lubricants, but that was similar to the metallic surface corrosion observed on in vivo CoCr femoral component retrievals. These findings support the hypothesis that the addition of HA to simulator lubricant is capable of producing CoCr femoral component surface damage similar to that observed in vivo.

Long-term biocompatibility of a corrodible peripheral iron stent in the porcine descending aorta

Currently there are no biodegradable stents available for treatment of vascular obstructions in patients with congenital heart defects. This study was performed to evaluate the safety of a corrodible stent produced from pure iron in a peripheral stent design (6-12mm diameter) in a slotted tube design similar to a commercially available 316-L stent which served as control. Both stents were implanted into the descending aorta of 29 minipigs with an overstretch injury without technical problems. Two animals died after the implantation not related to the iron stent. The remaining 27 minipigs were followed for 1-360 days. Histomorphometry and quantitative angiography showed no difference with regard to the amount of neointimal proliferation between 316-L and iron stents. Histopathological examination of heart, lung, spleen, liver, kidney and para-aortic lymphatic nodes demonstrated no signs of iron overload or iron-related organ toxicity. Adjacent to the iron stent struts, there was no evidence for local toxicity due to corrosion products. We conclude that iron is a suitable metal for the production of a large-size degradable stent with no local or systemic toxicity. A faster degradation rate, however, is desirable and further studies have to focus on the modification of the composition and design of the stent to expedite the degradation process.

Surface composition analysis of failed cementless CoCr- and Ti-base-alloy total hip implants

The surfaces of retrieved failed cementless total hip implants made of cobalt-chromium-molybdenum casting alloy and of wrought titanium 6-aluminum 4-vanadium alloy were studied with the use of scanning-electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). New implants of the same make served as controls. The XPS scans revealed a dense carbon layer on the entire analyzed specimen. The relative composition of the titanium alloy implants showed an overall agreement with the international standards for implants for surgery, and the overall surface composition did not change over the period of the implantation. However, an inhomogeneous distribution of the constituents could be demonstrated in the retrieved as well as in the new MEC-screw rings made of TiAl6V4 alloy, an implant that has been linked to a high early failure rate. In the CoCr-alloy components (Lord-screw rings) a high percentage of aluminum, mainly organized in aluminum inclusions, was found in the retrieved as well as in the new implants.