Zirconia phase transformation in retrieved, wear simulated, and artificially aged ceramic femoral heads

Spectrometric Analysis of the Wear from Metallic and Ceramic Dental Implants following Insertion: An In Vitro Study

Titanium wear is a growing area of interest within dental implantology. This study aimed to investigate titanium and zirconium wear from dental implants at the time of insertion using X-ray-fluorescence spectrometry (XRF) and an in vitro protocol utilizing artificial bovine bone plates. Five groups were analyzed using XRF-spectrometry: groups 1–4 (titanium implants) and group 5 (zirconia implants). The implants were inserted into two bone blocks held together by a vice. The blocks were separated, and the insertion sites were analyzed for titanium (Ti) and zirconium (Zr). Statistical descriptive analyses of Ti and Zr concentrations in the coronal, middle and apical bone interface were performed. A comparative analysis confirmed differences between the implant’s surface stability and Ti accumulation within the insertion sites of the bone block. There was a direct relationship between implant length and the quantity of titanium found on the bone block. The data generally indicates greater quantities of titanium in the coronal thirds of the implants, and less in the apical thirds. The titanium and zirconium found in the bone samples where the group 5 implants were inserted was not of statistical significance when compared to control osteotomies. The results of this study confirm wear from metallic, but not ceramic, dental implants at the time of insertion.

Analysis of Chemisorbed Tribo-Film for Ceramic-on-Ceramic Hip Joint Prostheses by Raman Spectroscopy

To understand the possible lubricant mechanism in ceramic-on-ceramic hip joint prostheses, biochemical reactions of the synovial fluid and the corresponding frictional coefficients were studied. The experiments were performed in a hip joint simulator using the ball-on-cup configuration with balls and cups made from two types of ceramics, BIOLOX^®forte and BIOLOX^®delta. Different lubricants, namely albumin, γ-globulin, hyaluronic acid and three model synovial fluids, were studied in the experiments and Raman spectroscopy was used to analyze the biochemical responses of these lubricants at the interface. BIOLOX^®delta surface was found less reactive to proteins and model fluid lubricants. In contrast, BIOLOX^®forte ball surface has shown chemisorption with both proteins, hyaluronic acid and model fluids imitating total joint replacement and osteoarthritic joint. There was no direct correlation between the measured frictional coefficient and the observed chemical reactions. In summary, the study reveals chemistry of lubricant film formation on ceramic hip implant surfaces with various model synovial fluids and their components.

Pushing Ceramic-on-Ceramic in the most extreme wear conditions: A hip simulator study

BACKGROUND

Hip revision surgery for fractured ceramic components may represent the worst-case wear scenario due to the high risks of recurrent dislocations, instability, and third body wear. The ideal bearing choice for the new prosthetic articulation is still subject of debate, while alumina matrix composite (AMC) articulations offer theoretical superior performances; the present work was designed to test the wear behaviour of ceramic on ceramic articulations (liner and head) in a worst-case scenario by adding ceramic third-body particles to the test lubricant with combined walking and subluxation cycles in a hip joint simulator. Therefore, we performed an in vitro study aiming to assess how does AMC articulation perform with 1) third-body particles added to the test environment and 2) under subluxation stresses.

HYPOTHESIS

We hypothesised that AMC articulations offer superior performances in such worst conditions.

MATERIALS AND METHODS

A hip simulator test was designed to analyse how AMC articulation performs with third-body particles added to the test environment and under subluxation stresses. Two different load patterns including level walking and subluxation of the ceramic liner were applied. The test fluid lubricant was contaminated by adding coarse ceramic particles during the first 2 million cycles and fine ceramic particles from 2 to 4 million cycles. Group 1 consisted of an alumina matrix composite articulation (liner and head); group 2 consisted of an alumina liner and an alumina matrix composite head. A control group consisting of an alumina ceramic liner articulated against an alumina matrix composite head was provided and only axially loaded. The liners of groups 1 and 2 were tested at an in vivo angle of 45° in the medial lateral plane (inclinationangle), which corresponds to an angle L=30° relative to the ISO standard fixated position used for in vitro testing. All mass measurements were performed using a high precision balance (Sartorius BP211D). During each examination, images on dedicated location of the bearing surfaces were taken using a digital microscope.

RESULTS

Mean cumulative wear of 0.09mg per million cycles between 2 and 4 million cycles was detected in group 2, and this value was significantly lower (p=0.016) in comparison with the average value in group 1 (0.21mg per million cycle). This result can be explained in light of a possible transformation phase of zirconia in AMC liners, probably due to excessive stress during subluxation cycles. However, wear levels observed are close to the gravimetric measurement detection limit of the Sartorious Balance (about 0.1-0.2mg); therefore, wear can be considered negligible in all groups.

CONCLUSION

Our results confirm that AMC couplings perform very well even in the worst-case wear scenario. Since AMC articulations revealed 25% lower cumulative wear respect to AMC on cross linked polyethylene in same simulator setup, AMC articulations should be considered the bearing of choice in revision surgery in light of the high risk of recurrent dislocations, instability, and third body wear.

LEVEL OF EVIDENCE

III, prospective case-control study, in vitro.

Adverse Reaction to Zirconia in a Modern Total Hip Arthroplasty with Ceramic Head

Hypersensitivity reactions to zirconia (ZrO2) or similar ceramics is highly unusual. Owing to the stable oxide formed between the base metal and oxygen, ceramics are considered relatively biologically inert. We report the case of an otherwise healthy 50-year-old woman with a 5-year history of progressively worsening right hip pain who underwent a ceramic-on-polyethylene total hip replacement and subsequently developed hypersensitivity reaction. After metal allergy testing showed her to be highly reactive to zirconium, the femoral head was revised to a custom titanium implant and her symptoms resolved.

Third generation delta ceramic-on-ceramic bearing for total hip arthroplasty at mid-term follow-up

Purpose

to evaluate the results of Delta ceramic-on-ceramic (CoC) for total-hip-arthroplasty (THA).

Methods

261 THA using Delta-CoC, retrospectively analyzed. A 36 mm head was used in 189 cases and a 32/40 mm in the others. The series have been compared to a group of 89 THA with Forte-CoC.

Results

The Harris-Hip-Score improved from 49.1 ± 14.3 to 92.0 ± 8.9 (P < 0.001). In the Delta group there were one ceramic fracture and 2 dislocations. Two hips underwent revision. There were one revision in the Forte group for instability and one squeaking hip.

Conclusions

The new ceramic bearings provides a safe bearing for THA, with rare complications.

Wear Simulation of Ceramic-on-Crosslinked Polyethylene Hip Prostheses: A New Non-Oxide Silicon Nitride versus the Gold Standard Composite Oxide Ceramic Femoral Heads

The purpose of the present study was to compare the wear behavior of ceramic-on-vitamin-E-diffused crosslinked polyethylene (Vit-E XLPE) hip bearings employing the gold standard oxide ceramic, zirconia (ZrO₂)-toughened alumina (Al₂O₃) (ZTA, BIOLOX^®delta) and a new non-oxide ceramic, silicon nitride (Si₃N₄, MC^2®). In vitro wear test was performed using a 12-station hip joint simulator. The test was carried out by applying the kinematic inputs and outputs as recommended by ISO 14242-1:2012. Vitamin-E-diffused crosslinked polyethylene (Vit-E XLPE) acetabular liners (E1^®) were coupled with Ø28-mm ZTA and Si₃N₄ femoral heads. XLPE liner weight loss over 5 million cycles (Mc) of testing was compared between the two different bearing couples. Surface topography, phase contents, and residual stresses were analyzed by contact profilometer and Raman microspectroscopy. Vit-E XLPE liners coupled with Si₃N₄ heads produced slightly lower wear rates than identical liners with ZTA heads. The mean wear rates (corrected for fluid absorption) of liners coupled with ZTA and Si₃N₄ heads were 0.53 ± 0.24 and 0.49 ± 0.23 mg/Mc after 5 Mc of simulated gait, respectively. However, after wear testing, the ZTA heads retained a smoother topography and showed fewer surface stresses than the Si₃N₄ ones. Note that no statistically significant differences were found in the above comparisons. This study suggests that the tribochemically formed soft silica layer on the Si₃N₄ heads may have reduced friction and slightly lowered the wear of the Vit-E XLPE liners. Considering also that the toughness of Si₃N₄ is superior to ZTA, the present wear data represent positive news in the future development of long-lasting hip components.

Zirconia Phase Transformation in Zirconia-Toughened Alumina Ceramic Femoral Heads: An Implant Retrieval Analysis

BACKGROUND

Zirconia-toughened alumina ceramic was introduced as a femoral head material for total hip arthroplasty. The material combines the stability of alumina with the toughness of zirconia. Despite inherent benefits for bearing surfaces, concern exists in the medical field that phase transformation of the zirconia grains could worsen wear resistance and lower the strength of the head. We examined these concerns in retrieved and artificially aged ceramic heads.

METHODS

Twenty-eight ceramic composite heads retrieved at revision surgery were combined with 5 pristine heads (as negative controls for phase transformation) and 5 artificially aged pristine heads (as positive controls). The extent of zirconia phase transformation at the bearing surfaces was examined through confocal Raman spectroscopy and X-ray diffraction. Burst testing was conducted on all pristine and aged heads and the 4 retrieved implants with the longest lengths of implantation.

RESULTS

Retrieved heads had higher maximum average volume fractions of the monoclinic phase compared to pristine or aged heads. Length of implantation was not correlated to the volume fraction of the monoclinic phase. All the heads achieved a burst load far above the 46 kN Food and Drug Administration acceptance criterion; 3 of the 4 retrieved heads had burst strengths exceeding 100kN.

CONCLUSION

Our results showed that phase transformation occurs in vivo in ceramic composite femoral heads, but the amount transformed did not increase with the length of time the head had been implanted. The negligible effect upon burst strength of the retrieved and artificially aged heads is reassuring. These results support continued clinical use of this alumina-zirconia composite material as a head material.

Phase Transformation and Roughening in Artificially Aged and Retrieved Zirconia-Toughened Alumina Femoral Heads

BACKGROUND

Zirconia-toughened alumina (ZTA) used in hip arthroplasty contains yttria-stabilized zirconia (Y-TZP) as a toughening agent. However, Y-TZP is well known to degrade in vivo from tetragonal to monoclinic phase transformation. The stability of never-implanted ZTA femoral heads was evaluated in a severe artificial aging test, with retrieved ZTA heads also evaluated for clinical relevance. We hypothesized that ZTA would degrade due to tetragonal-to-monoclinic phase transformation, with changes in surface topography and progressive roughening. Y-TZP specimens served as a positive comparison group, while magnesia-stabilized zirconia (Mg-PSZ), which does not undergo phase transformation, served as a stable comparison group.

METHODS

Monoclinic phase concentration, surface topography, and roughness of never-implanted ZTA, Y-TZP, and Mg-PSZ heads were measured by X-ray diffraction and optical profilometry, before and after 2 rounds of 24 hours of hydrothermal aging. Explanted ZTA heads were characterized by the same methods.

RESULTS

After 48 hours in an autoclave, the surface of ZTA heads exhibited irregularly spaced protrusions about 20-30 nm high by 100-150 μm in diameter, with significant increases in monoclinic phase concentration (from 12.2% to 21.3%) and surface roughness. Similar features were observed on the surface of explanted ZTA heads, with 33% monoclinic phase after 2.7 years in vivo.

CONCLUSION

Based on data collected from ZTA retrievals, this artificial aging test underestimated the amount of phase transformation in vivo. Phase transformation and surface roughening of ZTA heads steadily increased without reaching a plateau, which may lead to stress concentrations and weakening of the ceramic material, and could result in late fracture and wear.

Raman and Photoemission Spectroscopic Analyses of Explanted Biolox® Delta Femoral Heads Showing Metal Transfer

Biolox^® delta has been widely used in joint replacements thanks to its high strength and wear resistance. In this study, eleven Biolox^® delta femoral head retrievals affected by metal transfer (MT) were analysed by Raman spectroscopy to estimate the tetragonal to monoclinic zirconia phase transformation, whose occurrence may compromise ceramic chemical stability and mechanical strength. The residual stress state was evaluated by both Raman and photoemission spectroscopy. V_m monoclinic zirconia contents were higher near the centre of the articulating surface and in the MT area than in the border control area of the retrievals. In only one retrieval, stress related to MT appeared a more severe condition, able to induce zirconia phase transformation; for all the others, stresses related to loading in the central region and related to MT, were conducive to a zirconia phase transformation of nearly the same extent. V_m depth profiling analyses showed that the transformation involved different thicknesses in different samples. Raman data allowed for the investigation of the mechanism of zirconia phase transformation and confirmed that the growth stage was absent and the nucleation stage was not occurring as freely as it would in unconstrained zirconia.