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Zirconia Phase Transformation, Metal Transfer, and Surface Roughness in Retrieved Ceramic Composite Femoral Heads in Total Hip Arthroplasty
The Journal of Arthroplasty 29 (2014) 2219–2223
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Zirconia Phase Transformation, Metal Transfer, and Surface Roughness in Retrieved Ceramic Composite Femoral Heads in Total Hip Arthroplasty Marcella Elpers, BS a, Denis Nam, MD b, Susie Boydston-White, PhD c, Michael P. Ast, MD d, Timothy M. Wright, PhD a, Douglas E. Padgett, MD d a
Department of Biomechanics, Hospital for Special Surgery, New York, New York Department of Orthopaedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, Missouri c Science Department, City University of New York, Borough of Manhattan Community College, New York, New York d Adult Reconstruction and Joint Replacement Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, New York b
a r t i c l e
i n f o
Article history: Received 21 May 2014 Accepted 11 August 2014 Keywords: Biolox delta ceramic retrieval analysis phase transformation hip arthroplasty
a b s t r a c t Ceramic femoral heads have had promising results as a bearing surface in total hip arthroplasty. Our objective was to evaluate a series of retrieved alumina-zirconia composite ceramic femoral heads for evidence of the tetragonal to monoclinic zirconia phase transformation, metal transfer and articular surface roughness. Raman spectra showed evidence of the zirconia phase transformation in all retrieved specimens, with distinct monoclinic peaks at 183, 335, 383, and 479 cm −1. All components displayed metal transfer. An increase in the zirconia phase transformation was seen with increasing time in vivo. No correlation between extent of zirconia phase transformation and the surface roughness was found. These short-term results suggest that the use of an alumina-zirconia composite ceramic is a viable option for femoral heads in THA. © 2014 Elsevier Inc. All rights reserved.
In 2000, an alumina-zirconia composite ceramic (Biolox delta) was developed by CeramTec AG (Plochingen, Germany) for use as a bearing material in total hip arthroplasty (THA). The goal was to combine the strength and toughness of zirconia with the wear resistance and chemical and thermal stability of alumina [1]. Nano-sized particles of yttriastabilized tetragonal zirconia polycrystals (Y-TZP) are distributed in the alumina matrix to increase the composite toughness. The increased toughness of Y-TZP results from a stress-induced phase transformation that involves the transformation of metastable tetragonal grains to the monoclinic phase at the origin of a crack [2–4]. This transformation is accompanied by a 3–4% volume expansion that induces compressive stresses, thus hindering crack propagation [4]. Other additions to the composite include chromium oxide to increase the hardness of the material and strontium oxide that leads to formation of strontium aluminate crystals that further impede crack propagation. The final product is a mixture of approximately 75% alumina, 25% zirconia, and b1% chromium and strontium oxides [1,3,4]. Early positive clinical results have been reported, but concerns have arisen with the long term performance of this alumina–zirconia
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.08.011. Reprint requests: Douglas E. Padgett, MD, Adult Reconstruction and Joint Replacement Division, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021. http://dx.doi.org/10.1016/j.arth.2014.08.011 0883-5403/© 2014 Elsevier Inc. All rights reserved.
composite ceramic, underscored by reports of significant tetragonalmonoclinic phase transformation found in retrieved components [5,6]. An analysis of a fractured Biolox delta head demonstrated a 33% phase transformation of the zirconia [6]. This amount of phase transformation compromises the chemical stability and mechanical strength of the ceramic. Additionally, Santos et al showed a positive correlation, although slight, between increased monoclinic zirconia phase transformation and increased surface roughness [7]. Therefore, concerns remain regarding the long-term in vivo stability of Biolox delta femoral heads [4,8]. An additional concern with the use of ceramic femoral heads in THA is the occurrence of metal transfer to the bearing surface, a phenomenon observed regardless of whether the acetabular bearing material is polyethylene or ceramic [9–12]. The regions of metal transfer exhibit patterns that suggest the transfer initiates near the edge of the head and progresses toward the apex [12]. The presence of metal transfer alters the bearing surface and could have detrimental effects on wear [10–12]. Retrieval analyses have played a useful role in evaluating in vivo performance of total joint arthroplasties, and in understanding wear mechanisms in total hip arthroplasty. To our knowledge, few retrieval studies have been performed assessing the performance of Biolox delta femoral heads, and the number of retrieved heads has been very small [1,4]. Given the concerns that have been raised with historical ceramic THA components, we sought to evaluate a larger series of retrieved Biolox delta femoral heads, to address three main objectives: (1) Do these Biolox delta femoral heads undergo the t-m phase
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transformation? And if so, to what extent? (2) Is metal transfer still a concern? And (3) does the extent of t-m phase transformation or metal transfer affect the articular surface roughness? Materials and Methods Twenty-seven Biolox delta femoral heads were identified as part of our institution's ongoing implant retrieval program. Each head was part of a ceramic-on-polyethylene THA performed using noncemented acetabular and femoral components. Eight patients had their index procedure performed at our institution, while the remaining 19 of the THAs were performed at an outside hospital; all were revised at our institution. Clinical and demographic information was gathered from the patients' medical records (Table 1); including the length of implantation (LOI), age at index procedure, body mass index (BMI), sex, and revision diagnosis. Patient radiographs were available for the retrieved components, and were assessed for component alignment, including the abduction and anteversion angles of the acetabular component.
Table 2 Method of Grading the Severity of Metal Transfer. Grade Description 1 2 3 4 5
No markings present Some metal transfer present, light markings, or ≤3 dark markings ≤0.5″ long N3 dark markings ≤0.5″ long or ≥1 dark markings ≤1″ long Metal smear b20% of surface area or N3 lines 1″ long Metal smear N20% of surface area
the monoclinic phase was quantified as volume fraction (Vm) using the following equation [13]: 181
Vm ¼
190
Im þ Im 190 2:2 I147 þ I 181 t m þ Im
where I represents the area of the monoclinic bands identified at 181 and 190 cm −1 and the tetragonal band at 147 cm −1, respectively. This method has been used in several previous reports and preferred over a method proposed by Clarke and Adar [1,4,14].
Raman Spectroscopy Metal Transfer Evidence of a phase transformation at the bearing surfaces of the retrieved femoral heads was collected using Raman spectroscopy. Each head was placed on a custom-machined support of a WITec alpha300 R Confocal Raman Microscope (CRM). The CRM was equipped with a Nikon 20× objective (Nikon Instruments, Melville, NY), using the 488 nm excitation laser (WITec Wissenschaftliche Instrumente und Technologie GmbH, Ulm, Germany) with a resolution down to the optical diffraction limit of 200 nm and spectral resolution of 1 cm−1. Spectra were collected at full laser power of ~200 mW, with a 1 second integration time and 30 accumulations. The beam was focused by adjusting the Z-position of the objective to achieve the maximum possible CCD counts at the area of the spectrum corresponding to the vibration at ~180 cm−1. Three spectra were collected in each of three regions of interest on the bearing surface of the femoral head: the apex of the surface, around the equator, and below the equator. In addition, spectra were collected from areas immediately adjacent to regions of large amounts of metal transfer. The spectra were exported as both xy.txt text files and gramscompatible .spc spectral files for analysis. Spectral files were imported into Grams/AI Spectroscopy Software (Thermo Scientific, Waltham, MA). Using the software, spectra were truncated to the wavelengths of interest (100–800 cm − 1) and baselined to normalize the scans. To determine the extent of zirconia phase transformation,
The bearing surface of each ceramic head was assessed for metal transfer by two independent observers using a previously described subjective grading system [11]. Briefly, each head was graded for the severity of metal transfer on a 1 through 5 scale, based on the number of distinct occurrences of metal transfer, the intensity, and the surface area of the femoral head involved (Table 2). Each head was divided into 5 regions of interest (Fig. 1). The same three regions on the bearing surface (apex, equator, and below the equator) used for the Raman spectroscopy were individually graded for metal transfer. Two additional regions were defined on the female taper of the femoral head, which was divided into a proximal and a distal region. Each acetabular polyethylene liner was also examined for macroscopic signs of impingement. Surface Roughness A non-contact white light profiler (ADE Phase Shift MicroXAM, KLA-Tencor; Milpitas, CA) was used to measure surface roughness of the femoral heads using a previously described method [11]. All surfaces were wiped with acetone prior to performing the surface profilometry measurements. Each head was placed in a holder on the microscope platform of the profilometer, with the area of interest
Table 1 Patient Demographic Data for the 27 Biolox Delta Components Included in this Study. Variable Female Right Age at primary (years) BMI (kg/m2) LOI (months) Revision diagnosis Dislocation Loosening ALTR Periprosthetic fracture Infection Malposition Leg length discrepancy Heterotopic ossification Values reported are mean ± SD.
Number 15 14 62.5 ± 9.8 27.3 ± 4.3 24.3 ± 27.5 7 6 4 3 4 1 1 1
Fig. 1. Regions of interest identified on the articular and taper surface of the retrieved femoral heads. The taper surface was divided in half for consistency across samples, as we were unable to identify the most proximal point of trunnion engagement. All 5 regions were evaluated for metal transfer. The three regions on the articular surface of the femoral head were analyzed with surface roughness and Raman spectroscopy.
M. Elpers et al. / The Journal of Arthroplasty 29 (2014) 2219–2223
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oriented perpendicular to the objective lens (set at 10 ×). Three areas, ~ 600 μm × 800 μm in size, were scanned on each head, in the same three regions as were used for the Raman and metal transfer measurements: the apex of the bearing surface, around the equator, and below the equator (where little if any articulation had occurred). If a region of metal transfer was present, an additional scan was taken over the transfer region. If multiple regions of metal transfer were present, the most severe region was used for analysis. One unimplanted Biolox delta femoral head was analyzed over the same three regions of interest to establish control roughness values. After each scan, the spherical plane of the scanned area was corrected for the curvature of the femoral head. Average surface roughness, Sa, was calculated using Scanning Probe Image Processor (Image Metrology A/S, Hϕrsholm, Denmark) as: Sa ¼
1 M−1 N−1 ∑ ∑ jzðxk ; yl Þ−μ j MN k¼0 l¼0
where MN is the total number of pixels across the entire image, z(xk, yi) is the height of each pixel, and μ is the average height of all pixels.
Fig. 3. For all three regions on the articular surface, Vm increased significantly with increased time in vivo.
Raman spectra revealed the presence of monoclinic zirconia in the control and in all of the retrieved specimens (Fig. 2). Distinct markers for tetragonal and monoclinic phases were detected, with tetragonal marker bands featured at 145, 265, 315, and 646 cm−1 and prominent
monoclinic marker bands at 183, 335, 383, and 479 cm −1. No interference was detected due to the presence of the alumina; a weak alumina peak was identified at 415 cm − 1 consistently throughout the specimens. The average monoclinic zirconia volume fraction (Vm) for each region of interest on the bearing surface was: 0.25 ± 0.08 at the apex, 0.26 ± 0.09 at the equator, and 0.25 ± 0.08 below the equator. Seventeen of the 27 femoral heads had Raman spectra collected adjacent to regions of metal transfer with an average Vm of 0.24 ± 0.1. No difference in Vm was found among these 4 regions of interest (P = 0.864). No correlation was observed between the severity score for metal transfer or the surface roughness and the Vm, by region. However, Vm increased significantly with length of implantation for the apex (P = 0.0166), the equator (P = 0.000183), and below the equator (P = 0.0469) (Fig. 3). All 27 of the retrieved ceramic heads displayed metal transfer in one or more of the three regions. Sixty percent displayed metal transfer at the apex, with a mean score of 1.6 ± 0.5. At the equator, 95.6% displayed metal transfer, with a mean score of 2.2 ± 0.6. Below the equator, 100% of the retrieved femoral heads displayed metal transfer, with a mean score of 2.6 ± 0.9. The frequency of metal
Fig. 2. Micro-Raman spectra recorded on three representative Biolox delta femoral heads (from top to bottom): a non-implanted Biolox delta, retrieval #10 (time in vivo of 12 months), and retrieval #3 (time in vivo of 7 years). Increasing time in vivo correlated with increase Vm. Bands associated with alumina (a), tetragonal (t) and monoclinic (m) zirconia are indicated in the spectra.
Fig. 4. Retrieved alumina-zirconia composite head demonstrating metal transfer in both the superficial and deep regions of the female taper.
Statistical Analysis Non-parametric Kruskal–Wallis ANOVA on Ranks was used to evaluate the differences in the volume fraction of the monoclinic phase (Vm), metal transfer score, and surface roughness (Sa) among the three regions (apex, equator, and below the equator of the head). Pearson product–moment correlations were used to evaluate correlations between the three measured damage modes: Vm, metal transfer and Sa across the regions of interest, as well as the correlation of these variables with length of implantation. Interobserver correlation coefficients were determined for the metal transfer scoring using the following scale: excellent for 0.9 ≤ r ≤ 1.0, good for 0.7 ≤ r ≤ 0.89, fair/moderate for 0.5 ≤ r ≤ 0.69, low for 0.25 ≤ r ≤ 0.49, and poor for 0.0 ≤ r ≤ 0.24 [15]. A P-value b 0.05 was deemed significant. Results
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Only two of the polyethylene acetabular inserts demonstrated signs of impingement. One of these displayed impingement in the posterior-superior region at the rim of an elevated liner. This component had a metal transfer score of 3 at the equator, and 4 below the equator. Average surface roughness (Sa) was not different among the apex (32.6 ± 14.0 nm), the equator (35.4 ± 17.6 nm), and the below the equator (34.4 ± 13.3 nm) regions. The unimplanted Biolox delta femoral head used as a control was about 30% smoother than the retrieved heads, with an average surface roughness of 23.6 ± 4.9 nm. Regions of metal transfer were significantly rougher than the nonmetal transfer regions of the articular surface (P b 0.001). The average surface roughness of the metal transfer regions was twice that of the other three regions on the bearing surface at 74.5 ± 54.5 nm (Fig. 6). No correlations were found between the average monoclinic zirconia volume fraction and average surface roughness for the 3 regions of interest or for the metal transfer regions.
Fig. 5. Retrieved alumina–zirconia composite head demonstrating metal transfer on the articular surface of the femoral head. Center of image is the apex of the femoral head.
transfer was significantly greater at and below the equator compared to at the apex (P = 0.002, P = 0.003, respectively). All 27 of the femoral heads demonstrated metal transfer in both the proximal and distal regions of the female taper, with a mean score of 3.3 ± 0.7 and 3.3 ± 0.6, respectively (Fig. 4). The severity of metal transfer on the female taper was significantly more than on the articular surface of the femoral head (P b 0.001) (Fig. 5). Interobserver correlation coefficients were fair/moderate to good for all regions analyzed (r = 0.59–0.80).
Discussion With current concerns related to trunnion corrosion and metalon-metal bearings in THA, alternative bearings, such as the Biolox delta, have become a popular option among surgeons [16–19]. The early, clinical results with the use of Biolox delta bearing surfaces have been encouraging, with few bearing-related complications reported. Hamilton et al performed a prospective, randomized controlled trial comparing 177 Delta ceramic-on-ceramic (COC) articulations with 87 Delta ceramic head-cross-linked polyethylene (COP) articulations at a mean follow-up of 31.2 months. No differences were found between the two groups with regards to clinical, radiographic, and survivorship scores, but there were 3 instances of ceramic liner chipping or cracking in the COC cohort [5]. Lombardi et al performed a prospective
Fig. 6. Surface roughness plots that demonstrate the varying surface profiles of non-transfer (A) and metal transfer (B) regions. No differ.ence was observed in surface roughness between the non-transfer regions: apex, equator, and below the equator. All color scales are in nanometers.
M. Elpers et al. / The Journal of Arthroplasty 29 (2014) 2219–2223
analysis of 65 Biolox delta femoral heads articulating on alumina liners, and 45 zirconia femoral heads articulating on polyethylene liners. At a mean follow-up of 73 months, they found no significant difference between the two cohorts with regard to clinical and radiographic outcomes, or survivorship (95% in Biolox delta vs. 93% in zirconia). In each cohort, 3 patients were revised, but only one revision was attributed to the bearing surface. As was found in our series of Biolox delta heads, earlier retrieval studies demonstrated that the t-m phase transformation does occur at the bearing surface, but the authors of those studies suggested that the transformation resulted from the mechanical energy accompanying implant wear, rather than from in vivo aging of the material, perhaps because the retrievals that were examined had come from COC bearings. We observed the t-m phase transformation in all of our retrieved components. Given our large numbers of retrievals, we were able to establish strong positive correlations between the volume of transformation and the length of time that the components had been implanted regardless of whether the measurements were made in regions of the head that likely experienced wear or those that likely did not. Our results suggest that the source of energy that caused the transformation was not related to mechanical wear, since differences were not noted between regions expected to experience wear (e.g., the pole or areas adjacent to metal transfer) and those less likely to have been worn (e.g., below the equator). In addition to the t-m phase transformation, metal transfer has been commonly observed on retrieved ceramic femoral heads of all generations [9–12]. However, the mechanism by which metal transfer occurs is not entirely clear. Clinical series and case reports have described metal transfer occurring during intraoperative reductions or dislocations, originating near the rim of the component and extending toward the apex of the femoral head. Regardless of the underlying mechanism, it is clear that even with this new generation of ceramics metal transfer still occurs, and is not solely associated with the bearing materials. A consequence of the t-m phase transformation and metal transfer is the potential to alter the surface roughness of the articular surface. The tm transformation is accompanied by a 3–4% volume expansion, which could increase the surface roughness [4]. However, previous investigators did not find a correlation between an increase in percent monoclinic phase and increased surface roughness, with only mild trends of increased surface roughness observed [7,20]. Similarly, we did not observe any correlation between percent monoclinic phase and surface roughness. We previously showed that regions of metal transfer, however, are significantly rougher, almost ten times rougher, than non-transfer regions [11]. While we also observed an increase in surface roughness of the metal transfer regions in this series, these regions were only two times rougher than the non-transfer region, which is notably lower than our previous study. It is unclear as to the underlying mechanism by which metal transfer occurs; however, given the difference in roughness of the metal transfer regions in the two series, it suggests that two mechanisms are at work. Macroscopically, metal transfer in the previous series of alumina and zirconia femoral heads appeared as a “smear” on the surface, while in the Biolox delta heads cohort, the transfer appeared to be more distinct stripes across the surface. Regardless of the mechanism, in any bearing combination, this increase in surface roughness could cause increased wear on the counter-bearing surface and lead to a release of third body wear particles and eventually the need for revision of the component. Our study had limitations. The components were retrieved after short lengths of implantation, with an average LOI of just over two years. We cannot comment, therefore, on the long-term implications of the phase transformation and how it might impact clinical performance at longer follow-up. A limitation in applying techniques such as Raman spectroscopy and surface profilometry is the limited amount of the bearing surface that can be measured in a reasonable time and at a reasonable cost. Sampling more areas on the surfaces of the
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retrieved components might reveal different results, but the lack of variability among our results suggests that doing even more measurements would have not provided any added benefit. Finally, our sample included one component implanted before 2006. The average monoclinic zirconia content decreased in the manufactured ceramic from when it was first introduced in 1999 until about 2006 [1,4]. We did not consider implantation year in our analysis, but found no marked differences in the results of our one early component. Lastly, we did not evaluate the mechanical strength of the retrieved components, which could be affected by the t-m phase transformation. However, little data exist in the literature to support a direct correlation between an increase in Vm and a decrease in mechanical strength. In summary, this evaluation of retrieved Biolox delta femoral heads has demonstrated the presence of t-m phase transformation with no influence on the surface roughness, and observed metal transfer on the articular surface of all femoral heads, which was associated with increased surface roughness in the metal transfer regions. In addition, we saw an increase in t-m transformation with longer time in vivo, which warrants continual evaluation of these components. Despite this observation, the surface roughness still remains low, suggesting that the use of Biolox delta is a viable option for use as a bearing surface in THA. Acknowledgments This work made use of the Cornell Center for Materials Research Facilities supported by the National Science Foundation under Award Number DMR-1120296. References 1. Affatato S, Modena E, Toni A, et al. Retrieval analysis of three generations of biolox (R) femoral heads: spectroscopic and SEM characterisation. J Mech Behav Biomed Mater 2012:118. 2. Derbyshire B, Fisher J, Dowson D, et al. Comparative study of the wear of UHMWPE with zirconia ceramic and stainless steel femoral heads in artificial hip joints. Med Eng Phys 1994;3:229. 3. Piconi C, Maccauro G, Muratori F, et al. Alumina and zirconia ceramics in joint replacements. J Appl Biomater Biomech 2003;1:19. 4. Taddei P, Modena E, Traina F, et al. Raman and fluorescence investigations on retrieved Biolox delta femoral heads. J Ramana Spectrosc 2012;12:1868. 5. Hamilton WG, McAuley JP, Dennis DA, et al. THA with delta ceramic on ceramic: results of a multicenter investigational device exemption trial. Clin Orthop Relat Res 2010;2:358. 6. Lombardi Jr AV, Berend KR, Seng BE, et al. Delta ceramic-on-alumina ceramic articulation in primary THA: prospective, randomized FDA-IDE study and retrieval analysis. Clin Orthop Relat Res 2010;2:367. 7. Santos EM, Vohra S, Catledge SA, et al. Examination of surface and material properties of explanted zirconia femoral heads. J Arthroplasty 2004;7(Suppl 2):30. 8. Chevalier J. What future for zirconia as a biomaterial? Biomaterials 2006;4:535. 9. Bal BS, Rahaman MN, Aleto T, et al. The significance of metal staining on alumina femoral heads in total hip arthroplasty. J Arthroplasty 2007;1:14. 10. Brandt JM, Gascoyne TC, Guenther LE, et al. Clinical failure analysis of contemporary ceramic-on-ceramic total hip replacements. Proc Inst Mech Eng H 2013;8:833. 11. Chen D, Lin S, Cutrera N, et al. Ceramic bearings in total hip replacement: a retrieval analysis. Minerva Ortop Traumatol 2010:43. 12. Tomek IM, Currier JH, Mayor MB, et al. Metal transfer on a ceramic head with a single rim contact. J Arthroplasty 2012;2:324.e1. 13. Katagiri G, Ishida H, Ishitani A, et al. Direct determination by raman microprobe of the transformation zone size in Y2O3 containing tetrangonal ZrO2 polycrystals. Science and Technology of Zirconia; 1988. p. 537. 14. Clarke DR, Adar F. Measurement of the crystallographically transformed zone produced by fracture in ceramics containing tetragonal zirconia. J Am Ceram Soc 1982;6:284. 15. Munro BH. Correlation. Statistical Methods for Healthcare Research. 3rd ed. Lippincott-Raven; 1997. p. 224. 16. Cooper HJ, Della Valle CJ, Berger RA, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg Am 2012;18:1655. 17. Kwon YM, Jacobs JJ, MacDonald SJ, et al. Evidence-based understanding of management perils for metal-on-metal hip arthroplasty patients. J Arthroplasty 2012;8:20 [Suppl.]. 18. Nam D, Barrack RL, Potter HG. What are the advantages and disadvantages of imaging modalities to diagnose wear-related corrosion problems? Clin Orthop Relat Res 2014 (Epub ahead of print). 19. Nawabi DH, Gold S, Lyman S, et al. MRI predicts ALVAL and tissue damage in metalon-metal hip arthroplasty. Clin Orthop Relat Res 2014;2:471. 20. Kim YH, Ritchie A, Hardaker C. Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear. J Bone Joint Surg Am 2005; 3:577.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Zirconia Phase Transformation, Metal Transfer, and Surface Roughness in Retrieved Ceramic Composite Femoral Heads in Total Hip Arthroplasty Marcella Elpers, BS a, Denis Nam, MD b, Susie Boydston-White, PhD c, Michael P. Ast, MD d, Timothy M. Wright, PhD a, Douglas E. Padgett, MD d a
Department of Biomechanics, Hospital for Special Surgery, New York, New York Department of Orthopaedic Surgery, Washington University School of Medicine/Barnes-Jewish Hospital, St. Louis, Missouri c Science Department, City University of New York, Borough of Manhattan Community College, New York, New York d Adult Reconstruction and Joint Replacement Service, Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, New York b
a r t i c l e
i n f o
Article history: Received 21 May 2014 Accepted 11 August 2014 Keywords: Biolox delta ceramic retrieval analysis phase transformation hip arthroplasty
a b s t r a c t Ceramic femoral heads have had promising results as a bearing surface in total hip arthroplasty. Our objective was to evaluate a series of retrieved alumina-zirconia composite ceramic femoral heads for evidence of the tetragonal to monoclinic zirconia phase transformation, metal transfer and articular surface roughness. Raman spectra showed evidence of the zirconia phase transformation in all retrieved specimens, with distinct monoclinic peaks at 183, 335, 383, and 479 cm −1. All components displayed metal transfer. An increase in the zirconia phase transformation was seen with increasing time in vivo. No correlation between extent of zirconia phase transformation and the surface roughness was found. These short-term results suggest that the use of an alumina-zirconia composite ceramic is a viable option for femoral heads in THA. © 2014 Elsevier Inc. All rights reserved.
In 2000, an alumina-zirconia composite ceramic (Biolox delta) was developed by CeramTec AG (Plochingen, Germany) for use as a bearing material in total hip arthroplasty (THA). The goal was to combine the strength and toughness of zirconia with the wear resistance and chemical and thermal stability of alumina [1]. Nano-sized particles of yttriastabilized tetragonal zirconia polycrystals (Y-TZP) are distributed in the alumina matrix to increase the composite toughness. The increased toughness of Y-TZP results from a stress-induced phase transformation that involves the transformation of metastable tetragonal grains to the monoclinic phase at the origin of a crack [2–4]. This transformation is accompanied by a 3–4% volume expansion that induces compressive stresses, thus hindering crack propagation [4]. Other additions to the composite include chromium oxide to increase the hardness of the material and strontium oxide that leads to formation of strontium aluminate crystals that further impede crack propagation. The final product is a mixture of approximately 75% alumina, 25% zirconia, and b1% chromium and strontium oxides [1,3,4]. Early positive clinical results have been reported, but concerns have arisen with the long term performance of this alumina–zirconia
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.08.011. Reprint requests: Douglas E. Padgett, MD, Adult Reconstruction and Joint Replacement Division, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021. http://dx.doi.org/10.1016/j.arth.2014.08.011 0883-5403/© 2014 Elsevier Inc. All rights reserved.
composite ceramic, underscored by reports of significant tetragonalmonoclinic phase transformation found in retrieved components [5,6]. An analysis of a fractured Biolox delta head demonstrated a 33% phase transformation of the zirconia [6]. This amount of phase transformation compromises the chemical stability and mechanical strength of the ceramic. Additionally, Santos et al showed a positive correlation, although slight, between increased monoclinic zirconia phase transformation and increased surface roughness [7]. Therefore, concerns remain regarding the long-term in vivo stability of Biolox delta femoral heads [4,8]. An additional concern with the use of ceramic femoral heads in THA is the occurrence of metal transfer to the bearing surface, a phenomenon observed regardless of whether the acetabular bearing material is polyethylene or ceramic [9–12]. The regions of metal transfer exhibit patterns that suggest the transfer initiates near the edge of the head and progresses toward the apex [12]. The presence of metal transfer alters the bearing surface and could have detrimental effects on wear [10–12]. Retrieval analyses have played a useful role in evaluating in vivo performance of total joint arthroplasties, and in understanding wear mechanisms in total hip arthroplasty. To our knowledge, few retrieval studies have been performed assessing the performance of Biolox delta femoral heads, and the number of retrieved heads has been very small [1,4]. Given the concerns that have been raised with historical ceramic THA components, we sought to evaluate a larger series of retrieved Biolox delta femoral heads, to address three main objectives: (1) Do these Biolox delta femoral heads undergo the t-m phase
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M. Elpers et al. / The Journal of Arthroplasty 29 (2014) 2219–2223
transformation? And if so, to what extent? (2) Is metal transfer still a concern? And (3) does the extent of t-m phase transformation or metal transfer affect the articular surface roughness? Materials and Methods Twenty-seven Biolox delta femoral heads were identified as part of our institution's ongoing implant retrieval program. Each head was part of a ceramic-on-polyethylene THA performed using noncemented acetabular and femoral components. Eight patients had their index procedure performed at our institution, while the remaining 19 of the THAs were performed at an outside hospital; all were revised at our institution. Clinical and demographic information was gathered from the patients' medical records (Table 1); including the length of implantation (LOI), age at index procedure, body mass index (BMI), sex, and revision diagnosis. Patient radiographs were available for the retrieved components, and were assessed for component alignment, including the abduction and anteversion angles of the acetabular component.
Table 2 Method of Grading the Severity of Metal Transfer. Grade Description 1 2 3 4 5
No markings present Some metal transfer present, light markings, or ≤3 dark markings ≤0.5″ long N3 dark markings ≤0.5″ long or ≥1 dark markings ≤1″ long Metal smear b20% of surface area or N3 lines 1″ long Metal smear N20% of surface area
the monoclinic phase was quantified as volume fraction (Vm) using the following equation [13]: 181
Vm ¼
190
Im þ Im 190 2:2 I147 þ I 181 t m þ Im
where I represents the area of the monoclinic bands identified at 181 and 190 cm −1 and the tetragonal band at 147 cm −1, respectively. This method has been used in several previous reports and preferred over a method proposed by Clarke and Adar [1,4,14].
Raman Spectroscopy Metal Transfer Evidence of a phase transformation at the bearing surfaces of the retrieved femoral heads was collected using Raman spectroscopy. Each head was placed on a custom-machined support of a WITec alpha300 R Confocal Raman Microscope (CRM). The CRM was equipped with a Nikon 20× objective (Nikon Instruments, Melville, NY), using the 488 nm excitation laser (WITec Wissenschaftliche Instrumente und Technologie GmbH, Ulm, Germany) with a resolution down to the optical diffraction limit of 200 nm and spectral resolution of 1 cm−1. Spectra were collected at full laser power of ~200 mW, with a 1 second integration time and 30 accumulations. The beam was focused by adjusting the Z-position of the objective to achieve the maximum possible CCD counts at the area of the spectrum corresponding to the vibration at ~180 cm−1. Three spectra were collected in each of three regions of interest on the bearing surface of the femoral head: the apex of the surface, around the equator, and below the equator. In addition, spectra were collected from areas immediately adjacent to regions of large amounts of metal transfer. The spectra were exported as both xy.txt text files and gramscompatible .spc spectral files for analysis. Spectral files were imported into Grams/AI Spectroscopy Software (Thermo Scientific, Waltham, MA). Using the software, spectra were truncated to the wavelengths of interest (100–800 cm − 1) and baselined to normalize the scans. To determine the extent of zirconia phase transformation,
The bearing surface of each ceramic head was assessed for metal transfer by two independent observers using a previously described subjective grading system [11]. Briefly, each head was graded for the severity of metal transfer on a 1 through 5 scale, based on the number of distinct occurrences of metal transfer, the intensity, and the surface area of the femoral head involved (Table 2). Each head was divided into 5 regions of interest (Fig. 1). The same three regions on the bearing surface (apex, equator, and below the equator) used for the Raman spectroscopy were individually graded for metal transfer. Two additional regions were defined on the female taper of the femoral head, which was divided into a proximal and a distal region. Each acetabular polyethylene liner was also examined for macroscopic signs of impingement. Surface Roughness A non-contact white light profiler (ADE Phase Shift MicroXAM, KLA-Tencor; Milpitas, CA) was used to measure surface roughness of the femoral heads using a previously described method [11]. All surfaces were wiped with acetone prior to performing the surface profilometry measurements. Each head was placed in a holder on the microscope platform of the profilometer, with the area of interest
Table 1 Patient Demographic Data for the 27 Biolox Delta Components Included in this Study. Variable Female Right Age at primary (years) BMI (kg/m2) LOI (months) Revision diagnosis Dislocation Loosening ALTR Periprosthetic fracture Infection Malposition Leg length discrepancy Heterotopic ossification Values reported are mean ± SD.
Number 15 14 62.5 ± 9.8 27.3 ± 4.3 24.3 ± 27.5 7 6 4 3 4 1 1 1
Fig. 1. Regions of interest identified on the articular and taper surface of the retrieved femoral heads. The taper surface was divided in half for consistency across samples, as we were unable to identify the most proximal point of trunnion engagement. All 5 regions were evaluated for metal transfer. The three regions on the articular surface of the femoral head were analyzed with surface roughness and Raman spectroscopy.
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oriented perpendicular to the objective lens (set at 10 ×). Three areas, ~ 600 μm × 800 μm in size, were scanned on each head, in the same three regions as were used for the Raman and metal transfer measurements: the apex of the bearing surface, around the equator, and below the equator (where little if any articulation had occurred). If a region of metal transfer was present, an additional scan was taken over the transfer region. If multiple regions of metal transfer were present, the most severe region was used for analysis. One unimplanted Biolox delta femoral head was analyzed over the same three regions of interest to establish control roughness values. After each scan, the spherical plane of the scanned area was corrected for the curvature of the femoral head. Average surface roughness, Sa, was calculated using Scanning Probe Image Processor (Image Metrology A/S, Hϕrsholm, Denmark) as: Sa ¼
1 M−1 N−1 ∑ ∑ jzðxk ; yl Þ−μ j MN k¼0 l¼0
where MN is the total number of pixels across the entire image, z(xk, yi) is the height of each pixel, and μ is the average height of all pixels.
Fig. 3. For all three regions on the articular surface, Vm increased significantly with increased time in vivo.
Raman spectra revealed the presence of monoclinic zirconia in the control and in all of the retrieved specimens (Fig. 2). Distinct markers for tetragonal and monoclinic phases were detected, with tetragonal marker bands featured at 145, 265, 315, and 646 cm−1 and prominent
monoclinic marker bands at 183, 335, 383, and 479 cm −1. No interference was detected due to the presence of the alumina; a weak alumina peak was identified at 415 cm − 1 consistently throughout the specimens. The average monoclinic zirconia volume fraction (Vm) for each region of interest on the bearing surface was: 0.25 ± 0.08 at the apex, 0.26 ± 0.09 at the equator, and 0.25 ± 0.08 below the equator. Seventeen of the 27 femoral heads had Raman spectra collected adjacent to regions of metal transfer with an average Vm of 0.24 ± 0.1. No difference in Vm was found among these 4 regions of interest (P = 0.864). No correlation was observed between the severity score for metal transfer or the surface roughness and the Vm, by region. However, Vm increased significantly with length of implantation for the apex (P = 0.0166), the equator (P = 0.000183), and below the equator (P = 0.0469) (Fig. 3). All 27 of the retrieved ceramic heads displayed metal transfer in one or more of the three regions. Sixty percent displayed metal transfer at the apex, with a mean score of 1.6 ± 0.5. At the equator, 95.6% displayed metal transfer, with a mean score of 2.2 ± 0.6. Below the equator, 100% of the retrieved femoral heads displayed metal transfer, with a mean score of 2.6 ± 0.9. The frequency of metal
Fig. 2. Micro-Raman spectra recorded on three representative Biolox delta femoral heads (from top to bottom): a non-implanted Biolox delta, retrieval #10 (time in vivo of 12 months), and retrieval #3 (time in vivo of 7 years). Increasing time in vivo correlated with increase Vm. Bands associated with alumina (a), tetragonal (t) and monoclinic (m) zirconia are indicated in the spectra.
Fig. 4. Retrieved alumina-zirconia composite head demonstrating metal transfer in both the superficial and deep regions of the female taper.
Statistical Analysis Non-parametric Kruskal–Wallis ANOVA on Ranks was used to evaluate the differences in the volume fraction of the monoclinic phase (Vm), metal transfer score, and surface roughness (Sa) among the three regions (apex, equator, and below the equator of the head). Pearson product–moment correlations were used to evaluate correlations between the three measured damage modes: Vm, metal transfer and Sa across the regions of interest, as well as the correlation of these variables with length of implantation. Interobserver correlation coefficients were determined for the metal transfer scoring using the following scale: excellent for 0.9 ≤ r ≤ 1.0, good for 0.7 ≤ r ≤ 0.89, fair/moderate for 0.5 ≤ r ≤ 0.69, low for 0.25 ≤ r ≤ 0.49, and poor for 0.0 ≤ r ≤ 0.24 [15]. A P-value b 0.05 was deemed significant. Results
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Only two of the polyethylene acetabular inserts demonstrated signs of impingement. One of these displayed impingement in the posterior-superior region at the rim of an elevated liner. This component had a metal transfer score of 3 at the equator, and 4 below the equator. Average surface roughness (Sa) was not different among the apex (32.6 ± 14.0 nm), the equator (35.4 ± 17.6 nm), and the below the equator (34.4 ± 13.3 nm) regions. The unimplanted Biolox delta femoral head used as a control was about 30% smoother than the retrieved heads, with an average surface roughness of 23.6 ± 4.9 nm. Regions of metal transfer were significantly rougher than the nonmetal transfer regions of the articular surface (P b 0.001). The average surface roughness of the metal transfer regions was twice that of the other three regions on the bearing surface at 74.5 ± 54.5 nm (Fig. 6). No correlations were found between the average monoclinic zirconia volume fraction and average surface roughness for the 3 regions of interest or for the metal transfer regions.
Fig. 5. Retrieved alumina–zirconia composite head demonstrating metal transfer on the articular surface of the femoral head. Center of image is the apex of the femoral head.
transfer was significantly greater at and below the equator compared to at the apex (P = 0.002, P = 0.003, respectively). All 27 of the femoral heads demonstrated metal transfer in both the proximal and distal regions of the female taper, with a mean score of 3.3 ± 0.7 and 3.3 ± 0.6, respectively (Fig. 4). The severity of metal transfer on the female taper was significantly more than on the articular surface of the femoral head (P b 0.001) (Fig. 5). Interobserver correlation coefficients were fair/moderate to good for all regions analyzed (r = 0.59–0.80).
Discussion With current concerns related to trunnion corrosion and metalon-metal bearings in THA, alternative bearings, such as the Biolox delta, have become a popular option among surgeons [16–19]. The early, clinical results with the use of Biolox delta bearing surfaces have been encouraging, with few bearing-related complications reported. Hamilton et al performed a prospective, randomized controlled trial comparing 177 Delta ceramic-on-ceramic (COC) articulations with 87 Delta ceramic head-cross-linked polyethylene (COP) articulations at a mean follow-up of 31.2 months. No differences were found between the two groups with regards to clinical, radiographic, and survivorship scores, but there were 3 instances of ceramic liner chipping or cracking in the COC cohort [5]. Lombardi et al performed a prospective
Fig. 6. Surface roughness plots that demonstrate the varying surface profiles of non-transfer (A) and metal transfer (B) regions. No differ.ence was observed in surface roughness between the non-transfer regions: apex, equator, and below the equator. All color scales are in nanometers.
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analysis of 65 Biolox delta femoral heads articulating on alumina liners, and 45 zirconia femoral heads articulating on polyethylene liners. At a mean follow-up of 73 months, they found no significant difference between the two cohorts with regard to clinical and radiographic outcomes, or survivorship (95% in Biolox delta vs. 93% in zirconia). In each cohort, 3 patients were revised, but only one revision was attributed to the bearing surface. As was found in our series of Biolox delta heads, earlier retrieval studies demonstrated that the t-m phase transformation does occur at the bearing surface, but the authors of those studies suggested that the transformation resulted from the mechanical energy accompanying implant wear, rather than from in vivo aging of the material, perhaps because the retrievals that were examined had come from COC bearings. We observed the t-m phase transformation in all of our retrieved components. Given our large numbers of retrievals, we were able to establish strong positive correlations between the volume of transformation and the length of time that the components had been implanted regardless of whether the measurements were made in regions of the head that likely experienced wear or those that likely did not. Our results suggest that the source of energy that caused the transformation was not related to mechanical wear, since differences were not noted between regions expected to experience wear (e.g., the pole or areas adjacent to metal transfer) and those less likely to have been worn (e.g., below the equator). In addition to the t-m phase transformation, metal transfer has been commonly observed on retrieved ceramic femoral heads of all generations [9–12]. However, the mechanism by which metal transfer occurs is not entirely clear. Clinical series and case reports have described metal transfer occurring during intraoperative reductions or dislocations, originating near the rim of the component and extending toward the apex of the femoral head. Regardless of the underlying mechanism, it is clear that even with this new generation of ceramics metal transfer still occurs, and is not solely associated with the bearing materials. A consequence of the t-m phase transformation and metal transfer is the potential to alter the surface roughness of the articular surface. The tm transformation is accompanied by a 3–4% volume expansion, which could increase the surface roughness [4]. However, previous investigators did not find a correlation between an increase in percent monoclinic phase and increased surface roughness, with only mild trends of increased surface roughness observed [7,20]. Similarly, we did not observe any correlation between percent monoclinic phase and surface roughness. We previously showed that regions of metal transfer, however, are significantly rougher, almost ten times rougher, than non-transfer regions [11]. While we also observed an increase in surface roughness of the metal transfer regions in this series, these regions were only two times rougher than the non-transfer region, which is notably lower than our previous study. It is unclear as to the underlying mechanism by which metal transfer occurs; however, given the difference in roughness of the metal transfer regions in the two series, it suggests that two mechanisms are at work. Macroscopically, metal transfer in the previous series of alumina and zirconia femoral heads appeared as a “smear” on the surface, while in the Biolox delta heads cohort, the transfer appeared to be more distinct stripes across the surface. Regardless of the mechanism, in any bearing combination, this increase in surface roughness could cause increased wear on the counter-bearing surface and lead to a release of third body wear particles and eventually the need for revision of the component. Our study had limitations. The components were retrieved after short lengths of implantation, with an average LOI of just over two years. We cannot comment, therefore, on the long-term implications of the phase transformation and how it might impact clinical performance at longer follow-up. A limitation in applying techniques such as Raman spectroscopy and surface profilometry is the limited amount of the bearing surface that can be measured in a reasonable time and at a reasonable cost. Sampling more areas on the surfaces of the
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retrieved components might reveal different results, but the lack of variability among our results suggests that doing even more measurements would have not provided any added benefit. Finally, our sample included one component implanted before 2006. The average monoclinic zirconia content decreased in the manufactured ceramic from when it was first introduced in 1999 until about 2006 [1,4]. We did not consider implantation year in our analysis, but found no marked differences in the results of our one early component. Lastly, we did not evaluate the mechanical strength of the retrieved components, which could be affected by the t-m phase transformation. However, little data exist in the literature to support a direct correlation between an increase in Vm and a decrease in mechanical strength. In summary, this evaluation of retrieved Biolox delta femoral heads has demonstrated the presence of t-m phase transformation with no influence on the surface roughness, and observed metal transfer on the articular surface of all femoral heads, which was associated with increased surface roughness in the metal transfer regions. In addition, we saw an increase in t-m transformation with longer time in vivo, which warrants continual evaluation of these components. Despite this observation, the surface roughness still remains low, suggesting that the use of Biolox delta is a viable option for use as a bearing surface in THA. Acknowledgments This work made use of the Cornell Center for Materials Research Facilities supported by the National Science Foundation under Award Number DMR-1120296. References 1. Affatato S, Modena E, Toni A, et al. Retrieval analysis of three generations of biolox (R) femoral heads: spectroscopic and SEM characterisation. J Mech Behav Biomed Mater 2012:118. 2. Derbyshire B, Fisher J, Dowson D, et al. Comparative study of the wear of UHMWPE with zirconia ceramic and stainless steel femoral heads in artificial hip joints. Med Eng Phys 1994;3:229. 3. Piconi C, Maccauro G, Muratori F, et al. Alumina and zirconia ceramics in joint replacements. J Appl Biomater Biomech 2003;1:19. 4. Taddei P, Modena E, Traina F, et al. Raman and fluorescence investigations on retrieved Biolox delta femoral heads. J Ramana Spectrosc 2012;12:1868. 5. Hamilton WG, McAuley JP, Dennis DA, et al. THA with delta ceramic on ceramic: results of a multicenter investigational device exemption trial. Clin Orthop Relat Res 2010;2:358. 6. Lombardi Jr AV, Berend KR, Seng BE, et al. Delta ceramic-on-alumina ceramic articulation in primary THA: prospective, randomized FDA-IDE study and retrieval analysis. Clin Orthop Relat Res 2010;2:367. 7. Santos EM, Vohra S, Catledge SA, et al. Examination of surface and material properties of explanted zirconia femoral heads. J Arthroplasty 2004;7(Suppl 2):30. 8. Chevalier J. What future for zirconia as a biomaterial? Biomaterials 2006;4:535. 9. Bal BS, Rahaman MN, Aleto T, et al. The significance of metal staining on alumina femoral heads in total hip arthroplasty. J Arthroplasty 2007;1:14. 10. Brandt JM, Gascoyne TC, Guenther LE, et al. Clinical failure analysis of contemporary ceramic-on-ceramic total hip replacements. Proc Inst Mech Eng H 2013;8:833. 11. Chen D, Lin S, Cutrera N, et al. Ceramic bearings in total hip replacement: a retrieval analysis. Minerva Ortop Traumatol 2010:43. 12. Tomek IM, Currier JH, Mayor MB, et al. Metal transfer on a ceramic head with a single rim contact. J Arthroplasty 2012;2:324.e1. 13. Katagiri G, Ishida H, Ishitani A, et al. Direct determination by raman microprobe of the transformation zone size in Y2O3 containing tetrangonal ZrO2 polycrystals. Science and Technology of Zirconia; 1988. p. 537. 14. Clarke DR, Adar F. Measurement of the crystallographically transformed zone produced by fracture in ceramics containing tetragonal zirconia. J Am Ceram Soc 1982;6:284. 15. Munro BH. Correlation. Statistical Methods for Healthcare Research. 3rd ed. Lippincott-Raven; 1997. p. 224. 16. Cooper HJ, Della Valle CJ, Berger RA, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg Am 2012;18:1655. 17. Kwon YM, Jacobs JJ, MacDonald SJ, et al. Evidence-based understanding of management perils for metal-on-metal hip arthroplasty patients. J Arthroplasty 2012;8:20 [Suppl.]. 18. Nam D, Barrack RL, Potter HG. What are the advantages and disadvantages of imaging modalities to diagnose wear-related corrosion problems? Clin Orthop Relat Res 2014 (Epub ahead of print). 19. Nawabi DH, Gold S, Lyman S, et al. MRI predicts ALVAL and tissue damage in metalon-metal hip arthroplasty. Clin Orthop Relat Res 2014;2:471. 20. Kim YH, Ritchie A, Hardaker C. Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear. J Bone Joint Surg Am 2005; 3:577.