Eur J Orthop Surg Traumatol DOI 10.1007/s00590-013-1397-5
ORIGINAL ARTICLE
Retrieval analysis of new-generation yttria-stabilized zirconia femoral heads after total hip arthroplasty Kiyokazu Fukui • Ayumi Kaneuji • Tanzo Sugimori Toru Ichiseki • Tadami Matsumoto
•
Received: 24 September 2013 / Accepted: 16 December 2013 Ó Springer-Verlag France 2013
Abstract Zirconia femoral heads were introduced for total hip arthroplasty (THA) with the expectation of lower polyethylene (PE) wear and better clinical results. Because several studies reported poor survivorship of yttria-stabilized zirconia-PE THA, we investigated a new-generation yttria-stabilized zirconia head (diameter, 26 mm) manufactured by NGK Spark Plug. We retrieved six zirconia heads at revision THA after they had been in place for a mean of 8.6 years and measured their surface roughness and mean monoclinic content. Although their mean monoclinic content was higher than that of the unused head, surface roughness in the implanted heads was as low as that of the unused head, indicating that wear reduction may be possible with the selection of a suitable zirconia femoral head. Keywords Zirconia Femoral head Surface roughness Monoclinic content Wear reduction Total hip arthroplasty
K. Fukui (&) A. Kaneuji T. Sugimori T. Ichiseki T. Matsumoto Department of Orthopaedic Surgery, Kanazawa Medical University, 1-1 Daigaku, Uchinada-machi, Kahokugun, Ishikawa 920-0293, Japan e-mail: [email protected] A. Kaneuji e-mail: [email protected] T. Sugimori e-mail: [email protected] T. Ichiseki e-mail: [email protected] T. Matsumoto e-mail: [email protected]
Introduction Alumina ceramic heads were introduced in the early 1970s and had low polyethylene (PE) wear and revision rates [1]. Although alumina has improved in quality and alumina ceramic femoral heads have been implanted for more than 40 years [2, 3], 0.02–0.14 % alumina ceramic femoral heads fracture [4, 5]. In an attempt to address this problem, zirconia ceramic femoral heads were introduced clinically in the early 1980s. These produced lower PE wear in vitro, equaling that of alumina ceramics [6, 7]. Yttria-stabilized tetragonal zirconia polycrystal ceramics (Y-TZPs) have an even higher mechanical strength than alumina ceramics. Zirconia ceramics display 3 phases of crystal structure—monoclinic, tetragonal, and cubic—which transform according to temperature. The tetragonal phase shows the greatest mechanical strength of these phases but is unstable, and approximately 5 % of yttria is used for surgical-grade zirconia ceramics for stabilization. The monoclinic phase transforms into a tetragonal phase at temperatures \1,100 °C, whereas the tetragonal phase transforms into the cubic phase at 2,370 °C. Transformation from the tetragonal phase to a monoclinic phase of Y-TZPs leads to volumetric expansion of approximately 3–4 % [8], increased roughness of the zirconia head [8], and increased PE wear [9]. One retrieval study suggested transformation of as much as 80 % by 9 years after implantation [9]. Furthermore, Hernigou and Bahrami [10] demonstrated that an increase in the rate of wear with Y-TZPs was significantly higher than that with alumina heads, which may be linked to long-term biodegradation of zirconia in vivo, associated with the altered roughness. However, a report by Cales suggested poor survivorship of Y-TZP-PE prostheses in total hip
123
Eur J Orthop Surg Traumatol
arthroplasty (THA), with a rate for aseptic loosening of 14 % at a mean follow-up point of 5.8 years [7], and Haraguchi et al. [11] reported intensive phase transformation in the crystal structure of 20–30 % of retrieved zirconia heads, which can lead to increased roughness of the zirconia head, increased PE wear, and poor prosthesis survivorship [9]. Moreover, degradation of yttria-stabilized zirconia femoral heads in vivo has been a matter of concern, given their resultant increased roughening and even fracture [12]. Norwegian arthroplasty register revealed cemented THAs with zirconia heads had inferior survivorship than that with alumina or cobalt–chromium heads [13]. However, there have been only a small number of studies of retrieved zirconia heads. NGK Spark Plug (Nagoya, Japan) released a new-generation zirconia femoral head in 1998. The purpose of this study is to evaluate the changes in roughness and phase transformation observed in retrieved new-generation Y-TZP NGK heads, compared to a never-implanted head. We hypothesized that roughness and phase transformation of the retrieved new-generation Y-TZP NGK heads were similar to the other Y-TZP heads.
Materials Our study was approved by our institution’s review board, and all patients provided written confirmation of informed consent. We examined six zirconia femoral heads manufactured by the same company and retrieved from six patients during revision THA. The heads had been in place for a mean of 8.6 years (range 6.6–9.7 years). The average age of the patients at the time of revision surgery was 69 years (range 55–82 years). Their average weight was 57.8 kg (range 45–72 kg), and their average height was 153.5 cm (range 135–168 cm). Revision surgery was performed in 3 of the hips because of aseptic loosening of the acetabular component. Each of the 3 others required revision for different reasons: excessive wear of ultrahigh molecular weight PE and osteolysis, failure of the locking mechanism of the acetabular component, and infection. Harris-Galante Porous II (HGP II) cups (Zimmer, Warsaw, IN, USA) were used for all six patients. All six acetabular liners were made of conventional UHMWPE. It is reported that HGP II cups have a problem such as failure of the liner locking mechanism, and subsequent dissociation of the polyethylene liner from the metal-backed shell is a potential cause of failure [14]. The diameter of all zirconia heads was 26 mm. An unused zirconia femoral head with a 26 mm diameter manufactured by the same company in 2000 was also examined as a control. The chemical composition and the physical and mechanical properties of Y-TZPs are shown in Table 1.
123
Table 1 Chemical composition and mechanical and physical properties of zirconia head manufactured by NGK Spark Plug Ltd Parameters
Value
Chemical composition Zr2O ([90 %) ? Y2O3 ? Al2O3 ? a very small amount of other elements Flexural strength Young’s modulus
1,000 MPa 220 GPa
Fracture toughness
9.2 MPa/m
Physical properties Monoclinic phase
&0 %
Nagoya, Japan
Methods The surface roughness (measured in Ra) of a new head constructed of Y-TZPs was 0.006 lm of Ra (the arithmetic mean of the absolute value of the measured profile height deviation as measured from the graphical center line), and the monoclinic content, calculated by x-ray diffraction, was 1 %. Scanning electron microscopy (SEM) showed the same surface pores as in the retrieved head. The Ra value for each zirconia head was measured using a surface roughness measurement instrument (Surfcoder SE-2300, Kosaka Laboratory Ltd., Tokyo, Japan). The accuracy of this instrument is within ±3 % of the measured value, and its capacity is 0.001–100 lm. Crystal contents were evaluated using an X-ray diffractometer (RINT 2500 V, Rigaku Co., Tokyo, Japan). The measurement value of the monoclinic content and surface roughness was recorded as the average value of four measurements obtained by an expert observer with 10-year experience in assessing SEM findings. Statistical analysis was performed for the differences between groups using the unpaired Student’s t test and P \ 0.05 was considered significant.
Results To the naked eye, the retrieved heads appeared glossy (Fig. 1). In Fig. 1c, there was a severe, dark, metallicappearing smear on the surface of the head. For that head, we measured the part that was free of smearing. The monoclinic content of the retrieved heads was significantly greater than that of the unused head at any point on the surface. However, the increase in the mean values for surface roughness at any site on the retrieved heads was slight compared with that for the unused head, and it was not significant statistically (Table 2). SEM images of the retrieved heads and of the unused head showed a smooth,
Eur J Orthop Surg Traumatol
Fig. 1 Photographs showing the ball surfaces of six retrieval zirconia femoral heads. All except c are glossy
Table 2 Average surface roughness (Ra) and monoclinic content Site of measurement
Ra in lm (mean/SD)
% Monoclinic content (mean/SD)
Retrieved (n = 6)
Unused (n = 4)
P
Retrieved (n = 6)
Unused (n = 4)
P
Pole
0.006/0.002
0.004/0.006
0.3938
25.0/5.4
&0
\0.0001
5 mm above the equator
0.008/0.001
0.005/0.007
0.1995
31.8/4.9
&0
\0.0001
Equator
0.009/0.003
0.006/0.007
0.1619
34.7/3.4
&0
\0.0001
5 mm below the equator
0.008/0.001
0.005/0.005
0.1981
36.6/4.5
&0
\0.0001
Ra = the arithmetic mean of the absolute value of the measured profile height deviation as measured from the graphical center line
polished surface with small cracks or voids of \0.5 lm in diameter (Fig. 2).
Discussion The purpose of this study is to evaluate the changes in roughness and phase transformation observed in retrieved new-generation Y-TZP NGK heads, compared to a neverimplanted head. Despite the increase in surface roughness of retrieved zirconia heads with time in our study, the increase was relatively small. This might have been caused by a difference in the quality of zirconia used. Y-TZPs have problems not only in phase transformation but also related to the thermic conduction of Y-TZPs with a risk of increased temperature of PE. At this moment, most of the companies have stopped Y-TZPs. However, the PE wear rate against zirconia reported by Kim [15] in 2005 was low, and Kim et al. [16] suggested that the surface roughness of the ceramic head and an increased PE wear rate were associated with the presence of
embedded third-body metallic debris in the articulating PE liner. In fact, two of our six cases had third-body metallic debris. Imai et al. [17] suggested that there is a significant association between failure of the locking mechanism and linear PE wear in HGP cups. In our patient, we measured the surface roughness and monoclinic content in the part of the ball that was free of smearing, and we found that both the surface roughness and monoclinic content were the same as for the other retrieval head. In the reminder of aseptic loosening cases, we consider excessive PE wear caused by the failure of locking mechanism even though there was no obvious third-body metallic debris. Because of those findings, we suspect that new-generation Y-TZP NGK heads may not directly induce an increase in the PE wear rate, but the failure of the locking mechanism failure described by Imai et al. [17] or the presence of an embedded third body described by Kim [16] may influence the increase in PE wear. In a meta-analysis of THA with zirconia, Yoshitomi et al. [18] suggested that urgent cessation of zirconia-PE THA would not be justified, because the
123
Eur J Orthop Surg Traumatol
Fig. 2 At top left, a scanning electron microscopy (SEM) image (original magnification, 9500) of an unused (Un) specimen. a–c SEM images of the ball at the pole (a), at the equator (b), and at 5 mm below the equator (c) show almost identically smooth, polished
surfaces with some small voids of \0.5 lm. At bottom left, photograph (original magnification, 9500) of a retrieved zirconia head (Fig. 1a) indicating the pole (A), equator (B), and 5 mm below the equator (C)
zirconia supplied by some manufacturers seems to have clinical results equivalent to those of traditional materials. SEM analysis with high-power magnification in our retrieval study revealed some microscopic cracks or voids on the surface, but they were present when the heads were brand-new and had not extended by a mean point of 8.6 years after implantation (Fig. 3). THAs with highquality zirconia heads may have rates of prosthesis survivorship and PE wear equivalent to those of THAs with traditional materials, but heterogeneous quality among zirconia heads leads to poor prosthesis survivorship because of PE wear. At the front of the ball shown in Fig. 1c, there was a severe, dark, metallic-appearing smear. That ball was removed from a 62-year-old man
with osteoarthritis of the right hip joint; in 1998, he underwent THA that involved an HGP II cup. In 2006, we revised the patient’s liner and zirconia head because of liner breakage. Problems with the locking mechanism of the liner in this HGP II cup have been noted [19], and in our patient we found that the liner in the superolateral rim had a bucket-handle tear. This fact led us to think that both the locking mechanism failure and liner breakage caused the zirconia head to come into contact with the metal shell, leading to the dark metallic-appearing smear (Fig. 1c). Our study has several limitations. First, the surface characteristics and wear pattern of retrieved femoral heads at revision hip arthroplasty may not represent the surface characteristics of well-functioning total
123
Eur J Orthop Surg Traumatol
Fig. 3 Scanning electron microscopy images of one of the six retrieved zirconia heads at 9.7 years after implantation (a, b) and of the unused head (c, d). There were micropores not only in the retrieved heads but also in the unused head. The surface of the
retrieved head had no increase in roughness, but expansion of the micropores was apparent in comparison with the unused head. (a, c: original magnification 9500; b: original magnification 95,000; d: original magnification 97,000)
hip replacements. Additionally, the number of retrieved ceramic femoral heads that we examined was small and may affect our conclusions. However, we found no difference in Ra at any surface site between the retrieved heads and the unused zirconia head, although monoclinic content was increased at every site in the retrieved heads. In addition, SEM showed that the retrieved heads had a smooth polished surface, just like the unused head. In conclusion, our study shows that at an average of 8.6 years after prosthesis implantation, the surface roughness of zirconia femoral heads manufactured by NGK Spark Plug is as low as that of an unused head, whereas the surface monoclinic content continued to increase after implantation. Although a longer follow-up period is required for further confirmation, these results indicate that a reduction in wear may be possible if a suitable zirconia femoral head is selected.
patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.
Acknowledgments Medical editor Katharine O’Moore-Klopf, ELS (East Setauket, NY, USA) provided professional English-language editing of this article. Conflict of interest Each author certifies that he has no commercial associations (e.g., consultancies, stock ownership, equity interest,
Ethical standard Each author certifies that his institution approved the reporting of this case and that all investigations were conducted in conformity with ethical principles of research.
References 1. Fritsch E, Gleitz M (1996) Ceramic femoral head fractures in total hip arthroplasty. Clin Orthop Relat Res 328:129–136 2. Schu¨ller HM, Marti RK (1990) Ten-year socket wear in 66 arthroplasties: ceramic versus metal heads. Acta Orthop Scand 61:240–243 3. Zichner LP, Willert HG (1992) Comparison of alumina–polyethylene and metal–polyethylene in clinical trials. Clin Orthop Relat Res 282:86–94 4. Peiro´ A, Pardo J, Navarrete R, Rodriguez-Alonso L, Martos F (1991) Fracture of the ceramic head in total hip arthroplasty: report of two cases. J Arthroplast 6:371–374 5. Higuchi F, Shiba N, Inoue A, Wakebe I (1995) Fracture of an alumina ceramic head in total hip arthroplasty. J Arthroplast 10:851–854 6. Kumar P, Oka M, Ikeuchi K, Shimizu K et al (1991) Low wear rate of UHMWPE against zirconia ceramic (Y-PSZ) in comparison to alumina ceramic and SUS 316L alloy. J Biomed Mater Res 25:813–828
123
Eur J Orthop Surg Traumatol 7. Cales B (2000) Zirconia as a sliding material: histologic, laboratory, and clinical data. Clin Orthop Relat Res 379:94–112 8. Piconi C, Maccauro G (1999) Zirconia as a ceramic biomaterial. Biomaterials 20:1–25 9. Brown S, Green D, Pezzotti G, Donaldson T, Clarke I (2008) Possible triggers for phase transformation in zirconia hip balls. J Biomed Mater Res B Appl Biomater 85:444–452 10. Hernigou P, Bahrami T (2003) Zirconia and alumina ceramics in comparison with stainless-steel heads. Polyethylene wear after a minimum ten-year follow-up. J Bone Joint Surg Br 85:504–509 11. Haraguchi K, Sugano N, Nishii T, Miki H, Oka K, Yoshikawa H (2001) Phase transformation of a zirconia ceramic head after total hip arthroplasty. J Bone Joint Surg Br 83:996–1000 12. Fernandez-Fairen M, Blanco A, Murcia A, Sevilla P, Gil FJ (2007) Aging of retrieved zirconia femoral heads. Clin Orthop Relat Res 462:122–129 13. Kadar T, Dybvik E, Hallan G, Furnes O, Havelin LI (2012) Head material influences survival of a cemented total hip prosthesis in the Norwegian Arthroplasty Register. Clin Orthop Relat Res 470:3007–3013 14. Werle J, Goodman S, Schurman D, Lannin J (2002) Polyethylene liner dissociation in Harris-Galante acetabular components: a report of 7 cases. J Arthroplast 17:78–81
123
15. Kim YH (2005) Comparison of polyethylene wear associated with cobalt-chromium and zirconia heads after total hip replacement: a prospective, randomized study. J Bone Joint Surg Am 87:1769–1776 16. Kim YH, Ritchie A, Hardaker C (2005) Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear. J Bone Joint Surg Am 87:577–582 17. Imai H, Mashima N, Takahashi T, Yamamoto H (2009) The relationship between increased hip range of motion, wear, and locking mechanism failure in the Harris-Galante acetabular component. J Arthroplast 24:892–897 18. Yoshitomi H, Shikata S, Ito H, Nakayama T, Nakamura T (2009) Manufacturers affect clinical results of THA with zirconia heads: a systematic review. Clin Orthop Relat Res 467:2349–2355 19. Gonza´lez della Valle A, Ruzo PS, Li S, Pellicci P, Sculco TP, Salvati EA (2001) Dislodgment of polyethylene liners in first and second-generation Harris-Galante acetabular components: a report of eighteen cases. J Bone Joint Surg Am 83:553–559
ORIGINAL ARTICLE
Retrieval analysis of new-generation yttria-stabilized zirconia femoral heads after total hip arthroplasty Kiyokazu Fukui • Ayumi Kaneuji • Tanzo Sugimori Toru Ichiseki • Tadami Matsumoto
•
Received: 24 September 2013 / Accepted: 16 December 2013 Ó Springer-Verlag France 2013
Abstract Zirconia femoral heads were introduced for total hip arthroplasty (THA) with the expectation of lower polyethylene (PE) wear and better clinical results. Because several studies reported poor survivorship of yttria-stabilized zirconia-PE THA, we investigated a new-generation yttria-stabilized zirconia head (diameter, 26 mm) manufactured by NGK Spark Plug. We retrieved six zirconia heads at revision THA after they had been in place for a mean of 8.6 years and measured their surface roughness and mean monoclinic content. Although their mean monoclinic content was higher than that of the unused head, surface roughness in the implanted heads was as low as that of the unused head, indicating that wear reduction may be possible with the selection of a suitable zirconia femoral head. Keywords Zirconia Femoral head Surface roughness Monoclinic content Wear reduction Total hip arthroplasty
K. Fukui (&) A. Kaneuji T. Sugimori T. Ichiseki T. Matsumoto Department of Orthopaedic Surgery, Kanazawa Medical University, 1-1 Daigaku, Uchinada-machi, Kahokugun, Ishikawa 920-0293, Japan e-mail: [email protected] A. Kaneuji e-mail: [email protected] T. Sugimori e-mail: [email protected] T. Ichiseki e-mail: [email protected] T. Matsumoto e-mail: [email protected]
Introduction Alumina ceramic heads were introduced in the early 1970s and had low polyethylene (PE) wear and revision rates [1]. Although alumina has improved in quality and alumina ceramic femoral heads have been implanted for more than 40 years [2, 3], 0.02–0.14 % alumina ceramic femoral heads fracture [4, 5]. In an attempt to address this problem, zirconia ceramic femoral heads were introduced clinically in the early 1980s. These produced lower PE wear in vitro, equaling that of alumina ceramics [6, 7]. Yttria-stabilized tetragonal zirconia polycrystal ceramics (Y-TZPs) have an even higher mechanical strength than alumina ceramics. Zirconia ceramics display 3 phases of crystal structure—monoclinic, tetragonal, and cubic—which transform according to temperature. The tetragonal phase shows the greatest mechanical strength of these phases but is unstable, and approximately 5 % of yttria is used for surgical-grade zirconia ceramics for stabilization. The monoclinic phase transforms into a tetragonal phase at temperatures \1,100 °C, whereas the tetragonal phase transforms into the cubic phase at 2,370 °C. Transformation from the tetragonal phase to a monoclinic phase of Y-TZPs leads to volumetric expansion of approximately 3–4 % [8], increased roughness of the zirconia head [8], and increased PE wear [9]. One retrieval study suggested transformation of as much as 80 % by 9 years after implantation [9]. Furthermore, Hernigou and Bahrami [10] demonstrated that an increase in the rate of wear with Y-TZPs was significantly higher than that with alumina heads, which may be linked to long-term biodegradation of zirconia in vivo, associated with the altered roughness. However, a report by Cales suggested poor survivorship of Y-TZP-PE prostheses in total hip
123
Eur J Orthop Surg Traumatol
arthroplasty (THA), with a rate for aseptic loosening of 14 % at a mean follow-up point of 5.8 years [7], and Haraguchi et al. [11] reported intensive phase transformation in the crystal structure of 20–30 % of retrieved zirconia heads, which can lead to increased roughness of the zirconia head, increased PE wear, and poor prosthesis survivorship [9]. Moreover, degradation of yttria-stabilized zirconia femoral heads in vivo has been a matter of concern, given their resultant increased roughening and even fracture [12]. Norwegian arthroplasty register revealed cemented THAs with zirconia heads had inferior survivorship than that with alumina or cobalt–chromium heads [13]. However, there have been only a small number of studies of retrieved zirconia heads. NGK Spark Plug (Nagoya, Japan) released a new-generation zirconia femoral head in 1998. The purpose of this study is to evaluate the changes in roughness and phase transformation observed in retrieved new-generation Y-TZP NGK heads, compared to a never-implanted head. We hypothesized that roughness and phase transformation of the retrieved new-generation Y-TZP NGK heads were similar to the other Y-TZP heads.
Materials Our study was approved by our institution’s review board, and all patients provided written confirmation of informed consent. We examined six zirconia femoral heads manufactured by the same company and retrieved from six patients during revision THA. The heads had been in place for a mean of 8.6 years (range 6.6–9.7 years). The average age of the patients at the time of revision surgery was 69 years (range 55–82 years). Their average weight was 57.8 kg (range 45–72 kg), and their average height was 153.5 cm (range 135–168 cm). Revision surgery was performed in 3 of the hips because of aseptic loosening of the acetabular component. Each of the 3 others required revision for different reasons: excessive wear of ultrahigh molecular weight PE and osteolysis, failure of the locking mechanism of the acetabular component, and infection. Harris-Galante Porous II (HGP II) cups (Zimmer, Warsaw, IN, USA) were used for all six patients. All six acetabular liners were made of conventional UHMWPE. It is reported that HGP II cups have a problem such as failure of the liner locking mechanism, and subsequent dissociation of the polyethylene liner from the metal-backed shell is a potential cause of failure [14]. The diameter of all zirconia heads was 26 mm. An unused zirconia femoral head with a 26 mm diameter manufactured by the same company in 2000 was also examined as a control. The chemical composition and the physical and mechanical properties of Y-TZPs are shown in Table 1.
123
Table 1 Chemical composition and mechanical and physical properties of zirconia head manufactured by NGK Spark Plug Ltd Parameters
Value
Chemical composition Zr2O ([90 %) ? Y2O3 ? Al2O3 ? a very small amount of other elements Flexural strength Young’s modulus
1,000 MPa 220 GPa
Fracture toughness
9.2 MPa/m
Physical properties Monoclinic phase
&0 %
Nagoya, Japan
Methods The surface roughness (measured in Ra) of a new head constructed of Y-TZPs was 0.006 lm of Ra (the arithmetic mean of the absolute value of the measured profile height deviation as measured from the graphical center line), and the monoclinic content, calculated by x-ray diffraction, was 1 %. Scanning electron microscopy (SEM) showed the same surface pores as in the retrieved head. The Ra value for each zirconia head was measured using a surface roughness measurement instrument (Surfcoder SE-2300, Kosaka Laboratory Ltd., Tokyo, Japan). The accuracy of this instrument is within ±3 % of the measured value, and its capacity is 0.001–100 lm. Crystal contents were evaluated using an X-ray diffractometer (RINT 2500 V, Rigaku Co., Tokyo, Japan). The measurement value of the monoclinic content and surface roughness was recorded as the average value of four measurements obtained by an expert observer with 10-year experience in assessing SEM findings. Statistical analysis was performed for the differences between groups using the unpaired Student’s t test and P \ 0.05 was considered significant.
Results To the naked eye, the retrieved heads appeared glossy (Fig. 1). In Fig. 1c, there was a severe, dark, metallicappearing smear on the surface of the head. For that head, we measured the part that was free of smearing. The monoclinic content of the retrieved heads was significantly greater than that of the unused head at any point on the surface. However, the increase in the mean values for surface roughness at any site on the retrieved heads was slight compared with that for the unused head, and it was not significant statistically (Table 2). SEM images of the retrieved heads and of the unused head showed a smooth,
Eur J Orthop Surg Traumatol
Fig. 1 Photographs showing the ball surfaces of six retrieval zirconia femoral heads. All except c are glossy
Table 2 Average surface roughness (Ra) and monoclinic content Site of measurement
Ra in lm (mean/SD)
% Monoclinic content (mean/SD)
Retrieved (n = 6)
Unused (n = 4)
P
Retrieved (n = 6)
Unused (n = 4)
P
Pole
0.006/0.002
0.004/0.006
0.3938
25.0/5.4
&0
\0.0001
5 mm above the equator
0.008/0.001
0.005/0.007
0.1995
31.8/4.9
&0
\0.0001
Equator
0.009/0.003
0.006/0.007
0.1619
34.7/3.4
&0
\0.0001
5 mm below the equator
0.008/0.001
0.005/0.005
0.1981
36.6/4.5
&0
\0.0001
Ra = the arithmetic mean of the absolute value of the measured profile height deviation as measured from the graphical center line
polished surface with small cracks or voids of \0.5 lm in diameter (Fig. 2).
Discussion The purpose of this study is to evaluate the changes in roughness and phase transformation observed in retrieved new-generation Y-TZP NGK heads, compared to a neverimplanted head. Despite the increase in surface roughness of retrieved zirconia heads with time in our study, the increase was relatively small. This might have been caused by a difference in the quality of zirconia used. Y-TZPs have problems not only in phase transformation but also related to the thermic conduction of Y-TZPs with a risk of increased temperature of PE. At this moment, most of the companies have stopped Y-TZPs. However, the PE wear rate against zirconia reported by Kim [15] in 2005 was low, and Kim et al. [16] suggested that the surface roughness of the ceramic head and an increased PE wear rate were associated with the presence of
embedded third-body metallic debris in the articulating PE liner. In fact, two of our six cases had third-body metallic debris. Imai et al. [17] suggested that there is a significant association between failure of the locking mechanism and linear PE wear in HGP cups. In our patient, we measured the surface roughness and monoclinic content in the part of the ball that was free of smearing, and we found that both the surface roughness and monoclinic content were the same as for the other retrieval head. In the reminder of aseptic loosening cases, we consider excessive PE wear caused by the failure of locking mechanism even though there was no obvious third-body metallic debris. Because of those findings, we suspect that new-generation Y-TZP NGK heads may not directly induce an increase in the PE wear rate, but the failure of the locking mechanism failure described by Imai et al. [17] or the presence of an embedded third body described by Kim [16] may influence the increase in PE wear. In a meta-analysis of THA with zirconia, Yoshitomi et al. [18] suggested that urgent cessation of zirconia-PE THA would not be justified, because the
123
Eur J Orthop Surg Traumatol
Fig. 2 At top left, a scanning electron microscopy (SEM) image (original magnification, 9500) of an unused (Un) specimen. a–c SEM images of the ball at the pole (a), at the equator (b), and at 5 mm below the equator (c) show almost identically smooth, polished
surfaces with some small voids of \0.5 lm. At bottom left, photograph (original magnification, 9500) of a retrieved zirconia head (Fig. 1a) indicating the pole (A), equator (B), and 5 mm below the equator (C)
zirconia supplied by some manufacturers seems to have clinical results equivalent to those of traditional materials. SEM analysis with high-power magnification in our retrieval study revealed some microscopic cracks or voids on the surface, but they were present when the heads were brand-new and had not extended by a mean point of 8.6 years after implantation (Fig. 3). THAs with highquality zirconia heads may have rates of prosthesis survivorship and PE wear equivalent to those of THAs with traditional materials, but heterogeneous quality among zirconia heads leads to poor prosthesis survivorship because of PE wear. At the front of the ball shown in Fig. 1c, there was a severe, dark, metallic-appearing smear. That ball was removed from a 62-year-old man
with osteoarthritis of the right hip joint; in 1998, he underwent THA that involved an HGP II cup. In 2006, we revised the patient’s liner and zirconia head because of liner breakage. Problems with the locking mechanism of the liner in this HGP II cup have been noted [19], and in our patient we found that the liner in the superolateral rim had a bucket-handle tear. This fact led us to think that both the locking mechanism failure and liner breakage caused the zirconia head to come into contact with the metal shell, leading to the dark metallic-appearing smear (Fig. 1c). Our study has several limitations. First, the surface characteristics and wear pattern of retrieved femoral heads at revision hip arthroplasty may not represent the surface characteristics of well-functioning total
123
Eur J Orthop Surg Traumatol
Fig. 3 Scanning electron microscopy images of one of the six retrieved zirconia heads at 9.7 years after implantation (a, b) and of the unused head (c, d). There were micropores not only in the retrieved heads but also in the unused head. The surface of the
retrieved head had no increase in roughness, but expansion of the micropores was apparent in comparison with the unused head. (a, c: original magnification 9500; b: original magnification 95,000; d: original magnification 97,000)
hip replacements. Additionally, the number of retrieved ceramic femoral heads that we examined was small and may affect our conclusions. However, we found no difference in Ra at any surface site between the retrieved heads and the unused zirconia head, although monoclinic content was increased at every site in the retrieved heads. In addition, SEM showed that the retrieved heads had a smooth polished surface, just like the unused head. In conclusion, our study shows that at an average of 8.6 years after prosthesis implantation, the surface roughness of zirconia femoral heads manufactured by NGK Spark Plug is as low as that of an unused head, whereas the surface monoclinic content continued to increase after implantation. Although a longer follow-up period is required for further confirmation, these results indicate that a reduction in wear may be possible if a suitable zirconia femoral head is selected.
patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.
Acknowledgments Medical editor Katharine O’Moore-Klopf, ELS (East Setauket, NY, USA) provided professional English-language editing of this article. Conflict of interest Each author certifies that he has no commercial associations (e.g., consultancies, stock ownership, equity interest,
Ethical standard Each author certifies that his institution approved the reporting of this case and that all investigations were conducted in conformity with ethical principles of research.
References 1. Fritsch E, Gleitz M (1996) Ceramic femoral head fractures in total hip arthroplasty. Clin Orthop Relat Res 328:129–136 2. Schu¨ller HM, Marti RK (1990) Ten-year socket wear in 66 arthroplasties: ceramic versus metal heads. Acta Orthop Scand 61:240–243 3. Zichner LP, Willert HG (1992) Comparison of alumina–polyethylene and metal–polyethylene in clinical trials. Clin Orthop Relat Res 282:86–94 4. Peiro´ A, Pardo J, Navarrete R, Rodriguez-Alonso L, Martos F (1991) Fracture of the ceramic head in total hip arthroplasty: report of two cases. J Arthroplast 6:371–374 5. Higuchi F, Shiba N, Inoue A, Wakebe I (1995) Fracture of an alumina ceramic head in total hip arthroplasty. J Arthroplast 10:851–854 6. Kumar P, Oka M, Ikeuchi K, Shimizu K et al (1991) Low wear rate of UHMWPE against zirconia ceramic (Y-PSZ) in comparison to alumina ceramic and SUS 316L alloy. J Biomed Mater Res 25:813–828
123
Eur J Orthop Surg Traumatol 7. Cales B (2000) Zirconia as a sliding material: histologic, laboratory, and clinical data. Clin Orthop Relat Res 379:94–112 8. Piconi C, Maccauro G (1999) Zirconia as a ceramic biomaterial. Biomaterials 20:1–25 9. Brown S, Green D, Pezzotti G, Donaldson T, Clarke I (2008) Possible triggers for phase transformation in zirconia hip balls. J Biomed Mater Res B Appl Biomater 85:444–452 10. Hernigou P, Bahrami T (2003) Zirconia and alumina ceramics in comparison with stainless-steel heads. Polyethylene wear after a minimum ten-year follow-up. J Bone Joint Surg Br 85:504–509 11. Haraguchi K, Sugano N, Nishii T, Miki H, Oka K, Yoshikawa H (2001) Phase transformation of a zirconia ceramic head after total hip arthroplasty. J Bone Joint Surg Br 83:996–1000 12. Fernandez-Fairen M, Blanco A, Murcia A, Sevilla P, Gil FJ (2007) Aging of retrieved zirconia femoral heads. Clin Orthop Relat Res 462:122–129 13. Kadar T, Dybvik E, Hallan G, Furnes O, Havelin LI (2012) Head material influences survival of a cemented total hip prosthesis in the Norwegian Arthroplasty Register. Clin Orthop Relat Res 470:3007–3013 14. Werle J, Goodman S, Schurman D, Lannin J (2002) Polyethylene liner dissociation in Harris-Galante acetabular components: a report of 7 cases. J Arthroplast 17:78–81
123
15. Kim YH (2005) Comparison of polyethylene wear associated with cobalt-chromium and zirconia heads after total hip replacement: a prospective, randomized study. J Bone Joint Surg Am 87:1769–1776 16. Kim YH, Ritchie A, Hardaker C (2005) Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear. J Bone Joint Surg Am 87:577–582 17. Imai H, Mashima N, Takahashi T, Yamamoto H (2009) The relationship between increased hip range of motion, wear, and locking mechanism failure in the Harris-Galante acetabular component. J Arthroplast 24:892–897 18. Yoshitomi H, Shikata S, Ito H, Nakayama T, Nakamura T (2009) Manufacturers affect clinical results of THA with zirconia heads: a systematic review. Clin Orthop Relat Res 467:2349–2355 19. Gonza´lez della Valle A, Ruzo PS, Li S, Pellicci P, Sculco TP, Salvati EA (2001) Dislodgment of polyethylene liners in first and second-generation Harris-Galante acetabular components: a report of eighteen cases. J Bone Joint Surg Am 83:553–559
