Letter to the Editor

Abstract

We read with interest the article by Crawford et al [1Crawford R. Ranawat C.S. Rothman R.H. Metal on metal: is it worth the risk?.J Arthroplaty. 2010; 25: 1Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar] entitled “Metal on Metal: Is It Worth the Risk?” This article addressed the potential advantages or disadvantages of metal-on-metal bearing use.Although we acknowledge the wear as an inevitable consequence of total joint arthroplasty (even with hard-on-hard bearings), we would be interested in the authors' comments regarding the following issues:The authors stated than “the Australian National Joint Registry [2AOA Australian Orthopaedic Association National Joint Replacement Registry annual report. AOA, Adelaide2008Google Scholar] in 2008 showed that the bearing surface with the highest risk of revision was metal-on-metal.” However, it is not the firm conclusion of this registry [2AOA Australian Orthopaedic Association National Joint Replacement Registry annual report. AOA, Adelaide2008Google Scholar]. In fact, for hip arthroplasty performed with a diameter of 28 mm or less, the revision rate per 100, observed in a Table entitled “Primary Conventional Total Hip Replacement Requiring Revision by Bearing Surface and Femoral Component Head Size (Primary Diagnosis OA Excluding Infection),” was 0.8 for ceramic-on-ceramic bearing, 0.7 for ceramic-on-polyethylene, and 0.6 for metal-on-metal or metal-on-polyethylene bearing. For ceramic-on-ceramic and ceramic-on-polyethylene, these rates are statistically higher in comparison with metal-on-polyethylene (P ≤ .001). On the other hand, metal-on-metal revision rate is lower than ceramic-on-ceramic and/or ceramic-on-polyethylene bearings and do not show any significant difference with the other best bearing that is the metal-on-polyethylene (P = .350) (Table HT27 and figure HT22).Authors quoted studies from Park et al [3Park Y.S. Moon Y.W. Lim S.J. et al.Early osteolysis following second-generation metal-on-metal hip replacement.J Bone Joint Surg Am. 2005; 87: 1515Crossref PubMed Scopus (274) Google Scholar] and Korovessis et al [4Korovessis P. Petsinis G. Repanti M. et al.Metallosis after contemporary metal-on-metal total hip arthroplasty. Five to nine year follow-up.J Bone Joint Surg Am. 2006; 88: 1183Crossref PubMed Scopus (316) Google Scholar] that reported a high rate of osteolysis. However, for these 2 studies, the incriminated bearings (Ultima; DePuy [Leeds, UK], and Sikomet; Endoplus [Swindon, UK]) are henceforth removed from the present orthopedic market. The results from these series were bad because of poor tribological properties and low carbon content (low carbon is less wear resistant than those with higher carbon content). It seems inappropriate to generalize these poor results to other metal-on-metal bearings (with appropriate tribological properties: wrought metal, high carbon rate, adjusted clearance…) that have shown excellent long-term results [5Migaud H. Jobin A. Chantelot C. et al.Cementless metal-on-metal hip arthroplasty in patients less than 50 years of age: comparison with a matched control group using ceramic-on-polyethylene after a minimum 5-year follow-up.J Arthroplaty. 2004; 19: 23PubMed Scopus (100) Google Scholar, 6Delaunay C.P. Bonnomet F. Clavert P. et al.THA using metal-on-metal articulation in active patients younger than 50 years.Clin Orthop Relat Res. 2008; 466: 340Crossref PubMed Scopus (82) Google Scholar, 7Jacobsson S.A. Djerf K. Wahlstrom O. Twenty-year results of McKee-Farrar versus Charnley prosthesis.Clin Orthop. 1996; 329: S60Crossref PubMed Scopus (150) Google Scholar]. Other bad innovations such as the Hylamer polyethylene (with a new sterilization mode) led to catastrophic results without incriminating the “polyethylene concept” itself [8Norton M.R. Yarlagadda R. Anderson G. Catastrophic failure of the Elite Plus total hip replacement, with a Hylamer acetabulum and Zirconia ceramic femoral head.J Bone Joint Surg Br. 2002; 84: 631Crossref PubMed Scopus (68) Google Scholar].The frequency of pseudotumors after metal-on-metal implants has to be put in perspective and properly discussed. This frequency is infinitely more important for large diameter heads compare to small diameters (28 or 32 mm). To the author knowledge, there is only one case report in the literature of pseudotumor after insertion of a 28-mm metal-on-metal head. It was limited to an intrapelvic cystic lesion with groin swelling due to reaction to metallic debris without signs of osteolysis or bony destruction [9Gruber F.W. Bock A. Trattnig S. et al.Cystic lesion of the groin due to metallosis: a rare long-term complication of metal-on-metal total hip arthroplasty.J Arthroplaty. 2007; 22: 923Abstract Full Text Full Text PDF PubMed Scopus (80) Google Scholar].The authors seem to imply that the risk of cancer is increased after a metal-on-metal arthroplasty. To date, there is no study reporting increased carcinogenic risk after implantation of a metal-on-metal prosthesis compared to those with metal-on-polyethylene hip prostheses or the general population [10Visuri T. Pukkala E. Paavolainen P. et al.Cancer risk after metal on metal and polyethylene on metal total hip arthroplasty.Clin Orthop Relat Res. 1996; 329: 280Crossref Scopus (239) Google Scholar, 11Tharani R. Dorey F.J. Schmalzried T.P. The risk of cancer following total hip or knee arthroplasty.J Bone Joint Surg Am. 2001; 83: 774PubMed Google Scholar]. Moreover, it seems necessary to specify that all metal implants release metal ions secondary to corrosion. Metallic ions levels due to corrosion after total knee arthroplasty present similar metallic ions levels than after metal-on-metal hip arthroplasty [12Luetzner J. Krummenauer F. Lengel A.M. et al.Serum metal ion exposure after total knee arthroplasty.Clin Orthop Relat Res. 2007; 461: 136PubMed Google Scholar].Authors underline that chromosome aberrations have been reported in peripheral blood in patients with metal-on-metal total hip arthroplasties [13Ladon D. Doherty A. Newson R. et al.Changes in metal levels and chromosome aberrations in the peripheral blood of patients after metal-on-metal hip arthroplasty.J Arthroplaty. 2004; 19: 78Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar]. Interestingly, the same research team also demonstrated the presence of chromosome aberrations in whole blood of patients after ceramic-on-ceramic hip arthroplasty [14Ladon D. Bhamra M. Turner J. et al.Changes in chromosome aberrations and metal levels in the peripheral blood of patients after ceramic-on-ceramic hip replacement.in: 51st Annual Meeting of the Orthopaedic Research Society. 2005Google Scholar]. For theses authors, the pattern and level of chromosomal changes (aneuploidy and translocations) seems to be similar with those observed after metal-on-metal prosthesis [14Ladon D. Bhamra M. Turner J. et al.Changes in chromosome aberrations and metal levels in the peripheral blood of patients after ceramic-on-ceramic hip replacement.in: 51st Annual Meeting of the Orthopaedic Research Society. 2005Google Scholar]. They hypothesized that “the increase of chromosome aberrations may have been caused either by the stem of the prosthesis inserted into the bone marrow, by a small particle effect or by some nonspecific effect of surgery.”We feel that the authors' conclusion that their analyses provide a baseline for comparison with other bearings is not justified. For example, metal-on-metal bearing is to date the only hard-on-hard bearing that can be cemented in reconstruction procedure and could be a suitable option for young and active patients [15Girard J. Combes A. Herent S. et al.Metal-on-metal cups cemented into reinforcement rings: a possible new acetabular reconstruction procedure for young and active patients.J Arthroplasty. 2009; (Dec 17 [Epub ahead of print])PubMed Google Scholar]. We read with interest the article by Crawford et al [1Crawford R. Ranawat C.S. Rothman R.H. Metal on metal: is it worth the risk?.J Arthroplaty. 2010; 25: 1Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar] entitled “Metal on Metal: Is It Worth the Risk?” This article addressed the potential advantages or disadvantages of metal-on-metal bearing use. Although we acknowledge the wear as an inevitable consequence of total joint arthroplasty (even with hard-on-hard bearings), we would be interested in the authors' comments regarding the following issues: The authors stated than “the Australian National Joint Registry [2AOA Australian Orthopaedic Association National Joint Replacement Registry annual report. AOA, Adelaide2008Google Scholar] in 2008 showed that the bearing surface with the highest risk of revision was metal-on-metal.” However, it is not the firm conclusion of this registry [2AOA Australian Orthopaedic Association National Joint Replacement Registry annual report. AOA, Adelaide2008Google Scholar]. In fact, for hip arthroplasty performed with a diameter of 28 mm or less, the revision rate per 100, observed in a Table entitled “Primary Conventional Total Hip Replacement Requiring Revision by Bearing Surface and Femoral Component Head Size (Primary Diagnosis OA Excluding Infection),” was 0.8 for ceramic-on-ceramic bearing, 0.7 for ceramic-on-polyethylene, and 0.6 for metal-on-metal or metal-on-polyethylene bearing. For ceramic-on-ceramic and ceramic-on-polyethylene, these rates are statistically higher in comparison with metal-on-polyethylene (P ≤ .001). On the other hand, metal-on-metal revision rate is lower than ceramic-on-ceramic and/or ceramic-on-polyethylene bearings and do not show any significant difference with the other best bearing that is the metal-on-polyethylene (P = .350) (Table HT27 and figure HT22). Authors quoted studies from Park et al [3Park Y.S. Moon Y.W. Lim S.J. et al.Early osteolysis following second-generation metal-on-metal hip replacement.J Bone Joint Surg Am. 2005; 87: 1515Crossref PubMed Scopus (274) Google Scholar] and Korovessis et al [4Korovessis P. Petsinis G. Repanti M. et al.Metallosis after contemporary metal-on-metal total hip arthroplasty. Five to nine year follow-up.J Bone Joint Surg Am. 2006; 88: 1183Crossref PubMed Scopus (316) Google Scholar] that reported a high rate of osteolysis. However, for these 2 studies, the incriminated bearings (Ultima; DePuy [Leeds, UK], and Sikomet; Endoplus [Swindon, UK]) are henceforth removed from the present orthopedic market. The results from these series were bad because of poor tribological properties and low carbon content (low carbon is less wear resistant than those with higher carbon content). It seems inappropriate to generalize these poor results to other metal-on-metal bearings (with appropriate tribological properties: wrought metal, high carbon rate, adjusted clearance…) that have shown excellent long-term results [5Migaud H. Jobin A. Chantelot C. et al.Cementless metal-on-metal hip arthroplasty in patients less than 50 years of age: comparison with a matched control group using ceramic-on-polyethylene after a minimum 5-year follow-up.J Arthroplaty. 2004; 19: 23PubMed Scopus (100) Google Scholar, 6Delaunay C.P. Bonnomet F. Clavert P. et al.THA using metal-on-metal articulation in active patients younger than 50 years.Clin Orthop Relat Res. 2008; 466: 340Crossref PubMed Scopus (82) Google Scholar, 7Jacobsson S.A. Djerf K. Wahlstrom O. Twenty-year results of McKee-Farrar versus Charnley prosthesis.Clin Orthop. 1996; 329: S60Crossref PubMed Scopus (150) Google Scholar]. Other bad innovations such as the Hylamer polyethylene (with a new sterilization mode) led to catastrophic results without incriminating the “polyethylene concept” itself [8Norton M.R. Yarlagadda R. Anderson G. Catastrophic failure of the Elite Plus total hip replacement, with a Hylamer acetabulum and Zirconia ceramic femoral head.J Bone Joint Surg Br. 2002; 84: 631Crossref PubMed Scopus (68) Google Scholar]. The frequency of pseudotumors after metal-on-metal implants has to be put in perspective and properly discussed. This frequency is infinitely more important for large diameter heads compare to small diameters (28 or 32 mm). To the author knowledge, there is only one case report in the literature of pseudotumor after insertion of a 28-mm metal-on-metal head. It was limited to an intrapelvic cystic lesion with groin swelling due to reaction to metallic debris without signs of osteolysis or bony destruction [9Gruber F.W. Bock A. Trattnig S. et al.Cystic lesion of the groin due to metallosis: a rare long-term complication of metal-on-metal total hip arthroplasty.J Arthroplaty. 2007; 22: 923Abstract Full Text Full Text PDF PubMed Scopus (80) Google Scholar]. The authors seem to imply that the risk of cancer is increased after a metal-on-metal arthroplasty. To date, there is no study reporting increased carcinogenic risk after implantation of a metal-on-metal prosthesis compared to those with metal-on-polyethylene hip prostheses or the general population [10Visuri T. Pukkala E. Paavolainen P. et al.Cancer risk after metal on metal and polyethylene on metal total hip arthroplasty.Clin Orthop Relat Res. 1996; 329: 280Crossref Scopus (239) Google Scholar, 11Tharani R. Dorey F.J. Schmalzried T.P. The risk of cancer following total hip or knee arthroplasty.J Bone Joint Surg Am. 2001; 83: 774PubMed Google Scholar]. Moreover, it seems necessary to specify that all metal implants release metal ions secondary to corrosion. Metallic ions levels due to corrosion after total knee arthroplasty present similar metallic ions levels than after metal-on-metal hip arthroplasty [12Luetzner J. Krummenauer F. Lengel A.M. et al.Serum metal ion exposure after total knee arthroplasty.Clin Orthop Relat Res. 2007; 461: 136PubMed Google Scholar]. Authors underline that chromosome aberrations have been reported in peripheral blood in patients with metal-on-metal total hip arthroplasties [13Ladon D. Doherty A. Newson R. et al.Changes in metal levels and chromosome aberrations in the peripheral blood of patients after metal-on-metal hip arthroplasty.J Arthroplaty. 2004; 19: 78Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar]. Interestingly, the same research team also demonstrated the presence of chromosome aberrations in whole blood of patients after ceramic-on-ceramic hip arthroplasty [14Ladon D. Bhamra M. Turner J. et al.Changes in chromosome aberrations and metal levels in the peripheral blood of patients after ceramic-on-ceramic hip replacement.in: 51st Annual Meeting of the Orthopaedic Research Society. 2005Google Scholar]. For theses authors, the pattern and level of chromosomal changes (aneuploidy and translocations) seems to be similar with those observed after metal-on-metal prosthesis [14Ladon D. Bhamra M. Turner J. et al.Changes in chromosome aberrations and metal levels in the peripheral blood of patients after ceramic-on-ceramic hip replacement.in: 51st Annual Meeting of the Orthopaedic Research Society. 2005Google Scholar]. They hypothesized that “the increase of chromosome aberrations may have been caused either by the stem of the prosthesis inserted into the bone marrow, by a small particle effect or by some nonspecific effect of surgery.” We feel that the authors' conclusion that their analyses provide a baseline for comparison with other bearings is not justified. For example, metal-on-metal bearing is to date the only hard-on-hard bearing that can be cemented in reconstruction procedure and could be a suitable option for young and active patients [15Girard J. Combes A. Herent S. et al.Metal-on-metal cups cemented into reinforcement rings: a possible new acetabular reconstruction procedure for young and active patients.J Arthroplasty. 2009; (Dec 17 [Epub ahead of print])PubMed Google Scholar].