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Survivorship and Retrieval Analysis of Sikomet Metal-on-Metal Total Hip Replacements at a Mean of Seven Years
Ingrid Milošev, PhD1; Rihard Trebše, MD1; Simon Kovač, MD1; Andrej Cör, PhD2; Venčeslav Pišot, MD1
1 Orthopaedic Hospital Valdoltra, Jadranska c. 31, 6280 Ankaran, Slovenia. E-mail address for I. Milošev: ingrid.milosev@ijs.si. E-mail address for R. Trebše: rihard.trebse@ob-valdoltra.si. E-mail address for S. Kovac: simon.kovac@ob-valdoltra.si. E-mail address for V. Pišot: venceslav.pisot@ob-valdoltra.si
2 Faculty of Medicine, Institute of Histology and Embryology, University of Ljubljana, Korytkova 2, 1000 Ljubljana, Slovenia. E-mail address: andrej.coer@mf.uni-lj.si
View Disclosures and Other Information
Note: The work was supported by the Slovenian Research Agency through grants No. L3-6023 and P2-0148, and by Unior d.d. Zrece. The authors thank Mr. J. Fiser for roughness measurements and Dr. C. Rieker for CMM measurements.
In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from Plus Orthopedics AG, Rotkreuz, Switzerland. The work was also supported by the Slovenian Research Agency through grants No. L3-6023 and P2-0148, and by Unior d.d. Zrece. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Orthopaedic Hospital Valdoltra, Ankaran, Slovenia

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2006 Jun 01;88(6):1173-1182. doi: 10.2106/JBJS.E.00604
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Abstract

Background: Second-generation metal-on-metal total hip replacements were introduced in the early 1990s with the aim of eliminating polyethylene wear and the resulting complications of osteolysis and aseptic loosening. The goal of the present study was to evaluate the intermediate-term results in a series of patients who were managed with one of these implants.

Methods: Between 1994 and 2002, we performed 640 total hip replacements in 591 patients with use of a Bicon-Plus cementless threaded cup with a polyethylene liner housing a metal inlay made of Sikomet low-carbon cobalt-chromium-molybdenum alloy that articulates with a Sikomet metal femoral head. Clinical and radiographic evaluation was performed retrospectively at a mean of 7.1 years postoperatively. Histologic analysis was performed on specimens retrieved from seventeen hips that were revised, and wear measurements were made for six hips that were revised.

Results: Thirty-four hips (thirty-four patients) were revised because of infection (six hips), aseptic loosening (twenty-three hips), pain without loosening (two hips), or other reasons (three hips). The survival rate of the prosthesis as a whole at ten years, with revision for any reason as the end point, was 0.91 (95% confidence interval, 0.88 to 0.95). The survival rate of the cup was 0.94 (95% confidence interval, 0.90 to 0.97), and that of the stem was 0.96 (95% confidence interval, 0.94 to 0.98). Linear or expansile osteolysis, or both, was observed on the radiographs of sixteen (64%) of the twenty-five hips that were revised because of aseptic loosening and/or pain. Histological analysis of pericapsular tissue was performed for seventeen of the twenty-five hips that were revised because of aseptic loosening and/or pain. Thirteen of these seventeen hips demonstrated a hypersensitivity-like reaction with aseptic inflammatory changes accompanied by moderate to extensive diffuse and perivascular infiltration of lymphocytes. In the six retrieved specimens that were subjected to wear analysis, the main wear mode was abrasive wear. The mean cumulative linear wear for the bearing was 31.3 µm, and the mean annual wear rate was 6.3 µm/yr. The mean clearance was 87.6 µm.

Conclusions: After a mean duration of follow-up of seven years, aseptic loosening was the major reason for failure of Sikomet metal-on-metal prostheses. The histological findings and the prevalence of osteolysis suggest the possibility of a hypersensitivity-like immunological response to wear particles.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

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    References

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Ingrid Milosev, Ph.D.
    Posted on November 07, 2006
    Dr. Milosev et al. respond to Drs. Holloway and Zicat
    Orthopaedic Hospital Valdoltra,Ankaran, Slovenia

    We thank Dr. Holloway and Dr. Zicat for their interest regarding our paper on Sikomet metal-on-metal hip prosthesis(1). If we understand correctly, they would like us to comment on why we considered radiolucent lines as signs of developing osteolysis and not as a failure of ingrowth in an otherwise poorly performing prosthetic design.

    The Zweymüller threaded cup with polyethylene liner and tapered rectangular stem with metal or ceramic head is one of the most popular total hip replacements in continental Europe and among the best performing hip implants ever marketed(2-4). The grit blasted titanium surface of the cup is readily fixed to bone. In fact, one of its possible disadvantages is that it is extremely difficult to remove when necessary.

    The pathogenesis of radiolucencies of different morphologies is currently not yet fully understood and is a matter of debate. Despite indications that linear osteolysis tends to be a feature of cemented cups, as shown in the paper by Zicat et al.(5), we believe it is not a unique feature confined to them. In our series(1),linear radiolucent lines developed gradually, tended to be somewhat cuneiform in shape, and were not perfectly linear; thus their evolution was different from that of the linear osteolysis seen around a cemented cup, as described by Holloway and Zicat.

    We believe that the progressive radiolucent lines we identified in some hips can be attributed to the specific metal -on-metal bearing that we investigated, and represent the first stage in the cascade resulting in expanding osteolysis and loosening of the implant. Of interest, the same process resulting in loosening of two cups was also observed by Grübl et al. in the same prosthetic design but with conventional bearing(3).

    We agree that a radiographic analysis of the unrevised cases in our series is necessary and would contribute more data regarding the development and morphology of radiolucencies in metal-on-metal bearings. We are currently comparing two large cohorts of Zweymüller type hip replacements with either conventional or metal-on- metal bearings to find out if there are differences in the clinical and/or radiological outcomes.

    References:

    (1) I. Milošev, R. Trebše, S. Kovaè, A. Cör, V. Pišot. Survivorship and retrieval analysis of Sikomet metal-on-metal total hip replacements at a mean of seven years. J. Bone Joint Surg. Am. 2006; 88; 1173-1182.

    (2) A. Grübl, C. Chiari, M. Gruber, A. Kaider, F. Gottsauner-Wolf. Cementless total hip arthroplasty with a tapered, rectangular titanium stem and a threaded cup: a minimum ten-year follow-up. J. Bone Joint Surg. Am 2002; 84; 425-31.

    (3) A. Grübl, C. Chiari, A. Giurea, A. Kaider, M. Marker, H. Zehetgruber, F. Gottsauner-Wolf. Cementless total hip arthroplasty with the rectangular titanium Zweymüller stem: a concise follow-up, at a minimum of fifteen years, of a previous report. J. Bone Joint Surg. Am 2006; 88; 2210-15.

    (4) E. Garcia-Cimbrelo, A. Cruz-Pardos, R. Madero, M.Ortega-Andreu. Total hip arthroplasty with use of the cementless Zweymüller Alloclassic system. A ten to thirteen-year follow-up study. J. Bone Joint Surg. Am. 2003; 85; 296-303.

    (5) B. Zicat, CA Engh, E. Gokcen. Patterns of osteolysis around total hip components with and without cement. J. Bone Joint Surg. Am. 1995; 77; 432-9.

    Ian P. Holloway
    Posted on October 18, 2006
    Patterns of osteolysis with cementless cups
    Sydney Hip and Knee Surgeons

    To The Editor:

    We write regarding the recent article by Milosev et al. on the results of the Sikomet metal-on-metal hip prosthesis(1). The authors state that radiographic evidence of osteolysis was found in 16 of the 25 cups revised for pain and/or aseptic loosening. Of these 16, ten were classified as having radiographic evidence of linear osteolysis (two of these with additional expansile osteolysis). Radiographic data are only stated for the revised cases. There is no information on radiographic evidence of loosening or osteolysis in the unrevised hips.

    The acetabular component used in this series has a threaded titanium shell with no porous nor hydroxyapatite coated ingrowth surface. Previous reports of this type of shell with different liners has shown a rate of loosening of 7% in one series at a mean of 46 months(2) and the presence of radiolucent lines in one zone in 24% of patients in another(3).

    Linear osteolysis as defined by Zicat et al.(4) in their series of cemented and cementless cups was a feature which was described only in association with cemented acetabular components. Osteolysis in association with cementless cups tended to be of the expansile type which penetrated the subchondral bone.

    The so-called linear osteolysis in this series may be related to a failure of ingrowth where the threaded shell is separated from the subchondral bone by a gap akin to that found with cemented implants.

    The author(s) of this letter to the editor did not receive payment or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author(s) are affiliated or associated.

    References:

    1. Ingrid Milosev, Rihard Trebse, Simon Kovac, Andrej Cör, and Venceslav Pisot. Survivorship and Retrieval Analysis of Sikomet Metal-on- Metal Total Hip Replacements at a Mean of Seven Years. J Bone Joint Surg Am. 2006;88:1173-1182

    2. Garcia-Cimbrelo E, Cruz-Pardos A, Madero R, Ortega-Andreu M. Total hip arthroplasty with use of the cementless Zweymüller Alloclassic system. A ten to thirteen-year follow-up study.J Bone Joint Surg Am .2003; 85:296 - 303

    3. Grübl A, Chiari C, Gruber M, Kaider A, Gottsauner-Wolf F. Cementless total hip arthroplasty with a tapered, rectangular titanium stem and a threaded cup: a minimum ten-year follow-up.J Bone Joint Surg Am .2002; 84:425 -31

    4. Zicat B, Engh CA, Gokcen E. Patterns of osteolysis around total hip components inserted with and without cement.J Bone Joint Surg Am .1995; 77:432 -9

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