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Articles:
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 [Abstract] [Full text] [PDF]
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[Read Letter to the Editor] Dr. Milosev et al. respond to Drs. Holloway and Zicat
Ingrid Milosev, Ph.D., Rihard Trebse, M.D., Simon Kovac, M.D., Andrej Cor, Ph.D., Venceslav Pisot, M.D.   (8 November 2006)
[Read Letter to the Editor] Patterns of osteolysis with cementless cups
Ian P. Holloway, Bernie Zicat   (8 November 2006)

Dr. Milosev et al. respond to Drs. Holloway and Zicat 8 November 2006
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Ingrid Milosev, Ph.D.,
Senior Research Associate
Orthopaedic Hospital Valdoltra,Ankaran, Slovenia,
Rihard Trebse, M.D., Simon Kovac, M.D., Andrej Cor, Ph.D., Venceslav Pisot, M.D.

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Re: Dr. Milosev et al. respond to Drs. Holloway and Zicat

ingrid.milosev{at}ijs.si Ingrid Milosev, Ph.D., et al.

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.
Patterns of osteolysis with cementless cups 8 November 2006
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Ian P. Holloway,
Orthopaedic Surgeon
Sydney Hip and Knee Surgeons,
Bernie Zicat

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Re: Patterns of osteolysis with cementless cups

ianholloway{at}hotmail.com Ian P. Holloway, et al.

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