Second Letter to the Editor concerning ”Total hip arthroplasty for primary osteoarthrosis in younger patients in the Finnish arthroplasty register” by Eskelinen et al. and correspondence, Acta Orthop 2005; 76: 28-41, 604-607

Sir—We have read with great interest the comments of Drs. Eskelinen, Remes and Paavolainen on our Letter to the Editor.

Certainly, we agree with our colleagues that the reports by Capello et al. (2003), McLaughlin and Lee (2000), Aldinger et al. (2003) and Jacobsen et al. (2003) contain important information about uncemented hips. However, the authors agree with us that none of these reports have fulfilled the NICE criteria as was originally suggested in their paper.

We can accept the claim of the authors that the report by Kim et al. (2003) meets the NICE criteria; we already wrote in our previous letter that this paper approaches the minimum survival of 10 years, so we have no problem in accepting this as a paper on uncemented hips that meets the NICE criteria. Although there was no aseptic loosening of the components and a relatively low prevalence of osteolysis, the authors reported a high rate of linear wear of the polyethylene liner almost 10 years after surgery. It remains unclear if more revisions for this problem are pending in the coming years.

It was indeed remarkable that the report of McAuley et al. (2004) was not referred to in the original manuscript. Certainly, this report claims a survival rate of the THR of 89% at 10 years, with any reason as endpoint. Indeed, if liner exchange is excluded, the 10year survival of this uncemented THR is 95%. However, does this remark mean that the Finnish hip register does not consider a reoperation for liner exchange to be a hip revision, as is done in the Swedish and Norwegian hip registers? The report of McAuley et al. is also very important because this report shows us the longest published survival of uncemented hips in patients less than 50 years.

In our previous Letter to the Editor, we mentioned that all the published reports of cemented hip implants that fulfill the NICE criteria had been omitted from the original paper. We therefore have a major problem with the answer of Drs Eskelinen, Remes and Paavolainen on this issue, which suggests that only one report on cemented hips is available which fulfills the NICE criteria (Keener et al. 2003). Studies from hip registers do have a major influence on orthopedic practice, therefore these reports should be of the highest standard, with an adequate overview of the literature. Although we sincerely believe that they have reported this to the best of their knowledge, the truth is some-what different. We have found at least 8 studies on cemented hips in patients younger than 50 years and all of them have fulfilled the NICE criteria; many of them were already published some time ago (Boeree and Bannister 1993, Joshi et al. 1993, Devitt et al.1997, Emery et al. 1997, Kobayashi et al. 1997, Sochart et al. 1997a,b, Keener et al. 2003).

Long-term survival data in these reports on cemented hips (with revision for any reason as endpoint) are as follows: 60% after 30 years (Keener et al. 2003), 75% after 20 years (Joshi et al. 1993), again 75% after 20 years (Devitt et al. 1997) and 73% at 20 years (Sochart et al. 1997b). These long-term survival data of cemented hips are clearly superior to the longest report available of uncemented hips (McAuley et al. 2004), which has a survival rate at 15 years of 60% (endpoint: revision for any reason). After 10 years, there was a dramatic increase in liner problems and osteolysis. This problem of high wear of the liner was also reported in the only published study on uncemented hips that meets the NICE criteria (Kim et al. 2003).

In general, one should not be too optimistic about the survival of total hip implants, cemented or uncemented, in young patients. If concepts of hip implants inserted in young patients (less than 50 years old) are compared with the same implants in patients older than 70 years, the survival in the younger group is always less favorable. This is also shown by the data of the Norwegian and Swedish hip registers.

Certainly, one way of improving the outcome in younger patients is to choose the right implant. However, choosing the best combinations from the analyses of the Finnish register does not guarantee that young patients in Finland will indeed have the best outcome in future. First, concepts must be clinically proven over a period of at least 10 years, secondly ideal combinations may be less favorable in real clinical practice. In addition, both the Norwegian and Swedish hip registers and the study by McAuley et al. (2004) show that the results of uncemented hips deteriorate between 10 and 15 years after surgery. So, follow-ups even longer than 10 years are needed.

We are not “throwing away the baby with the bathwater”, as suggested. We also conclude that an uncemented stem with a cemented cup might perhaps offer young patients a better outcome. This so-called “reverse hybrid”combination is now popular in Norway. Time will tell us the outcome.

Indeed, we are looking forward with great interest to the analysis of results of THR designs (and combinations) in young patients from the Finnish arthroplasty register.