Total hip arthroplasty for primary osteoarthroses in younger patients in the Finnish arthroplasty register

Sir—Firstly, the Finnish Orthopaedic community should be complimented with this report of their experience with total hip arthroplasties in patients under 55 years. However, we would like to make some comments.

The report is based on 4,661 THAs performed in Finland in patients under 55 years of age with the diagnosis of primary osteoarthrosis. This is 45% of all THA implants in patients under 55, and the more difficult hips are thus excluded. From the report, it is clear that the market for young patients in Finland is dominated by uncemented implants nowadays; in 2000–2001, 81% of the stems and 88% of the cups were uncemented. The median follow-up time was 6.2 years. Considering this, the revision burden of 15% at that median follow-up time is relatively high. The reason may be that many less favorable implants have been performed in the past.

In the introduction, the authors adopt the criteria of the NICE (2003) report for a good long-term outcome of a hip prosthesis (< 90% survival rate of the whole implant at 10 years) and refer to some reports which claim to illustrate the excellent out-come of (non)cemented hips. However, the reports cited do not fulfill the criteria of the NICE report. Indeed, the reports cited suggest an excellent survival of one of the components of a noncemented hip implant. However, patients benefit from a total hip implant only if all the components of the implant survive at least 10 years. The survival rate of McLaughlin and Lee (2000) (44% at a mean of 10.2 years), Aldinger et al. 2003 (78% at 12 years), and Capello et al. (2003) (54% at 14 years) clearly do not fulfill the NICE criteria. Although the reports cited by Kim et al. (2002, 2003) approach a minimum of 10 years survival, they still do not have the minimum 10-year survival rate. The cited report of Jacobsen et al. (2003) has neither the minimal follow-up nor the required outcome (83% survival at 8 years). References to available reports of cemented hip implants in the literature that do fulfill the NICE criteria for at least the minimal 10-year follow-up are omitted.

When the authors compare the outcome for stem fixation (i.e. comparing cemented versus the noncemented concepts), they conclude that in the decade 1980–1990, survival of the noncemented stems was better than cemented stems. In the period 1990–2000, however, there was no difference in survival rates between noncemented stems and cemented stems at the endpoint “revisions of stem for any reason”. At this point in the discussion, the conclusions about cemented stems should have ended. However, the outcomes of the different types of noncemented stems are subsequently studied and compared to the overall group of cemented stems. This is not very realistic. Like noncemented stems, cemented stems have different outcomes (Swedish and Norwegian Hip Registers). The reason why the authors compared different types of noncemented stems with all cemented stems collected together in one group is unclear. Perhaps the number of different cemented stem designs was too small for comparison. Comparing the outcomes of the different types of noncemented stems individually should also be done with care; as is also concluded by the authors in the discussion, the mean FU of the different types of stems differs by a factor of 3 (FU HA-coated uncemented 3.4 years; ext. porous-coated 11 years).

Regarding cups, in the decade 1980–1990 the overall survival of cemented cups was better than that of noncemented cups, while between 1990 and 2000 the survival rates of cemented and non-cemented cups were comparable.

Based on this very informative report, the conclusion should therefore be that the outcome in young patients for both cemented and noncemented implants is still a problem, that the overall results of cemented versus noncemented stems in the last decade are comparable, that within the total group of noncemented stems, some designs have better outcomes than others, and that the outcome of modern noncemented cup designs is comparable to that of cemented all-polyethylene cups.

The most important information in this report is, however, lacking—and that is the overall survival, including any reoperation for any reason, of each type of implant in these young patients. Patients only benefit if all the components of an implant survive well. For example, in the Norwegian Register the Corail noncemented stem has an excellent survival rate of 15 years in young patients. Combined with a cup, it gave inferior results. Thus, looking at the overall survival of the total implant, the individual patient obtained no benefit from the stem and this is what really counts for the individual patient. The main question, therefore, is “has there been any combination of (non)cemented stems and (non)cemented cups implanted in patients which has a superior outcome and did this combination approach the requirements of the NICE criteria?” This would guide surgeons to use implants in young patients which really benefit them as individuals.