48. INCIDENCE OF ACETABULAR OSTEOLYSIS AFTER IMPLANTATION OF AN ATLAS® CUP: 217 PROSTHESES WITH MORE THAN 13 YEARS FOLLOW-UP

Abstract

Purpose of the study: Follow-up of patients with a total hip arthroplasty with an Atlas^® cup revealed unique acetabular osteolytic defects which remained asymptomatic for long periods. We thus conducted a systematic review.

Material and method: Our retrospective analysis included 217 Atlas^® elastic impactable cups implanted consecutively from January 1993 to June 1995 and reviewed clinically and radiographically at mean 13.1 years.

Results: The incidence of acetabular osteolysis was 16%, the leading cause of replacements which occurred on average 8.8 years after the initial implantation. The overall actuarial cup survival was 76% at 13.5 years and 81% taking revision for periprosthetic osteolysis as the endpoint. Univariate analysis found a significant link between osteolysis defects and significant wear (p< 0.0001), Devane activity 4 or 5 (p=0.0005), low thickness polyethylene (p=0.006), and use of Zircone or alumina heads versus metal heads (diameter 22). There was no statistical link between the presence or not of a hydroxyapatite coating, despite a trend for less osteolysis with hydroxyapatite coating. At multivariate analysis, the only factors significantly linked with the presence of osteolysis were significant wear and thin polyethylene insert in the metal back.

Discussion: Mid-term follow-up appeared sufficient to assess the development of osteolysis considering the delays describe by others. The incidence of osteolysis, despite the high incidence and early appearance in our series, was very probably underestimated by the radiographic analysis. These results suggest we should search for defects systematically with this type of implant, especially if there is measurable wear. Although it is difficult to set a cut off, a polyethylene thickness less than 10mm should be avoided to limit the high risk of osteolysis defects. A more powerful statistical analysis and examination of explants is advisable in order to ascertain the reasons for this abnormally high level of failure by osteolysis at 13 years follow-up.

Conclusion: Systematic radiological and clinical review of all patients demonstrated an insufficient overall actuarial survival and an important rate of periprosthetic osteolysis. The association between periprosthetic osteolysis and polyethylene were was confirmed. Thin inserts appear to play an important role in this osteolysis via an abnormal wear and poor tolerance to wear debris from these implants.