RADIOGRAPHIC-EVALUATED LINEAR WEAR AT 5 YEARS FOR CROSSLINKED VS CONVENTIONAL UHMWPE

Abstract

Aims: Crosslinked acetabular inserts have been introduced as a solution to the wear related periacetabular osteolysis, caused by the polyethylene wear debris. Laboratory tests and simulators have demonstrated that crosslinked-polyethylene has a higher resistance to wear than conventional polyethylene. However, studies have shown early crack or degeneration of crosslinked inserts. Concerns still remain about the clinical performances of crosslinked inserts. Although questionable, the roentgenographic measurement of the wear of the cup represents an indicator of the performance of the implant. Early catastrophic failures of other inserts taught us that for new materials it is mandatory to conduct an accurate clinical surveillance. In this work the radiographic-evaluated linear wear of a group of cross-linked inserts is compared to that of a non-crosslinked inserts for the same socket at 5 years.

Methods: From 2000 to 2002 we implanted a series of cups in which crosslinked and conventional acetabular inserts were placed randomly. Patients from each group underwent radiographic assessment after implantation, at 3 and 6 months and then yearly. Radiographs were obtained using a digitalized image system, which allowed a computerized bi-dimensional measurement by a specially developed Auto-CAD program. 12 healthy and active patients (6 crosslinke – 6 conevtional UHMWPE) have been selected for measurement.

Results: No macroscopic signs of loosening, mobilization and osteolysis were detected. Despite an increased wear rate for the conventional insert, no statistically sig-nificant differences of the linear wear were detected at five years for the two groups.

Conclusions: Longer follow-up and larger case studies are needed for more definitive conclusions. Nevertheless, this preliminary study shows that crosslinked polyethylene in vivo at 5 years does not give early failures and that its linear wear in the short term does not differ from that of a conventional polyethylene. Several other factors, such as the number and dimension of the debris, which are not detected by roentgenographic measurements, might be taken into consideration. Moreover it has been hypothesized for the crosslinked polyethylene an early plastic deformation, with consequent penetration of the head without wearing, which could affect the measurement on plan radiographs. Despite these limitations, roentgenographic measurements are quick and easy to perform, and therefore might be useful for the clinical practice of the periodical evaluation of the implants.