Introduction and purpose: Highly cross-linked polyethylenes (HXLPE) sterilized in an air-free environment have been used to prevent osteolysis and loosening of implants. This prospective randomized study analyzes the results of a series in which one single type of prosthesis but made with one of two different kinds of polyethylene (PE) has been used.

Materials and methods: We assessed 45 Allofit cups with a Sulene-PE liner (sterilized in nitrogen) and 45 with Durasul-PE liner (highly cross-linked) associated with an Alloclassic stem (femoral head: 28 mm) with a minimum follow-up of 5 years (mean 66.3 months). Femoral head penetration was analyzed by means of a digital program at 6 weeks, and at 6 and 12 months and once a year, using the Dorr method given the non-spherical shape of the cups.

Results: All assessed hips had good outcomes determined clinically and by x-rays. There was no loosening of any component. There were no radiolucent lines or osteolysis. Femoral head penetration at 6 weeks was 47.4% less in the Durasul group (0.19+0.06 mm for the Sulene-PE and 0.09+0.03 for the Durasul-PE [p< 0.0001]). Mean annual penetration was 20% less in the Durasul group (0.04+0.02 and 0.008+0.008 [p< 0.0001] respectively. The differences increased by the third year. Mean penetration at 5 years was 39.1% less in the Durasul group (p< 0.0001).

Conclusions: There was significant femoral reduction in the Durasul-PE group. Long term results are necessary to confirm that these prostheses lead to a lower rate of osteolysis.

Introdution. Gamma sterilisation in air produces free radicals in the polyethylene (PE) with the result of degrading its mechanical properties, increasing wear and debris, and producing osteolysis and loosening. PE sterilized in the absence of air and high cross-linked polyethylene (HXLPE) have been used to avoid osteolysis and loosening. This prospective randomized study has assessed results in a series using two different poly-ethylenes associated with the same prosthetic design.

Methods: We assessed 45 Allofit cups with Sulene-PE liner (sterilized with nitrogen) and 45 Allofit cups with Durasul-PE liner (HXLPE), both associated with an Alloclassic stem (28-mm femoral head) (Zimmer). The minimum follow-up is 5 years and the mean follow-up 66.3 months. The linear femoral head penetration was estimated at 6 weeks, at 6 and 12 months and annually thereafter, using a software package employing the Dorr method, given the nonspherical cup shape.

Results All assessed hips had good clinical and radiographic results. There was no loosening of any prosthetic component. There were no radiolucent lines or osteolysis. Femoral head penetration in the early postoperative radiographs was 47.4% less in the Durasul group (0.09+0.03 mm) than the Selene-PE group (0.19+0.06 mm)(p< 0.0001). The mean yearly linear femoral head penetration was 20% lower in the Durasul group (0.008+0.008) than the Sulene-PE group (0.04+0.02)(p< 0.0001). Differences increase after the third year. Mean linear femoral head penetration at 5 years was 39.1% less in the Durasul group (p< 0.0001).

Conclusions: Although the digitized method used is not totally accurate and is used only for a general estimate, there is a significant reduction in yearly linear femoral head penetration with Durasul-PE. Longer-term results are needed to confirm that this polyethylene generates less osteolysis.

Introduction and purpose: This is a prospective analysis of the clinical and radiographical results of two different types of PE, both associated to the same kind of prosthesis (Zimmer-Centerpulse).

Materials and methods: A total of 101 Allofit shells were analyzed; 56 had Sulene-PE (nitrogen sterilized) and 45 had Durasul highly cross-linked PE, associated to an Alloclassic stem (femoral head: 28 mm). They were all implanted between 1999 and 2002. Mean follow-up was 29.4 months for Sulene-PE and 25.3 for Durasul-PE. PE wear was assessed by means of image digitalization with special software (AutoCAD 14R) after six weeks (initial settling or position zero), after 6 and 12 months and on a yearly basis.

Results: Three cases dislocated and were thus excluded from the study. There were no infections. All cases assessed had good clinical and radiological results. There were no instances of implant loosening. There were no radiolucent lines, osteolysis, cortical hyperthrophy or proximal osteopenia. On the initial radiograph (position zero), the distance between the axes of the femoral head and those of the shell was 0.30+0.094 mm for the Sulene-PE group and 0.20+0.074 for the Durasul-PE one (p=0.029). Mean wear, taking position zero as a reference point, was 0.1035+0.0686 and 0.0819+0.078 (p=0.108) respectively.

Conclusions: In spite of the higher error rates found in the wear measurements of the Allofit cup, a greater position zero was found in Sulene-PE than in Durasul-PE. Although mean wear was higher in Sulene-PE than in Duarsul-PE, the differences found were not significant 3 years postop.