IN VIVO MIGRATION OF POLYETHYLENE PARTICLES AROUND NON-DISPLACED CEMENTED TOTAL HIP PROSTHESES: A THREE-PIECE AUTOPSY STUDY

Purpose: The purpose of this work was to demonstrate the presence of polyethylene particles at the fixation interfaces of the femoral and acetabular components of non-dislocated cemented hip prostheses that had functioned in vivo for several years. Material and methods: Three femoral components and two acetabular cups were recovered in two patients who died from an intercurrent cause. The first patient, an 85-year-old woman, had had a hip prosthesis for eight years. There was no radiological sign of displacement nor cup wear (stainless steel /polyethylene cup). For this same patient, the other hip had be revised for acetabular loosening three months prior to death. The femoral component was not loosened; it had been removed with its cement then reimplanted within the same cement sheath that was not removed. The cement/bone interface was thus preserved at eight years. In the second patient, a woman aged 88 years, the delay was nine years. This patient had no radiographic sign of loosening. The polyethylene acetabular insert exhibited 1 mm linear wear. This was a ceramic /polyethylene cup. The specimens were prepared by decalcification and defatting then fixation in buffered formol (pH 7.2) before embedding in polymethyl-metacrylate. After hardening, a diamond-tipped diatome to obtain transverse section of the femur at four levels: lesser trochanter, 2 cm below the lesser trochanter, 1 cm above the tip of the stem, 1 cm below the distal tip of the stem. After polishing, the 50 μ thick sections were stained with Picrofuschin von Jienson. The polyethylene acetabular cups were prepared likewise. Polyethylene particles were counted under polarised optic microscope at each cement /implant and cement /bone interface using an image analyser (Histolab, microvision instruments, Evry, France). Results: There was no evidence of a fibrous membrane between the bone and the cement. A 10 to 20 mm space was sometimes observed at the metal /cement interface. Polyethylene particles measuring 3 to 10 μm were found at both cement /bone and metal /cement interfaces, including at the distal femur level. Particles were observed in the cement at several sites. Conclusion: Large-sized polyethylene particles migrate around non-displaced cemented implants, partidularly between bone lines, and can follow the cement poriosity.