Introduction: There is little data available about numerical analysis of polyethylene particles from regions with different degrees of osteolysis in aseptic loosening of total hip replacements. Hence, it was the purpose of the present study to investigate, whether particles from large ostolitic lesions are different in size or shape to particles from regions with little or no osteolysis.

Methods: during hip revision surgery tissue samples from regions with maximal and minimal osteolysis at the stem and acetabulum were collected in five patients. The samples were examined histologically and numerically for each region. The polyethylene particles were isolated from one gram soft tissue by papain digestion and analyzed with a scanning electron microscope (SEM). Size, elongation, area, form factor and perimeter were calculated for a total of 6526 particles.

Results: The histological examination showed significantly more lymphocytes (p < 0,001), histiocytes (p < 0,01) und giant cells (p < 0,001) in large osteolitic lesions. The numerical SEM analysis also revealed significantly larger particles (p< 0,001) in regions with maximal osteolysis (Median acetabulum 1,44mmm und femur 1,89mmm) than in regions with minimal osteolysis (acetabulum 1,21mmm und femur 0,76mmm).

Discussion: Presently only the small micro particles were thought of importance for aseptic loosening. The present paper showed, that regions with large osteolitic lesions have not only more but also larger particles than small osteolitic lesions. The question arises whether the larger particles and giant cells may have an influence on the progression of osteolysis or not. Furthermore, periprosthetic tissue for wear particle analysis in revision surgery must be harvested from the same region in order to obtain conclusive results.