Despite all gain of knowledge, septic and aseptic loosening of endoprostheses still remain unsolved problems. In loosening of joint arthroplasty a periprosthetic membrane is found between the bone and the loosened implant. The characteristics of the membrane are influenced by the process that leads to the loosening of the endoprosthesis. The aim of the study was to introduce a classification system that enables a standardized diagnostic evaluation and helps to determine the aetiology of the loosening process.

Based on histomorphological criteria and polarized light microscopy, four types of periprosthetic membranes were defined: periprosthetic membranes of the wear particle type (type I), periprosthetic membranes of the infectious type (type II), periprosthetic membranes of the combined type (type III), and periprosthetic membranes of the indifferent type (type IV). Periprosthetic membranes of 268 patients were analyzed according to the defined criteria.

The interobserver reproducibility was sufficient (95%). The correlation between histopathological and microbiological diagnosis was high (89%, p< 0,001). The four types of periprosthetic membranes showed a significantly different time of revision.

This classification system enables a standardized diagnostic procedure. It therefore is a basis for further studies concerning the etiology and pathogenesis of prosthesis loosening. The reliability of this histomorphological examination in diagnosing infections is currently reviewed.