During the process of aseptic loosening of prostheses, particulate wear debris induces a continuous inflammatory-like response resulting in the formation of a layer of fibrous peri-prosthetic tissue at the bone-prosthesis interface. The current treatment for loosening is revision surgery which is associated with a high-morbidity rate, especially in old patients. Therefore, less invasive alternatives are necessary. One approach could be to re-establish osseointegration of the prosthesis by inducing osteoblast differentiation in the peri-prosthetic tissue. Therefore, the aim of this study was to investigate the capacity of peri-prosthetic tissue cells to differentiate into the osteoblast lineage. Cells isolated from peri-prosthetic tissue samples (n = 22)−obtained during revision surgeries−were cultured under normal and several osteogenic culture conditions. Osteogenic differentiation was assessed by measurement of Alkaline Phosphatse (ALP), mineralization of the matrix and expression of several osteogenic genes. Cells cultured in osteogenic medium showed a significant increase in ALP staining (p = 0.024), mineralization of the matrix (p < 0.001) and ALP gene expression (p = 0.014) compared to normal culture medium. Addition of bone morphogenetic proteins (BMPs), a specific GSK3β inhibitor (GIN) or a combination of BMP and GIN to osteogenic medium could not increase ALP staining, mineralization, and ALP gene expression. In one donor, addition of GIN was required to induce mineralization of the matrix. Overall, we observed a high-inter-donor variability in response to osteogenic stimuli. In conclusion, peri-prosthetic tissue cells, cultured under osteogenic conditions, can produce alkaline phosphatase and mineralized matrix, and therefore show characteristics of differentiation into the osteoblastic lineage.

Very little is known about the structure and properties of peri-prosthetic fibrous tissue that is found around loose orthopaedic implants. We describe a method for characterizing the structural organisation (histology, confocal microscopy) as well as the nano- and micro-scale mechanical behaviour (atomic force microscopy, nanoindentation) of peri-prosthetic fibrous tissue. The tissue was collected from 11 patients undergoing revision surgery due to aseptic loosening. Sirius Red and Movat histological staining procedures indicated that the tissue mainly consists of collagen fibres and ground substance. However, large inter- and intra-patient variations in the relative proportions of these tissue components were found, as well as in collagen fibre orientation and possibly also maturation. The nano-scale Young's moduli ranged from 0-950 kPa, but showed large inter-patient variability. When the results per sample were presented in a probability density function, we could roughly discriminate one peak in the 0-100 kPa range and/or one peak in the 100-500 Pa range. These nano-scale moduli seem to respectively present the mechanical properties of glycosaminoglycan (GAG) and collagen molecules. The majority of the micro-scale Young's moduli ranged between 0.5 and 2.0 kPa for all samples. This explorative study provides new insights in (the variations of) structural organisation and mechanical properties of peri-prosthetic tissue.