Structural and mechanical characterisation of the peri-prosthetic tissue surrounding loosened hip prostheses: An explorative study

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.