Strain adaptive bone remodelling in total joint replacement

Histomorphologic analyses of artificial joint components implanted into bone need special technology for processing and for documentation; published histological work systematically done therefore is rare. The histopathology, three-dimensionally analyzed in a complete sequence of sections is, however, the only precise answer in terms of biocompatibility and bone response. A complete analysis allows a type-related predictable prognosis of an implantation that is at least comparable to a finite element analysis with respect to load transfer to host bone. The histopathologic collection of the ZOW Munich is comprised of more than 5000 nondemineralized bone and joint specimens and more than 500 artificial joint components implanted in the human skeleton for up to 25 years. Fifty-nine implant-bone specimens without signs of loosening already have been processed and analyzed systematically. According to the strain-adapted bone remodelling, different types of anchorage clearly were differentiated and their morphologic substrate could be worked out. Based on that, the cemented standard anchorage could be distinguished histologically from the cemented press-fit procedure, and the noncemented press-fit from the porous ingrowths pattern. In terms of the topography of the bony integration, the proximal and distal press-fit and ingrowth pattern were analyzed; beside that, the cemented and noncemented epiphyseal resurfacings could be defined histologically. In all histologic specimens the remodelling appeared as a result of stress-related strain, reflecting stiffness of the implant and the resistance of bone to deformation. It clearly was worked out that all success of cemented components is based on preserved cancellous bone honeycombs stiffened by bone cement, representing an adaptation of bone in terms of stiffness to the stiff implants.