Bone-Implant Interface Biology ―― Foreign Body Reaction and Periprosthetic Osteolysis in Artificial Hip Joints――

Aseptic loosening and periprosthetic osteolysis are major problems in artificial hip joint surgery,for which a solution has yet to be found. Biological host response to wear debris combined with cyclic mechanical loading onto the bone bed around hip prosthetic implants has been considered as mechanism responsible for implant-mediated periprosthetic osteolysis. Any type of artificial joint gliding surface continuously produces wear debris,which are derived from implant materials,i.e.,ultra-high molecular weight polyethylene,ceramics and metals. Fragmented bone cement between the bone and implants is also a source of debris. Currently,generation of debris is still inevitable,although modern technology provides better biocompatible implants to lessen the debris. Debris induces foreign body reaction in periprosthetic connective tissues. The main loci are synovial regenerating capsular tissues and interface tissues between the bone and implants,where macrophages play an important role. Various cellular mediators and proteinases are produced in the process. The reaction affects periprosthetic bone remodeling and can provoke imbalanced bone metabolism around implants. It weakens the bone and causes periprosthetic osteolysis. In addition, the joint fluid, which is released from the inflamed connective tissues,has osteolytic potential. Pumping effect on gait and poor integration of bone-implant interface allow penetration of the fluid into intact interface,thus enhancing osteolytic reactions around implants. Further studies on interface biology and implant-related osteolysis with modern technique should lead to a better solution to provide longer survivorship of the artificial hip joint.