Fixation of orthopedic implants by bone ingrowth into porous surfaces is being investigated as an alternative to acrylic cement in total hip and knee arthroplasty. The long-term objectives of this project are to address three key issues in the use of metallic porous coatings for the tibial component in total knee arthroplasty: (1) the relationship between initial rigid body and tangential interface displacements and tissue ingrowth, (2) the mechanical correlates of the histology of the bone-implant interface and (3) long-term aspects of bone remodeling related to cementless total knee replacement. A total knee replacement model will be used in which the method of adjuvant fixation will be altered in order to vary the initial rigid body stability and pattern of tangential interface displacements. In the first of three experiments, physical measurements of the initial displacements will be correlated with histologic findings 1,6 and 24 months after surgery. In the second experiment, physical measurements of the interface displacements will be made after a six month period of implantation and correlated with the histology of the interface. In the third experiment, changes in the architecture and remodeling dynamics of the proximal tibia will be investigated as a function of the nature of the bone-implant interface at 1, 6 and 24 months. These experiments will (1) facilitate definition of the maximum amount of relative bone-implant micromotion compatible with bone ingrowth, (2) address the question of how much bone ingrowth is needed to ensure component stability and (3) determine how variation in the nature of the bone-implant interface affects bone remodeling in the proximal tibia.
