The interface between bone and artificial-joint implants consists of soft tissue. This tissue varies from fibrocartilage to loose fibrous tissue. Tissues that resemble those can be found in normal joints. Sixteen knees with unicompartmental knee prostheses, revised because of excessive wear of the tibial insert, were studied. Synovium, synovial fluid, cartilage, and bone from the nonreplaced compartment were studied with light microscopy. We found wear particles and reactions to those in all tissues except cartilage. In the subchondral bone, we found osteolytic-like processes undermining the cartilage peripherally. Our conclusion from these findings is that the histologic composition of the bone-implant interface might be an important factor regarding the reaction of the tissue to wear particles and, thus, component fixation. © 2004 Elsevier Inc. All rights reserved.