Histochemical and cellular changes induced in the rabbit knee joint by an intraarticular implantation of a sheet of polyethylene.

Implantation of a sterile rigid sheet of polyethylene into the right patellofemoral rabbit joint caused changes that resemble those found in human osteoarthritis. Initial synovial proliferation resulted in the isolation of the implant. Marginal osteophytes developed from soft cellular tissue which later underwent chondrification and finally became ossified. Articular cartilage under the area in contact with the implant showed early cell necrosis and diffuse loss of metachromasia. Focal superficial fibrillation followed and later developed into deep erosions and bone exposure. The first clefts appeared tangentially to the surface within an acellular electron-dense material. In spite of numerous mitotic divisions of viable chondrocytes, mainly in clusters or clones, cell density progressively decreased in every layer of articular cartilage beneath the implant. The present study suggests that necrosis of chondrocytes, and the later failure of viable cells to respond adequately to the altered environment, can lead to cartilage fibrillation and then to more severe lesions.