No abstract

This study examines the histological effects of different sizes of polyethylene particles implanted into the rabbit tibia. Seventeen mature New Zealand white female rabbits were allocated into three groups. Group 1 (5 rabbits) received polyethylene particles averaging approximately 16 microns in diameter, implanted into the right proximal tibia through a drill hole. Group 2 (5 animals) received particles averaging 26 microns, and Group 3 (7 rabbits) received particles averaging 67 microns. The left tibia was drilled but not implanted. Animals were sacrificed after 16 weeks. Histological analysis disclosed decreased hematopoietic activity within the left tibial drill hole. In all groups, the right tibia demonstrated positively birefringent polyethylene particles surrounded by, and within (smaller particles), histiocytes and giant cells in a fibrous tissue stroma. Statistical analysis disclosed more fibrocytes and less marrow cells at the interface of Group 3 (largest particles) compared to Group 1 and 2. Larger polyethylene particles, being less readily phagocytosed, appear to produce more fibrous encapsulation, compared to particles of a smaller size. The histological reaction stimulated by the different sizes of polyethylene particles resembled the membrane surrounding loose joint arthroplasties in humans.

No abstract

Twenty-eight mature New Zealand white female rabbits were allocated into 4 groups of 7 rabbits. Group 1 received a coiled wire of cobalt chrome alloy (Vitallium) (16 gauge x 1 cm). Group 2 received an equal weight of cobalt chrome particles averaging 15.4 microns in diameter. Group 3 received a coiled wire implant of commercially pure (C.P.) titanium (16 gauge x 1 cm). Group 4 received the same weight of C.P. titanium particles averaging 3.8 microns. The implants were placed through a drill hole in the proximal right tibia; the left tibia served as a prepared but nonimplanted control. The animals were killed after 16 weeks and quantitative histology was performed on undecalcified sections of the implant area. Bulk cobalt chrome and titanium implants were surrounded by a thin, incomplete, fibrous tissue layer with decreased numbers of cells. Trabeculae of bone were present within this connective tissue envelope. Fingerlike projections of bone enveloped the implant where it abutted endosteal bone. Clumped and loosely scattered cobalt chrome and titanium particles were surrounded by a minimal amount of fibrous connective tissue. Smaller particles were present within cells. Hematopoietic cells abutted the bulk or particulate implants directly. There was no evidence of acute or chronic inflammation or foreign body reaction. These results should be contrasted with those of Howie et al. in which intraarticular cobalt chrome particles stimulated a rapid proliferation of macrophages and synovial degeneration after 1 week. This may be due to a direct toxic effect of metals in an intra-articular environment, the smaller particle size used in that study, or to abrasive injury to the hyaline cartilage and subsequent synovitis. Our results underscore the general inert properties of these metals in the short term, when implanted into bone in the sizes and physical forms chosen.