Characterization and Comparison of Wear Debris from Failed Total Hip Implants of Different Types*

Abstract

Particles of wear debris have been associated with loosening of implants and with osteolysis, but few studies have examined the relationship between characteristics of the implant and clinical variables and the concentration of particles isolated from periarticular tissues. We isolated and quantified particles of wear debris from orthopaedic implants in 123 tissue samples that had been obtained adjacent to a failed total hip prosthesis from eighty-eight patients. The concentration of these particles in the tissue and the size of the particles were then analyzed in relation to patient and implant-related variables. The number of particles ranged from 8.5 x 10⁸ to 5.7 x 10¹¹ per gram of tissue (dry weight). More particles were found adjacent to failed titanium-alloy stems that had a cobalt-chromium-alloy modular head and failed titanium-alloy-backed cups than were found adjacent to all-cobalt-chromium-alloy prostheses. In addition, fewer particles were found adjacent to implants with a twenty-eight-millimeter femoral head than were found adjacent to implants with other femoral head sizes. Univariate analysis also showed correlations between a high concentration of particles and fixation without cement, an implant that had been in situ for a long duration, a young patient age, and an initial clinical diagnosis of avascular necrosis. Biopsy specimens from the proximal femoral membranes had higher concentrations than those from the joint capsules or the acetabular membranes. Although only five specimens were obtained directly from osteolytic lesions, the concentration of particles in those specimens was higher than that in biopsy specimens from other sites. Although many univariate correlations were identified, stepwise correlation regression analysis showed that the composition of the implant and the size of the modular femoral head were most strongly related to the concentration of debris in tissue.CLINICAL RELEVANCE: The results of this study show that most failed hip implants are associated with billions of debris particles and that the concentration of these particles in tissue is related to several factors that are thought to be associated with the extent of implant wear. There are probably many factors that influence the production of orthopaedic wear debris. Some are related to the design of the implant. Others, such as the level of activity, are related to the patient. Of the variables tested in this study, the composition of the implant and the size of the modular head appeared to be most closely linked with the production of particles. Our results do not necessarily reflect the extent of debris production by stable implants, but they suggest that the metallic composition of the femoral stem, the acetabular cup, and the modular head may have an important influence on the amount of wear debris.