Bio-ferrography (BF) is a method for magnetic isolation of particles suspended in liquid on a glass slide. The objective of the current research was to evaluate the potential use of BF in determining the wear level of artificial hip and knee joints based on analysis of aspirated synovial fluids.

Synovial fluid aspirates and prosthesis compartments removed by revision surgery from 14 patients were analyzed. The synovial fluid was centrifuged to separate the wear particles from the hyaluronic acid. The failed prostheses were washed in the lab with either saline or distilled water to remove and capture unbound wear particles. An erbium chloride (ErCl₃) solution was added in some cases to induce increased magnetization. The wear particles were isolated by means of a Bio-Ferrograph 2100 system, and characterized by means of several optical and scanning electron microscopy techniques as well as energy dispersive spectroscopy. The number and size of particles were quantified by image analysis. The failed prostheses were also characterized in order to determine whether BF can monitor the wear of artificial joints.

Results showed that metallic (namely, Ti-, Co- and Fe-based alloys), polymeric (namely, UHMWPE, POM and PMMA) and bone particles could be isolated on slides by BF. The isolated particles exhibited a variety of shapes and surface morphologies that were dependent on the process by which they had been formed. No other technique allows retrieval and isolation of so many tiny particles, either metallic or non-metallic, while preserving their shape for microscopic examination and chemical analysis. A correlation existed between the level of prosthesis degradation, as inspected during failure analysis, and the number and size of isolated particles; namely, an increase in number and size of particles represented increased prosthesis wear. When the prosthesis was visually in good condition, very few small particles were retrieved from the synovial fluid. The formation of metal and bone particles in several cases accelerated further wear of these prostheses.

On the basis of the good correlation between the classification of damage by BF and the level of artificial joint degradation as evaluated during failure analysis, it was concluded that BF of synovial fluids may be used in the study of artificial joints failure. In addition to monitoring the level of wear, it allows determination of the mechanism and cause of failure, thus providing feedback on problems associated with design, manufacturing and installation of artificial joints. The ability to draw samples quickly during joint aspiration with little discomfort to the patient could facilitate periodic ferrographic evaluation of specific joints. Such information may also prove invaluable in the design of improved prostheses. In these cases, the atlas of wear particles that was constructed in this project for the first time may be used as a reference.