Osteoarthritis (OA) is associated with biochemical and mechanical processes that release different wear particles into the synovial fluid. Unfortunately, symptoms such as pain, swelling and limited range of motion often do not correlate with the level of OA as observed by X-ray. In addition, the mechanisms of OA and the processes involved are still not clearly understood. Therefore, there is much interest in developing new diagnostic techniques that would provide means to both sensitive, objective determination of joint damage and studying the underlying mechanisms. Such a technique may also aid in evaluating the efficiency of drugs under development objectively and relatively quickly.

Bio-ferrography (BF) is a method for magnetic isolation of target cells or particles in a fluid. The current project was aimed at evaluating the applicability of BF for isolation and analysis of specific wear particles in human joints. Synovial fluid aspirates were drawn during either arthroscopy or total joint replacement from 14 patients with either OA or other types of chondropathy. Target components of bone and cartilage (collagen type I and type II, respectively) were labeled with monoclonal antibodies coupled to magnetic beads. The captured particles were isolated on microscope slides by means of BF and characterized by several optical and scanning electron microscopy techniques combined with chemical analysis. The number, size and shape of particles were quantified by image analysis.

Results showed that specific labeling of target collagens enables capture of a much higher number of particles in comparison to previous reports. A variety of particles with different morphologies and sizes were documented. The number of captured particles changed in different patients. In addition to bone and cartilage fragments, particles of repaired cartilage that contained collagen I, meniscus particles containing collagens I and II, and magnesium-rich particles that could form during biochemical dissolution of hydroxyapatite or precipitation from body fluids, were identified. Further in-depth characterization of these particles would shade more light on the mechanisms and processes involved in joint degradation. The evaluation of joint damage by BF was found to correlate with clinical observations.

It was concluded that BF has the potential of becoming a powerful tool in the study of human joint diseases. Future studies may use even more specific labeling of joint components. BF may become a routine diagnostic technique, aiding the orthopedist in determination of OA level in an objective manner. The ability to draw samples quickly during arthroscopy with little discomfort to the patient could facilitate routine serial assessment of particular joints.