Volumetric wear assessment of retrieved metal-on-metal hip prostheses and the impact of measurement uncertainty

• Published in: Wear 2012-01, Vol.274-275, p.212-219
• Main Authors: Bills, P.J., Racasan, R., Underwood, R.J., Cann, P., Skinner, J., Hart, A.J., Jiang, X., Blunt, L.
• Format: Article
• Language: English
• Subjects: Applied sciences; Assessments; Bearing; Biological and medical sciences; Biomedical materials; CMM; Diseases of the osteoarticular system. Orthopedic treatment; Exact sciences and technology; Fracture mechanics (crack, fatigue, damage...); Friction, wear, lubrication; Fundamental areas of phenomenology (including applications); Hip replacement; Machine components; Measurement uncertainty; Mechanical engineering. Machine design; Mechanical properties; Medical sciences; Physical properties; Physics; Polymer industry, paints, wood; Properties and testing; Prostheses; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Retrieved bearings; Solid mechanics; Structural and continuum mechanics; Surgical implants; Technology of polymers; Three dimensional; Uncertainty; Volumetric analysis; Wear; Wear measurement
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2011.08.030

► Comprehensive measurement method outlined based on current best practice. ► The effect of uncertainty of each part of the measurement process quantified. ► The method applied to the issue of wear of metal-on-metal retrieval bearings and issues discussed. ► Uncertainty found to be of a similar order to the wear measured if standard measurement method adopted. ► Problems with current standards identified and solutions presented. In hip replacement the use of hard bearing materials, which have been shown to have lower wear rates than traditional metal-UHMWPE couples, has been encouraged in an effort to extend component life-in-service. With a view to further extending this period of joint activity metal-on-metal hip resurfacings have been developed which allow for implantation into younger and more active patients. However, these bearings have recently been the subject of a MHRA device alert due to unexplained hip pain and reported soft tissue reactions and indeed are under investigation having been shown to exhibit high failure rates. This has highlighted the need for a traceable metrological approach to the quantification and characterization of in vivo wear as currently there is no standard dedicated to the measurement of such wear. This study is the first to develop a comprehensive method for measuring the wear geometry of retrieved bearings whilst also assessing and quantifying both the magnitude and effect of the three-dimensional measurement uncertainty on the measurement process as a whole. This study shows that the magnitude of the expanded measurement uncertainty is an important, and until now overlooked, factor and that a statement of uncertainty is vital in measuring retrieved components as a means of comparison between studies and as a measure of confidence in measurement data. Based on the results of this study, it is recommended that care be taken when performing wear measurements on retrieved bearings. Factors such as point pitch and scan line separation can have a great effect on the likely uncertainty of the obtained measurement result and indeed the uncertainty of the measurement can be of the same order as the wear being measured.