Digital Edge-Detection Measurement of Polyethylene Wear after Total Hip Arthroplasty*

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A novel digital edge-detection computer technique was developed to measure polyethylene wear after total hip arthroplasty. The new method objectively infers the margins of the component by evaluating gradients of gray-scale intensity on digitized images of the radiographs. Compared with previous methods for measurement of wear, digital edge detection substantially reduces observer subjectivity. The technique was validated directly by measuring wear artificially produced by spherical-front milling of polyethylene liners in a benchtop series. Under such conditions, digital edge detection proved 6.4 times more accurate and 7.1 times more reproducible than manual measurement with conventional circular templates.In addition, clinical application of the new digital imaging technique was illustrated in a series of forty-three patients in whom a metal-backed acetabular cup had been inserted with cement. A random-coefficients prediction algorithm was invoked to estimate long-term wear (mean late rate of wear for the cohort, 0.087 millimeter per year at a mean of 118 months after the operation) on the basis of measurements of short-term wear (mean early rate of wear for the cohort, 0.154 millimeter per year at a mean of twenty-four months).Clinical RelevancePolyethylene wear is a major factor affecting the longevity of a total hip prosthesis. As ten to twenty-year results become available for a variety of bearing surfaces and designs of acetabular components, problems with acetabular wear and loosening have been substantial in too many instances. New techniques for more accurate and reproducible measurement of polyethylene wear should allow earlier detection of deleteriously increased wear and thus permit earlier identification of patients who are at risk and of potentially unacceptable constructs or designs.

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