DIGITAL EDGE-DETECTION MEASUREMENT OF POLYETHYLENE WEAR AFTER TOTAL HIP-ARTHROPLASTY

A novel digital edge-detection computer technique was developed to mea sure polyethylene wear after total hip arthroplasty. The new method ob jectively infers the margins of the component by evaluating gradients of gray-scale intensity on digitized images of the radiographs. Compar ed,vith previous methods for measurement of weal; digital edge detecti on substantially reduces observer subjectivity, The technique was vali dated directly by measuring wear artificially produced by spherical-fr ont milling of polyethylene liners in a benchtop series, Under such co nditions, digital edge detection proved 6.4 times more accurate and 7. 1 times more reproducible than manual measurement with conventional ci rcular 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 lon gterm wear (mean late rate of wear for the cohort, 0.087 millimeter pe r year at a mean of 118 months after the operation) on the basis of me asurements 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 RELEVANCE: Polyethylene wear is a major factor affecting the longevity of a total hip prosthesis. As ten to twenty-year results become avail able for a variety of bearing surfaces and designs of acetabular compo nents, problems with acetabular wear and loosening have been substanti al in too many instances, New techniques for more accurate and reprodu cible 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 construct s or designs.