POLYETHYLENE WEAR MEASUREMENT IN TOTAL HIP ARTHROPLASTY: A COMPARISON OF FOUR COMPUTER ASSISTED TECHNIQUES.

Abstract

Introduction: Wear of the polyethylene (PE) acetabular component is widely regarded as the primary factor limiting the longevity of total hip arthroplasties (THA). To compare wear patterns of different polyethylene inserts computer assisted measurement techniques for in vivo polyethylene wear were developed. This study was performed to investigate which software out of four programs is most precise and easy to use in daily clinical practice.

Materials and Methods: 24 anteroposterior digital radiographs of patients with a THA (Stryker ABG-II with N2Vac and Duration PE inserts in metal backed cups) with an average of 8.0 years follow-up were measured twice by a blinded single observer for linear wear (head penetration) in a single image analysis. Four computer assisted wear measurement methods were compared, the commercially available Martell Hip Analysis suite 7.14 and Rogan Hyperview, a not yet available Rogan beta-version called View Pro-X and Roman v1.70, freely available software to download from the internet. While both Rogan software can read the DICOM format from the hospital image server, images had to be converted for Martell (greyscale TIFF only) and Roman (any format).

The annual wear rates were compared and intra-observer variability was calculated as the difference between both measurements (precision). The average time it takes to measure one image (without format conversions) was documented and practicality of daily clinical use was evaluated.

Results: The annual wear rates measured were (mean +/− SD): Martell=0.09+/−0.21,, Hyperview=0.14 +/−0.10, Pro-X=0.12+/−0.07 Roman=0.12 +/−0.06. Martell was the only method measured negative wear (7/24 cases).

The precision was (mean +/− SD): Martell = 1.74+/−1.53, Hyperview = 0.36 +/−0.92, Pro-X = 0.10+/−0.11 Roman = 0.08 +/−0.08.

The average measuring time per image was: Martell = 94s, Hyperview = 94s, Pro-X = 92s Roman = 158s.

Discussion: The Roman method is the most precise and easiest to use in daily practice, but takes the longest time to measure. The Rogan View Pro-X software is nearly as precise and easy to use but not on the market yet. It is an improvement over the Hyperview which looses precision by using a elliptical interpolation necessary for non-metal backed cups instead of circular interpolation which is more precise for metal backed cups. The Mar-tell method produced the intolerable low precision and in some cases “negative wear”. Only on large patient groups it may produce realistic average wear rates. We found out that the Martell edge detection method, originally developed for scanned analogue x-rays, functions inferiorly with digital images, the coming hospital standard. Image processing (smoothening) of the digital x-rays did increase accuracy and precision. We recommend the Roman software, a digital version of the Livermore method, for precision, ease of use and cost.