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MARKER-FREE AND AUTOMATED COMPUTER TOMOGRAPHY BASED SPATIAL ANALYSIS TOOL TO QUANTIFY HIP ARTHROPLASTY STEM MIGRATION. DEVELOPMENT AND VALIDATION This publication appears in: Hip International Authors: T. Scheerlinck, M. Polfliet, D. Rudi, G. Van Gompel, N. Buls, K. Van Royen and J. Vandemeulebroucke Publication Year: 2015
Abstract: Introduction: Accurate quantification of hip stem migration allows early detection of inferior implants and helps to diagnose stem loosening. Radiostereometric analysis (RSA) is accurate but requires bone markers and expensive stereo-radiographic equipment.Objectives: We developed and validated a marker-free automated ComputerTomography based Spatial Analysis tool (CTSA) to quantify stem-bone migrationin consecutive CT scans.Methods: We first segmented bone and stem within both three-dimensional images, then we pairwise registered these elements. By comparing the rigid transformations of stem and bone, we calculated stem migration compared to the bone and transferred the translation and rotation parameters to an anatomic coordinate system. Accuracy was assessed in a stembone model by calculating the difference between imposed and measured rotations and translations in 39 cases. Precision, defined as stem migration calculated in a zero-migration model, was assessed 8 experimental cases and in 5 patients.Results: The in-vitro accuracy of CTSA was below 0.20 mm for translations and 0.19° for rotations in all cases (95% tolerance interval (95% TI) below 0.22 mm and 0.20°, largest standard deviation of the signed error (SDSE) 0.081 mm and 0.057°). The in-vitro precision was below 0.05 mm and 0.08° in all cases (95% TI below 0.06 mm and 0.08°, largest SDSE 0.012 mm and 0.020°). The precision in five patients was below 0.48 mm and 0.37° (95% TI below 0.59 mm and 0.61°, largest SDSE 0.202 mm and 0.279°). However, this could be largely improved by optimizing scanning conditions. Conclusions: Our marker-free automated CT-based spatial analysis can detect hip stem migration with an accuracy and precision comparable to that of radiostereometric analysis (RSA), but without the burden of bone markers and the cost of stereo-radiographic equipment. As such, it could become a new standard to quantify of hip stem migration in an experimental setting but also in clinical practice.
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