## 1 Introduction
Within a 7-year follow-up clinical trial, the in vivo total wear data for vitamin E-diffused highly crosslinked polyethylene was reported to be 0.03 mm (SD 0.25), which was lower in comparison to a moderately crosslinked polyethylene of 0.04 mm (SD 0.29) [12]. Consequently, this means that the radiological methods mentioned above must have a sufficiently high resolution to measure beyond these values. With regard to the aforementioned dimensions of PE wear to be determined, it becomes clear in which resolution range the applied measuring methods must be able to work. It should be mentioned that the biological reaction to wear particle size and their quantity with different PE configurations is not the subject of this paper. 2D\({}_{\text{wear}}\) measurements based on conventional a.p. radiographs of the hip prosthesis are common in clinical routines since these radiographs are available at any hospital without the need for additional specialized equipment. However, these approaches yield only a 2D characterisation of the present wear and demonstrate less sensitivity to radiographic projection differences [16]. According to the sensitivity and the resulting radiographic projection differences, [PERSON] et al. [17] reported that the accuracy of wear results varied with acetabular component angulations. It could be stated, thus, that the greater the change of acetabular component angulations within the images, the larger the magnitude of wear measured. A general problem and limitation within a 2D\({}_{\text{wear}}\) approach is the detection of wear which occurs out of the image plane of the a.p. radiographs [18]. [PERSON] et al. [19] compared clinical hip wear data in 13 patients with THA 3 years after surgery using 4 different radiological methods: (i) RSA, (ii) the Scheier-Sandel method, (iii) the Charnley-Duo method and (iv) \"Ein-Bild-Roentgenanalyse (EBRA)\". Mean (SD)measurement error for EBRA was, in the worst case, 0.11 mm (\(\pm\)0.12 mm). After excluding radiographs with the presence of a pelvic tilt (rotation around the horizontal axis), the error decreased to 0.08 mm (\(\pm\)0.11 mm). In comparison to RSA, the mean difference of the Scheier-Sandel method was reported in a worst case to be 0.17 mm (SD 0.21 mm) and a best case to be 0.14 mm (SD 0.25 mm). For the Charnley-Duo method, the mean difference was 0.27 mm (SD 0.27 mm). The EBRA method was found to be the most accurate compared to the gold standard RSA, and the Scheier-Sandel method was not recommended for wear analysis. However, [PERSON] et al. [19] recommended the Charnley-Duo method, because this method demonstrated good correlation in relation to the RSA approach as the gold standard. Within a related paper, [PERSON] [20] identified a pelvic tilt as the main error influencing measured wear results. [PERSON] et al. [21] validated the computerized semiautomatic edge detection method for cemented PE components (Hip Analysis Suite, version 8.0.1.4.3; UCTech the University of Chicago) within an experimental setting. Accuracy and precision were reported to be 0.060 \(\pm\) 0.021 mm (mean \(\pm\) SD) and 0.207 \(\pm\) 0.099 mm, respectively. In comparison to validation values of the RSA approach [22], the accuracy was comparable to, and precision was inferior to, RSA. [PERSON] and [PERSON] [10] reported achieving a similar accuracy to RSA by using a customized 2D\({}_{\text{wear}}\) measurement tool. Bias, defined as the mean (SD) error of the simulated head penetration measurements, was about \(-\)0.002 mm (\(\pm\)0.028 mm), and precision was 0.055 mm for this 2D approach. RSA is a 3D\({}_{\text{wear}}\) approach which presents an accurate measurement tool for the in vivo assessment of polyethylene wear in THA [13] and is regarded as the gold standard [16; 23]. An associated disadvantage of the RSA approach is its complexity in the acquisition of RSA image pairs. In addition, a second X-ray source, as well as a calibration box, is required during image acquisition. Furthermore, special analysis software must be purchased.