## 4 Discussion
By the use of a second radiological plane, the lateral view, according to [PERSON], in addition to the a.p. pelvic overview, a comparable rate of exact matching between templated and implanted size of 40.0% \(\pm\) 20.8% was determined. With an allowed measuring tolerance of +/ - one stem size, a slightly increased accordance of 89.4% \(\pm\) 9.8% was reached, although the difference was not significant. A variation of more than +/ -2 stem sizes between templating and implanted size occurred in 0.7% of the cases when using two radiological planes compared to 6.2% when using only one plane (\(p\) = 0.18). This reduced range of dispersion indicates a higher accuracy when using two planes, although the difference was not significant. Results analyzing the rate of correctly planned size of preoperative templating of short stem implants are less documented in the literature. There are only two studies dealing with this question: on the one hand, for the METHA short stem by [PERSON] et al. [11] and on the other hand, for the MAYO short stem (Zimmer, Warsaw, IN, USA) by [PERSON] et al. [24]. Both of these short stem designs aim at a metaphyseal anchorage. [PERSON] et al. reported an exact match without size tolerance in 38% of the cases. [PERSON] et al. found for the METHA short stem an execitude of 49% of preoperative templating. In our study, we found similar results with up to 36.2% \(\pm\) 16.9%. The MAYO device showed predictability of 95%, [PERSON] et al. reported 89% for the METHA stem, and our study reports a comparable matching rate of 86.3% \(\pm\) 9.5% when tolerating a difference of one size. In analogy to the CTHA group, the second plane (lateral view) led to a smaller range of dispersion, matching the exact size in 50% \(\pm\) 27.5%, and in 89.9% \(\pm\) 12% with a tolerance of +/ -1 stem size. When comparing the STHA and CTHA groups, adding the second radiological plane increased the probability of matching the exact size in the STHA group (50.0% vs. 36.2%), but not in the CTHA group (40.0% vs. 44.4%). When tolerating a difference of +/ - one stem size, templating with two planes revealed comparable results between the groups that were not statistically significant (89.9% for STHA vs. 89.4% for CTHA). Although none of these results reached statistical significance, these data and the graphical illustration (Figure 4) imply that using two planes for preoperative templating is more likely to have a beneficial effect with regard to a short stem than to a conventional stem. In general, preoperative templating is important with regard to the risk of an intraoperative fracture of the femur that is a common complication in a non-cemented THA [25]. On the other hand, the undersizing of the implant may lead to early implant migration [26] that may, in turn, impair osseointegration and lead to early aseptic loosening [27]. Less experienced surgeons especially benefit from a profound preparation by means of preoperative templating that helps them to improve their orientation and to feel safer during bone preparation. The information derived from this study that the planned size tends to be too big for small implant sizes and too small for big implant sizes might be especially helpful for them. In this study, all templating was performed by digital techniques, but there are alternative analog techniques using plastic templates. Higher exactitude for digital templating was described in studies of [PERSON] et al. and [PERSON] et al. [12,28]. On the other hand, there are also studies that come to the conclusion that analog templating might have a higher rate of correctly planned size [23,29]. All studies showed that templating is a beneficial tool to avoid intraoperative complications.