## 3 Results
### Outcome Measures  
Both cadavers were CT scanned postoperatively and 3D models were extracted following the same workflow as described in Section 2.1. Pre- and postoperative models of the pelvic bone were registered using ICP [68; 69] enabling the 3D comparison of the preoperative plan with the postoperative models in a common coordinate system. Please refer to Figure 7 for the following description of outcome measures [57].  
One key measure of the outcome evaluation were the planned and performed osteotomy starting points \(PL_{1}\dots PL_{4}\) and \(PF_{1}\dots PF_{4}\), respectively. They were defined as follows:  
* \(PL_{1},PF_{1}\): most lateral point on intersection between supraacetabular osteotomy plane and corresponding pelvic 3D model (pre- and postoperative, respectively)
* \(PL_{2},PF_{2}\): most superior points on intersecting line between supraacetabular and retroacetabular osteotomy planes
* \(PL_{3},PF_{3}\): most superior points on intersecting line between retroacetabular and ischial osteotomy planes
* \(PL_{4},PF_{4}\): most inferior point on intersection between ischial osteotomy plane and corresponding pelvic 3D model (pre- and postoperative, respectively)  
For 2D measurements, \(PL_{1}\dots PL_{4}\) and \(PF_{1}\dots PF_{4}\) were projected onto a plane \(PL\) defined as the best fit in a least-squares sense by \(PL_{1}\dots PL_{4}\) (Figure 7). The projected points are denoted as \(PL_{1}^{\prime}\dots PL_{4}^{\prime}\) and \(PF_{1}^{\prime}\dots PF_{4}^{\prime}\) and the vectors connecting these points are:  
* \(\vec{VL}_{1}=PL_{2}^{\prime}-PL_{1}^{\prime}\), \(\vec{VL}_{2}=PL_{3}^{\prime}-PL_{2}^{\prime}\), \(\vec{VL}_{3}=PL_{4}^{\prime}-PL_{3}^{\prime}\)
* \(\vec{VF}_{1}=PF_{2}^{\prime}-PF_{1}^{\prime}\), \(\vec{VF}_{2}=PF_{3}^{\prime}-PF_{2}^{\prime}\), \(\vec{VF}_{3}=PF_{4}^{\prime}-PF_{3}^{\prime}\)  
The 2D angle between supra- and retroacetabular osteotomy is denoted as \(SRL\) (planned) and \(SRF\) (performed), and the one between retroacetabular and ischial osteotomy is denoted as \(RIL\) (planned) and \(RIF\) (performed). For both cadavers, the following outcome measures were calculated:  
* The 3D point distance between each pair of starting points \(PL_{i}\) and \(PF_{i}\)  
Figure 7: Visualization of outcome measures. The left image shows 3D osteotomy starting points and the projection plane for 2D measurements, which are shown on the right: projected osteotomy starting points, their connecting vectors and the angles between supra- and retroacetabular osteotomy and between retroacetabular and ischial osteotomy, respectively.  
* The 2D angle between each pair of projected starting point connecting vectors \(\vec{V}L_{i}\) and \(\vec{V}F_{i}\)
* The absolute 2D angle deviation between \(SRL\) and \(SRF\) and the absolute deviation between \(RIL\) and \(RIF\).
* The 3D absolute rotational errors in Euler angles between planned and performed fragment reorientation w.r.t. our APP CS.
* The LCE angles (planned and performed), determined by the angle between the y-axis of our APP CS and the vector connecting the origin of the CS and the projection of the most lateral point of the acetabular rim onto the y-z-plane of the CS.