# Computer-Aided Surgical Simulation for Correcting Complex Limb Deformities in Children
## 4 Discussion  
The most important result of our study is the development of an in-house CASS process, using open-source or free software and low-cost 3D printing technology as much as possible. Table 2 shows a comparison between our procedure and the most common ones found in the literature. The most common procedure is driven by Materialise Mimics, which is a commercial software, while the others can achieve limited results, since Paraview is mainly a 3D viewer and MeshMixer is not developed as Blender, or they have a commercial price such as Analyze 12 and Geomagic Wrap. In all cases, the other procedures are unable to perform 3D simulation. In our experience, CASS enabled the successful correction of the limb deformity according to the preoperative planning in four cases, while the only case in which the preoperative simulation was intentionally not reproduced during the operation showed recurrent deformity. These findings are consistent with the current literature, highlighting the effectiveness of computer-aided simulation in surgery. Despite the fact that computer-aided surgical planning and simulation is increasingly used in reconstructive surgery and trauma, the use of this technology in PO surgery is at the beginning. Several advantages have been reported in terms of the use of CASS in orthopaedic surgery [3; 4; 5; 21; 25]. The visuospatial understanding of the bony anatomy is enhanced by physical models, maybe because of the combination of both a tactile and an optic experience, which has been demonstrated to improve \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
\begin{tabular}{c} Materialise \\ Mimics \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Procedures comparison. Figure 11: Antero-posterior and lateral X-Ray of the affected forearm after surgery (**a**), two months later (**b**), and at the last control, five months after surgery (**c**). the execution of surgical procedures, especially in complex cases. We used intraoperative, sterile, true size 3D-printed models that, in some cases, allowed us to overcome the issues related to the limited visualization of the bony segments. CASS and 3D printed models may be crucial in case of arthroscopic or minimally invasive surgery, when only minimal parts of the bone can be inspected [18]. This aspect can stimulate surgeons to rehearse minimally invasive surgical approaches or arthroscopic techniques in a more precise and effective fashion. Additionally, the combination of surgical simulation and 3D printing allows us to produce patient-specific guides and jigs, potentially reducing the surgical equipment during operation, or even produce custom implants that match perfectly with the patient's unique anatomy. In our experience, CASS enabled the prepending of the hardware and the customization of massive allografts. While the prepending of the hardware by CASS has been demonstrated to reduce surgical time and bleeding, a customized massive allograft is of special interest, since it can be produced preoperatively in a clean room environment, further reducing surgical time and potential infections caused by contamination of the graft during intraoperative preparation, and allowing us to save a single bone harvested from one donor for multiple implants. [26]. Furthermore, the potential combination of CASS and virtual reality could be used for surgical training in PO surgery, while animation could be useful for supporting patient education before surgery [1; 27]. However, CASS and additive manufacturing are often expensive and not easily available for routine clinical use, limiting their application only for research purposes in a few highly specialized centers and university hospitals. It is essential to underline that all software applications but one (Creo Parametric) utilized in our study were open source or free, and very light in terms of using computer resources. The 3D printer was a low-cost entry-level machine.