I may start to develop an extension for planning of orthopedic surgeries of the lower extremities.
Focus will be on the hip an knee joint. One important feature will be the definition of bone coordinate systems based on bony landmarks to transform the reconstructed bones and their corresponding (sub)volume data from the CT coordinate system into a “neutral” joint alignment.
Are there any extensions that could serve as basis or inspiration for such project.
There are Slicer-based commercial systems that do this, but I don’t think there is much in open-source extensions.
Q3DC module in SlicerCMF does something similar for cranial procedures, but it is quite old, so it does not use current Slicer markups infrastructure.
I would recommend to look at methods for establishing bone coordinate systems that are commonly used clinically (and validated on many thousands of patients) and ask here for help if you are not sure how exactly to implement them in Slicer.
The commercial systems that I know of have not been announced publicly, so there is no further information available. Most often companies do not even acknowledge that they use Slicer internally even after the product is released, which demonstrates that the Slicer license is very commercial-friendly (no attribution is required) and the user interface layer can be customized so much that users don’t even realize that they use Slicer. But unfortunately this also means that there are very few Slicer-based products that we can use as a reference.
If you describe what you want to achieve then we may be able to provide links to relevant examples. Are you thinking about navigated surgery (optical tracked tools and bones), 3D-printed surgical guides, or robotic procedures?
The main goal would be preoperative planning with the reconstruction of biomechanical parameters based either on the contralateral leg or anthropometric values, in case the contralateral side cannot be used as reference.
Surgical guides are one option for the intraoperative transfer of the preoperative plan. However, a common CAD software might be used for the design of the guides rather than 3D Slicer.