Public domain computer-aided surgery (CAS) in orthodontic and maxillofacial surgery.

BACKGROUND

Computer-aided virtual three-dimensional (3D) surgical simulation assists the necessary visual understanding of complex pathological situations but has so far been dependent on expensive hardware and software.

METHOD: For the first time a non-commercial, user-orientated application for orthognathic and craniofacial surgical simulation has been introduced, based on freeware NIH Image 1.62 provided by the National Institute of Mental Health (NIMH). Use and limitations are demonstrated here by the example of hypertelorism surgery. The osteotomy lines and the amount of resection for outward positioning of the orbits were determined by the surgeon on a workstation using CT data. Possible movement patterns of the osteotomy fragments were rotations, sagittal and transversal movements or combinations of these. The program then allows the calculation of anatomical distances on the screen in a 1:1 relation. Normative values according to age and pathological anatomy determine the degree of displacement. The program calculates the new position of the osteotomy fragments and transfers the data of the segment movement to the original CT data.

RESULTS

3D visualization of bone and soft tissue contours have been produced with an acceptable quality on a workstation for the demonstration and visual understanding of the surgical plan. Evaluation of a postoperative CT showed that the amount of movement and size of bone resection in the simulation was slightly overestimated rather than underestimated. This was also dependent on the complexity of the pathological anatomy and on how experienced the surgeon was.

CONCLUSION

The use of 3D simulation programs allows a better understanding of the pathological anatomy in all dimensions, and in many cases enables limitations to be recognized in advance. The public domain program makes a major contribution to the quality of orthognathic and craniofacial surgical planning through cost-free usability, and supports continuous development and exchange of experience.