  Craniomaxillofacial reconstruction with patient-specific customized
craniofacial implants (CCIs) is most commonly performed for large-sized
skeletal defects. Because the exact size of skull resection may not be known
prior to the surgery, in the single-stage cranioplasty, a large CCI is
prefabricated and resized intraoperatively with a manual-cutting process
provided by a surgeon. The manual resizing, however, may be inaccurate and
significantly add to the operating time. This paper introduces a fast and
non-contact approach for intraoperatively determining the exact contour of the
skull resection and automatically resizing the implant to fit the resection
area. Our approach includes four steps: First, a patient's defect information
is acquired by a 3D scanner. Second, the scanned defect is aligned to the CCI
by registering the scanned defect to the reconstructed CT model. Third, a
cutting toolpath is generated from the contour of the scanned defect. Lastly,
the large CCI is resized by a cutting robot to fit the resection area according
to the given toolpath. To evaluate the resizing performance of our method, six
different resection shapes were used in the cutting experiments. We compared
the performance of our method to the performances of surgeon's manual resizing
and an existing technique which collects the defect contour with an optical
tracking system and projects the contour on the CCI to guide the manual
modification. The results show that our proposed method improves the resizing
accuracy by 56% compared to the surgeon's manual modification and 42% compared
to the projection method.
