Found in space: computer-assisted orthognathic alignment of a total face allograft in six degrees of freedom

Abstract

Purpose: Full facial osteomyocutaneous transplantation requires correct 3-dimensional (3D) alignment of donor osseous structures to a new cranial base with minimal reference points and 6 degrees of potential movement. We investigated whether computer-assisted design and manufacturing (CAD/CAM) could enable accurate placement of the facial skeleton.

Materials and methods: A prospective single-cohort study of Le Fort III-based maxillary-mandibular segment allotransplantation was performed in 5 cadaver pairs and 1 clinical pair. The osteotomies were modeled using computed tomography (CT) data and 3D modeling software and then translated to the donor-recipient pairs using surgical navigation and osteotomy cutting guides. The predicted values were calculated about all rotational axes (pitch, yaw, and roll) and along all translational axes (vertical, horizontal, and anteroposterior) and used as the independent variable. The primary outcome variable of the actual postoperative CT values was compared for fidelity to the prediction using the intraclass correlation coefficient (ICC). The similarity to the donor versus recipient values was calculated as a secondary independent variable, and both predicted and actual measurements were compared with it as a percentage.

Results: The postoperative fidelity to the plan was adequate to excellent (ICC 0.520 to 0.975) with the exception of lateral translation (2.94 ± 1.31 mm predicted left vs 3.92 ± 2.17 mm right actual displacement; ICC 0.243). The predicted and actual values were not consistently skewed toward the donor or recipient values.

Conclusions: We have demonstrated a novel application of CAD/CAM that enables orthognathic alignment of a maxillary-mandibular segment to a new cranial base. Quantification of the alignment in all 6 degrees of freedom delivers precise control compared with the planned changes and allows postoperative quality control.