Computer-assisted stability assessment of segmental bimaxillary surgery

Objectives
Stability assessment of orthognathic surgery is often time consuming, relies on manual re-identification of anatomical landmarks and on short-term follow-up. The purpose of the present study was to propose and validate a semi-automatic approach for three-dimensional assessment of long-term stability of segmental bimaxillary surgery from cone-beam computed tomography (CBCT).

Materials and Methods
A semi-automatic approach was developed and validated for long-term stability assessment of segmental bimaxillary surgery using postoperative two weeks and two years CBCT. The stability of the surgical outcome was calculated as three-dimensional translational and rotational differences between the short- and long-term postoperative positions of the individual bone segments after voxel-based registration. For reliability evaluation, mean absolute differences and intra-class correlation coefficients were calculated at a 95% confidence interval on measurements of two observers.

Results
Ten subjects (four female; mean age 24.4 years) class II and III, who underwent a combined three-piece Le Fort I osteotomy, bilateral sagittal split osteotomy (BSSO) and genioplasty, were included in the study. The intra- and inter-observer reliability was excellent, range [0.82 – 1.00]. Bland-Altman plots showed high degree of agreements, low biases and no systematic errors. The range of the mean absolute difference of the intra- and inter-observer translational and rotational measurements were [0.14 mm (0.13) – 0.44 mm (0.50)] and [0.20 degrees (0.16) – 0.92 degrees (0.78)]. The stability measurements of the smallest bone segments, the chin and the maxillary segments, were the least consistent.

Conclusion
The proposed approach has excellent reliability for three-dimensional assessment of long-term stability of segmental bimaxillary surgery, including segmental Le Fort I osteotomies, BSSO and genioplasty. The development and validation of robust automated computer-assisted surgical analysis is important due to the valuable information it can provide the surgeon in the clinical practice to optimize the outcome of orthognathic surgery by time efficient assessment of both surgical accuracy and postoperative stability.