Title: Accuracy of Maxillary Positioning in Orthognathic Surgery
Objectives: To determine the accuracy of maxillary repositioning during orthognathic surgery.
Methods:
Records of 72 consecutively surgically treated cases were assessed for inclusion, using the following criteria:
· Patients who had a LeFort I maxillary osteotomy
· Good quality pre-operative and immediate post-operative digital lateral cephalograms
· Surgical prescriptions based on prediction tracings and model surgery
· Patients with cleft palate or craniofacial syndromes were excluded.
The cephalometric images were assessed using OPAL (version 2.2) software. Landmark identification was performed by a single examiner, who was unaware of the surgical plan. Distances of landmarks from the reference lines (SN+7° and its perpendicular at Sella) were compared between pre- and post-surgical lateral cephalograms to calculate the maxillary movements. These were compared with the intended movements.
Repeatability study: Pre- and post-surgical lateral cephalograms of five randomly selected patients were plotted on two separate occasions, one week apart, to determine the repeatability of landmark identification.
Results:
The records of 28 patients were included.
Repeatability study: The repeat plots were analysed using the Bland Altman test and the concordance correlation coefficient (Lin). These showed good agreement between repeat identification of most landmarks. 95% limits of agreement for repeat plots of upper incisor tip were between -0.98mm and 0.92mm in the x-axis, and -1.1mm and 0.42mm in the y-axis. The least reliable landmark was the upper first molar distal cusp tip in the x-axis, with 95% limits of agreement between -1.87mm and 2.31mm.
Main study: Mean differences between intended and actual movements of maxillary landmarks ranged between 1.42mm (SD 0.98mm) and 1.71mm (SD 1.19mm) in the x-axis and 1.24mm (SD 0.86mm) and 1.94mm(SD 1.51mm) in the y-axis.
Conclusion:
Surgical maxillary repositioning is generally accurate to within 2mm, although there is a large amount of individual variation.