The Northeastern Society of Plastic Surgeons

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Correlation of soft-tissue to bony landmarks during Le Fort I orthognathic surgery
Cynthia Tsay, MPhil1, Raj Sawh-Martinez, MD2, Derek Steinbacher, DMD, MD2.
1Yale School of Medicine, New Haven, CT, USA, 2Section of Plastic and Reconstructive Surgery, Department of Surgery, Yale School of Medicine, New Haven, CT, USA.

Background: Le Fort I orthognathic surgery requires precise 3-dimensional bony repositioning. Vertical changes are critical to the overall aesthetic result. 3D planning enables vertical measurements from the rendered CT scan, but intraoperative points are ascribed from the soft-tissues. The purpose of this study is to compare intraoperative soft-tissue vertical measurements with pre and post CT-based values. We hypothesize a non-linear, but predictable relationship exists.
Methods: We examined a cohort of orthognathic procedures over a 20-month period. Patients were excluded if measurements and/or pre- and post-CT scans were lacking. Demographic, measurement, and perioperative data were tabulated. Clinical vertical measurements included: left medial canthus (LMC) to central incisor (CI), left medial canthus (LMC) to left canine (LC), and right medial canthus (RMC) to right canine (RC). Bone measurements were calculated using pre- and post-CBCT scans. Statistical analysis using a paired, two-variable Student's t-test was performed with a significance set at p<0.05.
Results: 168 sets of measurements were analyzed among 42patients. Average age was 23 years, 57.1% were female, and 76.2% had wire braces. Average vertical measurements in mm(LMC-CI, LMC-LC, RMC-RC) for pre-operative soft tissue were 64.45.5, 61.05.2, 60.95.3 and post-op normal values were66.45.8, 62.65.3, 62.45.3. Bony pre-operative measurements were 84.27.4, 82.67.2, 82.46.8 and normal post-operatives were 84.68.4, 83.68.3, 83.88.4. There was no significant difference between the absolute value pre- and post-operative between the two modalities but a significant difference between bony and soft tissue normal measurements (Table 1). Based on the average of the ratios between the difference between pre-op and normal values, a change of 1.0mm in the soft tissue correlated to a 1.5mm bony difference. Subset analysis demonstrated differences in the normal values between class II and class III cases.
Conclusion: Vertical changes in Le Fort I surgery provide a quantitative means to predict aesthetic results. Our results demonstrated a linear relationship between changes in vertical measurements. Therefore, intraoperative soft tissue measurements can be used with a predictable relationship to achieve the desired bony CT-based measurements.

Table 1: Le Fort I Vertical Measurements
CT bone (mm)Soft tissue (mm)P-value
Post-op CT vs Post-op soft tissue
Absolute difference Post-op to Pre-op CT vs Post-op to Pre-op Soft tissue

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