Influences of patient positioning and general anesthesia on condylar position and surgical accuracy in orthognathic surgery.

Objectives: To assess the effect of patient positioning and general anesthesia on the condylar position in orthognathic surgery.

Materials and methods: This prospective study included patients undergoing orthognathic surgery between 2019 and 2020. Four weeks prior to surgery (T0) cone-beam computed tomography (CBCT) scans and intra-oral scans (IOS) were acquired in an upright position. Additionally, two IOS were acquired in the operating theatre, one before (T1) and one after (T2) general anaesthesia in supine position. The condylar position was analysed by matching the mandible from CBCT data with IOS at T1, T2 and T3, calculating the spatial differences at the level of lateral condylar points.

Results: Based on 32 patients, patient positioning and general anesthesia on condylar position significantly affected condylar position. In supine position, the condyles moved primarily in the cranial direction by 0.94 ± 0.92 mm (p < 0.01). After anesthesia, the condyles moved posteriorly by 0.20 ± 0.45 mm (p = 0.02). These changes in condylar position resulted in the occlusal plane of the mandible being positioned more cranially (2.31 ± 2.61 mm; p < 0.01), anteriorly (0.70 ± 1.32 mm; p = 0.04), and counterclockwisely pitched (-1.42 ± 2.25°; p = 0.02).

Conclusion: The present study demonstrated that both supine position and general anesthesia significantly influenced the condylar position, the mandibular position, and, subsequently, the surgical accuracy of orthognathic surgery.

Clinical relevance: Surgeons should take these effects into consideration when planning orthognathic surgery as this might lead to under- or overcorrections.