(19) CBCT Analysis of the Descending Palatine Canal for LeFort I Osteotomy

Abstract: Statement of Problem and

Purpose:
The most significant morbidity from maxillary orthognathic surgery is blood loss. Since avascular necrosis may occur as a result of blood loss, the descending palatine artery (DPA) should be preserved whenever possible.1 This requires a clear understanding of the anatomic position of the descending palatine canal (DPC). Studies have delineated the position of DPA by measuring the piriform rim-to-DPC distance (PDC). However, the clinical applicability of the data is limited due to variability in the method of measurement and subject characteristics. One study2 showed that class III subjects with maxillary hypoplasia had shorter mean PDC lengths than those without maxillary hypoplasia. However, this computed tomography (CT) based study was subject to patient positioning variations because landmarks were identified on a single CT slice. This study will determine the PDC in subjects with differing skeletal patterns using cone beam computed tomography (CBCT), controlling for position, skeletal deformity, and sex.

Methods:
CBCT images were evaluated retrospectively to determine the PDC of 97 consecutive subjects aged 13-64 who have undergone bimaxillary or isolated mandibular orthognathic surgery at our institution between 1/1/2013 and 11/22/22, for class III dentoskeletal deformity. Maxillary sagittal position was verified by comparing the SNA between the two groups. Standardized 3D measurements of the PDC were made for each subject. The primary predictor variable was maxillary sagittal diagnosis, and the secondary predictor variable was sex. The primary outcome variable was PDC. Our null hypothesis was that the PDC does not differ between the two groups. The sample size required for each study group was 47 subjects (alpha = .05, power = 80%).

Results:
The SNA was lower in the bimaxillary surgery group (81.99°) vs the single jaw group (84.83°); p=0.002). The PDC of the bimaxillary surgery group was 1.54mm shorter than single jaw group (32.95 vs 34.48); p=0.05 (Figure 1). When controlling for sex, this difference was greater in males (3.21 mm), than in females (0.59 mm); p=0.047 (Figure 2). Sex alone did not have a statistically significant association with the PDC distance (p=0.192). The minimum PDC distance for the maxillary hypoplasia group was 25 mm vs 28 mm in the normal maxilla group (Table 1).

Conclusion:
PDC is lower in maxillary hypoplasia and is more evident in males with maxillary hypoplasia. This study showed shorter measurements than historical data, suggesting updates in the knowledge of the minimum PDC values which is critical for minimizing risk of iatrogenic injury to the DPA during maxillary orthognathic surgery.

References:

1 Li, K. K., Meara, J. G., & Alexander, A. (1996). Location of the descending palatine artery in relation to the Le Fort I osteotomy. Journal of Oral and Maxillofacial Surgery, 54(7), 822–825.
2 Ueki, K., Hashiba, Y., Marukawa, K., Nakagawa, K., Okabe, K., & Yamamoto, E. (2009). Determining the anatomy of the descending palatine artery and pterygoid plates with computed tomography in Class III patients. Journal of Cranio-Maxillofacial Surgery, 37(8), 469–473.

Figure 1. PDC measurements in maxillary hypoplasia vs. normal maxilla
Figure 2. PDC measurements based upon sex

Table 1. Overall PDC measurements