The Prediction and Prevention of Dysphagia after Occipitospinal Fusion by Use of the S-line (swallowing line).

STUDY DESIGN Clinical case series and risk factor analysis of dysphagia after occipitospinal fusion (OSF). OBJECTIVE To develop new criteria to avoid postoperative dysphagia by analyzing the relationship among the craniocervical alignment, the oropharyngeal space and the incidence of dysphagia after OSF. SUMMARY OF BACKGROUND DATA Craniocervical malalignment after OSF is considered to be one of the primary triggers of postoperative dysphagia. However, ideal craniocervical alignment has not been confirmed. METHODS Thirty-eight patients were included. We measured the O-C2 angle and the pharyngeal inlet angle (PIA) on the lateral cervical radiogram at follow-up. PIA is defined as the angle between McGregor's line and the line that links the center of the C1 anterior arch and the apex of cervical sagittal curvature. The impact of these two parameters on the diameter of pharyngeal airway space (PAS) and the incidence of the dysphagia were analyzed. RESULTS Six of 38 cases (15.8%) exhibited the dysphagia. A multiple regression analysis showed that PIA was significantly correlated with PAS (β=0.714, P = 0.005). ROC curves showed that PIA had a high accuracy as a predictor of the dysphagia with an AUC (area under the curve) of 0.90. Cases with a PIA less than 90 degrees showed significantly higher incidence of dysphagia (31.6%) than those with a 90 or more degrees of PIA (0.0%) (P = 0.008). CONCLUSION Our results indicated that PIA had the high possibility to predict postoperative dysphagia by OSF with the condition of PIA below 90 degrees. Based on these results, we defined "Swallowing-line (S-line)" for the reference of 90 degrees of PIA. S-line (-) is defined as PIA less than 90 degrees, where the apex of cervical lordosis protruded anterior to the "S-line", which should indicate the patient is at a risk of postoperative dysphagia. LEVEL OF EVIDENCE 4.