The O-C2 angle established at occipito-cervical fusion dictates the patient's destiny in terms of postoperative dyspnea and/or dysphagia

Abstract

Purpose: We have revealed that the cause of postoperative dyspnea and/or dysphagia after occipito-cervical (O-C) fusion is mechanical stenosis of the oropharyngeal space and the O-C2 alignment, rather than total or subaxial alignment, is the key to the development of dyspnea and/or dysphagia. The purpose of this study was to confirm the impact of occipito-C2 angle (O-C2A) on the oropharyngeal space and to investigate the chronological impact of a fixed O-C2A on the oropharyngeal space and dyspnea and/or dysphagia after O-C fusion.

Materials and methods: We reviewed 13 patients who had undergone O-C2 fusion, while retaining subaxial segmental motion (OC2 group) and 20 who had subaxial fusion without O-C2 fusion (SA group). The O-C2A, C2-C6 angle and the narrowest oropharyngeal airway space were measured on lateral dynamic X-rays preoperatively, when dynamic X-rays were taken for the first time postoperatively, and at the final follow-up. We also recorded the current dyspnea and/or dysphagia status at the final follow-up of patients who presented with it immediately after the O-C2 fusion.

Results: There was no significant difference in the mean preoperative values of the O-C2A (13.0 ± 7.5 in group OC2 and 20.1 ± 10.5 in group SA, Unpaired t test, P = 0.051) and the narrowest oropharyngeal airway space (17.8 ± 6.0 in group OC2 and 14.9 ± 3.9 in group SA, Unpaired t test, P = 0.105). In the OC2 group, the narrowest oropharyngeal airway space changed according to the cervical position preoperatively, but became constant postoperatively. In contrast, in the SA group, the narrowest oropharyngeal airway space changed according to the cervical position at any time point. Three patients who presented with dyspnea and/or dysphagia immediately after O-C2 fusion had not resolved completely at the final follow-up. The narrowest oropharyngeal airway space and postoperative dyspnea and/or dysphagia did not change with time once the O-C2A had been established at O-C fusion.

Conclusions: The O-C2A established at O-C fusion dictates the patient's destiny in terms of postoperative dyspnea and/or dysphagia. Surgeons should pay maximal attention when establishing the O-C2A during surgery, because their careless decision for the O-C2A may cause persistent dysphagia or a life-threatening consequence. We recommend that the O-C2A in O-C fusion should be kept at least at more than the preoperative O-C2A in the neutral position.

Fig. 1

Schematic drawing of the proposed mechanism of oropharyngeal stenosis. U uvula, E epiglottis, M mandible, T tongue root, O oropharynx, C cervical spine. a Sagittal computed tomography reconstruction of the cervical spine. Reduction in the O-C2A flexes the maxilla (curved white arrow), which makes the mandible shift posteriorly (black arrow) with the tongue root (thin white arrows). b Movement of the tongue root (while arrow) caused by the backward shift of the mandible (black arrow) results in oropharyngeal stenosis

Fig. 2

Representative radiographic measurements. E epiglottis tip, U uvula tip. The O-C2A represents the angle between McGregor’s line and the inferior endplate of C2. The C2–C6A represents the angle between the inferior endplates of C2 and C6. In both, a positive value indicates lordosis at the local segment. ‘nPAS’ represents the narrowest anteroposterior distance of the oropharynx between the tips of the uvula and epiglottis (double black arrow)

Fig. 3

A scatter diagram showing the association between the dOC2A and the %dnPAS. dOC2A (°) = (O-C2A in the X position) − (O-C2A in the neutral position). %dnPAS (%) = (nPAS in the X position − nPAS in the neutral position)/(nPAS in the neutral position) × 100. ‘X position’ indicates flexion or extension. a OC2 group: preoperative values. b OC2 group: final follow-up values. c SA group: preoperative values. d SA group: final follow-up values

Fig. 4

This line graph shows the chronological changes in the ΔnPAS between the 2 groups. Final F/U final follow-up, *statistically significance

Fig. 5

Postoperative lateral radiographs in the flexion and extension (a, b). A case in the OC2 group. The nPAS (double white arrow) became almost constant, once the O-C2A had been fixed (nPAS: 14.2 mm in flexion, and 15.4 mm in extension) (c, d). A case with C2–C7 posterior cervical fusion in the SA group. The changes in the nPAS had been maintained even after subaxial fusion (nPAS: 5.3 mm in flexion, and 32.9 mm in extension)