Influence of neck postural changes on cervical spine motion and angle during swallowing

Abstract

Occipitocervical (OC) fixation in a neck retraction position could be dangerous due to the risk of postoperative dysphagia. No previous study has demonstrated an association between the cervical posture change and cervical spine motion/angle during swallowing. So, we aimed to analyze the influence of neck posture on the cervical spine motion and angle change during swallowing.Thirty-seven asymptomatic volunteers were recruited for participation this study. A videoflurographic swallowing study was performed in the neutral and retracted neck posture. We analyzed the images of the oral and pharyngeal phases of swallowing and compared the angle and the position changes of each cervical segment.In the neutral posture, C1 and C2 were flexed, while C5, C6, and C7 were extended. C3, C4, C5, C6, and C7 moved posteriorly. All cervical levels, except for C5, moved superiorly. In the retraction posture, C0 and C1 were flexed, while C6 was extended during swallowing. All cervical levels moved posteriorly. C1, C2, C3, and C4 moved superiorly. The comparison between 2 postures shows that angle change is significantly different between C0, C2, and C5. Posterior translation change is significantly different in the upper cervical spine (C0, C1, and C2) and C7. Superior movement is significantly different in C0.C0 segment is most significantly different between neutral and retraction posture in terms of angle and position change. These data suggest that C0 segment could be a critical level of compensation that allows swallowing even in the retraction neck posture regarding motion and angle change. So, it is important not to do OC fixation in retraction posture. Also, sparing C0 segment could provide some degree of freedom for the compensatory movement and angle change to avoid dysphagia after OC fixation.

Figure 1

(A, B) Neutral posture and its videoflurographic image. (C, D) Retraction posture and its videoflurographic image. Hyperflexion of the upper cervical spine decreased the occipitocervical angle, which resulted in narrowing of the oropharyngeal space. This mechanical obstruction cause dysphagia after occipitocervical fusion.

Figure 2

(A) The 2 white dots are the reference points; mid-point of inferior vertebral body line and spino-lamina junction line. (B) Target position of cervical spine. The anterior-posterior coordinate is X, and the superior-inferior coordinate is Y. The large white dot is the target position; midpoint of the line connecting the 2 reference points. (C) Angle α. The white dotted line connects the 2 reference points. The white solid line is a horizontal line. The angle α is defined by these 2 lines and indicate the angle of each cervical vertebra.

Figure 3

(A) In neutral posture, changes in the angle of the cervical spine. (B) In retraction posture, changes in the angle of the cervical spine. Bar: mean ± SEM, ∗ Significant P < .05 in 1-sample t test, ^†Significant P < .05 in paired t test.

Figure 4

(A) In neutral posture, X movements (anterior-posterior direction) of the cervical spine. (B) In retraction posture, X movements (anterior-posterior direction) of the cervical spine. (C) In neutral posture, Y movements (Inferior-superior direction) of the cervical spine. (D) In retraction posture, Y movements (Inferior-superior direction) of the cervical spine. Bar: mean ± SEM, ∗Significant P < .05 in 1-sample t test, ^†Significant P < .05 in paired t test.