MRI Study of Contralateral C7 Transfer for Protecting Vertebral Artery and Exposing Bilateral C7 Nerves

The aim of the study was to locate the vertebral artery and proximal C7 nerve root, to investigate a safe zone to conduct contralateral C7 nerve transfer by analyzing MRI images of the brachial plexus.

A total of 40 patients who underwent contralateral C7 nerve transfer surgery were enrolled in this study. At the level of the C7 vertebral transverse process, the location of the proximal C7 nerve and vertebral artery was labeled using the cervical middle line and sternocleidomastoid muscle (SCM) as references on MRI images. The tilt angle of the vertebral artery to the sagittal plane was measured and calculated to determine the safe angles for penetrating the longus colli muscles according to the 95% confidence interval.

Based on the measurement on MRI images, there's a high fitting degree between the location of the SCM interval and the proximal C7 nerve root, and the horizontal location of the vertebral artery showed a fitting degree with the SCM medial edge, about 10 mm laterally, according to the horizontal distance to the cervical middle line at the level of C7 vertebral transverse process. The average tilt angle of the vertebral artery to the sagittal plane was 30.3° (SD 4.6°, range 22.5-39.8°, 95% confidence interval 28.1~32.4°).

As the contralateral C7 nerve transfer was performed, the proximal C7 nerve root could be exposed via the interval between the SCM (sternum and clavicle head). The vertebral artery could be protected through a safe zone of penetrating angle obtained through MRI images before surgery for establishing the trans-longus colli muscle tunnel required for this surgical route.