Fig. 1From: A novel method for measurement of the occipital-cervical distance via the occiput-C4 distanceA novel measurement method for estimating the occipital-cervical distance via the occiput-C4 distance (OC4D) in representative neutral, flexion, and extension positions. The OC4D was defined as the shortest distance from the center of the C4 vertebral body to the McGregor’s lineBack to article page