Fig. 2

Four types of cervical morphology classified according to a modified method of Toyama et al. A line AB was drawn from the midpoints of the inferior margin of C2 to the midpoints the superior margin of C7. And, the morphology was classified to four types according to the relative positions of the centroids of C3-6 to line AB. Lordotic: all centroids are anterior to AB and the distance between at least one centroid and AB is 2 mm or more; Straight: the distance between line AB and each centroid is less than 2 mm; Sigmoid: some centroids are anterior to and some posterior to line AB and the distance between line AB and at least one centroid is 2 mm or more; Kyphotic: all the centroids are posterior to line AB and the distance between at least one centroid and the AB is 2 mm or more