| | Definitions of pathology | Definitions of progression of pathology |
| | AAS | (i) Distance from the middle of the posterior border of the anterior part of the C1 arch until the anterior cortex of the odontoid peg (ADI) exceeding 3 mm in neutral position [16, 21, 23, 26]
(ii) Distance from the middle of the posterior border of the anterior part of the C1 arch until the anterior cortex of the odontoid peg (ADI) exceeding 3 mm in flexed position [6, 7, 18, 19, 22, 24] | (i) Increase of the ADI of more than 1 mm [6]
(ii) Increase of the ADI of more than 2 mm [16, 21] | | VS | (i) Odontoid peg entering more than 0 [20, 23] mm through the foramen magnum [20, 23]
(ii) Odontoid peg entering more than 4-5 mm through the foramen magnum [26]
(iii) Sakaguchi-Kauppi value being grades II, III, or IV [6, 18, 19, 22, 24]
(iv) Ranawat value being less than 13 mm [7, 16, 21] | (i) Increase of the Ranawat of more than 0 mm [6]
(ii) Increase of the Ranawat of more than 2mm [16, 21] | | SAS | (i) Dislocation of two vertebra in the neutral position of the cervical spine exceeding 3 mm [7, 16]
(ii) Dislocation of two vertebra in the neutral position of the cervical spine exceeding 3 mm [18, 19, 22, 24] | (i) Increase the SAS of more than 2 mm [16] |
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