• Taro Inoue, Kei Ando, Kazuyoshi Kobayashi, Hiroaki Nakashima, Keigo Ito, Yoshito Katayama, Masaaki Machino, Shunsuke Kanbara, Sadayuki Ito, Hidetoshi Yamaguchi, Hiroyuki Koshimizu, Naoki Segi, Fumihiko Kato, and Shiro Imagama.
• Department of Orthopedic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan.
• Spine. 2021 Apr 15; 46 (8): E474-E481.

Study DesignA cross-sectional analysis using T1 slope (T1S) and C7 slope (C7S) in asymptomatic individuals.ObjectiveThe aim of this study was to identify normative values, ranges of motion (ROMs), age-related changes in T1S and C7S, and correlation between the two slopes.Summary Of Background DataFew studies have reported age-related changes in the T1S and C7S angles. Additionally, studies investigating the effects of cervical position on these slopes are limited.MethodsA total of 388 asymptomatic subjects (162 males and 226 females) for whom T1S measurement was performed on radiographs were enrolled in the study. The T1S and C7S angles were measured using neutral radiography of the cervical spine. ROMs were assessed by measuring the difference in alignment in the neutral position, flexion, and extension.ResultsThe mean C7S and T1S angles were 19.6° (22.2° in males, 17.9° in females) and 24.0° (26.7° in men and 22.1° in women), respectively. The T1S angle was significantly greater than the C7S angle. Both the C7S and T1S angles significantly increased with age. The flexion ROM of C7S was higher than that of T1S, whereas no significant difference was detected between the extension ROMs of the two slopes. The flexion ROMs of the two slopes did not change, whereas the extension ROMs significantly increased with age. A significant positive correlation was observed between the C7S and T1S angles (r2 = 0.75).ConclusionThe normative values and age-related changes in C7S and T1S were analyzed. Both the C7S and T1S angles increased with age. The C7S angle was strongly correlated with the T1S angle, suggesting that C7S can substitute T1S on radiographic images.Level of Evidence: 3.Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.

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