Age-related Changes in T1 and C7 Slope and the Correlation Between Them in More Than 300 Asymptomatic Subjects

Study Design. A cross-sectional analysis using T1 slope (T1S) and C7 slope (C7S) in asymptomatic individuals. Objective. The 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 Data. Few 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. Methods. A 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. Results. The 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 ( r 2 = 0.75). Conclusion. The 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