Objective: The Cobb angle between the lower endplate of C2 and C7 (C2L–C7L angle) is a traditional parameter used for the assessment of the cervical alignment. However, when the lower cervical column is masked by the shoulder, measurements are difficult. In the present study, we inspected 191 X-ray films, measured the Cobb angle between C2L and the endplates at the several levels of the lower cervical column, and assessed their usefulness of such measurements for the determination of cervical sagittal alignment. Methods: We obtained X-ray films on 191 patients ranging in age from 20 to 93 years. The Cobb angle between C2L and the C7 upper (C7U), the C6 lower (C6L), the C6 upper (C6U), and the C5 lower endplate (C5L) was measured and compared with the C2L-C7L angle. Results: C7L was identified in 116 of 191 patients (60.7%). Except for C2L-C7U angle (P = 0.55), the difference in the mean between C2L-C7L angle and the angle between C2L and the other endplates was statistically significant (P < 0.05). There was a very strong correlation between C2L-C7L angle and C2L-C7U angle (r = 0.99), C2L-C6L angle (r = 0.96), C2L-C6U angle (r = 0.94), and C2L-C5L angle (r = 0.86). Conclusions: To measure the C2L-C7L angle on unclear X-ray films, C7U can be substituted for C7L. Our measurement data for the C6 and C5 endplates were statistically different; however, the correlation between the C2L-C7L angle and C2L-C6U angle, C2L-C6L angle or C2L-C5L angle was very strong. In patients with unclear lower vertebral bodies, cervical sagittal alignment can be predicted by using adjacent endplates.
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