Influence of the Occipital Orientation on Cervical Sagittal Alignment: A Prospective Radiographic Study on 335 Normal Subjects.

Cervical sagittal alignment is considered to have a special role in the pathogenesis and evaluation of cervical diseases. Previous studies have demonstrated that cervical sagittal alignment is correlated with thoracolumbar and pelvic alignments. As the direct anatomical structures connect to the cervical region, however, no parameters in the occiput have been reported to be intimately related to the alignment of the cervical spine. A retrospective radiographic study of 335 individuals (182 males and 153 females) between 18 and 60 years of age was performed between January 2007 and January 2016. The occipital incidence (OI), occipital slope (OS), occipital tilt (OT), C0-C2 angle, C2-C7 angle, C0-C7 angle, T1 slope and thoracic kyphosis were measured in every individual. The mean values of the occipital parameters of the cohort were 34.6° ± 3.1° for OI, 23.4° ± 7.4° for OS, and 11.8° ± 3.3° for OT. OI was constant throughout three age groups. No significant differences were noted between males and females. In addition, strong correlations were found between the occipital parameters and cervical parameters. The occipital orientation was an important factor that influenced the cervical sagittal alignment.