Purpose: To describe occipitocervical inclination (OCI), a new parameter that could compensate for defects in existing radiographic parameters, and to define occipitocervical neutral position.
Methods: Neutral, flexion, and extension lateral cervical spine radiographs of 200 patients (100 male and 100 female patients) judged to be normal were analyzed. The mean age was 45.19 years (range 11-74; 42.84 for male and 47.53 for female patients). For OCI, the angle formed by the line connecting the posterior border of the C4 vertebral body and McGregor's line was measured. Occipitocervical angle (OCA) and occipitocervical distance (OCD) were measured and compared with OCI.
Results: OCI on standard, neutral lateral cervical radiographs was 102.51° ± 8.87°. There was no significant gender difference in neutral OCI 102.81° ± 7.93° for male and 102.21° ± 9.74° for female patients (P = 0.631). The mean neutral OCA was 38.69° ± 9.23°, and the mean neutral OCD was 22.98 ± 5.10 mm. Pearson's correlation coefficient for the value of the cervical lordosis angle and that of neutral OCI was r = 0.274 (P < 0.001). Intraclass correlation coefficient values for inter- and intraobserver reliability for OCI were significantly higher than those for OCA (P < 0.001) and tended to be higher than those for OCD (P = 0.087).
Conclusions: OCI is a very useful parameter for the determination of neutral position during occipitocervical fusion for patients with altered C0-C2 anatomy.
Keywords: Occipitocervical angle; Occipitocervical distance; Occipitocervical fusion; Occipitocervical inclination; Occipitocervical neutral position.