Occipitocervical neutral position. Possible surgical implications.

Study Design. The study defines the occipitocervical neutral position using cervical radiographs from 30 subjects. Objective. To identify reproducible radiographic measures of the occipitocervical neutral position that can be used during surgery to optimize fusion position. of Background Data. When performing rigid internal fixation of the occiput to the cervical spine, the ability to determine that the occiput is in a neutral position in relation to the cervical spine is important. Currently, no objective radiographic measures for the occipitocervical neutral position exist. Methods. Thirty flexion, extension, and neutral lateral cervical spine radiographs interpreted as normal by an experienced radiologist were studied. The occipitocervical angle and occipitocervical distance were defined and calculated. Two investigators, an orthopedic resident and an experienced orthopedic spine surgeon, measured the occipitocervical angle and occipitocervical distance independently on all radiographs in a blinded manner. Correlation coefficients were obtained to determine interobserver reliability. Results. The mean occipitocervical angles were 24.2°, 44.0°, and 57.2° in flexion, neutral, and extension, respectively. The mean occipitocervical distances were 21.5 mm in neutral, 28.0 mm in flexion, and 14.8 mm in extension. The differences in the occipitocervical angle and occipitocervical distance in neutral, flexion, and extension were statistically significant (P < 0.05 and < 0.001, respectively). There were no significant interobserver differences in any of the measurements. Conclusions. The radiographic measures of the occipitocervical neutral position reported in this study are reliable, repeatable, and simple to determine on routine lateral radiographs. These measurements should be a valuable intra-operative tool for achieving occipitocervical fusion in appropriate alignment.