Abstract
Background: To describe and measure the occipital-cervical distance by a novel method utilizing the occiput-C4 distance (OC4D) in normal subjects that can be used to guide the restoration of vertical dislocation of the occipitocervical region in patients with basilar invagination and to perform standardized testing of occipitocervical constructs.Methods: Neutral, flexion, and extension lateral cervical spine radiographs of 150 asymptomatic subjects (73 males and 77 females) judged to be normal were analyzed. The mean age was 48.0±8.4 years old (range 20–69 years; 48.4±10.2 years old for males and 47.6±6.4 years old for females). Analysis consisted of measurement of the OC4D. The OC4D was defined as the shortest distance from the center of the C4 vertebral body to the McGregor’s line. Two spine surgeons measured the OC4D thrice in the normal population and obtained the average values. Height, weight, and body mass index (BMI) of each subject was recorded and analyze its correlation with OC4D.Results: The values of OC4D on neutral, flexion, and extension lateral cervical spine radiographs were 69.0±6.9 mm, 68.9±6.8 mm and 68.1±6.9 mm, respectively. There was no significantly different from the values measured in neutral、flexion and extension (P> 0.05). But the OC4D of males were higher than females in neutral, flexion, and extension (P < 0.001 for all). There was a positive correlation between OC4D and height and weight in neutral、flexion and extension (P <0.001 for all). The correlation between O-C4D and BMI was weak, and no significant in neutral, flexion, and extension (P > 0.05). The ICC values of inter- and intra-observer agreements for the radiographic parameter in all of the cervical positions were more than 0.93.Conclusions: OC4D, a new measurement method for occipital-cervical distance that is not affected by the change in neutral, flexion, and extension positions, should be a valuable parameter and intra-operative tool to guide the vertical restoration during OCF for patients with altered occiput-cervical anatomy.