Estimation of normal limits of the ratio of prevertebral shadow thickness to anteroposterior diameter of the corresponding vertebral body

Objectives An increase in prevertebral soft-tissue thickness (PVST) on lateral cervical spine radiographs raises suspicion of underlying cervical spine pathology. Variation in the magnification of radiographs performed at different institutions makes it difficult to differentiate between normal and abnormal. The ratio of PVST and anteroposterior diameter of the vertebral body eliminates the effect of magnification. Material and Methods One hundred normal lateral cervical-spine radiographs were assessed for individuals aged 18-63 years. The PVST and anteroposterior diameter of the corresponding vertebral body were calculated for C1-C7 level using a Vernier caliper (least count of 0.01 mm) by 3 independent observers. The ratio was calculated by dividing PVST by the anteroposterior diameter of the corresponding vertebral body. Mean, range, and standard deviation were calculated. Student’s t-test, analysis of variance (ANOVA), and Lin’s concordance correlation coefficient were used. Results The mean age of study subjects was 35.29 years (range: 18-63 years). Out of a total of 300 readings at each cervical vertebrae, the mean ratio of PVST and its corresponding anteroposterior diameter of vertebral body for C1 to C7 were 0.46, 0.31, 0.27, 0.47, 0.79, 0.77, and 0.66, respectively. This ratio was found to be maximum for C5 and minimum for C3 for all observers. The ratio was significantly higher in females at C4 level (p=0.002), whereas significantly higher in males at C6 level (p=0.04). No significant age-wise difference was observed except at the C7 level (p=0.02). Interobserver agreement between observers 1 and 2 was 0.92, whereas it was 0.89 and 0.90 between observers 2 and 3, and observers 1 and 3, respectively. Conclusion This study establishes the normal limits of the ratio of PVST and corresponding anteroposterior vertebral body diameter in the Indian population.