The effect of anterior translation of the vertebra on the canal size in the lower cervical spine: a computer-assisted anatomic study.

Eighteen adult dry-bone spine specimens were used in conjunction with computer analysis to determine the average axial spinal canal area at the levels of C6, C7, and T1 after different degrees of anterior translation of the cephalad vertebra. Simulating a distractive flexion injury, the cephalad vertebra was anteriorly displaced on the caudal vertebra at 1-mm intervals. After each displacement, the remaining axial spinal canal area of the caudal vertebra was calculated. The results showed that the average axial spinal canal areas for both male and female specimens were approximately 222 mm2 for C6, 217 mm2 for C7, and 210 mm2 for T1, respectively. After a 6-mm anterior translation of the cephalad vertebra (assuming 50% of anterior translation of the vertebral body), the average axial spinal canal area of the caudal vertebra for both sexes significantly decreased to 59% at C6, 51% at C7, and 56% at T1, respectively. This study suggests that the size of the axial spinal canal directly depends on the degree of anterior vertebral translation.