Cervical Inclination Angle: Normative Values in an Adult Multiethnic Asymptomatic Population.

Objective: The role of the craniocervical complex in spinal sagittal alignment has rarely been analyzed but it may play a fundamental role in postoperative mechanical complications. The aim of the study is to analyze the normative value of the cervical inclination angle (CIA) in an adult asymptomatic multiethnic population.
Methods: Standing full-spine EOS of adult asymptomatic volunteers from 5 different countries were analyzed. The CIA was analyzed globally and then in each decade of life. Different ethnicities were compared. Comparisons between different groups was performed using a t-test and statistical significance was considered with a p-value < 0.05.
Results: EOS of 468 volunteers were analyzed. The global mean CIA was 80.2° with a maximum difference of 9° between T1 and T12 (p < 0.001). The CIA remains constant until 60 years old then decreases significantly passing from a mean value before 20 years old of 82.25° to 73.65° after 70 years old. A statistically significant difference was found between the Arabics and other ethnicities with the formers having an inferior CIA: this was related to a mean older age (p < 0.05) and higher body mass index (p < 0.05) in the Arabics.
Conclusion: The CIA remains constant until 60 years old and then reduces slightly but never under 70°. This angle is helpful to evaluate the lever arm at the upper instrumented vertebra after an adult spinal deformity surgery and could predict the occurrence of a proximal junctional kyphosis when its value is lower than normal. Further clinical studies must confirm this theory.