Fig. 1.

a Normal craniocervical junction in the neutral position. The CXA varies from 150° to 165°. There is minimal or zero deformative strain in the neutral state. b Normal craniocervical junction in flexion. The neuraxis stretches by approximately 10% of its total length with flexion of the craniocervical junction creating a strain ε = 0.1. c Pathological craniocervical junction with an abnormal CXA in flexion. Upon full flexion at the craniocervical junction, the increase in the tangent arc creates a deformative strain approaching ε = 0.2 (i.e., 20% stretch). In vivo and in vitro models demonstrate decreased or loss of neurological function with strains of 0.2