Functional MR imaging of the craniocervical junction. correlation with alar ligaments and occipito-atlantoaxial joint morphology: a study in 50 asymptomatic subjects

Purpose: Whiplash injuries are frequent in industrialised countries. The ac ute and chronic symptoms following such injuries are incompletely understoo d and objective clinical or imaging findings are rare. Several authors have suspected that rear end collisions occurring when the head is rotated may result in tears of the alar ligaments. There has been experimental proof th at a torn alar ligament increases the rotation of the C0/C1 and C1/C2 segme nts to the contralateral side. Functional cross sectional imaging has there fore been proposed to diagnose injuries of the alar ligaments. So far, publ ished data on normal ranges of rotation in an asymptomatic population have been sparse. The aim of this study was to determine by MR imaging the norma l range of rotation in the first three cervical segments and their relation to the morphology of the alar ligaments and the occipito-atlantoaxial join ts. Material and methods: Functional MR imaging of the craniocervical junction in maximum active left and right head rotation was performed in 50 healthy volunteers with a mean age of 29.8 years (31 men, 19 women, range 19-47 yea rs). Measurements were independently performed by two musculoskeletal radio logists to assess interobserver error. The results were correlated with gen der and age, with morphological findings in the occipito-atlantoaxial joint s (i.e. joint symmetry, joint effusions, dens position), and with the form, course and symmetry of the alar ligaments. Results: The mean range of rotation for the C0/C1 joint was 2.7 degrees (st andard deviation [SD] 3.3 degrees) /3.3 degrees (SD 3.6 degrees) (right/lef t) and at the C1/C2 level 38 degrees (SD 6.5 degrees) /37.8 degrees (SD 6.4 degrees). The mean differences in left/right rotation were: C0/C1 3.5 degr ees (SD 2.8 degrees) and C1/C2 6.3 degrees (SD 4.4 degrees). No correlation was found between segmental rotation and morphological characteristics of the craniocervical joints or ligament structures. Conclusion: There is wide variation of segmental motion in the upper cervic al spine. Differences in right-to-left rotation are frequently encountered in an asymptomatic population. Therefore, these measurements are unsuitable for indirect diagnosis of soft tissue lesions after whiplash injury and sh ould not be used as a basis for treatment guidelines.