Does atlantoaxial dislocation influence the subaxial cervical spine?

Abstract

Introduction: Previous studies have reported that the alignments of the occipital-cervical and subaxial spine were closely interrelated in asymptomatic individuals; however, none have focused on a population with atlantoaxial dislocation.

Material and methods: From 2007 to 2011, 298 patients with atlantoaxial dislocation and atlas occipitalization were studied. Angles formed between Occiput-C2 and C2-C7 were measured. The relationship between the alignment of the occipital-cervical junction and the subaxial cervical spine was evaluated.

Results: The range of values for the angles measured was as followed: the Occiput-C2 angles were -35.2° to 44.8°, and the C2-C7 angles were -17.4° to 77.8°. Statistically significant negative correlations were observed between the Occiput-C2 and C2-C7 angles.

Conclusion: Anterior dislocations of the atlas are associated with diminished lordosis or even kyphosis of the occipital-cervical junction, and result in compensatory hyperlordosis of the subaxial cervical spine, collectively presenting as a "swan neck" deformity. Atlantoaxial dislocation may influence the global cervical alignment.

Fig. 1

Measurements of the angles on the neutral lateral X-rays

Fig. 2

Correlation coefficient of angulation between the Occiput-C2 and C2–C7 (Y = 25.648 − 0.688X, R² = 0.414, P = 0.000)

Fig. 3

A 33-year-old male with atlantoaxial dislocation and occipitalization. a X-ray showed severe dislocation and swan neck, with Occiput-C2 angle of −7.1° and C2–7 angle of 36.6°. b CT scan showed that C5–6 disc (the apex of the lordotic curve) had posterior osteophytosis (yellow arrow) and some sclerosis of vertebral plates. c–e MRI revealed C5–6 disc degeneration and herniation. f After atlantoaxial reduction and fixation, the swan neck deformity was corrected, with Occiput-C2 angle of 1.5° and C2–7 angle of 18.7°. g–i Post-operative MRI revealed C5–6 disc herniation decreased evidently after the swan neck correction