Relationship between congenital occipital atlas fusion, C2-3 fusion and basilar invagination

English Keywords:Pathogenesis basilar invagination  Congenital occipital-atlas fusion  Cervical 2-3 fusion

English Abstract:

  【Abstract】 Objectives: To investigate the role of occipital atlas and C2-3 fusion on the formation of basilar invagination associated with atlantoaxial dislocation.　Methods: From March 2009 to December 2011, 50 cases suffering from basilar invagination associated with atlantoaxial dislocation(observation group) were reviewed. All cases underwent X-ray, 3-dimensional reconstruction CT and MRI, and the numbers of occipital atlas fusion(C0-1),cervical 2-3 fusion(C2-3), wedge shape for atlas lateral mass, slope shape for upper facet of axis was counted respectively. Meanwhile, 50 normal persons with the same gender and age distribution were picked up from the image data base of our hospital for control. The following parameters such as basal-clivus angle (parameter α), distance from odontoid to chamberlain line(parameter a) and distance from odontoid to foramen magnum line(parameter b), distance from the projection of bone patella to the low rim of atlas lateral mass (h), and cervicomedullary angle(β) et al were measured respectively in both groups. Results: There were 40 (80%) C0-1 fusions, 28(56%) C2-3 fusions(including C2-3-4 fusion in 1 case), 20 C0-1 and C2-3 fusions together and 49 wedge shape for atlas lateral mass in the 50 basilar invagination patients. The basal-clivus angle(α) was 131°±11°(in observation group) and 135°±8°(in control group) respectively(P>0.05）; the parameter a, b, h and β was -8.6±3.7mm, -5.1±2.3mm, 4.8±1.8mm and 129°±15° respectively for observation group, and 6.9±2.9mm, 9.6±3.7mm, 17.7±2.3mm and 156°±17° for control group respectively. All parameters showed group-related statistical difference(P<0.05). Conclusions: The congenital occipital-atlas fusion brings the dens in a high position, which will lead to the formation of basilar invagination; the wedge shape of atlas mass and slope shape of the C2 upper facet may lead to C1-2 instability; the C0-1 and C2-3 fusion may lead to the stress concentration between the C1 and C2, which will bring C1-2 dislocation anatomically.