Craniocervical junction lies from cranium to 2nd cervical vertebrae. This area contains both neurovascular and complex osseoligamentous structures. Craniocervical junction is most active and most sensitive part of the whole vertebral column. The anatomical morphometric studies about this zone are rather limited in number. In this study, odontoid process sizes and atlantoaxial distance (AAD) are evaluated with MRI, differently from other studies. The goal of this evaluation to determine the mean value of ADD in 20-40 years old people and to specify if there is any difference in genders, chronological age and to define the accurate measures for Turkish population in odontoid fixation. Abovementioned measurements are taken from axial and sagittal MRI of 60 adult patients, which performed for different diseases.

30 of the patients are men, 30 of them are woman, and the mean age of all patients is 30.7 ± 4.7. Mean transvers diameter of all patients is 8.45 ± 1.11 mm, mean sagittal diameter is 6.70 ± 0.84 mm mean odontoid height is 31.49 ± 2.53 mm mean atlantoaxial distance is 1.40 ± 0.29 mm respectively.. When the groups of both sexes are compared, the mean values of both odontoid process height (t: 3.09, p<0.05) and anteroposterior diameter (t: 2.27, p<0.05) transverse diameter (t:6.61, p<0.05), were significantly different as statistical. On the other hand atlantoaxial mean values of men and women are determined different as statistically (t: 3.33, p< 0.05). In other words, the odontoid process sizes and atlantoaxial distance mean values are determinate bigger in women than in men. In this study, there is evident correlation between odontoid process sizes (height r: +0.887, anteroposterior diameter; r: +0.801, and transverse diameter r: +0.808) measured on MRI scan and ages of patients (p<0.05), after all there is not a strong correlation (r: +0.401) as statically between atlantoaxial distance and age (p>0.05). In this study, first of the result is that the average of atlantoaxial space is 1.4mm, maximally 2 mm at 20-40 years of age. Although this knowledge is in accordance with literature, it seems to be smaller value generally. On the basis of obtained values from this study we can have an idea that atlantoaxial instability is suspected in cases if measurement of atlantoaxial distance is above 2 mm especially at 20-40 years of ages. On other hand according to data on this study, it must be mandatory to use maximum 30 mm screws for men and 28 mm screws for women in the odontoid fixation. Screws that have maximal 2, 5 mm diameter can be safely used for both sexes in Turkish population.

Keywords: Vertebroplasty, kyphoplasty, osteoporotic vertebral fracture